Merge branch 'master' into debug-merge

195 files changed, 16428 insertions, 8065 deletions

diff --git a/src/build-remote/build-remote.cc b/src/build-remote/build-remote.cc
index 57f2cd32d..9d541b45d 100644
--- a/src/build-remote/build-remote.cc
+++ b/src/build-remote/build-remote.cc
@@ -18,6 +18,7 @@
 #include "derivations.hh"
 #include "local-store.hh"
 #include "legacy.hh"
+#include "experimental-features.hh"
 
 using namespace nix;
 using std::cin;
@@ -130,11 +131,14 @@ static int main_build_remote(int argc, char * * argv)
                 for (auto & m : machines) {
                     debug("considering building on remote machine '%s'", m.storeUri);
 
-                    if (m.enabled && std::find(m.systemTypes.begin(),
-                            m.systemTypes.end(),
-                            neededSystem) != m.systemTypes.end() &&
+                    if (m.enabled
+                        && (neededSystem == "builtin"
+                            || std::find(m.systemTypes.begin(),
+                                m.systemTypes.end(),
+                                neededSystem) != m.systemTypes.end()) &&
                         m.allSupported(requiredFeatures) &&
-                        m.mandatoryMet(requiredFeatures)) {
+                        m.mandatoryMet(requiredFeatures))
+                    {
                         rightType = true;
                         AutoCloseFD free;
                         uint64_t load = 0;
@@ -270,14 +274,23 @@ connected:
 
         {
             Activity act(*logger, lvlTalkative, actUnknown, fmt("copying dependencies to '%s'", storeUri));
-            copyPaths(store, ref<Store>(sshStore), store->parseStorePathSet(inputs), NoRepair, NoCheckSigs, substitute);
+            copyPaths(*store, *sshStore, store->parseStorePathSet(inputs), NoRepair, NoCheckSigs, substitute);
         }
 
         uploadLock = -1;
 
         auto drv = store->readDerivation(*drvPath);
         auto outputHashes = staticOutputHashes(*store, drv);
-        drv.inputSrcs = store->parseStorePathSet(inputs);
+
+        // Hijack the inputs paths of the derivation to include all the paths
+        // that come from the `inputDrvs` set.
+        // We don’t do that for the derivations whose `inputDrvs` is empty
+        // because
+        // 1. It’s not needed
+        // 2. Changing the `inputSrcs` set changes the associated output ids,
+        //  which break CA derivations
+        if (!drv.inputDrvs.empty())
+            drv.inputSrcs = store->parseStorePathSet(inputs);
 
         auto result = sshStore->buildDerivation(*drvPath, drv);
 
@@ -286,7 +299,7 @@ connected:
 
         std::set<Realisation> missingRealisations;
         StorePathSet missingPaths;
-        if (settings.isExperimentalFeatureEnabled("ca-derivations") && !derivationHasKnownOutputPaths(drv.type())) {
+        if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations) && !derivationHasKnownOutputPaths(drv.type())) {
             for (auto & outputName : wantedOutputs) {
                 auto thisOutputHash = outputHashes.at(outputName);
                 auto thisOutputId = DrvOutput{ thisOutputHash, outputName };
@@ -312,13 +325,13 @@ connected:
             if (auto localStore = store.dynamic_pointer_cast<LocalStore>())
                 for (auto & path : missingPaths)
                     localStore->locksHeld.insert(store->printStorePath(path)); /* FIXME: ugly */
-            copyPaths(ref<Store>(sshStore), store, missingPaths, NoRepair, NoCheckSigs, NoSubstitute);
+            copyPaths(*sshStore, *store, missingPaths, NoRepair, NoCheckSigs, NoSubstitute);
         }
         // XXX: Should be done as part of `copyPaths`
         for (auto & realisation : missingRealisations) {
             // Should hold, because if the feature isn't enabled the set
             // of missing realisations should be empty
-            settings.requireExperimentalFeature("ca-derivations");
+            settings.requireExperimentalFeature(Xp::CaDerivations);
             store->registerDrvOutput(realisation);
         }
 
diff --git a/src/libcmd/command.cc b/src/libcmd/command.cc
index 2c62bfa7f..4c5d985aa 100644
--- a/src/libcmd/command.cc
+++ b/src/libcmd/command.cc
@@ -95,8 +95,21 @@ EvalCommand::~EvalCommand()
         evalState->printStats();
 }
 
+ref<Store> EvalCommand::getEvalStore()
+{
+    if (!evalStore)
+        evalStore = evalStoreUrl ? openStore(*evalStoreUrl) : getStore();
+    return ref<Store>(evalStore);
+}
+
+ref<EvalState> EvalCommand::getEvalState()
+{
+    if (!evalState)
+        evalState = std::make_shared<EvalState>(searchPath, getEvalStore(), getStore());
+    return ref<EvalState>(evalState);
+}
 
-RealisedPathsCommand::RealisedPathsCommand(bool recursive)
+BuiltPathsCommand::BuiltPathsCommand(bool recursive)
     : recursive(recursive)
 {
     if (recursive)
@@ -123,44 +136,53 @@ RealisedPathsCommand::RealisedPathsCommand(bool recursive)
     });
 }
 
-void RealisedPathsCommand::run(ref<Store> store)
+void BuiltPathsCommand::run(ref<Store> store)
 {
-    std::vector<RealisedPath> paths;
+    BuiltPaths paths;
     if (all) {
         if (installables.size())
             throw UsageError("'--all' does not expect arguments");
         // XXX: Only uses opaque paths, ignores all the realisations
         for (auto & p : store->queryAllValidPaths())
-            paths.push_back(p);
+            paths.push_back(BuiltPath::Opaque{p});
     } else {
-        auto pathSet = toRealisedPaths(store, realiseMode, operateOn, installables);
+        paths = toBuiltPaths(getEvalStore(), store, realiseMode, operateOn, installables);
         if (recursive) {
-            auto roots = std::move(pathSet);
-            pathSet = {};
-            RealisedPath::closure(*store, roots, pathSet);
+            // XXX: This only computes the store path closure, ignoring
+            // intermediate realisations
+            StorePathSet pathsRoots, pathsClosure;
+            for (auto & root : paths) {
+                auto rootFromThis = root.outPaths();
+                pathsRoots.insert(rootFromThis.begin(), rootFromThis.end());
+            }
+            store->computeFSClosure(pathsRoots, pathsClosure);
+            for (auto & path : pathsClosure)
+                paths.push_back(BuiltPath::Opaque{path});
         }
-        for (auto & path : pathSet)
-            paths.push_back(path);
     }
 
     run(store, std::move(paths));
 }
 
 StorePathsCommand::StorePathsCommand(bool recursive)
-    : RealisedPathsCommand(recursive)
+    : BuiltPathsCommand(recursive)
 {
 }
 
-void StorePathsCommand::run(ref<Store> store, std::vector<RealisedPath> paths)
+void StorePathsCommand::run(ref<Store> store, BuiltPaths && paths)
 {
-    StorePaths storePaths;
-    for (auto & p : paths)
-        storePaths.push_back(p.path());
+    StorePathSet storePaths;
+    for (auto & builtPath : paths)
+        for (auto & p : builtPath.outPaths())
+            storePaths.insert(p);
+
+    auto sorted = store->topoSortPaths(storePaths);
+    std::reverse(sorted.begin(), sorted.end());
 
-    run(store, std::move(storePaths));
+    run(store, std::move(sorted));
 }
 
-void StorePathCommand::run(ref<Store> store, std::vector<StorePath> storePaths)
+void StorePathCommand::run(ref<Store> store, std::vector<StorePath> && storePaths)
 {
     if (storePaths.size() != 1)
         throw UsageError("this command requires exactly one store path");
@@ -204,7 +226,7 @@ void MixProfile::updateProfile(const StorePath & storePath)
             profile2, storePath));
 }
 
-void MixProfile::updateProfile(const DerivedPathsWithHints & buildables)
+void MixProfile::updateProfile(const BuiltPaths & buildables)
 {
     if (!profile) return;
 
@@ -212,22 +234,19 @@ void MixProfile::updateProfile(const DerivedPathsWithHints & buildables)
 
     for (auto & buildable : buildables) {
         std::visit(overloaded {
-            [&](DerivedPathWithHints::Opaque bo) {
+            [&](const BuiltPath::Opaque & bo) {
                 result.push_back(bo.path);
             },
-            [&](DerivedPathWithHints::Built bfd) {
+            [&](const BuiltPath::Built & bfd) {
                 for (auto & output : bfd.outputs) {
-                    /* Output path should be known because we just tried to
-                       build it. */
-                    assert(output.second);
-                    result.push_back(*output.second);
+                    result.push_back(output.second);
                 }
             },
         }, buildable.raw());
     }
 
     if (result.size() != 1)
-        throw Error("'--profile' requires that the arguments produce a single store path, but there are %d", result.size());
+        throw UsageError("'--profile' requires that the arguments produce a single store path, but there are %d", result.size());
 
     updateProfile(result[0]);
 }
diff --git a/src/libcmd/command.hh b/src/libcmd/command.hh
index 8566e3a6d..0d847d255 100644
--- a/src/libcmd/command.hh
+++ b/src/libcmd/command.hh
@@ -47,13 +47,18 @@ struct EvalCommand : virtual StoreCommand, MixEvalArgs
 {
     bool startReplOnEvalErrors = false;
 
+    EvalCommand();
+
+    ~EvalCommand();
+
+    ref<Store> getEvalStore();
+
     ref<EvalState> getEvalState();
 
-    EvalCommand();
+private:
+    std::shared_ptr<Store> evalStore;
 
     std::shared_ptr<EvalState> evalState;
-
-    ~EvalCommand();
 };
 
 struct MixFlakeOptions : virtual Args, EvalCommand
@@ -105,6 +110,8 @@ enum class Realise {
        exists. */
     Derivation,
     /* Evaluate in dry-run mode. Postcondition: nothing. */
+    // FIXME: currently unused, but could be revived if we can
+    // evaluate derivations in-memory.
     Nothing
 };
 
@@ -147,7 +154,7 @@ private:
 };
 
 /* A command that operates on zero or more store paths. */
-struct RealisedPathsCommand : public InstallablesCommand
+struct BuiltPathsCommand : public InstallablesCommand
 {
 private:
 
@@ -160,26 +167,26 @@ protected:
 
 public:
 
-    RealisedPathsCommand(bool recursive = false);
+    BuiltPathsCommand(bool recursive = false);
 
     using StoreCommand::run;
 
-    virtual void run(ref<Store> store, std::vector<RealisedPath> paths) = 0;
+    virtual void run(ref<Store> store, BuiltPaths && paths) = 0;
 
     void run(ref<Store> store) override;
 
     bool useDefaultInstallables() override { return !all; }
 };
 
-struct StorePathsCommand : public RealisedPathsCommand
+struct StorePathsCommand : public BuiltPathsCommand
 {
     StorePathsCommand(bool recursive = false);
 
-    using RealisedPathsCommand::run;
+    using BuiltPathsCommand::run;
 
-    virtual void run(ref<Store> store, std::vector<StorePath> storePaths) = 0;
+    virtual void run(ref<Store> store, std::vector<StorePath> && storePaths) = 0;
 
-    void run(ref<Store> store, std::vector<RealisedPath> paths) override;
+    void run(ref<Store> store, BuiltPaths && paths) override;
 };
 
 /* A command that operates on exactly one store path. */
@@ -189,7 +196,7 @@ struct StorePathCommand : public StorePathsCommand
 
     virtual void run(ref<Store> store, const StorePath & storePath) = 0;
 
-    void run(ref<Store> store, std::vector<StorePath> storePaths) override;
+    void run(ref<Store> store, std::vector<StorePath> && storePaths) override;
 };
 
 /* A helper class for registering commands globally. */
@@ -220,26 +227,37 @@ static RegisterCommand registerCommand2(std::vector<std::string> && name)
     return RegisterCommand(std::move(name), [](){ return make_ref<T>(); });
 }
 
-DerivedPathsWithHints build(ref<Store> store, Realise mode,
-    std::vector<std::shared_ptr<Installable>> installables, BuildMode bMode = bmNormal);
+BuiltPaths build(
+    ref<Store> evalStore,
+    ref<Store> store, Realise mode,
+    const std::vector<std::shared_ptr<Installable>> & installables,
+    BuildMode bMode = bmNormal);
 
-std::set<StorePath> toStorePaths(ref<Store> store,
-    Realise mode, OperateOn operateOn,
-    std::vector<std::shared_ptr<Installable>> installables);
+std::set<StorePath> toStorePaths(
+    ref<Store> evalStore,
+    ref<Store> store,
+    Realise mode,
+    OperateOn operateOn,
+    const std::vector<std::shared_ptr<Installable>> & installables);
 
-StorePath toStorePath(ref<Store> store,
-    Realise mode, OperateOn operateOn,
+StorePath toStorePath(
+    ref<Store> evalStore,
+    ref<Store> store,
+    Realise mode,
+    OperateOn operateOn,
     std::shared_ptr<Installable> installable);
 
-std::set<StorePath> toDerivations(ref<Store> store,
-    std::vector<std::shared_ptr<Installable>> installables,
+std::set<StorePath> toDerivations(
+    ref<Store> store,
+    const std::vector<std::shared_ptr<Installable>> & installables,
     bool useDeriver = false);
 
-std::set<RealisedPath> toRealisedPaths(
+BuiltPaths toBuiltPaths(
+    ref<Store> evalStore,
     ref<Store> store,
     Realise mode,
     OperateOn operateOn,
-    std::vector<std::shared_ptr<Installable>> installables);
+    const std::vector<std::shared_ptr<Installable>> & installables);
 
 /* Helper function to generate args that invoke $EDITOR on
    filename:lineno. */
@@ -256,7 +274,7 @@ struct MixProfile : virtual StoreCommand
 
     /* If 'profile' is set, make it point at the store path produced
        by 'buildables'. */
-    void updateProfile(const DerivedPathsWithHints & buildables);
+    void updateProfile(const BuiltPaths & buildables);
 };
 
 struct MixDefaultProfile : MixProfile
diff --git a/src/libcmd/installables.cc b/src/libcmd/installables.cc
index 7f7a89b37..5758b52ad 100644
--- a/src/libcmd/installables.cc
+++ b/src/libcmd/installables.cc
@@ -58,9 +58,13 @@ MixFlakeOptions::MixFlakeOptions()
 
     addFlag({
         .longName = "no-registries",
-        .description = "Don't allow lookups in the flake registries.",
+        .description =
+          "Don't allow lookups in the flake registries. This option is deprecated; use `--no-use-registries`.",
         .category = category,
-        .handler = {&lockFlags.useRegistries, false}
+        .handler = {[&]() {
+            lockFlags.useRegistries = false;
+            warn("'--no-registries' is deprecated; use '--no-use-registries'");
+        }}
     });
 
     addFlag({
@@ -171,14 +175,50 @@ Strings SourceExprCommand::getDefaultFlakeAttrPathPrefixes()
 
 void SourceExprCommand::completeInstallable(std::string_view prefix)
 {
-    if (file) return; // FIXME
+    if (file) {
+        evalSettings.pureEval = false;
+        auto state = getEvalState();
+        Expr *e = state->parseExprFromFile(
+            resolveExprPath(state->checkSourcePath(lookupFileArg(*state, *file)))
+        );
+
+        Value root;
+        state->eval(e, root);
+
+        auto autoArgs = getAutoArgs(*state);
 
-    completeFlakeRefWithFragment(
-        getEvalState(),
-        lockFlags,
-        getDefaultFlakeAttrPathPrefixes(),
-        getDefaultFlakeAttrPaths(),
-        prefix);
+        std::string prefix_ = std::string(prefix);
+        auto sep = prefix_.rfind('.');
+        std::string searchWord;
+        if (sep != std::string::npos) {
+            searchWord = prefix_.substr(sep, std::string::npos);
+            prefix_ = prefix_.substr(0, sep);
+        } else {
+            searchWord = prefix_;
+            prefix_ = "";
+        }
+
+        Value &v1(*findAlongAttrPath(*state, prefix_, *autoArgs, root).first);
+        state->forceValue(v1);
+        Value v2;
+        state->autoCallFunction(*autoArgs, v1, v2);
+
+        if (v2.type() == nAttrs) {
+            for (auto & i : *v2.attrs) {
+                std::string name = i.name;
+                if (name.find(searchWord) == 0) {
+                    completions->add(i.name);
+                }
+            }
+        }
+    } else {
+        completeFlakeRefWithFragment(
+            getEvalState(),
+            lockFlags,
+            getDefaultFlakeAttrPathPrefixes(),
+            getDefaultFlakeAttrPaths(),
+            prefix);
+    }
 }
 
 void completeFlakeRefWithFragment(
@@ -249,7 +289,6 @@ void completeFlakeRefWithFragment(
     completeFlakeRef(evalState->store, prefix);
 }
 
-
 void completeFlakeRef(ref<Store> store, std::string_view prefix)
 {
     if (prefix == "")
@@ -273,9 +312,9 @@ void completeFlakeRef(ref<Store> store, std::string_view prefix)
     }
 }
 
-DerivedPathWithHints Installable::toDerivedPathWithHints()
+DerivedPath Installable::toDerivedPath()
 {
-    auto buildables = toDerivedPathsWithHints();
+    auto buildables = toDerivedPaths();
     if (buildables.size() != 1)
         throw Error("installable '%s' evaluates to %d derivations, where only one is expected", what(), buildables.size());
     return std::move(buildables[0]);
@@ -309,22 +348,19 @@ struct InstallableStorePath : Installable
 
     std::string what() override { return store->printStorePath(storePath); }
 
-    DerivedPathsWithHints toDerivedPathsWithHints() override
+    DerivedPaths toDerivedPaths() override
     {
         if (storePath.isDerivation()) {
-            std::map<std::string, std::optional<StorePath>> outputs;
             auto drv = store->readDerivation(storePath);
-            for (auto & [name, output] : drv.outputsAndOptPaths(*store))
-                outputs.emplace(name, output.second);
             return {
-                DerivedPathWithHints::Built {
+                DerivedPath::Built {
                     .drvPath = storePath,
-                    .outputs = std::move(outputs)
+                    .outputs = drv.outputNames(),
                 }
             };
         } else {
             return {
-                DerivedPathWithHints::Opaque {
+                DerivedPath::Opaque {
                     .path = storePath,
                 }
             };
@@ -337,22 +373,24 @@ struct InstallableStorePath : Installable
     }
 };
 
-DerivedPathsWithHints InstallableValue::toDerivedPathsWithHints()
+DerivedPaths InstallableValue::toDerivedPaths()
 {
-    DerivedPathsWithHints res;
+    DerivedPaths res;
 
-    std::map<StorePath, std::map<std::string, std::optional<StorePath>>> drvsToOutputs;
+    std::map<StorePath, std::set<std::string>> drvsToOutputs;
+    RealisedPath::Set drvsToCopy;
 
     // Group by derivation, helps with .all in particular
     for (auto & drv : toDerivations()) {
         auto outputName = drv.outputName;
         if (outputName == "")
             throw Error("derivation '%s' lacks an 'outputName' attribute", state->store->printStorePath(drv.drvPath));
-        drvsToOutputs[drv.drvPath].insert_or_assign(outputName, drv.outPath);
+        drvsToOutputs[drv.drvPath].insert(outputName);
+        drvsToCopy.insert(drv.drvPath);
     }
 
     for (auto & i : drvsToOutputs)
-        res.push_back(DerivedPathWithHints::Built { i.first, i.second });
+        res.push_back(DerivedPath::Built { i.first, i.second });
 
     return res;
 }
@@ -564,10 +602,10 @@ InstallableFlake::getCursors(EvalState & state)
 
 std::shared_ptr<flake::LockedFlake> InstallableFlake::getLockedFlake() const
 {
+    flake::LockFlags lockFlagsApplyConfig = lockFlags;
+    lockFlagsApplyConfig.applyNixConfig = true;
     if (!_lockedFlake) {
-        _lockedFlake = std::make_shared<flake::LockedFlake>(lockFlake(*state, flakeRef, lockFlags));
-        _lockedFlake->flake.config.apply();
-        // FIXME: send new config to the daemon.
+        _lockedFlake = std::make_shared<flake::LockedFlake>(lockFlake(*state, flakeRef, lockFlagsApplyConfig));
     }
     return _lockedFlake;
 }
@@ -616,6 +654,17 @@ std::vector<std::shared_ptr<Installable>> SourceExprCommand::parseInstallables(
         for (auto & s : ss) {
             std::exception_ptr ex;
 
+            if (s.find('/') != std::string::npos) {
+                try {
+                    result.push_back(std::make_shared<InstallableStorePath>(store, store->followLinksToStorePath(s)));
+                    continue;
+                } catch (BadStorePath &) {
+                } catch (...) {
+                    if (!ex)
+                        ex = std::current_exception();
+                }
+            }
+
             try {
                 auto [flakeRef, fragment] = parseFlakeRefWithFragment(s, absPath("."));
                 result.push_back(std::make_shared<InstallableFlake>(
@@ -630,25 +679,7 @@ std::vector<std::shared_ptr<Installable>> SourceExprCommand::parseInstallables(
                 ex = std::current_exception();
             }
 
-            if (s.find('/') != std::string::npos) {
-                try {
-                    result.push_back(std::make_shared<InstallableStorePath>(store, store->followLinksToStorePath(s)));
-                    continue;
-                } catch (BadStorePath &) {
-                } catch (...) {
-                    if (!ex)
-                        ex = std::current_exception();
-                }
-            }
-
             std::rethrow_exception(ex);
-
-            /*
-            throw Error(
-                pathExists(s)
-                ? "path '%s' is not a flake or a store path"
-                : "don't know how to handle argument '%s'", s);
-            */
         }
     }
 
@@ -663,107 +694,121 @@ std::shared_ptr<Installable> SourceExprCommand::parseInstallable(
     return installables.front();
 }
 
-DerivedPathsWithHints build(ref<Store> store, Realise mode,
-    std::vector<std::shared_ptr<Installable>> installables, BuildMode bMode)
+BuiltPaths getBuiltPaths(ref<Store> evalStore, ref<Store> store, const DerivedPaths & hopefullyBuiltPaths)
+{
+    BuiltPaths res;
+    for (const auto & b : hopefullyBuiltPaths)
+        std::visit(
+            overloaded{
+                [&](const DerivedPath::Opaque & bo) {
+                    res.push_back(BuiltPath::Opaque{bo.path});
+                },
+                [&](const DerivedPath::Built & bfd) {
+                    OutputPathMap outputs;
+                    auto drv = evalStore->readDerivation(bfd.drvPath);
+                    auto outputHashes = staticOutputHashes(*evalStore, drv); // FIXME: expensive
+                    auto drvOutputs = drv.outputsAndOptPaths(*store);
+                    for (auto & output : bfd.outputs) {
+                        if (!outputHashes.count(output))
+                            throw Error(
+                                "the derivation '%s' doesn't have an output named '%s'",
+                                store->printStorePath(bfd.drvPath), output);
+                        if (settings.isExperimentalFeatureEnabled(
+                                Xp::CaDerivations)) {
+                            auto outputId =
+                                DrvOutput{outputHashes.at(output), output};
+                            auto realisation =
+                                store->queryRealisation(outputId);
+                            if (!realisation)
+                                throw Error(
+                                    "cannot operate on an output of unbuilt "
+                                    "content-addressed derivation '%s'",
+                                    outputId.to_string());
+                            outputs.insert_or_assign(
+                                output, realisation->outPath);
+                        } else {
+                            // If ca-derivations isn't enabled, assume that
+                            // the output path is statically known.
+                            assert(drvOutputs.count(output));
+                            assert(drvOutputs.at(output).second);
+                            outputs.insert_or_assign(
+                                output, *drvOutputs.at(output).second);
+                        }
+                    }
+                    res.push_back(BuiltPath::Built{bfd.drvPath, outputs});
+                },
+            },
+            b.raw());
+
+    return res;
+}
+
+BuiltPaths build(
+    ref<Store> evalStore,
+    ref<Store> store,
+    Realise mode,
+    const std::vector<std::shared_ptr<Installable>> & installables,
+    BuildMode bMode)
 {
     if (mode == Realise::Nothing)
         settings.readOnlyMode = true;
 
-    DerivedPathsWithHints buildables;
-
     std::vector<DerivedPath> pathsToBuild;
 
     for (auto & i : installables) {
-        for (auto & b : i->toDerivedPathsWithHints()) {
-            std::visit(overloaded {
-                [&](DerivedPathWithHints::Opaque bo) {
-                    pathsToBuild.push_back(bo);
-                },
-                [&](DerivedPathWithHints::Built bfd) {
-                    StringSet outputNames;
-                    for (auto & output : bfd.outputs)
-                        outputNames.insert(output.first);
-                    pathsToBuild.push_back(
-                        DerivedPath::Built{bfd.drvPath, outputNames});
-                },
-            }, b.raw());
-            buildables.push_back(std::move(b));
-        }
+        auto b = i->toDerivedPaths();
+        pathsToBuild.insert(pathsToBuild.end(), b.begin(), b.end());
     }
 
-    if (mode == Realise::Nothing)
+    if (mode == Realise::Nothing || mode == Realise::Derivation)
         printMissing(store, pathsToBuild, lvlError);
     else if (mode == Realise::Outputs)
-        store->buildPaths(pathsToBuild, bMode);
+        store->buildPaths(pathsToBuild, bMode, evalStore);
 
-    return buildables;
+    return getBuiltPaths(evalStore, store, pathsToBuild);
 }
 
-std::set<RealisedPath> toRealisedPaths(
+BuiltPaths toBuiltPaths(
+    ref<Store> evalStore,
     ref<Store> store,
     Realise mode,
     OperateOn operateOn,
-    std::vector<std::shared_ptr<Installable>> installables)
+    const std::vector<std::shared_ptr<Installable>> & installables)
 {
-    std::set<RealisedPath> res;
-    if (operateOn == OperateOn::Output) {
-        for (auto & b : build(store, mode, installables))
-            std::visit(overloaded {
-                [&](DerivedPathWithHints::Opaque bo) {
-                    res.insert(bo.path);
-                },
-                [&](DerivedPathWithHints::Built bfd) {
-                    auto drv = store->readDerivation(bfd.drvPath);
-                    auto outputHashes = staticOutputHashes(*store, drv);
-                    for (auto & output : bfd.outputs) {
-                        if (settings.isExperimentalFeatureEnabled("ca-derivations")) {
-                            if (!outputHashes.count(output.first))
-                                throw Error(
-                                    "the derivation '%s' doesn't have an output named '%s'",
-                                    store->printStorePath(bfd.drvPath),
-                                    output.first);
-                            auto outputId = DrvOutput{outputHashes.at(output.first), output.first};
-                            auto realisation = store->queryRealisation(outputId);
-                            if (!realisation)
-                                throw Error("cannot operate on an output of unbuilt content-addresed derivation '%s'", outputId.to_string());
-                            res.insert(RealisedPath{*realisation});
-                        }
-                        else {
-                            // If ca-derivations isn't enabled, behave as if
-                            // all the paths are opaque to keep the default
-                            // behavior
-                            assert(output.second);
-                            res.insert(*output.second);
-                        }
-                    }
-                },
-            }, b.raw());
-    } else {
+    if (operateOn == OperateOn::Output)
+        return build(evalStore, store, mode, installables);
+    else {
         if (mode == Realise::Nothing)
             settings.readOnlyMode = true;
 
-        auto drvPaths = toDerivations(store, installables, true);
-        res.insert(drvPaths.begin(), drvPaths.end());
+        BuiltPaths res;
+        for (auto & drvPath : toDerivations(store, installables, true))
+            res.push_back(BuiltPath::Opaque{drvPath});
+        return res;
     }
-
-    return res;
 }
 
-StorePathSet toStorePaths(ref<Store> store,
+StorePathSet toStorePaths(
+    ref<Store> evalStore,
+    ref<Store> store,
     Realise mode, OperateOn operateOn,
-    std::vector<std::shared_ptr<Installable>> installables)
+    const std::vector<std::shared_ptr<Installable>> & installables)
 {
     StorePathSet outPaths;
-    for (auto & path : toRealisedPaths(store, mode, operateOn, installables))
-            outPaths.insert(path.path());
+    for (auto & path : toBuiltPaths(evalStore, store, mode, operateOn, installables)) {
+        auto thisOutPaths = path.outPaths();
+        outPaths.insert(thisOutPaths.begin(), thisOutPaths.end());
+    }
     return outPaths;
 }
 
-StorePath toStorePath(ref<Store> store,
+StorePath toStorePath(
+    ref<Store> evalStore,
+    ref<Store> store,
     Realise mode, OperateOn operateOn,
     std::shared_ptr<Installable> installable)
 {
-    auto paths = toStorePaths(store, mode, operateOn, {installable});
+    auto paths = toStorePaths(evalStore, store, mode, operateOn, {installable});
 
     if (paths.size() != 1)
         throw Error("argument '%s' should evaluate to one store path", installable->what());
@@ -771,15 +816,17 @@ StorePath toStorePath(ref<Store> store,
     return *paths.begin();
 }
 
-StorePathSet toDerivations(ref<Store> store,
-    std::vector<std::shared_ptr<Installable>> installables, bool useDeriver)
+StorePathSet toDerivations(
+    ref<Store> store,
+    const std::vector<std::shared_ptr<Installable>> & installables,
+    bool useDeriver)
 {
     StorePathSet drvPaths;
 
-    for (auto & i : installables)
-        for (auto & b : i->toDerivedPathsWithHints())
+    for (const auto & i : installables)
+        for (const auto & b : i->toDerivedPaths())
             std::visit(overloaded {
-                [&](DerivedPathWithHints::Opaque bo) {
+                [&](const DerivedPath::Opaque & bo) {
                     if (!useDeriver)
                         throw Error("argument '%s' did not evaluate to a derivation", i->what());
                     auto derivers = store->queryValidDerivers(bo.path);
@@ -788,7 +835,7 @@ StorePathSet toDerivations(ref<Store> store,
                     // FIXME: use all derivers?
                     drvPaths.insert(*derivers.begin());
                 },
-                [&](DerivedPathWithHints::Built bfd) {
+                [&](const DerivedPath::Built & bfd) {
                     drvPaths.insert(bfd.drvPath);
                 },
             }, b.raw());
diff --git a/src/libcmd/installables.hh b/src/libcmd/installables.hh
index 403403c07..79931ad3e 100644
--- a/src/libcmd/installables.hh
+++ b/src/libcmd/installables.hh
@@ -23,17 +23,23 @@ struct App
     // FIXME: add args, sandbox settings, metadata, ...
 };
 
+struct UnresolvedApp
+{
+    App unresolved;
+    App resolve(ref<Store> evalStore, ref<Store> store);
+};
+
 struct Installable
 {
     virtual ~Installable() { }
 
     virtual std::string what() = 0;
 
-    virtual DerivedPathsWithHints toDerivedPathsWithHints() = 0;
+    virtual DerivedPaths toDerivedPaths() = 0;
 
-    DerivedPathWithHints toDerivedPathWithHints();
+    DerivedPath toDerivedPath();
 
-    App toApp(EvalState & state);
+    UnresolvedApp toApp(EvalState & state);
 
     virtual std::pair<Value *, Pos> toValue(EvalState & state)
     {
@@ -74,7 +80,7 @@ struct InstallableValue : Installable
 
     virtual std::vector<DerivationInfo> toDerivations() = 0;
 
-    DerivedPathsWithHints toDerivedPathsWithHints() override;
+    DerivedPaths toDerivedPaths() override;
 };
 
 struct InstallableFlake : InstallableValue
diff --git a/src/libcmd/local.mk b/src/libcmd/local.mk
index df904612b..1ec258a54 100644
--- a/src/libcmd/local.mk
+++ b/src/libcmd/local.mk
@@ -8,8 +8,9 @@ libcmd_SOURCES := $(wildcard $(d)/*.cc)
 
 libcmd_CXXFLAGS += -I src/libutil -I src/libstore -I src/libexpr -I src/libmain -I src/libfetchers -I src/nix
 
-libcmd_LDFLAGS = $(EDITLINE_LIBS) -llowdown
+# libcmd_LDFLAGS = $(EDITLINE_LIBS) -llowdown
+libcmd_LDFLAGS += -llowdown -pthread
 
 libcmd_LIBS = libstore libutil libexpr libmain libfetchers libnix
 
-$(eval $(call install-file-in, $(d)/nix-cmd.pc, $(prefix)/lib/pkgconfig, 0644))
+$(eval $(call install-file-in, $(d)/nix-cmd.pc, $(libdir)/pkgconfig, 0644))
diff --git a/src/libcmd/markdown.cc b/src/libcmd/markdown.cc
index d25113d93..29bb4d31e 100644
--- a/src/libcmd/markdown.cc
+++ b/src/libcmd/markdown.cc
@@ -12,7 +12,7 @@ std::string renderMarkdownToTerminal(std::string_view markdown)
     struct lowdown_opts opts {
         .type = LOWDOWN_TERM,
         .maxdepth = 20,
-        .cols = std::min(getWindowSize().second, (unsigned short) 80),
+        .cols = std::max(getWindowSize().second, (unsigned short) 80),
         .hmargin = 0,
         .vmargin = 0,
         .feat = LOWDOWN_COMMONMARK | LOWDOWN_FENCED | LOWDOWN_DEFLIST | LOWDOWN_TABLES,
@@ -25,7 +25,7 @@ std::string renderMarkdownToTerminal(std::string_view markdown)
     Finally freeDoc([&]() { lowdown_doc_free(doc); });
 
     size_t maxn = 0;
-    auto node = lowdown_doc_parse(doc, &maxn, markdown.data(), markdown.size());
+    auto node = lowdown_doc_parse(doc, &maxn, markdown.data(), markdown.size(), nullptr);
     if (!node)
         throw Error("cannot parse Markdown document");
     Finally freeNode([&]() { lowdown_node_free(node); });
@@ -40,11 +40,11 @@ std::string renderMarkdownToTerminal(std::string_view markdown)
         throw Error("cannot allocate Markdown output buffer");
     Finally freeBuffer([&]() { lowdown_buf_free(buf); });
 
-    int rndr_res = lowdown_term_rndr(buf, nullptr, renderer, node);
+    int rndr_res = lowdown_term_rndr(buf, renderer, node);
     if (!rndr_res)
         throw Error("allocation error while rendering Markdown");
 
-    return std::string(buf->data, buf->size);
+    return filterANSIEscapes(std::string(buf->data, buf->size), !shouldANSI());
 }
 
 }
diff --git a/src/libcmd/repl.cc b/src/libcmd/repl.cc
index bfc131d27..6faa9f9fa 100644
--- a/src/libcmd/repl.cc
+++ b/src/libcmd/repl.cc
@@ -68,6 +68,7 @@ struct NixRepl
     StorePath getDerivationPath(Value & v);
     bool processLine(string line);
     void loadFile(const Path & path);
+    void loadFlake(const std::string & flakeRef);
     void initEnv();
     void reloadFiles();
     void addAttrsToScope(Value & attrs);
@@ -104,6 +105,25 @@ NixRepl::~NixRepl()
     write_history(historyFile.c_str());
 }
 
+string runNix(Path program, const Strings & args,
+    const std::optional<std::string> & input = {})
+{
+    auto subprocessEnv = getEnv();
+    subprocessEnv["NIX_CONFIG"] = globalConfig.toKeyValue();
+
+    auto res = runProgram(RunOptions {
+        .program = settings.nixBinDir+ "/" + program,
+        .args = args,
+        .environment = subprocessEnv,
+        .input = input,
+    });
+
+    if (!statusOk(res.first))
+        throw ExecError(res.first, fmt("program '%1%' %2%", program, statusToString(res.first)));
+
+    return res.second;
+}
+
 static NixRepl * curRepl; // ugly
 
 static char * completionCallback(char * s, int *match) {
@@ -180,15 +200,14 @@ namespace {
 void NixRepl::mainLoop(const std::vector<std::string> & files)
 {
     string error = ANSI_RED "error:" ANSI_NORMAL " ";
-    std::cout << "Welcome to Nix version " << nixVersion << ". Type :? for help." << std::endl << std::endl;
+    notice("Welcome to Nix " + nixVersion + ". Type :? for help.\n");
 
     if (!files.empty()) {
         for (auto & i : files)
             loadedFiles.push_back(i);
 
-        reloadFiles();
-        if (!loadedFiles.empty()) std::cout << std::endl;
-    }
+    reloadFiles();
+    if (!loadedFiles.empty()) notice("");
 
     // Allow nix-repl specific settings in .inputrc
     rl_readline_name = "nix-repl";
@@ -378,6 +397,8 @@ bool NixRepl::processLine(string line)
 {
     if (line == "") return true;
 
+    _isInterrupted = false;
+
     string command, arg;
 
     if (line[0] == ':') {
@@ -397,9 +418,10 @@ bool NixRepl::processLine(string line)
              << "  <x> = <expr>  Bind expression to variable\n"
              << "  :a <expr>     Add attributes from resulting set to scope\n"
              << "  :b <expr>     Build derivation\n"
-             << "  :e <expr>     Open the derivation in $EDITOR\n"
+             << "  :e <expr>     Open package or function in $EDITOR\n"
              << "  :i <expr>     Build derivation, then install result into current profile\n"
              << "  :l <path>     Load Nix expression and add it to scope\n"
+             << "  :lf <ref>     Load Nix flake and add it to scope\n"
              << "  :p <expr>     Evaluate and print expression recursively\n"
              << "  :q            Exit nix-repl\n"
              << "  :r            Reload all files\n"
@@ -420,6 +442,10 @@ bool NixRepl::processLine(string line)
         loadFile(arg);
     }
 
+    else if (command == ":lf" || command == ":load-flake") {
+        loadFlake(arg);
+    }
+
     else if (command == ":r" || command == ":reload") {
         state->resetFileCache();
         reloadFiles();
@@ -439,14 +465,17 @@ bool NixRepl::processLine(string line)
             pos = v.lambda.fun->pos;
         } else {
             // assume it's a derivation
-            pos = findDerivationFilename(*state, v, arg);
+            pos = findPackageFilename(*state, v, arg);
         }
 
         // Open in EDITOR
         auto args = editorFor(pos);
         auto editor = args.front();
         args.pop_front();
-        runProgram(editor, true, args);
+
+        // runProgram redirects stdout to a StringSink,
+        // using runProgram2 to allow editors to display their UI
+        runProgram2(RunOptions { .program = editor, .searchPath = true, .args = args });
 
         // Reload right after exiting the editor
         state->resetFileCache();
@@ -456,16 +485,17 @@ bool NixRepl::processLine(string line)
     else if (command == ":t") {
         Value v;
         evalString(arg, v);
-        std::cout << showType(v) << std::endl;
+        logger->cout(showType(v));
+    }
 
-    } else if (command == ":u") {
+    else if (command == ":u") {
         Value v, f, result;
         evalString(arg, v);
         evalString("drv: (import <nixpkgs> {}).runCommand \"shell\" { buildInputs = [ drv ]; } \"\"", f);
         state->callFunction(f, v, result, Pos());
 
         StorePath drvPath = getDerivationPath(result);
-        runProgram(settings.nixBinDir + "/nix-shell", true, {state->store->printStorePath(drvPath)});
+        runNix("nix-shell", {state->store->printStorePath(drvPath)});
     }
 
     else if (command == ":b" || command == ":i" || command == ":s") {
@@ -475,21 +505,15 @@ bool NixRepl::processLine(string line)
         Path drvPathRaw = state->store->printStorePath(drvPath);
 
         if (command == ":b") {
-            /* We could do the build in this process using buildPaths(),
-               but doing it in a child makes it easier to recover from
-               problems / SIGINT. */
-            try {
-                runProgram(settings.nixBinDir + "/nix", true, {"build", "--no-link", drvPathRaw});
-                auto drv = state->store->readDerivation(drvPath);
-                std::cout << std::endl << "this derivation produced the following outputs:" << std::endl;
-                for (auto & i : drv.outputsAndOptPaths(*state->store))
-                    std::cout << fmt("  %s -> %s\n", i.first, state->store->printStorePath(*i.second.second));
-            } catch (ExecError &) {
-            }
+            state->store->buildPaths({DerivedPath::Built{drvPath}});
+            auto drv = state->store->readDerivation(drvPath);
+            logger->cout("\nThis derivation produced the following outputs:");
+            for (auto & [outputName, outputPath] : state->store->queryDerivationOutputMap(drvPath))
+                logger->cout("  %s -> %s", outputName, state->store->printStorePath(outputPath));
         } else if (command == ":i") {
-            runProgram(settings.nixBinDir + "/nix-env", true, {"-i", drvPathRaw});
+            runNix("nix-env", {"-i", drvPathRaw});
         } else {
-            runProgram(settings.nixBinDir + "/nix-shell", true, {drvPathRaw});
+            runNix("nix-shell", {drvPathRaw});
         }
     }
 
@@ -518,9 +542,9 @@ bool NixRepl::processLine(string line)
                     + concatStringsSep(" ", args) + "\n\n";
             }
 
-            markdown += trim(stripIndentation(doc->doc));
+            markdown += stripIndentation(doc->doc);
 
-            std::cout << renderMarkdownToTerminal(markdown);
+            logger->cout(trim(renderMarkdownToTerminal(markdown)));
         } else
             throw Error("value does not have documentation");
     }
@@ -561,6 +585,25 @@ void NixRepl::loadFile(const Path & path)
     addAttrsToScope(v2);
 }
 
+void NixRepl::loadFlake(const std::string & flakeRefS)
+{
+    auto flakeRef = parseFlakeRef(flakeRefS, absPath("."), true);
+    if (evalSettings.pureEval && !flakeRef.input.isImmutable())
+        throw Error("cannot use ':load-flake' on mutable flake reference '%s' (use --impure to override)", flakeRefS);
+
+    Value v;
+
+    flake::callFlake(*state,
+        flake::lockFlake(*state, flakeRef,
+            flake::LockFlags {
+                .updateLockFile = false,
+                .useRegistries = !evalSettings.pureEval,
+                .allowMutable  = !evalSettings.pureEval,
+            }),
+        v);
+    addAttrsToScope(v);
+}
+
 
 void NixRepl::initEnv()
 {
@@ -584,9 +627,9 @@ void NixRepl::reloadFiles()
 
     bool first = true;
     for (auto & i : old) {
-        if (!first) std::cout << std::endl;
+        if (!first) notice("");
         first = false;
-        std::cout << format("Loading '%1%'...") % i << std::endl;
+        notice("Loading '%1%'...", i);
         loadFile(i);
     }
 }
@@ -596,8 +639,8 @@ void NixRepl::addAttrsToScope(Value & attrs)
 {
     state->forceAttrs(attrs);
     for (auto & i : *attrs.attrs)
-        addVarToScope(i.name, i.value);
-    std::cout << format("Added %1% variables.") % attrs.attrs->size() << std::endl;
+        addVarToScope(i.name, *i.value);
+    notice("Added %1% variables.", attrs.attrs->size());
 }
 
 
@@ -605,8 +648,9 @@ void NixRepl::addVarToScope(const Symbol & name, Value * v)
 {
     if (displ >= envSize)
         throw Error("environment full; cannot add more variables");
-    staticEnv->vars[name] = displ;
-    env->values[displ++] = v;
+    staticEnv->vars.emplace_back(name, displ);
+    staticEnv->sort();
+    env->values[displ++] = &v;
     varNames.insert((string) name);
 }
 
@@ -665,7 +709,7 @@ std::ostream & NixRepl::printValue(std::ostream & str, Value & v, unsigned int m
         break;
 
     case nString:
-        str << ANSI_YELLOW;
+        str << ANSI_WARNING;
         printStringValue(str, v.string.s);
         str << ANSI_NORMAL;
         break;
diff --git a/src/libexpr/attr-path.cc b/src/libexpr/attr-path.cc
index 9dd557205..c50c6d92b 100644
--- a/src/libexpr/attr-path.cc
+++ b/src/libexpr/attr-path.cc
@@ -19,7 +19,7 @@ static Strings parseAttrPath(std::string_view s)
             ++i;
             while (1) {
                 if (i == s.end())
-                    throw Error("missing closing quote in selection path '%1%'", s);
+                    throw ParseError("missing closing quote in selection path '%1%'", s);
                 if (*i == '"') break;
                 cur.push_back(*i++);
             }
@@ -100,7 +100,7 @@ std::pair<Value *, Pos> findAlongAttrPath(EvalState & state, const string & attr
 }
 
 
-Pos findDerivationFilename(EvalState & state, Value & v, std::string what)
+Pos findPackageFilename(EvalState & state, Value & v, std::string what)
 {
     Value * v2;
     try {
@@ -116,14 +116,14 @@ Pos findDerivationFilename(EvalState & state, Value & v, std::string what)
 
     auto colon = pos.rfind(':');
     if (colon == std::string::npos)
-        throw Error("cannot parse meta.position attribute '%s'", pos);
+        throw ParseError("cannot parse meta.position attribute '%s'", pos);
 
     std::string filename(pos, 0, colon);
     unsigned int lineno;
     try {
         lineno = std::stoi(std::string(pos, colon + 1));
     } catch (std::invalid_argument & e) {
-        throw Error("cannot parse line number '%s'", pos);
+        throw ParseError("cannot parse line number '%s'", pos);
     }
 
     Symbol file = state.symbols.create(filename);
diff --git a/src/libexpr/attr-path.hh b/src/libexpr/attr-path.hh
index d9d74ab2d..2ee3ea089 100644
--- a/src/libexpr/attr-path.hh
+++ b/src/libexpr/attr-path.hh
@@ -14,7 +14,7 @@ std::pair<Value *, Pos> findAlongAttrPath(EvalState & state, const string & attr
     Bindings & autoArgs, Value & vIn);
 
 /* Heuristic to find the filename and lineno or a nix value. */
-Pos findDerivationFilename(EvalState & state, Value & v, std::string what);
+Pos findPackageFilename(EvalState & state, Value & v, std::string what);
 
 std::vector<Symbol> parseAttrPath(EvalState & state, std::string_view s);
 
diff --git a/src/libexpr/attr-set.hh b/src/libexpr/attr-set.hh
index 1da8d91df..7d6ffc9f3 100644
--- a/src/libexpr/attr-set.hh
+++ b/src/libexpr/attr-set.hh
@@ -17,8 +17,8 @@ struct Attr
 {
     Symbol name;
     Value * value;
-    Pos * pos;
-    Attr(Symbol name, Value * value, Pos * pos = &noPos)
+    ptr<Pos> pos;
+    Attr(Symbol name, Value * value, ptr<Pos> pos = ptr(&noPos))
         : name(name), value(value), pos(pos) { };
     Attr() : pos(&noPos) { };
     bool operator < (const Attr & a) const
@@ -35,13 +35,13 @@ class Bindings
 {
 public:
     typedef uint32_t size_t;
-    Pos *pos;
+    ptr<Pos> pos;
 
 private:
     size_t size_, capacity_;
     Attr attrs[0];
 
-    Bindings(size_t capacity) : size_(0), capacity_(capacity) { }
+    Bindings(size_t capacity) : pos(&noPos), size_(0), capacity_(capacity) { }
     Bindings(const Bindings & bindings) = delete;
 
 public:
diff --git a/src/libexpr/common-eval-args.cc b/src/libexpr/common-eval-args.cc
index aa14bf79b..fb0932c00 100644
--- a/src/libexpr/common-eval-args.cc
+++ b/src/libexpr/common-eval-args.cc
@@ -61,6 +61,14 @@ MixEvalArgs::MixEvalArgs()
             fetchers::overrideRegistry(from.input, to.input, extraAttrs);
         }}
     });
+
+    addFlag({
+        .longName = "eval-store",
+        .description = "The Nix store to use for evaluations.",
+        .category = category,
+        .labels = {"store-url"},
+        .handler = {&evalStoreUrl},
+    });
 }
 
 Bindings * MixEvalArgs::getAutoArgs(EvalState & state)
diff --git a/src/libexpr/common-eval-args.hh b/src/libexpr/common-eval-args.hh
index be7fda783..0e113fff1 100644
--- a/src/libexpr/common-eval-args.hh
+++ b/src/libexpr/common-eval-args.hh
@@ -16,8 +16,9 @@ struct MixEvalArgs : virtual Args
 
     Strings searchPath;
 
-private:
+    std::optional<std::string> evalStoreUrl;
 
+private:
     std::map<std::string, std::string> autoArgs;
 };
 
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 11a61da26..a20123f34 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -65,7 +65,11 @@ static char * dupStringWithLen(const char * s, size_t size)
 
 RootValue allocRootValue(Value * v)
 {
+#if HAVE_BOEHMGC
     return std::allocate_shared<Value *>(traceable_allocator<Value *>(), v);
+#else
+    return std::make_shared<Value *>(v);
+#endif
 }
 
 
@@ -234,22 +238,34 @@ static void * oomHandler(size_t requested)
 }
 
 class BoehmGCStackAllocator : public StackAllocator {
-  boost::coroutines2::protected_fixedsize_stack stack {
-    // We allocate 8 MB, the default max stack size on NixOS.
-    // A smaller stack might be quicker to allocate but reduces the stack
-    // depth available for source filter expressions etc.
-    std::max(boost::context::stack_traits::default_size(), static_cast<std::size_t>(8 * 1024 * 1024))
+    boost::coroutines2::protected_fixedsize_stack stack {
+        // We allocate 8 MB, the default max stack size on NixOS.
+        // A smaller stack might be quicker to allocate but reduces the stack
+        // depth available for source filter expressions etc.
+        std::max(boost::context::stack_traits::default_size(), static_cast<std::size_t>(8 * 1024 * 1024))
     };
 
+    // This is specific to boost::coroutines2::protected_fixedsize_stack.
+    // The stack protection page is included in sctx.size, so we have to
+    // subtract one page size from the stack size.
+    std::size_t pfss_usable_stack_size(boost::context::stack_context &sctx) {
+        return sctx.size - boost::context::stack_traits::page_size();
+    }
+
   public:
     boost::context::stack_context allocate() override {
         auto sctx = stack.allocate();
-        GC_add_roots(static_cast<char *>(sctx.sp) - sctx.size, sctx.sp);
+
+        // Stacks generally start at a high address and grow to lower addresses.
+        // Architectures that do the opposite are rare; in fact so rare that
+        // boost_routine does not implement it.
+        // So we subtract the stack size.
+        GC_add_roots(static_cast<char *>(sctx.sp) - pfss_usable_stack_size(sctx), sctx.sp);
         return sctx;
     }
 
     void deallocate(boost::context::stack_context sctx) override {
-        GC_remove_roots(static_cast<char *>(sctx.sp) - sctx.size, sctx.sp);
+        GC_remove_roots(static_cast<char *>(sctx.sp) - pfss_usable_stack_size(sctx), sctx.sp);
         stack.deallocate(sctx);
     }
 
@@ -363,7 +379,10 @@ static Strings parseNixPath(const string & s)
 }
 
 
-EvalState::EvalState(const Strings & _searchPath, ref<Store> store)
+EvalState::EvalState(
+    const Strings & _searchPath,
+    ref<Store> store,
+    std::shared_ptr<Store> buildStore)
     : sWith(symbols.create("<with>"))
     , sOutPath(symbols.create("outPath"))
     , sDrvPath(symbols.create("drvPath"))
@@ -396,6 +415,7 @@ EvalState::EvalState(const Strings & _searchPath, ref<Store> store)
     , sEpsilon(symbols.create(""))
     , repair(NoRepair)
     , store(store)
+    , buildStore(buildStore ? buildStore : store)
     , regexCache(makeRegexCache())
     , baseEnv(allocEnv(128))
     , staticBaseEnv(new StaticEnv(false, 0))
@@ -426,12 +446,12 @@ EvalState::EvalState(const Strings & _searchPath, ref<Store> store)
                     StorePathSet closure;
                     store->computeFSClosure(store->toStorePath(r.second).first, closure);
                     for (auto & path : closure)
-                        allowedPaths->insert(store->printStorePath(path));
+                        allowPath(path);
                 } catch (InvalidPath &) {
-                    allowedPaths->insert(r.second);
+                    allowPath(r.second);
                 }
             } else
-                allowedPaths->insert(r.second);
+                allowPath(r.second);
         }
     }
 
@@ -446,6 +466,35 @@ EvalState::~EvalState()
 }
 
 
+void EvalState::requireExperimentalFeatureOnEvaluation(
+    const ExperimentalFeature & feature,
+    const std::string_view fName,
+    const Pos & pos)
+{
+    if (!settings.isExperimentalFeatureEnabled(feature)) {
+        throw EvalError({
+            .msg = hintfmt(
+                "Cannot call '%2%' because experimental Nix feature '%1%' is disabled. You can enable it via '--extra-experimental-features %1%'.",
+                feature,
+                fName
+            ),
+            .errPos = pos
+        });
+    }
+}
+
+void EvalState::allowPath(const Path & path)
+{
+    if (allowedPaths)
+        allowedPaths->insert(path);
+}
+
+void EvalState::allowPath(const StorePath & storePath)
+{
+    if (allowedPaths)
+        allowedPaths->insert(store->toRealPath(storePath));
+}
+
 Path EvalState::checkSourcePath(const Path & path_)
 {
     if (!allowedPaths) return path_;
@@ -472,7 +521,7 @@ Path EvalState::checkSourcePath(const Path & path_)
     }
 
     if (!found)
-        throw RestrictedPathError("access to path '%1%' is forbidden in restricted mode", abspath);
+        throw RestrictedPathError("access to absolute path '%1%' is forbidden in restricted mode", abspath);
 
     /* Resolve symlinks. */
     debug(format("checking access to '%s'") % abspath);
@@ -485,7 +534,7 @@ Path EvalState::checkSourcePath(const Path & path_)
         }
     }
 
-    throw RestrictedPathError("access to path '%1%' is forbidden in restricted mode", path);
+    throw RestrictedPathError("access to canonical path '%1%' is forbidden in restricted mode", path);
 }
 
 
@@ -535,14 +584,20 @@ Value * EvalState::addConstant(const string & name, Value & v)
 {
     Value * v2 = allocValue();
     *v2 = v;
-    staticBaseEnv->vars[symbols.create(name)] = baseEnvDispl;
-    baseEnv.values[baseEnvDispl++] = v2;
-    string name2 = string(name, 0, 2) == "__" ? string(name, 2) : name;
-    baseEnv.values[0]->attrs->push_back(Attr(symbols.create(name2), v2));
+    addConstant(name, v2);
     return v2;
 }
 
 
+void EvalState::addConstant(const string & name, Value * v)
+{
+    staticBaseEnv.vars.emplace_back(symbols.create(name), baseEnvDispl);
+    baseEnv.values[baseEnvDispl++] = v;
+    string name2 = string(name, 0, 2) == "__" ? string(name, 2) : name;
+    baseEnv.values[0]->attrs->push_back(Attr(symbols.create(name2), v));
+}
+
+
 Value * EvalState::addPrimOp(const string & name,
     size_t arity, PrimOpFun primOp)
 {
@@ -561,7 +616,7 @@ Value * EvalState::addPrimOp(const string & name,
 
     Value * v = allocValue();
     v->mkPrimOp(new PrimOp { .fun = primOp, .arity = arity, .name = sym });
-    staticBaseEnv->vars[symbols.create(name)] = baseEnvDispl;
+    staticBaseEnv->vars.emplace_back(symbols.create(name), baseEnvDispl);
     baseEnv.values[baseEnvDispl++] = v;
     baseEnv.values[0]->attrs->push_back(Attr(sym, v));
     return v;
@@ -587,7 +642,7 @@ Value * EvalState::addPrimOp(PrimOp && primOp)
 
     Value * v = allocValue();
     v->mkPrimOp(new PrimOp(std::move(primOp)));
-    staticBaseEnv->vars[envName] = baseEnvDispl;
+    staticBaseEnv->vars.emplace_back(envName, baseEnvDispl);
     baseEnv.values[baseEnvDispl++] = v;
     baseEnv.values[0]->attrs->push_back(Attr(primOp.name, v));
     return v;
@@ -861,7 +916,7 @@ void mkPath(Value & v, const char * s)
 
 inline Value * EvalState::lookupVar(Env * env, const ExprVar & var, bool noEval)
 {
-    for (size_t l = var.level; l; --l, env = env->up) ;
+    for (auto l = var.level; l; --l, env = env->up) ;
 
     if (!var.fromWith) return env->values[var.displ];
 
@@ -875,7 +930,7 @@ inline Value * EvalState::lookupVar(Env * env, const ExprVar & var, bool noEval)
         }
         Bindings::iterator j = env->values[0]->attrs->find(var.name);
         if (j != env->values[0]->attrs->end()) {
-            if (countCalls && j->pos) attrSelects[*j->pos]++;
+            if (countCalls) attrSelects[*j->pos]++;
             return j->value;
         }
         if (!env->prevWith) {
@@ -886,18 +941,10 @@ inline Value * EvalState::lookupVar(Env * env, const ExprVar & var, bool noEval)
 }
 
 
-std::atomic<uint64_t> nrValuesFreed{0};
-
-void finalizeValue(void * obj, void * data)
-{
-    nrValuesFreed++;
-}
-
 Value * EvalState::allocValue()
 {
     nrValues++;
     auto v = (Value *) allocBytes(sizeof(Value));
-    //GC_register_finalizer_no_order(v, finalizeValue, nullptr, nullptr, nullptr);
     return v;
 }
 
@@ -949,9 +996,9 @@ void EvalState::mkThunk_(Value & v, Expr * expr)
 }
 
 
-void EvalState::mkPos(Value & v, Pos * pos)
+void EvalState::mkPos(Value & v, ptr<Pos> pos)
 {
-    if (pos && pos->file.set()) {
+    if (pos->file.set()) {
         mkAttrs(v, 3);
         mkString(*allocAttr(v, sFile), pos->file);
         mkInt(*allocAttr(v, sLine), pos->line);
@@ -974,39 +1021,37 @@ Value * Expr::maybeThunk(EvalState & state, Env & env)
 }
 
 
-unsigned long nrAvoided = 0;
-
 Value * ExprVar::maybeThunk(EvalState & state, Env & env)
 {
     Value * v = state.lookupVar(&env, *this, true);
     /* The value might not be initialised in the environment yet.
        In that case, ignore it. */
-    if (v) { nrAvoided++; return v; }
+    if (v) { state.nrAvoided++; return v; }
     return Expr::maybeThunk(state, env);
 }
 
 
 Value * ExprString::maybeThunk(EvalState & state, Env & env)
 {
-    nrAvoided++;
+    state.nrAvoided++;
     return &v;
 }
 
 Value * ExprInt::maybeThunk(EvalState & state, Env & env)
 {
-    nrAvoided++;
+    state.nrAvoided++;
     return &v;
 }
 
 Value * ExprFloat::maybeThunk(EvalState & state, Env & env)
 {
-    nrAvoided++;
+    state.nrAvoided++;
     return &v;
 }
 
 Value * ExprPath::maybeThunk(EvalState & state, Env & env)
 {
-    nrAvoided++;
+    state.nrAvoided++;
     return &v;
 }
 
@@ -1021,45 +1066,56 @@ void EvalState::evalFile(const Path & path_, Value & v, bool mustBeTrivial)
         return;
     }
 
-    Path path2 = resolveExprPath(path);
-    if ((i = fileEvalCache.find(path2)) != fileEvalCache.end()) {
+    Path resolvedPath = resolveExprPath(path);
+    if ((i = fileEvalCache.find(resolvedPath)) != fileEvalCache.end()) {
         v = i->second;
         return;
     }
 
-    printTalkative("evaluating file '%1%'", path2);
+    printTalkative("evaluating file '%1%'", resolvedPath);
     Expr * e = nullptr;
 
-    auto j = fileParseCache.find(path2);
+    auto j = fileParseCache.find(resolvedPath);
     if (j != fileParseCache.end())
         e = j->second;
 
     if (!e)
-        e = parseExprFromFile(checkSourcePath(path2));
+        e = parseExprFromFile(checkSourcePath(resolvedPath));
+
+    cacheFile(path, resolvedPath, e, v, mustBeTrivial);
+}
+
+
+void EvalState::resetFileCache()
+{
+    fileEvalCache.clear();
+    fileParseCache.clear();
+}
 
-    fileParseCache[path2] = e;
+
+void EvalState::cacheFile(
+    const Path & path,
+    const Path & resolvedPath,
+    Expr * e,
+    Value & v,
+    bool mustBeTrivial)
+{
+    fileParseCache[resolvedPath] = e;
 
     try {
         // Enforce that 'flake.nix' is a direct attrset, not a
         // computation.
         if (mustBeTrivial &&
             !(dynamic_cast<ExprAttrs *>(e)))
-            throw Error("file '%s' must be an attribute set", path);
+            throw EvalError("file '%s' must be an attribute set", path);
         eval(e, v);
     } catch (Error & e) {
-        addErrorTrace(e, "while evaluating the file '%1%':", path2);
+        addErrorTrace(e, "while evaluating the file '%1%':", resolvedPath);
         throw;
     }
 
-    fileEvalCache[path2] = v;
-    if (path != path2) fileEvalCache[path] = v;
-}
-
-
-void EvalState::resetFileCache()
-{
-    fileEvalCache.clear();
-    fileParseCache.clear();
+    fileEvalCache[resolvedPath] = v;
+    if (path != resolvedPath) fileEvalCache[path] = v;
 }
 
 
@@ -1144,7 +1200,7 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
         /* The recursive attributes are evaluated in the new
            environment, while the inherited attributes are evaluated
            in the original environment. */
-        size_t displ = 0;
+        Displacement displ = 0;
         for (auto & i : attrs) {
             Value * vAttr;
             if (hasOverrides && !i.second.inherited) {
@@ -1153,7 +1209,7 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
             } else
                 vAttr = i.second.e->maybeThunk(state, i.second.inherited ? env : env2);
             env2.values[displ++] = vAttr;
-            v.attrs->push_back(Attr(i.first, vAttr, &i.second.pos));
+            v.attrs->push_back(Attr(i.first, vAttr, ptr(&i.second.pos)));
         }
 
         /* If the rec contains an attribute called `__overrides', then
@@ -1185,7 +1241,7 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
 
     else
         for (auto & i : attrs)
-            v.attrs->push_back(Attr(i.first, i.second.e->maybeThunk(state, env), &i.second.pos));
+            v.attrs->push_back(Attr(i.first, i.second.e->maybeThunk(state, env), ptr(&i.second.pos)));
 
     /* Dynamic attrs apply *after* rec and __overrides. */
     for (auto & i : dynamicAttrs) {
@@ -1203,11 +1259,11 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
 
         i.valueExpr->setName(nameSym);
         /* Keep sorted order so find can catch duplicates */
-        v.attrs->push_back(Attr(nameSym, i.valueExpr->maybeThunk(state, *dynamicEnv), &i.pos));
+        v.attrs->push_back(Attr(nameSym, i.valueExpr->maybeThunk(state, *dynamicEnv), ptr(&i.pos)));
         v.attrs->sort(); // FIXME: inefficient
     }
 
-    v.attrs->pos = &pos;
+    v.attrs->pos = ptr(&pos);
 }
 
 
@@ -1221,7 +1277,7 @@ void ExprLet::eval(EvalState & state, Env & env, Value & v)
     /* The recursive attributes are evaluated in the new environment,
        while the inherited attributes are evaluated in the original
        environment. */
-    size_t displ = 0;
+    Displacement displ = 0;
     for (auto & i : attrs->attrs)
         env2.values[displ++] = i.second.e->maybeThunk(state, i.second.inherited ? env : env2);
 
@@ -1262,12 +1318,10 @@ static string showAttrPath(EvalState & state, Env & env, const AttrPath & attrPa
 }
 
 
-unsigned long nrLookups = 0;
-
 void ExprSelect::eval(EvalState & state, Env & env, Value & v)
 {
     Value vTmp;
-    Pos * pos2 = 0;
+    ptr<Pos> pos2(&noPos);
     Value * vAttrs = &vTmp;
 
     e->eval(state, env, vTmp);
@@ -1275,7 +1329,7 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
     try {
 
         for (auto & i : attrPath) {
-            nrLookups++;
+            state.nrLookups++;
             Bindings::iterator j;
             Symbol name = getName(i, state, env);
             if (def) {
@@ -1293,13 +1347,13 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
             }
             vAttrs = j->value;
             pos2 = j->pos;
-            if (state.countCalls && pos2) state.attrSelects[*pos2]++;
+            if (state.countCalls) state.attrSelects[*pos2]++;
         }
 
-        state.forceValue(*vAttrs, ( pos2 != NULL ? *pos2 : this->pos ) );
+        state.forceValue(*vAttrs, (*pos2 != noPos ? *pos2 : this->pos ) );
 
     } catch (Error & e) {
-        if (pos2 && pos2->file != state.sDerivationNix)
+        if (*pos2 != noPos && pos2->file != state.sDerivationNix)
             addErrorTrace(e, *pos2, "while evaluating the attribute '%1%'",
                 showAttrPath(state, env, attrPath));
         throw;
@@ -1340,160 +1394,183 @@ void ExprLambda::eval(EvalState & state, Env & env, Value & v)
 }
 
 
-void ExprApp::eval(EvalState & state, Env & env, Value & v)
+void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value & vRes, const Pos & pos)
 {
-    /* FIXME: vFun prevents GCC from doing tail call optimisation. */
-    Value vFun;
-    e1->eval(state, env, vFun);
-    state.callFunction(vFun, *(e2->maybeThunk(state, env)), v, pos);
-}
+    auto trace = evalSettings.traceFunctionCalls ? std::make_unique<FunctionCallTrace>(pos) : nullptr;
 
+    forceValue(fun, pos);
 
-void EvalState::callPrimOp(Value & fun, Value & arg, Value & v, const Pos & pos)
-{
-    /* Figure out the number of arguments still needed. */
-    size_t argsDone = 0;
-    Value * primOp = &fun;
-    while (primOp->isPrimOpApp()) {
-        argsDone++;
-        primOp = primOp->primOpApp.left;
-    }
-    assert(primOp->isPrimOp());
-    auto arity = primOp->primOp->arity;
-    auto argsLeft = arity - argsDone;
-
-    if (argsLeft == 1) {
-        /* We have all the arguments, so call the primop. */
-
-        /* Put all the arguments in an array. */
-        Value * vArgs[arity];
-        auto n = arity - 1;
-        vArgs[n--] = &arg;
-        for (Value * arg = &fun; arg->isPrimOpApp(); arg = arg->primOpApp.left)
-            vArgs[n--] = arg->primOpApp.right;
-
-        /* And call the primop. */
-        nrPrimOpCalls++;
-        if (countCalls) primOpCalls[primOp->primOp->name]++;
-        primOp->primOp->fun(*this, pos, vArgs, v);
-    } else {
-        Value * fun2 = allocValue();
-        *fun2 = fun;
-        v.mkPrimOpApp(fun2, &arg);
-    }
-}
+    Value vCur(fun);
 
+    auto makeAppChain = [&]()
+    {
+        vRes = vCur;
+        for (size_t i = 0; i < nrArgs; ++i) {
+            auto fun2 = allocValue();
+            *fun2 = vRes;
+            vRes.mkPrimOpApp(fun2, args[i]);
+        }
+    };
 
-void EvalState::callFunction(Value & fun, Value & arg, Value & v, const Pos & pos)
-{
-    auto trace = evalSettings.traceFunctionCalls ? std::make_unique<FunctionCallTrace>(pos) : nullptr;
+    Attr * functor;
 
-    forceValue(fun, pos);
+    while (nrArgs > 0) {
 
-    if (fun.isPrimOp() || fun.isPrimOpApp()) {
-        callPrimOp(fun, arg, v, pos);
-        return;
-    }
+        if (vCur.isLambda()) {
 
-    if (fun.type() == nAttrs) {
-      auto found = fun.attrs->find(sFunctor);
-      if (found != fun.attrs->end()) {
-        /* fun may be allocated on the stack of the calling function,
-         * but for functors we may keep a reference, so heap-allocate
-         * a copy and use that instead.
-         */
-        auto & fun2 = *allocValue();
-        fun2 = fun;
-        /* !!! Should we use the attr pos here? */
-        Value v2;
-        callFunction(*found->value, fun2, v2, pos);
-        return callFunction(v2, arg, v, pos);
-      }
-    }
+            ExprLambda & lambda(*vCur.lambda.fun);
 
-    if (!fun.isLambda()) {
-        throwTypeError(
-          pos,
-          "attempt to call something which is not a function but %1%",
-          showType(fun).c_str(),
-          fakeEnv(1), 0);
-    }
+            auto size =
+                (lambda.arg.empty() ? 0 : 1) +
+                (lambda.hasFormals() ? lambda.formals->formals.size() : 0);
+            Env & env2(allocEnv(size));
+            env2.up = vCur.lambda.env;
 
-    ExprLambda & lambda(*fun.lambda.fun);
+            Displacement displ = 0;
 
-    auto size =
-        (lambda.arg.empty() ? 0 : 1) +
-        (lambda.matchAttrs ? lambda.formals->formals.size() : 0);
-    Env & env2(allocEnv(size));
-    env2.up = fun.lambda.env;
+            if (!lambda.hasFormals())
+                env2.values[displ++] = args[0];
+            else {
+                forceAttrs(*args[0], pos);
 
-    size_t displ = 0;
+                if (!lambda.arg.empty())
+                    env2.values[displ++] = args[0];
 
-    if (!lambda.matchAttrs){
-        env2.values[displ++] = &arg;
-    }
-    else {
-        forceAttrs(arg, pos);
-
-        if (!lambda.arg.empty())
-            env2.values[displ++] = &arg;
-
-        /* For each formal argument, get the actual argument.  If
-           there is no matching actual argument but the formal
-           argument has a default, use the default. */
-        size_t attrsUsed = 0;
-        for (auto & i : lambda.formals->formals) {
-            Bindings::iterator j = arg.attrs->find(i.name);
-            if (j == arg.attrs->end()) {
-                if (!i.def)
-                    throwTypeError(
-                        pos,
-                        "%1% called without required argument '%2%'",
-                        lambda,
-                        i.name,
-                        *fun.lambda.env, &lambda);
-                env2.values[displ++] = i.def->maybeThunk(*this, env2);
+                /* For each formal argument, get the actual argument.  If
+                   there is no matching actual argument but the formal
+                   argument has a default, use the default. */
+                size_t attrsUsed = 0;
+                for (auto & i : lambda.formals->formals) {
+                    auto j = args[0]->attrs->get(i.name);
+                    if (!j) {
+                        if (!i.def) throwTypeError(pos, "%1% called without required argument '%2%'",
+                            lambda, i.name, *fun.lambda.env, &lambda);
+                        env2.values[displ++] = i.def->maybeThunk(*this, env2);
+                    } else {
+                        attrsUsed++;
+                        env2.values[displ++] = j->value;
+                    }
+                }
+
+                /* Check that each actual argument is listed as a formal
+                   argument (unless the attribute match specifies a `...'). */
+                if (!lambda.formals->ellipsis && attrsUsed != args[0]->attrs->size()) {
+                    /* Nope, so show the first unexpected argument to the
+                       user. */
+                    for (auto & i : *args[0]->attrs)
+                        if (lambda.formals->argNames.find(i.name) == lambda.formals->argNames.end())
+                            throwTypeError(pos, "%1% called with unexpected argument '%2%'", lambda, i.name);
+                    abort(); // can't happen
+                }
+            }
+
+            nrFunctionCalls++;
+            if (countCalls) incrFunctionCall(&lambda);
+
+            /* Evaluate the body. */
+            try {
+                lambda.body->eval(*this, env2, vCur);
+            } catch (Error & e) {
+                if (loggerSettings.showTrace.get()) {
+                    addErrorTrace(e, lambda.pos, "while evaluating %s",
+                        (lambda.name.set()
+                            ? "'" + (string) lambda.name + "'"
+                            : "anonymous lambda"));
+                    addErrorTrace(e, pos, "from call site%s", "");
+                }
+                throw;
+            }
+
+            nrArgs--;
+            args += 1;
+        }
+
+        else if (vCur.isPrimOp()) {
+
+            size_t argsLeft = vCur.primOp->arity;
+
+            if (nrArgs < argsLeft) {
+                /* We don't have enough arguments, so create a tPrimOpApp chain. */
+                makeAppChain();
+                return;
             } else {
-                attrsUsed++;
-                env2.values[displ++] = j->value;
+                /* We have all the arguments, so call the primop. */
+                nrPrimOpCalls++;
+                if (countCalls) primOpCalls[vCur.primOp->name]++;
+                vCur.primOp->fun(*this, pos, args, vCur);
+
+                nrArgs -= argsLeft;
+                args += argsLeft;
             }
         }
 
+        else if (vCur.isPrimOpApp()) {
+            /* Figure out the number of arguments still needed. */
+            size_t argsDone = 0;
+            Value * primOp = &vCur;
+            while (primOp->isPrimOpApp()) {
+                argsDone++;
+                primOp = primOp->primOpApp.left;
+            }
+            assert(primOp->isPrimOp());
+            auto arity = primOp->primOp->arity;
+            auto argsLeft = arity - argsDone;
+
+            if (nrArgs < argsLeft) {
+                /* We still don't have enough arguments, so extend the tPrimOpApp chain. */
+                makeAppChain();
+                return;
+            } else {
+                /* We have all the arguments, so call the primop with
+                   the previous and new arguments. */
+
+                Value * vArgs[arity];
+                auto n = argsDone;
+                for (Value * arg = &vCur; arg->isPrimOpApp(); arg = arg->primOpApp.left)
+                    vArgs[--n] = arg->primOpApp.right;
+
+                for (size_t i = 0; i < argsLeft; ++i)
+                    vArgs[argsDone + i] = args[i];
+
+                nrPrimOpCalls++;
+                if (countCalls) primOpCalls[primOp->primOp->name]++;
+                primOp->primOp->fun(*this, pos, vArgs, vCur);
+
+                nrArgs -= argsLeft;
+                args += argsLeft;
+            }
+        }
 
-        /* Check that each actual argument is listed as a formal
-           argument (unless the attribute match specifies a `...'). */
-        if (!lambda.formals->ellipsis && attrsUsed != arg.attrs->size()) {
-            /* Nope, so show the first unexpected argument to the
-               user. */
-            for (auto & i : *arg.attrs)
-                if (lambda.formals->argNames.find(i.name) == lambda.formals->argNames.end())
-                    throwTypeError(pos,
-                        "%1% called with unexpected argument '%2%'",
-                        lambda,
-                        i.name,
-                        *fun.lambda.env, &lambda);
-            abort(); // can't happen
+        else if (vCur.type() == nAttrs && (functor = vCur.attrs->get(sFunctor))) {
+            /* 'vCur' may be allocated on the stack of the calling
+               function, but for functors we may keep a reference, so
+               heap-allocate a copy and use that instead. */
+            Value * args2[] = {allocValue(), args[0]};
+            *args2[0] = vCur;
+            /* !!! Should we use the attr pos here? */
+            callFunction(*functor->value, 2, args2, vCur, pos);
+            nrArgs--;
+            args++;
         }
+
+        else
+            throwTypeError(pos, "attempt to call something which is not a function but %1%", vCur);
     }
 
-    nrFunctionCalls++;
-    if (countCalls) incrFunctionCall(&lambda);
+    vRes = vCur;
+}
 
-    /* Evaluate the body.  This is conditional on showTrace, because
-       catching exceptions makes this function not tail-recursive. */
-    if (loggerSettings.showTrace.get())
-        try {
-            lambda.body->eval(*this, env2, v);
-        } catch (Error & e) {
-            addErrorTrace(e, lambda.pos, "while evaluating %s",
-              (lambda.name.set()
-                  ? "'" + (string) lambda.name + "'"
-                  : "anonymous lambda"));
-            addErrorTrace(e, pos, "from call site%s", "");
-            throw;
-        }
-    else
-        fun.lambda.fun->body->eval(*this, env2, v);
+
+void ExprCall::eval(EvalState & state, Env & env, Value & v)
+{
+    Value vFun;
+    fun->eval(state, env, vFun);
+
+    Value * vArgs[args.size()];
+    for (size_t i = 0; i < args.size(); ++i)
+        vArgs[i] = args[i]->maybeThunk(state, env);
+
+    state.callFunction(vFun, args.size(), vArgs, v, pos);
 }
 
 
@@ -1519,7 +1596,7 @@ void EvalState::autoCallFunction(Bindings & args, Value & fun, Value & res)
         }
     }
 
-    if (!fun.isLambda() || !fun.lambda.fun->matchAttrs) {
+    if (!fun.isLambda() || !fun.lambda.fun->hasFormals()) {
         res = fun;
         return;
     }
@@ -1722,7 +1799,6 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
            and none of the strings are allowed to have contexts. */
         if (first) {
             firstType = vTmp.type();
-            first = false;
         }
 
         if (firstType == nInt) {
@@ -1744,7 +1820,12 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
             } else
                 throwEvalError(pos, "cannot add %1% to a float", showType(vTmp), env, this);
         } else
-            s << state.coerceToString(pos, vTmp, context, false, firstType == nString);
+            /* skip canonization of first path, which would only be not
+            canonized in the first place if it's coming from a ./${foo} type
+            path */
+            s << state.coerceToString(pos, vTmp, context, false, firstType == nString, !first);
+
+        first = false;
     }
 
     if (firstType == nInt)
@@ -1763,7 +1844,7 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
 
 void ExprPos::eval(EvalState & state, Env & env, Value & v)
 {
-    state.mkPos(v, &pos);
+    state.mkPos(v, ptr(&pos));
 }
 
 
@@ -1935,7 +2016,7 @@ std::optional<string> EvalState::tryAttrsToString(const Pos & pos, Value & v,
 }
 
 string EvalState::coerceToString(const Pos & pos, Value & v, PathSet & context,
-    bool coerceMore, bool copyToStore)
+    bool coerceMore, bool copyToStore, bool canonicalizePath)
 {
     forceValue(v, pos);
 
@@ -1947,7 +2028,7 @@ string EvalState::coerceToString(const Pos & pos, Value & v, PathSet & context,
     }
 
     if (v.type() == nPath) {
-        Path path(canonPath(v.path));
+        Path path(canonicalizePath ? canonPath(v.path) : v.path);
         return copyToStore ? copyPathToStore(context, path) : path;
     }
 
@@ -2010,6 +2091,7 @@ string EvalState::copyPathToStore(PathSet & context, const Path & path)
             ? store->computeStorePathForPath(std::string(baseNameOf(path)), checkSourcePath(path)).first
             : store->addToStore(std::string(baseNameOf(path)), checkSourcePath(path), FileIngestionMethod::Recursive, htSHA256, defaultPathFilter, repair);
         dstPath = store->printStorePath(p);
+        allowPath(p);
         srcToStore.insert_or_assign(path, std::move(p));
         printMsg(lvlChatty, "copied source '%1%' -> '%2%'", path, dstPath);
     }
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 91e43ddfe..485c2df83 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -5,6 +5,7 @@
 #include "nixexpr.hh"
 #include "symbol-table.hh"
 #include "config.hh"
+#include "experimental-features.hh"
 
 #include <map>
 #include <optional>
@@ -98,8 +99,14 @@ public:
 
     Value vEmptySet;
 
+    /* Store used to materialise .drv files. */
     const ref<Store> store;
 
+    /* Store used to build stuff. */
+    const ref<Store> buildStore;
+
+    RootValue vCallFlake = nullptr;
+    RootValue vImportedDrvToDerivation = nullptr;
 
 private:
     SrcToStore srcToStore;
@@ -132,13 +139,31 @@ private:
 
 public:
 
-    EvalState(const Strings & _searchPath, ref<Store> store);
+    EvalState(
+        const Strings & _searchPath,
+        ref<Store> store,
+        std::shared_ptr<Store> buildStore = nullptr);
     ~EvalState();
 
+    void requireExperimentalFeatureOnEvaluation(
+        const ExperimentalFeature &,
+        const std::string_view fName,
+        const Pos & pos
+    );
+
     void addToSearchPath(const string & s);
 
     SearchPath getSearchPath() { return searchPath; }
 
+    /* Allow access to a path. */
+    void allowPath(const Path & path);
+
+    /* Allow access to a store path. Note that this gets remapped to
+       the real store path if `store` is a chroot store. */
+    void allowPath(const StorePath & storePath);
+
+    /* Check whether access to a path is allowed and throw an error if
+       not. Otherwise return the canonicalised path. */
     Path checkSourcePath(const Path & path);
 
     void checkURI(const std::string & uri);
@@ -167,6 +192,14 @@ public:
        trivial (i.e. doesn't require arbitrary computation). */
     void evalFile(const Path & path, Value & v, bool mustBeTrivial = false);
 
+    /* Like `cacheFile`, but with an already parsed expression. */
+    void cacheFile(
+        const Path & path,
+        const Path & resolvedPath,
+        Expr * e,
+        Value & v,
+        bool mustBeTrivial = false);
+
     void resetFileCache();
 
     /* Look up a file in the search path. */
@@ -221,7 +254,8 @@ public:
        booleans and lists to a string.  If `copyToStore' is set,
        referenced paths are copied to the Nix store as a side effect. */
     string coerceToString(const Pos & pos, Value & v, PathSet & context,
-        bool coerceMore = false, bool copyToStore = true);
+        bool coerceMore = false, bool copyToStore = true,
+        bool canonicalizePath = true);
 
     string copyPathToStore(PathSet & context, const Path & path);
 
@@ -247,6 +281,8 @@ private:
 
     Value * addConstant(const string & name, Value & v);
 
+    void addConstant(const string & name, Value * v);
+
     Value * addPrimOp(const string & name,
         size_t arity, PrimOpFun primOp);
 
@@ -286,8 +322,14 @@ public:
 
     bool isFunctor(Value & fun);
 
-    void callFunction(Value & fun, Value & arg, Value & v, const Pos & pos);
-    void callPrimOp(Value & fun, Value & arg, Value & v, const Pos & pos);
+    // FIXME: use std::span
+    void callFunction(Value & fun, size_t nrArgs, Value * * args, Value & vRes, const Pos & pos);
+
+    void callFunction(Value & fun, Value & arg, Value & vRes, const Pos & pos)
+    {
+        Value * args[] = {&arg};
+        callFunction(fun, 1, args, vRes, pos);
+    }
 
     /* Automatically call a function for which each argument has a
        default value or has a binding in the `args' map. */
@@ -305,7 +347,7 @@ public:
     void mkList(Value & v, size_t length);
     void mkAttrs(Value & v, size_t capacity);
     void mkThunk_(Value & v, Expr * expr);
-    void mkPos(Value & v, Pos * pos);
+    void mkPos(Value & v, ptr<Pos> pos);
 
     void concatLists(Value & v, size_t nrLists, Value * * lists, const Pos & pos);
 
@@ -320,8 +362,10 @@ private:
     unsigned long nrValuesInEnvs = 0;
     unsigned long nrValues = 0;
     unsigned long nrListElems = 0;
+    unsigned long nrLookups = 0;
     unsigned long nrAttrsets = 0;
     unsigned long nrAttrsInAttrsets = 0;
+    unsigned long nrAvoided = 0;
     unsigned long nrOpUpdates = 0;
     unsigned long nrOpUpdateValuesCopied = 0;
     unsigned long nrListConcats = 0;
@@ -343,6 +387,11 @@ private:
 
     friend struct ExprOpUpdate;
     friend struct ExprOpConcatLists;
+    friend struct ExprVar;
+    friend struct ExprString;
+    friend struct ExprInt;
+    friend struct ExprFloat;
+    friend struct ExprPath;
     friend struct ExprSelect;
     friend void prim_getAttr(EvalState & state, const Pos & pos, Value * * args, Value & v);
     friend void prim_match(EvalState & state, const Pos & pos, Value * * args, Value & v);
diff --git a/src/libexpr/flake/config.cc b/src/libexpr/flake/config.cc
index 63566131e..c03f4106c 100644
--- a/src/libexpr/flake/config.cc
+++ b/src/libexpr/flake/config.cc
@@ -1,4 +1,5 @@
 #include "flake.hh"
+#include "globals.hh"
 
 #include <nlohmann/json.hpp>
 
@@ -22,12 +23,14 @@ static TrustedList readTrustedList()
 
 static void writeTrustedList(const TrustedList & trustedList)
 {
-    writeFile(trustedListPath(), nlohmann::json(trustedList).dump());
+    auto path = trustedListPath();
+    createDirs(dirOf(path));
+    writeFile(path, nlohmann::json(trustedList).dump());
 }
 
 void ConfigFile::apply()
 {
-    std::set<std::string> whitelist{"bash-prompt", "bash-prompt-suffix"};
+    std::set<std::string> whitelist{"bash-prompt", "bash-prompt-suffix", "flake-registry"};
 
     for (auto & [name, value] : settings) {
 
@@ -50,21 +53,19 @@ void ConfigFile::apply()
             auto trustedList = readTrustedList();
 
             bool trusted = false;
-
-            if (auto saved = get(get(trustedList, name).value_or(std::map<std::string, bool>()), valueS)) {
+            if (nix::settings.acceptFlakeConfig){
+                trusted = true;
+            } else if (auto saved = get(get(trustedList, name).value_or(std::map<std::string, bool>()), valueS)) {
                 trusted = *saved;
+                warn("Using saved setting for '%s = %s' from ~/.local/share/nix/trusted-settings.json.", name,valueS);
             } else {
                 // FIXME: filter ANSI escapes, newlines, \r, etc.
-                if (std::tolower(logger->ask(fmt("do you want to allow configuration setting '%s' to be set to '" ANSI_RED "%s" ANSI_NORMAL "' (y/N)?", name, valueS)).value_or('n')) != 'y') {
-                    if (std::tolower(logger->ask("do you want to permanently mark this value as untrusted (y/N)?").value_or('n')) == 'y') {
-                        trustedList[name][valueS] = false;
-                        writeTrustedList(trustedList);
-                    }
-                } else {
-                    if (std::tolower(logger->ask("do you want to permanently mark this value as trusted (y/N)?").value_or('n')) == 'y') {
-                        trustedList[name][valueS] = trusted = true;
-                        writeTrustedList(trustedList);
-                    }
+                if (std::tolower(logger->ask(fmt("do you want to allow configuration setting '%s' to be set to '" ANSI_RED "%s" ANSI_NORMAL "' (y/N)?", name, valueS)).value_or('n')) == 'y') {
+                    trusted = true;
+                }
+                if (std::tolower(logger->ask(fmt("do you want to permanently mark this value as %s (y/N)?",  trusted ? "trusted": "untrusted" )).value_or('n')) == 'y') {
+                    trustedList[name][valueS] = trusted;
+                    writeTrustedList(trustedList);
                 }
             }
 
diff --git a/src/libexpr/flake/flake.cc b/src/libexpr/flake/flake.cc
index 2e94490d4..f5be67d67 100644
--- a/src/libexpr/flake/flake.cc
+++ b/src/libexpr/flake/flake.cc
@@ -1,4 +1,5 @@
 #include "flake.hh"
+#include "eval.hh"
 #include "lockfile.hh"
 #include "primops.hh"
 #include "eval-inline.hh"
@@ -63,8 +64,7 @@ static std::tuple<fetchers::Tree, FlakeRef, FlakeRef> fetchOrSubstituteTree(
     debug("got tree '%s' from '%s'",
         state.store->printStorePath(tree.storePath), lockedRef);
 
-    if (state.allowedPaths)
-        state.allowedPaths->insert(tree.actualPath);
+    state.allowPath(tree.storePath);
 
     assert(!originalRef.input.getNarHash() || tree.storePath == originalRef.input.computeStorePath(*state.store));
 
@@ -88,10 +88,12 @@ static void expectType(EvalState & state, ValueType type,
 }
 
 static std::map<FlakeId, FlakeInput> parseFlakeInputs(
-    EvalState & state, Value * value, const Pos & pos);
+    EvalState & state, Value * value, const Pos & pos,
+    const std::optional<Path> & baseDir);
 
 static FlakeInput parseFlakeInput(EvalState & state,
-    const std::string & inputName, Value * value, const Pos & pos)
+    const std::string & inputName, Value * value, const Pos & pos,
+    const std::optional<Path> & baseDir)
 {
     expectType(state, nAttrs, *value, pos);
 
@@ -115,7 +117,7 @@ static FlakeInput parseFlakeInput(EvalState & state,
                 expectType(state, nBool, *attr.value, *attr.pos);
                 input.isFlake = attr.value->boolean;
             } else if (attr.name == sInputs) {
-                input.overrides = parseFlakeInputs(state, attr.value, *attr.pos);
+                input.overrides = parseFlakeInputs(state, attr.value, *attr.pos, baseDir);
             } else if (attr.name == sFollows) {
                 expectType(state, nString, *attr.value, *attr.pos);
                 input.follows = parseInputPath(attr.value->string.s);
@@ -153,7 +155,7 @@ static FlakeInput parseFlakeInput(EvalState & state,
         if (!attrs.empty())
             throw Error("unexpected flake input attribute '%s', at %s", attrs.begin()->first, pos);
         if (url)
-            input.ref = parseFlakeRef(*url, {}, true);
+            input.ref = parseFlakeRef(*url, baseDir, true);
     }
 
     if (!input.follows && !input.ref)
@@ -163,7 +165,8 @@ static FlakeInput parseFlakeInput(EvalState & state,
 }
 
 static std::map<FlakeId, FlakeInput> parseFlakeInputs(
-    EvalState & state, Value * value, const Pos & pos)
+    EvalState & state, Value * value, const Pos & pos,
+    const std::optional<Path> & baseDir)
 {
     std::map<FlakeId, FlakeInput> inputs;
 
@@ -174,7 +177,8 @@ static std::map<FlakeId, FlakeInput> parseFlakeInputs(
             parseFlakeInput(state,
                 inputAttr.name,
                 inputAttr.value,
-                *inputAttr.pos));
+                *inputAttr.pos,
+                baseDir));
     }
 
     return inputs;
@@ -190,7 +194,8 @@ static Flake getFlake(
         state, originalRef, allowLookup, flakeCache);
 
     // Guard against symlink attacks.
-    auto flakeFile = canonPath(sourceInfo.actualPath + "/" + lockedRef.subdir + "/flake.nix");
+    auto flakeDir = canonPath(sourceInfo.actualPath + "/" + lockedRef.subdir);
+    auto flakeFile = canonPath(flakeDir + "/flake.nix");
     if (!isInDir(flakeFile, sourceInfo.actualPath))
         throw Error("'flake.nix' file of flake '%s' escapes from '%s'",
             lockedRef, state.store->printStorePath(sourceInfo.storePath));
@@ -218,14 +223,14 @@ static Flake getFlake(
     auto sInputs = state.symbols.create("inputs");
 
     if (auto inputs = vInfo.attrs->get(sInputs))
-        flake.inputs = parseFlakeInputs(state, inputs->value, *inputs->pos);
+        flake.inputs = parseFlakeInputs(state, inputs->value, *inputs->pos, flakeDir);
 
     auto sOutputs = state.symbols.create("outputs");
 
     if (auto outputs = vInfo.attrs->get(sOutputs)) {
         expectType(state, nFunction, *outputs->value, *outputs->pos);
 
-        if (outputs->value->isLambda() && outputs->value->lambda.fun->matchAttrs) {
+        if (outputs->value->isLambda() && outputs->value->lambda.fun->hasFormals()) {
             for (auto & formal : outputs->value->lambda.fun->formals->formals) {
                 if (formal.name != state.sSelf)
                     flake.inputs.emplace(formal.name, FlakeInput {
@@ -292,11 +297,18 @@ LockedFlake lockFlake(
     const FlakeRef & topRef,
     const LockFlags & lockFlags)
 {
-    settings.requireExperimentalFeature("flakes");
+    settings.requireExperimentalFeature(Xp::Flakes);
 
     FlakeCache flakeCache;
 
-    auto flake = getFlake(state, topRef, lockFlags.useRegistries, flakeCache);
+    auto useRegistries = lockFlags.useRegistries.value_or(settings.useRegistries);
+
+    auto flake = getFlake(state, topRef, useRegistries, flakeCache);
+
+    if (lockFlags.applyNixConfig) {
+        flake.config.apply();
+        state.store->setOptions();
+    }
 
     try {
 
@@ -317,25 +329,38 @@ LockedFlake lockFlake(
 
         std::vector<FlakeRef> parents;
 
+        struct LockParent {
+            /* The path to this parent. */
+            InputPath path;
+
+            /* Whether we are currently inside a top-level lockfile
+               (inputs absolute) or subordinate lockfile (inputs
+               relative). */
+            bool absolute;
+        };
+
         std::function<void(
             const FlakeInputs & flakeInputs,
             std::shared_ptr<Node> node,
             const InputPath & inputPathPrefix,
-            std::shared_ptr<const Node> oldNode)>
+            std::shared_ptr<const Node> oldNode,
+            const LockParent & parent,
+            const Path & parentPath)>
             computeLocks;
 
         computeLocks = [&](
             const FlakeInputs & flakeInputs,
             std::shared_ptr<Node> node,
             const InputPath & inputPathPrefix,
-            std::shared_ptr<const Node> oldNode)
+            std::shared_ptr<const Node> oldNode,
+            const LockParent & parent,
+            const Path & parentPath)
         {
             debug("computing lock file node '%s'", printInputPath(inputPathPrefix));
 
             /* Get the overrides (i.e. attributes of the form
                'inputs.nixops.inputs.nixpkgs.url = ...'). */
-            // FIXME: check this
-            for (auto & [id, input] : flake.inputs) {
+            for (auto & [id, input] : flakeInputs) {
                 for (auto & [idOverride, inputOverride] : input.overrides) {
                     auto inputPath(inputPathPrefix);
                     inputPath.push_back(id);
@@ -359,22 +384,31 @@ LockedFlake lockFlake(
                        ancestors? */
                     auto i = overrides.find(inputPath);
                     bool hasOverride = i != overrides.end();
-                    if (hasOverride) overridesUsed.insert(inputPath);
+                    if (hasOverride) {
+                        overridesUsed.insert(inputPath);
+                        // Respect the “flakeness” of the input even if we
+                        // override it
+                        i->second.isFlake = input2.isFlake;
+                    }
                     auto & input = hasOverride ? i->second : input2;
 
                     /* Resolve 'follows' later (since it may refer to an input
                        path we haven't processed yet. */
                     if (input.follows) {
                         InputPath target;
-                        if (hasOverride || input.absolute)
-                            /* 'follows' from an override is relative to the
-                               root of the graph. */
+
+                        if (parent.absolute && !hasOverride) {
                             target = *input.follows;
-                        else {
-                            /* Otherwise, it's relative to the current flake. */
-                            target = inputPathPrefix;
+                        } else {
+                            if (hasOverride) {
+                                target = inputPathPrefix;
+                                target.pop_back();
+                            } else
+                                target = parent.path;
+
                             for (auto & i : *input.follows) target.push_back(i);
                         }
+
                         debug("input '%s' follows '%s'", inputPathS, printInputPath(target));
                         node->inputs.insert_or_assign(id, target);
                         continue;
@@ -412,22 +446,18 @@ LockedFlake lockFlake(
                            update it. */
                         auto lb = lockFlags.inputUpdates.lower_bound(inputPath);
 
-                        auto hasChildUpdate =
+                        auto mustRefetch =
                             lb != lockFlags.inputUpdates.end()
                             && lb->size() > inputPath.size()
                             && std::equal(inputPath.begin(), inputPath.end(), lb->begin());
 
-                        if (hasChildUpdate) {
-                            auto inputFlake = getFlake(
-                                state, oldLock->lockedRef, false, flakeCache);
-                            computeLocks(inputFlake.inputs, childNode, inputPath, oldLock);
-                        } else {
+                        FlakeInputs fakeInputs;
+
+                        if (!mustRefetch) {
                             /* No need to fetch this flake, we can be
                                lazy. However there may be new overrides on the
                                inputs of this flake, so we need to check
                                those. */
-                            FlakeInputs fakeInputs;
-
                             for (auto & i : oldLock->inputs) {
                                 if (auto lockedNode = std::get_if<0>(&i.second)) {
                                     fakeInputs.emplace(i.first, FlakeInput {
@@ -435,16 +465,28 @@ LockedFlake lockFlake(
                                         .isFlake = (*lockedNode)->isFlake,
                                     });
                                 } else if (auto follows = std::get_if<1>(&i.second)) {
+                                    auto o = input.overrides.find(i.first);
+                                    // If the override disappeared, we have to refetch the flake,
+                                    // since some of the inputs may not be present in the lockfile.
+                                    if (o == input.overrides.end()) {
+                                        mustRefetch = true;
+                                        // There's no point populating the rest of the fake inputs,
+                                        // since we'll refetch the flake anyways.
+                                        break;
+                                    }
                                     fakeInputs.emplace(i.first, FlakeInput {
                                         .follows = *follows,
-                                        .absolute = true
                                     });
                                 }
                             }
-
-                            computeLocks(fakeInputs, childNode, inputPath, oldLock);
                         }
 
+                        computeLocks(
+                            mustRefetch
+                            ? getFlake(state, oldLock->lockedRef, false, flakeCache).inputs
+                            : fakeInputs,
+                            childNode, inputPath, oldLock, parent, parentPath);
+
                     } else {
                         /* We need to create a new lock file entry. So fetch
                            this input. */
@@ -454,7 +496,15 @@ LockedFlake lockFlake(
                             throw Error("cannot update flake input '%s' in pure mode", inputPathS);
 
                         if (input.isFlake) {
-                            auto inputFlake = getFlake(state, *input.ref, lockFlags.useRegistries, flakeCache);
+                            Path localPath = parentPath;
+                            FlakeRef localRef = *input.ref;
+
+                            // If this input is a path, recurse it down.
+                            // This allows us to resolve path inputs relative to the current flake.
+                            if (localRef.input.getType() == "path")
+                                localPath = absPath(*input.ref->input.getSourcePath(), parentPath);
+
+                            auto inputFlake = getFlake(state, localRef, useRegistries, flakeCache);
 
                             /* Note: in case of an --override-input, we use
                                the *original* ref (input2.ref) for the
@@ -475,6 +525,13 @@ LockedFlake lockFlake(
                             parents.push_back(*input.ref);
                             Finally cleanup([&]() { parents.pop_back(); });
 
+                            // Follows paths from existing inputs in the top-level lockfile are absolute,
+                            // whereas paths in subordinate lockfiles are relative to those lockfiles.
+                            LockParent newParent {
+                                .path = inputPath,
+                                .absolute = oldLock ? true : false
+                            };
+
                             /* Recursively process the inputs of this
                                flake. Also, unless we already have this flake
                                in the top-level lock file, use this flake's
@@ -484,12 +541,13 @@ LockedFlake lockFlake(
                                 oldLock
                                 ? std::dynamic_pointer_cast<const Node>(oldLock)
                                 : LockFile::read(
-                                    inputFlake.sourceInfo->actualPath + "/" + inputFlake.lockedRef.subdir + "/flake.lock").root);
+                                    inputFlake.sourceInfo->actualPath + "/" + inputFlake.lockedRef.subdir + "/flake.lock").root,
+                                newParent, localPath);
                         }
 
                         else {
                             auto [sourceInfo, resolvedRef, lockedRef] = fetchOrSubstituteTree(
-                                state, *input.ref, lockFlags.useRegistries, flakeCache);
+                                state, *input.ref, useRegistries, flakeCache);
                             node->inputs.insert_or_assign(id,
                                 std::make_shared<LockedNode>(lockedRef, *input.ref, false));
                         }
@@ -502,9 +560,17 @@ LockedFlake lockFlake(
             }
         };
 
+        LockParent parent {
+            .path = {},
+            .absolute = true
+        };
+
+        // Bring in the current ref for relative path resolution if we have it
+        auto parentPath = canonPath(flake.sourceInfo->actualPath + "/" + flake.lockedRef.subdir);
+
         computeLocks(
             flake.inputs, newLockFile.root, {},
-            lockFlags.recreateLockFile ? nullptr : oldLockFile.root);
+            lockFlags.recreateLockFile ? nullptr : oldLockFile.root, parent, parentPath);
 
         for (auto & i : lockFlags.inputOverrides)
             if (!overridesUsed.count(i.first))
@@ -554,8 +620,8 @@ LockedFlake lockFlake(
                         topRef.input.markChangedFile(
                             (topRef.subdir == "" ? "" : topRef.subdir + "/") + "flake.lock",
                             lockFlags.commitLockFile
-                            ? std::optional<std::string>(fmt("%s: %s\n\nFlake input changes:\n\n%s",
-                                    relPath, lockFileExists ? "Update" : "Add", diff))
+                            ? std::optional<std::string>(fmt("%s: %s\n\nFlake lock file changes:\n\n%s",
+                                    relPath, lockFileExists ? "Update" : "Add", filterANSIEscapes(diff, true)))
                             : std::nullopt);
 
                         /* Rewriting the lockfile changed the top-level
@@ -563,7 +629,7 @@ LockedFlake lockFlake(
                            also just clear the 'rev' field... */
                         auto prevLockedRef = flake.lockedRef;
                         FlakeCache dummyCache;
-                        flake = getFlake(state, topRef, lockFlags.useRegistries, dummyCache);
+                        flake = getFlake(state, topRef, useRegistries, dummyCache);
 
                         if (lockFlags.commitLockFile &&
                             flake.lockedRef.input.getRev() &&
@@ -580,8 +646,10 @@ LockedFlake lockFlake(
                     }
                 } else
                     throw Error("cannot write modified lock file of flake '%s' (use '--no-write-lock-file' to ignore)", topRef);
-            } else
+            } else {
                 warn("not writing modified lock file of flake '%s':\n%s", topRef, chomp(diff));
+                flake.forceDirty = true;
+            }
         }
 
         return LockedFlake { .flake = std::move(flake), .lockFile = std::move(newLockFile) };
@@ -604,26 +672,32 @@ void callFlake(EvalState & state,
 
     mkString(*vLocks, lockedFlake.lockFile.to_string());
 
-    emitTreeAttrs(state, *lockedFlake.flake.sourceInfo, lockedFlake.flake.lockedRef.input, *vRootSrc);
+    emitTreeAttrs(
+        state,
+        *lockedFlake.flake.sourceInfo,
+        lockedFlake.flake.lockedRef.input,
+        *vRootSrc,
+        false,
+        lockedFlake.flake.forceDirty);
 
     mkString(*vRootSubdir, lockedFlake.flake.lockedRef.subdir);
 
-    static RootValue vCallFlake = nullptr;
-
-    if (!vCallFlake) {
-        vCallFlake = allocRootValue(state.allocValue());
+    if (!state.vCallFlake) {
+        state.vCallFlake = allocRootValue(state.allocValue());
         state.eval(state.parseExprFromString(
             #include "call-flake.nix.gen.hh"
-            , "/"), **vCallFlake);
+            , "/"), **state.vCallFlake);
     }
 
-    state.callFunction(**vCallFlake, *vLocks, *vTmp1, noPos);
+    state.callFunction(**state.vCallFlake, *vLocks, *vTmp1, noPos);
     state.callFunction(*vTmp1, *vRootSrc, *vTmp2, noPos);
     state.callFunction(*vTmp2, *vRootSubdir, vRes, noPos);
 }
 
 static void prim_getFlake(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
+    state.requireExperimentalFeatureOnEvaluation(Xp::Flakes, "builtins.getFlake", pos);
+
     auto flakeRefS = state.forceStringNoCtx(*args[0], pos);
     auto flakeRef = parseFlakeRef(flakeRefS, {}, true);
     if (evalSettings.pureEval && !flakeRef.input.isImmutable())
@@ -633,13 +707,13 @@ static void prim_getFlake(EvalState & state, const Pos & pos, Value * * args, Va
         lockFlake(state, flakeRef,
             LockFlags {
                 .updateLockFile = false,
-                .useRegistries = !evalSettings.pureEval,
+                .useRegistries = !evalSettings.pureEval && settings.useRegistries,
                 .allowMutable  = !evalSettings.pureEval,
             }),
         v);
 }
 
-static RegisterPrimOp r2("__getFlake", 1, prim_getFlake, "flakes");
+static RegisterPrimOp r2("__getFlake", 1, prim_getFlake);
 
 }
 
@@ -649,8 +723,9 @@ Fingerprint LockedFlake::getFingerprint() const
     // and we haven't changed it, then it's sufficient to use
     // flake.sourceInfo.storePath for the fingerprint.
     return hashString(htSHA256,
-        fmt("%s;%d;%d;%s",
+        fmt("%s;%s;%d;%d;%s",
             flake.sourceInfo->storePath.to_string(),
+            flake.lockedRef.subdir,
             flake.lockedRef.input.getRevCount().value_or(0),
             flake.lockedRef.input.getLastModified().value_or(0),
             lockFile));
diff --git a/src/libexpr/flake/flake.hh b/src/libexpr/flake/flake.hh
index d17d5e183..524b18af1 100644
--- a/src/libexpr/flake/flake.hh
+++ b/src/libexpr/flake/flake.hh
@@ -43,7 +43,6 @@ struct FlakeInput
     std::optional<FlakeRef> ref;
     bool isFlake = true;  // true = process flake to get outputs, false = (fetched) static source path
     std::optional<InputPath> follows;
-    bool absolute = false; // whether 'follows' is relative to the flake root
     FlakeInputs overrides;
 };
 
@@ -59,9 +58,10 @@ struct ConfigFile
 /* The contents of a flake.nix file. */
 struct Flake
 {
-    FlakeRef originalRef;   // the original flake specification (by the user)
-    FlakeRef resolvedRef;   // registry references and caching resolved to the specific underlying flake
-    FlakeRef lockedRef;     // the specific local store result of invoking the fetcher
+    FlakeRef originalRef; // the original flake specification (by the user)
+    FlakeRef resolvedRef; // registry references and caching resolved to the specific underlying flake
+    FlakeRef lockedRef; // the specific local store result of invoking the fetcher
+    bool forceDirty = false; // pretend that 'lockedRef' is dirty
     std::optional<std::string> description;
     std::shared_ptr<const fetchers::Tree> sourceInfo;
     FlakeInputs inputs;
@@ -102,7 +102,11 @@ struct LockFlags
 
     /* Whether to use the registries to lookup indirect flake
        references like 'nixpkgs'. */
-    bool useRegistries = true;
+    std::optional<bool> useRegistries = std::nullopt;
+
+    /* Whether to apply flake's nixConfig attribute to the configuration */
+
+    bool applyNixConfig = false;
 
     /* Whether mutable flake references (i.e. those without a Git
        revision or similar) without a corresponding lock are
@@ -137,6 +141,8 @@ void emitTreeAttrs(
     EvalState & state,
     const fetchers::Tree & tree,
     const fetchers::Input & input,
-    Value & v, bool emptyRevFallback = false);
+    Value & v,
+    bool emptyRevFallback = false,
+    bool forceDirty = false);
 
 }
diff --git a/src/libexpr/flake/flakeref.cc b/src/libexpr/flake/flakeref.cc
index 833e8a776..29128d789 100644
--- a/src/libexpr/flake/flakeref.cc
+++ b/src/libexpr/flake/flakeref.cc
@@ -172,8 +172,12 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
         auto parsedURL = parseURL(url);
         std::string fragment;
         std::swap(fragment, parsedURL.fragment);
+
+        auto input = Input::fromURL(parsedURL);
+        input.parent = baseDir;
+
         return std::make_pair(
-            FlakeRef(Input::fromURL(parsedURL), get(parsedURL.query, "dir").value_or("")),
+            FlakeRef(std::move(input), get(parsedURL.query, "dir").value_or("")),
             fragment);
     }
 }
diff --git a/src/libexpr/flake/lockfile.cc b/src/libexpr/flake/lockfile.cc
index 6089d1363..fda340789 100644
--- a/src/libexpr/flake/lockfile.cc
+++ b/src/libexpr/flake/lockfile.cc
@@ -2,6 +2,8 @@
 #include "store-api.hh"
 #include "url-parts.hh"
 
+#include <iomanip>
+
 #include <nlohmann/json.hpp>
 
 namespace nix::flake {
@@ -268,10 +270,20 @@ std::map<InputPath, Node::Edge> LockFile::getAllInputs() const
     return res;
 }
 
+static std::string describe(const FlakeRef & flakeRef)
+{
+    auto s = fmt("'%s'", flakeRef.to_string());
+
+    if (auto lastModified = flakeRef.input.getLastModified())
+        s += fmt(" (%s)", std::put_time(std::gmtime(&*lastModified), "%Y-%m-%d"));
+
+    return s;
+}
+
 std::ostream & operator <<(std::ostream & stream, const Node::Edge & edge)
 {
     if (auto node = std::get_if<0>(&edge))
-        stream << "'" << (*node)->lockedRef << "'";
+        stream << describe((*node)->lockedRef);
     else if (auto follows = std::get_if<1>(&edge))
         stream << fmt("follows '%s'", printInputPath(*follows));
     return stream;
@@ -299,14 +311,15 @@ std::string LockFile::diff(const LockFile & oldLocks, const LockFile & newLocks)
 
     while (i != oldFlat.end() || j != newFlat.end()) {
         if (j != newFlat.end() && (i == oldFlat.end() || i->first > j->first)) {
-            res += fmt("* Added '%s': %s\n", printInputPath(j->first), j->second);
+            res += fmt("• " ANSI_GREEN "Added input '%s':" ANSI_NORMAL "\n    %s\n",
+                printInputPath(j->first), j->second);
             ++j;
         } else if (i != oldFlat.end() && (j == newFlat.end() || i->first < j->first)) {
-            res += fmt("* Removed '%s'\n", printInputPath(i->first));
+            res += fmt("• " ANSI_RED "Removed input '%s'" ANSI_NORMAL "\n", printInputPath(i->first));
             ++i;
         } else {
             if (!equals(i->second, j->second)) {
-                res += fmt("* Updated '%s': %s -> %s\n",
+                res += fmt("• " ANSI_BOLD "Updated input '%s':" ANSI_NORMAL "\n    %s\n  → %s\n",
                     printInputPath(i->first),
                     i->second,
                     j->second);
diff --git a/src/libexpr/lexer.l b/src/libexpr/lexer.l
index 7298419d9..c18877e29 100644
--- a/src/libexpr/lexer.l
+++ b/src/libexpr/lexer.l
@@ -9,6 +9,9 @@
 %s DEFAULT
 %x STRING
 %x IND_STRING
+%x INPATH
+%x INPATH_SLASH
+%x PATH_START
 
 
 %{
@@ -25,6 +28,8 @@ using namespace nix;
 
 namespace nix {
 
+// backup to recover from yyless(0)
+YYLTYPE prev_yylloc;
 
 static void initLoc(YYLTYPE * loc)
 {
@@ -35,14 +40,18 @@ static void initLoc(YYLTYPE * loc)
 
 static void adjustLoc(YYLTYPE * loc, const char * s, size_t len)
 {
+    prev_yylloc = *loc;
+
     loc->first_line = loc->last_line;
     loc->first_column = loc->last_column;
 
-    while (len--) {
+    for (size_t i = 0; i < len; i++) {
        switch (*s++) {
        case '\r':
-           if (*s == '\n') /* cr/lf */
+           if (*s == '\n') { /* cr/lf */
+               i++;
                s++;
+           }
            /* fall through */
        case '\n':
            ++loc->last_line;
@@ -55,6 +64,7 @@ static void adjustLoc(YYLTYPE * loc, const char * s, size_t len)
 }
 
 
+// FIXME: optimize
 static Expr * unescapeStr(SymbolTable & symbols, const char * s, size_t length)
 {
     string t;
@@ -95,9 +105,12 @@ ANY         .|\n
 ID          [a-zA-Z\_][a-zA-Z0-9\_\'\-]*
 INT         [0-9]+
 FLOAT       (([1-9][0-9]*\.[0-9]*)|(0?\.[0-9]+))([Ee][+-]?[0-9]+)?
-PATH        [a-zA-Z0-9\.\_\-\+]*(\/[a-zA-Z0-9\.\_\-\+]+)+\/?
-HPATH       \~(\/[a-zA-Z0-9\.\_\-\+]+)+\/?
-SPATH       \<[a-zA-Z0-9\.\_\-\+]+(\/[a-zA-Z0-9\.\_\-\+]+)*\>
+PATH_CHAR   [a-zA-Z0-9\.\_\-\+]
+PATH        {PATH_CHAR}*(\/{PATH_CHAR}+)+\/?
+PATH_SEG    {PATH_CHAR}*\/
+HPATH       \~(\/{PATH_CHAR}+)+\/?
+HPATH_START \~\/
+SPATH       \<{PATH_CHAR}+(\/{PATH_CHAR}+)*\>
 URI         [a-zA-Z][a-zA-Z0-9\+\-\.]*\:[a-zA-Z0-9\%\/\?\:\@\&\=\+\$\,\-\_\.\!\~\*\']+
 
 
@@ -198,17 +211,75 @@ or          { return OR_KW; }
                    return IND_STR;
                  }
 
+{PATH_SEG}\$\{ |
+{HPATH_START}\$\{ {
+  PUSH_STATE(PATH_START);
+  yyless(0);
+  *yylloc = prev_yylloc;
+}
+
+<PATH_START>{PATH_SEG} {
+  POP_STATE();
+  PUSH_STATE(INPATH_SLASH);
+  yylval->path = strdup(yytext);
+  return PATH;
+}
+
+<PATH_START>{HPATH_START} {
+  POP_STATE();
+  PUSH_STATE(INPATH_SLASH);
+  yylval->path = strdup(yytext);
+  return HPATH;
+}
+
+{PATH} {
+  if (yytext[yyleng-1] == '/')
+    PUSH_STATE(INPATH_SLASH);
+  else
+    PUSH_STATE(INPATH);
+  yylval->path = strdup(yytext);
+  return PATH;
+}
+{HPATH} {
+  if (yytext[yyleng-1] == '/')
+    PUSH_STATE(INPATH_SLASH);
+  else
+    PUSH_STATE(INPATH);
+  yylval->path = strdup(yytext);
+  return HPATH;
+}
+
+<INPATH,INPATH_SLASH>\$\{ {
+  POP_STATE();
+  PUSH_STATE(INPATH);
+  PUSH_STATE(DEFAULT);
+  return DOLLAR_CURLY;
+}
+<INPATH,INPATH_SLASH>{PATH}|{PATH_SEG}|{PATH_CHAR}+ {
+  POP_STATE();
+  if (yytext[yyleng-1] == '/')
+      PUSH_STATE(INPATH_SLASH);
+  else
+      PUSH_STATE(INPATH);
+  yylval->e = new ExprString(data->symbols.create(string(yytext)));
+  return STR;
+}
+<INPATH>{ANY} |
+<INPATH><<EOF>> {
+  /* if we encounter a non-path character we inform the parser that the path has
+     ended with a PATH_END token and re-parse this character in the default
+     context (it may be ')', ';', or something of that sort) */
+  POP_STATE();
+  yyless(0);
+  *yylloc = prev_yylloc;
+  return PATH_END;
+}
+
+<INPATH_SLASH>{ANY} |
+<INPATH_SLASH><<EOF>> {
+  throw ParseError("path has a trailing slash");
+}
 
-{PATH}      { if (yytext[yyleng-1] == '/')
-                  throw ParseError("path '%s' has a trailing slash", yytext);
-              yylval->path = strdup(yytext);
-              return PATH;
-            }
-{HPATH}     { if (yytext[yyleng-1] == '/')
-                  throw ParseError("path '%s' has a trailing slash", yytext);
-              yylval->path = strdup(yytext);
-              return HPATH;
-            }
 {SPATH}     { yylval->path = strdup(yytext); return SPATH; }
 {URI}       { yylval->uri = strdup(yytext); return URI; }
 
diff --git a/src/libexpr/local.mk b/src/libexpr/local.mk
index 26c53d301..016631647 100644
--- a/src/libexpr/local.mk
+++ b/src/libexpr/local.mk
@@ -15,8 +15,8 @@ libexpr_CXXFLAGS += -I src/libutil -I src/libstore -I src/libfetchers -I src/lib
 
 libexpr_LIBS = libutil libstore libfetchers
 
-libexpr_LDFLAGS = -lboost_context
-ifneq ($(OS), FreeBSD)
+libexpr_LDFLAGS += -lboost_context -pthread
+ifdef HOST_LINUX
  libexpr_LDFLAGS += -ldl
 endif
 
@@ -35,7 +35,7 @@ $(d)/lexer-tab.cc $(d)/lexer-tab.hh: $(d)/lexer.l
 
 clean-files += $(d)/parser-tab.cc $(d)/parser-tab.hh $(d)/lexer-tab.cc $(d)/lexer-tab.hh
 
-$(eval $(call install-file-in, $(d)/nix-expr.pc, $(prefix)/lib/pkgconfig, 0644))
+$(eval $(call install-file-in, $(d)/nix-expr.pc, $(libdir)/pkgconfig, 0644))
 
 $(foreach i, $(wildcard src/libexpr/flake/*.hh), \
   $(eval $(call install-file-in, $(i), $(includedir)/nix/flake, 0644)))
diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
index 3e42789a2..696b149e3 100644
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -123,7 +123,7 @@ void ExprList::show(std::ostream & str) const
 void ExprLambda::show(std::ostream & str) const
 {
     str << "(";
-    if (matchAttrs) {
+    if (hasFormals()) {
         str << "{ ";
         bool first = true;
         for (auto & i : formals->formals) {
@@ -142,6 +142,16 @@ void ExprLambda::show(std::ostream & str) const
     str << ": " << *body << ")";
 }
 
+void ExprCall::show(std::ostream & str) const
+{
+    str << '(' << *fun;
+    for (auto e : args) {
+        str <<  ' ';
+        str << *e;
+    }
+    str << ')';
+}
+
 void ExprLet::show(std::ostream & str) const
 {
     str << "(let ";
@@ -273,13 +283,13 @@ void ExprVar::bindVars(const std::shared_ptr<const StaticEnv> &env)
     /* Check whether the variable appears in the environment.  If so,
        set its level and displacement. */
     const StaticEnv * curEnv;
-    unsigned int level;
+    Level level;
     int withLevel = -1;
     for (curEnv = env.get(), level = 0; curEnv; curEnv = curEnv->up, level++) {
         if (curEnv->isWith) {
             if (withLevel == -1) withLevel = level;
         } else {
-            StaticEnv::Vars::const_iterator i = curEnv->vars.find(name);
+            auto i = curEnv->find(name);
             if (i != curEnv->vars.end()) {
                 fromWith = false;
                 this->level = level;
@@ -332,12 +342,13 @@ void ExprAttrs::bindVars(const std::shared_ptr<const StaticEnv> &env)
         staticenv = env;
 
     if (recursive) {
-        auto newEnv = std::shared_ptr<StaticEnv>(new StaticEnv(false, env.get()));  
+        auto newEnv = std::shared_ptr<StaticEnv>(new StaticEnv(false, env.get(), recursive ? attrs.size() : 0));  
 
-        unsigned int displ = 0;
-        for (auto & i : attrs) {
-            newEnv->vars[i.first] = i.second.displ = displ++;
-        }
+        Displacement displ = 0;
+        for (auto & i : attrs)
+            newEnv.vars.emplace_back(i.first, i.second.displ = displ++);
+
+        // No need to sort newEnv since attrs is in sorted order.
 
         for (auto & i : attrs)
             i.second.e->bindVars(i.second.inherited ? env : newEnv);
@@ -372,15 +383,21 @@ void ExprLambda::bindVars(const std::shared_ptr<const StaticEnv> &env)
     if (debuggerHook)
         staticenv = env;
 
-    auto newEnv = std::shared_ptr<StaticEnv>(new StaticEnv(false, env.get()));
+    auto newEnv = std::shared_ptr<StaticEnv>(
+        new StaticEnv(
+                false, env.get(),
+                (hasFormals() ? formals->formals.size() : 0) +
+                (arg.empty() ? 0 : 1)));
 
-    unsigned int displ = 0;
+    Displacement displ = 0;
 
-    if (!arg.empty()) newEnv->vars[arg] = displ++;
+    if (!arg.empty()) newEnv.vars.emplace_back(arg, displ++);
 
-    if (matchAttrs) {
+    if (hasFormals()) {
         for (auto & i : formals->formals)
-            newEnv->vars[i.name] = displ++;
+            newEnv.vars.emplace_back(i.name, displ++);
+
+        newEnv.sort();
 
         for (auto & i : formals->formals)
             if (i.def) i.def->bindVars(newEnv);
@@ -389,16 +406,28 @@ void ExprLambda::bindVars(const std::shared_ptr<const StaticEnv> &env)
     body->bindVars(newEnv);
 }
 
-void ExprLet::bindVars(const std::shared_ptr<const StaticEnv> &env)
+void ExprCall::bindVars(const StaticEnv & env)
 {
     if (debuggerHook)
         staticenv = env;
 
-    auto newEnv = std::shared_ptr<StaticEnv>(new StaticEnv(false, env.get()));
+    fun->bindVars(env);
+    for (auto e : args)
+        e->bindVars(env);
+}
+
+void ExprLet::bindVars(const StaticEnv & env)
+{
+    if (debuggerHook)
+        staticenv = env;
+
+    auto newEnv = std::shared_ptr<StaticEnv>(new StaticEnv(false, env.get(), attrs->attrs.size()));
 
-    unsigned int displ = 0;
+    Displacement displ = 0;
     for (auto & i : attrs->attrs)
-        newEnv->vars[i.first] = i.second.displ = displ++;
+        newEnv.vars.emplace_back(i.first, i.second.displ = displ++);
+
+    // No need to sort newEnv since attrs->attrs is in sorted order.
 
     for (auto & i : attrs->attrs)
         i.second.e->bindVars(i.second.inherited ? env : newEnv);
@@ -415,7 +444,7 @@ void ExprWith::bindVars(const std::shared_ptr<const StaticEnv> &env)
        level so that `lookupVar' can look up variables in the previous
        `with' if this one doesn't contain the desired attribute. */
     const StaticEnv * curEnv;
-    unsigned int level;
+    Level level;
     prevWith = 0;
     for (curEnv = env.get(), level = 1; curEnv; curEnv = curEnv->up, level++)
         if (curEnv->isWith) {
@@ -503,5 +532,4 @@ size_t SymbolTable::totalSize() const
     return n;
 }
 
-
 }
diff --git a/src/libexpr/nixexpr.hh b/src/libexpr/nixexpr.hh
index a78ea6215..825933fa1 100644
--- a/src/libexpr/nixexpr.hh
+++ b/src/libexpr/nixexpr.hh
@@ -4,8 +4,6 @@
 #include "symbol-table.hh"
 #include "error.hh"
 
-#include <map>
-
 
 namespace nix {
 
@@ -138,6 +136,9 @@ struct ExprPath : Expr
     Value * maybeThunk(EvalState & state, Env & env);
 };
 
+typedef uint32_t Level;
+typedef uint32_t Displacement;
+
 struct ExprVar : Expr
 {
     Pos pos;
@@ -153,8 +154,8 @@ struct ExprVar : Expr
        value is obtained by getting the attribute named `name' from
        the set stored in the environment that is `level' levels up
        from the current one.*/
-    unsigned int level;
-    unsigned int displ;
+    Level level;
+    Displacement displ;
 
     ExprVar(const Symbol & name) : name(name) { };
     ExprVar(const Pos & pos, const Symbol & name) : pos(pos), name(name) { };
@@ -188,7 +189,7 @@ struct ExprAttrs : Expr
         bool inherited;
         Expr * e;
         Pos pos;
-        unsigned int displ; // displacement
+        Displacement displ; // displacement
         AttrDef(Expr * e, const Pos & pos, bool inherited=false)
             : inherited(inherited), e(e), pos(pos) { };
         AttrDef() { };
@@ -236,11 +237,10 @@ struct ExprLambda : Expr
     Pos pos;
     Symbol name;
     Symbol arg;
-    bool matchAttrs;
     Formals * formals;
     Expr * body;
-    ExprLambda(const Pos & pos, const Symbol & arg, bool matchAttrs, Formals * formals, Expr * body)
-        : pos(pos), arg(arg), matchAttrs(matchAttrs), formals(formals), body(body)
+    ExprLambda(const Pos & pos, const Symbol & arg, Formals * formals, Expr * body)
+        : pos(pos), arg(arg), formals(formals), body(body)
     {
         if (!arg.empty() && formals && formals->argNames.find(arg) != formals->argNames.end())
             throw ParseError({
@@ -250,6 +250,18 @@ struct ExprLambda : Expr
     };
     void setName(Symbol & name);
     string showNamePos() const;
+    inline bool hasFormals() const { return formals != nullptr; }
+    COMMON_METHODS
+};
+
+struct ExprCall : Expr
+{
+    Expr * fun;
+    std::vector<Expr *> args;
+    Pos pos;
+    ExprCall(const Pos & pos, Expr * fun, std::vector<Expr *> && args)
+        : fun(fun), args(args), pos(pos)
+    { }
     COMMON_METHODS
 };
 
@@ -311,7 +323,6 @@ struct ExprOpNot : Expr
         void eval(EvalState & state, Env & env, Value & v); \
     };
 
-MakeBinOp(ExprApp, "")
 MakeBinOp(ExprOpEq, "==")
 MakeBinOp(ExprOpNEq, "!=")
 MakeBinOp(ExprOpAnd, "&&")
@@ -345,9 +356,28 @@ struct StaticEnv
 {
     bool isWith;
     const StaticEnv * up;
-    typedef std::map<Symbol, unsigned int> Vars;
+
+    // Note: these must be in sorted order.
+    typedef std::vector<std::pair<Symbol, Displacement>> Vars;
     Vars vars;
-    StaticEnv(bool isWith, const StaticEnv * up) : isWith(isWith), up(up) { };
+
+    StaticEnv(bool isWith, const StaticEnv * up, size_t expectedSize = 0) : isWith(isWith), up(up) {
+        vars.reserve(expectedSize);
+    };
+
+    void sort()
+    {
+        std::sort(vars.begin(), vars.end(),
+            [](const Vars::value_type & a, const Vars::value_type & b) { return a.first < b.first; });
+    }
+
+    Vars::const_iterator find(const Symbol & name) const
+    {
+        Vars::value_type key(name, 0);
+        auto i = std::lower_bound(vars.begin(), vars.end(), key);
+        if (i != vars.end() && i->first == name) return i;
+        return vars.end();
+    }
 };
 
 
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index d1e898677..58af0df7d 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -33,11 +33,9 @@ namespace nix {
         Symbol file;
         FileOrigin origin;
         std::optional<ErrorInfo> error;
-        Symbol sLetBody;
         ParseData(EvalState & state)
             : state(state)
             , symbols(state.symbols)
-            , sLetBody(symbols.create("<let-body>"))
             { };
     };
 
@@ -126,14 +124,14 @@ static void addAttr(ExprAttrs * attrs, AttrPath & attrPath,
                     auto j2 = jAttrs->attrs.find(ad.first);
                     if (j2 != jAttrs->attrs.end()) // Attr already defined in iAttrs, error.
                         dupAttr(ad.first, j2->second.pos, ad.second.pos);
-                    jAttrs->attrs[ad.first] = ad.second;
+                    jAttrs->attrs.emplace(ad.first, ad.second);
                 }
             } else {
                 dupAttr(attrPath, pos, j->second.pos);
             }
         } else {
             // This attr path is not defined. Let's create it.
-            attrs->attrs[i->symbol] = ExprAttrs::AttrDef(e, pos);
+            attrs->attrs.emplace(i->symbol, ExprAttrs::AttrDef(e, pos));
             e->setName(i->symbol);
         }
     } else {
@@ -283,20 +281,20 @@ void yyerror(YYLTYPE * loc, yyscan_t scanner, ParseData * data, const char * err
 }
 
 %type <e> start expr expr_function expr_if expr_op
-%type <e> expr_app expr_select expr_simple
+%type <e> expr_select expr_simple expr_app
 %type <list> expr_list
 %type <attrs> binds
 %type <formals> formals
 %type <formal> formal
 %type <attrNames> attrs attrpath
 %type <string_parts> string_parts_interpolated ind_string_parts
-%type <e> string_parts string_attr
+%type <e> path_start string_parts string_attr
 %type <id> attr
 %token <id> ID ATTRPATH
 %token <e> STR IND_STR
 %token <n> INT
 %token <nf> FLOAT
-%token <path> PATH HPATH SPATH
+%token <path> PATH HPATH SPATH PATH_END
 %token <uri> URI
 %token IF THEN ELSE ASSERT WITH LET IN REC INHERIT EQ NEQ AND OR IMPL OR_KW
 %token DOLLAR_CURLY /* == ${ */
@@ -324,13 +322,13 @@ expr: expr_function;
 
 expr_function
   : ID ':' expr_function
-    { $$ = new ExprLambda(CUR_POS, data->symbols.create($1), false, 0, $3); }
+    { $$ = new ExprLambda(CUR_POS, data->symbols.create($1), 0, $3); }
   | '{' formals '}' ':' expr_function
-    { $$ = new ExprLambda(CUR_POS, data->symbols.create(""), true, $2, $5); }
+    { $$ = new ExprLambda(CUR_POS, data->symbols.create(""), $2, $5); }
   | '{' formals '}' '@' ID ':' expr_function
-    { $$ = new ExprLambda(CUR_POS, data->symbols.create($5), true, $2, $7); }
+    { $$ = new ExprLambda(CUR_POS, data->symbols.create($5), $2, $7); }
   | ID '@' '{' formals '}' ':' expr_function
-    { $$ = new ExprLambda(CUR_POS, data->symbols.create($1), true, $4, $7); }
+    { $$ = new ExprLambda(CUR_POS, data->symbols.create($1), $4, $7); }
   | ASSERT expr ';' expr_function
     { $$ = new ExprAssert(CUR_POS, $2, $4); }
   | WITH expr ';' expr_function
@@ -353,13 +351,13 @@ expr_if
 
 expr_op
   : '!' expr_op %prec NOT { $$ = new ExprOpNot($2); }
-  | '-' expr_op %prec NEGATE { $$ = new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.create("__sub")), new ExprInt(0)), $2); }
+  | '-' expr_op %prec NEGATE { $$ = new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__sub")), {new ExprInt(0), $2}); }
   | expr_op EQ expr_op { $$ = new ExprOpEq($1, $3); }
   | expr_op NEQ expr_op { $$ = new ExprOpNEq($1, $3); }
-  | expr_op '<' expr_op { $$ = new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.create("__lessThan")), $1), $3); }
-  | expr_op LEQ expr_op { $$ = new ExprOpNot(new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.create("__lessThan")), $3), $1)); }
-  | expr_op '>' expr_op { $$ = new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.create("__lessThan")), $3), $1); }
-  | expr_op GEQ expr_op { $$ = new ExprOpNot(new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.create("__lessThan")), $1), $3)); }
+  | expr_op '<' expr_op { $$ = new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__lessThan")), {$1, $3}); }
+  | expr_op LEQ expr_op { $$ = new ExprOpNot(new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__lessThan")), {$3, $1})); }
+  | expr_op '>' expr_op { $$ = new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__lessThan")), {$3, $1}); }
+  | expr_op GEQ expr_op { $$ = new ExprOpNot(new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__lessThan")), {$1, $3})); }
   | expr_op AND expr_op { $$ = new ExprOpAnd(CUR_POS, $1, $3); }
   | expr_op OR expr_op { $$ = new ExprOpOr(CUR_POS, $1, $3); }
   | expr_op IMPL expr_op { $$ = new ExprOpImpl(CUR_POS, $1, $3); }
@@ -367,17 +365,22 @@ expr_op
   | expr_op '?' attrpath { $$ = new ExprOpHasAttr($1, *$3); }
   | expr_op '+' expr_op
     { $$ = new ExprConcatStrings(CUR_POS, false, new vector<Expr *>({$1, $3})); }
-  | expr_op '-' expr_op { $$ = new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.create("__sub")), $1), $3); }
-  | expr_op '*' expr_op { $$ = new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.create("__mul")), $1), $3); }
-  | expr_op '/' expr_op { $$ = new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.create("__div")), $1), $3); }
+  | expr_op '-' expr_op { $$ = new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__sub")), {$1, $3}); }
+  | expr_op '*' expr_op { $$ = new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__mul")), {$1, $3}); }
+  | expr_op '/' expr_op { $$ = new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__div")), {$1, $3}); }
   | expr_op CONCAT expr_op { $$ = new ExprOpConcatLists(CUR_POS, $1, $3); }
   | expr_app
   ;
 
 expr_app
-  : expr_app expr_select
-    { $$ = new ExprApp(CUR_POS, $1, $2); }
-  | expr_select { $$ = $1; }
+  : expr_app expr_select {
+      if (auto e2 = dynamic_cast<ExprCall *>($1)) {
+          e2->args.push_back($2);
+          $$ = $1;
+      } else
+          $$ = new ExprCall(CUR_POS, $1, {$2});
+  }
+  | expr_select
   ;
 
 expr_select
@@ -388,7 +391,7 @@ expr_select
   | /* Backwards compatibility: because Nixpkgs has a rarely used
        function named ‘or’, allow stuff like ‘map or [...]’. */
     expr_simple OR_KW
-    { $$ = new ExprApp(CUR_POS, $1, new ExprVar(CUR_POS, data->symbols.create("or"))); }
+    { $$ = new ExprCall(CUR_POS, $1, {new ExprVar(CUR_POS, data->symbols.create("or"))}); }
   | expr_simple { $$ = $1; }
   ;
 
@@ -405,17 +408,20 @@ expr_simple
   | IND_STRING_OPEN ind_string_parts IND_STRING_CLOSE {
       $$ = stripIndentation(CUR_POS, data->symbols, *$2);
   }
-  | PATH { $$ = new ExprPath(absPath($1, data->basePath)); }
-  | HPATH { $$ = new ExprPath(getHome() + string{$1 + 1}); }
+  | path_start PATH_END { $$ = $1; }
+  | path_start string_parts_interpolated PATH_END {
+      $2->insert($2->begin(), $1);
+      $$ = new ExprConcatStrings(CUR_POS, false, $2);
+  }
   | SPATH {
       string path($1 + 1, strlen($1) - 2);
-      $$ = new ExprApp(CUR_POS,
-          new ExprApp(new ExprVar(data->symbols.create("__findFile")),
-              new ExprVar(data->symbols.create("__nixPath"))),
-          new ExprString(data->symbols.create(path)));
+      $$ = new ExprCall(CUR_POS,
+          new ExprVar(data->symbols.create("__findFile")),
+          {new ExprVar(data->symbols.create("__nixPath")),
+           new ExprString(data->symbols.create(path))});
   }
   | URI {
-      static bool noURLLiterals = settings.isExperimentalFeatureEnabled("no-url-literals");
+      static bool noURLLiterals = settings.isExperimentalFeatureEnabled(Xp::NoUrlLiterals);
       if (noURLLiterals)
           throw ParseError({
               .msg = hintfmt("URL literals are disabled"),
@@ -452,6 +458,20 @@ string_parts_interpolated
     }
   ;
 
+path_start
+  : PATH {
+    Path path(absPath($1, data->basePath));
+    /* add back in the trailing '/' to the first segment */
+    if ($1[strlen($1)-1] == '/' && strlen($1) > 1)
+      path += "/";
+    $$ = new ExprPath(path);
+  }
+  | HPATH {
+    Path path(getHome() + string($1 + 1));
+    $$ = new ExprPath(path);
+  }
+  ;
+
 ind_string_parts
   : ind_string_parts IND_STR { $$ = $1; $1->push_back($2); }
   | ind_string_parts DOLLAR_CURLY expr '}' { $$ = $1; $1->push_back($3); }
@@ -466,7 +486,7 @@ binds
           if ($$->attrs.find(i.symbol) != $$->attrs.end())
               dupAttr(i.symbol, makeCurPos(@3, data), $$->attrs[i.symbol].pos);
           Pos pos = makeCurPos(@3, data);
-          $$->attrs[i.symbol] = ExprAttrs::AttrDef(new ExprVar(CUR_POS, i.symbol), pos, true);
+          $$->attrs.emplace(i.symbol, ExprAttrs::AttrDef(new ExprVar(CUR_POS, i.symbol), pos, true));
       }
     }
   | binds INHERIT '(' expr ')' attrs ';'
@@ -475,7 +495,7 @@ binds
       for (auto & i : *$6) {
           if ($$->attrs.find(i.symbol) != $$->attrs.end())
               dupAttr(i.symbol, makeCurPos(@6, data), $$->attrs[i.symbol].pos);
-          $$->attrs[i.symbol] = ExprAttrs::AttrDef(new ExprSelect(CUR_POS, $4, i.symbol), makeCurPos(@6, data));
+          $$->attrs.emplace(i.symbol, ExprAttrs::AttrDef(new ExprSelect(CUR_POS, $4, i.symbol), makeCurPos(@6, data)));
       }
     }
   | { $$ = new ExprAttrs(makeCurPos(@0, data)); }
@@ -735,7 +755,7 @@ std::pair<bool, std::string> EvalState::resolveSearchPathElem(const SearchPathEl
             res = { true, path };
         else {
             logWarning({
-                .msg = hintfmt("warning: Nix search path entry '%1%' does not exist, ignoring", elem.second)
+                .msg = hintfmt("Nix search path entry '%1%' does not exist, ignoring", elem.second)
             });
             res = { false, "" };
         }
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 0400c8942..a9ee96bfa 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -21,6 +21,8 @@
 #include <regex>
 #include <dlfcn.h>
 
+#include <cmath>
+
 
 namespace nix {
 
@@ -50,16 +52,13 @@ void EvalState::realiseContext(const PathSet & context)
     if (drvs.empty()) return;
 
     if (!evalSettings.enableImportFromDerivation)
-        throw EvalError("attempted to realize '%1%' during evaluation but 'allow-import-from-derivation' is false",
+        throw Error(
+            "cannot build '%1%' during evaluation because the option 'allow-import-from-derivation' is disabled",
             store->printStorePath(drvs.begin()->drvPath));
 
-    /* For performance, prefetch all substitute info. */
-    StorePathSet willBuild, willSubstitute, unknown;
-    uint64_t downloadSize, narSize;
+    /* Build/substitute the context. */
     std::vector<DerivedPath> buildReqs;
     for (auto & d : drvs) buildReqs.emplace_back(DerivedPath { d });
-    store->queryMissing(buildReqs, willBuild, willSubstitute, unknown, downloadSize, narSize);
-
     store->buildPaths(buildReqs);
 
     /* Add the output of this derivations to the allowed
@@ -71,7 +70,7 @@ void EvalState::realiseContext(const PathSet & context)
                 if (outputPaths.count(outputName) == 0)
                     throw Error("derivation '%s' does not have an output named '%s'",
                             store->printStorePath(drvPath), outputName);
-                allowedPaths->insert(store->printStorePath(outputPaths.at(outputName)));
+                allowPath(outputPaths.at(outputName));
             }
         }
     }
@@ -122,7 +121,7 @@ static void import(EvalState & state, const Pos & pos, Value & vPath, Value * vS
         });
     } catch (Error & e) {
         e.addTrace(pos, "while importing '%s'", path);
-        throw e;
+        throw;
     }
 
     Path realPath = state.checkSourcePath(state.toRealPath(path, context));
@@ -158,16 +157,15 @@ static void import(EvalState & state, const Pos & pos, Value & vPath, Value * vS
         }
         w.attrs->sort();
 
-        static RootValue fun;
-        if (!fun) {
-            fun = allocRootValue(state.allocValue());
+        if (!state.vImportedDrvToDerivation) {
+            state.vImportedDrvToDerivation = allocRootValue(state.allocValue());
             state.eval(state.parseExprFromString(
                 #include "imported-drv-to-derivation.nix.gen.hh"
-                , "/"), **fun);
+                , "/"), **state.vImportedDrvToDerivation);
         }
 
-        state.forceFunction(**fun, pos);
-        mkApp(v, **fun, w);
+        state.forceFunction(**state.vImportedDrvToDerivation, pos);
+        mkApp(v, **state.vImportedDrvToDerivation, w);
         state.forceAttrs(v, pos);
     }
 
@@ -186,14 +184,17 @@ static void import(EvalState & state, const Pos & pos, Value & vPath, Value * vS
             Env * env = &state.allocEnv(vScope->attrs->size());
             env->up = &state.baseEnv;
 
-            auto staticEnv = std::shared_ptr<StaticEnv>(new StaticEnv(false, state.staticBaseEnv.get()));
+            auto staticEnv = std::shared_ptr<StaticEnv>(new StaticEnv(false, state.staticBaseEnv.get(), vScope->attrs->size()));
 
             unsigned int displ = 0;
             for (auto & attr : *vScope->attrs) {
-                staticEnv->vars[attr.name] = displ;
+                staticEnv.vars.emplace_back(attr.name, displ);
                 env->values[displ++] = attr.value;
             }
 
+            // No need to call staticEnv.sort(), because
+            // args[0]->attrs is already sorted.
+
             printTalkative("evaluating file '%1%'", realPath);
             Expr * e = state.parseExprFromFile(resolveExprPath(realPath), staticEnv);
 
@@ -412,7 +413,7 @@ static RegisterPrimOp primop_isNull({
       Return `true` if *e* evaluates to `null`, and `false` otherwise.
 
       > **Warning**
-      > 
+      >
       > This function is *deprecated*; just write `e == null` instead.
     )",
     .fun = prim_isNull,
@@ -516,7 +517,11 @@ static RegisterPrimOp primop_isPath({
 
 struct CompareValues
 {
-    bool operator () (const Value * v1, const Value * v2) const
+    EvalState & state;
+
+    CompareValues(EvalState & state) : state(state) { };
+
+    bool operator () (Value * v1, Value * v2) const
     {
         if (v1->type() == nFloat && v2->type() == nInt)
             return v1->fpoint < v2->integer;
@@ -533,6 +538,17 @@ struct CompareValues
                 return strcmp(v1->string.s, v2->string.s) < 0;
             case nPath:
                 return strcmp(v1->path, v2->path) < 0;
+            case nList:
+                // Lexicographic comparison
+                for (size_t i = 0;; i++) {
+                    if (i == v2->listSize()) {
+                        return false;
+                    } else if (i == v1->listSize()) {
+                        return true;
+                    } else if (!state.eqValues(*v1->listElems()[i], *v2->listElems()[i])) {
+                        return (*this)(v1->listElems()[i], v2->listElems()[i]);
+                    }
+                }
             default:
                 throw EvalError("cannot compare %1% with %2%", showType(*v1), showType(*v2));
         }
@@ -620,7 +636,8 @@ static void prim_genericClosure(EvalState & state, const Pos & pos, Value * * ar
     ValueList res;
     // `doneKeys' doesn't need to be a GC root, because its values are
     // reachable from res.
-    set<Value *, CompareValues> doneKeys;
+    auto cmp = CompareValues(state);
+    set<Value *, decltype(cmp)> doneKeys(cmp);
     while (!workSet.empty()) {
         Value * e = *(workSet.begin());
         workSet.pop_front();
@@ -714,6 +731,44 @@ static RegisterPrimOp primop_addErrorContext(RegisterPrimOp::Info {
     .fun = prim_addErrorContext,
 });
 
+static void prim_ceil(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    auto value = state.forceFloat(*args[0], args[0]->determinePos(pos));
+    mkInt(v, ceil(value));
+}
+
+static RegisterPrimOp primop_ceil({
+    .name = "__ceil",
+    .args = {"double"},
+    .doc = R"(
+        Converts an IEEE-754 double-precision floating-point number (*double*) to
+        the next higher integer.
+
+        If the datatype is neither an integer nor a "float", an evaluation error will be
+        thrown.
+    )",
+    .fun = prim_ceil,
+});
+
+static void prim_floor(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    auto value = state.forceFloat(*args[0], args[0]->determinePos(pos));
+    mkInt(v, floor(value));
+}
+
+static RegisterPrimOp primop_floor({
+    .name = "__floor",
+    .args = {"double"},
+    .doc = R"(
+        Converts an IEEE-754 double-precision floating-point number (*double*) to
+        the next lower integer.
+
+        If the datatype is neither an integer nor a "float", an evaluation error will be
+        thrown.
+    )",
+    .fun = prim_floor,
+});
+
 /* Try evaluating the argument. Success => {success=true; value=something;},
  * else => {success=false; value=false;} */
 static void prim_tryEval(EvalState & state, const Pos & pos, Value * * args, Value & v)
@@ -949,8 +1004,9 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
             }
 
             if (i->name == state.sContentAddressed) {
-                settings.requireExperimentalFeature("ca-derivations");
                 contentAddressed = state.forceBool(*i->value, pos);
+                if (contentAddressed)
+                    settings.requireExperimentalFeature(Xp::CaDerivations);
             }
 
             /* The `args' attribute is special: it supplies the
@@ -972,7 +1028,7 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
                     if (i->name == state.sStructuredAttrs) continue;
 
                     auto placeholder(jsonObject->placeholder(key));
-                    printValueAsJSON(state, true, *i->value, placeholder, context);
+                    printValueAsJSON(state, true, *i->value, pos, placeholder, context);
 
                     if (i->name == state.sBuilder)
                         drv.builder = state.forceString(*i->value, context, posDrvName);
@@ -1134,7 +1190,7 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
         // hash per output.
         auto hashModulo = hashDerivationModulo(*state.store, Derivation(drv), true);
         std::visit(overloaded {
-            [&](Hash h) {
+            [&](Hash & h) {
                 for (auto & i : outputs) {
                     auto outPath = state.store->makeOutputPath(i, h, drvName);
                     drv.env[i] = state.store->printStorePath(outPath);
@@ -1146,11 +1202,11 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
                         });
                 }
             },
-            [&](CaOutputHashes) {
+            [&](CaOutputHashes &) {
                 // Shouldn't happen as the toplevel derivation is not CA.
                 assert(false);
             },
-            [&](DeferredHash _) {
+            [&](DeferredHash &) {
                 for (auto & i : outputs) {
                     drv.outputs.insert_or_assign(i,
                         DerivationOutput {
@@ -1453,15 +1509,20 @@ static void prim_hashFile(EvalState & state, const Pos & pos, Value * * args, Va
     string type = state.forceStringNoCtx(*args[0], pos);
     std::optional<HashType> ht = parseHashType(type);
     if (!ht)
-      throw Error({
-          .msg = hintfmt("unknown hash type '%1%'", type),
-          .errPos = pos
-      });
+        throw Error({
+            .msg = hintfmt("unknown hash type '%1%'", type),
+            .errPos = pos
+        });
 
-    PathSet context; // discarded
-    Path p = state.coerceToPath(pos, *args[1], context);
+    PathSet context;
+    Path path = state.coerceToPath(pos, *args[1], context);
+    try {
+        state.realiseContext(context);
+    } catch (InvalidPathError & e) {
+        throw EvalError("cannot read '%s' since path '%s' is not valid, at %s", path, e.path, pos);
+    }
 
-    mkString(v, hashFile(*ht, state.checkSourcePath(p)).to_string(Base16, false), context);
+    mkString(v, hashFile(*ht, state.checkSourcePath(state.toRealPath(path, context))).to_string(Base16, false));
 }
 
 static RegisterPrimOp primop_hashFile({
@@ -1538,7 +1599,7 @@ static void prim_toXML(EvalState & state, const Pos & pos, Value * * args, Value
 {
     std::ostringstream out;
     PathSet context;
-    printValueAsXML(state, true, false, *args[0], out, context);
+    printValueAsXML(state, true, false, *args[0], out, context, pos);
     mkString(v, out.str(), context);
 }
 
@@ -1646,7 +1707,7 @@ static void prim_toJSON(EvalState & state, const Pos & pos, Value * * args, Valu
 {
     std::ostringstream out;
     PathSet context;
-    printValueAsJSON(state, true, *args[0], out, context);
+    printValueAsJSON(state, true, *args[0], pos, out, context);
     mkString(v, out.str(), context);
 }
 
@@ -1672,7 +1733,7 @@ static void prim_fromJSON(EvalState & state, const Pos & pos, Value * * args, Va
         parseJSON(state, s, v);
     } catch (JSONParseError &e) {
         e.addTrace(pos, "while decoding a JSON string");
-        throw e;
+        throw;
     }
 }
 
@@ -1802,50 +1863,79 @@ static RegisterPrimOp primop_toFile({
     .fun = prim_toFile,
 });
 
-static void addPath(EvalState & state, const Pos & pos, const string & name, const Path & path_,
-    Value * filterFun, FileIngestionMethod method, const std::optional<Hash> expectedHash, Value & v)
+static void addPath(
+    EvalState & state,
+    const Pos & pos,
+    const string & name,
+    Path path,
+    Value * filterFun,
+    FileIngestionMethod method,
+    const std::optional<Hash> expectedHash,
+    Value & v,
+    const PathSet & context)
 {
-    const auto path = evalSettings.pureEval && expectedHash ?
-        path_ :
-        state.checkSourcePath(path_);
-    PathFilter filter = filterFun ? ([&](const Path & path) {
-        auto st = lstat(path);
+    try {
+        // FIXME: handle CA derivation outputs (where path needs to
+        // be rewritten to the actual output).
+        state.realiseContext(context);
 
-        /* Call the filter function.  The first argument is the path,
-           the second is a string indicating the type of the file. */
-        Value arg1;
-        mkString(arg1, path);
+        StorePathSet refs;
 
-        Value fun2;
-        state.callFunction(*filterFun, arg1, fun2, noPos);
+        if (state.store->isInStore(path)) {
+            auto [storePath, subPath] = state.store->toStorePath(path);
+            // FIXME: we should scanForReferences on the path before adding it
+            refs = state.store->queryPathInfo(storePath)->references;
+            path = state.store->toRealPath(storePath) + subPath;
+        }
 
-        Value arg2;
-        mkString(arg2,
-            S_ISREG(st.st_mode) ? "regular" :
-            S_ISDIR(st.st_mode) ? "directory" :
-            S_ISLNK(st.st_mode) ? "symlink" :
-            "unknown" /* not supported, will fail! */);
+        path = evalSettings.pureEval && expectedHash
+            ? path
+            : state.checkSourcePath(path);
 
-        Value res;
-        state.callFunction(fun2, arg2, res, noPos);
+        PathFilter filter = filterFun ? ([&](const Path & path) {
+            auto st = lstat(path);
+
+            /* Call the filter function.  The first argument is the path,
+               the second is a string indicating the type of the file. */
+            Value arg1;
+            mkString(arg1, path);
+
+            Value arg2;
+            mkString(arg2,
+                S_ISREG(st.st_mode) ? "regular" :
+                S_ISDIR(st.st_mode) ? "directory" :
+                S_ISLNK(st.st_mode) ? "symlink" :
+                "unknown" /* not supported, will fail! */);
+
+            Value * args []{&arg1, &arg2};
+            Value res;
+            state.callFunction(*filterFun, 2, args, res, pos);
+
+            return state.forceBool(res, pos);
+        }) : defaultPathFilter;
+
+        std::optional<StorePath> expectedStorePath;
+        if (expectedHash)
+            expectedStorePath = state.store->makeFixedOutputPath(method, *expectedHash, name);
 
-        return state.forceBool(res, pos);
-    }) : defaultPathFilter;
+        Path dstPath;
+        if (!expectedHash || !state.store->isValidPath(*expectedStorePath)) {
+            dstPath = state.store->printStorePath(settings.readOnlyMode
+                ? state.store->computeStorePathForPath(name, path, method, htSHA256, filter).first
+                : state.store->addToStore(name, path, method, htSHA256, filter, state.repair, refs));
+            if (expectedHash && expectedStorePath != state.store->parseStorePath(dstPath))
+                throw Error("store path mismatch in (possibly filtered) path added from '%s'", path);
+        } else
+            dstPath = state.store->printStorePath(*expectedStorePath);
 
-    std::optional<StorePath> expectedStorePath;
-    if (expectedHash)
-        expectedStorePath = state.store->makeFixedOutputPath(method, *expectedHash, name);
-    Path dstPath;
-    if (!expectedHash || !state.store->isValidPath(*expectedStorePath)) {
-        dstPath = state.store->printStorePath(settings.readOnlyMode
-            ? state.store->computeStorePathForPath(name, path, method, htSHA256, filter).first
-            : state.store->addToStore(name, path, method, htSHA256, filter, state.repair));
-        if (expectedHash && expectedStorePath != state.store->parseStorePath(dstPath))
-            throw Error("store path mismatch in (possibly filtered) path added from '%s'", path);
-    } else
-        dstPath = state.store->printStorePath(*expectedStorePath);
+        mkString(v, dstPath, {dstPath});
 
-    mkString(v, dstPath, {dstPath});
+        state.allowPath(dstPath);
+
+    } catch (Error & e) {
+        e.addTrace(pos, "while adding path '%s'", path);
+        throw;
+    }
 }
 
 
@@ -1853,11 +1943,6 @@ static void prim_filterSource(EvalState & state, const Pos & pos, Value * * args
 {
     PathSet context;
     Path path = state.coerceToPath(pos, *args[1], context);
-    if (!context.empty())
-        throw EvalError({
-            .msg = hintfmt("string '%1%' cannot refer to other paths", path),
-            .errPos = pos
-        });
 
     state.forceValue(*args[0], pos);
     if (args[0]->type() != nFunction)
@@ -1868,13 +1953,26 @@ static void prim_filterSource(EvalState & state, const Pos & pos, Value * * args
             .errPos = pos
         });
 
-    addPath(state, pos, std::string(baseNameOf(path)), path, args[0], FileIngestionMethod::Recursive, std::nullopt, v);
+    addPath(state, pos, std::string(baseNameOf(path)), path, args[0], FileIngestionMethod::Recursive, std::nullopt, v, context);
 }
 
 static RegisterPrimOp primop_filterSource({
     .name = "__filterSource",
     .args = {"e1", "e2"},
     .doc = R"(
+      > **Warning**
+      >
+      > `filterSource` should not be used to filter store paths. Since
+      > `filterSource` uses the name of the input directory while naming
+      > the output directory, doing so will produce a directory name in
+      > the form of `<hash2>-<hash>-<name>`, where `<hash>-<name>` is
+      > the name of the input directory. Since `<hash>` depends on the
+      > unfiltered directory, the name of the output directory will
+      > indirectly depend on files that are filtered out by the
+      > function. This will trigger a rebuild even when a filtered out
+      > file is changed. Use `builtins.path` instead, which allows
+      > specifying the name of the output directory.
+
       This function allows you to copy sources into the Nix store while
       filtering certain files. For instance, suppose that you want to use
       the directory `source-dir` as an input to a Nix expression, e.g.
@@ -1921,18 +2019,13 @@ static void prim_path(EvalState & state, const Pos & pos, Value * * args, Value
     Value * filterFun = nullptr;
     auto method = FileIngestionMethod::Recursive;
     std::optional<Hash> expectedHash;
+    PathSet context;
 
     for (auto & attr : *args[0]->attrs) {
         const string & n(attr.name);
-        if (n == "path") {
-            PathSet context;
+        if (n == "path")
             path = state.coerceToPath(*attr.pos, *attr.value, context);
-            if (!context.empty())
-                throw EvalError({
-                    .msg = hintfmt("string '%1%' cannot refer to other paths", path),
-                    .errPos = *attr.pos
-                });
-        } else if (attr.name == state.sName)
+        else if (attr.name == state.sName)
             name = state.forceStringNoCtx(*attr.value, *attr.pos);
         else if (n == "filter") {
             state.forceValue(*attr.value, pos);
@@ -1955,7 +2048,7 @@ static void prim_path(EvalState & state, const Pos & pos, Value * * args, Value
     if (name.empty())
         name = baseNameOf(path);
 
-    addPath(state, pos, name, path, filterFun, method, expectedHash, v);
+    addPath(state, pos, name, path, filterFun, method, expectedHash, v, context);
 }
 
 static RegisterPrimOp primop_path({
@@ -2069,7 +2162,7 @@ void prim_getAttr(EvalState & state, const Pos & pos, Value * * args, Value & v)
         pos
     );
     // !!! add to stack trace?
-    if (state.countCalls && i->pos) state.attrSelects[*i->pos]++;
+    if (state.countCalls && *i->pos != noPos) state.attrSelects[*i->pos]++;
     state.forceValue(*i->value, pos);
     v = *i->value;
 }
@@ -2320,7 +2413,7 @@ static void prim_functionArgs(EvalState & state, const Pos & pos, Value * * args
             .errPos = pos
         });
 
-    if (!args[0]->lambda.fun->matchAttrs) {
+    if (!args[0]->lambda.fun->hasFormals()) {
         state.mkAttrs(v, 0);
         return;
     }
@@ -2329,7 +2422,7 @@ static void prim_functionArgs(EvalState & state, const Pos & pos, Value * * args
     for (auto & i : args[0]->lambda.fun->formals->formals) {
         // !!! should optimise booleans (allocate only once)
         Value * value = state.allocValue();
-        v.attrs->push_back(Attr(i.name, value, &i.pos));
+        v.attrs->push_back(Attr(i.name, value, ptr(&i.pos)));
         mkBool(*value, i.def);
     }
     v.attrs->sort();
@@ -2475,7 +2568,7 @@ static RegisterPrimOp primop_tail({
       the argument isn’t a list or is an empty list.
 
       > **Warning**
-      > 
+      >
       > This function should generally be avoided since it's inefficient:
       > unlike Haskell's `tail`, it takes O(n) time, so recursing over a
       > list by repeatedly calling `tail` takes O(n^2) time.
@@ -2617,10 +2710,9 @@ static void prim_foldlStrict(EvalState & state, const Pos & pos, Value * * args,
         Value * vCur = args[1];
 
         for (unsigned int n = 0; n < args[2]->listSize(); ++n) {
-            Value vTmp;
-            state.callFunction(*args[0], *vCur, vTmp, pos);
+            Value * vs []{vCur, args[2]->listElems()[n]};
             vCur = n == args[2]->listSize() - 1 ? &v : state.allocValue();
-            state.callFunction(vTmp, *args[2]->listElems()[n], *vCur, pos);
+            state.callFunction(*args[0], 2, vs, *vCur, pos);
         }
         state.forceValue(v, pos);
     } else {
@@ -2634,9 +2726,9 @@ static RegisterPrimOp primop_foldlStrict({
     .args = {"op", "nul", "list"},
     .doc = R"(
       Reduce a list by applying a binary operator, from left to right,
-      e.g. `foldl’ op nul [x0 x1 x2 ...] = op (op (op nul x0) x1) x2)
+      e.g. `foldl' op nul [x0 x1 x2 ...] = op (op (op nul x0) x1) x2)
       ...`. The operator is applied strictly, i.e., its arguments are
-      evaluated first. For example, `foldl’ (x: y: x + y) 0 [1 2 3]`
+      evaluated first. For example, `foldl' (x: y: x + y) 0 [1 2 3]`
       evaluates to 6.
     )",
     .fun = prim_foldlStrict,
@@ -2741,17 +2833,16 @@ static void prim_sort(EvalState & state, const Pos & pos, Value * * args, Value
         v.listElems()[n] = args[1]->listElems()[n];
     }
 
-
     auto comparator = [&](Value * a, Value * b) {
         /* Optimization: if the comparator is lessThan, bypass
            callFunction. */
         if (args[0]->isPrimOp() && args[0]->primOp->fun == prim_lessThan)
-            return CompareValues()(a, b);
+            return CompareValues(state)(a, b);
 
-        Value vTmp1, vTmp2;
-        state.callFunction(*args[0], *a, vTmp1, pos);
-        state.callFunction(vTmp1, *b, vTmp2, pos);
-        return state.forceBool(vTmp2, pos);
+        Value * vs[] = {a, b};
+        Value vBool;
+        state.callFunction(*args[0], 2, vs, vBool, pos);
+        return state.forceBool(vBool, pos);
     };
 
     /* FIXME: std::sort can segfault if the comparator is not a strict
@@ -2857,7 +2948,7 @@ static void prim_concatMap(EvalState & state, const Pos & pos, Value * * args, V
             state.forceList(lists[n], lists[n].determinePos(args[0]->determinePos(pos)));
         } catch (TypeError &e) {
             e.addTrace(pos, hintfmt("while invoking '%s'", "concatMap"));
-            throw e;
+            throw;
         }
         len += lists[n].listSize();
     }
@@ -3028,7 +3119,7 @@ static void prim_lessThan(EvalState & state, const Pos & pos, Value * * args, Va
 {
     state.forceValue(*args[0], pos);
     state.forceValue(*args[1], pos);
-    CompareValues comp;
+    CompareValues comp{state};
     mkBool(v, comp(args[0], args[1]));
 }
 
@@ -3069,7 +3160,7 @@ static RegisterPrimOp primop_toString({
 
         - A path (e.g., `toString /foo/bar` yields `"/foo/bar"`.
 
-        - A set containing `{ __toString = self: ...; }`.
+        - A set containing `{ __toString = self: ...; }` or `{ outPath = ...; }`.
 
         - An integer.
 
@@ -3154,7 +3245,7 @@ static void prim_hashString(EvalState & state, const Pos & pos, Value * * args,
     PathSet context; // discarded
     string s = state.forceString(*args[1], context, pos);
 
-    mkString(v, hashString(*ht, s).to_string(Base16, false), context);
+    mkString(v, hashString(*ht, s).to_string(Base16, false));
 }
 
 static RegisterPrimOp primop_hashString({
@@ -3561,15 +3652,13 @@ static RegisterPrimOp primop_splitVersion({
 RegisterPrimOp::PrimOps * RegisterPrimOp::primOps;
 
 
-RegisterPrimOp::RegisterPrimOp(std::string name, size_t arity, PrimOpFun fun,
-    std::optional<std::string> requiredFeature)
+RegisterPrimOp::RegisterPrimOp(std::string name, size_t arity, PrimOpFun fun)
 {
     if (!primOps) primOps = new PrimOps;
     primOps->push_back({
         .name = name,
         .args = {},
         .arity = arity,
-        .requiredFeature = std::move(requiredFeature),
         .fun = fun
     });
 }
@@ -3605,9 +3694,7 @@ void EvalState::createBaseEnv()
     if (!evalSettings.pureEval) {
         mkInt(v, time(0));
         addConstant("__currentTime", v);
-    }
 
-    if (!evalSettings.pureEval) {
         mkString(v, settings.thisSystem.get());
         addConstant("__currentSystem", v);
     }
@@ -3622,7 +3709,7 @@ void EvalState::createBaseEnv()
        language feature gets added.  It's not necessary to increase it
        when primops get added, because you can just use `builtins ?
        primOp' to check. */
-    mkInt(v, 5);
+    mkInt(v, 6);
     addConstant("__langVersion", v);
 
     // Miscellaneous
@@ -3645,26 +3732,31 @@ void EvalState::createBaseEnv()
 
     if (RegisterPrimOp::primOps)
         for (auto & primOp : *RegisterPrimOp::primOps)
-            if (!primOp.requiredFeature || settings.isExperimentalFeatureEnabled(*primOp.requiredFeature))
-                addPrimOp({
-                    .fun = primOp.fun,
-                    .arity = std::max(primOp.args.size(), primOp.arity),
-                    .name = symbols.create(primOp.name),
-                    .args = std::move(primOp.args),
-                    .doc = primOp.doc,
-                });
+            addPrimOp({
+                .fun = primOp.fun,
+                .arity = std::max(primOp.args.size(), primOp.arity),
+                .name = symbols.create(primOp.name),
+                .args = std::move(primOp.args),
+                .doc = primOp.doc,
+            });
 
     /* Add a wrapper around the derivation primop that computes the
        `drvPath' and `outPath' attributes lazily. */
     sDerivationNix = symbols.create("//builtin/derivation.nix");
-    eval(parse(
-        #include "primops/derivation.nix.gen.hh"
-        , foFile, sDerivationNix, "/", staticBaseEnv), v);
-    addConstant("derivation", v);
+    auto vDerivation = allocValue();
+    addConstant("derivation", vDerivation);
 
     /* Now that we've added all primops, sort the `builtins' set,
        because attribute lookups expect it to be sorted. */
     baseEnv.values[0]->attrs->sort();
+
+    staticBaseEnv.sort();
+
+    /* Note: we have to initialize the 'derivation' constant *after*
+       building baseEnv/staticBaseEnv because it uses 'builtins'. */
+    eval(parse(
+        #include "primops/derivation.nix.gen.hh"
+        , foFile, sDerivationNix, "/", staticBaseEnv), *vDerivation);
 }
 
 
diff --git a/src/libexpr/primops.hh b/src/libexpr/primops.hh
index 9d42d6539..5b16e075f 100644
--- a/src/libexpr/primops.hh
+++ b/src/libexpr/primops.hh
@@ -15,7 +15,6 @@ struct RegisterPrimOp
         std::vector<std::string> args;
         size_t arity = 0;
         const char * doc;
-        std::optional<std::string> requiredFeature;
         PrimOpFun fun;
     };
 
@@ -28,8 +27,7 @@ struct RegisterPrimOp
     RegisterPrimOp(
         std::string name,
         size_t arity,
-        PrimOpFun fun,
-        std::optional<std::string> requiredFeature = {});
+        PrimOpFun fun);
 
     RegisterPrimOp(Info && info);
 };
diff --git a/src/libexpr/primops/fetchMercurial.cc b/src/libexpr/primops/fetchMercurial.cc
index 4830ebec3..c23480853 100644
--- a/src/libexpr/primops/fetchMercurial.cc
+++ b/src/libexpr/primops/fetchMercurial.cc
@@ -15,7 +15,7 @@ static void prim_fetchMercurial(EvalState & state, const Pos & pos, Value * * ar
     std::string name = "source";
     PathSet context;
 
-    state.forceValue(*args[0]);
+    state.forceValue(*args[0], pos);
 
     if (args[0]->type() == nAttrs) {
 
@@ -62,6 +62,7 @@ static void prim_fetchMercurial(EvalState & state, const Pos & pos, Value * * ar
     fetchers::Attrs attrs;
     attrs.insert_or_assign("type", "hg");
     attrs.insert_or_assign("url", url.find("://") != std::string::npos ? url : "file://" + url);
+    attrs.insert_or_assign("name", name);
     if (ref) attrs.insert_or_assign("ref", *ref);
     if (rev) attrs.insert_or_assign("rev", rev->gitRev());
     auto input = fetchers::Input::fromAttrs(std::move(attrs));
@@ -83,8 +84,7 @@ static void prim_fetchMercurial(EvalState & state, const Pos & pos, Value * * ar
         mkInt(*state.allocAttr(v, state.symbols.create("revCount")), *revCount);
     v.attrs->sort();
 
-    if (state.allowedPaths)
-        state.allowedPaths->insert(tree.actualPath);
+    state.allowPath(tree.storePath);
 }
 
 static RegisterPrimOp r_fetchMercurial("fetchMercurial", 1, prim_fetchMercurial);
diff --git a/src/libexpr/primops/fetchTree.cc b/src/libexpr/primops/fetchTree.cc
index b8b99d4fa..079513873 100644
--- a/src/libexpr/primops/fetchTree.cc
+++ b/src/libexpr/primops/fetchTree.cc
@@ -7,6 +7,7 @@
 
 #include <ctime>
 #include <iomanip>
+#include <regex>
 
 namespace nix {
 
@@ -15,7 +16,8 @@ void emitTreeAttrs(
     const fetchers::Tree & tree,
     const fetchers::Input & input,
     Value & v,
-    bool emptyRevFallback)
+    bool emptyRevFallback,
+    bool forceDirty)
 {
     assert(input.isImmutable());
 
@@ -32,24 +34,28 @@ void emitTreeAttrs(
     mkString(*state.allocAttr(v, state.symbols.create("narHash")),
         narHash->to_string(SRI, true));
 
-    if (auto rev = input.getRev()) {
-        mkString(*state.allocAttr(v, state.symbols.create("rev")), rev->gitRev());
-        mkString(*state.allocAttr(v, state.symbols.create("shortRev")), rev->gitShortRev());
-    } else if (emptyRevFallback) {
-        // Backwards compat for `builtins.fetchGit`: dirty repos return an empty sha1 as rev
-        auto emptyHash = Hash(htSHA1);
-        mkString(*state.allocAttr(v, state.symbols.create("rev")), emptyHash.gitRev());
-        mkString(*state.allocAttr(v, state.symbols.create("shortRev")), emptyHash.gitShortRev());
-    }
-
     if (input.getType() == "git")
         mkBool(*state.allocAttr(v, state.symbols.create("submodules")),
             fetchers::maybeGetBoolAttr(input.attrs, "submodules").value_or(false));
 
-    if (auto revCount = input.getRevCount())
-        mkInt(*state.allocAttr(v, state.symbols.create("revCount")), *revCount);
-    else if (emptyRevFallback)
-        mkInt(*state.allocAttr(v, state.symbols.create("revCount")), 0);
+    if (!forceDirty) {
+
+        if (auto rev = input.getRev()) {
+            mkString(*state.allocAttr(v, state.symbols.create("rev")), rev->gitRev());
+            mkString(*state.allocAttr(v, state.symbols.create("shortRev")), rev->gitShortRev());
+        } else if (emptyRevFallback) {
+            // Backwards compat for `builtins.fetchGit`: dirty repos return an empty sha1 as rev
+            auto emptyHash = Hash(htSHA1);
+            mkString(*state.allocAttr(v, state.symbols.create("rev")), emptyHash.gitRev());
+            mkString(*state.allocAttr(v, state.symbols.create("shortRev")), emptyHash.gitShortRev());
+        }
+
+        if (auto revCount = input.getRevCount())
+            mkInt(*state.allocAttr(v, state.symbols.create("revCount")), *revCount);
+        else if (emptyRevFallback)
+            mkInt(*state.allocAttr(v, state.symbols.create("revCount")), 0);
+
+    }
 
     if (auto lastModified = input.getLastModified()) {
         mkInt(*state.allocAttr(v, state.symbols.create("lastModified")), *lastModified);
@@ -60,47 +66,74 @@ void emitTreeAttrs(
     v.attrs->sort();
 }
 
-std::string fixURI(std::string uri, EvalState &state)
+std::string fixURI(std::string uri, EvalState & state, const std::string & defaultScheme = "file")
 {
     state.checkURI(uri);
-    return uri.find("://") != std::string::npos ? uri : "file://" + uri;
+    return uri.find("://") != std::string::npos ? uri : defaultScheme + "://" + uri;
 }
 
-void addURI(EvalState &state, fetchers::Attrs &attrs, Symbol name, std::string v)
+std::string fixURIForGit(std::string uri, EvalState & state)
 {
-    string n(name);
-    attrs.emplace(name, n == "url" ? fixURI(v, state) : v);
+    /* Detects scp-style uris (e.g. git@github.com:NixOS/nix) and fixes
+     * them by removing the `:` and assuming a scheme of `ssh://`
+     * */
+    static std::regex scp_uri("([^/]*)@(.*):(.*)");
+    if (uri[0] != '/' && std::regex_match(uri, scp_uri))
+        return fixURI(std::regex_replace(uri, scp_uri, "$1@$2/$3"), state, "ssh");
+    else
+        return fixURI(uri, state);
 }
 
+struct FetchTreeParams {
+    bool emptyRevFallback = false;
+    bool allowNameArgument = false;
+};
+
 static void fetchTree(
-    EvalState &state,
-    const Pos &pos,
-    Value **args,
-    Value &v,
-    const std::optional<std::string> type,
-    bool emptyRevFallback = false
+    EvalState & state,
+    const Pos & pos,
+    Value * * args,
+    Value & v,
+    std::optional<std::string> type,
+    const FetchTreeParams & params = FetchTreeParams{}
 ) {
     fetchers::Input input;
     PathSet context;
 
-    state.forceValue(*args[0]);
+    state.forceValue(*args[0], pos);
 
     if (args[0]->type() == nAttrs) {
         state.forceAttrs(*args[0], pos);
 
         fetchers::Attrs attrs;
 
+        if (auto aType = args[0]->attrs->get(state.sType)) {
+            if (type)
+                throw Error({
+                    .msg = hintfmt("unexpected attribute 'type'"),
+                    .errPos = pos
+                });
+            type = state.forceStringNoCtx(*aType->value, *aType->pos);
+        } else if (!type)
+            throw Error({
+                .msg = hintfmt("attribute 'type' is missing in call to 'fetchTree'"),
+                .errPos = pos
+            });
+
+        attrs.emplace("type", type.value());
+
         for (auto & attr : *args[0]->attrs) {
-            state.forceValue(*attr.value);
-            if (attr.value->type() == nPath || attr.value->type() == nString)
-                addURI(
-                    state,
-                    attrs,
-                    attr.name,
-                    state.coerceToString(*attr.pos, *attr.value, context, false, false)
-                );
-            else if (attr.value->type() == nString)
-                addURI(state, attrs, attr.name, attr.value->string.s);
+            if (attr.name == state.sType) continue;
+            state.forceValue(*attr.value, *attr.pos);
+            if (attr.value->type() == nPath || attr.value->type() == nString) {
+                auto s = state.coerceToString(*attr.pos, *attr.value, context, false, false);
+                attrs.emplace(attr.name,
+                    attr.name == "url"
+                    ? type == "git"
+                      ? fixURIForGit(s, state)
+                      : fixURI(s, state)
+                    : s);
+            }
             else if (attr.value->type() == nBool)
                 attrs.emplace(attr.name, Explicit<bool>{attr.value->boolean});
             else if (attr.value->type() == nInt)
@@ -110,26 +143,24 @@ static void fetchTree(
                     attr.name, showType(*attr.value));
         }
 
-        if (type)
-            attrs.emplace("type", type.value());
-
-        if (!attrs.count("type"))
-            throw Error({
-                .msg = hintfmt("attribute 'type' is missing in call to 'fetchTree'"),
-                .errPos = pos
-            });
+        if (!params.allowNameArgument)
+            if (auto nameIter = attrs.find("name"); nameIter != attrs.end())
+                throw Error({
+                    .msg = hintfmt("attribute 'name' isn’t supported in call to 'fetchTree'"),
+                    .errPos = pos
+                });
 
         input = fetchers::Input::fromAttrs(std::move(attrs));
     } else {
-        auto url = fixURI(state.coerceToString(pos, *args[0], context, false, false), state);
+        auto url = state.coerceToString(pos, *args[0], context, false, false);
 
         if (type == "git") {
             fetchers::Attrs attrs;
             attrs.emplace("type", "git");
-            attrs.emplace("url", url);
+            attrs.emplace("url", fixURIForGit(url, state));
             input = fetchers::Input::fromAttrs(std::move(attrs));
         } else {
-            input = fetchers::Input::fromURL(url);
+            input = fetchers::Input::fromURL(fixURI(url, state));
         }
     }
 
@@ -141,16 +172,15 @@ static void fetchTree(
 
     auto [tree, input2] = input.fetch(state.store);
 
-    if (state.allowedPaths)
-        state.allowedPaths->insert(tree.actualPath);
+    state.allowPath(tree.storePath);
 
-    emitTreeAttrs(state, tree, input2, v, emptyRevFallback);
+    emitTreeAttrs(state, tree, input2, v, params.emptyRevFallback, false);
 }
 
 static void prim_fetchTree(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    settings.requireExperimentalFeature("flakes");
-    fetchTree(state, pos, args, v, std::nullopt);
+    settings.requireExperimentalFeature(Xp::Flakes);
+    fetchTree(state, pos, args, v, std::nullopt, FetchTreeParams { .allowNameArgument = false });
 }
 
 // FIXME: document
@@ -162,7 +192,7 @@ static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
     std::optional<std::string> url;
     std::optional<Hash> expectedHash;
 
-    state.forceValue(*args[0]);
+    state.forceValue(*args[0], pos);
 
     if (args[0]->type() == nAttrs) {
 
@@ -206,20 +236,18 @@ static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
         ? fetchers::downloadTarball(state.store, *url, name, (bool) expectedHash).first.storePath
         : fetchers::downloadFile(state.store, *url, name, (bool) expectedHash).storePath;
 
-    auto path = state.store->toRealPath(storePath);
-
     if (expectedHash) {
         auto hash = unpack
             ? state.store->queryPathInfo(storePath)->narHash
-            : hashFile(htSHA256, path);
+            : hashFile(htSHA256, state.store->toRealPath(storePath));
         if (hash != *expectedHash)
             throw Error((unsigned int) 102, "hash mismatch in file downloaded from '%s':\n  specified: %s\n  got:       %s",
                 *url, expectedHash->to_string(Base32, true), hash.to_string(Base32, true));
     }
 
-    if (state.allowedPaths)
-        state.allowedPaths->insert(path);
+    state.allowPath(storePath);
 
+    auto path = state.store->printStorePath(storePath);
     mkString(v, path, PathSet({path}));
 }
 
@@ -262,13 +290,13 @@ static RegisterPrimOp primop_fetchTarball({
       stdenv.mkDerivation { … }
       ```
 
-      The fetched tarball is cached for a certain amount of time (1 hour
-      by default) in `~/.cache/nix/tarballs/`. You can change the cache
-      timeout either on the command line with `--option tarball-ttl number
-      of seconds` or in the Nix configuration file with this option: ` 
-      number of seconds to cache `.
+      The fetched tarball is cached for a certain amount of time (1
+      hour by default) in `~/.cache/nix/tarballs/`. You can change the
+      cache timeout either on the command line with `--tarball-ttl`
+      *number-of-seconds* or in the Nix configuration file by adding
+      the line `tarball-ttl = ` *number-of-seconds*.
 
-      Note that when obtaining the hash with ` nix-prefetch-url ` the
+      Note that when obtaining the hash with `nix-prefetch-url` the
       option `--unpack` is required.
 
       This function can also verify the contents against a hash. In that
@@ -292,7 +320,7 @@ static RegisterPrimOp primop_fetchTarball({
 
 static void prim_fetchGit(EvalState &state, const Pos &pos, Value **args, Value &v)
 {
-    fetchTree(state, pos, args, v, "git", true);
+    fetchTree(state, pos, args, v, "git", FetchTreeParams { .emptyRevFallback = true, .allowNameArgument = true });
 }
 
 static RegisterPrimOp primop_fetchGit({
@@ -368,7 +396,7 @@ static RegisterPrimOp primop_fetchGit({
           ```
 
           > **Note**
-          > 
+          >
           > It is nice to always specify the branch which a revision
           > belongs to. Without the branch being specified, the fetcher
           > might fail if the default branch changes. Additionally, it can
@@ -405,12 +433,12 @@ static RegisterPrimOp primop_fetchGit({
           ```
 
           > **Note**
-          > 
+          >
           > Nix will refetch the branch in accordance with
           > the option `tarball-ttl`.
 
           > **Note**
-          > 
+          >
           > This behavior is disabled in *Pure evaluation mode*.
     )",
     .fun = prim_fetchGit,
diff --git a/src/libexpr/value-to-json.cc b/src/libexpr/value-to-json.cc
index bfea24d40..4d642c720 100644
--- a/src/libexpr/value-to-json.cc
+++ b/src/libexpr/value-to-json.cc
@@ -10,11 +10,11 @@
 namespace nix {
 
 void printValueAsJSON(EvalState & state, bool strict,
-    Value & v, JSONPlaceholder & out, PathSet & context)
+    Value & v, const Pos & pos, JSONPlaceholder & out, PathSet & context)
 {
     checkInterrupt();
 
-    if (strict) state.forceValue(v);
+    if (strict) state.forceValue(v, pos);
 
     switch (v.type()) {
 
@@ -40,7 +40,7 @@ void printValueAsJSON(EvalState & state, bool strict,
             break;
 
         case nAttrs: {
-            auto maybeString = state.tryAttrsToString(noPos, v, context, false, false);
+            auto maybeString = state.tryAttrsToString(pos, v, context, false, false);
             if (maybeString) {
                 out.write(*maybeString);
                 break;
@@ -54,10 +54,10 @@ void printValueAsJSON(EvalState & state, bool strict,
                 for (auto & j : names) {
                     Attr & a(*v.attrs->find(state.symbols.create(j)));
                     auto placeholder(obj.placeholder(j));
-                    printValueAsJSON(state, strict, *a.value, placeholder, context);
+                    printValueAsJSON(state, strict, *a.value, *a.pos, placeholder, context);
                 }
             } else
-                printValueAsJSON(state, strict, *i->value, out, context);
+                printValueAsJSON(state, strict, *i->value, *i->pos, out, context);
             break;
         }
 
@@ -65,7 +65,7 @@ void printValueAsJSON(EvalState & state, bool strict,
             auto list(out.list());
             for (unsigned int n = 0; n < v.listSize(); ++n) {
                 auto placeholder(list.placeholder());
-                printValueAsJSON(state, strict, *v.listElems()[n], placeholder, context);
+                printValueAsJSON(state, strict, *v.listElems()[n], pos, placeholder, context);
             }
             break;
         }
@@ -79,18 +79,20 @@ void printValueAsJSON(EvalState & state, bool strict,
             break;
 
         case nThunk:
-            throw TypeError("cannot convert %1% to JSON", showType(v));
-
         case nFunction:
-            throw TypeError("cannot convert %1% to JSON", showType(v));
+            auto e = TypeError({
+                .msg = hintfmt("cannot convert %1% to JSON", showType(v)),
+                .errPos = v.determinePos(pos)
+            });
+            throw e.addTrace(pos, hintfmt("message for the trace"));
     }
 }
 
 void printValueAsJSON(EvalState & state, bool strict,
-    Value & v, std::ostream & str, PathSet & context)
+    Value & v, const Pos & pos, std::ostream & str, PathSet & context)
 {
     JSONPlaceholder out(str);
-    printValueAsJSON(state, strict, v, out, context);
+    printValueAsJSON(state, strict, v, pos, out, context);
 }
 
 void ExternalValueBase::printValueAsJSON(EvalState & state, bool strict,
diff --git a/src/libexpr/value-to-json.hh b/src/libexpr/value-to-json.hh
index 67fed6487..c2f797b29 100644
--- a/src/libexpr/value-to-json.hh
+++ b/src/libexpr/value-to-json.hh
@@ -11,9 +11,9 @@ namespace nix {
 class JSONPlaceholder;
 
 void printValueAsJSON(EvalState & state, bool strict,
-    Value & v, JSONPlaceholder & out, PathSet & context);
+    Value & v, const Pos & pos, JSONPlaceholder & out, PathSet & context);
 
 void printValueAsJSON(EvalState & state, bool strict,
-    Value & v, std::ostream & str, PathSet & context);
+    Value & v, const Pos & pos, std::ostream & str, PathSet & context);
 
 }
diff --git a/src/libexpr/value-to-xml.cc b/src/libexpr/value-to-xml.cc
index 7464455d8..54268ece0 100644
--- a/src/libexpr/value-to-xml.cc
+++ b/src/libexpr/value-to-xml.cc
@@ -18,7 +18,8 @@ static XMLAttrs singletonAttrs(const string & name, const string & value)
 
 
 static void printValueAsXML(EvalState & state, bool strict, bool location,
-    Value & v, XMLWriter & doc, PathSet & context, PathSet & drvsSeen);
+    Value & v, XMLWriter & doc, PathSet & context, PathSet & drvsSeen,
+    const Pos & pos);
 
 
 static void posToXML(XMLAttrs & xmlAttrs, const Pos & pos)
@@ -42,21 +43,22 @@ static void showAttrs(EvalState & state, bool strict, bool location,
 
         XMLAttrs xmlAttrs;
         xmlAttrs["name"] = i;
-        if (location && a.pos != &noPos) posToXML(xmlAttrs, *a.pos);
+        if (location && a.pos != ptr(&noPos)) posToXML(xmlAttrs, *a.pos);
 
         XMLOpenElement _(doc, "attr", xmlAttrs);
         printValueAsXML(state, strict, location,
-            *a.value, doc, context, drvsSeen);
+            *a.value, doc, context, drvsSeen, *a.pos);
     }
 }
 
 
 static void printValueAsXML(EvalState & state, bool strict, bool location,
-    Value & v, XMLWriter & doc, PathSet & context, PathSet & drvsSeen)
+    Value & v, XMLWriter & doc, PathSet & context, PathSet & drvsSeen,
+    const Pos & pos)
 {
     checkInterrupt();
 
-    if (strict) state.forceValue(v);
+    if (strict) state.forceValue(v, pos);
 
     switch (v.type()) {
 
@@ -91,14 +93,14 @@ static void printValueAsXML(EvalState & state, bool strict, bool location,
                 Path drvPath;
                 a = v.attrs->find(state.sDrvPath);
                 if (a != v.attrs->end()) {
-                    if (strict) state.forceValue(*a->value);
+                    if (strict) state.forceValue(*a->value, *a->pos);
                     if (a->value->type() == nString)
                         xmlAttrs["drvPath"] = drvPath = a->value->string.s;
                 }
 
                 a = v.attrs->find(state.sOutPath);
                 if (a != v.attrs->end()) {
-                    if (strict) state.forceValue(*a->value);
+                    if (strict) state.forceValue(*a->value, *a->pos);
                     if (a->value->type() == nString)
                         xmlAttrs["outPath"] = a->value->string.s;
                 }
@@ -121,7 +123,7 @@ static void printValueAsXML(EvalState & state, bool strict, bool location,
         case nList: {
             XMLOpenElement _(doc, "list");
             for (unsigned int n = 0; n < v.listSize(); ++n)
-                printValueAsXML(state, strict, location, *v.listElems()[n], doc, context, drvsSeen);
+                printValueAsXML(state, strict, location, *v.listElems()[n], doc, context, drvsSeen, pos);
             break;
         }
 
@@ -135,7 +137,7 @@ static void printValueAsXML(EvalState & state, bool strict, bool location,
             if (location) posToXML(xmlAttrs, v.lambda.fun->pos);
             XMLOpenElement _(doc, "function", xmlAttrs);
 
-            if (v.lambda.fun->matchAttrs) {
+            if (v.lambda.fun->hasFormals()) {
                 XMLAttrs attrs;
                 if (!v.lambda.fun->arg.empty()) attrs["name"] = v.lambda.fun->arg;
                 if (v.lambda.fun->formals->ellipsis) attrs["ellipsis"] = "1";
@@ -149,7 +151,7 @@ static void printValueAsXML(EvalState & state, bool strict, bool location,
         }
 
         case nExternal:
-            v.external->printValueAsXML(state, strict, location, doc, context, drvsSeen);
+            v.external->printValueAsXML(state, strict, location, doc, context, drvsSeen, pos);
             break;
 
         case nFloat:
@@ -163,19 +165,20 @@ static void printValueAsXML(EvalState & state, bool strict, bool location,
 
 
 void ExternalValueBase::printValueAsXML(EvalState & state, bool strict,
-    bool location, XMLWriter & doc, PathSet & context, PathSet & drvsSeen) const
+    bool location, XMLWriter & doc, PathSet & context, PathSet & drvsSeen,
+    const Pos & pos) const
 {
     doc.writeEmptyElement("unevaluated");
 }
 
 
 void printValueAsXML(EvalState & state, bool strict, bool location,
-    Value & v, std::ostream & out, PathSet & context)
+    Value & v, std::ostream & out, PathSet & context, const Pos & pos)
 {
     XMLWriter doc(true, out);
     XMLOpenElement root(doc, "expr");
     PathSet drvsSeen;
-    printValueAsXML(state, strict, location, v, doc, context, drvsSeen);
+    printValueAsXML(state, strict, location, v, doc, context, drvsSeen, pos);
 }
 
 
diff --git a/src/libexpr/value-to-xml.hh b/src/libexpr/value-to-xml.hh
index 97657327e..cc778a2cb 100644
--- a/src/libexpr/value-to-xml.hh
+++ b/src/libexpr/value-to-xml.hh
@@ -9,6 +9,6 @@
 namespace nix {
 
 void printValueAsXML(EvalState & state, bool strict, bool location,
-    Value & v, std::ostream & out, PathSet & context);
-    
+    Value & v, std::ostream & out, PathSet & context, const Pos & pos);
+
 }
diff --git a/src/libexpr/value.hh b/src/libexpr/value.hh
index a1f131f9e..3bb97b3c2 100644
--- a/src/libexpr/value.hh
+++ b/src/libexpr/value.hh
@@ -94,7 +94,8 @@ class ExternalValueBase
 
     /* Print the value as XML. Defaults to unevaluated */
     virtual void printValueAsXML(EvalState & state, bool strict, bool location,
-        XMLWriter & doc, PathSet & context, PathSet & drvsSeen) const;
+        XMLWriter & doc, PathSet & context, PathSet & drvsSeen,
+        const Pos & pos) const;
 
     virtual ~ExternalValueBase()
     {
diff --git a/src/libfetchers/attrs.hh b/src/libfetchers/attrs.hh
index a2d53a7bf..e41037633 100644
--- a/src/libfetchers/attrs.hh
+++ b/src/libfetchers/attrs.hh
@@ -6,6 +6,8 @@
 
 #include <nlohmann/json_fwd.hpp>
 
+#include <optional>
+
 namespace nix::fetchers {
 
 typedef std::variant<std::string, uint64_t, Explicit<bool>> Attr;
diff --git a/src/libfetchers/fetchers.cc b/src/libfetchers/fetchers.cc
index 916e0a8e8..e158d914b 100644
--- a/src/libfetchers/fetchers.cc
+++ b/src/libfetchers/fetchers.cc
@@ -200,12 +200,17 @@ void Input::markChangedFile(
     return scheme->markChangedFile(*this, file, commitMsg);
 }
 
+std::string Input::getName() const
+{
+    return maybeGetStrAttr(attrs, "name").value_or("source");
+}
+
 StorePath Input::computeStorePath(Store & store) const
 {
     auto narHash = getNarHash();
     if (!narHash)
         throw Error("cannot compute store path for mutable input '%s'", to_string());
-    return store.makeFixedOutputPath(FileIngestionMethod::Recursive, *narHash, "source");
+    return store.makeFixedOutputPath(FileIngestionMethod::Recursive, *narHash, getName());
 }
 
 std::string Input::getType() const
diff --git a/src/libfetchers/fetchers.hh b/src/libfetchers/fetchers.hh
index a72cfafa4..c43b047a7 100644
--- a/src/libfetchers/fetchers.hh
+++ b/src/libfetchers/fetchers.hh
@@ -38,6 +38,9 @@ struct Input
     bool immutable = false;
     bool direct = true;
 
+    /* path of the parent of this input, used for relative path resolution */
+    std::optional<Path> parent;
+
 public:
     static Input fromURL(const std::string & url);
 
@@ -81,6 +84,8 @@ public:
         std::string_view file,
         std::optional<std::string> commitMsg) const;
 
+    std::string getName() const;
+
     StorePath computeStorePath(Store & store) const;
 
     // Convenience functions for common attributes.
diff --git a/src/libfetchers/git.cc b/src/libfetchers/git.cc
index d8e0dbe0a..544d2ffbf 100644
--- a/src/libfetchers/git.cc
+++ b/src/libfetchers/git.cc
@@ -4,6 +4,7 @@
 #include "tarfile.hh"
 #include "store-api.hh"
 #include "url-parts.hh"
+#include "pathlocks.hh"
 
 #include <sys/time.h>
 #include <sys/wait.h>
@@ -12,6 +13,12 @@ using namespace std::string_literals;
 
 namespace nix::fetchers {
 
+// Explicit initial branch of our bare repo to suppress warnings from new version of git.
+// The value itself does not matter, since we always fetch a specific revision or branch.
+// It is set with `-c init.defaultBranch=` instead of `--initial-branch=` to stay compatible with
+// old version of git, which will ignore unrecognized `-c` options.
+const std::string gitInitialBranch = "__nix_dummy_branch";
+
 static std::string readHead(const Path & path)
 {
     return chomp(runProgram("git", true, { "-C", path, "rev-parse", "--abbrev-ref", "HEAD" }));
@@ -44,7 +51,7 @@ struct GitInputScheme : InputScheme
         for (auto &[name, value] : url.query) {
             if (name == "rev" || name == "ref")
                 attrs.emplace(name, value);
-            else if (name == "shallow")
+            else if (name == "shallow" || name == "submodules")
                 attrs.emplace(name, Explicit<bool> { value == "1" });
             else
                 url2.query.emplace(name, value);
@@ -60,7 +67,7 @@ struct GitInputScheme : InputScheme
         if (maybeGetStrAttr(attrs, "type") != "git") return {};
 
         for (auto & [name, value] : attrs)
-            if (name != "type" && name != "url" && name != "ref" && name != "rev" && name != "shallow" && name != "submodules" && name != "lastModified" && name != "revCount" && name != "narHash" && name != "allRefs")
+            if (name != "type" && name != "url" && name != "ref" && name != "rev" && name != "shallow" && name != "submodules" && name != "lastModified" && name != "revCount" && name != "narHash" && name != "allRefs" && name != "name")
                 throw Error("unsupported Git input attribute '%s'", name);
 
         parseURL(getStrAttr(attrs, "url"));
@@ -167,10 +174,10 @@ struct GitInputScheme : InputScheme
 
     std::pair<Tree, Input> fetch(ref<Store> store, const Input & _input) override
     {
-        auto name = "source";
-
         Input input(_input);
 
+        std::string name = input.getName();
+
         bool shallow = maybeGetBoolAttr(input.attrs, "shallow").value_or(false);
         bool submodules = maybeGetBoolAttr(input.attrs, "submodules").value_or(false);
         bool allRefs = maybeGetBoolAttr(input.attrs, "allRefs").value_or(false);
@@ -270,7 +277,7 @@ struct GitInputScheme : InputScheme
                     return files.count(file);
                 };
 
-                auto storePath = store->addToStore("source", actualUrl, FileIngestionMethod::Recursive, htSHA256, filter);
+                auto storePath = store->addToStore(input.getName(), actualUrl, FileIngestionMethod::Recursive, htSHA256, filter);
 
                 // FIXME: maybe we should use the timestamp of the last
                 // modified dirty file?
@@ -317,9 +324,11 @@ struct GitInputScheme : InputScheme
             Path cacheDir = getCacheDir() + "/nix/gitv3/" + hashString(htSHA256, actualUrl).to_string(Base32, false);
             repoDir = cacheDir;
 
+            createDirs(dirOf(cacheDir));
+            PathLocks cacheDirLock({cacheDir + ".lock"});
+
             if (!pathExists(cacheDir)) {
-                createDirs(dirOf(cacheDir));
-                runProgram("git", true, { "init", "--bare", repoDir });
+                runProgram("git", true, { "-c", "init.defaultBranch=" + gitInitialBranch, "init", "--bare", repoDir });
             }
 
             Path localRefFile =
@@ -386,6 +395,8 @@ struct GitInputScheme : InputScheme
 
             if (!input.getRev())
                 input.attrs.insert_or_assign("rev", Hash::parseAny(chomp(readFile(localRefFile)), htSHA1).gitRev());
+
+            // cache dir lock is removed at scope end; we will only use read-only operations on specific revisions in the remainder
         }
 
         bool isShallow = chomp(runProgram("git", true, { "-C", repoDir, "rev-parse", "--is-shallow-repository" })) == "true";
@@ -406,17 +417,14 @@ struct GitInputScheme : InputScheme
         AutoDelete delTmpDir(tmpDir, true);
         PathFilter filter = defaultPathFilter;
 
-        RunOptions checkCommitOpts(
-            "git",
-            { "-C", repoDir, "cat-file", "commit", input.getRev()->gitRev() }
-        );
-        checkCommitOpts.searchPath = true;
-        checkCommitOpts.mergeStderrToStdout = true;
-
-        auto result = runProgram(checkCommitOpts);
+        auto result = runProgram(RunOptions {
+            .program = "git",
+            .args = { "-C", repoDir, "cat-file", "commit", input.getRev()->gitRev() },
+            .mergeStderrToStdout = true
+        });
         if (WEXITSTATUS(result.first) == 128
-            && result.second.find("bad file") != std::string::npos
-        ) {
+            && result.second.find("bad file") != std::string::npos)
+        {
             throw Error(
                 "Cannot find Git revision '%s' in ref '%s' of repository '%s'! "
                     "Please make sure that the " ANSI_BOLD "rev" ANSI_NORMAL " exists on the "
@@ -432,7 +440,7 @@ struct GitInputScheme : InputScheme
             Path tmpGitDir = createTempDir();
             AutoDelete delTmpGitDir(tmpGitDir, true);
 
-            runProgram("git", true, { "init", tmpDir, "--separate-git-dir", tmpGitDir });
+            runProgram("git", true, { "-c", "init.defaultBranch=" + gitInitialBranch, "init", tmpDir, "--separate-git-dir", tmpGitDir });
             // TODO: repoDir might lack the ref (it only checks if rev
             // exists, see FIXME above) so use a big hammer and fetch
             // everything to ensure we get the rev.
@@ -448,9 +456,11 @@ struct GitInputScheme : InputScheme
             // FIXME: should pipe this, or find some better way to extract a
             // revision.
             auto source = sinkToSource([&](Sink & sink) {
-                RunOptions gitOptions("git", { "-C", repoDir, "archive", input.getRev()->gitRev() });
-                gitOptions.standardOut = &sink;
-                runProgram2(gitOptions);
+                runProgram2({
+                    .program = "git",
+                    .args = { "-C", repoDir, "archive", input.getRev()->gitRev() },
+                    .standardOut = &sink
+                });
             });
 
             unpackTarfile(*source, tmpDir);
diff --git a/src/libfetchers/github.cc b/src/libfetchers/github.cc
index 8352ef02d..1c539b80e 100644
--- a/src/libfetchers/github.cc
+++ b/src/libfetchers/github.cc
@@ -207,7 +207,7 @@ struct GitArchiveInputScheme : InputScheme
 
         auto url = getDownloadUrl(input);
 
-        auto [tree, lastModified] = downloadTarball(store, url.url, "source", true, url.headers);
+        auto [tree, lastModified] = downloadTarball(store, url.url, input.getName(), true, url.headers);
 
         input.attrs.insert_or_assign("lastModified", uint64_t(lastModified));
 
@@ -273,9 +273,9 @@ struct GitHubInputScheme : GitArchiveInputScheme
     void clone(const Input & input, const Path & destDir) override
     {
         auto host = maybeGetStrAttr(input.attrs, "host").value_or("github.com");
-        Input::fromURL(fmt("git+ssh://git@%s/%s/%s.git",
+        Input::fromURL(fmt("git+https://%s/%s/%s.git",
                 host, getStrAttr(input.attrs, "owner"), getStrAttr(input.attrs, "repo")))
-            .applyOverrides(input.getRef().value_or("HEAD"), input.getRev())
+            .applyOverrides(input.getRef(), input.getRev())
             .clone(destDir);
     }
 };
@@ -300,7 +300,7 @@ struct GitLabInputScheme : GitArchiveInputScheme
         if ("PAT" == token.substr(0, fldsplit))
             return std::make_pair("Private-token", token.substr(fldsplit+1));
         warn("Unrecognized GitLab token type %s",  token.substr(0, fldsplit));
-        return std::nullopt;
+        return std::make_pair(token.substr(0,fldsplit), token.substr(fldsplit+1));
     }
 
     Hash getRevFromRef(nix::ref<Store> store, const Input & input) const override
@@ -341,9 +341,9 @@ struct GitLabInputScheme : GitArchiveInputScheme
     {
         auto host = maybeGetStrAttr(input.attrs, "host").value_or("gitlab.com");
         // FIXME: get username somewhere
-        Input::fromURL(fmt("git+ssh://git@%s/%s/%s.git",
+        Input::fromURL(fmt("git+https://%s/%s/%s.git",
                 host, getStrAttr(input.attrs, "owner"), getStrAttr(input.attrs, "repo")))
-            .applyOverrides(input.getRef().value_or("HEAD"), input.getRev())
+            .applyOverrides(input.getRef(), input.getRev())
             .clone(destDir);
     }
 };
diff --git a/src/libfetchers/local.mk b/src/libfetchers/local.mk
index cfd705e22..2e8869d83 100644
--- a/src/libfetchers/local.mk
+++ b/src/libfetchers/local.mk
@@ -8,4 +8,6 @@ libfetchers_SOURCES := $(wildcard $(d)/*.cc)
 
 libfetchers_CXXFLAGS += -I src/libutil -I src/libstore
 
+libfetchers_LDFLAGS += -pthread
+
 libfetchers_LIBS = libutil libstore
diff --git a/src/libfetchers/mercurial.cc b/src/libfetchers/mercurial.cc
index 0eb401e10..d52d4641b 100644
--- a/src/libfetchers/mercurial.cc
+++ b/src/libfetchers/mercurial.cc
@@ -11,34 +11,32 @@ using namespace std::string_literals;
 
 namespace nix::fetchers {
 
-namespace {
-
-RunOptions hgOptions(const Strings & args) {
-	RunOptions opts("hg", args);
-	opts.searchPath = true;
-
-	auto env = getEnv();
-	// Set HGPLAIN: this means we get consistent output from hg and avoids leakage from a user or system .hgrc.
-	env["HGPLAIN"] = "";
-	opts.environment = env;
-
-	return opts;
+static RunOptions hgOptions(const Strings & args)
+{
+    auto env = getEnv();
+    // Set HGPLAIN: this means we get consistent output from hg and avoids leakage from a user or system .hgrc.
+    env["HGPLAIN"] = "";
+
+    return {
+        .program = "hg",
+        .searchPath = true,
+        .args = args,
+        .environment = env
+    };
 }
 
 // runProgram wrapper that uses hgOptions instead of stock RunOptions.
-string runHg(const Strings & args, const std::optional<std::string> & input = {})
+static string runHg(const Strings & args, const std::optional<std::string> & input = {})
 {
-	RunOptions opts = hgOptions(args);
-	opts.input = input;
+    RunOptions opts = hgOptions(args);
+    opts.input = input;
 
-	auto res = runProgram(opts);
+    auto res = runProgram(std::move(opts));
 
-	if (!statusOk(res.first))
-		throw ExecError(res.first, fmt("hg %1%", statusToString(res.first)));
-
-	return res.second;
-}
+    if (!statusOk(res.first))
+        throw ExecError(res.first, fmt("hg %1%", statusToString(res.first)));
 
+    return res.second;
 }
 
 struct MercurialInputScheme : InputScheme
@@ -74,7 +72,7 @@ struct MercurialInputScheme : InputScheme
         if (maybeGetStrAttr(attrs, "type") != "hg") return {};
 
         for (auto & [name, value] : attrs)
-            if (name != "type" && name != "url" && name != "ref" && name != "rev" && name != "revCount" && name != "narHash")
+            if (name != "type" && name != "url" && name != "ref" && name != "rev" && name != "revCount" && name != "narHash" && name != "name")
                 throw Error("unsupported Mercurial input attribute '%s'", name);
 
         parseURL(getStrAttr(attrs, "url"));
@@ -147,10 +145,10 @@ struct MercurialInputScheme : InputScheme
 
     std::pair<Tree, Input> fetch(ref<Store> store, const Input & _input) override
     {
-        auto name = "source";
-
         Input input(_input);
 
+        auto name = input.getName();
+
         auto [isLocal, actualUrl_] = getActualUrl(input);
         auto actualUrl = actualUrl_; // work around clang bug
 
@@ -193,7 +191,7 @@ struct MercurialInputScheme : InputScheme
                     return files.count(file);
                 };
 
-                auto storePath = store->addToStore("source", actualUrl, FileIngestionMethod::Recursive, htSHA256, filter);
+                auto storePath = store->addToStore(input.getName(), actualUrl, FileIngestionMethod::Recursive, htSHA256, filter);
 
                 return {
                     Tree(store->toRealPath(storePath), std::move(storePath)),
@@ -253,9 +251,7 @@ struct MercurialInputScheme : InputScheme
            have to pull again. */
         if (!(input.getRev()
                 && pathExists(cacheDir)
-                && runProgram(
-                    hgOptions({ "log", "-R", cacheDir, "-r", input.getRev()->gitRev(), "--template", "1" })
-                    .killStderr(true)).second == "1"))
+                && runProgram(hgOptions({ "log", "-R", cacheDir, "-r", input.getRev()->gitRev(), "--template", "1" })).second == "1"))
         {
             Activity act(*logger, lvlTalkative, actUnknown, fmt("fetching Mercurial repository '%s'", actualUrl));
 
diff --git a/src/libfetchers/path.cc b/src/libfetchers/path.cc
index d1003de57..fb5702c4c 100644
--- a/src/libfetchers/path.cc
+++ b/src/libfetchers/path.cc
@@ -82,18 +82,38 @@ struct PathInputScheme : InputScheme
 
     std::pair<Tree, Input> fetch(ref<Store> store, const Input & input) override
     {
+        std::string absPath;
         auto path = getStrAttr(input.attrs, "path");
 
-        // FIXME: check whether access to 'path' is allowed.
+        if (path[0] != '/') {
+            if (!input.parent)
+                throw Error("cannot fetch input '%s' because it uses a relative path", input.to_string());
+
+            auto parent = canonPath(*input.parent);
 
-        auto storePath = store->maybeParseStorePath(path);
+            // the path isn't relative, prefix it
+            absPath = nix::absPath(path, parent);
+
+            // for security, ensure that if the parent is a store path, it's inside it
+            if (store->isInStore(parent)) {
+                auto storePath = store->printStorePath(store->toStorePath(parent).first);
+                if (!isInDir(absPath, storePath))
+                    throw BadStorePath("relative path '%s' points outside of its parent's store path '%s'", path, storePath);
+            }
+        } else
+            absPath = path;
+
+        Activity act(*logger, lvlTalkative, actUnknown, fmt("copying '%s'", absPath));
+
+        // FIXME: check whether access to 'path' is allowed.
+        auto storePath = store->maybeParseStorePath(absPath);
 
         if (storePath)
             store->addTempRoot(*storePath);
 
         if (!storePath || storePath->name() != "source" || !store->isValidPath(*storePath))
             // FIXME: try to substitute storePath.
-            storePath = store->addToStore("source", path);
+            storePath = store->addToStore("source", absPath);
 
         return {
             Tree(store->toRealPath(*storePath), std::move(*storePath)),
diff --git a/src/libfetchers/registry.cc b/src/libfetchers/registry.cc
index 74376adc0..f35359d4b 100644
--- a/src/libfetchers/registry.cc
+++ b/src/libfetchers/registry.cc
@@ -124,6 +124,13 @@ std::shared_ptr<Registry> getUserRegistry()
     return userRegistry;
 }
 
+std::shared_ptr<Registry> getCustomRegistry(const Path & p)
+{
+    static auto customRegistry =
+        Registry::read(p, Registry::Custom);
+    return customRegistry;
+}
+
 static std::shared_ptr<Registry> flagRegistry =
     std::make_shared<Registry>(Registry::Flag);
 
diff --git a/src/libfetchers/registry.hh b/src/libfetchers/registry.hh
index 1077af020..260a2c460 100644
--- a/src/libfetchers/registry.hh
+++ b/src/libfetchers/registry.hh
@@ -14,6 +14,7 @@ struct Registry
         User = 1,
         System = 2,
         Global = 3,
+        Custom = 4,
     };
 
     RegistryType type;
@@ -48,6 +49,8 @@ typedef std::vector<std::shared_ptr<Registry>> Registries;
 
 std::shared_ptr<Registry> getUserRegistry();
 
+std::shared_ptr<Registry> getCustomRegistry(const Path & p);
+
 Path getUserRegistryPath();
 
 Registries getRegistries(ref<Store> store);
diff --git a/src/libfetchers/tarball.cc b/src/libfetchers/tarball.cc
index b8d7d2c70..031ccc5f7 100644
--- a/src/libfetchers/tarball.cc
+++ b/src/libfetchers/tarball.cc
@@ -178,7 +178,8 @@ struct TarballInputScheme : InputScheme
             && !hasSuffix(url.path, ".tar")
             && !hasSuffix(url.path, ".tar.gz")
             && !hasSuffix(url.path, ".tar.xz")
-            && !hasSuffix(url.path, ".tar.bz2"))
+            && !hasSuffix(url.path, ".tar.bz2")
+            && !hasSuffix(url.path, ".tar.zst"))
             return {};
 
         Input input;
@@ -195,7 +196,7 @@ struct TarballInputScheme : InputScheme
         if (maybeGetStrAttr(attrs, "type") != "tarball") return {};
 
         for (auto & [name, value] : attrs)
-            if (name != "type" && name != "url" && /* name != "hash" && */ name != "narHash")
+            if (name != "type" && name != "url" && /* name != "hash" && */ name != "narHash" && name != "name")
                 throw Error("unsupported tarball input attribute '%s'", name);
 
         Input input;
@@ -225,7 +226,7 @@ struct TarballInputScheme : InputScheme
 
     std::pair<Tree, Input> fetch(ref<Store> store, const Input & input) override
     {
-        auto tree = downloadTarball(store, getStrAttr(input.attrs, "url"), "source", false).first;
+        auto tree = downloadTarball(store, getStrAttr(input.attrs, "url"), input.getName(), false).first;
         return {std::move(tree), input};
     }
 };
diff --git a/src/libmain/local.mk b/src/libmain/local.mk
index a8eed6c65..99da95e27 100644
--- a/src/libmain/local.mk
+++ b/src/libmain/local.mk
@@ -8,10 +8,10 @@ libmain_SOURCES := $(wildcard $(d)/*.cc)
 
 libmain_CXXFLAGS += -I src/libutil -I src/libstore
 
-libmain_LDFLAGS = $(OPENSSL_LIBS)
+libmain_LDFLAGS += $(OPENSSL_LIBS)
 
 libmain_LIBS = libstore libutil
 
 libmain_ALLOW_UNDEFINED = 1
 
-$(eval $(call install-file-in, $(d)/nix-main.pc, $(prefix)/lib/pkgconfig, 0644))
+$(eval $(call install-file-in, $(d)/nix-main.pc, $(libdir)/pkgconfig, 0644))
diff --git a/src/libmain/progress-bar.cc b/src/libmain/progress-bar.cc
index 15354549a..63955eed1 100644
--- a/src/libmain/progress-bar.cc
+++ b/src/libmain/progress-bar.cc
@@ -103,17 +103,19 @@ public:
     ~ProgressBar()
     {
         stop();
-        updateThread.join();
     }
 
     void stop() override
     {
-        auto state(state_.lock());
-        if (!state->active) return;
-        state->active = false;
-        writeToStderr("\r\e[K");
-        updateCV.notify_one();
-        quitCV.notify_one();
+        {
+            auto state(state_.lock());
+            if (!state->active) return;
+            state->active = false;
+            writeToStderr("\r\e[K");
+            updateCV.notify_one();
+            quitCV.notify_one();
+        }
+        updateThread.join();
     }
 
     bool isVerbose() override {
@@ -484,7 +486,7 @@ Logger * makeProgressBar(bool printBuildLogs)
 {
     return new ProgressBar(
         printBuildLogs,
-        isatty(STDERR_FILENO) && getEnv("TERM").value_or("dumb") != "dumb"
+        shouldANSI()
     );
 }
 
diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc
index 86930c2e3..85f9f0d58 100644
--- a/src/libmain/shared.cc
+++ b/src/libmain/shared.cc
@@ -15,6 +15,9 @@
 #include <sys/stat.h>
 #include <unistd.h>
 #include <signal.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netdb.h>
 
 #include <openssl/crypto.h>
 
@@ -110,6 +113,31 @@ static void opensslLockCallback(int mode, int type, const char * file, int line)
 }
 #endif
 
+static std::once_flag dns_resolve_flag;
+
+static void preloadNSS() {
+    /* builtin:fetchurl can trigger a DNS lookup, which with glibc can trigger a dynamic library load of
+       one of the glibc NSS libraries in a sandboxed child, which will fail unless the library's already
+       been loaded in the parent. So we force a lookup of an invalid domain to force the NSS machinery to
+       load its lookup libraries in the parent before any child gets a chance to. */
+    std::call_once(dns_resolve_flag, []() {
+        struct addrinfo *res = NULL;
+
+        /* nss will only force the "local" (not through nscd) dns resolution if its on the LOCALDOMAIN.
+           We need the resolution to be done locally, as nscd socket will not be accessible in the
+           sandbox. */
+        char * previous_env = getenv("LOCALDOMAIN");
+        setenv("LOCALDOMAIN", "invalid", 1);
+        if (getaddrinfo("this.pre-initializes.the.dns.resolvers.invalid.", "http", NULL, &res) == 0) {
+            if (res) freeaddrinfo(res);
+        }
+        if (previous_env) {
+             setenv("LOCALDOMAIN", previous_env, 1);
+        } else {
+             unsetenv("LOCALDOMAIN");
+        }
+    });
+}
 
 static void sigHandler(int signo) { }
 
@@ -176,6 +204,8 @@ void initNix()
     if (hasPrefix(getEnv("TMPDIR").value_or("/tmp"), "/var/folders/"))
         unsetenv("TMPDIR");
 #endif
+
+    preloadNSS();
 }
 
 
@@ -238,7 +268,7 @@ LegacyArgs::LegacyArgs(const std::string & programName,
     addFlag({
         .longName = "no-gc-warning",
         .description = "Disable warnings about not using `--add-root`.",
-        .handler = {&gcWarning, true},
+        .handler = {&gcWarning, false},
     });
 
     addFlag({
diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index 09e1c254b..13c086a46 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -52,9 +52,9 @@ void BinaryCacheStore::init()
                     throw Error("binary cache '%s' is for Nix stores with prefix '%s', not '%s'",
                         getUri(), value, storeDir);
             } else if (name == "WantMassQuery") {
-                wantMassQuery.setDefault(value == "1" ? "true" : "false");
+                wantMassQuery.setDefault(value == "1");
             } else if (name == "Priority") {
-                priority.setDefault(fmt("%d", std::stoi(value)));
+                priority.setDefault(std::stoi(value));
             }
         }
     }
@@ -111,15 +111,15 @@ void BinaryCacheStore::writeNarInfo(ref<NarInfo> narInfo)
 
     upsertFile(narInfoFile, narInfo->to_string(*this), "text/x-nix-narinfo");
 
-    std::string hashPart(narInfo->path.hashPart());
-
     {
         auto state_(state.lock());
-        state_->pathInfoCache.upsert(hashPart, PathInfoCacheValue { .value = std::shared_ptr<NarInfo>(narInfo) });
+        state_->pathInfoCache.upsert(
+            std::string(narInfo->path.to_string()),
+            PathInfoCacheValue { .value = std::shared_ptr<NarInfo>(narInfo) });
     }
 
     if (diskCache)
-        diskCache->upsertNarInfo(getUri(), hashPart, std::shared_ptr<NarInfo>(narInfo));
+        diskCache->upsertNarInfo(getUri(), std::string(narInfo->path.hashPart()), std::shared_ptr<NarInfo>(narInfo));
 }
 
 AutoCloseFD openFile(const Path & path)
@@ -130,17 +130,6 @@ AutoCloseFD openFile(const Path & path)
     return fd;
 }
 
-struct FileSource : FdSource
-{
-    AutoCloseFD fd2;
-
-    FileSource(const Path & path)
-        : fd2(openFile(path))
-    {
-        fd = fd2.get();
-    }
-};
-
 ref<const ValidPathInfo> BinaryCacheStore::addToStoreCommon(
     Source & narSource, RepairFlag repair, CheckSigsFlag checkSigs,
     std::function<ValidPathInfo(HashResult)> mkInfo)
@@ -160,7 +149,7 @@ ref<const ValidPathInfo> BinaryCacheStore::addToStoreCommon(
     {
     FdSink fileSink(fdTemp.get());
     TeeSink teeSinkCompressed { fileSink, fileHashSink };
-    auto compressionSink = makeCompressionSink(compression, teeSinkCompressed);
+    auto compressionSink = makeCompressionSink(compression, teeSinkCompressed, parallelCompression, compressionLevel);
     TeeSink teeSinkUncompressed { *compressionSink, narHashSink };
     TeeSource teeSource { narSource, teeSinkUncompressed };
     narAccessor = makeNarAccessor(teeSource);
@@ -319,16 +308,17 @@ void BinaryCacheStore::addToStore(const ValidPathInfo & info, Source & narSource
 }
 
 StorePath BinaryCacheStore::addToStoreFromDump(Source & dump, const string & name,
-    FileIngestionMethod method, HashType hashAlgo, RepairFlag repair)
+    FileIngestionMethod method, HashType hashAlgo, RepairFlag repair, const StorePathSet & references)
 {
     if (method != FileIngestionMethod::Recursive || hashAlgo != htSHA256)
         unsupported("addToStoreFromDump");
     return addToStoreCommon(dump, repair, CheckSigs, [&](HashResult nar) {
         ValidPathInfo info {
-            makeFixedOutputPath(method, nar.first, name),
+            makeFixedOutputPath(method, nar.first, name, references),
             nar.first,
         };
         info.narSize = nar.second;
+        info.references = references;
         return info;
     })->path;
 }
@@ -396,7 +386,7 @@ void BinaryCacheStore::queryPathInfoUncached(const StorePath & storePath,
 }
 
 StorePath BinaryCacheStore::addToStore(const string & name, const Path & srcPath,
-    FileIngestionMethod method, HashType hashAlgo, PathFilter & filter, RepairFlag repair)
+    FileIngestionMethod method, HashType hashAlgo, PathFilter & filter, RepairFlag repair, const StorePathSet & references)
 {
     /* FIXME: Make BinaryCacheStore::addToStoreCommon support
        non-recursive+sha256 so we can just use the default
@@ -415,10 +405,11 @@ StorePath BinaryCacheStore::addToStore(const string & name, const Path & srcPath
     });
     return addToStoreCommon(*source, repair, CheckSigs, [&](HashResult nar) {
         ValidPathInfo info {
-            makeFixedOutputPath(method, h, name),
+            makeFixedOutputPath(method, h, name, references),
             nar.first,
         };
         info.narSize = nar.second;
+        info.references = references;
         info.ca = FixedOutputHash {
             .method = method,
             .hash = h,
@@ -448,20 +439,34 @@ StorePath BinaryCacheStore::addTextToStore(const string & name, const string & s
     })->path;
 }
 
-std::optional<const Realisation> BinaryCacheStore::queryRealisation(const DrvOutput & id)
+void BinaryCacheStore::queryRealisationUncached(const DrvOutput & id,
+    Callback<std::shared_ptr<const Realisation>> callback) noexcept
 {
     auto outputInfoFilePath = realisationsPrefix + "/" + id.to_string() + ".doi";
-    auto rawOutputInfo = getFile(outputInfoFilePath);
 
-    if (rawOutputInfo) {
-        return {Realisation::fromJSON(
-            nlohmann::json::parse(*rawOutputInfo), outputInfoFilePath)};
-    } else {
-        return std::nullopt;
-    }
+    auto callbackPtr = std::make_shared<decltype(callback)>(std::move(callback));
+
+    Callback<std::shared_ptr<std::string>> newCallback = {
+        [=](std::future<std::shared_ptr<std::string>> fut) {
+            try {
+                auto data = fut.get();
+                if (!data) return (*callbackPtr)(nullptr);
+
+                auto realisation = Realisation::fromJSON(
+                    nlohmann::json::parse(*data), outputInfoFilePath);
+                return (*callbackPtr)(std::make_shared<const Realisation>(realisation));
+            } catch (...) {
+                callbackPtr->rethrow();
+            }
+        }
+    };
+
+    getFile(outputInfoFilePath, std::move(newCallback));
 }
 
 void BinaryCacheStore::registerDrvOutput(const Realisation& info) {
+    if (diskCache)
+        diskCache->upsertRealisation(getUri(), info);
     auto filePath = realisationsPrefix + "/" + info.id.to_string() + ".doi";
     upsertFile(filePath, info.toJSON().dump(), "application/json");
 }
diff --git a/src/libstore/binary-cache-store.hh b/src/libstore/binary-cache-store.hh
index c2163166c..9815af591 100644
--- a/src/libstore/binary-cache-store.hh
+++ b/src/libstore/binary-cache-store.hh
@@ -15,13 +15,17 @@ struct BinaryCacheStoreConfig : virtual StoreConfig
 {
     using StoreConfig::StoreConfig;
 
-    const Setting<std::string> compression{(StoreConfig*) this, "xz", "compression", "NAR compression method ('xz', 'bzip2', or 'none')"};
+    const Setting<std::string> compression{(StoreConfig*) this, "xz", "compression", "NAR compression method ('xz', 'bzip2', 'gzip', 'zstd', or 'none')"};
     const Setting<bool> writeNARListing{(StoreConfig*) this, false, "write-nar-listing", "whether to write a JSON file listing the files in each NAR"};
     const Setting<bool> writeDebugInfo{(StoreConfig*) this, false, "index-debug-info", "whether to index DWARF debug info files by build ID"};
     const Setting<Path> secretKeyFile{(StoreConfig*) this, "", "secret-key", "path to secret key used to sign the binary cache"};
     const Setting<Path> localNarCache{(StoreConfig*) this, "", "local-nar-cache", "path to a local cache of NARs"};
     const Setting<bool> parallelCompression{(StoreConfig*) this, false, "parallel-compression",
-        "enable multi-threading compression, available for xz only currently"};
+        "enable multi-threading compression for NARs, available for xz and zstd only currently"};
+    const Setting<int> compressionLevel{(StoreConfig*) this, -1, "compression-level",
+        "specify 'preset level' of compression to be used with NARs: "
+        "meaning and accepted range of values depends on compression method selected, "
+        "other than -1 which we reserve to indicate Nix defaults should be used"};
 };
 
 class BinaryCacheStore : public virtual BinaryCacheStoreConfig, public virtual Store
@@ -34,7 +38,7 @@ private:
 protected:
 
     // The prefix under which realisation infos will be stored
-    const std::string realisationsPrefix = "/realisations";
+    const std::string realisationsPrefix = "realisations";
 
     BinaryCacheStore(const Params & params);
 
@@ -93,18 +97,19 @@ public:
         RepairFlag repair, CheckSigsFlag checkSigs) override;
 
     StorePath addToStoreFromDump(Source & dump, const string & name,
-        FileIngestionMethod method, HashType hashAlgo, RepairFlag repair) override;
+        FileIngestionMethod method, HashType hashAlgo, RepairFlag repair, const StorePathSet & references ) override;
 
     StorePath addToStore(const string & name, const Path & srcPath,
         FileIngestionMethod method, HashType hashAlgo,
-        PathFilter & filter, RepairFlag repair) override;
+        PathFilter & filter, RepairFlag repair, const StorePathSet & references) override;
 
     StorePath addTextToStore(const string & name, const string & s,
         const StorePathSet & references, RepairFlag repair) override;
 
     void registerDrvOutput(const Realisation & info) override;
 
-    std::optional<const Realisation> queryRealisation(const DrvOutput &) override;
+    void queryRealisationUncached(const DrvOutput &,
+        Callback<std::shared_ptr<const Realisation>> callback) noexcept override;
 
     void narFromPath(const StorePath & path, Sink & sink) override;
 
diff --git a/src/libstore/build/derivation-goal.cc b/src/libstore/build/derivation-goal.cc
index 9100d3333..b924d23b2 100644
--- a/src/libstore/build/derivation-goal.cc
+++ b/src/libstore/build/derivation-goal.cc
@@ -143,7 +143,6 @@ void DerivationGoal::work()
     (this->*state)();
 }
 
-
 void DerivationGoal::addWantedOutputs(const StringSet & outputs)
 {
     /* If we already want all outputs, there is nothing to do. */
@@ -166,7 +165,7 @@ void DerivationGoal::getDerivation()
     /* The first thing to do is to make sure that the derivation
        exists.  If it doesn't, it may be created through a
        substitute. */
-    if (buildMode == bmNormal && worker.store.isValidPath(drvPath)) {
+    if (buildMode == bmNormal && worker.evalStore.isValidPath(drvPath)) {
         loadDerivation();
         return;
     }
@@ -189,12 +188,12 @@ void DerivationGoal::loadDerivation()
     /* `drvPath' should already be a root, but let's be on the safe
        side: if the user forgot to make it a root, we wouldn't want
        things being garbage collected while we're busy. */
-    worker.store.addTempRoot(drvPath);
+    worker.evalStore.addTempRoot(drvPath);
 
-    assert(worker.store.isValidPath(drvPath));
+    assert(worker.evalStore.isValidPath(drvPath));
 
     /* Get the derivation. */
-    drv = std::make_unique<Derivation>(worker.store.derivationFromPath(drvPath));
+    drv = std::make_unique<Derivation>(worker.evalStore.derivationFromPath(drvPath));
 
     haveDerivation();
 }
@@ -205,7 +204,7 @@ void DerivationGoal::haveDerivation()
     trace("have derivation");
 
     if (drv->type() == DerivationType::CAFloating)
-        settings.requireExperimentalFeature("ca-derivations");
+        settings.requireExperimentalFeature(Xp::CaDerivations);
 
     retrySubstitution = false;
 
@@ -213,8 +212,8 @@ void DerivationGoal::haveDerivation()
         if (i.second.second)
             worker.store.addTempRoot(*i.second.second);
 
-    auto outputHashes = staticOutputHashes(worker.store, *drv);
-    for (auto &[outputName, outputHash] : outputHashes)
+    auto outputHashes = staticOutputHashes(worker.evalStore, *drv);
+    for (auto & [outputName, outputHash] : outputHashes)
       initialOutputs.insert({
             outputName,
             InitialOutput{
@@ -338,6 +337,15 @@ void DerivationGoal::gaveUpOnSubstitution()
         for (auto & i : dynamic_cast<Derivation *>(drv.get())->inputDrvs)
             addWaitee(worker.makeDerivationGoal(i.first, i.second, buildMode == bmRepair ? bmRepair : bmNormal));
 
+    /* Copy the input sources from the eval store to the build
+       store. */
+    if (&worker.evalStore != &worker.store) {
+        RealisedPath::Set inputSrcs;
+        for (auto & i : drv->inputSrcs)
+            inputSrcs.insert(i);
+        copyClosure(worker.evalStore, worker.store, inputSrcs);
+    }
+
     for (auto & i : drv->inputSrcs) {
         if (worker.store.isValidPath(i)) continue;
         if (!settings.useSubstitutes)
@@ -445,7 +453,7 @@ void DerivationGoal::inputsRealised()
     if (useDerivation) {
         auto & fullDrv = *dynamic_cast<Derivation *>(drv.get());
 
-        if (settings.isExperimentalFeatureEnabled("ca-derivations") &&
+        if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations) &&
             ((!fullDrv.inputDrvs.empty() && derivationIsCA(fullDrv.type()))
             || fullDrv.type() == DerivationType::DeferredInputAddressed)) {
             /* We are be able to resolve this derivation based on the
@@ -479,8 +487,8 @@ void DerivationGoal::inputsRealised()
             /* Add the relevant output closures of the input derivation
                `i' as input paths.  Only add the closures of output paths
                that are specified as inputs. */
-            assert(worker.store.isValidPath(drvPath));
-            auto outputs = worker.store.queryPartialDerivationOutputMap(depDrvPath);
+            assert(worker.evalStore.isValidPath(drvPath));
+            auto outputs = worker.evalStore.queryPartialDerivationOutputMap(depDrvPath);
             for (auto & j : wantedDepOutputs) {
                 if (outputs.count(j) > 0) {
                     auto optRealizedInput = outputs.at(j);
@@ -545,7 +553,7 @@ void DerivationGoal::tryToBuild()
     PathSet lockFiles;
     /* FIXME: Should lock something like the drv itself so we don't build same
        CA drv concurrently */
-    if (dynamic_cast<LocalStore *>(&worker.store))
+    if (dynamic_cast<LocalStore *>(&worker.store)) {
         /* If we aren't a local store, we might need to use the local store as
            a build remote, but that would cause a deadlock. */
         /* FIXME: Make it so we can use ourselves as a build remote even if we
@@ -553,9 +561,15 @@ void DerivationGoal::tryToBuild()
         /* FIXME: find some way to lock for scheduling for the other stores so
            a forking daemon with --store still won't farm out redundant builds.
            */
-        for (auto & i : drv->outputsAndOptPaths(worker.store))
+        for (auto & i : drv->outputsAndOptPaths(worker.store)) {
             if (i.second.second)
                 lockFiles.insert(worker.store.Store::toRealPath(*i.second.second));
+            else
+                lockFiles.insert(
+                    worker.store.Store::toRealPath(drvPath) + "." + i.first
+                );
+        }
+    }
 
     if (!outputLocks.lockPaths(lockFiles, "", false)) {
         if (!actLock)
@@ -602,7 +616,9 @@ void DerivationGoal::tryToBuild()
     /* Don't do a remote build if the derivation has the attribute
        `preferLocalBuild' set.  Also, check and repair modes are only
        supported for local builds. */
-    bool buildLocally = buildMode != bmNormal || parsedDrv->willBuildLocally(worker.store);
+    bool buildLocally =
+        (buildMode != bmNormal || parsedDrv->willBuildLocally(worker.store))
+        && settings.maxBuildJobs.get() != 0;
 
     if (!buildLocally) {
         switch (tryBuildHook()) {
@@ -739,6 +755,64 @@ void DerivationGoal::cleanupPostOutputsRegisteredModeNonCheck()
 {
 }
 
+void runPostBuildHook(
+    Store & store,
+    Logger & logger,
+    const StorePath & drvPath,
+    StorePathSet outputPaths
+)
+{
+    auto hook = settings.postBuildHook;
+    if (hook == "")
+        return;
+
+    Activity act(logger, lvlInfo, actPostBuildHook,
+            fmt("running post-build-hook '%s'", settings.postBuildHook),
+            Logger::Fields{store.printStorePath(drvPath)});
+    PushActivity pact(act.id);
+    std::map<std::string, std::string> hookEnvironment = getEnv();
+
+    hookEnvironment.emplace("DRV_PATH", store.printStorePath(drvPath));
+    hookEnvironment.emplace("OUT_PATHS", chomp(concatStringsSep(" ", store.printStorePathSet(outputPaths))));
+    hookEnvironment.emplace("NIX_CONFIG", globalConfig.toKeyValue());
+
+    struct LogSink : Sink {
+        Activity & act;
+        std::string currentLine;
+
+        LogSink(Activity & act) : act(act) { }
+
+        void operator() (std::string_view data) override {
+            for (auto c : data) {
+                if (c == '\n') {
+                    flushLine();
+                } else {
+                    currentLine += c;
+                }
+            }
+        }
+
+        void flushLine() {
+            act.result(resPostBuildLogLine, currentLine);
+            currentLine.clear();
+        }
+
+        ~LogSink() {
+            if (currentLine != "") {
+                currentLine += '\n';
+                flushLine();
+            }
+        }
+    };
+    LogSink sink(act);
+
+    runProgram2({
+        .program = settings.postBuildHook,
+        .environment = hookEnvironment,
+        .standardOut = &sink,
+        .mergeStderrToStdout = true,
+    });
+}
 
 void DerivationGoal::buildDone()
 {
@@ -804,57 +878,15 @@ void DerivationGoal::buildDone()
            being valid. */
         registerOutputs();
 
-        if (settings.postBuildHook != "") {
-            Activity act(*logger, lvlInfo, actPostBuildHook,
-                fmt("running post-build-hook '%s'", settings.postBuildHook),
-                Logger::Fields{worker.store.printStorePath(drvPath)});
-            PushActivity pact(act.id);
-            StorePathSet outputPaths;
-            for (auto i : drv->outputs) {
-                outputPaths.insert(finalOutputs.at(i.first));
-            }
-            std::map<std::string, std::string> hookEnvironment = getEnv();
-
-            hookEnvironment.emplace("DRV_PATH", worker.store.printStorePath(drvPath));
-            hookEnvironment.emplace("OUT_PATHS", chomp(concatStringsSep(" ", worker.store.printStorePathSet(outputPaths))));
-
-            RunOptions opts(settings.postBuildHook, {});
-            opts.environment = hookEnvironment;
-
-            struct LogSink : Sink {
-                Activity & act;
-                std::string currentLine;
-
-                LogSink(Activity & act) : act(act) { }
-
-                void operator() (std::string_view data) override {
-                    for (auto c : data) {
-                        if (c == '\n') {
-                            flushLine();
-                        } else {
-                            currentLine += c;
-                        }
-                    }
-                }
-
-                void flushLine() {
-                    act.result(resPostBuildLogLine, currentLine);
-                    currentLine.clear();
-                }
-
-                ~LogSink() {
-                    if (currentLine != "") {
-                        currentLine += '\n';
-                        flushLine();
-                    }
-                }
-            };
-            LogSink sink(act);
-
-            opts.standardOut = &sink;
-            opts.mergeStderrToStdout = true;
-            runProgram2(opts);
-        }
+        StorePathSet outputPaths;
+        for (auto & [_, path] : finalOutputs)
+            outputPaths.insert(path);
+        runPostBuildHook(
+            worker.store,
+            *logger,
+            drvPath,
+            outputPaths
+        );
 
         if (buildMode == bmCheck) {
             cleanupPostOutputsRegisteredModeCheck();
@@ -910,6 +942,8 @@ void DerivationGoal::resolvedFinished() {
 
     auto resolvedHashes = staticOutputHashes(worker.store, *resolvedDrv);
 
+    StorePathSet outputPaths;
+
     // `wantedOutputs` might be empty, which means “all the outputs”
     auto realWantedOutputs = wantedOutputs;
     if (realWantedOutputs.empty())
@@ -927,8 +961,10 @@ void DerivationGoal::resolvedFinished() {
             auto newRealisation = *realisation;
             newRealisation.id = DrvOutput{initialOutputs.at(wantedOutput).outputHash, wantedOutput};
             newRealisation.signatures.clear();
+            newRealisation.dependentRealisations = drvOutputReferences(worker.store, *drv, realisation->outPath);
             signRealisation(newRealisation);
             worker.store.registerDrvOutput(newRealisation);
+            outputPaths.insert(realisation->outPath);
         } else {
             // If we don't have a realisation, then it must mean that something
             // failed when building the resolved drv
@@ -936,6 +972,13 @@ void DerivationGoal::resolvedFinished() {
         }
     }
 
+    runPostBuildHook(
+        worker.store,
+        *logger,
+        drvPath,
+        outputPaths
+    );
+
     // This is potentially a bit fishy in terms of error reporting. Not sure
     // how to do it in a cleaner way
     amDone(nrFailed == 0 ? ecSuccess : ecFailed, ex);
@@ -968,7 +1011,7 @@ HookReply DerivationGoal::tryBuildHook()
                     return readLine(worker.hook->fromHook.readSide.get());
                 } catch (Error & e) {
                     e.addTrace({}, "while reading the response from the build hook");
-                    throw e;
+                    throw;
                 }
             }();
             if (handleJSONLogMessage(s, worker.act, worker.hook->activities, true))
@@ -1014,7 +1057,7 @@ HookReply DerivationGoal::tryBuildHook()
         machineName = readLine(hook->fromHook.readSide.get());
     } catch (Error & e) {
         e.addTrace({}, "while reading the machine name from the build hook");
-        throw e;
+        throw;
     }
 
     /* Tell the hook all the inputs that have to be copied to the
@@ -1048,42 +1091,6 @@ HookReply DerivationGoal::tryBuildHook()
 }
 
 
-StorePathSet DerivationGoal::exportReferences(const StorePathSet & storePaths)
-{
-    StorePathSet paths;
-
-    for (auto & storePath : storePaths) {
-        if (!inputPaths.count(storePath))
-            throw BuildError("cannot export references of path '%s' because it is not in the input closure of the derivation", worker.store.printStorePath(storePath));
-
-        worker.store.computeFSClosure({storePath}, paths);
-    }
-
-    /* If there are derivations in the graph, then include their
-       outputs as well.  This is useful if you want to do things
-       like passing all build-time dependencies of some path to a
-       derivation that builds a NixOS DVD image. */
-    auto paths2 = paths;
-
-    for (auto & j : paths2) {
-        if (j.isDerivation()) {
-            Derivation drv = worker.store.derivationFromPath(j);
-            for (auto & k : drv.outputsAndOptPaths(worker.store)) {
-                if (!k.second.second)
-                    /* FIXME: I am confused why we are calling
-                       `computeFSClosure` on the output path, rather than
-                       derivation itself. That doesn't seem right to me, so I
-                       won't try to implemented this for CA derivations. */
-                    throw UnimplementedError("exportReferences on CA derivations is not yet implemented");
-                worker.store.computeFSClosure(*k.second.second, paths);
-            }
-        }
-    }
-
-    return paths;
-}
-
-
 void DerivationGoal::registerOutputs()
 {
     /* When using a build hook, the build hook can register the output
@@ -1268,7 +1275,7 @@ void DerivationGoal::checkPathValidity()
                     : PathStatus::Corrupt,
             };
         }
-        if (settings.isExperimentalFeatureEnabled("ca-derivations")) {
+        if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations)) {
             auto drvOutput = DrvOutput{initialOutputs.at(i.first).outputHash, i.first};
             if (auto real = worker.store.queryRealisation(drvOutput)) {
                 info.known = {
diff --git a/src/libstore/build/drv-output-substitution-goal.cc b/src/libstore/build/drv-output-substitution-goal.cc
index a5ac4c49d..b9602e696 100644
--- a/src/libstore/build/drv-output-substitution-goal.cc
+++ b/src/libstore/build/drv-output-substitution-goal.cc
@@ -1,6 +1,8 @@
 #include "drv-output-substitution-goal.hh"
+#include "finally.hh"
 #include "worker.hh"
 #include "substitution-goal.hh"
+#include "callback.hh"
 
 namespace nix {
 
@@ -17,6 +19,13 @@ DrvOutputSubstitutionGoal::DrvOutputSubstitutionGoal(const DrvOutput& id, Worker
 void DrvOutputSubstitutionGoal::init()
 {
     trace("init");
+
+    /* If the derivation already exists, we’re done */
+    if (worker.store.queryRealisation(id)) {
+        amDone(ecSuccess);
+        return;
+    }
+
     subs = settings.useSubstitutes ? getDefaultSubstituters() : std::list<ref<Store>>();
     tryNext();
 }
@@ -43,14 +52,62 @@ void DrvOutputSubstitutionGoal::tryNext()
         return;
     }
 
-    auto sub = subs.front();
+    sub = subs.front();
     subs.pop_front();
 
     // FIXME: Make async
-    outputInfo = sub->queryRealisation(id);
+    // outputInfo = sub->queryRealisation(id);
+    outPipe.create();
+    promise = decltype(promise)();
+
+    sub->queryRealisation(
+        id, { [&](std::future<std::shared_ptr<const Realisation>> res) {
+            try {
+                Finally updateStats([this]() { outPipe.writeSide.close(); });
+                promise.set_value(res.get());
+            } catch (...) {
+                promise.set_exception(std::current_exception());
+            }
+        } });
+
+    worker.childStarted(shared_from_this(), {outPipe.readSide.get()}, true, false);
+
+    state = &DrvOutputSubstitutionGoal::realisationFetched;
+}
+
+void DrvOutputSubstitutionGoal::realisationFetched()
+{
+    worker.childTerminated(this);
+
+    try {
+        outputInfo = promise.get_future().get();
+    } catch (std::exception & e) {
+        printError(e.what());
+        substituterFailed = true;
+    }
+
     if (!outputInfo) {
-        tryNext();
-        return;
+        return tryNext();
+    }
+
+    for (const auto & [depId, depPath] : outputInfo->dependentRealisations) {
+        if (depId != id) {
+            if (auto localOutputInfo = worker.store.queryRealisation(depId);
+                localOutputInfo && localOutputInfo->outPath != depPath) {
+                warn(
+                    "substituter '%s' has an incompatible realisation for '%s', ignoring.\n"
+                    "Local:  %s\n"
+                    "Remote: %s",
+                    sub->getUri(),
+                    depId.to_string(),
+                    worker.store.printStorePath(localOutputInfo->outPath),
+                    worker.store.printStorePath(depPath)
+                );
+                tryNext();
+                return;
+            }
+            addWaitee(worker.makeDrvOutputSubstitutionGoal(depId));
+        }
     }
 
     addWaitee(worker.makePathSubstitutionGoal(outputInfo->outPath));
@@ -92,4 +149,10 @@ void DrvOutputSubstitutionGoal::work()
     (this->*state)();
 }
 
+void DrvOutputSubstitutionGoal::handleEOF(int fd)
+{
+    if (fd == outPipe.readSide.get()) worker.wakeUp(shared_from_this());
+}
+
+
 }
diff --git a/src/libstore/build/drv-output-substitution-goal.hh b/src/libstore/build/drv-output-substitution-goal.hh
index 63ab53d89..67ae2624a 100644
--- a/src/libstore/build/drv-output-substitution-goal.hh
+++ b/src/libstore/build/drv-output-substitution-goal.hh
@@ -3,6 +3,8 @@
 #include "store-api.hh"
 #include "goal.hh"
 #include "realisation.hh"
+#include <thread>
+#include <future>
 
 namespace nix {
 
@@ -20,11 +22,18 @@ private:
 
     // The realisation corresponding to the given output id.
     // Will be filled once we can get it.
-    std::optional<Realisation> outputInfo;
+    std::shared_ptr<const Realisation> outputInfo;
 
     /* The remaining substituters. */
     std::list<ref<Store>> subs;
 
+    /* The current substituter. */
+    std::shared_ptr<Store> sub;
+
+    Pipe outPipe;
+    std::thread thr;
+    std::promise<std::shared_ptr<const Realisation>> promise;
+
     /* Whether a substituter failed. */
     bool substituterFailed = false;
 
@@ -36,6 +45,7 @@ public:
 
     void init();
     void tryNext();
+    void realisationFetched();
     void outPathValid();
     void finished();
 
@@ -44,7 +54,7 @@ public:
     string key() override;
 
     void work() override;
-
+    void handleEOF(int fd) override;
 };
 
 }
diff --git a/src/libstore/build/entry-points.cc b/src/libstore/build/entry-points.cc
index 732d4785d..9b4cfd835 100644
--- a/src/libstore/build/entry-points.cc
+++ b/src/libstore/build/entry-points.cc
@@ -1,4 +1,3 @@
-#include "machines.hh"
 #include "worker.hh"
 #include "substitution-goal.hh"
 #include "derivation-goal.hh"
@@ -6,17 +5,17 @@
 
 namespace nix {
 
-void Store::buildPaths(const std::vector<DerivedPath> & reqs, BuildMode buildMode)
+void Store::buildPaths(const std::vector<DerivedPath> & reqs, BuildMode buildMode, std::shared_ptr<Store> evalStore)
 {
-    Worker worker(*this);
+    Worker worker(*this, evalStore ? *evalStore : *this);
 
     Goals goals;
-    for (auto & br : reqs) {
+    for (const auto & br : reqs) {
         std::visit(overloaded {
-            [&](DerivedPath::Built bfd) {
+            [&](const DerivedPath::Built & bfd) {
                 goals.insert(worker.makeDerivationGoal(bfd.drvPath, bfd.outputs, buildMode));
             },
-            [&](DerivedPath::Opaque bo) {
+            [&](const DerivedPath::Opaque & bo) {
                 goals.insert(worker.makePathSubstitutionGoal(bo.path, buildMode == bmRepair ? Repair : NoRepair));
             },
         }, br.raw());
@@ -51,7 +50,7 @@ void Store::buildPaths(const std::vector<DerivedPath> & reqs, BuildMode buildMod
 BuildResult Store::buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
     BuildMode buildMode)
 {
-    Worker worker(*this);
+    Worker worker(*this, *this);
     auto goal = worker.makeBasicDerivationGoal(drvPath, drv, {}, buildMode);
 
     BuildResult result;
@@ -74,7 +73,7 @@ BuildResult Store::buildDerivation(const StorePath & drvPath, const BasicDerivat
                     outputId,
                     Realisation{ outputId, *staticOutput.second}
                     );
-        if (settings.isExperimentalFeatureEnabled("ca-derivations") && !derivationHasKnownOutputPaths(drv.type())) {
+        if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations) && !derivationHasKnownOutputPaths(drv.type())) {
             auto realisation = this->queryRealisation(outputId);
             if (realisation)
                 result.builtOutputs.insert_or_assign(
@@ -93,7 +92,7 @@ void Store::ensurePath(const StorePath & path)
     /* If the path is already valid, we're done. */
     if (isValidPath(path)) return;
 
-    Worker worker(*this);
+    Worker worker(*this, *this);
     GoalPtr goal = worker.makePathSubstitutionGoal(path);
     Goals goals = {goal};
 
@@ -111,7 +110,7 @@ void Store::ensurePath(const StorePath & path)
 
 void LocalStore::repairPath(const StorePath & path)
 {
-    Worker worker(*this);
+    Worker worker(*this, *this);
     GoalPtr goal = worker.makePathSubstitutionGoal(path, Repair);
     Goals goals = {goal};
 
diff --git a/src/libstore/build/goal.cc b/src/libstore/build/goal.cc
index 9de40bdf2..7c985128b 100644
--- a/src/libstore/build/goal.cc
+++ b/src/libstore/build/goal.cc
@@ -13,11 +13,9 @@ bool CompareGoalPtrs::operator() (const GoalPtr & a, const GoalPtr & b) const {
 
 void addToWeakGoals(WeakGoals & goals, GoalPtr p)
 {
-    // FIXME: necessary?
-    // FIXME: O(n)
-    for (auto & i : goals)
-        if (i.lock() == p) return;
-    goals.push_back(p);
+    if (goals.find(p) != goals.end())
+        return;
+    goals.insert(p);
 }
 
 
@@ -46,10 +44,7 @@ void Goal::waiteeDone(GoalPtr waitee, ExitCode result)
         /* If we failed and keepGoing is not set, we remove all
            remaining waitees. */
         for (auto & goal : waitees) {
-            WeakGoals waiters2;
-            for (auto & j : goal->waiters)
-                if (j.lock() != shared_from_this()) waiters2.push_back(j);
-            goal->waiters = waiters2;
+            goal->waiters.extract(shared_from_this());
         }
         waitees.clear();
 
diff --git a/src/libstore/build/goal.hh b/src/libstore/build/goal.hh
index e6bf628cb..192e416d2 100644
--- a/src/libstore/build/goal.hh
+++ b/src/libstore/build/goal.hh
@@ -19,7 +19,7 @@ struct CompareGoalPtrs {
 
 /* Set of goals. */
 typedef set<GoalPtr, CompareGoalPtrs> Goals;
-typedef list<WeakGoalPtr> WeakGoals;
+typedef set<WeakGoalPtr, std::owner_less<WeakGoalPtr>> WeakGoals;
 
 /* A map of paths to goals (and the other way around). */
 typedef std::map<StorePath, WeakGoalPtr> WeakGoalMap;
diff --git a/src/libstore/build/local-derivation-goal.cc b/src/libstore/build/local-derivation-goal.cc
index 7c1402918..c9a4a31e7 100644
--- a/src/libstore/build/local-derivation-goal.cc
+++ b/src/libstore/build/local-derivation-goal.cc
@@ -17,16 +17,14 @@
 #include <regex>
 #include <queue>
 
-#include <sys/types.h>
-#include <sys/socket.h>
 #include <sys/un.h>
-#include <netdb.h>
 #include <fcntl.h>
 #include <termios.h>
 #include <unistd.h>
 #include <sys/mman.h>
 #include <sys/utsname.h>
 #include <sys/resource.h>
+#include <sys/socket.h>
 
 #if HAVE_STATVFS
 #include <sys/statvfs.h>
@@ -34,7 +32,6 @@
 
 /* Includes required for chroot support. */
 #if __linux__
-#include <sys/socket.h>
 #include <sys/ioctl.h>
 #include <net/if.h>
 #include <netinet/ip.h>
@@ -70,12 +67,14 @@ void handleDiffHook(
     auto diffHook = settings.diffHook;
     if (diffHook != "" && settings.runDiffHook) {
         try {
-            RunOptions diffHookOptions(diffHook,{tryA, tryB, drvPath, tmpDir});
-            diffHookOptions.searchPath = true;
-            diffHookOptions.uid = uid;
-            diffHookOptions.gid = gid;
-            diffHookOptions.chdir = "/";
-            auto diffRes = runProgram(diffHookOptions);
+            auto diffRes = runProgram(RunOptions {
+                .program = diffHook,
+                .searchPath = true,
+                .args = {tryA, tryB, drvPath, tmpDir},
+                .uid = uid,
+                .gid = gid,
+                .chdir = "/"
+            });
             if (!statusOk(diffRes.first))
                 throw ExecError(diffRes.first,
                     "diff-hook program '%1%' %2%",
@@ -153,6 +152,7 @@ void LocalDerivationGoal::killChild()
 void LocalDerivationGoal::tryLocalBuild() {
     unsigned int curBuilds = worker.getNrLocalBuilds();
     if (curBuilds >= settings.maxBuildJobs) {
+        state = &DerivationGoal::tryToBuild;
         worker.waitForBuildSlot(shared_from_this());
         outputLocks.unlock();
         return;
@@ -291,7 +291,7 @@ bool LocalDerivationGoal::cleanupDecideWhetherDiskFull()
         auto & localStore = getLocalStore();
         uint64_t required = 8ULL * 1024 * 1024; // FIXME: make configurable
         struct statvfs st;
-        if (statvfs(localStore.realStoreDir.c_str(), &st) == 0 &&
+        if (statvfs(localStore.realStoreDir.get().c_str(), &st) == 0 &&
             (uint64_t) st.f_bavail * st.f_bsize < required)
             diskFull = true;
         if (statvfs(tmpDir.c_str(), &st) == 0 &&
@@ -342,24 +342,7 @@ int childEntry(void * arg)
     return 1;
 }
 
-
-static std::once_flag dns_resolve_flag;
-
-static void preloadNSS() {
-    /* builtin:fetchurl can trigger a DNS lookup, which with glibc can trigger a dynamic library load of
-       one of the glibc NSS libraries in a sandboxed child, which will fail unless the library's already
-       been loaded in the parent. So we force a lookup of an invalid domain to force the NSS machinery to
-       load its lookup libraries in the parent before any child gets a chance to. */
-    std::call_once(dns_resolve_flag, []() {
-        struct addrinfo *res = NULL;
-
-        if (getaddrinfo("this.pre-initializes.the.dns.resolvers.invalid.", "http", NULL, &res) != 0) {
-            if (res) freeaddrinfo(res);
-        }
-    });
-}
-
-
+#if __linux__
 static void linkOrCopy(const Path & from, const Path & to)
 {
     if (link(from.c_str(), to.c_str()) == -1) {
@@ -375,6 +358,7 @@ static void linkOrCopy(const Path & from, const Path & to)
         copyPath(from, to);
     }
 }
+#endif
 
 
 void LocalDerivationGoal::startBuilder()
@@ -388,9 +372,6 @@ void LocalDerivationGoal::startBuilder()
             settings.thisSystem,
             concatStringsSep<StringSet>(", ", worker.store.systemFeatures));
 
-    if (drv->isBuiltin())
-        preloadNSS();
-
 #if __APPLE__
     additionalSandboxProfile = parsedDrv->getStringAttr("__sandboxProfile").value_or("");
 #endif
@@ -416,7 +397,7 @@ void LocalDerivationGoal::startBuilder()
     }
 
     auto & localStore = getLocalStore();
-    if (localStore.storeDir != localStore.realStoreDir) {
+    if (localStore.storeDir != localStore.realStoreDir.get()) {
         #if __linux__
             useChroot = true;
         #else
@@ -517,7 +498,7 @@ void LocalDerivationGoal::startBuilder()
             /* Write closure info to <fileName>. */
             writeFile(tmpDir + "/" + fileName,
                 worker.store.makeValidityRegistration(
-                    exportReferences({storePath}), false, false));
+                    worker.store.exportReferences({storePath}, inputPaths), false, false));
         }
     }
 
@@ -581,7 +562,9 @@ void LocalDerivationGoal::startBuilder()
                 throw Error("derivation '%s' requested impure path '%s', but it was not in allowed-impure-host-deps",
                     worker.store.printStorePath(drvPath), i);
 
-            dirsInChroot[i] = i;
+            /* Allow files in __impureHostDeps to be missing; e.g.
+               macOS 11+ has no /usr/lib/libSystem*.dylib */
+            dirsInChroot[i] = {i, true};
         }
 
 #if __linux__
@@ -729,6 +712,7 @@ void LocalDerivationGoal::startBuilder()
     if (!builderOut.readSide)
         throw SysError("opening pseudoterminal master");
 
+    // FIXME: not thread-safe, use ptsname_r
     std::string slaveName(ptsname(builderOut.readSide.get()));
 
     if (buildUser) {
@@ -772,7 +756,6 @@ void LocalDerivationGoal::startBuilder()
     result.startTime = time(0);
 
     /* Fork a child to build the package. */
-    ProcessOptions options;
 
 #if __linux__
     if (useChroot) {
@@ -815,8 +798,6 @@ void LocalDerivationGoal::startBuilder()
 
         userNamespaceSync.create();
 
-        options.allowVfork = false;
-
         Path maxUserNamespaces = "/proc/sys/user/max_user_namespaces";
         static bool userNamespacesEnabled =
             pathExists(maxUserNamespaces)
@@ -874,7 +855,7 @@ void LocalDerivationGoal::startBuilder()
             writeFull(builderOut.writeSide.get(),
                 fmt("%d %d\n", usingUserNamespace, child));
             _exit(0);
-        }, options);
+        });
 
         int res = helper.wait();
         if (res != 0 && settings.sandboxFallback) {
@@ -937,11 +918,12 @@ void LocalDerivationGoal::startBuilder()
     } else
 #endif
     {
+#if __linux__
     fallback:
-        options.allowVfork = !buildUser && !drv->isBuiltin();
+#endif
         pid = startProcess([&]() {
             runChild();
-        }, options);
+        });
     }
 
     /* parent */
@@ -956,9 +938,12 @@ void LocalDerivationGoal::startBuilder()
             try {
                 return readLine(builderOut.readSide.get());
             } catch (Error & e) {
-                e.addTrace({}, "while waiting for the build environment to initialize (previous messages: %s)",
+                auto status = pid.wait();
+                e.addTrace({}, "while waiting for the build environment for '%s' to initialize (%s, previous messages: %s)",
+                    worker.store.printStorePath(drvPath),
+                    statusToString(status),
                     concatStringsSep("|", msgs));
-                throw e;
+                throw;
             }
         }();
         if (string(msg, 0, 1) == "\2") break;
@@ -1081,123 +1066,38 @@ void LocalDerivationGoal::initEnv()
 }
 
 
-static std::regex shVarName("[A-Za-z_][A-Za-z0-9_]*");
-
-
 void LocalDerivationGoal::writeStructuredAttrs()
 {
-    auto structuredAttrs = parsedDrv->getStructuredAttrs();
-    if (!structuredAttrs) return;
-
-    auto json = *structuredAttrs;
-
-    /* Add an "outputs" object containing the output paths. */
-    nlohmann::json outputs;
-    for (auto & i : drv->outputs) {
-        /* The placeholder must have a rewrite, so we use it to cover both the
-           cases where we know or don't know the output path ahead of time. */
-        outputs[i.first] = rewriteStrings(hashPlaceholder(i.first), inputRewrites);
-    }
-    json["outputs"] = outputs;
-
-    /* Handle exportReferencesGraph. */
-    auto e = json.find("exportReferencesGraph");
-    if (e != json.end() && e->is_object()) {
-        for (auto i = e->begin(); i != e->end(); ++i) {
-            std::ostringstream str;
-            {
-                JSONPlaceholder jsonRoot(str, true);
-                StorePathSet storePaths;
-                for (auto & p : *i)
-                    storePaths.insert(worker.store.parseStorePath(p.get<std::string>()));
-                worker.store.pathInfoToJSON(jsonRoot,
-                    exportReferences(storePaths), false, true);
-            }
-            json[i.key()] = nlohmann::json::parse(str.str()); // urgh
-        }
-    }
-
-    writeFile(tmpDir + "/.attrs.json", rewriteStrings(json.dump(), inputRewrites));
-    chownToBuilder(tmpDir + "/.attrs.json");
-
-    /* As a convenience to bash scripts, write a shell file that
-       maps all attributes that are representable in bash -
-       namely, strings, integers, nulls, Booleans, and arrays and
-       objects consisting entirely of those values. (So nested
-       arrays or objects are not supported.) */
-
-    auto handleSimpleType = [](const nlohmann::json & value) -> std::optional<std::string> {
-        if (value.is_string())
-            return shellEscape(value);
-
-        if (value.is_number()) {
-            auto f = value.get<float>();
-            if (std::ceil(f) == f)
-                return std::to_string(value.get<int>());
+    if (auto structAttrsJson = parsedDrv->prepareStructuredAttrs(worker.store, inputPaths)) {
+        auto json = structAttrsJson.value();
+        nlohmann::json rewritten;
+        for (auto & [i, v] : json["outputs"].get<nlohmann::json::object_t>()) {
+            /* The placeholder must have a rewrite, so we use it to cover both the
+               cases where we know or don't know the output path ahead of time. */
+            rewritten[i] = rewriteStrings(v, inputRewrites);
         }
 
-        if (value.is_null())
-            return std::string("''");
-
-        if (value.is_boolean())
-            return value.get<bool>() ? std::string("1") : std::string("");
-
-        return {};
-    };
-
-    std::string jsonSh;
+        json["outputs"] = rewritten;
 
-    for (auto i = json.begin(); i != json.end(); ++i) {
+        auto jsonSh = writeStructuredAttrsShell(json);
 
-        if (!std::regex_match(i.key(), shVarName)) continue;
-
-        auto & value = i.value();
-
-        auto s = handleSimpleType(value);
-        if (s)
-            jsonSh += fmt("declare %s=%s\n", i.key(), *s);
-
-        else if (value.is_array()) {
-            std::string s2;
-            bool good = true;
-
-            for (auto i = value.begin(); i != value.end(); ++i) {
-                auto s3 = handleSimpleType(i.value());
-                if (!s3) { good = false; break; }
-                s2 += *s3; s2 += ' ';
-            }
-
-            if (good)
-                jsonSh += fmt("declare -a %s=(%s)\n", i.key(), s2);
-        }
-
-        else if (value.is_object()) {
-            std::string s2;
-            bool good = true;
-
-            for (auto i = value.begin(); i != value.end(); ++i) {
-                auto s3 = handleSimpleType(i.value());
-                if (!s3) { good = false; break; }
-                s2 += fmt("[%s]=%s ", shellEscape(i.key()), *s3);
-            }
-
-            if (good)
-                jsonSh += fmt("declare -A %s=(%s)\n", i.key(), s2);
-        }
+        writeFile(tmpDir + "/.attrs.sh", rewriteStrings(jsonSh, inputRewrites));
+        chownToBuilder(tmpDir + "/.attrs.sh");
+        env["NIX_ATTRS_SH_FILE"] = tmpDir + "/.attrs.sh";
+        writeFile(tmpDir + "/.attrs.json", rewriteStrings(json.dump(), inputRewrites));
+        chownToBuilder(tmpDir + "/.attrs.json");
+        env["NIX_ATTRS_JSON_FILE"] = tmpDir + "/.attrs.json";
     }
-
-    writeFile(tmpDir + "/.attrs.sh", rewriteStrings(jsonSh, inputRewrites));
-    chownToBuilder(tmpDir + "/.attrs.sh");
 }
 
 
 static StorePath pathPartOfReq(const DerivedPath & req)
 {
     return std::visit(overloaded {
-        [&](DerivedPath::Opaque bo) {
+        [&](const DerivedPath::Opaque & bo) {
             return bo.path;
         },
-        [&](DerivedPath::Built bfd)  {
+        [&](const DerivedPath::Built & bfd)  {
             return bfd.drvPath;
         },
     }, req.raw());
@@ -1282,7 +1182,8 @@ struct RestrictedStore : public virtual RestrictedStoreConfig, public virtual Lo
 
     StorePath addToStore(const string & name, const Path & srcPath,
         FileIngestionMethod method = FileIngestionMethod::Recursive, HashType hashAlgo = htSHA256,
-        PathFilter & filter = defaultPathFilter, RepairFlag repair = NoRepair) override
+        PathFilter & filter = defaultPathFilter, RepairFlag repair = NoRepair,
+        const StorePathSet & references = StorePathSet()) override
     { throw Error("addToStore"); }
 
     void addToStore(const ValidPathInfo & info, Source & narSource,
@@ -1301,9 +1202,10 @@ struct RestrictedStore : public virtual RestrictedStoreConfig, public virtual Lo
     }
 
     StorePath addToStoreFromDump(Source & dump, const string & name,
-        FileIngestionMethod method = FileIngestionMethod::Recursive, HashType hashAlgo = htSHA256, RepairFlag repair = NoRepair) override
+        FileIngestionMethod method = FileIngestionMethod::Recursive, HashType hashAlgo = htSHA256, RepairFlag repair = NoRepair,
+        const StorePathSet & references = StorePathSet()) override
     {
-        auto path = next->addToStoreFromDump(dump, name, method, hashAlgo, repair);
+        auto path = next->addToStoreFromDump(dump, name, method, hashAlgo, repair, references);
         goal.addDependency(path);
         return path;
     }
@@ -1327,16 +1229,24 @@ struct RestrictedStore : public virtual RestrictedStoreConfig, public virtual Lo
     // corresponds to an allowed derivation
     { throw Error("registerDrvOutput"); }
 
-    std::optional<const Realisation> queryRealisation(const DrvOutput & id) override
+    void queryRealisationUncached(const DrvOutput & id,
+        Callback<std::shared_ptr<const Realisation>> callback) noexcept override
     // XXX: This should probably be allowed if the realisation corresponds to
     // an allowed derivation
-    { throw Error("queryRealisation"); }
+    {
+        if (!goal.isAllowed(id))
+            callback(nullptr);
+        next->queryRealisation(id, std::move(callback));
+    }
 
-    void buildPaths(const std::vector<DerivedPath> & paths, BuildMode buildMode) override
+    void buildPaths(const std::vector<DerivedPath> & paths, BuildMode buildMode, std::shared_ptr<Store> evalStore) override
     {
+        assert(!evalStore);
+
         if (buildMode != bmNormal) throw Error("unsupported build mode");
 
         StorePathSet newPaths;
+        std::set<Realisation> newRealisations;
 
         for (auto & req : paths) {
             if (!goal.isAllowed(req))
@@ -1349,16 +1259,28 @@ struct RestrictedStore : public virtual RestrictedStoreConfig, public virtual Lo
             auto p =  std::get_if<DerivedPath::Built>(&path);
             if (!p) continue;
             auto & bfd = *p;
+            auto drv = readDerivation(bfd.drvPath);
+            auto drvHashes = staticOutputHashes(*this, drv);
             auto outputs = next->queryDerivationOutputMap(bfd.drvPath);
             for (auto & [outputName, outputPath] : outputs)
-                if (wantOutput(outputName, bfd.outputs))
+                if (wantOutput(outputName, bfd.outputs)) {
                     newPaths.insert(outputPath);
+                    if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations)) {
+                        auto thisRealisation = next->queryRealisation(
+                            DrvOutput{drvHashes.at(outputName), outputName}
+                        );
+                        assert(thisRealisation);
+                        newRealisations.insert(*thisRealisation);
+                    }
+                }
         }
 
         StorePathSet closure;
         next->computeFSClosure(newPaths, closure);
         for (auto & path : closure)
             goal.addDependency(path);
+        for (auto & real : Realisation::closure(*next, newRealisations))
+            goal.addedDrvOutputs.insert(real.id);
     }
 
     BuildResult buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
@@ -1404,7 +1326,7 @@ struct RestrictedStore : public virtual RestrictedStoreConfig, public virtual Lo
 
 void LocalDerivationGoal::startDaemon()
 {
-    settings.requireExperimentalFeature("recursive-nix");
+    settings.requireExperimentalFeature(Xp::RecursiveNix);
 
     Store::Params params;
     params["path-info-cache-size"] = "0";
@@ -1437,7 +1359,7 @@ void LocalDerivationGoal::startDaemon()
             AutoCloseFD remote = accept(daemonSocket.get(),
                 (struct sockaddr *) &remoteAddr, &remoteAddrLen);
             if (!remote) {
-                if (errno == EINTR) continue;
+                if (errno == EINTR || errno == EAGAIN) continue;
                 if (errno == EINVAL) break;
                 throw SysError("accepting connection");
             }
@@ -1734,7 +1656,7 @@ void LocalDerivationGoal::runChild()
                 /* N.B. it is realistic that these paths might not exist. It
                    happens when testing Nix building fixed-output derivations
                    within a pure derivation. */
-                for (auto & path : { "/etc/resolv.conf", "/etc/services", "/etc/hosts", "/var/run/nscd/socket" })
+                for (auto & path : { "/etc/resolv.conf", "/etc/services", "/etc/hosts" })
                     if (pathExists(path))
                         ss.push_back(path);
             }
@@ -1916,7 +1838,7 @@ void LocalDerivationGoal::runChild()
         /* Fill in the arguments. */
         Strings args;
 
-        const char *builder = "invalid";
+        std::string builder = "invalid";
 
         if (drv->isBuiltin()) {
             ;
@@ -2042,13 +1964,13 @@ void LocalDerivationGoal::runChild()
                 }
                 args.push_back(drv->builder);
             } else {
-                builder = drv->builder.c_str();
+                builder = drv->builder;
                 args.push_back(std::string(baseNameOf(drv->builder)));
             }
         }
 #else
         else {
-            builder = drv->builder.c_str();
+            builder = drv->builder;
             args.push_back(std::string(baseNameOf(drv->builder)));
         }
 #endif
@@ -2075,7 +1997,7 @@ void LocalDerivationGoal::runChild()
                 else if (drv->builder == "builtin:unpack-channel")
                     builtinUnpackChannel(drv2);
                 else
-                    throw Error("unsupported builtin function '%1%'", string(drv->builder, 8));
+                    throw Error("unsupported builtin builder '%1%'", string(drv->builder, 8));
                 _exit(0);
             } catch (std::exception & e) {
                 writeFull(STDERR_FILENO, e.what() + std::string("\n"));
@@ -2104,9 +2026,9 @@ void LocalDerivationGoal::runChild()
             posix_spawnattr_setbinpref_np(&attrp, 1, &cpu, NULL);
         }
 
-        posix_spawn(NULL, builder, NULL, &attrp, stringsToCharPtrs(args).data(), stringsToCharPtrs(envStrs).data());
+        posix_spawn(NULL, builder.c_str(), NULL, &attrp, stringsToCharPtrs(args).data(), stringsToCharPtrs(envStrs).data());
 #else
-        execve(builder, stringsToCharPtrs(args).data(), stringsToCharPtrs(envStrs).data());
+        execve(builder.c_str(), stringsToCharPtrs(args).data(), stringsToCharPtrs(envStrs).data());
 #endif
 
         throw SysError("executing '%1%'", drv->builder);
@@ -2221,8 +2143,7 @@ void LocalDerivationGoal::registerOutputs()
 
         /* Pass blank Sink as we are not ready to hash data at this stage. */
         NullSink blank;
-        auto references = worker.store.parseStorePathSet(
-            scanForReferences(blank, actualPath, worker.store.printStorePathSet(referenceablePaths)));
+        auto references = scanForReferences(blank, actualPath, referenceablePaths);
 
         outputReferencesIfUnregistered.insert_or_assign(
             outputName,
@@ -2236,8 +2157,8 @@ void LocalDerivationGoal::registerOutputs()
                 /* Since we'll use the already installed versions of these, we
                    can treat them as leaves and ignore any references they
                    have. */
-                [&](AlreadyRegistered _) { return StringSet {}; },
-                [&](PerhapsNeedToRegister refs) {
+                [&](const AlreadyRegistered &) { return StringSet {}; },
+                [&](const PerhapsNeedToRegister & refs) {
                     StringSet referencedOutputs;
                     /* FIXME build inverted map up front so no quadratic waste here */
                     for (auto & r : refs.refs)
@@ -2273,11 +2194,11 @@ void LocalDerivationGoal::registerOutputs()
         };
 
         std::optional<StorePathSet> referencesOpt = std::visit(overloaded {
-            [&](AlreadyRegistered skippedFinalPath) -> std::optional<StorePathSet> {
+            [&](const AlreadyRegistered & skippedFinalPath) -> std::optional<StorePathSet> {
                 finish(skippedFinalPath.path);
                 return std::nullopt;
             },
-            [&](PerhapsNeedToRegister r) -> std::optional<StorePathSet> {
+            [&](const PerhapsNeedToRegister & r) -> std::optional<StorePathSet> {
                 return r.refs;
             },
         }, outputReferencesIfUnregistered.at(outputName));
@@ -2289,7 +2210,7 @@ void LocalDerivationGoal::registerOutputs()
         auto rewriteOutput = [&]() {
             /* Apply hash rewriting if necessary. */
             if (!outputRewrites.empty()) {
-                warn("rewriting hashes in '%1%'; cross fingers", actualPath);
+                debug("rewriting hashes in '%1%'; cross fingers", actualPath);
 
                 /* FIXME: this is in-memory. */
                 StringSink sink;
@@ -2298,10 +2219,6 @@ void LocalDerivationGoal::registerOutputs()
                 sink.s = make_ref<std::string>(rewriteStrings(*sink.s, outputRewrites));
                 StringSource source(*sink.s);
                 restorePath(actualPath, source);
-
-                /* FIXME: set proper permissions in restorePath() so
-                   we don't have to do another traversal. */
-                canonicalisePathMetaData(actualPath, -1, inodesSeen);
             }
         };
 
@@ -2355,32 +2272,19 @@ void LocalDerivationGoal::registerOutputs()
             }
             auto got = caSink.finish().first;
             auto refs = rewriteRefs();
-            HashModuloSink narSink { htSHA256, oldHashPart };
-            dumpPath(actualPath, narSink);
-            auto narHashAndSize = narSink.finish();
-            ValidPathInfo newInfo0 {
-                worker.store.makeFixedOutputPath(
+
+            auto finalPath = worker.store.makeFixedOutputPath(
                     outputHash.method,
                     got,
                     outputPathName(drv->name, outputName),
                     refs.second,
-                    refs.first),
-                narHashAndSize.first,
-            };
-            newInfo0.narSize = narHashAndSize.second;
-            newInfo0.ca = FixedOutputHash {
-                .method = outputHash.method,
-                .hash = got,
-            };
-            newInfo0.references = refs.second;
-            if (refs.first)
-                newInfo0.references.insert(newInfo0.path);
-            if (scratchPath != newInfo0.path) {
+                    refs.first);
+            if (scratchPath != finalPath) {
                 // Also rewrite the output path
                 auto source = sinkToSource([&](Sink & nextSink) {
                     StringSink sink;
                     dumpPath(actualPath, sink);
-                    RewritingSink rsink2(oldHashPart, std::string(newInfo0.path.hashPart()), nextSink);
+                    RewritingSink rsink2(oldHashPart, std::string(finalPath.hashPart()), nextSink);
                     rsink2(*sink.s);
                     rsink2.flush();
                 });
@@ -2390,12 +2294,27 @@ void LocalDerivationGoal::registerOutputs()
                 movePath(tmpPath, actualPath);
             }
 
+            HashResult narHashAndSize = hashPath(htSHA256, actualPath);
+            ValidPathInfo newInfo0 {
+                finalPath,
+                narHashAndSize.first,
+            };
+
+            newInfo0.narSize = narHashAndSize.second;
+            newInfo0.ca = FixedOutputHash {
+                .method = outputHash.method,
+                .hash = got,
+            };
+            newInfo0.references = refs.second;
+            if (refs.first)
+                newInfo0.references.insert(newInfo0.path);
+
             assert(newInfo0.ca);
             return newInfo0;
         };
 
         ValidPathInfo newInfo = std::visit(overloaded {
-            [&](DerivationOutputInputAddressed output) {
+            [&](const DerivationOutputInputAddressed & output) {
                 /* input-addressed case */
                 auto requiredFinalPath = output.path;
                 /* Preemptively add rewrite rule for final hash, as that is
@@ -2414,14 +2333,14 @@ void LocalDerivationGoal::registerOutputs()
                     newInfo0.references.insert(newInfo0.path);
                 return newInfo0;
             },
-            [&](DerivationOutputCAFixed dof) {
+            [&](const DerivationOutputCAFixed & dof) {
                 auto newInfo0 = newInfoFromCA(DerivationOutputCAFloating {
                     .method = dof.hash.method,
                     .hashType = dof.hash.hash.type,
                 });
 
                 /* Check wanted hash */
-                Hash & wanted = dof.hash.hash;
+                const Hash & wanted = dof.hash.hash;
                 assert(newInfo0.ca);
                 auto got = getContentAddressHash(*newInfo0.ca);
                 if (wanted != got) {
@@ -2450,6 +2369,10 @@ void LocalDerivationGoal::registerOutputs()
             },
         }, output.output);
 
+        /* FIXME: set proper permissions in restorePath() so
+            we don't have to do another traversal. */
+        canonicalisePathMetaData(actualPath, -1, inodesSeen);
+
         /* Calculate where we'll move the output files. In the checking case we
            will leave leave them where they are, for now, rather than move to
            their usual "final destination" */
@@ -2459,6 +2382,7 @@ void LocalDerivationGoal::registerOutputs()
            floating CA derivations and hash-mismatching fixed-output
            derivations. */
         PathLocks dynamicOutputLock;
+        dynamicOutputLock.setDeletion(true);
         auto optFixedPath = output.path(worker.store, drv->name, outputName);
         if (!optFixedPath ||
             worker.store.printStorePath(*optFixedPath) != finalDestPath)
@@ -2482,6 +2406,7 @@ void LocalDerivationGoal::registerOutputs()
                 assert(newInfo.ca);
             } else {
                 auto destPath = worker.store.toRealPath(finalDestPath);
+                deletePath(destPath);
                 movePath(actualPath, destPath);
                 actualPath = destPath;
             }
@@ -2551,7 +2476,13 @@ void LocalDerivationGoal::registerOutputs()
         infos.emplace(outputName, std::move(newInfo));
     }
 
-    if (buildMode == bmCheck) return;
+    if (buildMode == bmCheck) {
+        // In case of FOD mismatches on `--check` an error must be thrown as this is also
+        // a source for non-determinism.
+        if (delayedException)
+            std::rethrow_exception(delayedException);
+        return;
+    }
 
     /* Apply output checks. */
     checkOutputs(infos);
@@ -2636,7 +2567,7 @@ void LocalDerivationGoal::registerOutputs()
        that for floating CA derivations, which otherwise couldn't be cached,
        but it's fine to do in all cases. */
 
-    if (settings.isExperimentalFeatureEnabled("ca-derivations")) {
+    if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations)) {
         for (auto& [outputName, newInfo] : infos) {
             auto thisRealisation = Realisation{
                 .id = DrvOutput{initialOutputs.at(outputName).outputHash,
diff --git a/src/libstore/build/local-derivation-goal.hh b/src/libstore/build/local-derivation-goal.hh
index d30be2351..088a57209 100644
--- a/src/libstore/build/local-derivation-goal.hh
+++ b/src/libstore/build/local-derivation-goal.hh
@@ -108,6 +108,9 @@ struct LocalDerivationGoal : public DerivationGoal
     /* Paths that were added via recursive Nix calls. */
     StorePathSet addedPaths;
 
+    /* Realisations that were added via recursive Nix calls. */
+    std::set<DrvOutput> addedDrvOutputs;
+
     /* Recursive Nix calls are only allowed to build or realize paths
        in the original input closure or added via a recursive Nix call
        (so e.g. you can't do 'nix-store -r /nix/store/<bla>' where
@@ -116,6 +119,11 @@ struct LocalDerivationGoal : public DerivationGoal
     {
         return inputPaths.count(path) || addedPaths.count(path);
     }
+    bool isAllowed(const DrvOutput & id)
+    {
+        return addedDrvOutputs.count(id);
+    }
+
     bool isAllowed(const DerivedPath & req);
 
     friend struct RestrictedStore;
diff --git a/src/libstore/build/substitution-goal.cc b/src/libstore/build/substitution-goal.cc
index e56cfadbe..29a8cfb87 100644
--- a/src/libstore/build/substitution-goal.cc
+++ b/src/libstore/build/substitution-goal.cc
@@ -204,7 +204,7 @@ void PathSubstitutionGoal::tryToRun()
             Activity act(*logger, actSubstitute, Logger::Fields{worker.store.printStorePath(storePath), sub->getUri()});
             PushActivity pact(act.id);
 
-            copyStorePath(ref<Store>(sub), ref<Store>(worker.store.shared_from_this()),
+            copyStorePath(*sub, worker.store,
                 subPath ? *subPath : storePath, repair, sub->isTrusted ? NoCheckSigs : CheckSigs);
 
             promise.set_value();
diff --git a/src/libstore/build/worker.cc b/src/libstore/build/worker.cc
index 0f2ade348..55afb5cca 100644
--- a/src/libstore/build/worker.cc
+++ b/src/libstore/build/worker.cc
@@ -9,11 +9,12 @@
 
 namespace nix {
 
-Worker::Worker(Store & store)
+Worker::Worker(Store & store, Store & evalStore)
     : act(*logger, actRealise)
     , actDerivations(*logger, actBuilds)
     , actSubstitutions(*logger, actCopyPaths)
     , store(store)
+    , evalStore(evalStore)
 {
     /* Debugging: prevent recursive workers. */
     nrLocalBuilds = 0;
@@ -238,7 +239,7 @@ void Worker::run(const Goals & _topGoals)
         }
     }
 
-    /* Call queryMissing() efficiently query substitutes. */
+    /* Call queryMissing() to efficiently query substitutes. */
     StorePathSet willBuild, willSubstitute, unknown;
     uint64_t downloadSize, narSize;
     store.queryMissing(topPaths, willBuild, willSubstitute, unknown, downloadSize, narSize);
diff --git a/src/libstore/build/worker.hh b/src/libstore/build/worker.hh
index 918de35f6..6a3b99c02 100644
--- a/src/libstore/build/worker.hh
+++ b/src/libstore/build/worker.hh
@@ -110,6 +110,7 @@ public:
     bool checkMismatch;
 
     Store & store;
+    Store & evalStore;
 
     std::unique_ptr<HookInstance> hook;
 
@@ -131,7 +132,7 @@ public:
        it answers with "decline-permanently", we don't try again. */
     bool tryBuildHook = true;
 
-    Worker(Store & store);
+    Worker(Store & store, Store & evalStore);
     ~Worker();
 
     /* Make a goal (with caching). */
diff --git a/src/libstore/ca-specific-schema.sql b/src/libstore/ca-specific-schema.sql
index 20ee046a1..08af0cc1f 100644
--- a/src/libstore/ca-specific-schema.sql
+++ b/src/libstore/ca-specific-schema.sql
@@ -3,10 +3,19 @@
 -- is enabled
 
 create table if not exists Realisations (
+    id integer primary key autoincrement not null,
     drvPath text not null,
     outputName text not null, -- symbolic output id, usually "out"
     outputPath integer not null,
     signatures text, -- space-separated list
-    primary key (drvPath, outputName),
     foreign key (outputPath) references ValidPaths(id) on delete cascade
 );
+
+create index if not exists IndexRealisations on Realisations(drvPath, outputName);
+
+create table if not exists RealisationsRefs (
+    referrer integer not null,
+    realisationReference integer,
+    foreign key (referrer) references Realisations(id) on delete cascade,
+    foreign key (realisationReference) references Realisations(id) on delete restrict
+);
diff --git a/src/libstore/content-address.cc b/src/libstore/content-address.cc
index 90a3ad1f5..cf32ccdc4 100644
--- a/src/libstore/content-address.cc
+++ b/src/libstore/content-address.cc
@@ -31,10 +31,10 @@ std::string makeFixedOutputCA(FileIngestionMethod method, const Hash & hash)
 std::string renderContentAddress(ContentAddress ca)
 {
     return std::visit(overloaded {
-        [](TextHash th) {
+        [](TextHash & th) {
             return "text:" + th.hash.to_string(Base32, true);
         },
-        [](FixedOutputHash fsh) {
+        [](FixedOutputHash & fsh) {
             return makeFixedOutputCA(fsh.method, fsh.hash);
         }
     }, ca);
@@ -43,10 +43,10 @@ std::string renderContentAddress(ContentAddress ca)
 std::string renderContentAddressMethod(ContentAddressMethod cam)
 {
     return std::visit(overloaded {
-        [](TextHashMethod &th) {
+        [](TextHashMethod & th) {
             return std::string{"text:"} + printHashType(htSHA256);
         },
-        [](FixedOutputHashMethod &fshm) {
+        [](FixedOutputHashMethod & fshm) {
             return "fixed:" + makeFileIngestionPrefix(fshm.fileIngestionMethod) + printHashType(fshm.hashType);
         }
     }, cam);
@@ -104,12 +104,12 @@ ContentAddress parseContentAddress(std::string_view rawCa) {
 
     return std::visit(
         overloaded {
-            [&](TextHashMethod thm) {
+            [&](TextHashMethod & thm) {
                 return ContentAddress(TextHash {
                     .hash = Hash::parseNonSRIUnprefixed(rest, htSHA256)
                 });
             },
-            [&](FixedOutputHashMethod fohMethod) {
+            [&](FixedOutputHashMethod & fohMethod) {
                 return ContentAddress(FixedOutputHash {
                     .method = fohMethod.fileIngestionMethod,
                     .hash = Hash::parseNonSRIUnprefixed(rest, std::move(fohMethod.hashType)),
@@ -120,8 +120,10 @@ ContentAddress parseContentAddress(std::string_view rawCa) {
 
 ContentAddressMethod parseContentAddressMethod(std::string_view caMethod)
 {
-    std::string_view asPrefix {std::string{caMethod} + ":"};
-    return parseContentAddressMethodPrefix(asPrefix);
+    std::string asPrefix = std::string{caMethod} + ":";
+    // parseContentAddressMethodPrefix takes its argument by reference
+    std::string_view asPrefixView = asPrefix;
+    return parseContentAddressMethodPrefix(asPrefixView);
 }
 
 std::optional<ContentAddress> parseContentAddressOpt(std::string_view rawCaOpt)
@@ -137,10 +139,10 @@ std::string renderContentAddress(std::optional<ContentAddress> ca)
 Hash getContentAddressHash(const ContentAddress & ca)
 {
     return std::visit(overloaded {
-        [](TextHash th) {
+        [](const TextHash & th) {
             return th.hash;
         },
-        [](FixedOutputHash fsh) {
+        [](const FixedOutputHash & fsh) {
             return fsh.hash;
         }
     }, ca);
diff --git a/src/libstore/daemon.cc b/src/libstore/daemon.cc
index 0be9d2c54..2eb566080 100644
--- a/src/libstore/daemon.cc
+++ b/src/libstore/daemon.cc
@@ -227,8 +227,15 @@ struct ClientSettings
             try {
                 if (name == "ssh-auth-sock") // obsolete
                     ;
+                else if (name == settings.experimentalFeatures.name) {
+                    // We don’t want to forward the experimental features to
+                    // the daemon, as that could cause some pretty weird stuff
+                    if (parseFeatures(tokenizeString<StringSet>(value)) != settings.experimentalFeatures.get())
+                        debug("Ignoring the client-specified experimental features");
+                }
                 else if (trusted
                     || name == settings.buildTimeout.name
+                    || name == settings.buildRepeat.name
                     || name == "connect-timeout"
                     || (name == "builders" && value == ""))
                     settings.set(name, value);
@@ -243,27 +250,10 @@ struct ClientSettings
     }
 };
 
-static void writeValidPathInfo(
-    ref<Store> store,
-    unsigned int clientVersion,
-    Sink & to,
-    std::shared_ptr<const ValidPathInfo> info)
-{
-    to << (info->deriver ? store->printStorePath(*info->deriver) : "")
-       << info->narHash.to_string(Base16, false);
-    worker_proto::write(*store, to, info->references);
-    to << info->registrationTime << info->narSize;
-    if (GET_PROTOCOL_MINOR(clientVersion) >= 16) {
-        to << info->ultimate
-           << info->sigs
-           << renderContentAddress(info->ca);
-    }
-}
-
 static std::vector<DerivedPath> readDerivedPaths(Store & store, unsigned int clientVersion, Source & from)
 {
     std::vector<DerivedPath> reqs;
-    if (GET_PROTOCOL_MINOR(clientVersion) >= 29) {
+    if (GET_PROTOCOL_MINOR(clientVersion) >= 30) {
         reqs = worker_proto::read(store, from, Phantom<std::vector<DerivedPath>> {});
     } else {
         for (auto & s : readStrings<Strings>(from))
@@ -406,25 +396,21 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
                 FramedSource source(from);
                 // TODO this is essentially RemoteStore::addCAToStore. Move it up to Store.
                 return std::visit(overloaded {
-                    [&](TextHashMethod &_) {
+                    [&](TextHashMethod &) {
                         // We could stream this by changing Store
                         std::string contents = source.drain();
                         auto path = store->addTextToStore(name, contents, refs, repair);
                         return store->queryPathInfo(path);
                     },
-                    [&](FixedOutputHashMethod &fohm) {
-                        if (!refs.empty())
-                            throw UnimplementedError("cannot yet have refs with flat or nar-hashed data");
-                        auto path = store->addToStoreFromDump(source, name, fohm.fileIngestionMethod, fohm.hashType, repair);
+                    [&](FixedOutputHashMethod & fohm) {
+                        auto path = store->addToStoreFromDump(source, name, fohm.fileIngestionMethod, fohm.hashType, repair, refs);
                         return store->queryPathInfo(path);
                     },
                 }, contentAddressMethod);
             }();
             logger->stopWork();
 
-            to << store->printStorePath(pathInfo->path);
-            writeValidPathInfo(store, clientVersion, to, pathInfo);
-
+            pathInfo->write(to, *store, GET_PROTOCOL_MINOR(clientVersion));
         } else {
             HashType hashAlgo;
             std::string baseName;
@@ -471,6 +457,21 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         break;
     }
 
+    case wopAddMultipleToStore: {
+        bool repair, dontCheckSigs;
+        from >> repair >> dontCheckSigs;
+        if (!trusted && dontCheckSigs)
+            dontCheckSigs = false;
+
+        logger->startWork();
+        FramedSource source(from);
+        store->addMultipleToStore(source,
+            RepairFlag{repair},
+            dontCheckSigs ? NoCheckSigs : CheckSigs);
+        logger->stopWork();
+        break;
+    }
+
     case wopAddTextToStore: {
         string suffix = readString(from);
         string s = readString(from);
@@ -622,9 +623,9 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         break;
     }
 
+    // Obsolete.
     case wopSyncWithGC: {
         logger->startWork();
-        store->syncWithGC();
         logger->stopWork();
         to << 1;
         break;
@@ -770,7 +771,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         if (info) {
             if (GET_PROTOCOL_MINOR(clientVersion) >= 17)
                 to << 1;
-            writeValidPathInfo(store, clientVersion, to, info);
+            info->write(to, *store, GET_PROTOCOL_MINOR(clientVersion), false);
         } else {
             assert(GET_PROTOCOL_MINOR(clientVersion) >= 17);
             to << 0;
@@ -885,10 +886,15 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
 
     case wopRegisterDrvOutput: {
         logger->startWork();
-        auto outputId = DrvOutput::parse(readString(from));
-        auto outputPath = StorePath(readString(from));
-        store->registerDrvOutput(Realisation{
-            .id = outputId, .outPath = outputPath});
+        if (GET_PROTOCOL_MINOR(clientVersion) < 31) {
+            auto outputId = DrvOutput::parse(readString(from));
+            auto outputPath = StorePath(readString(from));
+            store->registerDrvOutput(Realisation{
+                .id = outputId, .outPath = outputPath});
+        } else {
+            auto realisation = worker_proto::read(*store, from, Phantom<Realisation>());
+            store->registerDrvOutput(realisation);
+        }
         logger->stopWork();
         break;
     }
@@ -898,9 +904,15 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         auto outputId = DrvOutput::parse(readString(from));
         auto info = store->queryRealisation(outputId);
         logger->stopWork();
-        std::set<StorePath> outPaths;
-        if (info) outPaths.insert(info->outPath);
-        worker_proto::write(*store, to, outPaths);
+        if (GET_PROTOCOL_MINOR(clientVersion) < 31) {
+            std::set<StorePath> outPaths;
+            if (info) outPaths.insert(info->outPath);
+            worker_proto::write(*store, to, outPaths);
+        } else {
+            std::set<Realisation> realisations;
+            if (info) realisations.insert(*info);
+            worker_proto::write(*store, to, realisations);
+        }
         break;
     }
 
diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index f6defd98f..b926bb711 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -10,18 +10,18 @@ namespace nix {
 std::optional<StorePath> DerivationOutput::path(const Store & store, std::string_view drvName, std::string_view outputName) const
 {
     return std::visit(overloaded {
-        [](DerivationOutputInputAddressed doi) -> std::optional<StorePath> {
+        [](const DerivationOutputInputAddressed & doi) -> std::optional<StorePath> {
             return { doi.path };
         },
-        [&](DerivationOutputCAFixed dof) -> std::optional<StorePath> {
+        [&](const DerivationOutputCAFixed & dof) -> std::optional<StorePath> {
             return {
                 dof.path(store, drvName, outputName)
             };
         },
-        [](DerivationOutputCAFloating dof) -> std::optional<StorePath> {
+        [](const DerivationOutputCAFloating & dof) -> std::optional<StorePath> {
             return std::nullopt;
         },
-        [](DerivationOutputDeferred) -> std::optional<StorePath> {
+        [](const DerivationOutputDeferred &) -> std::optional<StorePath> {
             return std::nullopt;
         },
     }, output);
@@ -187,7 +187,7 @@ static DerivationOutput parseDerivationOutput(const Store & store,
                 },
             };
         } else {
-            settings.requireExperimentalFeature("ca-derivations");
+            settings.requireExperimentalFeature(Xp::CaDerivations);
             assert(pathS == "");
             return DerivationOutput {
                 .output = DerivationOutputCAFloating {
@@ -332,22 +332,22 @@ string Derivation::unparse(const Store & store, bool maskOutputs,
         if (first) first = false; else s += ',';
         s += '('; printUnquotedString(s, i.first);
         std::visit(overloaded {
-            [&](DerivationOutputInputAddressed doi) {
+            [&](const DerivationOutputInputAddressed & doi) {
                 s += ','; printUnquotedString(s, maskOutputs ? "" : store.printStorePath(doi.path));
                 s += ','; printUnquotedString(s, "");
                 s += ','; printUnquotedString(s, "");
             },
-            [&](DerivationOutputCAFixed dof) {
+            [&](const DerivationOutputCAFixed & dof) {
                 s += ','; printUnquotedString(s, maskOutputs ? "" : store.printStorePath(dof.path(store, name, i.first)));
                 s += ','; printUnquotedString(s, dof.hash.printMethodAlgo());
                 s += ','; printUnquotedString(s, dof.hash.hash.to_string(Base16, false));
             },
-            [&](DerivationOutputCAFloating dof) {
+            [&](const DerivationOutputCAFloating & dof) {
                 s += ','; printUnquotedString(s, "");
                 s += ','; printUnquotedString(s, makeFileIngestionPrefix(dof.method) + printHashType(dof.hashType));
                 s += ','; printUnquotedString(s, "");
             },
-            [&](DerivationOutputDeferred) {
+            [&](const DerivationOutputDeferred &) {
                 s += ','; printUnquotedString(s, "");
                 s += ','; printUnquotedString(s, "");
                 s += ','; printUnquotedString(s, "");
@@ -420,13 +420,13 @@ DerivationType BasicDerivation::type() const
     std::optional<HashType> floatingHashType;
     for (auto & i : outputs) {
         std::visit(overloaded {
-            [&](DerivationOutputInputAddressed _) {
+            [&](const DerivationOutputInputAddressed &) {
                inputAddressedOutputs.insert(i.first);
             },
-            [&](DerivationOutputCAFixed _) {
+            [&](const DerivationOutputCAFixed &) {
                 fixedCAOutputs.insert(i.first);
             },
-            [&](DerivationOutputCAFloating dof) {
+            [&](const DerivationOutputCAFloating & dof) {
                 floatingCAOutputs.insert(i.first);
                 if (!floatingHashType) {
                     floatingHashType = dof.hashType;
@@ -435,7 +435,7 @@ DerivationType BasicDerivation::type() const
                         throw Error("All floating outputs must use the same hash type");
                 }
             },
-            [&](DerivationOutputDeferred _) {
+            [&](const DerivationOutputDeferred &) {
                deferredIAOutputs.insert(i.first);
             },
         }, i.second.output);
@@ -538,15 +538,15 @@ DrvHashModulo hashDerivationModulo(Store & store, const Derivation & drv, bool m
         const auto & res = pathDerivationModulo(store, i.first);
         std::visit(overloaded {
             // Regular non-CA derivation, replace derivation
-            [&](Hash drvHash) {
+            [&](const Hash & drvHash) {
                 inputs2.insert_or_assign(drvHash.to_string(Base16, false), i.second);
             },
-            [&](DeferredHash deferredHash) {
+            [&](const DeferredHash & deferredHash) {
                 isDeferred = true;
                 inputs2.insert_or_assign(deferredHash.hash.to_string(Base16, false), i.second);
             },
             // CA derivation's output hashes
-            [&](CaOutputHashes outputHashes) {
+            [&](const CaOutputHashes & outputHashes) {
                 std::set<std::string> justOut = { "out" };
                 for (auto & output : i.second) {
                     /* Put each one in with a single "out" output.. */
@@ -568,21 +568,21 @@ DrvHashModulo hashDerivationModulo(Store & store, const Derivation & drv, bool m
 }
 
 
-std::map<std::string, Hash> staticOutputHashes(Store& store, const Derivation& drv)
+std::map<std::string, Hash> staticOutputHashes(Store & store, const Derivation & drv)
 {
     std::map<std::string, Hash> res;
     std::visit(overloaded {
-        [&](Hash drvHash) {
+        [&](const Hash & drvHash) {
             for (auto & outputName : drv.outputNames()) {
                 res.insert({outputName, drvHash});
             }
         },
-        [&](DeferredHash deferredHash) {
+        [&](const DeferredHash & deferredHash) {
             for (auto & outputName : drv.outputNames()) {
                 res.insert({outputName, deferredHash.hash});
             }
         },
-        [&](CaOutputHashes outputHashes) {
+        [&](const CaOutputHashes & outputHashes) {
             res = outputHashes;
         },
     }, hashDerivationModulo(store, drv, true));
@@ -666,22 +666,22 @@ void writeDerivation(Sink & out, const Store & store, const BasicDerivation & dr
     for (auto & i : drv.outputs) {
         out << i.first;
         std::visit(overloaded {
-            [&](DerivationOutputInputAddressed doi) {
+            [&](const DerivationOutputInputAddressed & doi) {
                 out << store.printStorePath(doi.path)
                     << ""
                     << "";
             },
-            [&](DerivationOutputCAFixed dof) {
+            [&](const DerivationOutputCAFixed & dof) {
                 out << store.printStorePath(dof.path(store, drv.name, i.first))
                     << dof.hash.printMethodAlgo()
                     << dof.hash.hash.to_string(Base16, false);
             },
-            [&](DerivationOutputCAFloating dof) {
+            [&](const DerivationOutputCAFloating & dof) {
                 out << ""
                     << (makeFileIngestionPrefix(dof.method) + printHashType(dof.hashType))
                     << "";
             },
-            [&](DerivationOutputDeferred) {
+            [&](const DerivationOutputDeferred &) {
                 out << ""
                     << ""
                     << "";
diff --git a/src/libstore/derivations.hh b/src/libstore/derivations.hh
index 2df440536..b1cb68194 100644
--- a/src/libstore/derivations.hh
+++ b/src/libstore/derivations.hh
@@ -138,8 +138,8 @@ struct Derivation : BasicDerivation
 
     /* Return the underlying basic derivation but with these changes:
 
-	   1. Input drvs are emptied, but the outputs of them that were used are
-	      added directly to input sources.
+       1. Input drvs are emptied, but the outputs of them that were used are
+          added directly to input sources.
 
        2. Input placeholders are replaced with realized input store paths. */
     std::optional<BasicDerivation> tryResolve(Store & store);
diff --git a/src/libstore/derived-path.cc b/src/libstore/derived-path.cc
index 13833c58e..3d188e981 100644
--- a/src/libstore/derived-path.cc
+++ b/src/libstore/derived-path.cc
@@ -11,18 +11,33 @@ nlohmann::json DerivedPath::Opaque::toJSON(ref<Store> store) const {
     return res;
 }
 
-nlohmann::json DerivedPathWithHints::Built::toJSON(ref<Store> store) const {
+nlohmann::json BuiltPath::Built::toJSON(ref<Store> store) const {
     nlohmann::json res;
     res["drvPath"] = store->printStorePath(drvPath);
     for (const auto& [output, path] : outputs) {
-        res["outputs"][output] = path ? store->printStorePath(*path) : "";
+        res["outputs"][output] = store->printStorePath(path);
     }
     return res;
 }
 
-nlohmann::json derivedPathsWithHintsToJSON(const DerivedPathsWithHints & buildables, ref<Store> store) {
+StorePathSet BuiltPath::outPaths() const
+{
+    return std::visit(
+        overloaded{
+            [](const BuiltPath::Opaque & p) { return StorePathSet{p.path}; },
+            [](const BuiltPath::Built & b) {
+                StorePathSet res;
+                for (auto & [_, path] : b.outputs)
+                    res.insert(path);
+                return res;
+            },
+        }, raw()
+    );
+}
+
+nlohmann::json derivedPathsWithHintsToJSON(const BuiltPaths & buildables, ref<Store> store) {
     auto res = nlohmann::json::array();
-    for (const DerivedPathWithHints & buildable : buildables) {
+    for (const BuiltPath & buildable : buildables) {
         std::visit([&res, store](const auto & buildable) {
             res.push_back(buildable.toJSON(store));
         }, buildable.raw());
@@ -62,7 +77,7 @@ DerivedPath::Built DerivedPath::Built::parse(const Store & store, std::string_vi
     auto outputsS = s.substr(n + 1);
     std::set<string> outputs;
     if (outputsS != "*")
-        outputs = tokenizeString<std::set<string>>(outputsS);
+        outputs = tokenizeString<std::set<string>>(outputsS, ",");
     return {drvPath, outputs};
 }
 
@@ -74,4 +89,30 @@ DerivedPath DerivedPath::parse(const Store & store, std::string_view s)
         : (DerivedPath) DerivedPath::Built::parse(store, s);
 }
 
+RealisedPath::Set BuiltPath::toRealisedPaths(Store & store) const
+{
+    RealisedPath::Set res;
+    std::visit(
+        overloaded{
+            [&](const BuiltPath::Opaque & p) { res.insert(p.path); },
+            [&](const BuiltPath::Built & p) {
+                auto drvHashes =
+                    staticOutputHashes(store, store.readDerivation(p.drvPath));
+                for (auto& [outputName, outputPath] : p.outputs) {
+                    if (settings.isExperimentalFeatureEnabled(
+                                Xp::CaDerivations)) {
+                        auto thisRealisation = store.queryRealisation(
+                            DrvOutput{drvHashes.at(outputName), outputName});
+                        assert(thisRealisation);  // We’ve built it, so we must h
+                                                  // ve the realisation
+                        res.insert(*thisRealisation);
+                    } else {
+                        res.insert(outputPath);
+                    }
+                }
+            },
+        },
+        raw());
+    return res;
+}
 }
diff --git a/src/libstore/derived-path.hh b/src/libstore/derived-path.hh
index 7a2fe59de..9d6ace069 100644
--- a/src/libstore/derived-path.hh
+++ b/src/libstore/derived-path.hh
@@ -2,6 +2,7 @@
 
 #include "util.hh"
 #include "path.hh"
+#include "realisation.hh"
 
 #include <optional>
 
@@ -79,51 +80,44 @@ struct DerivedPath : _DerivedPathRaw {
 /**
  * A built derived path with hints in the form of optional concrete output paths.
  *
- * See 'DerivedPathWithHints' for more an explanation.
+ * See 'BuiltPath' for more an explanation.
  */
-struct DerivedPathWithHintsBuilt {
+struct BuiltPathBuilt {
     StorePath drvPath;
-    std::map<std::string, std::optional<StorePath>> outputs;
+    std::map<std::string, StorePath> outputs;
 
     nlohmann::json toJSON(ref<Store> store) const;
-    static DerivedPathWithHintsBuilt parse(const Store & store, std::string_view);
+    static BuiltPathBuilt parse(const Store & store, std::string_view);
 };
 
-using _DerivedPathWithHintsRaw = std::variant<
+using _BuiltPathRaw = std::variant<
     DerivedPath::Opaque,
-    DerivedPathWithHintsBuilt
+    BuiltPathBuilt
 >;
 
 /**
- * A derived path with hints in the form of optional concrete output paths in the built case.
- *
- * This type is currently just used by the CLI. The paths are filled in
- * during evaluation for derivations that know what paths they will
- * produce in advanced, i.e. input-addressed or fixed-output content
- * addressed derivations.
- *
- * That isn't very good, because it puts floating content-addressed
- * derivations "at a disadvantage". It would be better to never rely on
- * the output path of unbuilt derivations, and exclusively use the
- * realizations types to work with built derivations' concrete output
- * paths.
+ * A built path. Similar to a `DerivedPath`, but enriched with the corresponding
+ * output path(s).
  */
-// FIXME Stop using and delete this, or if that is not possible move out of libstore to libcmd.
-struct DerivedPathWithHints : _DerivedPathWithHintsRaw {
-    using Raw = _DerivedPathWithHintsRaw;
+struct BuiltPath : _BuiltPathRaw {
+    using Raw = _BuiltPathRaw;
     using Raw::Raw;
 
     using Opaque = DerivedPathOpaque;
-    using Built = DerivedPathWithHintsBuilt;
+    using Built = BuiltPathBuilt;
 
     inline const Raw & raw() const {
         return static_cast<const Raw &>(*this);
     }
 
+    StorePathSet outPaths() const;
+    RealisedPath::Set toRealisedPaths(Store & store) const;
+
 };
 
-typedef std::vector<DerivedPathWithHints> DerivedPathsWithHints;
+typedef std::vector<DerivedPath> DerivedPaths;
+typedef std::vector<BuiltPath> BuiltPaths;
 
-nlohmann::json derivedPathsWithHintsToJSON(const DerivedPathsWithHints & buildables, ref<Store> store);
+nlohmann::json derivedPathsWithHintsToJSON(const BuiltPaths & buildables, ref<Store> store);
 
 }
diff --git a/src/libstore/dummy-store.cc b/src/libstore/dummy-store.cc
index 8f26af685..62dc21c59 100644
--- a/src/libstore/dummy-store.cc
+++ b/src/libstore/dummy-store.cc
@@ -43,11 +43,6 @@ struct DummyStore : public virtual DummyStoreConfig, public virtual Store
         RepairFlag repair, CheckSigsFlag checkSigs) override
     { unsupported("addToStore"); }
 
-    StorePath addToStore(const string & name, const Path & srcPath,
-        FileIngestionMethod method, HashType hashAlgo,
-        PathFilter & filter, RepairFlag repair) override
-    { unsupported("addToStore"); }
-
     StorePath addTextToStore(const string & name, const string & s,
         const StorePathSet & references, RepairFlag repair) override
     { unsupported("addTextToStore"); }
@@ -55,8 +50,9 @@ struct DummyStore : public virtual DummyStoreConfig, public virtual Store
     void narFromPath(const StorePath & path, Sink & sink) override
     { unsupported("narFromPath"); }
 
-    std::optional<const Realisation> queryRealisation(const DrvOutput&) override
-    { unsupported("queryRealisation"); }
+    void queryRealisationUncached(const DrvOutput &,
+        Callback<std::shared_ptr<const Realisation>> callback) noexcept override
+    { callback(nullptr); }
 };
 
 static RegisterStoreImplementation<DummyStore, DummyStoreConfig> regDummyStore;
diff --git a/src/libstore/filetransfer.cc b/src/libstore/filetransfer.cc
index 514ab3bf9..4621a8217 100644
--- a/src/libstore/filetransfer.cc
+++ b/src/libstore/filetransfer.cc
@@ -7,7 +7,7 @@
 #include "finally.hh"
 #include "callback.hh"
 
-#ifdef ENABLE_S3
+#if ENABLE_S3
 #include <aws/core/client/ClientConfiguration.h>
 #endif
 
@@ -544,6 +544,14 @@ struct curlFileTransfer : public FileTransfer
             stopWorkerThread();
         });
 
+#ifdef __linux__
+        /* Cause this thread to not share any FS attributes with the main thread,
+           because this causes setns() in restoreMountNamespace() to fail.
+           Ideally, this would happen in the std::thread() constructor. */
+        if (unshare(CLONE_FS) != 0)
+            throw SysError("unsharing filesystem state in download thread");
+#endif
+
         std::map<CURL *, std::shared_ptr<TransferItem>> items;
 
         bool quit = false;
@@ -665,7 +673,7 @@ struct curlFileTransfer : public FileTransfer
         writeFull(wakeupPipe.writeSide.get(), " ");
     }
 
-#ifdef ENABLE_S3
+#if ENABLE_S3
     std::tuple<std::string, std::string, Store::Params> parseS3Uri(std::string uri)
     {
         auto [path, params] = splitUriAndParams(uri);
@@ -688,7 +696,7 @@ struct curlFileTransfer : public FileTransfer
         if (hasPrefix(request.uri, "s3://")) {
             // FIXME: do this on a worker thread
             try {
-#ifdef ENABLE_S3
+#if ENABLE_S3
                 auto [bucketName, key, params] = parseS3Uri(request.uri);
 
                 std::string profile = get(params, "profile").value_or("");
@@ -716,15 +724,24 @@ struct curlFileTransfer : public FileTransfer
     }
 };
 
+ref<curlFileTransfer> makeCurlFileTransfer()
+{
+    return make_ref<curlFileTransfer>();
+}
+
 ref<FileTransfer> getFileTransfer()
 {
-    static ref<FileTransfer> fileTransfer = makeFileTransfer();
+    static ref<curlFileTransfer> fileTransfer = makeCurlFileTransfer();
+
+    if (fileTransfer->state_.lock()->quit)
+        fileTransfer = makeCurlFileTransfer();
+
     return fileTransfer;
 }
 
 ref<FileTransfer> makeFileTransfer()
 {
-    return make_ref<curlFileTransfer>();
+    return makeCurlFileTransfer();
 }
 
 std::future<FileTransferResult> FileTransfer::enqueueFileTransfer(const FileTransferRequest & request)
diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index bc692ca42..7a414da6b 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -10,48 +10,22 @@
 #include <regex>
 #include <random>
 
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <sys/statvfs.h>
+#include <climits>
 #include <errno.h>
 #include <fcntl.h>
+#include <poll.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/statvfs.h>
+#include <sys/types.h>
+#include <sys/un.h>
 #include <unistd.h>
-#include <climits>
 
 namespace nix {
 
 
-static string gcLockName = "gc.lock";
-static string gcRootsDir = "gcroots";
-
-
-/* Acquire the global GC lock.  This is used to prevent new Nix
-   processes from starting after the temporary root files have been
-   read.  To be precise: when they try to create a new temporary root
-   file, they will block until the garbage collector has finished /
-   yielded the GC lock. */
-AutoCloseFD LocalStore::openGCLock(LockType lockType)
-{
-    Path fnGCLock = (format("%1%/%2%")
-        % stateDir % gcLockName).str();
-
-    debug(format("acquiring global GC lock '%1%'") % fnGCLock);
-
-    AutoCloseFD fdGCLock = open(fnGCLock.c_str(), O_RDWR | O_CREAT | O_CLOEXEC, 0600);
-    if (!fdGCLock)
-        throw SysError("opening global GC lock '%1%'", fnGCLock);
-
-    if (!lockFile(fdGCLock.get(), lockType, false)) {
-        printInfo("waiting for the big garbage collector lock...");
-        lockFile(fdGCLock.get(), lockType, true);
-    }
-
-    /* !!! Restrict read permission on the GC root.  Otherwise any
-       process that can open the file for reading can DoS the
-       collector. */
-
-    return fdGCLock;
-}
+static std::string gcSocketPath = "/gc-socket/socket";
+static std::string gcRootsDir = "gcroots";
 
 
 static void makeSymlink(const Path & link, const Path & target)
@@ -71,12 +45,6 @@ static void makeSymlink(const Path & link, const Path & target)
 }
 
 
-void LocalStore::syncWithGC()
-{
-    AutoCloseFD fdGCLock = openGCLock(ltRead);
-}
-
-
 void LocalStore::addIndirectRoot(const Path & path)
 {
     string hash = hashString(htSHA1, path).to_string(Base32, false);
@@ -95,6 +63,12 @@ Path LocalFSStore::addPermRoot(const StorePath & storePath, const Path & _gcRoot
                 "creating a garbage collector root (%1%) in the Nix store is forbidden "
                 "(are you running nix-build inside the store?)", gcRoot);
 
+    /* Register this root with the garbage collector, if it's
+       running. This should be superfluous since the caller should
+       have registered this root yet, but let's be on the safe
+       side. */
+    addTempRoot(storePath);
+
     /* Don't clobber the link if it already exists and doesn't
        point to the Nix store. */
     if (pathExists(gcRoot) && (!isLink(gcRoot) || !isInStore(readLink(gcRoot))))
@@ -102,11 +76,6 @@ Path LocalFSStore::addPermRoot(const StorePath & storePath, const Path & _gcRoot
     makeSymlink(gcRoot, printStorePath(storePath));
     addIndirectRoot(gcRoot);
 
-    /* Grab the global GC root, causing us to block while a GC is in
-       progress.  This prevents the set of permanent roots from
-       increasing while a GC is in progress. */
-    syncWithGC();
-
     return gcRoot;
 }
 
@@ -119,8 +88,6 @@ void LocalStore::addTempRoot(const StorePath & path)
     if (!state->fdTempRoots) {
 
         while (1) {
-            AutoCloseFD fdGCLock = openGCLock(ltRead);
-
             if (pathExists(fnTempRoots))
                 /* It *must* be stale, since there can be no two
                    processes with the same pid. */
@@ -128,10 +95,8 @@ void LocalStore::addTempRoot(const StorePath & path)
 
             state->fdTempRoots = openLockFile(fnTempRoots, true);
 
-            fdGCLock = -1;
-
-            debug(format("acquiring read lock on '%1%'") % fnTempRoots);
-            lockFile(state->fdTempRoots.get(), ltRead, true);
+            debug("acquiring write lock on '%s'", fnTempRoots);
+            lockFile(state->fdTempRoots.get(), ltWrite, true);
 
             /* Check whether the garbage collector didn't get in our
                way. */
@@ -147,24 +112,55 @@ void LocalStore::addTempRoot(const StorePath & path)
 
     }
 
-    /* Upgrade the lock to a write lock.  This will cause us to block
-       if the garbage collector is holding our lock. */
-    debug(format("acquiring write lock on '%1%'") % fnTempRoots);
-    lockFile(state->fdTempRoots.get(), ltWrite, true);
+    if (!state->fdGCLock)
+        state->fdGCLock = openGCLock();
+
+ restart:
+    FdLock gcLock(state->fdGCLock.get(), ltRead, false, "");
+
+    if (!gcLock.acquired) {
+        /* We couldn't get a shared global GC lock, so the garbage
+           collector is running. So we have to connect to the garbage
+           collector and inform it about our root. */
+        if (!state->fdRootsSocket) {
+            auto socketPath = stateDir.get() + gcSocketPath;
+            debug("connecting to '%s'", socketPath);
+            state->fdRootsSocket = createUnixDomainSocket();
+            nix::connect(state->fdRootsSocket.get(), socketPath);
+        }
+
+        try {
+            debug("sending GC root '%s'", printStorePath(path));
+            writeFull(state->fdRootsSocket.get(), printStorePath(path) + "\n", false);
+            char c;
+            readFull(state->fdRootsSocket.get(), &c, 1);
+            assert(c == '1');
+            debug("got ack for GC root '%s'", printStorePath(path));
+        } catch (SysError & e) {
+            /* The garbage collector may have exited, so we need to
+               restart. */
+            if (e.errNo == EPIPE) {
+                debug("GC socket disconnected");
+                state->fdRootsSocket.close();
+                goto restart;
+            }
+        } catch (EndOfFile & e) {
+            debug("GC socket disconnected");
+            state->fdRootsSocket.close();
+            goto restart;
+        }
+    }
 
+    /* Append the store path to the temporary roots file. */
     string s = printStorePath(path) + '\0';
     writeFull(state->fdTempRoots.get(), s);
-
-    /* Downgrade to a read lock. */
-    debug(format("downgrading to read lock on '%1%'") % fnTempRoots);
-    lockFile(state->fdTempRoots.get(), ltRead, true);
 }
 
 
 static std::string censored = "{censored}";
 
 
-void LocalStore::findTempRoots(FDs & fds, Roots & tempRoots, bool censor)
+void LocalStore::findTempRoots(Roots & tempRoots, bool censor)
 {
     /* Read the `temproots' directory for per-process temporary root
        files. */
@@ -179,35 +175,25 @@ void LocalStore::findTempRoots(FDs & fds, Roots & tempRoots, bool censor)
         pid_t pid = std::stoi(i.name);
 
         debug(format("reading temporary root file '%1%'") % path);
-        FDPtr fd(new AutoCloseFD(open(path.c_str(), O_CLOEXEC | O_RDWR, 0666)));
-        if (!*fd) {
+        AutoCloseFD fd(open(path.c_str(), O_CLOEXEC | O_RDWR, 0666));
+        if (!fd) {
             /* It's okay if the file has disappeared. */
             if (errno == ENOENT) continue;
             throw SysError("opening temporary roots file '%1%'", path);
         }
 
-        /* This should work, but doesn't, for some reason. */
-        //FDPtr fd(new AutoCloseFD(openLockFile(path, false)));
-        //if (*fd == -1) continue;
-
         /* Try to acquire a write lock without blocking.  This can
            only succeed if the owning process has died.  In that case
            we don't care about its temporary roots. */
-        if (lockFile(fd->get(), ltWrite, false)) {
+        if (lockFile(fd.get(), ltWrite, false)) {
             printInfo("removing stale temporary roots file '%1%'", path);
             unlink(path.c_str());
-            writeFull(fd->get(), "d");
+            writeFull(fd.get(), "d");
             continue;
         }
 
-        /* Acquire a read lock.  This will prevent the owning process
-           from upgrading to a write lock, therefore it will block in
-           addTempRoot(). */
-        debug(format("waiting for read lock on '%1%'") % path);
-        lockFile(fd->get(), ltRead, true);
-
         /* Read the entire file. */
-        string contents = readFile(fd->get());
+        string contents = readFile(fd.get());
 
         /* Extract the roots. */
         string::size_type pos = 0, end;
@@ -218,8 +204,6 @@ void LocalStore::findTempRoots(FDs & fds, Roots & tempRoots, bool censor)
             tempRoots[parseStorePath(root)].emplace(censor ? censored : fmt("{temp:%d}", pid));
             pos = end + 1;
         }
-
-        fds.push_back(fd); /* keep open */
     }
 }
 
@@ -304,8 +288,7 @@ Roots LocalStore::findRoots(bool censor)
     Roots roots;
     findRootsNoTemp(roots, censor);
 
-    FDs fds;
-    findTempRoots(fds, roots, censor);
+    findTempRoots(roots, censor);
 
     return roots;
 }
@@ -341,6 +324,7 @@ static string quoteRegexChars(const string & raw)
     return std::regex_replace(raw, specialRegex, R"(\$&)");
 }
 
+#if __linux__
 static void readFileRoots(const char * path, UncheckedRoots & roots)
 {
     try {
@@ -350,6 +334,7 @@ static void readFileRoots(const char * path, UncheckedRoots & roots)
             throw;
     }
 }
+#endif
 
 void LocalStore::findRuntimeRoots(Roots & roots, bool censor)
 {
@@ -431,7 +416,7 @@ void LocalStore::findRuntimeRoots(Roots & roots, bool censor)
     }
 #endif
 
-#if defined(__linux__)
+#if __linux__
     readFileRoots("/proc/sys/kernel/modprobe", unchecked);
     readFileRoots("/proc/sys/kernel/fbsplash", unchecked);
     readFileRoots("/proc/sys/kernel/poweroff_cmd", unchecked);
@@ -455,391 +440,397 @@ void LocalStore::findRuntimeRoots(Roots & roots, bool censor)
 struct GCLimitReached { };
 
 
-struct LocalStore::GCState
-{
-    const GCOptions & options;
-    GCResults & results;
-    StorePathSet roots;
-    StorePathSet tempRoots;
-    StorePathSet dead;
-    StorePathSet alive;
-    bool gcKeepOutputs;
-    bool gcKeepDerivations;
-    uint64_t bytesInvalidated;
-    bool moveToTrash = true;
-    bool shouldDelete;
-    GCState(const GCOptions & options, GCResults & results)
-        : options(options), results(results), bytesInvalidated(0) { }
-};
-
-
-bool LocalStore::isActiveTempFile(const GCState & state,
-    const Path & path, const string & suffix)
+void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
 {
-    return hasSuffix(path, suffix)
-        && state.tempRoots.count(parseStorePath(string(path, 0, path.size() - suffix.size())));
-}
+    bool shouldDelete = options.action == GCOptions::gcDeleteDead || options.action == GCOptions::gcDeleteSpecific;
+    bool gcKeepOutputs = settings.gcKeepOutputs;
+    bool gcKeepDerivations = settings.gcKeepDerivations;
 
+    StorePathSet roots, dead, alive;
 
-void LocalStore::deleteGarbage(GCState & state, const Path & path)
-{
-    uint64_t bytesFreed;
-    deletePath(path, bytesFreed);
-    state.results.bytesFreed += bytesFreed;
-}
+    struct Shared
+    {
+        // The temp roots only store the hash part to make it easier to
+        // ignore suffixes like '.lock', '.chroot' and '.check'.
+        std::unordered_set<std::string> tempRoots;
 
+        // Hash part of the store path currently being deleted, if
+        // any.
+        std::optional<std::string> pending;
+    };
 
-void LocalStore::deletePathRecursive(GCState & state, const Path & path)
-{
-    checkInterrupt();
-
-    uint64_t size = 0;
-
-    auto storePath = maybeParseStorePath(path);
-    if (storePath && isValidPath(*storePath)) {
-        StorePathSet referrers;
-        queryReferrers(*storePath, referrers);
-        for (auto & i : referrers)
-            if (printStorePath(i) != path) deletePathRecursive(state, printStorePath(i));
-        size = queryPathInfo(*storePath)->narSize;
-        invalidatePathChecked(*storePath);
-    }
+    Sync<Shared> _shared;
 
-    Path realPath = realStoreDir + "/" + std::string(baseNameOf(path));
+    std::condition_variable wakeup;
 
-    struct stat st;
-    if (lstat(realPath.c_str(), &st)) {
-        if (errno == ENOENT) return;
-        throw SysError("getting status of %1%", realPath);
+    /* Using `--ignore-liveness' with `--delete' can have unintended
+       consequences if `keep-outputs' or `keep-derivations' are true
+       (the garbage collector will recurse into deleting the outputs
+       or derivers, respectively).  So disable them. */
+    if (options.action == GCOptions::gcDeleteSpecific && options.ignoreLiveness) {
+        gcKeepOutputs = false;
+        gcKeepDerivations = false;
     }
 
-    printInfo(format("deleting '%1%'") % path);
-
-    state.results.paths.insert(path);
+    if (shouldDelete)
+        deletePath(reservedPath);
 
-    /* If the path is not a regular file or symlink, move it to the
-       trash directory.  The move is to ensure that later (when we're
-       not holding the global GC lock) we can delete the path without
-       being afraid that the path has become alive again.  Otherwise
-       delete it right away. */
-    if (state.moveToTrash && S_ISDIR(st.st_mode)) {
-        // Estimate the amount freed using the narSize field.  FIXME:
-        // if the path was not valid, need to determine the actual
-        // size.
-        try {
-            if (chmod(realPath.c_str(), st.st_mode | S_IWUSR) == -1)
-                throw SysError("making '%1%' writable", realPath);
-            Path tmp = trashDir + "/" + std::string(baseNameOf(path));
-            if (rename(realPath.c_str(), tmp.c_str()))
-                throw SysError("unable to rename '%1%' to '%2%'", realPath, tmp);
-            state.bytesInvalidated += size;
-        } catch (SysError & e) {
-            if (e.errNo == ENOSPC) {
-                printInfo(format("note: can't create move '%1%': %2%") % realPath % e.msg());
-                deleteGarbage(state, realPath);
+    /* Acquire the global GC root. Note: we don't use fdGCLock
+       here because then in auto-gc mode, another thread could
+       downgrade our exclusive lock. */
+    auto fdGCLock = openGCLock();
+    FdLock gcLock(fdGCLock.get(), ltWrite, true, "waiting for the big garbage collector lock...");
+
+    /* Start the server for receiving new roots. */
+    auto socketPath = stateDir.get() + gcSocketPath;
+    createDirs(dirOf(socketPath));
+    auto fdServer = createUnixDomainSocket(socketPath, 0666);
+
+    if (fcntl(fdServer.get(), F_SETFL, fcntl(fdServer.get(), F_GETFL) | O_NONBLOCK) == -1)
+        throw SysError("making socket '%1%' non-blocking", socketPath);
+
+    Pipe shutdownPipe;
+    shutdownPipe.create();
+
+    std::thread serverThread([&]() {
+        Sync<std::map<int, std::thread>> connections;
+
+        Finally cleanup([&]() {
+            debug("GC roots server shutting down");
+            while (true) {
+                auto item = remove_begin(*connections.lock());
+                if (!item) break;
+                auto & [fd, thread] = *item;
+                shutdown(fd, SHUT_RDWR);
+                thread.join();
             }
-        }
-    } else
-        deleteGarbage(state, realPath);
-
-    if (state.results.bytesFreed + state.bytesInvalidated > state.options.maxFreed) {
-        printInfo(format("deleted or invalidated more than %1% bytes; stopping") % state.options.maxFreed);
-        throw GCLimitReached();
-    }
-}
-
-
-bool LocalStore::canReachRoot(GCState & state, StorePathSet & visited, const StorePath & path)
-{
-    if (visited.count(path)) return false;
-
-    if (state.alive.count(path)) return true;
-
-    if (state.dead.count(path)) return false;
-
-    if (state.roots.count(path)) {
-        debug("cannot delete '%1%' because it's a root", printStorePath(path));
-        state.alive.insert(path);
-        return true;
-    }
-
-    visited.insert(path);
-
-    if (!isValidPath(path)) return false;
-
-    StorePathSet incoming;
-
-    /* Don't delete this path if any of its referrers are alive. */
-    queryReferrers(path, incoming);
-
-    /* If keep-derivations is set and this is a derivation, then
-       don't delete the derivation if any of the outputs are alive. */
-    if (state.gcKeepDerivations && path.isDerivation()) {
-        for (auto & [name, maybeOutPath] : queryPartialDerivationOutputMap(path))
-            if (maybeOutPath &&
-                isValidPath(*maybeOutPath) &&
-                queryPathInfo(*maybeOutPath)->deriver == path
-                )
-                incoming.insert(*maybeOutPath);
-    }
-
-    /* If keep-outputs is set, then don't delete this path if there
-       are derivers of this path that are not garbage. */
-    if (state.gcKeepOutputs) {
-        auto derivers = queryValidDerivers(path);
-        for (auto & i : derivers)
-            incoming.insert(i);
-    }
+        });
+
+        while (true) {
+            std::vector<struct pollfd> fds;
+            fds.push_back({.fd = shutdownPipe.readSide.get(), .events = POLLIN});
+            fds.push_back({.fd = fdServer.get(), .events = POLLIN});
+            auto count = poll(fds.data(), fds.size(), -1);
+            assert(count != -1);
+
+            if (fds[0].revents)
+                /* Parent is asking us to quit. */
+                break;
+
+            if (fds[1].revents) {
+                /* Accept a new connection. */
+                assert(fds[1].revents & POLLIN);
+                AutoCloseFD fdClient = accept(fdServer.get(), nullptr, nullptr);
+                if (!fdClient) continue;
+
+                /* Process the connection in a separate thread. */
+                auto fdClient_ = fdClient.get();
+                std::thread clientThread([&, fdClient = std::move(fdClient)]() {
+                    Finally cleanup([&]() {
+                        auto conn(connections.lock());
+                        auto i = conn->find(fdClient.get());
+                        if (i != conn->end()) {
+                            i->second.detach();
+                            conn->erase(i);
+                        }
+                    });
+
+                    while (true) {
+                        try {
+                            auto path = readLine(fdClient.get());
+                            auto storePath = maybeParseStorePath(path);
+                            if (storePath) {
+                                debug("got new GC root '%s'", path);
+                                auto hashPart = std::string(storePath->hashPart());
+                                auto shared(_shared.lock());
+                                shared->tempRoots.insert(hashPart);
+                                /* If this path is currently being
+                                   deleted, then we have to wait until
+                                   deletion is finished to ensure that
+                                   the client doesn't start
+                                   re-creating it before we're
+                                   done. FIXME: ideally we would use a
+                                   FD for this so we don't block the
+                                   poll loop. */
+                                while (shared->pending == hashPart) {
+                                    debug("synchronising with deletion of path '%s'", path);
+                                    shared.wait(wakeup);
+                                }
+                            } else
+                                printError("received garbage instead of a root from client");
+                            writeFull(fdClient.get(), "1", false);
+                        } catch (Error &) { break; }
+                    }
+                });
 
-    for (auto & i : incoming)
-        if (i != path)
-            if (canReachRoot(state, visited, i)) {
-                state.alive.insert(path);
-                return true;
+                connections.lock()->insert({fdClient_, std::move(clientThread)});
             }
+        }
+    });
 
-    return false;
-}
-
-
-void LocalStore::tryToDelete(GCState & state, const Path & path)
-{
-    checkInterrupt();
-
-    auto realPath = realStoreDir + "/" + std::string(baseNameOf(path));
-    if (realPath == linksDir || realPath == trashDir) return;
-
-    //Activity act(*logger, lvlDebug, format("considering whether to delete '%1%'") % path);
-
-    auto storePath = maybeParseStorePath(path);
-
-    if (!storePath || !isValidPath(*storePath)) {
-        /* A lock file belonging to a path that we're building right
-           now isn't garbage. */
-        if (isActiveTempFile(state, path, ".lock")) return;
+    Finally stopServer([&]() {
+        writeFull(shutdownPipe.writeSide.get(), "x", false);
+        wakeup.notify_all();
+        if (serverThread.joinable()) serverThread.join();
+    });
 
-        /* Don't delete .chroot directories for derivations that are
-           currently being built. */
-        if (isActiveTempFile(state, path, ".chroot")) return;
+    /* Find the roots.  Since we've grabbed the GC lock, the set of
+       permanent roots cannot increase now. */
+    printInfo("finding garbage collector roots...");
+    Roots rootMap;
+    if (!options.ignoreLiveness)
+        findRootsNoTemp(rootMap, true);
 
-        /* Don't delete .check directories for derivations that are
-           currently being built, because we may need to run
-           diff-hook. */
-        if (isActiveTempFile(state, path, ".check")) return;
-    }
+    for (auto & i : rootMap) roots.insert(i.first);
 
-    StorePathSet visited;
-
-    if (storePath && canReachRoot(state, visited, *storePath)) {
-        debug("cannot delete '%s' because it's still reachable", path);
-    } else {
-        /* No path we visited was a root, so everything is garbage.
-           But we only delete ‘path’ and its referrers here so that
-           ‘nix-store --delete’ doesn't have the unexpected effect of
-           recursing into derivations and outputs. */
-        for (auto & i : visited)
-            state.dead.insert(i);
-        if (state.shouldDelete)
-            deletePathRecursive(state, path);
+    /* Read the temporary roots created before we acquired the global
+       GC root. Any new roots will be sent to our socket. */
+    Roots tempRoots;
+    findTempRoots(tempRoots, true);
+    for (auto & root : tempRoots) {
+        _shared.lock()->tempRoots.insert(std::string(root.first.hashPart()));
+        roots.insert(root.first);
     }
-}
 
+    /* Helper function that deletes a path from the store and throws
+       GCLimitReached if we've deleted enough garbage. */
+    auto deleteFromStore = [&](std::string_view baseName)
+    {
+        Path path = storeDir + "/" + std::string(baseName);
+        Path realPath = realStoreDir + "/" + std::string(baseName);
 
-/* Unlink all files in /nix/store/.links that have a link count of 1,
-   which indicates that there are no other links and so they can be
-   safely deleted.  FIXME: race condition with optimisePath(): we
-   might see a link count of 1 just before optimisePath() increases
-   the link count. */
-void LocalStore::removeUnusedLinks(const GCState & state)
-{
-    AutoCloseDir dir(opendir(linksDir.c_str()));
-    if (!dir) throw SysError("opening directory '%1%'", linksDir);
-
-    int64_t actualSize = 0, unsharedSize = 0;
+        printInfo("deleting '%1%'", path);
 
-    struct dirent * dirent;
-    while (errno = 0, dirent = readdir(dir.get())) {
-        checkInterrupt();
-        string name = dirent->d_name;
-        if (name == "." || name == "..") continue;
-        Path path = linksDir + "/" + name;
+        results.paths.insert(path);
 
-        auto st = lstat(path);
+        uint64_t bytesFreed;
+        deletePath(realPath, bytesFreed);
+        results.bytesFreed += bytesFreed;
 
-        if (st.st_nlink != 1) {
-            actualSize += st.st_size;
-            unsharedSize += (st.st_nlink - 1) * st.st_size;
-            continue;
+        if (results.bytesFreed > options.maxFreed) {
+            printInfo("deleted more than %d bytes; stopping", options.maxFreed);
+            throw GCLimitReached();
         }
+    };
 
-        printMsg(lvlTalkative, format("deleting unused link '%1%'") % path);
-
-        if (unlink(path.c_str()) == -1)
-            throw SysError("deleting '%1%'", path);
+    std::map<StorePath, StorePathSet> referrersCache;
 
-        state.results.bytesFreed += st.st_size;
-    }
+    /* Helper function that visits all paths reachable from `start`
+       via the referrers edges and optionally derivers and derivation
+       output edges. If none of those paths are roots, then all
+       visited paths are garbage and are deleted. */
+    auto deleteReferrersClosure = [&](const StorePath & start) {
+        StorePathSet visited;
+        std::queue<StorePath> todo;
 
-    struct stat st;
-    if (stat(linksDir.c_str(), &st) == -1)
-        throw SysError("statting '%1%'", linksDir);
-    int64_t overhead = st.st_blocks * 512ULL;
+        /* Wake up any GC client waiting for deletion of the paths in
+           'visited' to finish. */
+        Finally releasePending([&]() {
+            auto shared(_shared.lock());
+            shared->pending.reset();
+            wakeup.notify_all();
+        });
 
-    printInfo("note: currently hard linking saves %.2f MiB",
-        ((unsharedSize - actualSize - overhead) / (1024.0 * 1024.0)));
-}
+        auto enqueue = [&](const StorePath & path) {
+            if (visited.insert(path).second)
+                todo.push(path);
+        };
 
+        enqueue(start);
 
-void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
-{
-    GCState state(options, results);
-    state.gcKeepOutputs = settings.gcKeepOutputs;
-    state.gcKeepDerivations = settings.gcKeepDerivations;
+        while (auto path = pop(todo)) {
+            checkInterrupt();
 
-    /* Using `--ignore-liveness' with `--delete' can have unintended
-       consequences if `keep-outputs' or `keep-derivations' are true
-       (the garbage collector will recurse into deleting the outputs
-       or derivers, respectively).  So disable them. */
-    if (options.action == GCOptions::gcDeleteSpecific && options.ignoreLiveness) {
-        state.gcKeepOutputs = false;
-        state.gcKeepDerivations = false;
-    }
+            /* Bail out if we've previously discovered that this path
+               is alive. */
+            if (alive.count(*path)) {
+                alive.insert(start);
+                return;
+            }
 
-    state.shouldDelete = options.action == GCOptions::gcDeleteDead || options.action == GCOptions::gcDeleteSpecific;
+            /* If we've previously deleted this path, we don't have to
+               handle it again. */
+            if (dead.count(*path)) continue;
 
-    if (state.shouldDelete)
-        deletePath(reservedPath);
+            auto markAlive = [&]()
+            {
+                alive.insert(*path);
+                alive.insert(start);
+                try {
+                    StorePathSet closure;
+                    computeFSClosure(*path, closure);
+                    for (auto & p : closure)
+                        alive.insert(p);
+                } catch (InvalidPath &) { }
+            };
+
+            /* If this is a root, bail out. */
+            if (roots.count(*path)) {
+                debug("cannot delete '%s' because it's a root", printStorePath(*path));
+                return markAlive();
+            }
 
-    /* Acquire the global GC root.  This prevents
-       a) New roots from being added.
-       b) Processes from creating new temporary root files. */
-    AutoCloseFD fdGCLock = openGCLock(ltWrite);
+            if (options.action == GCOptions::gcDeleteSpecific
+                && !options.pathsToDelete.count(*path))
+                return;
 
-    /* Find the roots.  Since we've grabbed the GC lock, the set of
-       permanent roots cannot increase now. */
-    printInfo("finding garbage collector roots...");
-    Roots rootMap;
-    if (!options.ignoreLiveness)
-        findRootsNoTemp(rootMap, true);
+            {
+                auto hashPart = std::string(path->hashPart());
+                auto shared(_shared.lock());
+                if (shared->tempRoots.count(hashPart)) {
+                    debug("cannot delete '%s' because it's a temporary root", printStorePath(*path));
+                    return markAlive();
+                }
+                shared->pending = hashPart;
+            }
 
-    for (auto & i : rootMap) state.roots.insert(i.first);
+            if (isValidPath(*path)) {
 
-    /* Read the temporary roots.  This acquires read locks on all
-       per-process temporary root files.  So after this point no paths
-       can be added to the set of temporary roots. */
-    FDs fds;
-    Roots tempRoots;
-    findTempRoots(fds, tempRoots, true);
-    for (auto & root : tempRoots) {
-        state.tempRoots.insert(root.first);
-        state.roots.insert(root.first);
-    }
+                /* Visit the referrers of this path. */
+                auto i = referrersCache.find(*path);
+                if (i == referrersCache.end()) {
+                    StorePathSet referrers;
+                    queryReferrers(*path, referrers);
+                    referrersCache.emplace(*path, std::move(referrers));
+                    i = referrersCache.find(*path);
+                }
+                for (auto & p : i->second)
+                    enqueue(p);
+
+                /* If keep-derivations is set and this is a
+                   derivation, then visit the derivation outputs. */
+                if (gcKeepDerivations && path->isDerivation()) {
+                    for (auto & [name, maybeOutPath] : queryPartialDerivationOutputMap(*path))
+                        if (maybeOutPath &&
+                            isValidPath(*maybeOutPath) &&
+                            queryPathInfo(*maybeOutPath)->deriver == *path)
+                            enqueue(*maybeOutPath);
+                }
 
-    /* After this point the set of roots or temporary roots cannot
-       increase, since we hold locks on everything.  So everything
-       that is not reachable from `roots' is garbage. */
+                /* If keep-outputs is set, then visit the derivers. */
+                if (gcKeepOutputs) {
+                    auto derivers = queryValidDerivers(*path);
+                    for (auto & i : derivers)
+                        enqueue(i);
+                }
+            }
+        }
 
-    if (state.shouldDelete) {
-        if (pathExists(trashDir)) deleteGarbage(state, trashDir);
-        try {
-            createDirs(trashDir);
-        } catch (SysError & e) {
-            if (e.errNo == ENOSPC) {
-                printInfo("note: can't create trash directory: %s", e.msg());
-                state.moveToTrash = false;
+        for (auto & path : topoSortPaths(visited)) {
+            if (!dead.insert(path).second) continue;
+            if (shouldDelete) {
+                invalidatePathChecked(path);
+                deleteFromStore(path.to_string());
+                referrersCache.erase(path);
             }
         }
-    }
+    };
 
-    /* Now either delete all garbage paths, or just the specified
-       paths (for gcDeleteSpecific). */
+    /* Synchronisation point for testing, see tests/gc-concurrent.sh. */
+    if (auto p = getEnv("_NIX_TEST_GC_SYNC"))
+        readFile(*p);
 
+    /* Either delete all garbage paths, or just the specified
+       paths (for gcDeleteSpecific). */
     if (options.action == GCOptions::gcDeleteSpecific) {
 
         for (auto & i : options.pathsToDelete) {
-            tryToDelete(state, printStorePath(i));
-            if (state.dead.find(i) == state.dead.end())
+            deleteReferrersClosure(i);
+            if (!dead.count(i))
                 throw Error(
-                    "cannot delete path '%1%' since it is still alive. "
-                    "To find out why use: "
+                    "Cannot delete path '%1%' since it is still alive. "
+                    "To find out why, use: "
                     "nix-store --query --roots",
                     printStorePath(i));
         }
 
     } else if (options.maxFreed > 0) {
 
-        if (state.shouldDelete)
+        if (shouldDelete)
             printInfo("deleting garbage...");
         else
             printInfo("determining live/dead paths...");
 
         try {
-
-            AutoCloseDir dir(opendir(realStoreDir.c_str()));
+            AutoCloseDir dir(opendir(realStoreDir.get().c_str()));
             if (!dir) throw SysError("opening directory '%1%'", realStoreDir);
 
-            /* Read the store and immediately delete all paths that
-               aren't valid.  When using --max-freed etc., deleting
-               invalid paths is preferred over deleting unreachable
-               paths, since unreachable paths could become reachable
-               again.  We don't use readDirectory() here so that GCing
-               can start faster. */
+            /* Read the store and delete all paths that are invalid or
+               unreachable. We don't use readDirectory() here so that
+               GCing can start faster. */
+            auto linksName = baseNameOf(linksDir);
             Paths entries;
             struct dirent * dirent;
             while (errno = 0, dirent = readdir(dir.get())) {
                 checkInterrupt();
                 string name = dirent->d_name;
-                if (name == "." || name == "..") continue;
-                Path path = storeDir + "/" + name;
-                auto storePath = maybeParseStorePath(path);
-                if (storePath && isValidPath(*storePath))
-                    entries.push_back(path);
-                else
-                    tryToDelete(state, path);
-            }
-
-            dir.reset();
-
-            /* Now delete the unreachable valid paths.  Randomise the
-               order in which we delete entries to make the collector
-               less biased towards deleting paths that come
-               alphabetically first (e.g. /nix/store/000...).  This
-               matters when using --max-freed etc. */
-            vector<Path> entries_(entries.begin(), entries.end());
-            std::mt19937 gen(1);
-            std::shuffle(entries_.begin(), entries_.end(), gen);
+                if (name == "." || name == ".." || name == linksName) continue;
 
-            for (auto & i : entries_)
-                tryToDelete(state, i);
+                if (auto storePath = maybeParseStorePath(storeDir + "/" + name))
+                    deleteReferrersClosure(*storePath);
+                else
+                    deleteFromStore(name);
 
+            }
         } catch (GCLimitReached & e) {
         }
     }
 
-    if (state.options.action == GCOptions::gcReturnLive) {
-        for (auto & i : state.alive)
-            state.results.paths.insert(printStorePath(i));
+    if (options.action == GCOptions::gcReturnLive) {
+        for (auto & i : alive)
+            results.paths.insert(printStorePath(i));
         return;
     }
 
-    if (state.options.action == GCOptions::gcReturnDead) {
-        for (auto & i : state.dead)
-            state.results.paths.insert(printStorePath(i));
+    if (options.action == GCOptions::gcReturnDead) {
+        for (auto & i : dead)
+            results.paths.insert(printStorePath(i));
         return;
     }
 
-    /* Allow other processes to add to the store from here on. */
-    fdGCLock = -1;
-    fds.clear();
-
-    /* Delete the trash directory. */
-    printInfo(format("deleting '%1%'") % trashDir);
-    deleteGarbage(state, trashDir);
-
-    /* Clean up the links directory. */
+    /* Unlink all files in /nix/store/.links that have a link count of 1,
+       which indicates that there are no other links and so they can be
+       safely deleted.  FIXME: race condition with optimisePath(): we
+       might see a link count of 1 just before optimisePath() increases
+       the link count. */
     if (options.action == GCOptions::gcDeleteDead || options.action == GCOptions::gcDeleteSpecific) {
         printInfo("deleting unused links...");
-        removeUnusedLinks(state);
+
+        AutoCloseDir dir(opendir(linksDir.c_str()));
+        if (!dir) throw SysError("opening directory '%1%'", linksDir);
+
+        int64_t actualSize = 0, unsharedSize = 0;
+
+        struct dirent * dirent;
+        while (errno = 0, dirent = readdir(dir.get())) {
+            checkInterrupt();
+            string name = dirent->d_name;
+            if (name == "." || name == "..") continue;
+            Path path = linksDir + "/" + name;
+
+            auto st = lstat(path);
+
+            if (st.st_nlink != 1) {
+                actualSize += st.st_size;
+                unsharedSize += (st.st_nlink - 1) * st.st_size;
+                continue;
+            }
+
+            printMsg(lvlTalkative, format("deleting unused link '%1%'") % path);
+
+            if (unlink(path.c_str()) == -1)
+                throw SysError("deleting '%1%'", path);
+
+            results.bytesFreed += st.st_size;
+        }
+
+        struct stat st;
+        if (stat(linksDir.c_str(), &st) == -1)
+            throw SysError("statting '%1%'", linksDir);
+        int64_t overhead = st.st_blocks * 512ULL;
+
+        printInfo("note: currently hard linking saves %.2f MiB",
+            ((unsharedSize - actualSize - overhead) / (1024.0 * 1024.0)));
     }
 
     /* While we're at it, vacuum the database. */
@@ -856,7 +847,7 @@ void LocalStore::autoGC(bool sync)
             return std::stoll(readFile(*fakeFreeSpaceFile));
 
         struct statvfs st;
-        if (statvfs(realStoreDir.c_str(), &st))
+        if (statvfs(realStoreDir.get().c_str(), &st))
             throw SysError("getting filesystem info about '%s'", realStoreDir);
 
         return (uint64_t) st.f_bavail * st.f_frsize;
diff --git a/src/libstore/globals.cc b/src/libstore/globals.cc
index d3b27d7be..9f1a88130 100644
--- a/src/libstore/globals.cc
+++ b/src/libstore/globals.cc
@@ -148,7 +148,8 @@ StringSet Settings::getDefaultExtraPlatforms()
     // machines. Note that we can’t force processes from executing
     // x86_64 in aarch64 environments or vice versa since they can
     // always exec with their own binary preferences.
-    if (pathExists("/Library/Apple/System/Library/LaunchDaemons/com.apple.oahd.plist")) {
+    if (pathExists("/Library/Apple/System/Library/LaunchDaemons/com.apple.oahd.plist") ||
+        pathExists("/System/Library/LaunchDaemons/com.apple.oahd.plist")) {
         if (std::string{SYSTEM} == "x86_64-darwin")
             extraPlatforms.insert("aarch64-darwin");
         else if (std::string{SYSTEM} == "aarch64-darwin")
@@ -159,21 +160,16 @@ StringSet Settings::getDefaultExtraPlatforms()
     return extraPlatforms;
 }
 
-bool Settings::isExperimentalFeatureEnabled(const std::string & name)
+bool Settings::isExperimentalFeatureEnabled(const ExperimentalFeature & feature)
 {
     auto & f = experimentalFeatures.get();
-    return std::find(f.begin(), f.end(), name) != f.end();
+    return std::find(f.begin(), f.end(), feature) != f.end();
 }
 
-MissingExperimentalFeature::MissingExperimentalFeature(std::string feature)
-    : Error("experimental Nix feature '%1%' is disabled; use '--experimental-features %1%' to override", feature)
-    , missingFeature(feature)
-    {}
-
-void Settings::requireExperimentalFeature(const std::string & name)
+void Settings::requireExperimentalFeature(const ExperimentalFeature & feature)
 {
-    if (!isExperimentalFeatureEnabled(name))
-        throw MissingExperimentalFeature(name);
+    if (!isExperimentalFeatureEnabled(feature))
+        throw MissingExperimentalFeature(feature);
 }
 
 bool Settings::isWSL1()
diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
index 6f8749254..a50eb6803 100644
--- a/src/libstore/globals.hh
+++ b/src/libstore/globals.hh
@@ -3,6 +3,7 @@
 #include "types.hh"
 #include "config.hh"
 #include "util.hh"
+#include "experimental-features.hh"
 
 #include <map>
 #include <limits>
@@ -45,15 +46,6 @@ struct PluginFilesSetting : public BaseSetting<Paths>
     void set(const std::string & str, bool append = false) override;
 };
 
-class MissingExperimentalFeature: public Error
-{
-public:
-    std::string missingFeature;
-
-    MissingExperimentalFeature(std::string feature);
-    virtual const char* sname() const override { return "MissingExperimentalFeature"; }
-};
-
 class Settings : public Config {
 
     unsigned int getDefaultCores();
@@ -617,8 +609,10 @@ public:
         Strings{"https://cache.nixos.org/"},
         "substituters",
         R"(
-          A list of URLs of substituters, separated by whitespace. The default
-          is `https://cache.nixos.org`.
+          A list of URLs of substituters, separated by whitespace. Substituters
+          are tried based on their Priority value, which each substituter can set
+          independently. Lower value means higher priority.
+          The default is `https://cache.nixos.org`, with a Priority of 40.
         )",
         {"binary-caches"}};
 
@@ -923,12 +917,12 @@ public:
           value.
           )"};
 
-    Setting<Strings> experimentalFeatures{this, {}, "experimental-features",
+    Setting<std::set<ExperimentalFeature>> experimentalFeatures{this, {}, "experimental-features",
         "Experimental Nix features to enable."};
 
-    bool isExperimentalFeatureEnabled(const std::string & name);
+    bool isExperimentalFeatureEnabled(const ExperimentalFeature &);
 
-    void requireExperimentalFeature(const std::string & name);
+    void requireExperimentalFeature(const ExperimentalFeature &);
 
     Setting<bool> allowDirty{this, true, "allow-dirty",
         "Whether to allow dirty Git/Mercurial trees."};
@@ -954,6 +948,12 @@ public:
           resolves to a different location from that of the build machine. You
           can enable this setting if you are sure you're not going to do that.
         )"};
+
+    Setting<bool> useRegistries{this, true, "use-registries",
+        "Whether to use flake registries to resolve flake references."};
+
+    Setting<bool> acceptFlakeConfig{this, false, "accept-flake-config",
+        "Whether to accept nix configuration from a flake without prompting."};
 };
 
 
diff --git a/src/libstore/http-binary-cache-store.cc b/src/libstore/http-binary-cache-store.cc
index 0a3afcd51..605ec4b28 100644
--- a/src/libstore/http-binary-cache-store.cc
+++ b/src/libstore/http-binary-cache-store.cc
@@ -57,8 +57,8 @@ public:
     {
         // FIXME: do this lazily?
         if (auto cacheInfo = diskCache->cacheExists(cacheUri)) {
-            wantMassQuery.setDefault(cacheInfo->wantMassQuery ? "true" : "false");
-            priority.setDefault(fmt("%d", cacheInfo->priority));
+            wantMassQuery.setDefault(cacheInfo->wantMassQuery);
+            priority.setDefault(cacheInfo->priority);
         } else {
             try {
                 BinaryCacheStore::init();
diff --git a/src/libstore/legacy-ssh-store.cc b/src/libstore/legacy-ssh-store.cc
index edaf75136..4861d185e 100644
--- a/src/libstore/legacy-ssh-store.cc
+++ b/src/libstore/legacy-ssh-store.cc
@@ -82,9 +82,20 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
             conn->to << SERVE_MAGIC_1 << SERVE_PROTOCOL_VERSION;
             conn->to.flush();
 
-            unsigned int magic = readInt(conn->from);
-            if (magic != SERVE_MAGIC_2)
-                throw Error("protocol mismatch with 'nix-store --serve' on '%s'", host);
+            StringSink saved;
+            try {
+                TeeSource tee(conn->from, saved);
+                unsigned int magic = readInt(tee);
+                if (magic != SERVE_MAGIC_2)
+                    throw Error("'nix-store --serve' protocol mismatch from '%s'", host);
+            } catch (SerialisationError & e) {
+                /* In case the other side is waiting for our input,
+                   close it. */
+                conn->sshConn->in.close();
+                auto msg = conn->from.drain();
+                throw Error("'nix-store --serve' protocol mismatch from '%s', got '%s'",
+                    host, chomp(*saved.s + msg));
+            }
             conn->remoteVersion = readInt(conn->from);
             if (GET_PROTOCOL_MAJOR(conn->remoteVersion) != 0x200)
                 throw Error("unsupported 'nix-store --serve' protocol version on '%s'", host);
@@ -216,7 +227,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
 
     StorePath addToStore(const string & name, const Path & srcPath,
         FileIngestionMethod method, HashType hashAlgo,
-        PathFilter & filter, RepairFlag repair) override
+        PathFilter & filter, RepairFlag repair, const StorePathSet & references) override
     { unsupported("addToStore"); }
 
     StorePath addTextToStore(const string & name, const string & s,
@@ -237,6 +248,10 @@ private:
             conn.to
                 << settings.buildRepeat
                 << settings.enforceDeterminism;
+
+        if (GET_PROTOCOL_MINOR(conn.remoteVersion) >= 7) {
+            conn.to << ((int) settings.keepFailed);
+        }
     }
 
 public:
@@ -267,8 +282,11 @@ public:
         return status;
     }
 
-    void buildPaths(const std::vector<DerivedPath> & drvPaths, BuildMode buildMode) override
+    void buildPaths(const std::vector<DerivedPath> & drvPaths, BuildMode buildMode, std::shared_ptr<Store> evalStore) override
     {
+        if (evalStore && evalStore.get() != this)
+            throw Error("building on an SSH store is incompatible with '--eval-store'");
+
         auto conn(connections->get());
 
         conn->to << cmdBuildPaths;
@@ -276,10 +294,10 @@ public:
         for (auto & p : drvPaths) {
             auto sOrDrvPath = StorePathWithOutputs::tryFromDerivedPath(p);
             std::visit(overloaded {
-                [&](StorePathWithOutputs s) {
+                [&](const StorePathWithOutputs & s) {
                     ss.push_back(s.to_string(*this));
                 },
-                [&](StorePath drvPath) {
+                [&](const StorePath & drvPath) {
                     throw Error("wanted to fetch '%s' but the legacy ssh protocol doesn't support merely substituting drv files via the build paths command. It would build them instead. Try using ssh-ng://", printStorePath(drvPath));
                 },
             }, sOrDrvPath);
@@ -349,7 +367,8 @@ public:
         return conn->remoteVersion;
     }
 
-    std::optional<const Realisation> queryRealisation(const DrvOutput&) override
+    void queryRealisationUncached(const DrvOutput &,
+        Callback<std::shared_ptr<const Realisation>> callback) noexcept override
     // TODO: Implement
     { unsupported("queryRealisation"); }
 };
diff --git a/src/libstore/local-binary-cache-store.cc b/src/libstore/local-binary-cache-store.cc
index 964c4017e..f93111fce 100644
--- a/src/libstore/local-binary-cache-store.cc
+++ b/src/libstore/local-binary-cache-store.cc
@@ -93,7 +93,7 @@ protected:
 void LocalBinaryCacheStore::init()
 {
     createDirs(binaryCacheDir + "/nar");
-    createDirs(binaryCacheDir + realisationsPrefix);
+    createDirs(binaryCacheDir + "/" + realisationsPrefix);
     if (writeDebugInfo)
         createDirs(binaryCacheDir + "/debuginfo");
     BinaryCacheStore::init();
diff --git a/src/libstore/local-fs-store.hh b/src/libstore/local-fs-store.hh
index 55941b771..f8b19d00d 100644
--- a/src/libstore/local-fs-store.hh
+++ b/src/libstore/local-fs-store.hh
@@ -18,6 +18,9 @@ struct LocalFSStoreConfig : virtual StoreConfig
     const PathSetting logDir{(StoreConfig*) this, false,
         rootDir != "" ? rootDir + "/nix/var/log/nix" : settings.nixLogDir,
         "log", "directory where Nix will store state"};
+    const PathSetting realStoreDir{(StoreConfig*) this, false,
+        rootDir != "" ? rootDir + "/nix/store" : storeDir, "real",
+        "physical path to the Nix store"};
 };
 
 class LocalFSStore : public virtual LocalFSStoreConfig, public virtual Store
@@ -34,7 +37,7 @@ public:
     /* Register a permanent GC root. */
     Path addPermRoot(const StorePath & storePath, const Path & gcRoot);
 
-    virtual Path getRealStoreDir() { return storeDir; }
+    virtual Path getRealStoreDir() { return realStoreDir; }
 
     Path toRealPath(const Path & storePath) override
     {
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 83daa7506..64019314f 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -53,12 +53,15 @@ struct LocalStore::State::Stmts {
     SQLiteStmt InvalidatePath;
     SQLiteStmt AddDerivationOutput;
     SQLiteStmt RegisterRealisedOutput;
+    SQLiteStmt UpdateRealisedOutput;
     SQLiteStmt QueryValidDerivers;
     SQLiteStmt QueryDerivationOutputs;
     SQLiteStmt QueryRealisedOutput;
     SQLiteStmt QueryAllRealisedOutputs;
     SQLiteStmt QueryPathFromHashPart;
     SQLiteStmt QueryValidPaths;
+    SQLiteStmt QueryRealisationReferences;
+    SQLiteStmt AddRealisationReference;
 };
 
 int getSchema(Path schemaPath)
@@ -76,7 +79,7 @@ int getSchema(Path schemaPath)
 
 void migrateCASchema(SQLite& db, Path schemaPath, AutoCloseFD& lockFd)
 {
-    const int nixCASchemaVersion = 1;
+    const int nixCASchemaVersion = 2;
     int curCASchema = getSchema(schemaPath);
     if (curCASchema != nixCASchemaVersion) {
         if (curCASchema > nixCASchemaVersion) {
@@ -94,7 +97,39 @@ void migrateCASchema(SQLite& db, Path schemaPath, AutoCloseFD& lockFd)
               #include "ca-specific-schema.sql.gen.hh"
                 ;
             db.exec(schema);
+            curCASchema = nixCASchemaVersion;
         }
+
+        if (curCASchema < 2) {
+            SQLiteTxn txn(db);
+            // Ugly little sql dance to add a new `id` column and make it the primary key
+            db.exec(R"(
+                create table Realisations2 (
+                    id integer primary key autoincrement not null,
+                    drvPath text not null,
+                    outputName text not null, -- symbolic output id, usually "out"
+                    outputPath integer not null,
+                    signatures text, -- space-separated list
+                    foreign key (outputPath) references ValidPaths(id) on delete cascade
+                );
+                insert into Realisations2 (drvPath, outputName, outputPath, signatures)
+                    select drvPath, outputName, outputPath, signatures from Realisations;
+                drop table Realisations;
+                alter table Realisations2 rename to Realisations;
+            )");
+            db.exec(R"(
+                create index if not exists IndexRealisations on Realisations(drvPath, outputName);
+
+                create table if not exists RealisationsRefs (
+                    referrer integer not null,
+                    realisationReference integer,
+                    foreign key (referrer) references Realisations(id) on delete cascade,
+                    foreign key (realisationReference) references Realisations(id) on delete restrict
+                );
+            )");
+            txn.commit();
+        }
+
         writeFile(schemaPath, fmt("%d", nixCASchemaVersion));
         lockFile(lockFd.get(), ltRead, true);
     }
@@ -106,14 +141,10 @@ LocalStore::LocalStore(const Params & params)
     , LocalStoreConfig(params)
     , Store(params)
     , LocalFSStore(params)
-    , realStoreDir_{this, false, rootDir != "" ? rootDir + "/nix/store" : storeDir, "real",
-        "physical path to the Nix store"}
-    , realStoreDir(realStoreDir_)
     , dbDir(stateDir + "/db")
     , linksDir(realStoreDir + "/.links")
     , reservedPath(dbDir + "/reserved")
     , schemaPath(dbDir + "/schema")
-    , trashDir(realStoreDir + "/trash")
     , tempRootsDir(stateDir + "/temproots")
     , fnTempRoots(fmt("%s/%d", tempRootsDir, getpid()))
     , locksHeld(tokenizeString<PathSet>(getEnv("NIX_HELD_LOCKS").value_or("")))
@@ -153,13 +184,13 @@ LocalStore::LocalStore(const Params & params)
             printError("warning: the group '%1%' specified in 'build-users-group' does not exist", settings.buildUsersGroup);
         else {
             struct stat st;
-            if (stat(realStoreDir.c_str(), &st))
+            if (stat(realStoreDir.get().c_str(), &st))
                 throw SysError("getting attributes of path '%1%'", realStoreDir);
 
             if (st.st_uid != 0 || st.st_gid != gr->gr_gid || (st.st_mode & ~S_IFMT) != perm) {
-                if (chown(realStoreDir.c_str(), 0, gr->gr_gid) == -1)
+                if (chown(realStoreDir.get().c_str(), 0, gr->gr_gid) == -1)
                     throw SysError("changing ownership of path '%1%'", realStoreDir);
-                if (chmod(realStoreDir.c_str(), perm) == -1)
+                if (chmod(realStoreDir.get().c_str(), perm) == -1)
                     throw SysError("changing permissions on path '%1%'", realStoreDir);
             }
         }
@@ -277,7 +308,7 @@ LocalStore::LocalStore(const Params & params)
 
     else openDB(*state, false);
 
-    if (settings.isExperimentalFeatureEnabled("ca-derivations")) {
+    if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations)) {
         migrateCASchema(state->db, dbDir + "/ca-schema", globalLock);
     }
 
@@ -307,16 +338,25 @@ LocalStore::LocalStore(const Params & params)
     state->stmts->QueryPathFromHashPart.create(state->db,
         "select path from ValidPaths where path >= ? limit 1;");
     state->stmts->QueryValidPaths.create(state->db, "select path from ValidPaths");
-    if (settings.isExperimentalFeatureEnabled("ca-derivations")) {
+    if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations)) {
         state->stmts->RegisterRealisedOutput.create(state->db,
             R"(
-                insert or replace into Realisations (drvPath, outputName, outputPath, signatures)
+                insert into Realisations (drvPath, outputName, outputPath, signatures)
                 values (?, ?, (select id from ValidPaths where path = ?), ?)
                 ;
             )");
+        state->stmts->UpdateRealisedOutput.create(state->db,
+            R"(
+                update Realisations
+                    set signatures = ?
+                where
+                    drvPath = ? and
+                    outputName = ?
+                ;
+            )");
         state->stmts->QueryRealisedOutput.create(state->db,
             R"(
-                select Output.path, Realisations.signatures from Realisations
+                select Realisations.id, Output.path, Realisations.signatures from Realisations
                     inner join ValidPaths as Output on Output.id = Realisations.outputPath
                     where drvPath = ? and outputName = ?
                     ;
@@ -328,10 +368,33 @@ LocalStore::LocalStore(const Params & params)
                     where drvPath = ?
                     ;
             )");
+        state->stmts->QueryRealisationReferences.create(state->db,
+            R"(
+                select drvPath, outputName from Realisations
+                    join RealisationsRefs on realisationReference = Realisations.id
+                    where referrer = ?;
+            )");
+        state->stmts->AddRealisationReference.create(state->db,
+            R"(
+                insert or replace into RealisationsRefs (referrer, realisationReference)
+                values (
+                    (select id from Realisations where drvPath = ? and outputName = ?),
+                    (select id from Realisations where drvPath = ? and outputName = ?));
+            )");
     }
 }
 
 
+AutoCloseFD LocalStore::openGCLock()
+{
+    Path fnGCLock = stateDir + "/gc.lock";
+    auto fdGCLock = open(fnGCLock.c_str(), O_RDWR | O_CREAT | O_CLOEXEC, 0600);
+    if (!fdGCLock)
+        throw SysError("opening global GC lock '%1%'", fnGCLock);
+    return fdGCLock;
+}
+
+
 LocalStore::~LocalStore()
 {
     std::shared_future<void> future;
@@ -437,14 +500,11 @@ void LocalStore::makeStoreWritable()
     if (getuid() != 0) return;
     /* Check if /nix/store is on a read-only mount. */
     struct statvfs stat;
-    if (statvfs(realStoreDir.c_str(), &stat) != 0)
+    if (statvfs(realStoreDir.get().c_str(), &stat) != 0)
         throw SysError("getting info about the Nix store mount point");
 
     if (stat.f_flag & ST_RDONLY) {
-        if (unshare(CLONE_NEWNS) == -1)
-            throw SysError("setting up a private mount namespace");
-
-        if (mount(0, realStoreDir.c_str(), "none", MS_REMOUNT | MS_BIND, 0) == -1)
+        if (mount(0, realStoreDir.get().c_str(), "none", MS_REMOUNT | MS_BIND, 0) == -1)
             throw SysError("remounting %1% writable", realStoreDir);
     }
 #endif
@@ -627,7 +687,7 @@ void LocalStore::checkDerivationOutputs(const StorePath & drvPath, const Derivat
     std::optional<Hash> h;
     for (auto & i : drv.outputs) {
         std::visit(overloaded {
-            [&](DerivationOutputInputAddressed doia) {
+            [&](const DerivationOutputInputAddressed & doia) {
                 if (!h) {
                     // somewhat expensive so we do lazily
                     auto temp = hashDerivationModulo(*this, drv, true);
@@ -639,14 +699,14 @@ void LocalStore::checkDerivationOutputs(const StorePath & drvPath, const Derivat
                         printStorePath(drvPath), printStorePath(doia.path), printStorePath(recomputed));
                 envHasRightPath(doia.path, i.first);
             },
-            [&](DerivationOutputCAFixed dof) {
+            [&](const DerivationOutputCAFixed & dof) {
                 StorePath path = makeFixedOutputPath(dof.hash.method, dof.hash.hash, drvName);
                 envHasRightPath(path, i.first);
             },
-            [&](DerivationOutputCAFloating _) {
+            [&](const DerivationOutputCAFloating &) {
                 /* Nothing to check */
             },
-            [&](DerivationOutputDeferred) {
+            [&](const DerivationOutputDeferred &) {
             },
         }, i.second.output);
     }
@@ -654,7 +714,7 @@ void LocalStore::checkDerivationOutputs(const StorePath & drvPath, const Derivat
 
 void LocalStore::registerDrvOutput(const Realisation & info, CheckSigsFlag checkSigs)
 {
-    settings.requireExperimentalFeature("ca-derivations");
+    settings.requireExperimentalFeature(Xp::CaDerivations);
     if (checkSigs == NoCheckSigs || !realisationIsUntrusted(info))
         registerDrvOutput(info);
     else
@@ -663,15 +723,55 @@ void LocalStore::registerDrvOutput(const Realisation & info, CheckSigsFlag check
 
 void LocalStore::registerDrvOutput(const Realisation & info)
 {
-    settings.requireExperimentalFeature("ca-derivations");
-    auto state(_state.lock());
+    settings.requireExperimentalFeature(Xp::CaDerivations);
     retrySQLite<void>([&]() {
-        state->stmts->RegisterRealisedOutput.use()
-            (info.id.strHash())
-            (info.id.outputName)
-            (printStorePath(info.outPath))
-            (concatStringsSep(" ", info.signatures))
-            .exec();
+        auto state(_state.lock());
+        if (auto oldR = queryRealisation_(*state, info.id)) {
+            if (info.isCompatibleWith(*oldR)) {
+                auto combinedSignatures = oldR->signatures;
+                combinedSignatures.insert(info.signatures.begin(),
+                    info.signatures.end());
+                state->stmts->UpdateRealisedOutput.use()
+                    (concatStringsSep(" ", combinedSignatures))
+                    (info.id.strHash())
+                    (info.id.outputName)
+                    .exec();
+            } else {
+                throw Error("Trying to register a realisation of '%s', but we already "
+                            "have another one locally.\n"
+                            "Local:  %s\n"
+                            "Remote: %s",
+                    info.id.to_string(),
+                    printStorePath(oldR->outPath),
+                    printStorePath(info.outPath)
+                );
+            }
+        } else {
+            state->stmts->RegisterRealisedOutput.use()
+                (info.id.strHash())
+                (info.id.outputName)
+                (printStorePath(info.outPath))
+                (concatStringsSep(" ", info.signatures))
+                .exec();
+        }
+        for (auto & [outputId, depPath] : info.dependentRealisations) {
+            auto localRealisation = queryRealisationCore_(*state, outputId);
+            if (!localRealisation)
+                throw Error("unable to register the derivation '%s' as it "
+                            "depends on the non existent '%s'",
+                    info.id.to_string(), outputId.to_string());
+            if (localRealisation->second.outPath != depPath)
+                throw Error("unable to register the derivation '%s' as it "
+                            "depends on a realisation of '%s' that doesn’t"
+                            "match what we have locally",
+                    info.id.to_string(), outputId.to_string());
+            state->stmts->AddRealisationReference.use()
+                (info.id.strHash())
+                (info.id.outputName)
+                (outputId.strHash())
+                (outputId.outputName)
+                .exec();
+        }
     });
 }
 
@@ -731,7 +831,7 @@ uint64_t LocalStore::addValidPath(State & state,
 
     {
         auto state_(Store::state.lock());
-        state_->pathInfoCache.upsert(std::string(info.path.hashPart()),
+        state_->pathInfoCache.upsert(std::string(info.path.to_string()),
             PathInfoCacheValue{ .value = std::make_shared<const ValidPathInfo>(info) });
     }
 
@@ -909,7 +1009,7 @@ LocalStore::queryPartialDerivationOutputMap(const StorePath & path_)
         return outputs;
     });
 
-    if (!settings.isExperimentalFeatureEnabled("ca-derivations"))
+    if (!settings.isExperimentalFeatureEnabled(Xp::CaDerivations))
         return outputs;
 
     auto drv = readInvalidDerivation(path);
@@ -977,14 +1077,19 @@ StorePathSet LocalStore::querySubstitutablePaths(const StorePathSet & paths)
 }
 
 
+// FIXME: move this, it's not specific to LocalStore.
 void LocalStore::querySubstitutablePathInfos(const StorePathCAMap & paths, SubstitutablePathInfos & infos)
 {
     if (!settings.useSubstitutes) return;
     for (auto & sub : getDefaultSubstituters()) {
         for (auto & path : paths) {
+            if (infos.count(path.first))
+                // Choose first succeeding substituter.
+                continue;
+
             auto subPath(path.first);
 
-            // recompute store path so that we can use a different store root
+            // Recompute store path so that we can use a different store root.
             if (path.second) {
                 subPath = makeFixedOutputPathFromCA(path.first.name(), *path.second);
                 if (sub->storeDir == storeDir)
@@ -1099,7 +1204,7 @@ void LocalStore::invalidatePath(State & state, const StorePath & path)
 
     {
         auto state_(Store::state.lock());
-        state_->pathInfoCache.erase(std::string(path.hashPart()));
+        state_->pathInfoCache.erase(std::string(path.to_string()));
     }
 }
 
@@ -1145,24 +1250,15 @@ void LocalStore::addToStore(const ValidPathInfo & info, Source & source,
 
             deletePath(realPath);
 
-            // text hashing has long been allowed to have non-self-references because it is used for drv files.
-            bool refersToSelf = info.references.count(info.path) > 0;
-            if (info.ca.has_value() && !info.references.empty() && !(std::holds_alternative<TextHash>(*info.ca) && !refersToSelf))
-                settings.requireExperimentalFeature("ca-references");
-
             /* While restoring the path from the NAR, compute the hash
                of the NAR. */
-            std::unique_ptr<AbstractHashSink> hashSink;
-            if (!info.ca.has_value() || !info.references.count(info.path))
-                hashSink = std::make_unique<HashSink>(htSHA256);
-            else
-                hashSink = std::make_unique<HashModuloSink>(htSHA256, std::string(info.path.hashPart()));
+            HashSink hashSink(htSHA256);
 
-            TeeSource wrapperSource { source, *hashSink };
+            TeeSource wrapperSource { source, hashSink };
 
             restorePath(realPath, wrapperSource);
 
-            auto hashResult = hashSink->finish();
+            auto hashResult = hashSink.finish();
 
             if (hashResult.first != info.narHash)
                 throw Error("hash mismatch importing path '%s';\n  specified: %s\n  got:       %s",
@@ -1172,6 +1268,31 @@ void LocalStore::addToStore(const ValidPathInfo & info, Source & source,
                 throw Error("size mismatch importing path '%s';\n  specified: %s\n  got:       %s",
                     printStorePath(info.path), info.narSize, hashResult.second);
 
+            if (info.ca) {
+                if (auto foHash = std::get_if<FixedOutputHash>(&*info.ca)) {
+                    auto actualFoHash = hashCAPath(
+                        foHash->method,
+                        foHash->hash.type,
+                        info.path
+                    );
+                    if (foHash->hash != actualFoHash.hash) {
+                        throw Error("ca hash mismatch importing path '%s';\n  specified: %s\n  got:       %s",
+                            printStorePath(info.path),
+                            foHash->hash.to_string(Base32, true),
+                            actualFoHash.hash.to_string(Base32, true));
+                    }
+                }
+                if (auto textHash = std::get_if<TextHash>(&*info.ca)) {
+                    auto actualTextHash = hashString(htSHA256, readFile(realPath));
+                    if (textHash->hash != actualTextHash) {
+                        throw Error("ca hash mismatch importing path '%s';\n  specified: %s\n  got:       %s",
+                            printStorePath(info.path),
+                            textHash->hash.to_string(Base32, true),
+                            actualTextHash.to_string(Base32, true));
+                    }
+                }
+            }
+
             autoGC();
 
             canonicalisePathMetaData(realPath, -1);
@@ -1187,7 +1308,7 @@ void LocalStore::addToStore(const ValidPathInfo & info, Source & source,
 
 
 StorePath LocalStore::addToStoreFromDump(Source & source0, const string & name,
-    FileIngestionMethod method, HashType hashAlgo, RepairFlag repair)
+    FileIngestionMethod method, HashType hashAlgo, RepairFlag repair, const StorePathSet & references)
 {
     /* For computing the store path. */
     auto hashSink = std::make_unique<HashSink>(hashAlgo);
@@ -1243,7 +1364,7 @@ StorePath LocalStore::addToStoreFromDump(Source & source0, const string & name,
 
     auto [hash, size] = hashSink->finish();
 
-    auto dstPath = makeFixedOutputPath(method, hash, name);
+    auto dstPath = makeFixedOutputPath(method, hash, name, references);
 
     addTempRoot(dstPath);
 
@@ -1290,6 +1411,7 @@ StorePath LocalStore::addToStoreFromDump(Source & source0, const string & name,
 
             ValidPathInfo info { dstPath, narHash.first };
             info.narSize = narHash.second;
+            info.references = references;
             info.ca = FixedOutputHash { .method = method, .hash = hash };
             registerValidPath(info);
         }
@@ -1390,7 +1512,8 @@ bool LocalStore::verifyStore(bool checkContents, RepairFlag repair)
 
     /* Acquire the global GC lock to get a consistent snapshot of
        existing and valid paths. */
-    AutoCloseFD fdGCLock = openGCLock(ltWrite);
+    auto fdGCLock = openGCLock();
+    FdLock gcLock(fdGCLock.get(), ltRead, true, "waiting for the big garbage collector lock...");
 
     StringSet store;
     for (auto & i : readDirectory(realStoreDir)) store.insert(i.name);
@@ -1401,8 +1524,6 @@ bool LocalStore::verifyStore(bool checkContents, RepairFlag repair)
     StorePathSet validPaths;
     PathSet done;
 
-    fdGCLock = -1;
-
     for (auto & i : queryAllValidPaths())
         verifyPath(printStorePath(i), store, done, validPaths, repair, errors);
 
@@ -1440,14 +1561,10 @@ bool LocalStore::verifyStore(bool checkContents, RepairFlag repair)
                 /* Check the content hash (optionally - slow). */
                 printMsg(lvlTalkative, "checking contents of '%s'", printStorePath(i));
 
-                std::unique_ptr<AbstractHashSink> hashSink;
-                if (!info->ca || !info->references.count(info->path))
-                    hashSink = std::make_unique<HashSink>(info->narHash.type);
-                else
-                    hashSink = std::make_unique<HashModuloSink>(info->narHash.type, std::string(info->path.hashPart()));
+                auto hashSink = HashSink(info->narHash.type);
 
-                dumpPath(Store::toRealPath(i), *hashSink);
-                auto current = hashSink->finish();
+                dumpPath(Store::toRealPath(i), hashSink);
+                auto current = hashSink.finish();
 
                 if (info->narHash != nullHash && info->narHash != current.first) {
                     printError("path '%s' was modified! expected hash '%s', got '%s'",
@@ -1665,19 +1782,108 @@ void LocalStore::createUser(const std::string & userName, uid_t userId)
     }
 }
 
-std::optional<const Realisation> LocalStore::queryRealisation(
-    const DrvOutput& id) {
-    typedef std::optional<const Realisation> Ret;
-    return retrySQLite<Ret>([&]() -> Ret {
-        auto state(_state.lock());
-        auto use(state->stmts->QueryRealisedOutput.use()(id.strHash())(
-            id.outputName));
-        if (!use.next())
-            return std::nullopt;
-        auto outputPath = parseStorePath(use.getStr(0));
-        auto signatures = tokenizeString<StringSet>(use.getStr(1));
-        return Ret{Realisation{
-            .id = id, .outPath = outputPath, .signatures = signatures}};
-    });
+std::optional<std::pair<int64_t, Realisation>> LocalStore::queryRealisationCore_(
+        LocalStore::State & state,
+        const DrvOutput & id)
+{
+    auto useQueryRealisedOutput(
+            state.stmts->QueryRealisedOutput.use()
+                (id.strHash())
+                (id.outputName));
+    if (!useQueryRealisedOutput.next())
+        return std::nullopt;
+    auto realisationDbId = useQueryRealisedOutput.getInt(0);
+    auto outputPath = parseStorePath(useQueryRealisedOutput.getStr(1));
+    auto signatures =
+        tokenizeString<StringSet>(useQueryRealisedOutput.getStr(2));
+
+    return {{
+        realisationDbId,
+        Realisation{
+            .id = id,
+            .outPath = outputPath,
+            .signatures = signatures,
+        }
+    }};
+}
+
+std::optional<const Realisation> LocalStore::queryRealisation_(
+            LocalStore::State & state,
+            const DrvOutput & id)
+{
+    auto maybeCore = queryRealisationCore_(state, id);
+    if (!maybeCore)
+        return std::nullopt;
+    auto [realisationDbId, res] = *maybeCore;
+
+    std::map<DrvOutput, StorePath> dependentRealisations;
+    auto useRealisationRefs(
+        state.stmts->QueryRealisationReferences.use()
+            (realisationDbId));
+    while (useRealisationRefs.next()) {
+        auto depId = DrvOutput {
+            Hash::parseAnyPrefixed(useRealisationRefs.getStr(0)),
+            useRealisationRefs.getStr(1),
+        };
+        auto dependentRealisation = queryRealisationCore_(state, depId);
+        assert(dependentRealisation); // Enforced by the db schema
+        auto outputPath = dependentRealisation->second.outPath;
+        dependentRealisations.insert({depId, outputPath});
+    }
+
+    res.dependentRealisations = dependentRealisations;
+
+    return { res };
+}
+
+void LocalStore::queryRealisationUncached(const DrvOutput & id,
+        Callback<std::shared_ptr<const Realisation>> callback) noexcept
+{
+    try {
+        auto maybeRealisation
+            = retrySQLite<std::optional<const Realisation>>([&]() {
+                  auto state(_state.lock());
+                  return queryRealisation_(*state, id);
+              });
+        if (maybeRealisation)
+            callback(
+                std::make_shared<const Realisation>(maybeRealisation.value()));
+        else
+            callback(nullptr);
+
+    } catch (...) {
+        callback.rethrow();
+    }
+}
+
+FixedOutputHash LocalStore::hashCAPath(
+    const FileIngestionMethod & method, const HashType & hashType,
+    const StorePath & path)
+{
+    return hashCAPath(method, hashType, Store::toRealPath(path), path.hashPart());
+}
+
+FixedOutputHash LocalStore::hashCAPath(
+    const FileIngestionMethod & method,
+    const HashType & hashType,
+    const Path & path,
+    const std::string_view pathHash
+)
+{
+    HashModuloSink caSink ( hashType, std::string(pathHash) );
+    switch (method) {
+    case FileIngestionMethod::Recursive:
+        dumpPath(path, caSink);
+        break;
+    case FileIngestionMethod::Flat:
+        readFile(path, caSink);
+        break;
+    }
+    auto hash = caSink.finish().first;
+    return FixedOutputHash{
+        .method = method,
+        .hash = hash,
+    };
 }
+
 }  // namespace nix
diff --git a/src/libstore/local-store.hh b/src/libstore/local-store.hh
index 26e034a82..115ea046a 100644
--- a/src/libstore/local-store.hh
+++ b/src/libstore/local-store.hh
@@ -58,9 +58,15 @@ private:
         struct Stmts;
         std::unique_ptr<Stmts> stmts;
 
+        /* The global GC lock  */
+        AutoCloseFD fdGCLock;
+
         /* The file to which we write our temporary roots. */
         AutoCloseFD fdTempRoots;
 
+        /* Connection to the garbage collector. */
+        AutoCloseFD fdRootsSocket;
+
         /* The last time we checked whether to do an auto-GC, or an
            auto-GC finished. */
         std::chrono::time_point<std::chrono::steady_clock> lastGCCheck;
@@ -83,14 +89,10 @@ private:
 
 public:
 
-    PathSetting realStoreDir_;
-
-    const Path realStoreDir;
     const Path dbDir;
     const Path linksDir;
     const Path reservedPath;
     const Path schemaPath;
-    const Path trashDir;
     const Path tempRootsDir;
     const Path fnTempRoots;
 
@@ -143,7 +145,7 @@ public:
         RepairFlag repair, CheckSigsFlag checkSigs) override;
 
     StorePath addToStoreFromDump(Source & dump, const string & name,
-        FileIngestionMethod method, HashType hashAlgo, RepairFlag repair) override;
+        FileIngestionMethod method, HashType hashAlgo, RepairFlag repair, const StorePathSet & references) override;
 
     StorePath addTextToStore(const string & name, const string & s,
         const StorePathSet & references, RepairFlag repair) override;
@@ -152,14 +154,11 @@ public:
 
     void addIndirectRoot(const Path & path) override;
 
-    void syncWithGC() override;
-
 private:
 
-    typedef std::shared_ptr<AutoCloseFD> FDPtr;
-    typedef list<FDPtr> FDs;
+    void findTempRoots(Roots & roots, bool censor);
 
-    void findTempRoots(FDs & fds, Roots & roots, bool censor);
+    AutoCloseFD openGCLock();
 
 public:
 
@@ -206,7 +205,10 @@ public:
     void registerDrvOutput(const Realisation & info, CheckSigsFlag checkSigs) override;
     void cacheDrvOutputMapping(State & state, const uint64_t deriver, const string & outputName, const StorePath & output);
 
-    std::optional<const Realisation> queryRealisation(const DrvOutput&) override;
+    std::optional<const Realisation> queryRealisation_(State & state, const DrvOutput & id);
+    std::optional<std::pair<int64_t, Realisation>> queryRealisationCore_(State & state, const DrvOutput & id);
+    void queryRealisationUncached(const DrvOutput&,
+        Callback<std::shared_ptr<const Realisation>> callback) noexcept override;
 
 private:
 
@@ -237,29 +239,12 @@ private:
     PathSet queryValidPathsOld();
     ValidPathInfo queryPathInfoOld(const Path & path);
 
-    struct GCState;
-
-    void deleteGarbage(GCState & state, const Path & path);
-
-    void tryToDelete(GCState & state, const Path & path);
-
-    bool canReachRoot(GCState & state, StorePathSet & visited, const StorePath & path);
-
-    void deletePathRecursive(GCState & state, const Path & path);
-
-    bool isActiveTempFile(const GCState & state,
-        const Path & path, const string & suffix);
-
-    AutoCloseFD openGCLock(LockType lockType);
-
     void findRoots(const Path & path, unsigned char type, Roots & roots);
 
     void findRootsNoTemp(Roots & roots, bool censor);
 
     void findRuntimeRoots(Roots & roots, bool censor);
 
-    void removeUnusedLinks(const GCState & state);
-
     Path createTempDirInStore();
 
     void checkDerivationOutputs(const StorePath & drvPath, const Derivation & drv);
@@ -279,10 +264,21 @@ private:
     void signPathInfo(ValidPathInfo & info);
     void signRealisation(Realisation &);
 
-    Path getRealStoreDir() override { return realStoreDir; }
-
     void createUser(const std::string & userName, uid_t userId) override;
 
+    // XXX: Make a generic `Store` method
+    FixedOutputHash hashCAPath(
+        const FileIngestionMethod & method,
+        const HashType & hashType,
+        const StorePath & path);
+
+    FixedOutputHash hashCAPath(
+        const FileIngestionMethod & method,
+        const HashType & hashType,
+        const Path & path,
+        const std::string_view pathHash
+    );
+
     friend struct LocalDerivationGoal;
     friend struct PathSubstitutionGoal;
     friend struct SubstitutionGoal;
diff --git a/src/libstore/local.mk b/src/libstore/local.mk
index cf0933705..b992bcbc0 100644
--- a/src/libstore/local.mk
+++ b/src/libstore/local.mk
@@ -8,12 +8,12 @@ libstore_SOURCES := $(wildcard $(d)/*.cc $(d)/builtins/*.cc $(d)/build/*.cc)
 
 libstore_LIBS = libutil
 
-libstore_LDFLAGS = $(SQLITE3_LIBS) -lbz2 $(LIBCURL_LIBS) $(SODIUM_LIBS) -pthread
-ifneq ($(OS), FreeBSD)
+libstore_LDFLAGS += $(SQLITE3_LIBS) $(LIBCURL_LIBS) $(SODIUM_LIBS) -pthread
+ifdef HOST_LINUX
  libstore_LDFLAGS += -ldl
 endif
 
-ifeq ($(OS), Darwin)
+ifdef HOST_DARWIN
 libstore_FILES = sandbox-defaults.sb sandbox-minimal.sb sandbox-network.sb
 endif
 
@@ -23,7 +23,7 @@ ifeq ($(ENABLE_S3), 1)
 	libstore_LDFLAGS += -laws-cpp-sdk-transfer -laws-cpp-sdk-s3 -laws-cpp-sdk-core
 endif
 
-ifeq ($(OS), SunOS)
+ifdef HOST_SOLARIS
 	libstore_LDFLAGS += -lsocket
 endif
 
@@ -60,7 +60,7 @@ $(d)/build.cc:
 
 clean-files += $(d)/schema.sql.gen.hh $(d)/ca-specific-schema.sql.gen.hh
 
-$(eval $(call install-file-in, $(d)/nix-store.pc, $(prefix)/lib/pkgconfig, 0644))
+$(eval $(call install-file-in, $(d)/nix-store.pc, $(libdir)/pkgconfig, 0644))
 
 $(foreach i, $(wildcard src/libstore/builtins/*.hh), \
   $(eval $(call install-file-in, $(i), $(includedir)/nix/builtins, 0644)))
diff --git a/src/libstore/machines.cc b/src/libstore/machines.cc
index b42e5e434..b6270a81b 100644
--- a/src/libstore/machines.cc
+++ b/src/libstore/machines.cc
@@ -16,13 +16,18 @@ Machine::Machine(decltype(storeUri) storeUri,
     decltype(mandatoryFeatures) mandatoryFeatures,
     decltype(sshPublicHostKey) sshPublicHostKey) :
     storeUri(
-        // Backwards compatibility: if the URI is a hostname,
-        // prepend ssh://.
+        // Backwards compatibility: if the URI is schemeless, is not a path,
+        // and is not one of the special store connection words, prepend
+        // ssh://.
         storeUri.find("://") != std::string::npos
-        || hasPrefix(storeUri, "local")
-        || hasPrefix(storeUri, "remote")
-        || hasPrefix(storeUri, "auto")
-        || hasPrefix(storeUri, "/")
+        || storeUri.find("/") != std::string::npos
+        || storeUri == "auto"
+        || storeUri == "daemon"
+        || storeUri == "local"
+        || hasPrefix(storeUri, "auto?")
+        || hasPrefix(storeUri, "daemon?")
+        || hasPrefix(storeUri, "local?")
+        || hasPrefix(storeUri, "?")
         ? storeUri
         : "ssh://" + storeUri),
     systemTypes(systemTypes),
@@ -34,7 +39,8 @@ Machine::Machine(decltype(storeUri) storeUri,
     sshPublicHostKey(sshPublicHostKey)
 {}
 
-bool Machine::allSupported(const std::set<string> & features) const {
+bool Machine::allSupported(const std::set<string> & features) const
+{
     return std::all_of(features.begin(), features.end(),
         [&](const string & feature) {
             return supportedFeatures.count(feature) ||
@@ -42,14 +48,16 @@ bool Machine::allSupported(const std::set<string> & features) const {
         });
 }
 
-bool Machine::mandatoryMet(const std::set<string> & features) const {
+bool Machine::mandatoryMet(const std::set<string> & features) const
+{
     return std::all_of(mandatoryFeatures.begin(), mandatoryFeatures.end(),
         [&](const string & feature) {
             return features.count(feature);
         });
 }
 
-ref<Store> Machine::openStore() const {
+ref<Store> Machine::openStore() const
+{
     Store::Params storeParams;
     if (hasPrefix(storeUri, "ssh://")) {
         storeParams["max-connections"] = "1";
@@ -78,53 +86,86 @@ ref<Store> Machine::openStore() const {
     return nix::openStore(storeUri, storeParams);
 }
 
-void parseMachines(const std::string & s, Machines & machines)
+static std::vector<std::string> expandBuilderLines(const std::string & builders)
 {
-    for (auto line : tokenizeString<std::vector<string>>(s, "\n;")) {
+    std::vector<std::string> result;
+    for (auto line : tokenizeString<std::vector<string>>(builders, "\n;")) {
         trim(line);
         line.erase(std::find(line.begin(), line.end(), '#'), line.end());
         if (line.empty()) continue;
 
         if (line[0] == '@') {
-            auto file = trim(std::string(line, 1));
+            const std::string path = trim(std::string(line, 1));
+            std::string text;
             try {
-                parseMachines(readFile(file), machines);
+                text = readFile(path);
             } catch (const SysError & e) {
                 if (e.errNo != ENOENT)
                     throw;
-                debug("cannot find machines file '%s'", file);
+                debug("cannot find machines file '%s'", path);
             }
+
+            const auto lines = expandBuilderLines(text);
+            result.insert(end(result), begin(lines), end(lines));
             continue;
         }
 
-        auto tokens = tokenizeString<std::vector<string>>(line);
-        auto sz = tokens.size();
-        if (sz < 1)
-            throw FormatError("bad machine specification '%s'", line);
+        result.emplace_back(line);
+    }
+    return result;
+}
 
-        auto isSet = [&](size_t n) {
-            return tokens.size() > n && tokens[n] != "" && tokens[n] != "-";
-        };
+static Machine parseBuilderLine(const std::string & line)
+{
+    const auto tokens = tokenizeString<std::vector<string>>(line);
 
-        machines.emplace_back(tokens[0],
-            isSet(1) ? tokenizeString<std::vector<string>>(tokens[1], ",") : std::vector<string>{settings.thisSystem},
-            isSet(2) ? tokens[2] : "",
-            isSet(3) ? std::stoull(tokens[3]) : 1LL,
-            isSet(4) ? std::stoull(tokens[4]) : 1LL,
-            isSet(5) ? tokenizeString<std::set<string>>(tokens[5], ",") : std::set<string>{},
-            isSet(6) ? tokenizeString<std::set<string>>(tokens[6], ",") : std::set<string>{},
-            isSet(7) ? tokens[7] : "");
-    }
+    auto isSet = [&](size_t fieldIndex) {
+        return tokens.size() > fieldIndex && tokens[fieldIndex] != "" && tokens[fieldIndex] != "-";
+    };
+
+    auto parseUnsignedIntField = [&](size_t fieldIndex) {
+        const auto result = string2Int<unsigned int>(tokens[fieldIndex]);
+        if (!result) {
+            throw FormatError("bad machine specification: failed to convert column #%lu in a row: '%s' to 'unsigned int'", fieldIndex, line);
+        }
+        return result.value();
+    };
+
+    auto ensureBase64 = [&](size_t fieldIndex) {
+        const auto & str = tokens[fieldIndex];
+        try {
+            base64Decode(str);
+        } catch (const Error & e) {
+            throw FormatError("bad machine specification: a column #%lu in a row: '%s' is not valid base64 string: %s", fieldIndex, line, e.what());
+        }
+        return str;
+    };
+
+    if (!isSet(0))
+        throw FormatError("bad machine specification: store URL was not found at the first column of a row: '%s'", line);
+
+    return {
+        tokens[0],
+        isSet(1) ? tokenizeString<std::vector<string>>(tokens[1], ",") : std::vector<string>{settings.thisSystem},
+        isSet(2) ? tokens[2] : "",
+        isSet(3) ? parseUnsignedIntField(3) : 1U,
+        isSet(4) ? parseUnsignedIntField(4) : 1U,
+        isSet(5) ? tokenizeString<std::set<string>>(tokens[5], ",") : std::set<string>{},
+        isSet(6) ? tokenizeString<std::set<string>>(tokens[6], ",") : std::set<string>{},
+        isSet(7) ? ensureBase64(7) : ""
+    };
+}
+
+static Machines parseBuilderLines(const std::vector<std::string>& builders) {
+    Machines result;
+    std::transform(builders.begin(), builders.end(), std::back_inserter(result), parseBuilderLine);
+    return result;
 }
 
 Machines getMachines()
 {
-    static auto machines = [&]() {
-        Machines machines;
-        parseMachines(settings.builders, machines);
-        return machines;
-    }();
-    return machines;
+    const auto builderLines = expandBuilderLines(settings.builders);
+    return parseBuilderLines(builderLines);
 }
 
 }
diff --git a/src/libstore/misc.cc b/src/libstore/misc.cc
index a99a2fc78..32786e963 100644
--- a/src/libstore/misc.cc
+++ b/src/libstore/misc.cc
@@ -6,98 +6,73 @@
 #include "thread-pool.hh"
 #include "topo-sort.hh"
 #include "callback.hh"
+#include "closure.hh"
 
 namespace nix {
 
-
 void Store::computeFSClosure(const StorePathSet & startPaths,
     StorePathSet & paths_, bool flipDirection, bool includeOutputs, bool includeDerivers)
 {
-    struct State
-    {
-        size_t pending;
-        StorePathSet & paths;
-        std::exception_ptr exc;
-    };
-
-    Sync<State> state_(State{0, paths_, 0});
-
-    std::function<void(const StorePath &)> enqueue;
-
-    std::condition_variable done;
-
-    enqueue = [&](const StorePath & path) -> void {
-        {
-            auto state(state_.lock());
-            if (state->exc) return;
-            if (!state->paths.insert(path).second) return;
-            state->pending++;
-        }
-
-        queryPathInfo(path, {[&](std::future<ref<const ValidPathInfo>> fut) {
-            // FIXME: calls to isValidPath() should be async
-
-            try {
-                auto info = fut.get();
-
-                if (flipDirection) {
-
-                    StorePathSet referrers;
-                    queryReferrers(path, referrers);
-                    for (auto & ref : referrers)
-                        if (ref != path)
-                            enqueue(ref);
-
-                    if (includeOutputs)
-                        for (auto & i : queryValidDerivers(path))
-                            enqueue(i);
-
-                    if (includeDerivers && path.isDerivation())
-                        for (auto & i : queryDerivationOutputs(path))
-                            if (isValidPath(i) && queryPathInfo(i)->deriver == path)
-                                enqueue(i);
-
-                } else {
-
-                    for (auto & ref : info->references)
-                        if (ref != path)
-                            enqueue(ref);
-
-                    if (includeOutputs && path.isDerivation())
-                        for (auto & i : queryDerivationOutputs(path))
-                            if (isValidPath(i)) enqueue(i);
-
-                    if (includeDerivers && info->deriver && isValidPath(*info->deriver))
-                        enqueue(*info->deriver);
-
-                }
-
-                {
-                    auto state(state_.lock());
-                    assert(state->pending);
-                    if (!--state->pending) done.notify_one();
-                }
-
-            } catch (...) {
-                auto state(state_.lock());
-                if (!state->exc) state->exc = std::current_exception();
-                assert(state->pending);
-                if (!--state->pending) done.notify_one();
-            };
-        }});
-    };
-
-    for (auto & startPath : startPaths)
-        enqueue(startPath);
-
-    {
-        auto state(state_.lock());
-        while (state->pending) state.wait(done);
-        if (state->exc) std::rethrow_exception(state->exc);
-    }
+    std::function<std::set<StorePath>(const StorePath & path, std::future<ref<const ValidPathInfo>> &)> queryDeps;
+    if (flipDirection)
+        queryDeps = [&](const StorePath& path,
+                        std::future<ref<const ValidPathInfo>> & fut) {
+            StorePathSet res;
+            StorePathSet referrers;
+            queryReferrers(path, referrers);
+            for (auto& ref : referrers)
+                if (ref != path)
+                    res.insert(ref);
+
+            if (includeOutputs)
+                for (auto& i : queryValidDerivers(path))
+                    res.insert(i);
+
+            if (includeDerivers && path.isDerivation())
+                for (auto& [_, maybeOutPath] : queryPartialDerivationOutputMap(path))
+                    if (maybeOutPath && isValidPath(*maybeOutPath))
+                        res.insert(*maybeOutPath);
+            return res;
+        };
+    else
+        queryDeps = [&](const StorePath& path,
+                        std::future<ref<const ValidPathInfo>> & fut) {
+            StorePathSet res;
+            auto info = fut.get();
+            for (auto& ref : info->references)
+                if (ref != path)
+                    res.insert(ref);
+
+            if (includeOutputs && path.isDerivation())
+                for (auto& [_, maybeOutPath] : queryPartialDerivationOutputMap(path))
+                    if (maybeOutPath && isValidPath(*maybeOutPath))
+                        res.insert(*maybeOutPath);
+
+            if (includeDerivers && info->deriver && isValidPath(*info->deriver))
+                res.insert(*info->deriver);
+            return res;
+        };
+
+    computeClosure<StorePath>(
+        startPaths, paths_,
+        [&](const StorePath& path,
+            std::function<void(std::promise<std::set<StorePath>>&)>
+                processEdges) {
+            std::promise<std::set<StorePath>> promise;
+            std::function<void(std::future<ref<const ValidPathInfo>>)>
+                getDependencies =
+                    [&](std::future<ref<const ValidPathInfo>> fut) {
+                        try {
+                            promise.set_value(queryDeps(path, fut));
+                        } catch (...) {
+                            promise.set_exception(std::current_exception());
+                        }
+                    };
+            queryPathInfo(path, getDependencies);
+            processEdges(promise);
+        });
 }
 
-
 void Store::computeFSClosure(const StorePath & startPath,
     StorePathSet & paths_, bool flipDirection, bool includeOutputs, bool includeDerivers)
 {
@@ -191,7 +166,7 @@ void Store::queryMissing(const std::vector<DerivedPath> & targets,
         }
 
         std::visit(overloaded {
-          [&](DerivedPath::Built bfd) {
+          [&](const DerivedPath::Built & bfd) {
             if (!isValidPath(bfd.drvPath)) {
                 // FIXME: we could try to substitute the derivation.
                 auto state(state_.lock());
@@ -224,7 +199,7 @@ void Store::queryMissing(const std::vector<DerivedPath> & targets,
                 mustBuildDrv(bfd.drvPath, *drv);
 
           },
-          [&](DerivedPath::Opaque bo) {
+          [&](const DerivedPath::Opaque & bo) {
 
             if (isValidPath(bo.path)) return;
 
@@ -264,12 +239,11 @@ StorePaths Store::topoSortPaths(const StorePathSet & paths)
 {
     return topoSort(paths,
         {[&](const StorePath & path) {
-            StorePathSet references;
             try {
-                references = queryPathInfo(path)->references;
+                return queryPathInfo(path)->references;
             } catch (InvalidPath &) {
+                return StorePathSet();
             }
-            return references;
         }},
         {[&](const StorePath & path, const StorePath & parent) {
             return BuildError(
@@ -279,5 +253,44 @@ StorePaths Store::topoSortPaths(const StorePathSet & paths)
         }});
 }
 
+std::map<DrvOutput, StorePath> drvOutputReferences(
+    const std::set<Realisation> & inputRealisations,
+    const StorePathSet & pathReferences)
+{
+    std::map<DrvOutput, StorePath> res;
 
+    for (const auto & input : inputRealisations) {
+        if (pathReferences.count(input.outPath)) {
+            res.insert({input.id, input.outPath});
+        }
+    }
+
+    return res;
+}
+
+std::map<DrvOutput, StorePath> drvOutputReferences(
+    Store & store,
+    const Derivation & drv,
+    const StorePath & outputPath)
+{
+    std::set<Realisation> inputRealisations;
+
+    for (const auto& [inputDrv, outputNames] : drv.inputDrvs) {
+        auto outputHashes =
+            staticOutputHashes(store, store.readDerivation(inputDrv));
+        for (const auto& outputName : outputNames) {
+            auto thisRealisation = store.queryRealisation(
+                DrvOutput{outputHashes.at(outputName), outputName});
+            if (!thisRealisation)
+                throw Error(
+                    "output '%s' of derivation '%s' isn’t built", outputName,
+                    store.printStorePath(inputDrv));
+            inputRealisations.insert(*thisRealisation);
+        }
+    }
+
+    auto info = store.queryPathInfo(outputPath);
+
+    return drvOutputReferences(Realisation::closure(store, inputRealisations), info->references);
+}
 }
diff --git a/src/libstore/nar-info-disk-cache.cc b/src/libstore/nar-info-disk-cache.cc
index 1d8d2d57e..9dd81ddfb 100644
--- a/src/libstore/nar-info-disk-cache.cc
+++ b/src/libstore/nar-info-disk-cache.cc
@@ -4,6 +4,7 @@
 #include "globals.hh"
 
 #include <sqlite3.h>
+#include <nlohmann/json.hpp>
 
 namespace nix {
 
@@ -38,6 +39,15 @@ create table if not exists NARs (
     foreign key (cache) references BinaryCaches(id) on delete cascade
 );
 
+create table if not exists Realisations (
+    cache integer not null,
+    outputId text not null,
+    content blob, -- Json serialisation of the realisation, or null if the realisation is absent
+    timestamp        integer not null,
+    primary key (cache, outputId),
+    foreign key (cache) references BinaryCaches(id) on delete cascade
+);
+
 create table if not exists LastPurge (
     dummy            text primary key,
     value            integer
@@ -63,7 +73,9 @@ public:
     struct State
     {
         SQLite db;
-        SQLiteStmt insertCache, queryCache, insertNAR, insertMissingNAR, queryNAR, purgeCache;
+        SQLiteStmt insertCache, queryCache, insertNAR, insertMissingNAR,
+            queryNAR, insertRealisation, insertMissingRealisation,
+            queryRealisation, purgeCache;
         std::map<std::string, Cache> caches;
     };
 
@@ -98,6 +110,26 @@ public:
         state->queryNAR.create(state->db,
             "select present, namePart, url, compression, fileHash, fileSize, narHash, narSize, refs, deriver, sigs, ca from NARs where cache = ? and hashPart = ? and ((present = 0 and timestamp > ?) or (present = 1 and timestamp > ?))");
 
+        state->insertRealisation.create(state->db,
+            R"(
+                insert or replace into Realisations(cache, outputId, content, timestamp)
+                    values (?, ?, ?, ?)
+            )");
+
+        state->insertMissingRealisation.create(state->db,
+            R"(
+                insert or replace into Realisations(cache, outputId, timestamp)
+                    values (?, ?, ?)
+            )");
+
+        state->queryRealisation.create(state->db,
+            R"(
+                select content from Realisations
+                    where cache = ? and outputId = ?  and
+                        ((content is null and timestamp > ?) or
+                         (content is not null and timestamp > ?))
+            )");
+
         /* Periodically purge expired entries from the database. */
         retrySQLite<void>([&]() {
             auto now = time(0);
@@ -212,6 +244,38 @@ public:
         });
     }
 
+    std::pair<Outcome, std::shared_ptr<Realisation>> lookupRealisation(
+        const std::string & uri, const DrvOutput & id) override
+    {
+        return retrySQLite<std::pair<Outcome, std::shared_ptr<Realisation>>>(
+            [&]() -> std::pair<Outcome, std::shared_ptr<Realisation>> {
+            auto state(_state.lock());
+
+            auto & cache(getCache(*state, uri));
+
+            auto now = time(0);
+
+            auto queryRealisation(state->queryRealisation.use()
+                (cache.id)
+                (id.to_string())
+                (now - settings.ttlNegativeNarInfoCache)
+                (now - settings.ttlPositiveNarInfoCache));
+
+            if (!queryRealisation.next())
+                return {oUnknown, 0};
+
+            if (queryRealisation.isNull(0))
+                return {oInvalid, 0};
+
+            auto realisation =
+                std::make_shared<Realisation>(Realisation::fromJSON(
+                    nlohmann::json::parse(queryRealisation.getStr(0)),
+                    "Local disk cache"));
+
+            return {oValid, realisation};
+        });
+    }
+
     void upsertNarInfo(
         const std::string & uri, const std::string & hashPart,
         std::shared_ptr<const ValidPathInfo> info) override
@@ -251,6 +315,39 @@ public:
             }
         });
     }
+
+    void upsertRealisation(
+        const std::string & uri,
+        const Realisation & realisation) override
+    {
+        retrySQLite<void>([&]() {
+            auto state(_state.lock());
+
+            auto & cache(getCache(*state, uri));
+
+            state->insertRealisation.use()
+                (cache.id)
+                (realisation.id.to_string())
+                (realisation.toJSON().dump())
+                (time(0)).exec();
+        });
+
+    }
+
+    virtual void upsertAbsentRealisation(
+        const std::string & uri,
+        const DrvOutput & id) override
+    {
+        retrySQLite<void>([&]() {
+            auto state(_state.lock());
+
+            auto & cache(getCache(*state, uri));
+            state->insertMissingRealisation.use()
+                (cache.id)
+                (id.to_string())
+                (time(0)).exec();
+        });
+    }
 };
 
 ref<NarInfoDiskCache> getNarInfoDiskCache()
diff --git a/src/libstore/nar-info-disk-cache.hh b/src/libstore/nar-info-disk-cache.hh
index 04de2c5eb..2dcaa76a4 100644
--- a/src/libstore/nar-info-disk-cache.hh
+++ b/src/libstore/nar-info-disk-cache.hh
@@ -2,6 +2,7 @@
 
 #include "ref.hh"
 #include "nar-info.hh"
+#include "realisation.hh"
 
 namespace nix {
 
@@ -29,6 +30,15 @@ public:
     virtual void upsertNarInfo(
         const std::string & uri, const std::string & hashPart,
         std::shared_ptr<const ValidPathInfo> info) = 0;
+
+    virtual void upsertRealisation(
+        const std::string & uri,
+        const Realisation & realisation) = 0;
+    virtual void upsertAbsentRealisation(
+        const std::string & uri,
+        const DrvOutput & id) = 0;
+    virtual std::pair<Outcome, std::shared_ptr<Realisation>> lookupRealisation(
+        const std::string & uri, const DrvOutput & id) = 0;
 };
 
 /* Return a singleton cache object that can be used concurrently by
diff --git a/src/libstore/optimise-store.cc b/src/libstore/optimise-store.cc
index 78d587139..d95e54af1 100644
--- a/src/libstore/optimise-store.cc
+++ b/src/libstore/optimise-store.cc
@@ -198,7 +198,7 @@ void LocalStore::optimisePath_(Activity * act, OptimiseStats & stats,
     /* Make the containing directory writable, but only if it's not
        the store itself (we don't want or need to mess with its
        permissions). */
-    bool mustToggle = dirOf(path) != realStoreDir;
+    bool mustToggle = dirOf(path) != realStoreDir.get();
     if (mustToggle) makeWritable(dirOf(path));
 
     /* When we're done, make the directory read-only again and reset
diff --git a/src/libstore/parsed-derivations.cc b/src/libstore/parsed-derivations.cc
index c5c3ae3dc..caddba9b1 100644
--- a/src/libstore/parsed-derivations.cc
+++ b/src/libstore/parsed-derivations.cc
@@ -1,6 +1,8 @@
 #include "parsed-derivations.hh"
 
 #include <nlohmann/json.hpp>
+#include <regex>
+#include "json.hh"
 
 namespace nix {
 
@@ -91,6 +93,8 @@ StringSet ParsedDerivation::getRequiredSystemFeatures() const
     StringSet res;
     for (auto & i : getStringsAttr("requiredSystemFeatures").value_or(Strings()))
         res.insert(i);
+    if (!derivationHasKnownOutputPaths(drv.type()))
+        res.insert("ca-derivations");
     return res;
 }
 
@@ -121,4 +125,107 @@ bool ParsedDerivation::substitutesAllowed() const
     return getBoolAttr("allowSubstitutes", true);
 }
 
+static std::regex shVarName("[A-Za-z_][A-Za-z0-9_]*");
+
+std::optional<nlohmann::json> ParsedDerivation::prepareStructuredAttrs(Store & store, const StorePathSet & inputPaths)
+{
+    auto structuredAttrs = getStructuredAttrs();
+    if (!structuredAttrs) return std::nullopt;
+
+    auto json = *structuredAttrs;
+
+    /* Add an "outputs" object containing the output paths. */
+    nlohmann::json outputs;
+    for (auto & i : drv.outputs)
+        outputs[i.first] = hashPlaceholder(i.first);
+    json["outputs"] = outputs;
+
+    /* Handle exportReferencesGraph. */
+    auto e = json.find("exportReferencesGraph");
+    if (e != json.end() && e->is_object()) {
+        for (auto i = e->begin(); i != e->end(); ++i) {
+            std::ostringstream str;
+            {
+                JSONPlaceholder jsonRoot(str, true);
+                StorePathSet storePaths;
+                for (auto & p : *i)
+                    storePaths.insert(store.parseStorePath(p.get<std::string>()));
+                store.pathInfoToJSON(jsonRoot,
+                    store.exportReferences(storePaths, inputPaths), false, true);
+            }
+            json[i.key()] = nlohmann::json::parse(str.str()); // urgh
+        }
+    }
+
+    return json;
+}
+
+/* As a convenience to bash scripts, write a shell file that
+   maps all attributes that are representable in bash -
+   namely, strings, integers, nulls, Booleans, and arrays and
+   objects consisting entirely of those values. (So nested
+   arrays or objects are not supported.) */
+std::string writeStructuredAttrsShell(const nlohmann::json & json)
+{
+
+    auto handleSimpleType = [](const nlohmann::json & value) -> std::optional<std::string> {
+        if (value.is_string())
+            return shellEscape(value);
+
+        if (value.is_number()) {
+            auto f = value.get<float>();
+            if (std::ceil(f) == f)
+                return std::to_string(value.get<int>());
+        }
+
+        if (value.is_null())
+            return std::string("''");
+
+        if (value.is_boolean())
+            return value.get<bool>() ? std::string("1") : std::string("");
+
+        return {};
+    };
+
+    std::string jsonSh;
+
+    for (auto & [key, value] : json.items()) {
+
+        if (!std::regex_match(key, shVarName)) continue;
+
+        auto s = handleSimpleType(value);
+        if (s)
+            jsonSh += fmt("declare %s=%s\n", key, *s);
+
+        else if (value.is_array()) {
+            std::string s2;
+            bool good = true;
+
+            for (auto & value2 : value) {
+                auto s3 = handleSimpleType(value2);
+                if (!s3) { good = false; break; }
+                s2 += *s3; s2 += ' ';
+            }
+
+            if (good)
+                jsonSh += fmt("declare -a %s=(%s)\n", key, s2);
+        }
+
+        else if (value.is_object()) {
+            std::string s2;
+            bool good = true;
+
+            for (auto & [key2, value2] : value.items()) {
+                auto s3 = handleSimpleType(value2);
+                if (!s3) { good = false; break; }
+                s2 += fmt("[%s]=%s ", shellEscape(key2), *s3);
+            }
+
+            if (good)
+                jsonSh += fmt("declare -A %s=(%s)\n", key, s2);
+        }
+    }
+
+    return jsonSh;
+}
 }
diff --git a/src/libstore/parsed-derivations.hh b/src/libstore/parsed-derivations.hh
index c9fbe68c4..effcf099d 100644
--- a/src/libstore/parsed-derivations.hh
+++ b/src/libstore/parsed-derivations.hh
@@ -36,6 +36,10 @@ public:
     bool willBuildLocally(Store & localStore) const;
 
     bool substitutesAllowed() const;
+
+    std::optional<nlohmann::json> prepareStructuredAttrs(Store & store, const StorePathSet & inputPaths);
 };
 
+std::string writeStructuredAttrsShell(const nlohmann::json & json);
+
 }
diff --git a/src/libstore/path-info.cc b/src/libstore/path-info.cc
new file mode 100644
index 000000000..fda55b2b6
--- /dev/null
+++ b/src/libstore/path-info.cc
@@ -0,0 +1,46 @@
+#include "path-info.hh"
+#include "worker-protocol.hh"
+
+namespace nix {
+
+ValidPathInfo ValidPathInfo::read(Source & source, const Store & store, unsigned int format)
+{
+    return read(source, store, format, store.parseStorePath(readString(source)));
+}
+
+ValidPathInfo ValidPathInfo::read(Source & source, const Store & store, unsigned int format, StorePath && path)
+{
+    auto deriver = readString(source);
+    auto narHash = Hash::parseAny(readString(source), htSHA256);
+    ValidPathInfo info(path, narHash);
+    if (deriver != "") info.deriver = store.parseStorePath(deriver);
+    info.references = worker_proto::read(store, source, Phantom<StorePathSet> {});
+    source >> info.registrationTime >> info.narSize;
+    if (format >= 16) {
+        source >> info.ultimate;
+        info.sigs = readStrings<StringSet>(source);
+        info.ca = parseContentAddressOpt(readString(source));
+    }
+    return info;
+}
+
+void ValidPathInfo::write(
+    Sink & sink,
+    const Store & store,
+    unsigned int format,
+    bool includePath) const
+{
+    if (includePath)
+        sink << store.printStorePath(path);
+    sink << (deriver ? store.printStorePath(*deriver) : "")
+         << narHash.to_string(Base16, false);
+    worker_proto::write(store, sink, references);
+    sink << registrationTime << narSize;
+    if (format >= 16) {
+        sink << ultimate
+             << sigs
+             << renderContentAddress(ca);
+    }
+}
+
+}
diff --git a/src/libstore/path-info.hh b/src/libstore/path-info.hh
index de87f8b33..b4b54e593 100644
--- a/src/libstore/path-info.hh
+++ b/src/libstore/path-info.hh
@@ -105,6 +105,11 @@ struct ValidPathInfo
     ValidPathInfo(const StorePath & path, Hash narHash) : path(path), narHash(narHash) { };
 
     virtual ~ValidPathInfo() { }
+
+    static ValidPathInfo read(Source & source, const Store & store, unsigned int format);
+    static ValidPathInfo read(Source & source, const Store & store, unsigned int format, StorePath && path);
+
+    void write(Sink & sink, const Store & store, unsigned int format, bool includePath = true) const;
 };
 
 typedef std::map<StorePath, ValidPathInfo> ValidPathInfos;
diff --git a/src/libstore/path-with-outputs.cc b/src/libstore/path-with-outputs.cc
index 865d64cf2..e5a121e00 100644
--- a/src/libstore/path-with-outputs.cc
+++ b/src/libstore/path-with-outputs.cc
@@ -31,14 +31,14 @@ std::vector<DerivedPath> toDerivedPaths(const std::vector<StorePathWithOutputs>
 std::variant<StorePathWithOutputs, StorePath> StorePathWithOutputs::tryFromDerivedPath(const DerivedPath & p)
 {
     return std::visit(overloaded {
-        [&](DerivedPath::Opaque bo) -> std::variant<StorePathWithOutputs, StorePath> {
+        [&](const DerivedPath::Opaque & bo) -> std::variant<StorePathWithOutputs, StorePath> {
             if (bo.path.isDerivation()) {
                 // drv path gets interpreted as "build", not "get drv file itself"
                 return bo.path;
             }
             return StorePathWithOutputs { bo.path };
         },
-        [&](DerivedPath::Built bfd) -> std::variant<StorePathWithOutputs, StorePath> {
+        [&](const DerivedPath::Built & bfd) -> std::variant<StorePathWithOutputs, StorePath> {
             return StorePathWithOutputs { bfd.drvPath, bfd.outputs };
         },
     }, p.raw());
diff --git a/src/libstore/pathlocks.cc b/src/libstore/pathlocks.cc
index 926f4ea1e..2da74e262 100644
--- a/src/libstore/pathlocks.cc
+++ b/src/libstore/pathlocks.cc
@@ -176,4 +176,17 @@ void PathLocks::setDeletion(bool deletePaths)
 }
 
 
+FdLock::FdLock(int fd, LockType lockType, bool wait, std::string_view waitMsg)
+    : fd(fd)
+{
+    if (wait) {
+        if (!lockFile(fd, lockType, false)) {
+            printInfo("%s", waitMsg);
+            acquired = lockFile(fd, lockType, true);
+        }
+    } else
+        acquired = lockFile(fd, lockType, false);
+}
+
+
 }
diff --git a/src/libstore/pathlocks.hh b/src/libstore/pathlocks.hh
index 411da0222..919c8904c 100644
--- a/src/libstore/pathlocks.hh
+++ b/src/libstore/pathlocks.hh
@@ -35,4 +35,18 @@ public:
     void setDeletion(bool deletePaths);
 };
 
+struct FdLock
+{
+    int fd;
+    bool acquired = false;
+
+    FdLock(int fd, LockType lockType, bool wait, std::string_view waitMsg);
+
+    ~FdLock()
+    {
+        if (acquired)
+            lockFile(fd, ltNone, false);
+    }
+};
+
 }
diff --git a/src/libstore/profiles.cc b/src/libstore/profiles.cc
index 5d1723886..73163424c 100644
--- a/src/libstore/profiles.cc
+++ b/src/libstore/profiles.cc
@@ -126,9 +126,9 @@ void deleteGeneration(const Path & profile, GenerationNumber gen)
 static void deleteGeneration2(const Path & profile, GenerationNumber gen, bool dryRun)
 {
     if (dryRun)
-        printInfo(format("would remove generation %1%") % gen);
+        notice("would remove profile version %1%", gen);
     else {
-        printInfo(format("removing generation %1%") % gen);
+        notice("removing profile version %1%", gen);
         deleteGeneration(profile, gen);
     }
 }
@@ -142,7 +142,7 @@ void deleteGenerations(const Path & profile, const std::set<GenerationNumber> &
     auto [gens, curGen] = findGenerations(profile);
 
     if (gensToDelete.count(*curGen))
-        throw Error("cannot delete current generation of profile %1%'", profile);
+        throw Error("cannot delete current version of profile %1%'", profile);
 
     for (auto & i : gens) {
         if (!gensToDelete.count(i.number)) continue;
@@ -211,12 +211,15 @@ void deleteGenerationsOlderThan(const Path & profile, time_t t, bool dryRun)
 
 void deleteGenerationsOlderThan(const Path & profile, const string & timeSpec, bool dryRun)
 {
+    if (timeSpec.empty() || timeSpec[timeSpec.size() - 1] != 'd')
+        throw UsageError("invalid number of days specifier '%1%', expected something like '14d'", timeSpec);
+
     time_t curTime = time(0);
     string strDays = string(timeSpec, 0, timeSpec.size() - 1);
     auto days = string2Int<int>(strDays);
 
     if (!days || *days < 1)
-        throw Error("invalid number of days specifier '%1%'", timeSpec);
+        throw UsageError("invalid number of days specifier '%1%'", timeSpec);
 
     time_t oldTime = curTime - *days * 24 * 3600;
 
@@ -233,6 +236,37 @@ void switchLink(Path link, Path target)
 }
 
 
+void switchGeneration(
+    const Path & profile,
+    std::optional<GenerationNumber> dstGen,
+    bool dryRun)
+{
+    PathLocks lock;
+    lockProfile(lock, profile);
+
+    auto [gens, curGen] = findGenerations(profile);
+
+    std::optional<Generation> dst;
+    for (auto & i : gens)
+        if ((!dstGen && i.number < curGen) ||
+            (dstGen && i.number == *dstGen))
+            dst = i;
+
+    if (!dst) {
+        if (dstGen)
+            throw Error("profile version %1% does not exist", *dstGen);
+        else
+            throw Error("no profile version older than the current (%1%) exists", curGen.value_or(0));
+    }
+
+    notice("switching profile from version %d to %d", curGen.value_or(0), dst->number);
+
+    if (dryRun) return;
+
+    switchLink(profile, dst->path);
+}
+
+
 void lockProfile(PathLocks & lock, const Path & profile)
 {
     lock.lockPaths({profile}, (format("waiting for lock on profile '%1%'") % profile).str());
diff --git a/src/libstore/profiles.hh b/src/libstore/profiles.hh
index be55a65d4..d100c970c 100644
--- a/src/libstore/profiles.hh
+++ b/src/libstore/profiles.hh
@@ -11,7 +11,7 @@ namespace nix {
 class StorePath;
 
 
-typedef unsigned int GenerationNumber;
+typedef uint64_t GenerationNumber;
 
 struct Generation
 {
@@ -46,6 +46,13 @@ void deleteGenerationsOlderThan(const Path & profile, const string & timeSpec, b
 
 void switchLink(Path link, Path target);
 
+/* Roll back a profile to the specified generation, or to the most
+   recent one older than the current. */
+void switchGeneration(
+    const Path & profile,
+    std::optional<GenerationNumber> dstGen,
+    bool dryRun);
+
 /* Ensure exclusive access to a profile.  Any command that modifies
    the profile first acquires this lock. */
 void lockProfile(PathLocks & lock, const Path & profile);
diff --git a/src/libstore/realisation.cc b/src/libstore/realisation.cc
index 638065547..f871e6437 100644
--- a/src/libstore/realisation.cc
+++ b/src/libstore/realisation.cc
@@ -1,5 +1,6 @@
 #include "realisation.hh"
 #include "store-api.hh"
+#include "closure.hh"
 #include <nlohmann/json.hpp>
 
 namespace nix {
@@ -21,11 +22,52 @@ std::string DrvOutput::to_string() const {
     return strHash() + "!" + outputName;
 }
 
+std::set<Realisation> Realisation::closure(Store & store, const std::set<Realisation> & startOutputs)
+{
+    std::set<Realisation> res;
+    Realisation::closure(store, startOutputs, res);
+    return res;
+}
+
+void Realisation::closure(Store & store, const std::set<Realisation> & startOutputs, std::set<Realisation> & res)
+{
+    auto getDeps = [&](const Realisation& current) -> std::set<Realisation> {
+        std::set<Realisation> res;
+        for (auto& [currentDep, _] : current.dependentRealisations) {
+            if (auto currentRealisation = store.queryRealisation(currentDep))
+                res.insert(*currentRealisation);
+            else
+                throw Error(
+                    "Unrealised derivation '%s'", currentDep.to_string());
+        }
+        return res;
+    };
+
+    computeClosure<Realisation>(
+        startOutputs, res,
+        [&](const Realisation& current,
+            std::function<void(std::promise<std::set<Realisation>>&)>
+                processEdges) {
+            std::promise<std::set<Realisation>> promise;
+            try {
+                auto res = getDeps(current);
+                promise.set_value(res);
+            } catch (...) {
+                promise.set_exception(std::current_exception());
+            }
+            return processEdges(promise);
+        });
+}
+
 nlohmann::json Realisation::toJSON() const {
+    auto jsonDependentRealisations = nlohmann::json::object();
+    for (auto & [depId, depOutPath] : dependentRealisations)
+        jsonDependentRealisations.emplace(depId.to_string(), depOutPath.to_string());
     return nlohmann::json{
         {"id", id.to_string()},
         {"outPath", outPath.to_string()},
         {"signatures", signatures},
+        {"dependentRealisations", jsonDependentRealisations},
     };
 }
 
@@ -51,10 +93,16 @@ Realisation Realisation::fromJSON(
     if (auto signaturesIterator = json.find("signatures"); signaturesIterator != json.end())
         signatures.insert(signaturesIterator->begin(), signaturesIterator->end());
 
+    std::map <DrvOutput, StorePath> dependentRealisations;
+    if (auto jsonDependencies = json.find("dependentRealisations"); jsonDependencies != json.end())
+        for (auto & [jsonDepId, jsonDepOutPath] : jsonDependencies->get<std::map<std::string, std::string>>())
+            dependentRealisations.insert({DrvOutput::parse(jsonDepId), StorePath(jsonDepOutPath)});
+
     return Realisation{
         .id = DrvOutput::parse(getField("id")),
         .outPath = StorePath(getField("outPath")),
         .signatures = signatures,
+        .dependentRealisations = dependentRealisations,
     };
 }
 
@@ -92,6 +140,24 @@ StorePath RealisedPath::path() const {
     return std::visit([](auto && arg) { return arg.getPath(); }, raw);
 }
 
+bool Realisation::isCompatibleWith(const Realisation & other) const
+{
+    assert (id == other.id);
+    if (outPath == other.outPath) {
+        if (dependentRealisations.empty() != other.dependentRealisations.empty()) {
+            warn(
+                "Encountered a realisation for '%s' with an empty set of "
+                "dependencies. This is likely an artifact from an older Nix. "
+                "I’ll try to fix the realisation if I can",
+                id.to_string());
+            return true;
+        } else if (dependentRealisations == other.dependentRealisations) {
+            return true;
+        }
+    }
+    return false;
+}
+
 void RealisedPath::closure(
     Store& store,
     const RealisedPath::Set& startPaths,
diff --git a/src/libstore/realisation.hh b/src/libstore/realisation.hh
index f5049c9e9..9070a6ee2 100644
--- a/src/libstore/realisation.hh
+++ b/src/libstore/realisation.hh
@@ -28,6 +28,14 @@ struct Realisation {
 
     StringSet signatures;
 
+    /**
+     * The realisations that are required for the current one to be valid.
+     *
+     * When importing this realisation, the store will first check that all its
+     * dependencies exist, and map to the correct output path
+     */
+    std::map<DrvOutput, StorePath> dependentRealisations;
+
     nlohmann::json toJSON() const;
     static Realisation fromJSON(const nlohmann::json& json, const std::string& whence);
 
@@ -36,6 +44,11 @@ struct Realisation {
     bool checkSignature(const PublicKeys & publicKeys, const std::string & sig) const;
     size_t checkSignatures(const PublicKeys & publicKeys) const;
 
+    static std::set<Realisation> closure(Store &, const std::set<Realisation> &);
+    static void closure(Store &, const std::set<Realisation> &, std::set<Realisation> & res);
+
+    bool isCompatibleWith(const Realisation & other) const;
+
     StorePath getPath() const { return outPath; }
 
     GENERATE_CMP(Realisation, me->id, me->outPath);
diff --git a/src/libstore/references.cc b/src/libstore/references.cc
index 39c4970c6..91b3fc142 100644
--- a/src/libstore/references.cc
+++ b/src/libstore/references.cc
@@ -5,27 +5,29 @@
 
 #include <map>
 #include <cstdlib>
+#include <mutex>
 
 
 namespace nix {
 
 
-static unsigned int refLength = 32; /* characters */
+static size_t refLength = 32; /* characters */
 
 
-static void search(const unsigned char * s, size_t len,
-    StringSet & hashes, StringSet & seen)
+static void search(
+    std::string_view s,
+    StringSet & hashes,
+    StringSet & seen)
 {
-    static bool initialised = false;
+    static std::once_flag initialised;
     static bool isBase32[256];
-    if (!initialised) {
+    std::call_once(initialised, [](){
         for (unsigned int i = 0; i < 256; ++i) isBase32[i] = false;
         for (unsigned int i = 0; i < base32Chars.size(); ++i)
             isBase32[(unsigned char) base32Chars[i]] = true;
-        initialised = true;
-    }
+    });
 
-    for (size_t i = 0; i + refLength <= len; ) {
+    for (size_t i = 0; i + refLength <= s.size(); ) {
         int j;
         bool match = true;
         for (j = refLength - 1; j >= 0; --j)
@@ -35,7 +37,7 @@ static void search(const unsigned char * s, size_t len,
                 break;
             }
         if (!match) continue;
-        string ref((const char *) s + i, refLength);
+        std::string ref(s.substr(i, refLength));
         if (hashes.erase(ref)) {
             debug(format("found reference to '%1%' at offset '%2%'")
                   % ref % i);
@@ -46,69 +48,60 @@ static void search(const unsigned char * s, size_t len,
 }
 
 
-struct RefScanSink : Sink
+void RefScanSink::operator () (std::string_view data)
 {
-    StringSet hashes;
-    StringSet seen;
-
-    string tail;
-
-    RefScanSink() { }
-
-    void operator () (std::string_view data) override
-    {
-        /* It's possible that a reference spans the previous and current
-           fragment, so search in the concatenation of the tail of the
-           previous fragment and the start of the current fragment. */
-        string s = tail + std::string(data, 0, refLength);
-        search((const unsigned char *) s.data(), s.size(), hashes, seen);
-
-        search((const unsigned char *) data.data(), data.size(), hashes, seen);
-
-        size_t tailLen = data.size() <= refLength ? data.size() : refLength;
-        tail = std::string(tail, tail.size() < refLength - tailLen ? 0 : tail.size() - (refLength - tailLen));
-        tail.append({data.data() + data.size() - tailLen, tailLen});
-    }
-};
+    /* It's possible that a reference spans the previous and current
+       fragment, so search in the concatenation of the tail of the
+       previous fragment and the start of the current fragment. */
+    auto s = tail;
+    auto tailLen = std::min(data.size(), refLength);
+    s.append(data.data(), tailLen);
+    search(s, hashes, seen);
+
+    search(data, hashes, seen);
+
+    auto rest = refLength - tailLen;
+    if (rest < tail.size())
+        tail = tail.substr(tail.size() - rest);
+    tail.append(data.data() + data.size() - tailLen, tailLen);
+}
 
 
-std::pair<PathSet, HashResult> scanForReferences(const string & path,
-    const PathSet & refs)
+std::pair<StorePathSet, HashResult> scanForReferences(
+    const string & path,
+    const StorePathSet & refs)
 {
     HashSink hashSink { htSHA256 };
     auto found = scanForReferences(hashSink, path, refs);
     auto hash = hashSink.finish();
-    return std::pair<PathSet, HashResult>(found, hash);
+    return std::pair<StorePathSet, HashResult>(found, hash);
 }
 
-PathSet scanForReferences(Sink & toTee,
-    const string & path, const PathSet & refs)
+StorePathSet scanForReferences(
+    Sink & toTee,
+    const Path & path,
+    const StorePathSet & refs)
 {
-    RefScanSink refsSink;
-    TeeSink sink { refsSink, toTee };
-    std::map<string, Path> backMap;
+    StringSet hashes;
+    std::map<std::string, StorePath> backMap;
 
     for (auto & i : refs) {
-        auto baseName = std::string(baseNameOf(i));
-        string::size_type pos = baseName.find('-');
-        if (pos == string::npos)
-            throw Error("bad reference '%1%'", i);
-        string s = string(baseName, 0, pos);
-        assert(s.size() == refLength);
-        assert(backMap.find(s) == backMap.end());
-        // parseHash(htSHA256, s);
-        refsSink.hashes.insert(s);
-        backMap[s] = i;
+        std::string hashPart(i.hashPart());
+        auto inserted = backMap.emplace(hashPart, i).second;
+        assert(inserted);
+        hashes.insert(hashPart);
     }
 
     /* Look for the hashes in the NAR dump of the path. */
+    RefScanSink refsSink(std::move(hashes));
+    TeeSink sink { refsSink, toTee };
     dumpPath(path, sink);
 
     /* Map the hashes found back to their store paths. */
-    PathSet found;
-    for (auto & i : refsSink.seen) {
-        std::map<string, Path>::iterator j;
-        if ((j = backMap.find(i)) == backMap.end()) abort();
+    StorePathSet found;
+    for (auto & i : refsSink.getResult()) {
+        auto j = backMap.find(i);
+        assert(j != backMap.end());
         found.insert(j->second);
     }
 
diff --git a/src/libstore/references.hh b/src/libstore/references.hh
index 4f12e6b21..a6119c861 100644
--- a/src/libstore/references.hh
+++ b/src/libstore/references.hh
@@ -1,13 +1,31 @@
 #pragma once
 
-#include "types.hh"
 #include "hash.hh"
+#include "path.hh"
 
 namespace nix {
 
-std::pair<PathSet, HashResult> scanForReferences(const Path & path, const PathSet & refs);
+std::pair<StorePathSet, HashResult> scanForReferences(const Path & path, const StorePathSet & refs);
 
-PathSet scanForReferences(Sink & toTee, const Path & path, const PathSet & refs);
+StorePathSet scanForReferences(Sink & toTee, const Path & path, const StorePathSet & refs);
+
+class RefScanSink : public Sink
+{
+    StringSet hashes;
+    StringSet seen;
+
+    std::string tail;
+
+public:
+
+    RefScanSink(StringSet && hashes) : hashes(hashes)
+    { }
+
+    StringSet & getResult()
+    { return seen; }
+
+    void operator () (std::string_view data) override;
+};
 
 struct RewritingSink : Sink
 {
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 761b4a087..a627e9cf1 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -162,8 +162,19 @@ void RemoteStore::initConnection(Connection & conn)
     try {
         conn.to << WORKER_MAGIC_1;
         conn.to.flush();
-        unsigned int magic = readInt(conn.from);
-        if (magic != WORKER_MAGIC_2) throw Error("protocol mismatch");
+        StringSink saved;
+        try {
+            TeeSource tee(conn.from, saved);
+            unsigned int magic = readInt(tee);
+            if (magic != WORKER_MAGIC_2)
+                throw Error("protocol mismatch");
+        } catch (SerialisationError & e) {
+            /* In case the other side is waiting for our input, close
+               it. */
+            conn.closeWrite();
+            auto msg = conn.from.drain();
+            throw Error("protocol mismatch, got '%s'", chomp(*saved.s + msg));
+        }
 
         conn.from >> conn.daemonVersion;
         if (GET_PROTOCOL_MAJOR(conn.daemonVersion) != GET_PROTOCOL_MAJOR(PROTOCOL_VERSION))
@@ -222,6 +233,7 @@ void RemoteStore::setOptions(Connection & conn)
         overrides.erase(settings.buildCores.name);
         overrides.erase(settings.useSubstitutes.name);
         overrides.erase(loggerSettings.showTrace.name);
+        overrides.erase(settings.experimentalFeatures.name);
         conn.to << overrides.size();
         for (auto & i : overrides)
             conn.to << i.first << i.second.value;
@@ -278,6 +290,10 @@ ConnectionHandle RemoteStore::getConnection()
     return ConnectionHandle(connections->get());
 }
 
+void RemoteStore::setOptions()
+{
+    setOptions(*(getConnection().handle));
+}
 
 bool RemoteStore::isValidPathUncached(const StorePath & path)
 {
@@ -386,23 +402,6 @@ void RemoteStore::querySubstitutablePathInfos(const StorePathCAMap & pathsMap, S
 }
 
 
-ref<const ValidPathInfo> RemoteStore::readValidPathInfo(ConnectionHandle & conn, const StorePath & path)
-{
-    auto deriver = readString(conn->from);
-    auto narHash = Hash::parseAny(readString(conn->from), htSHA256);
-    auto info = make_ref<ValidPathInfo>(path, narHash);
-    if (deriver != "") info->deriver = parseStorePath(deriver);
-    info->references = worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
-    conn->from >> info->registrationTime >> info->narSize;
-    if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 16) {
-        conn->from >> info->ultimate;
-        info->sigs = readStrings<StringSet>(conn->from);
-        info->ca = parseContentAddressOpt(readString(conn->from));
-    }
-    return info;
-}
-
-
 void RemoteStore::queryPathInfoUncached(const StorePath & path,
     Callback<std::shared_ptr<const ValidPathInfo>> callback) noexcept
 {
@@ -423,7 +422,8 @@ void RemoteStore::queryPathInfoUncached(const StorePath & path,
                 bool valid; conn->from >> valid;
                 if (!valid) throw InvalidPath("path '%s' is not valid", printStorePath(path));
             }
-            info = readValidPathInfo(conn, path);
+            info = std::make_shared<ValidPathInfo>(
+                ValidPathInfo::read(conn->from, *this, GET_PROTOCOL_MINOR(conn->daemonVersion), StorePath{path}));
         }
         callback(std::move(info));
     } catch (...) { callback.rethrow(); }
@@ -525,20 +525,20 @@ ref<const ValidPathInfo> RemoteStore::addCAToStore(
             });
         }
 
-        auto path = parseStorePath(readString(conn->from));
-        return readValidPathInfo(conn, path);
+        return make_ref<ValidPathInfo>(
+            ValidPathInfo::read(conn->from, *this, GET_PROTOCOL_MINOR(conn->daemonVersion)));
     }
     else {
         if (repair) throw Error("repairing is not supported when building through the Nix daemon protocol < 1.25");
 
         std::visit(overloaded {
-            [&](TextHashMethod thm) -> void {
+            [&](const TextHashMethod & thm) -> void {
                 std::string s = dump.drain();
                 conn->to << wopAddTextToStore << name << s;
                 worker_proto::write(*this, conn->to, references);
                 conn.processStderr();
             },
-            [&](FixedOutputHashMethod fohm) -> void {
+            [&](const FixedOutputHashMethod & fohm) -> void {
                 conn->to
                     << wopAddToStore
                     << name
@@ -582,9 +582,8 @@ ref<const ValidPathInfo> RemoteStore::addCAToStore(
 
 
 StorePath RemoteStore::addToStoreFromDump(Source & dump, const string & name,
-        FileIngestionMethod method, HashType hashType, RepairFlag repair)
+      FileIngestionMethod method, HashType hashType, RepairFlag repair, const StorePathSet & references)
 {
-    StorePathSet references;
     return addCAToStore(dump, name, FixedOutputHashMethod{ .fileIngestionMethod = method, .hashType = hashType }, references, repair)->path;
 }
 
@@ -642,6 +641,25 @@ void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
 }
 
 
+void RemoteStore::addMultipleToStore(
+    Source & source,
+    RepairFlag repair,
+    CheckSigsFlag checkSigs)
+{
+    if (GET_PROTOCOL_MINOR(getConnection()->daemonVersion) >= 32) {
+        auto conn(getConnection());
+        conn->to
+            << wopAddMultipleToStore
+            << repair
+            << !checkSigs;
+        conn.withFramedSink([&](Sink & sink) {
+            source.drainInto(sink);
+        });
+    } else
+        Store::addMultipleToStore(source, repair, checkSigs);
+}
+
+
 StorePath RemoteStore::addTextToStore(const string & name, const string & s,
     const StorePathSet & references, RepairFlag repair)
 {
@@ -653,36 +671,57 @@ void RemoteStore::registerDrvOutput(const Realisation & info)
 {
     auto conn(getConnection());
     conn->to << wopRegisterDrvOutput;
-    conn->to << info.id.to_string();
-    conn->to << std::string(info.outPath.to_string());
+    if (GET_PROTOCOL_MINOR(conn->daemonVersion) < 31) {
+        conn->to << info.id.to_string();
+        conn->to << std::string(info.outPath.to_string());
+    } else {
+        worker_proto::write(*this, conn->to, info);
+    }
     conn.processStderr();
 }
 
-std::optional<const Realisation> RemoteStore::queryRealisation(const DrvOutput & id)
+void RemoteStore::queryRealisationUncached(const DrvOutput & id,
+    Callback<std::shared_ptr<const Realisation>> callback) noexcept
 {
     auto conn(getConnection());
     conn->to << wopQueryRealisation;
     conn->to << id.to_string();
     conn.processStderr();
-    auto outPaths = worker_proto::read(*this, conn->from, Phantom<std::set<StorePath>>{});
-    if (outPaths.empty())
-        return std::nullopt;
-    return {Realisation{.id = id, .outPath = *outPaths.begin()}};
+
+    auto real = [&]() -> std::shared_ptr<const Realisation> {
+        if (GET_PROTOCOL_MINOR(conn->daemonVersion) < 31) {
+            auto outPaths = worker_proto::read(
+                *this, conn->from, Phantom<std::set<StorePath>> {});
+            if (outPaths.empty())
+                return nullptr;
+            return std::make_shared<const Realisation>(Realisation { .id = id, .outPath = *outPaths.begin() });
+        } else {
+            auto realisations = worker_proto::read(
+                *this, conn->from, Phantom<std::set<Realisation>> {});
+            if (realisations.empty())
+                return nullptr;
+            return std::make_shared<const Realisation>(*realisations.begin());
+        }
+    }();
+
+    try {
+        callback(std::shared_ptr<const Realisation>(real));
+    } catch (...) { return callback.rethrow(); }
 }
 
 static void writeDerivedPaths(RemoteStore & store, ConnectionHandle & conn, const std::vector<DerivedPath> & reqs)
 {
-    if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 29) {
+    if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 30) {
         worker_proto::write(store, conn->to, reqs);
     } else {
         Strings ss;
         for (auto & p : reqs) {
             auto sOrDrvPath = StorePathWithOutputs::tryFromDerivedPath(p);
             std::visit(overloaded {
-                [&](StorePathWithOutputs s) {
+                [&](const StorePathWithOutputs & s) {
                     ss.push_back(s.to_string(store));
                 },
-                [&](StorePath drvPath) {
+                [&](const StorePath & drvPath) {
                     throw Error("trying to request '%s', but daemon protocol %d.%d is too old (< 1.29) to request a derivation file",
                         store.printStorePath(drvPath),
                         GET_PROTOCOL_MAJOR(conn->daemonVersion),
@@ -694,8 +733,18 @@ static void writeDerivedPaths(RemoteStore & store, ConnectionHandle & conn, cons
     }
 }
 
-void RemoteStore::buildPaths(const std::vector<DerivedPath> & drvPaths, BuildMode buildMode)
+void RemoteStore::buildPaths(const std::vector<DerivedPath> & drvPaths, BuildMode buildMode, std::shared_ptr<Store> evalStore)
 {
+    if (evalStore && evalStore.get() != this) {
+        /* The remote doesn't have a way to access evalStore, so copy
+           the .drvs. */
+        RealisedPath::Set drvPaths2;
+        for (auto & i : drvPaths)
+            if (auto p = std::get_if<DerivedPath::Built>(&i))
+                drvPaths2.insert(p->drvPath);
+        copyClosure(*evalStore, *this, drvPaths2);
+    }
+
     auto conn(getConnection());
     conn->to << wopBuildPaths;
     assert(GET_PROTOCOL_MINOR(conn->daemonVersion) >= 13);
@@ -761,15 +810,6 @@ void RemoteStore::addIndirectRoot(const Path & path)
 }
 
 
-void RemoteStore::syncWithGC()
-{
-    auto conn(getConnection());
-    conn->to << wopSyncWithGC;
-    conn.processStderr();
-    readInt(conn->from);
-}
-
-
 Roots RemoteStore::findRoots(bool censor)
 {
     auto conn(getConnection());
@@ -990,14 +1030,14 @@ std::exception_ptr RemoteStore::Connection::processStderr(Sink * sink, Source *
     return nullptr;
 }
 
-void ConnectionHandle::withFramedSink(std::function<void(Sink &sink)> fun)
+void ConnectionHandle::withFramedSink(std::function<void(Sink & sink)> fun)
 {
     (*this)->to.flush();
 
     std::exception_ptr ex;
 
-    /* Handle log messages / exceptions from the remote on a
-        separate thread. */
+    /* Handle log messages / exceptions from the remote on a separate
+       thread. */
     std::thread stderrThread([&]()
     {
         try {
@@ -1030,7 +1070,6 @@ void ConnectionHandle::withFramedSink(std::function<void(Sink &sink)> fun)
     stderrThread.join();
     if (ex)
         std::rethrow_exception(ex);
-
 }
 
 }
diff --git a/src/libstore/remote-store.hh b/src/libstore/remote-store.hh
index 6cf76a46d..0fd67f371 100644
--- a/src/libstore/remote-store.hh
+++ b/src/libstore/remote-store.hh
@@ -73,19 +73,25 @@ public:
 
     /* Add a content-addressable store path. Does not support references. `dump` will be drained. */
     StorePath addToStoreFromDump(Source & dump, const string & name,
-        FileIngestionMethod method = FileIngestionMethod::Recursive, HashType hashAlgo = htSHA256, RepairFlag repair = NoRepair) override;
+        FileIngestionMethod method = FileIngestionMethod::Recursive, HashType hashAlgo = htSHA256, RepairFlag repair = NoRepair, const StorePathSet & references = StorePathSet()) override;
 
     void addToStore(const ValidPathInfo & info, Source & nar,
         RepairFlag repair, CheckSigsFlag checkSigs) override;
 
+    void addMultipleToStore(
+        Source & source,
+        RepairFlag repair,
+        CheckSigsFlag checkSigs) override;
+
     StorePath addTextToStore(const string & name, const string & s,
         const StorePathSet & references, RepairFlag repair) override;
 
     void registerDrvOutput(const Realisation & info) override;
 
-    std::optional<const Realisation> queryRealisation(const DrvOutput &) override;
+    void queryRealisationUncached(const DrvOutput &,
+        Callback<std::shared_ptr<const Realisation>> callback) noexcept override;
 
-    void buildPaths(const std::vector<DerivedPath> & paths, BuildMode buildMode) override;
+    void buildPaths(const std::vector<DerivedPath> & paths, BuildMode buildMode, std::shared_ptr<Store> evalStore) override;
 
     BuildResult buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
         BuildMode buildMode) override;
@@ -96,8 +102,6 @@ public:
 
     void addIndirectRoot(const Path & path) override;
 
-    void syncWithGC() override;
-
     Roots findRoots(bool censor) override;
 
     void collectGarbage(const GCOptions & options, GCResults & results) override;
@@ -120,7 +124,6 @@ public:
 
     struct Connection
     {
-        AutoCloseFD fd;
         FdSink to;
         FdSource from;
         unsigned int daemonVersion;
@@ -128,6 +131,8 @@ public:
 
         virtual ~Connection();
 
+        virtual void closeWrite() = 0;
+
         std::exception_ptr processStderr(Sink * sink = 0, Source * source = 0, bool flush = true);
     };
 
@@ -143,6 +148,8 @@ protected:
 
     virtual void setOptions(Connection & conn);
 
+    void setOptions() override;
+
     ConnectionHandle getConnection();
 
     friend struct ConnectionHandle;
@@ -151,8 +158,6 @@ protected:
 
     virtual void narFromPath(const StorePath & path, Sink & sink) override;
 
-    ref<const ValidPathInfo> readValidPathInfo(ConnectionHandle & conn, const StorePath & path);
-
 private:
 
     std::atomic_bool failed{false};
diff --git a/src/libstore/s3-binary-cache-store.cc b/src/libstore/s3-binary-cache-store.cc
index 6bfbee044..7accad7f4 100644
--- a/src/libstore/s3-binary-cache-store.cc
+++ b/src/libstore/s3-binary-cache-store.cc
@@ -209,7 +209,7 @@ struct S3BinaryCacheStoreImpl : virtual S3BinaryCacheStoreConfig, public virtual
     S3Helper s3Helper;
 
     S3BinaryCacheStoreImpl(
-        const std::string & scheme,
+        const std::string & uriScheme,
         const std::string & bucketName,
         const Params & params)
         : StoreConfig(params)
@@ -232,8 +232,8 @@ struct S3BinaryCacheStoreImpl : virtual S3BinaryCacheStoreConfig, public virtual
     void init() override
     {
         if (auto cacheInfo = diskCache->cacheExists(getUri())) {
-            wantMassQuery.setDefault(cacheInfo->wantMassQuery ? "true" : "false");
-            priority.setDefault(fmt("%d", cacheInfo->priority));
+            wantMassQuery.setDefault(cacheInfo->wantMassQuery);
+            priority.setDefault(cacheInfo->priority);
         } else {
             BinaryCacheStore::init();
             diskCache->createCache(getUri(), storeDir, wantMassQuery, priority);
diff --git a/src/libstore/sandbox-defaults.sb b/src/libstore/sandbox-defaults.sb
index 351037822..56b35c3fe 100644
--- a/src/libstore/sandbox-defaults.sb
+++ b/src/libstore/sandbox-defaults.sb
@@ -32,7 +32,9 @@
        (literal "/tmp") (subpath TMPDIR))
 
 ; Some packages like to read the system version.
-(allow file-read* (literal "/System/Library/CoreServices/SystemVersion.plist"))
+(allow file-read*
+       (literal "/System/Library/CoreServices/SystemVersion.plist")
+       (literal "/System/Library/CoreServices/SystemVersionCompat.plist"))
 
 ; Without this line clang cannot write to /dev/null, breaking some configure tests.
 (allow file-read-metadata (literal "/dev"))
@@ -95,3 +97,8 @@
 ; This is used by /bin/sh on macOS 10.15 and later.
 (allow file*
        (literal "/private/var/select/sh"))
+
+; Allow Rosetta 2 to run x86_64 binaries on aarch64-darwin.
+(allow file-read*
+       (subpath "/Library/Apple/usr/libexec/oah")
+       (subpath "/System/Library/Apple/usr/libexec/oah"))
diff --git a/src/libstore/serve-protocol.hh b/src/libstore/serve-protocol.hh
index 02d0810cc..3f76baa82 100644
--- a/src/libstore/serve-protocol.hh
+++ b/src/libstore/serve-protocol.hh
@@ -5,7 +5,7 @@ namespace nix {
 #define SERVE_MAGIC_1 0x390c9deb
 #define SERVE_MAGIC_2 0x5452eecb
 
-#define SERVE_PROTOCOL_VERSION (2 << 8 | 6)
+#define SERVE_PROTOCOL_VERSION (2 << 8 | 7)
 #define GET_PROTOCOL_MAJOR(x) ((x) & 0xff00)
 #define GET_PROTOCOL_MINOR(x) ((x) & 0x00ff)
 
diff --git a/src/libstore/sqlite.cc b/src/libstore/sqlite.cc
index 447b4179b..1d6baf02d 100644
--- a/src/libstore/sqlite.cc
+++ b/src/libstore/sqlite.cc
@@ -1,4 +1,5 @@
 #include "sqlite.hh"
+#include "globals.hh"
 #include "util.hh"
 
 #include <sqlite3.h>
@@ -27,8 +28,12 @@ namespace nix {
 
 SQLite::SQLite(const Path & path, bool create)
 {
+    // useSQLiteWAL also indicates what virtual file system we need.  Using
+    // `unix-dotfile` is needed on NFS file systems and on Windows' Subsystem
+    // for Linux (WSL) where useSQLiteWAL should be false by default.
+    const char *vfs = settings.useSQLiteWAL ? 0 : "unix-dotfile";
     if (sqlite3_open_v2(path.c_str(), &db,
-            SQLITE_OPEN_READWRITE | (create ? SQLITE_OPEN_CREATE : 0), 0) != SQLITE_OK)
+            SQLITE_OPEN_READWRITE | (create ? SQLITE_OPEN_CREATE : 0), vfs) != SQLITE_OK)
         throw Error("cannot open SQLite database '%s'", path);
 
     if (sqlite3_busy_timeout(db, 60 * 60 * 1000) != SQLITE_OK)
diff --git a/src/libstore/ssh-store.cc b/src/libstore/ssh-store.cc
index f2caf2aeb..bb03daef4 100644
--- a/src/libstore/ssh-store.cc
+++ b/src/libstore/ssh-store.cc
@@ -57,6 +57,11 @@ private:
     struct Connection : RemoteStore::Connection
     {
         std::unique_ptr<SSHMaster::Connection> sshConn;
+
+        void closeWrite() override
+        {
+            sshConn->in.close();
+        }
     };
 
     ref<RemoteStore::Connection> openConnection() override;
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 93fcb068f..c88dfe179 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -9,6 +9,7 @@
 #include "url.hh"
 #include "archive.hh"
 #include "callback.hh"
+#include "remote-store.hh"
 
 #include <regex>
 
@@ -198,10 +199,10 @@ StorePath Store::makeFixedOutputPathFromCA(std::string_view name, ContentAddress
 {
     // New template
     return std::visit(overloaded {
-        [&](TextHash th) {
+        [&](const TextHash & th) {
             return makeTextPath(name, th.hash, references);
         },
-        [&](FixedOutputHash fsh) {
+        [&](const FixedOutputHash & fsh) {
             return makeFixedOutputPath(fsh.method, fsh.hash, name, references, hasSelfReference);
         }
     }, ca);
@@ -236,7 +237,7 @@ StorePath Store::computeStorePathForText(const string & name, const string & s,
 
 
 StorePath Store::addToStore(const string & name, const Path & _srcPath,
-    FileIngestionMethod method, HashType hashAlgo, PathFilter & filter, RepairFlag repair)
+    FileIngestionMethod method, HashType hashAlgo, PathFilter & filter, RepairFlag repair, const StorePathSet & references)
 {
     Path srcPath(absPath(_srcPath));
     auto source = sinkToSource([&](Sink & sink) {
@@ -245,7 +246,21 @@ StorePath Store::addToStore(const string & name, const Path & _srcPath,
         else
             readFile(srcPath, sink);
     });
-    return addToStoreFromDump(*source, name, method, hashAlgo, repair);
+    return addToStoreFromDump(*source, name, method, hashAlgo, repair, references);
+}
+
+
+void Store::addMultipleToStore(
+    Source & source,
+    RepairFlag repair,
+    CheckSigsFlag checkSigs)
+{
+    auto expected = readNum<uint64_t>(source);
+    for (uint64_t i = 0; i < expected; ++i) {
+        auto info = ValidPathInfo::read(source, *this, 16);
+        info.ultimate = false;
+        addToStore(info, source, repair, checkSigs);
+    }
 }
 
 
@@ -337,6 +352,13 @@ ValidPathInfo Store::addToStoreSlow(std::string_view name, const Path & srcPath,
     return info;
 }
 
+StringSet StoreConfig::getDefaultSystemFeatures()
+{
+    auto res = settings.systemFeatures.get();
+    if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations))
+        res.insert("ca-derivations");
+    return res;
+}
 
 Store::Store(const Params & params)
     : StoreConfig(params)
@@ -392,11 +414,9 @@ StorePathSet Store::queryDerivationOutputs(const StorePath & path)
 
 bool Store::isValidPath(const StorePath & storePath)
 {
-    std::string hashPart(storePath.hashPart());
-
     {
         auto state_(state.lock());
-        auto res = state_->pathInfoCache.get(hashPart);
+        auto res = state_->pathInfoCache.get(std::string(storePath.to_string()));
         if (res && res->isKnownNow()) {
             stats.narInfoReadAverted++;
             return res->didExist();
@@ -404,11 +424,11 @@ bool Store::isValidPath(const StorePath & storePath)
     }
 
     if (diskCache) {
-        auto res = diskCache->lookupNarInfo(getUri(), hashPart);
+        auto res = diskCache->lookupNarInfo(getUri(), std::string(storePath.hashPart()));
         if (res.first != NarInfoDiskCache::oUnknown) {
             stats.narInfoReadAverted++;
             auto state_(state.lock());
-            state_->pathInfoCache.upsert(hashPart,
+            state_->pathInfoCache.upsert(std::string(storePath.to_string()),
                 res.first == NarInfoDiskCache::oInvalid ? PathInfoCacheValue{} : PathInfoCacheValue { .value = res.second });
             return res.first == NarInfoDiskCache::oValid;
         }
@@ -418,7 +438,7 @@ bool Store::isValidPath(const StorePath & storePath)
 
     if (diskCache && !valid)
         // FIXME: handle valid = true case.
-        diskCache->upsertNarInfo(getUri(), hashPart, 0);
+        diskCache->upsertNarInfo(getUri(), std::string(storePath.hashPart()), 0);
 
     return valid;
 }
@@ -465,13 +485,11 @@ static bool goodStorePath(const StorePath & expected, const StorePath & actual)
 void Store::queryPathInfo(const StorePath & storePath,
     Callback<ref<const ValidPathInfo>> callback) noexcept
 {
-    std::string hashPart;
+    auto hashPart = std::string(storePath.hashPart());
 
     try {
-        hashPart = storePath.hashPart();
-
         {
-            auto res = state.lock()->pathInfoCache.get(hashPart);
+            auto res = state.lock()->pathInfoCache.get(std::string(storePath.to_string()));
             if (res && res->isKnownNow()) {
                 stats.narInfoReadAverted++;
                 if (!res->didExist())
@@ -486,7 +504,7 @@ void Store::queryPathInfo(const StorePath & storePath,
                 stats.narInfoReadAverted++;
                 {
                     auto state_(state.lock());
-                    state_->pathInfoCache.upsert(hashPart,
+                    state_->pathInfoCache.upsert(std::string(storePath.to_string()),
                         res.first == NarInfoDiskCache::oInvalid ? PathInfoCacheValue{} : PathInfoCacheValue{ .value = res.second });
                     if (res.first == NarInfoDiskCache::oInvalid ||
                         !goodStorePath(storePath, res.second->path))
@@ -501,7 +519,7 @@ void Store::queryPathInfo(const StorePath & storePath,
     auto callbackPtr = std::make_shared<decltype(callback)>(std::move(callback));
 
     queryPathInfoUncached(storePath,
-        {[this, storePathS{printStorePath(storePath)}, hashPart, callbackPtr](std::future<std::shared_ptr<const ValidPathInfo>> fut) {
+        {[this, storePath, hashPart, callbackPtr](std::future<std::shared_ptr<const ValidPathInfo>> fut) {
 
             try {
                 auto info = fut.get();
@@ -511,14 +529,12 @@ void Store::queryPathInfo(const StorePath & storePath,
 
                 {
                     auto state_(state.lock());
-                    state_->pathInfoCache.upsert(hashPart, PathInfoCacheValue { .value = info });
+                    state_->pathInfoCache.upsert(std::string(storePath.to_string()), PathInfoCacheValue { .value = info });
                 }
 
-                auto storePath = parseStorePath(storePathS);
-
                 if (!info || !goodStorePath(storePath, info->path)) {
                     stats.narInfoMissing++;
-                    throw InvalidPath("path '%s' is not valid", storePathS);
+                    throw InvalidPath("path '%s' is not valid", printStorePath(storePath));
                 }
 
                 (*callbackPtr)(ref<const ValidPathInfo>(info));
@@ -526,6 +542,74 @@ void Store::queryPathInfo(const StorePath & storePath,
         }});
 }
 
+void Store::queryRealisation(const DrvOutput & id,
+        Callback<std::shared_ptr<const Realisation>> callback) noexcept
+{
+
+    try {
+        if (diskCache) {
+            auto [cacheOutcome, maybeCachedRealisation]
+                = diskCache->lookupRealisation(getUri(), id);
+            switch (cacheOutcome) {
+            case NarInfoDiskCache::oValid:
+                debug("Returning a cached realisation for %s", id.to_string());
+                callback(maybeCachedRealisation);
+                return;
+            case NarInfoDiskCache::oInvalid:
+                debug(
+                    "Returning a cached missing realisation for %s",
+                    id.to_string());
+                callback(nullptr);
+                return;
+            case NarInfoDiskCache::oUnknown:
+                break;
+            }
+        }
+    } catch (...) {
+        return callback.rethrow();
+    }
+
+    auto callbackPtr
+        = std::make_shared<decltype(callback)>(std::move(callback));
+
+    queryRealisationUncached(
+        id,
+        { [this, id, callbackPtr](
+              std::future<std::shared_ptr<const Realisation>> fut) {
+            try {
+                auto info = fut.get();
+
+                if (diskCache) {
+                    if (info)
+                        diskCache->upsertRealisation(getUri(), *info);
+                    else
+                        diskCache->upsertAbsentRealisation(getUri(), id);
+                }
+
+                (*callbackPtr)(std::shared_ptr<const Realisation>(info));
+
+            } catch (...) {
+                callbackPtr->rethrow();
+            }
+        } });
+}
+
+std::shared_ptr<const Realisation> Store::queryRealisation(const DrvOutput & id)
+{
+    using RealPtr = std::shared_ptr<const Realisation>;
+    std::promise<RealPtr> promise;
+
+    queryRealisation(id,
+        {[&](std::future<RealPtr> result) {
+            try {
+                promise.set_value(result.get());
+            } catch (...) {
+                promise.set_exception(std::current_exception());
+            }
+        }});
+
+    return promise.get_future().get();
+}
 
 void Store::substitutePaths(const StorePathSet & paths)
 {
@@ -627,6 +711,42 @@ string Store::makeValidityRegistration(const StorePathSet & paths,
 }
 
 
+StorePathSet Store::exportReferences(const StorePathSet & storePaths, const StorePathSet & inputPaths)
+{
+    StorePathSet paths;
+
+    for (auto & storePath : storePaths) {
+        if (!inputPaths.count(storePath))
+            throw BuildError("cannot export references of path '%s' because it is not in the input closure of the derivation", printStorePath(storePath));
+
+        computeFSClosure({storePath}, paths);
+    }
+
+    /* If there are derivations in the graph, then include their
+       outputs as well.  This is useful if you want to do things
+       like passing all build-time dependencies of some path to a
+       derivation that builds a NixOS DVD image. */
+    auto paths2 = paths;
+
+    for (auto & j : paths2) {
+        if (j.isDerivation()) {
+            Derivation drv = derivationFromPath(j);
+            for (auto & k : drv.outputsAndOptPaths(*this)) {
+                if (!k.second.second)
+                    /* FIXME: I am confused why we are calling
+                       `computeFSClosure` on the output path, rather than
+                       derivation itself. That doesn't seem right to me, so I
+                       won't try to implemented this for CA derivations. */
+                    throw UnimplementedError("exportReferences on CA derivations is not yet implemented");
+                computeFSClosure(*k.second.second, paths);
+            }
+        }
+    }
+
+    return paths;
+}
+
+
 void Store::pathInfoToJSON(JSONPlaceholder & jsonOut, const StorePathSet & storePaths,
     bool includeImpureInfo, bool showClosureSize,
     Base hashBase,
@@ -727,30 +847,43 @@ const Store::Stats & Store::getStats()
 }
 
 
-void copyStorePath(ref<Store> srcStore, ref<Store> dstStore,
-    const StorePath & storePath, RepairFlag repair, CheckSigsFlag checkSigs)
+static std::string makeCopyPathMessage(
+    std::string_view srcUri,
+    std::string_view dstUri,
+    std::string_view storePath)
 {
-    auto srcUri = srcStore->getUri();
-    auto dstUri = dstStore->getUri();
+    return srcUri == "local" || srcUri == "daemon"
+        ? fmt("copying path '%s' to '%s'", storePath, dstUri)
+        : dstUri == "local" || dstUri == "daemon"
+        ? fmt("copying path '%s' from '%s'", storePath, srcUri)
+        : fmt("copying path '%s' from '%s' to '%s'", storePath, srcUri, dstUri);
+}
+
 
+void copyStorePath(
+    Store & srcStore,
+    Store & dstStore,
+    const StorePath & storePath,
+    RepairFlag repair,
+    CheckSigsFlag checkSigs)
+{
+    auto srcUri = srcStore.getUri();
+    auto dstUri = dstStore.getUri();
+    auto storePathS = srcStore.printStorePath(storePath);
     Activity act(*logger, lvlInfo, actCopyPath,
-        srcUri == "local" || srcUri == "daemon"
-        ? fmt("copying path '%s' to '%s'", srcStore->printStorePath(storePath), dstUri)
-          : dstUri == "local" || dstUri == "daemon"
-        ? fmt("copying path '%s' from '%s'", srcStore->printStorePath(storePath), srcUri)
-          : fmt("copying path '%s' from '%s' to '%s'", srcStore->printStorePath(storePath), srcUri, dstUri),
-        {srcStore->printStorePath(storePath), srcUri, dstUri});
+        makeCopyPathMessage(srcUri, dstUri, storePathS),
+        {storePathS, srcUri, dstUri});
     PushActivity pact(act.id);
 
-    auto info = srcStore->queryPathInfo(storePath);
+    auto info = srcStore.queryPathInfo(storePath);
 
     uint64_t total = 0;
 
     // recompute store path on the chance dstStore does it differently
     if (info->ca && info->references.empty()) {
         auto info2 = make_ref<ValidPathInfo>(*info);
-        info2->path = dstStore->makeFixedOutputPathFromCA(info->path.name(), *info->ca);
-        if (dstStore->storeDir == srcStore->storeDir)
+        info2->path = dstStore.makeFixedOutputPathFromCA(info->path.name(), *info->ca);
+        if (dstStore.storeDir == srcStore.storeDir)
             assert(info->path == info2->path);
         info = info2;
     }
@@ -767,37 +900,61 @@ void copyStorePath(ref<Store> srcStore, ref<Store> dstStore,
             act.progress(total, info->narSize);
         });
         TeeSink tee { sink, progressSink };
-        srcStore->narFromPath(storePath, tee);
+        srcStore.narFromPath(storePath, tee);
     }, [&]() {
-           throw EndOfFile("NAR for '%s' fetched from '%s' is incomplete", srcStore->printStorePath(storePath), srcStore->getUri());
+           throw EndOfFile("NAR for '%s' fetched from '%s' is incomplete", srcStore.printStorePath(storePath), srcStore.getUri());
     });
 
-    dstStore->addToStore(*info, *source, repair, checkSigs);
+    dstStore.addToStore(*info, *source, repair, checkSigs);
 }
 
 
-std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStore, const RealisedPath::Set & paths,
-    RepairFlag repair, CheckSigsFlag checkSigs, SubstituteFlag substitute)
+std::map<StorePath, StorePath> copyPaths(
+    Store & srcStore,
+    Store & dstStore,
+    const RealisedPath::Set & paths,
+    RepairFlag repair,
+    CheckSigsFlag checkSigs,
+    SubstituteFlag substitute)
 {
     StorePathSet storePaths;
-    std::set<Realisation> realisations;
+    std::set<Realisation> toplevelRealisations;
     for (auto & path : paths) {
         storePaths.insert(path.path());
         if (auto realisation = std::get_if<Realisation>(&path.raw)) {
-            settings.requireExperimentalFeature("ca-derivations");
-            realisations.insert(*realisation);
+            settings.requireExperimentalFeature(Xp::CaDerivations);
+            toplevelRealisations.insert(*realisation);
         }
     }
     auto pathsMap = copyPaths(srcStore, dstStore, storePaths, repair, checkSigs, substitute);
+
+    ThreadPool pool;
+
     try {
-        for (auto & realisation : realisations) {
-            dstStore->registerDrvOutput(realisation, checkSigs);
-        }
+        // Copy the realisation closure
+        processGraph<Realisation>(
+            pool, Realisation::closure(srcStore, toplevelRealisations),
+            [&](const Realisation & current) -> std::set<Realisation> {
+                std::set<Realisation> children;
+                for (const auto & [drvOutput, _] : current.dependentRealisations) {
+                    auto currentChild = srcStore.queryRealisation(drvOutput);
+                    if (!currentChild)
+                        throw Error(
+                            "incomplete realisation closure: '%s' is a "
+                            "dependency of '%s' but isn't registered",
+                            drvOutput.to_string(), current.id.to_string());
+                    children.insert(*currentChild);
+                }
+                return children;
+            },
+            [&](const Realisation& current) -> void {
+                dstStore.registerDrvOutput(current, checkSigs);
+            });
     } catch (MissingExperimentalFeature & e) {
         // Don't fail if the remote doesn't support CA derivations is it might
         // not be within our control to change that, and we might still want
         // to at least copy the output paths.
-        if (e.missingFeature == "ca-derivations")
+        if (e.missingFeature == Xp::CaDerivations)
             ignoreException();
         else
             throw;
@@ -806,10 +963,15 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
     return pathsMap;
 }
 
-std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStore, const StorePathSet & storePaths,
-    RepairFlag repair, CheckSigsFlag checkSigs, SubstituteFlag substitute)
+std::map<StorePath, StorePath> copyPaths(
+    Store & srcStore,
+    Store & dstStore,
+    const StorePathSet & storePaths,
+    RepairFlag repair,
+    CheckSigsFlag checkSigs,
+    SubstituteFlag substitute)
 {
-    auto valid = dstStore->queryValidPaths(storePaths, substitute);
+    auto valid = dstStore.queryValidPaths(storePaths, substitute);
 
     StorePathSet missing;
     for (auto & path : storePaths)
@@ -819,9 +981,31 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
     for (auto & path : storePaths)
         pathsMap.insert_or_assign(path, path);
 
-
     Activity act(*logger, lvlInfo, actCopyPaths, fmt("copying %d paths", missing.size()));
 
+    auto sorted = srcStore.topoSortPaths(missing);
+    std::reverse(sorted.begin(), sorted.end());
+
+    auto source = sinkToSource([&](Sink & sink) {
+        sink << sorted.size();
+        for (auto & storePath : sorted) {
+            auto srcUri = srcStore.getUri();
+            auto dstUri = dstStore.getUri();
+            auto storePathS = srcStore.printStorePath(storePath);
+            Activity act(*logger, lvlInfo, actCopyPath,
+                makeCopyPathMessage(srcUri, dstUri, storePathS),
+                {storePathS, srcUri, dstUri});
+            PushActivity pact(act.id);
+
+            auto info = srcStore.queryPathInfo(storePath);
+            info->write(sink, srcStore, 16);
+            srcStore.narFromPath(storePath, sink);
+        }
+    });
+
+    dstStore.addMultipleToStore(*source, repair, checkSigs);
+
+    #if 0
     std::atomic<size_t> nrDone{0};
     std::atomic<size_t> nrFailed{0};
     std::atomic<uint64_t> bytesExpected{0};
@@ -837,18 +1021,21 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
         StorePathSet(missing.begin(), missing.end()),
 
         [&](const StorePath & storePath) {
-            auto info = srcStore->queryPathInfo(storePath);
+            auto info = srcStore.queryPathInfo(storePath);
             auto storePathForDst = storePath;
             if (info->ca && info->references.empty()) {
-                storePathForDst = dstStore->makeFixedOutputPathFromCA(storePath.name(), *info->ca);
-                if (dstStore->storeDir == srcStore->storeDir)
+                storePathForDst = dstStore.makeFixedOutputPathFromCA(storePath.name(), *info->ca);
+                if (dstStore.storeDir == srcStore.storeDir)
                     assert(storePathForDst == storePath);
                 if (storePathForDst != storePath)
-                    debug("replaced path '%s' to '%s' for substituter '%s'", srcStore->printStorePath(storePath), dstStore->printStorePath(storePathForDst), dstStore->getUri());
+                    debug("replaced path '%s' to '%s' for substituter '%s'",
+                        srcStore.printStorePath(storePath),
+                        dstStore.printStorePath(storePathForDst),
+                        dstStore.getUri());
             }
             pathsMap.insert_or_assign(storePath, storePathForDst);
 
-            if (dstStore->isValidPath(storePath)) {
+            if (dstStore.isValidPath(storePath)) {
                 nrDone++;
                 showProgress();
                 return StorePathSet();
@@ -863,19 +1050,22 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
         [&](const StorePath & storePath) {
             checkInterrupt();
 
-            auto info = srcStore->queryPathInfo(storePath);
+            auto info = srcStore.queryPathInfo(storePath);
 
             auto storePathForDst = storePath;
             if (info->ca && info->references.empty()) {
-                storePathForDst = dstStore->makeFixedOutputPathFromCA(storePath.name(), *info->ca);
-                if (dstStore->storeDir == srcStore->storeDir)
+                storePathForDst = dstStore.makeFixedOutputPathFromCA(storePath.name(), *info->ca);
+                if (dstStore.storeDir == srcStore.storeDir)
                     assert(storePathForDst == storePath);
                 if (storePathForDst != storePath)
-                    debug("replaced path '%s' to '%s' for substituter '%s'", srcStore->printStorePath(storePath), dstStore->printStorePath(storePathForDst), dstStore->getUri());
+                    debug("replaced path '%s' to '%s' for substituter '%s'",
+                        srcStore.printStorePath(storePath),
+                        dstStore.printStorePath(storePathForDst),
+                        dstStore.getUri());
             }
             pathsMap.insert_or_assign(storePath, storePathForDst);
 
-            if (!dstStore->isValidPath(storePathForDst)) {
+            if (!dstStore.isValidPath(storePathForDst)) {
                 MaintainCount<decltype(nrRunning)> mc(nrRunning);
                 showProgress();
                 try {
@@ -884,7 +1074,7 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
                     nrFailed++;
                     if (!settings.keepGoing)
                         throw e;
-                    logger->log(lvlError, fmt("could not copy %s: %s", dstStore->printStorePath(storePath), e.what()));
+                    logger->log(lvlError, fmt("could not copy %s: %s", dstStore.printStorePath(storePath), e.what()));
                     showProgress();
                     return;
                 }
@@ -893,9 +1083,27 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
             nrDone++;
             showProgress();
         });
+    #endif
+
     return pathsMap;
 }
 
+void copyClosure(
+    Store & srcStore,
+    Store & dstStore,
+    const RealisedPath::Set & paths,
+    RepairFlag repair,
+    CheckSigsFlag checkSigs,
+    SubstituteFlag substitute)
+{
+    if (&srcStore == &dstStore) return;
+
+    RealisedPath::Set closure;
+    RealisedPath::closure(srcStore, paths, closure);
+
+    copyPaths(srcStore, dstStore, closure, repair, checkSigs, substitute);
+}
+
 std::optional<ValidPathInfo> decodeValidPathInfo(const Store & store, std::istream & str, std::optional<HashResult> hashGiven)
 {
     std::string path;
@@ -968,10 +1176,10 @@ bool ValidPathInfo::isContentAddressed(const Store & store) const
     if (! ca) return false;
 
     auto caPath = std::visit(overloaded {
-        [&](TextHash th) {
+        [&](const TextHash & th) {
             return store.makeTextPath(path.name(), th.hash, references);
         },
-        [&](FixedOutputHash fsh) {
+        [&](const FixedOutputHash & fsh) {
             auto refs = references;
             bool hasSelfReference = false;
             if (refs.count(path)) {
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index f66298991..aa44651d4 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -180,6 +180,8 @@ struct StoreConfig : public Config
 
     StoreConfig() = delete;
 
+    StringSet getDefaultSystemFeatures();
+
     virtual ~StoreConfig() { }
 
     virtual const std::string name() = 0;
@@ -196,7 +198,7 @@ struct StoreConfig : public Config
 
     Setting<bool> wantMassQuery{this, false, "want-mass-query", "whether this substituter can be queried efficiently for path validity"};
 
-    Setting<StringSet> systemFeatures{this, settings.systemFeatures,
+    Setting<StringSet> systemFeatures{this, getDefaultSystemFeatures(),
         "system-features",
         "Optional features that the system this store builds on implements (like \"kvm\")."};
 
@@ -230,7 +232,6 @@ protected:
 
     struct State
     {
-        // FIXME: fix key
         LRUCache<std::string, PathInfoCacheValue> pathInfoCache;
     };
 
@@ -368,6 +369,14 @@ public:
     void queryPathInfo(const StorePath & path,
         Callback<ref<const ValidPathInfo>> callback) noexcept;
 
+    /* Query the information about a realisation. */
+    std::shared_ptr<const Realisation> queryRealisation(const DrvOutput &);
+
+    /* Asynchronous version of queryRealisation(). */
+    void queryRealisation(const DrvOutput &,
+        Callback<std::shared_ptr<const Realisation>> callback) noexcept;
+
+
     /* Check whether the given valid path info is sufficiently attested, by
        either being signed by a trusted public key or content-addressed, in
        order to be included in the given store.
@@ -392,11 +401,11 @@ protected:
 
     virtual void queryPathInfoUncached(const StorePath & path,
         Callback<std::shared_ptr<const ValidPathInfo>> callback) noexcept = 0;
+    virtual void queryRealisationUncached(const DrvOutput &,
+        Callback<std::shared_ptr<const Realisation>> callback) noexcept = 0;
 
 public:
 
-    virtual std::optional<const Realisation> queryRealisation(const DrvOutput &) = 0;
-
     /* Queries the set of incoming FS references for a store path.
        The result is not cleared. */
     virtual void queryReferrers(const StorePath & path, StorePathSet & referrers)
@@ -428,9 +437,10 @@ public:
     virtual StorePathSet querySubstitutablePaths(const StorePathSet & paths) { return {}; };
 
     /* Query substitute info (i.e. references, derivers and download
-       sizes) of a map of paths to their optional ca values. If a path
-       does not have substitute info, it's omitted from the resulting
-       ‘infos’ map. */
+       sizes) of a map of paths to their optional ca values. The info
+       of the first succeeding substituter for each path will be
+       returned. If a path does not have substitute info, it's omitted
+       from the resulting ‘infos’ map. */
     virtual void querySubstitutablePathInfos(const StorePathCAMap & paths,
         SubstitutablePathInfos & infos) { return; };
 
@@ -438,13 +448,19 @@ public:
     virtual void addToStore(const ValidPathInfo & info, Source & narSource,
         RepairFlag repair = NoRepair, CheckSigsFlag checkSigs = CheckSigs) = 0;
 
+    /* Import multiple paths into the store. */
+    virtual void addMultipleToStore(
+        Source & source,
+        RepairFlag repair = NoRepair,
+        CheckSigsFlag checkSigs = CheckSigs);
+
     /* Copy the contents of a path to the store and register the
        validity the resulting path.  The resulting path is returned.
        The function object `filter' can be used to exclude files (see
        libutil/archive.hh). */
     virtual StorePath addToStore(const string & name, const Path & srcPath,
         FileIngestionMethod method = FileIngestionMethod::Recursive, HashType hashAlgo = htSHA256,
-        PathFilter & filter = defaultPathFilter, RepairFlag repair = NoRepair);
+        PathFilter & filter = defaultPathFilter, RepairFlag repair = NoRepair, const StorePathSet & references = StorePathSet());
 
     /* Copy the contents of a path to the store and register the
        validity the resulting path, using a constant amount of
@@ -460,7 +476,8 @@ public:
        `dump` may be drained */
     // FIXME: remove?
     virtual StorePath addToStoreFromDump(Source & dump, const string & name,
-        FileIngestionMethod method = FileIngestionMethod::Recursive, HashType hashAlgo = htSHA256, RepairFlag repair = NoRepair)
+        FileIngestionMethod method = FileIngestionMethod::Recursive, HashType hashAlgo = htSHA256, RepairFlag repair = NoRepair,
+        const StorePathSet & references = StorePathSet())
     { unsupported("addToStoreFromDump"); }
 
     /* Like addToStore, but the contents written to the output path is
@@ -495,7 +512,8 @@ public:
        not derivations, substitute them. */
     virtual void buildPaths(
         const std::vector<DerivedPath> & paths,
-        BuildMode buildMode = bmNormal);
+        BuildMode buildMode = bmNormal,
+        std::shared_ptr<Store> evalStore = nullptr);
 
     /* Build a single non-materialized derivation (i.e. not from an
        on-disk .drv file).
@@ -541,7 +559,7 @@ public:
     /* Add a store path as a temporary root of the garbage collector.
        The root disappears as soon as we exit. */
     virtual void addTempRoot(const StorePath & path)
-    { warn("not creating temp root, store doesn't support GC"); }
+    { debug("not creating temporary root, store doesn't support GC"); }
 
     /* Add an indirect root, which is merely a symlink to `path' from
        /nix/var/nix/gcroots/auto/<hash of `path'>.  `path' is supposed
@@ -551,26 +569,6 @@ public:
     virtual void addIndirectRoot(const Path & path)
     { unsupported("addIndirectRoot"); }
 
-    /* Acquire the global GC lock, then immediately release it.  This
-       function must be called after registering a new permanent root,
-       but before exiting.  Otherwise, it is possible that a running
-       garbage collector doesn't see the new root and deletes the
-       stuff we've just built.  By acquiring the lock briefly, we
-       ensure that either:
-
-       - The collector is already running, and so we block until the
-         collector is finished.  The collector will know about our
-         *temporary* locks, which should include whatever it is we
-         want to register as a permanent lock.
-
-       - The collector isn't running, or it's just started but hasn't
-         acquired the GC lock yet.  In that case we get and release
-         the lock right away, then exit.  The collector scans the
-         permanent root and sees ours.
-
-       In either case the permanent root is seen by the collector. */
-    virtual void syncWithGC() { };
-
     /* Find the roots of the garbage collector.  Each root is a pair
        (link, storepath) where `link' is the path of the symlink
        outside of the Nix store that point to `storePath'. If
@@ -695,6 +693,11 @@ public:
 
     const Stats & getStats();
 
+    /* Computes the full closure of of a set of store-paths for e.g.
+       derivations that need this information for `exportReferencesGraph`.
+     */
+    StorePathSet exportReferences(const StorePathSet & storePaths, const StorePathSet & inputPaths);
+
     /* Return the build log of the specified store path, if available,
        or null otherwise. */
     virtual std::shared_ptr<std::string> getBuildLog(const StorePath & path)
@@ -730,6 +733,11 @@ public:
     virtual void createUser(const std::string & userName, uid_t userId)
     { }
 
+    /*
+     * Synchronises the options of the client with those of the daemon
+     * (a no-op when there’s no daemon)
+     */
+    virtual void setOptions() { }
 protected:
 
     Stats stats;
@@ -744,8 +752,12 @@ protected:
 
 
 /* Copy a path from one store to another. */
-void copyStorePath(ref<Store> srcStore, ref<Store> dstStore,
-    const StorePath & storePath, RepairFlag repair = NoRepair, CheckSigsFlag checkSigs = CheckSigs);
+void copyStorePath(
+    Store & srcStore,
+    Store & dstStore,
+    const StorePath & storePath,
+    RepairFlag repair = NoRepair,
+    CheckSigsFlag checkSigs = CheckSigs);
 
 
 /* Copy store paths from one store to another. The paths may be copied
@@ -754,17 +766,27 @@ void copyStorePath(ref<Store> srcStore, ref<Store> dstStore,
    of store paths is not automatically closed; use copyClosure() for
    that. Returns a map of what each path was copied to the dstStore
    as. */
-std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStore,
+std::map<StorePath, StorePath> copyPaths(
+    Store & srcStore, Store & dstStore,
     const RealisedPath::Set &,
     RepairFlag repair = NoRepair,
     CheckSigsFlag checkSigs = CheckSigs,
     SubstituteFlag substitute = NoSubstitute);
-std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStore,
-    const StorePathSet& paths,
+
+std::map<StorePath, StorePath> copyPaths(
+    Store & srcStore, Store & dstStore,
+    const StorePathSet & paths,
     RepairFlag repair = NoRepair,
     CheckSigsFlag checkSigs = CheckSigs,
     SubstituteFlag substitute = NoSubstitute);
 
+/* Copy the closure of `paths` from `srcStore` to `dstStore`. */
+void copyClosure(
+    Store & srcStore, Store & dstStore,
+    const RealisedPath::Set & paths,
+    RepairFlag repair = NoRepair,
+    CheckSigsFlag checkSigs = CheckSigs,
+    SubstituteFlag substitute = NoSubstitute);
 
 /* Remove the temporary roots file for this process.  Any temporary
    root becomes garbage after this point unless it has been registered
@@ -864,4 +886,9 @@ std::pair<std::string, Store::Params> splitUriAndParams(const std::string & uri)
 
 std::optional<ContentAddress> getDerivationCA(const BasicDerivation & drv);
 
+std::map<DrvOutput, StorePath> drvOutputReferences(
+    Store & store,
+    const Derivation & drv,
+    const StorePath & outputPath);
+
 }
diff --git a/src/libstore/tests/local.mk b/src/libstore/tests/local.mk
new file mode 100644
index 000000000..f74295d97
--- /dev/null
+++ b/src/libstore/tests/local.mk
@@ -0,0 +1,15 @@
+check: libstore-tests_RUN
+
+programs += libstore-tests
+
+libstore-tests_DIR := $(d)
+
+libstore-tests_INSTALL_DIR :=
+
+libstore-tests_SOURCES := $(wildcard $(d)/*.cc)
+
+libstore-tests_CXXFLAGS += -I src/libstore -I src/libutil
+
+libstore-tests_LIBS = libstore libutil
+
+libstore-tests_LDFLAGS := $(GTEST_LIBS)
diff --git a/src/libstore/tests/machines.cc b/src/libstore/tests/machines.cc
new file mode 100644
index 000000000..f51052b14
--- /dev/null
+++ b/src/libstore/tests/machines.cc
@@ -0,0 +1,169 @@
+#include "machines.hh"
+#include "globals.hh"
+
+#include <gmock/gmock-matchers.h>
+
+using testing::Contains;
+using testing::ElementsAre;
+using testing::EndsWith;
+using testing::Eq;
+using testing::Field;
+using testing::SizeIs;
+
+using nix::absPath;
+using nix::FormatError;
+using nix::getMachines;
+using nix::Machine;
+using nix::Machines;
+using nix::pathExists;
+using nix::Settings;
+using nix::settings;
+
+class Environment : public ::testing::Environment {
+  public:
+    void SetUp() override { settings.thisSystem = "TEST_ARCH-TEST_OS"; }
+};
+
+testing::Environment* const foo_env =
+    testing::AddGlobalTestEnvironment(new Environment);
+
+TEST(machines, getMachinesWithEmptyBuilders) {
+    settings.builders = "";
+    Machines actual = getMachines();
+    ASSERT_THAT(actual, SizeIs(0));
+}
+
+TEST(machines, getMachinesUriOnly) {
+    settings.builders = "nix@scratchy.labs.cs.uu.nl";
+    Machines actual = getMachines();
+    ASSERT_THAT(actual, SizeIs(1));
+    EXPECT_THAT(actual[0], Field(&Machine::storeUri, Eq("ssh://nix@scratchy.labs.cs.uu.nl")));
+    EXPECT_THAT(actual[0], Field(&Machine::systemTypes, ElementsAre("TEST_ARCH-TEST_OS")));
+    EXPECT_THAT(actual[0], Field(&Machine::sshKey, SizeIs(0)));
+    EXPECT_THAT(actual[0], Field(&Machine::maxJobs, Eq(1)));
+    EXPECT_THAT(actual[0], Field(&Machine::speedFactor, Eq(1)));
+    EXPECT_THAT(actual[0], Field(&Machine::supportedFeatures, SizeIs(0)));
+    EXPECT_THAT(actual[0], Field(&Machine::mandatoryFeatures, SizeIs(0)));
+    EXPECT_THAT(actual[0], Field(&Machine::sshPublicHostKey, SizeIs(0)));
+}
+
+TEST(machines, getMachinesDefaults) {
+    settings.builders = "nix@scratchy.labs.cs.uu.nl - - - - - - -";
+    Machines actual = getMachines();
+    ASSERT_THAT(actual, SizeIs(1));
+    EXPECT_THAT(actual[0], Field(&Machine::storeUri, Eq("ssh://nix@scratchy.labs.cs.uu.nl")));
+    EXPECT_THAT(actual[0], Field(&Machine::systemTypes, ElementsAre("TEST_ARCH-TEST_OS")));
+    EXPECT_THAT(actual[0], Field(&Machine::sshKey, SizeIs(0)));
+    EXPECT_THAT(actual[0], Field(&Machine::maxJobs, Eq(1)));
+    EXPECT_THAT(actual[0], Field(&Machine::speedFactor, Eq(1)));
+    EXPECT_THAT(actual[0], Field(&Machine::supportedFeatures, SizeIs(0)));
+    EXPECT_THAT(actual[0], Field(&Machine::mandatoryFeatures, SizeIs(0)));
+    EXPECT_THAT(actual[0], Field(&Machine::sshPublicHostKey, SizeIs(0)));
+}
+
+TEST(machines, getMachinesWithNewLineSeparator) {
+    settings.builders = "nix@scratchy.labs.cs.uu.nl\nnix@itchy.labs.cs.uu.nl";
+    Machines actual = getMachines();
+    ASSERT_THAT(actual, SizeIs(2));
+    EXPECT_THAT(actual, Contains(Field(&Machine::storeUri, EndsWith("nix@scratchy.labs.cs.uu.nl"))));
+    EXPECT_THAT(actual, Contains(Field(&Machine::storeUri, EndsWith("nix@itchy.labs.cs.uu.nl"))));
+}
+
+TEST(machines, getMachinesWithSemicolonSeparator) {
+    settings.builders = "nix@scratchy.labs.cs.uu.nl ; nix@itchy.labs.cs.uu.nl";
+    Machines actual = getMachines();
+    EXPECT_THAT(actual, SizeIs(2));
+    EXPECT_THAT(actual, Contains(Field(&Machine::storeUri, EndsWith("nix@scratchy.labs.cs.uu.nl"))));
+    EXPECT_THAT(actual, Contains(Field(&Machine::storeUri, EndsWith("nix@itchy.labs.cs.uu.nl"))));
+}
+
+TEST(machines, getMachinesWithCorrectCompleteSingleBuilder) {
+    settings.builders = "nix@scratchy.labs.cs.uu.nl     i686-linux      "
+                        "/home/nix/.ssh/id_scratchy_auto        8 3 kvm "
+                        "benchmark SSH+HOST+PUBLIC+KEY+BASE64+ENCODED==";
+    Machines actual = getMachines();
+    ASSERT_THAT(actual, SizeIs(1));
+    EXPECT_THAT(actual[0], Field(&Machine::storeUri, EndsWith("nix@scratchy.labs.cs.uu.nl")));
+    EXPECT_THAT(actual[0], Field(&Machine::systemTypes, ElementsAre("i686-linux")));
+    EXPECT_THAT(actual[0], Field(&Machine::sshKey, Eq("/home/nix/.ssh/id_scratchy_auto")));
+    EXPECT_THAT(actual[0], Field(&Machine::maxJobs, Eq(8)));
+    EXPECT_THAT(actual[0], Field(&Machine::speedFactor, Eq(3)));
+    EXPECT_THAT(actual[0], Field(&Machine::supportedFeatures, ElementsAre("kvm")));
+    EXPECT_THAT(actual[0], Field(&Machine::mandatoryFeatures, ElementsAre("benchmark")));
+    EXPECT_THAT(actual[0], Field(&Machine::sshPublicHostKey, Eq("SSH+HOST+PUBLIC+KEY+BASE64+ENCODED==")));
+}
+
+TEST(machines,
+     getMachinesWithCorrectCompleteSingleBuilderWithTabColumnDelimiter) {
+    settings.builders =
+        "nix@scratchy.labs.cs.uu.nl\ti686-linux\t/home/nix/.ssh/"
+        "id_scratchy_auto\t8\t3\tkvm\tbenchmark\tSSH+HOST+PUBLIC+"
+        "KEY+BASE64+ENCODED==";
+    Machines actual = getMachines();
+    ASSERT_THAT(actual, SizeIs(1));
+    EXPECT_THAT(actual[0], Field(&Machine::storeUri, EndsWith("nix@scratchy.labs.cs.uu.nl")));
+    EXPECT_THAT(actual[0], Field(&Machine::systemTypes, ElementsAre("i686-linux")));
+    EXPECT_THAT(actual[0], Field(&Machine::sshKey, Eq("/home/nix/.ssh/id_scratchy_auto")));
+    EXPECT_THAT(actual[0], Field(&Machine::maxJobs, Eq(8)));
+    EXPECT_THAT(actual[0], Field(&Machine::speedFactor, Eq(3)));
+    EXPECT_THAT(actual[0], Field(&Machine::supportedFeatures, ElementsAre("kvm")));
+    EXPECT_THAT(actual[0], Field(&Machine::mandatoryFeatures, ElementsAre("benchmark")));
+    EXPECT_THAT(actual[0], Field(&Machine::sshPublicHostKey, Eq("SSH+HOST+PUBLIC+KEY+BASE64+ENCODED==")));
+}
+
+TEST(machines, getMachinesWithMultiOptions) {
+    settings.builders = "nix@scratchy.labs.cs.uu.nl Arch1,Arch2 - - - "
+                        "SupportedFeature1,SupportedFeature2 "
+                        "MandatoryFeature1,MandatoryFeature2";
+    Machines actual = getMachines();
+    ASSERT_THAT(actual, SizeIs(1));
+    EXPECT_THAT(actual[0], Field(&Machine::storeUri, EndsWith("nix@scratchy.labs.cs.uu.nl")));
+    EXPECT_THAT(actual[0], Field(&Machine::systemTypes, ElementsAre("Arch1", "Arch2")));
+    EXPECT_THAT(actual[0], Field(&Machine::supportedFeatures, ElementsAre("SupportedFeature1", "SupportedFeature2")));
+    EXPECT_THAT(actual[0], Field(&Machine::mandatoryFeatures, ElementsAre("MandatoryFeature1", "MandatoryFeature2")));
+}
+
+TEST(machines, getMachinesWithIncorrectFormat) {
+    settings.builders = "nix@scratchy.labs.cs.uu.nl - - eight";
+    EXPECT_THROW(getMachines(), FormatError);
+    settings.builders = "nix@scratchy.labs.cs.uu.nl - - -1";
+    EXPECT_THROW(getMachines(), FormatError);
+    settings.builders = "nix@scratchy.labs.cs.uu.nl - - 8 three";
+    EXPECT_THROW(getMachines(), FormatError);
+    settings.builders = "nix@scratchy.labs.cs.uu.nl - - 8 -3";
+    EXPECT_THROW(getMachines(), FormatError);
+    settings.builders = "nix@scratchy.labs.cs.uu.nl - - 8 3 - - BAD_BASE64";
+    EXPECT_THROW(getMachines(), FormatError);
+}
+
+TEST(machines, getMachinesWithCorrectFileReference) {
+    auto path = absPath("src/libstore/tests/test-data/machines.valid");
+    ASSERT_TRUE(pathExists(path));
+
+    settings.builders = std::string("@") + path;
+    Machines actual = getMachines();
+    ASSERT_THAT(actual, SizeIs(3));
+    EXPECT_THAT(actual, Contains(Field(&Machine::storeUri, EndsWith("nix@scratchy.labs.cs.uu.nl"))));
+    EXPECT_THAT(actual, Contains(Field(&Machine::storeUri, EndsWith("nix@itchy.labs.cs.uu.nl"))));
+    EXPECT_THAT(actual, Contains(Field(&Machine::storeUri, EndsWith("nix@poochie.labs.cs.uu.nl"))));
+}
+
+TEST(machines, getMachinesWithCorrectFileReferenceToEmptyFile) {
+    auto path = "/dev/null";
+    ASSERT_TRUE(pathExists(path));
+
+    settings.builders = std::string("@") + path;
+    Machines actual = getMachines();
+    ASSERT_THAT(actual, SizeIs(0));
+}
+
+TEST(machines, getMachinesWithIncorrectFileReference) {
+    settings.builders = std::string("@") + absPath("/not/a/file");
+    Machines actual = getMachines();
+    ASSERT_THAT(actual, SizeIs(0));
+}
+
+TEST(machines, getMachinesWithCorrectFileReferenceToIncorrectFile) {
+    settings.builders = std::string("@") + absPath("src/libstore/tests/test-data/machines.bad_format");
+    EXPECT_THROW(getMachines(), FormatError);
+}
diff --git a/src/libstore/tests/references.cc b/src/libstore/tests/references.cc
new file mode 100644
index 000000000..d91d1cedd
--- /dev/null
+++ b/src/libstore/tests/references.cc
@@ -0,0 +1,45 @@
+#include "references.hh"
+
+#include <gtest/gtest.h>
+
+namespace nix {
+
+TEST(references, scan)
+{
+    std::string hash1 = "dc04vv14dak1c1r48qa0m23vr9jy8sm0";
+    std::string hash2 = "zc842j0rz61mjsp3h3wp5ly71ak6qgdn";
+
+    {
+        RefScanSink scanner(StringSet{hash1});
+        auto s = "foobar";
+        scanner(s);
+        ASSERT_EQ(scanner.getResult(), StringSet{});
+    }
+
+    {
+        RefScanSink scanner(StringSet{hash1});
+        auto s = "foobar" + hash1 + "xyzzy";
+        scanner(s);
+        ASSERT_EQ(scanner.getResult(), StringSet{hash1});
+    }
+
+    {
+        RefScanSink scanner(StringSet{hash1, hash2});
+        auto s = "foobar" + hash1 + "xyzzy" + hash2;
+        scanner(((std::string_view) s).substr(0, 10));
+        scanner(((std::string_view) s).substr(10, 5));
+        scanner(((std::string_view) s).substr(15, 5));
+        scanner(((std::string_view) s).substr(20));
+        ASSERT_EQ(scanner.getResult(), StringSet({hash1, hash2}));
+    }
+
+    {
+        RefScanSink scanner(StringSet{hash1, hash2});
+        auto s = "foobar" + hash1 + "xyzzy" + hash2;
+        for (auto & i : s)
+            scanner(std::string(1, i));
+        ASSERT_EQ(scanner.getResult(), StringSet({hash1, hash2}));
+    }
+}
+
+}
diff --git a/src/libstore/tests/test-data/machines.bad_format b/src/libstore/tests/test-data/machines.bad_format
new file mode 100644
index 000000000..7255a1216
--- /dev/null
+++ b/src/libstore/tests/test-data/machines.bad_format
@@ -0,0 +1 @@
+nix@scratchy.labs.cs.uu.nl - - eight
diff --git a/src/libstore/tests/test-data/machines.valid b/src/libstore/tests/test-data/machines.valid
new file mode 100644
index 000000000..1a6c8017c
--- /dev/null
+++ b/src/libstore/tests/test-data/machines.valid
@@ -0,0 +1,3 @@
+nix@scratchy.labs.cs.uu.nl  i686-linux      /home/nix/.ssh/id_scratchy_auto        8 1 kvm
+nix@itchy.labs.cs.uu.nl     i686-linux      /home/nix/.ssh/id_scratchy_auto        8 2
+nix@poochie.labs.cs.uu.nl   i686-linux      /home/nix/.ssh/id_scratchy_auto        1 2 kvm benchmark 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
diff --git a/src/libstore/uds-remote-store.cc b/src/libstore/uds-remote-store.cc
index cac4fa036..5c38323cd 100644
--- a/src/libstore/uds-remote-store.cc
+++ b/src/libstore/uds-remote-store.cc
@@ -45,30 +45,20 @@ std::string UDSRemoteStore::getUri()
 }
 
 
+void UDSRemoteStore::Connection::closeWrite()
+{
+    shutdown(fd.get(), SHUT_WR);
+}
+
+
 ref<RemoteStore::Connection> UDSRemoteStore::openConnection()
 {
     auto conn = make_ref<Connection>();
 
     /* Connect to a daemon that does the privileged work for us. */
-    conn->fd = socket(PF_UNIX, SOCK_STREAM
-        #ifdef SOCK_CLOEXEC
-        | SOCK_CLOEXEC
-        #endif
-        , 0);
-    if (!conn->fd)
-        throw SysError("cannot create Unix domain socket");
-    closeOnExec(conn->fd.get());
-
-    string socketPath = path ? *path : settings.nixDaemonSocketFile;
-
-    struct sockaddr_un addr;
-    addr.sun_family = AF_UNIX;
-    if (socketPath.size() + 1 >= sizeof(addr.sun_path))
-        throw Error("socket path '%1%' is too long", socketPath);
-    strcpy(addr.sun_path, socketPath.c_str());
-
-    if (::connect(conn->fd.get(), (struct sockaddr *) &addr, sizeof(addr)) == -1)
-        throw SysError("cannot connect to daemon at '%1%'", socketPath);
+    conn->fd = createUnixDomainSocket();
+
+    nix::connect(conn->fd.get(), path ? *path : settings.nixDaemonSocketFile);
 
     conn->from.fd = conn->fd.get();
     conn->to.fd = conn->fd.get();
diff --git a/src/libstore/uds-remote-store.hh b/src/libstore/uds-remote-store.hh
index ddc7716cd..f8dfcca70 100644
--- a/src/libstore/uds-remote-store.hh
+++ b/src/libstore/uds-remote-store.hh
@@ -40,6 +40,12 @@ public:
 
 private:
 
+    struct Connection : RemoteStore::Connection
+    {
+        AutoCloseFD fd;
+        void closeWrite() override;
+    };
+
     ref<RemoteStore::Connection> openConnection() override;
     std::optional<std::string> path;
 };
diff --git a/src/libstore/worker-protocol.hh b/src/libstore/worker-protocol.hh
index 001ed25e3..93cf546d2 100644
--- a/src/libstore/worker-protocol.hh
+++ b/src/libstore/worker-protocol.hh
@@ -9,7 +9,7 @@ namespace nix {
 #define WORKER_MAGIC_1 0x6e697863
 #define WORKER_MAGIC_2 0x6478696f
 
-#define PROTOCOL_VERSION (1 << 8 | 29)
+#define PROTOCOL_VERSION (1 << 8 | 32)
 #define GET_PROTOCOL_MAJOR(x) ((x) & 0xff00)
 #define GET_PROTOCOL_MINOR(x) ((x) & 0x00ff)
 
@@ -55,6 +55,7 @@ typedef enum {
     wopQueryDerivationOutputMap = 41,
     wopRegisterDrvOutput = 42,
     wopQueryRealisation = 43,
+    wopAddMultipleToStore = 44,
 } WorkerOp;
 
 
diff --git a/src/libutil/ansicolor.hh b/src/libutil/ansicolor.hh
index ae741f867..38305e71c 100644
--- a/src/libutil/ansicolor.hh
+++ b/src/libutil/ansicolor.hh
@@ -9,7 +9,7 @@ namespace nix {
 #define ANSI_ITALIC "\e[3m"
 #define ANSI_RED "\e[31;1m"
 #define ANSI_GREEN "\e[32;1m"
-#define ANSI_YELLOW "\e[33;1m"
+#define ANSI_WARNING "\e[35;1m"
 #define ANSI_BLUE "\e[34;1m"
 #define ANSI_MAGENTA "\e[35;1m"
 #define ANSI_CYAN "\e[36;1m"
diff --git a/src/libutil/archive.cc b/src/libutil/archive.cc
index ed0eb2fb5..d78ec2b93 100644
--- a/src/libutil/archive.cc
+++ b/src/libutil/archive.cc
@@ -42,7 +42,7 @@ static string caseHackSuffix = "~nix~case~hack~";
 PathFilter defaultPathFilter = [](const Path &) { return true; };
 
 
-static void dumpContents(const Path & path, size_t size,
+static void dumpContents(const Path & path, off_t size,
     Sink & sink)
 {
     sink << "contents" << size;
@@ -76,7 +76,7 @@ static void dump(const Path & path, Sink & sink, PathFilter & filter)
         sink << "type" << "regular";
         if (st.st_mode & S_IXUSR)
             sink << "executable" << "";
-        dumpContents(path, (size_t) st.st_size, sink);
+        dumpContents(path, st.st_size, sink);
     }
 
     else if (S_ISDIR(st.st_mode)) {
diff --git a/src/libutil/args.cc b/src/libutil/args.cc
index afed0670f..9df279faf 100644
--- a/src/libutil/args.cc
+++ b/src/libutil/args.cc
@@ -331,6 +331,7 @@ MultiCommand::MultiCommand(const Commands & commands_)
             if (i == commands.end())
                 throw UsageError("'%s' is not a recognised command", s);
             command = {s, i->second()};
+            command->second->parent = this;
         }}
     });
 
diff --git a/src/libutil/args.hh b/src/libutil/args.hh
index c08ba8abd..7521b3065 100644
--- a/src/libutil/args.hh
+++ b/src/libutil/args.hh
@@ -12,6 +12,8 @@ namespace nix {
 
 enum HashType : char;
 
+class MultiCommand;
+
 class Args
 {
 public:
@@ -89,6 +91,14 @@ protected:
               })
             , arity(1)
         { }
+
+        template<class I>
+        Handler(std::optional<I> * dest)
+            : fun([=](std::vector<std::string> ss) {
+                *dest = string2IntWithUnitPrefix<I>(ss[0]);
+            })
+            , arity(1)
+        { }
     };
 
     /* Options. */
@@ -169,11 +179,13 @@ public:
     virtual nlohmann::json toJSON();
 
     friend class MultiCommand;
+
+    MultiCommand * parent = nullptr;
 };
 
 /* A command is an argument parser that can be executed by calling its
    run() method. */
-struct Command : virtual Args
+struct Command : virtual public Args
 {
     friend class MultiCommand;
 
@@ -193,7 +205,7 @@ typedef std::map<std::string, std::function<ref<Command>()>> Commands;
 
 /* An argument parser that supports multiple subcommands,
    i.e. ‘<command> <subcommand>’. */
-class MultiCommand : virtual Args
+class MultiCommand : virtual public Args
 {
 public:
     Commands commands;
diff --git a/src/libutil/closure.hh b/src/libutil/closure.hh
new file mode 100644
index 000000000..779b9b2d5
--- /dev/null
+++ b/src/libutil/closure.hh
@@ -0,0 +1,69 @@
+#include <set>
+#include <future>
+#include "sync.hh"
+
+using std::set;
+
+namespace nix {
+
+template<typename T>
+using GetEdgesAsync = std::function<void(const T &, std::function<void(std::promise<set<T>> &)>)>;
+
+template<typename T>
+void computeClosure(
+    const set<T> startElts,
+    set<T> & res,
+    GetEdgesAsync<T> getEdgesAsync
+)
+{
+    struct State
+    {
+        size_t pending;
+        set<T> & res;
+        std::exception_ptr exc;
+    };
+
+    Sync<State> state_(State{0, res, 0});
+
+    std::function<void(const T &)> enqueue;
+
+    std::condition_variable done;
+
+    enqueue = [&](const T & current) -> void {
+        {
+            auto state(state_.lock());
+            if (state->exc) return;
+            if (!state->res.insert(current).second) return;
+            state->pending++;
+        }
+
+        getEdgesAsync(current, [&](std::promise<set<T>> & prom) {
+            try {
+                auto children = prom.get_future().get();
+                for (auto & child : children)
+                    enqueue(child);
+                {
+                    auto state(state_.lock());
+                    assert(state->pending);
+                    if (!--state->pending) done.notify_one();
+                }
+            } catch (...) {
+                auto state(state_.lock());
+                if (!state->exc) state->exc = std::current_exception();
+                assert(state->pending);
+                if (!--state->pending) done.notify_one();
+            };
+        });
+    };
+
+    for (auto & startElt : startElts)
+        enqueue(startElt);
+
+    {
+        auto state(state_.lock());
+        while (state->pending) state.wait(done);
+        if (state->exc) std::rethrow_exception(state->exc);
+    }
+}
+
+}
diff --git a/src/libutil/comparator.hh b/src/libutil/comparator.hh
index 0315dc506..eecd5b819 100644
--- a/src/libutil/comparator.hh
+++ b/src/libutil/comparator.hh
@@ -25,6 +25,8 @@
     }
 #define GENERATE_EQUAL(args...) GENERATE_ONE_CMP(==, args)
 #define GENERATE_LEQ(args...) GENERATE_ONE_CMP(<, args)
+#define GENERATE_NEQ(args...) GENERATE_ONE_CMP(!=, args)
 #define GENERATE_CMP(args...) \
     GENERATE_EQUAL(args) \
-    GENERATE_LEQ(args)
+    GENERATE_LEQ(args) \
+    GENERATE_NEQ(args)
diff --git a/src/libutil/compression.cc b/src/libutil/compression.cc
index 7e725cae1..f80ca664c 100644
--- a/src/libutil/compression.cc
+++ b/src/libutil/compression.cc
@@ -12,12 +12,12 @@
 #include <brotli/decode.h>
 #include <brotli/encode.h>
 
-#include <zlib.h>
-
 #include <iostream>
 
 namespace nix {
 
+static const int COMPRESSION_LEVEL_DEFAULT = -1;
+
 // Don't feed brotli too much at once.
 struct ChunkedCompressionSink : CompressionSink
 {
@@ -67,14 +67,16 @@ struct ArchiveCompressionSink : CompressionSink
     Sink & nextSink;
     struct archive * archive;
 
-    ArchiveCompressionSink(Sink & nextSink, std::string format, bool parallel) : nextSink(nextSink) {
+    ArchiveCompressionSink(Sink & nextSink, std::string format, bool parallel, int level = COMPRESSION_LEVEL_DEFAULT) : nextSink(nextSink)
+    {
         archive = archive_write_new();
         if (!archive) throw Error("failed to initialize libarchive");
         check(archive_write_add_filter_by_name(archive, format.c_str()), "couldn't initialize compression (%s)");
         check(archive_write_set_format_raw(archive));
-        if (format == "xz" && parallel) {
+        if (parallel)
             check(archive_write_set_filter_option(archive, format.c_str(), "threads", "0"));
-        }
+        if (level != COMPRESSION_LEVEL_DEFAULT)
+            check(archive_write_set_filter_option(archive, format.c_str(), "compression-level", std::to_string(level).c_str()));
         // disable internal buffering
         check(archive_write_set_bytes_per_block(archive, 0));
         // disable output padding
@@ -128,7 +130,11 @@ private:
 struct NoneSink : CompressionSink
 {
     Sink & nextSink;
-    NoneSink(Sink & nextSink) : nextSink(nextSink) { }
+    NoneSink(Sink & nextSink, int level = COMPRESSION_LEVEL_DEFAULT) : nextSink(nextSink)
+    {
+        if (level != COMPRESSION_LEVEL_DEFAULT)
+            warn("requested compression level '%d' not supported by compression method 'none'", level);
+    }
     void finish() override { flush(); }
     void write(std::string_view data) override { nextSink(data); }
 };
@@ -259,13 +265,13 @@ struct BrotliCompressionSink : ChunkedCompressionSink
     }
 };
 
-ref<CompressionSink> makeCompressionSink(const std::string & method, Sink & nextSink, const bool parallel)
+ref<CompressionSink> makeCompressionSink(const std::string & method, Sink & nextSink, const bool parallel, int level)
 {
     std::vector<std::string> la_supports = {
         "bzip2", "compress", "grzip", "gzip", "lrzip", "lz4", "lzip", "lzma", "lzop", "xz", "zstd"
     };
     if (std::find(la_supports.begin(), la_supports.end(), method) != la_supports.end()) {
-        return make_ref<ArchiveCompressionSink>(nextSink, method, parallel);
+        return make_ref<ArchiveCompressionSink>(nextSink, method, parallel, level);
     }
     if (method == "none")
         return make_ref<NoneSink>(nextSink);
@@ -275,10 +281,10 @@ ref<CompressionSink> makeCompressionSink(const std::string & method, Sink & next
         throw UnknownCompressionMethod("unknown compression method '%s'", method);
 }
 
-ref<std::string> compress(const std::string & method, const std::string & in, const bool parallel)
+ref<std::string> compress(const std::string & method, const std::string & in, const bool parallel, int level)
 {
     StringSink ssink;
-    auto sink = makeCompressionSink(method, ssink, parallel);
+    auto sink = makeCompressionSink(method, ssink, parallel, level);
     (*sink)(in);
     sink->finish();
     return ssink.s;
diff --git a/src/libutil/compression.hh b/src/libutil/compression.hh
index 338a0d9f2..9b1e4a9d4 100644
--- a/src/libutil/compression.hh
+++ b/src/libutil/compression.hh
@@ -19,9 +19,9 @@ ref<std::string> decompress(const std::string & method, const std::string & in);
 
 std::unique_ptr<FinishSink> makeDecompressionSink(const std::string & method, Sink & nextSink);
 
-ref<std::string> compress(const std::string & method, const std::string & in, const bool parallel = false);
+ref<std::string> compress(const std::string & method, const std::string & in, const bool parallel = false, int level = -1);
 
-ref<CompressionSink> makeCompressionSink(const std::string & method, Sink & nextSink, const bool parallel = false);
+ref<CompressionSink> makeCompressionSink(const std::string & method, Sink & nextSink, const bool parallel = false, int level = -1);
 
 MakeError(UnknownCompressionMethod, Error);
 
diff --git a/src/libutil/config.cc b/src/libutil/config.cc
index bda07cd55..92ab265d3 100644
--- a/src/libutil/config.cc
+++ b/src/libutil/config.cc
@@ -1,6 +1,7 @@
 #include "config.hh"
 #include "args.hh"
 #include "abstract-setting-to-json.hh"
+#include "experimental-features.hh"
 
 #include <nlohmann/json.hpp>
 
@@ -152,6 +153,16 @@ nlohmann::json Config::toJSON()
     return res;
 }
 
+std::string Config::toKeyValue()
+{
+    auto res = std::string();
+    for (auto & s : _settings)
+        if (!s.second.isAlias) {
+            res += fmt("%s = %s\n", s.first, s.second.setting->to_string());
+        }
+    return res;
+}
+
 void Config::convertToArgs(Args & args, const std::string & category)
 {
     for (auto & s : _settings)
@@ -167,11 +178,6 @@ AbstractSetting::AbstractSetting(
 {
 }
 
-void AbstractSetting::setDefault(const std::string & str)
-{
-    if (!overridden) set(str);
-}
-
 nlohmann::json AbstractSetting::toJSON()
 {
     return nlohmann::json(toJSONObject());
@@ -308,6 +314,31 @@ template<> std::string BaseSetting<StringSet>::to_string() const
     return concatStringsSep(" ", value);
 }
 
+template<> void BaseSetting<std::set<ExperimentalFeature>>::set(const std::string & str, bool append)
+{
+    if (!append) value.clear();
+    for (auto & s : tokenizeString<StringSet>(str)) {
+        auto thisXpFeature = parseExperimentalFeature(s);
+        if (thisXpFeature)
+            value.insert(thisXpFeature.value());
+        else
+            warn("unknown experimental feature '%s'", s);
+    }
+}
+
+template<> bool BaseSetting<std::set<ExperimentalFeature>>::isAppendable()
+{
+    return true;
+}
+
+template<> std::string BaseSetting<std::set<ExperimentalFeature>>::to_string() const
+{
+    StringSet stringifiedXpFeatures;
+    for (auto & feature : value)
+        stringifiedXpFeatures.insert(std::string(showExperimentalFeature(feature)));
+    return concatStringsSep(" ", stringifiedXpFeatures);
+}
+
 template<> void BaseSetting<StringMap>::set(const std::string & str, bool append)
 {
     if (!append) value.clear();
@@ -343,6 +374,7 @@ template class BaseSetting<std::string>;
 template class BaseSetting<Strings>;
 template class BaseSetting<StringSet>;
 template class BaseSetting<StringMap>;
+template class BaseSetting<std::set<ExperimentalFeature>>;
 
 void PathSetting::set(const std::string & str, bool append)
 {
@@ -385,6 +417,16 @@ nlohmann::json GlobalConfig::toJSON()
     return res;
 }
 
+std::string GlobalConfig::toKeyValue()
+{
+    std::string res;
+    std::map<std::string, Config::SettingInfo> settings;
+    globalConfig.getSettings(settings);
+    for (auto & s : settings)
+        res += fmt("%s = %s\n", s.first, s.second.value);
+    return res;
+}
+
 void GlobalConfig::convertToArgs(Args & args, const std::string & category)
 {
     for (auto & config : *configRegistrations)
diff --git a/src/libutil/config.hh b/src/libutil/config.hh
index bf81b4892..736810bf3 100644
--- a/src/libutil/config.hh
+++ b/src/libutil/config.hh
@@ -100,6 +100,12 @@ public:
     virtual nlohmann::json toJSON() = 0;
 
     /**
+     * Outputs all settings in a key-value pair format suitable to be used as
+     * `nix.conf`
+     */
+    virtual std::string toKeyValue() = 0;
+
+    /**
      * Converts settings to `Args` to be used on the command line interface
      * - args: args to write to
      * - category: category of the settings
@@ -169,6 +175,8 @@ public:
 
     nlohmann::json toJSON() override;
 
+    std::string toKeyValue() override;
+
     void convertToArgs(Args & args, const std::string & category) override;
 };
 
@@ -186,8 +194,6 @@ public:
 
     bool overridden = false;
 
-    void setDefault(const std::string & str);
-
 protected:
 
     AbstractSetting(
@@ -245,6 +251,7 @@ public:
     bool operator !=(const T & v2) const { return value != v2; }
     void operator =(const T & v) { assign(v); }
     virtual void assign(const T & v) { value = v; }
+    void setDefault(const T & v) { if (!overridden) value = v; }
 
     void set(const std::string & str, bool append = false) override;
 
@@ -330,6 +337,8 @@ struct GlobalConfig : public AbstractConfig
 
     nlohmann::json toJSON() override;
 
+    std::string toKeyValue() override;
+
     void convertToArgs(Args & args, const std::string & category) override;
 
     struct Register
diff --git a/src/libutil/error.cc b/src/libutil/error.cc
index 0eea3455d..203d79087 100644
--- a/src/libutil/error.cc
+++ b/src/libutil/error.cc
@@ -185,15 +185,15 @@ void printAtPos(const ErrPos & pos, std::ostream & out)
     if (pos) {
         switch (pos.origin) {
             case foFile: {
-                out << fmt(ANSI_BLUE "at " ANSI_YELLOW "%s:%s" ANSI_NORMAL ":", pos.file, showErrPos(pos));
+                out << fmt(ANSI_BLUE "at " ANSI_WARNING "%s:%s" ANSI_NORMAL ":", pos.file, showErrPos(pos));
                 break;
             }
             case foString: {
-                out << fmt(ANSI_BLUE "at " ANSI_YELLOW "«string»:%s" ANSI_NORMAL ":", showErrPos(pos));
+                out << fmt(ANSI_BLUE "at " ANSI_WARNING "«string»:%s" ANSI_NORMAL ":", showErrPos(pos));
                 break;
             }
             case foStdin: {
-                out << fmt(ANSI_BLUE "at " ANSI_YELLOW "«stdin»:%s" ANSI_NORMAL ":", showErrPos(pos));
+                out << fmt(ANSI_BLUE "at " ANSI_WARNING "«stdin»:%s" ANSI_NORMAL ":", showErrPos(pos));
                 break;
             }
             default:
@@ -232,7 +232,7 @@ std::ostream & showErrorInfo(std::ostream & out, const ErrorInfo & einfo, bool s
             break;
         }
         case Verbosity::lvlWarn: {
-            prefix = ANSI_YELLOW "warning";
+            prefix = ANSI_WARNING "warning";
             break;
         }
         case Verbosity::lvlInfo: {
@@ -252,7 +252,7 @@ std::ostream & showErrorInfo(std::ostream & out, const ErrorInfo & einfo, bool s
             break;
         }
         case Verbosity::lvlDebug: {
-            prefix = ANSI_YELLOW "debug";
+            prefix = ANSI_WARNING "debug";
             break;
         }
         default:
diff --git a/src/libutil/experimental-features.cc b/src/libutil/experimental-features.cc
new file mode 100644
index 000000000..b49f47e1d
--- /dev/null
+++ b/src/libutil/experimental-features.cc
@@ -0,0 +1,59 @@
+#include "experimental-features.hh"
+#include "util.hh"
+
+#include "nlohmann/json.hpp"
+
+namespace nix {
+
+std::map<ExperimentalFeature, std::string> stringifiedXpFeatures = {
+    { Xp::CaDerivations, "ca-derivations" },
+    { Xp::Flakes, "flakes" },
+    { Xp::NixCommand, "nix-command" },
+    { Xp::RecursiveNix, "recursive-nix" },
+    { Xp::NoUrlLiterals, "no-url-literals" },
+};
+
+const std::optional<ExperimentalFeature> parseExperimentalFeature(const std::string_view & name)
+{
+    using ReverseXpMap = std::map<std::string_view, ExperimentalFeature>;
+
+    static auto reverseXpMap = []()
+    {
+        auto reverseXpMap = std::make_unique<ReverseXpMap>();
+        for (auto & [feature, name] : stringifiedXpFeatures)
+            (*reverseXpMap)[name] = feature;
+        return reverseXpMap;
+    }();
+
+    if (auto feature = get(*reverseXpMap, name))
+        return *feature;
+    else
+        return std::nullopt;
+}
+
+std::string_view showExperimentalFeature(const ExperimentalFeature feature)
+{
+    return stringifiedXpFeatures.at(feature);
+}
+
+std::set<ExperimentalFeature> parseFeatures(const std::set<std::string> & rawFeatures)
+{
+    std::set<ExperimentalFeature> res;
+    for (auto & rawFeature : rawFeatures) {
+        if (auto feature = parseExperimentalFeature(rawFeature))
+            res.insert(*feature);
+    }
+    return res;
+}
+
+MissingExperimentalFeature::MissingExperimentalFeature(ExperimentalFeature feature)
+    : Error("experimental Nix feature '%1%' is disabled; use '--extra-experimental-features %1%' to override", showExperimentalFeature(feature))
+    , missingFeature(feature)
+{}
+
+std::ostream & operator <<(std::ostream & str, const ExperimentalFeature & feature)
+{
+    return str << showExperimentalFeature(feature);
+}
+
+}
diff --git a/src/libutil/experimental-features.hh b/src/libutil/experimental-features.hh
new file mode 100644
index 000000000..291a58e32
--- /dev/null
+++ b/src/libutil/experimental-features.hh
@@ -0,0 +1,56 @@
+#pragma once
+
+#include "comparator.hh"
+#include "error.hh"
+#include "nlohmann/json_fwd.hpp"
+#include "types.hh"
+
+namespace nix {
+
+/**
+ * The list of available experimental features.
+ *
+ * If you update this, don’t forget to also change the map defining their
+ * string representation in the corresponding `.cc` file.
+ **/
+enum struct ExperimentalFeature
+{
+    CaDerivations,
+    Flakes,
+    NixCommand,
+    RecursiveNix,
+    NoUrlLiterals
+};
+
+/**
+ * Just because writing `ExperimentalFeature::CaDerivations` is way too long
+ */
+using Xp = ExperimentalFeature;
+
+const std::optional<ExperimentalFeature> parseExperimentalFeature(
+        const std::string_view & name);
+std::string_view showExperimentalFeature(const ExperimentalFeature);
+
+std::ostream & operator<<(
+        std::ostream & str,
+        const ExperimentalFeature & feature);
+
+/**
+ * Parse a set of strings to the corresponding set of experimental features,
+ * ignoring (but warning for) any unkwown feature.
+ */
+std::set<ExperimentalFeature> parseFeatures(const std::set<std::string> &);
+
+class MissingExperimentalFeature : public Error
+{
+public:
+    ExperimentalFeature missingFeature;
+
+    MissingExperimentalFeature(ExperimentalFeature);
+    virtual const char * sname() const override
+    {
+        return "MissingExperimentalFeature";
+    }
+};
+
+}
diff --git a/src/libutil/fmt.hh b/src/libutil/fmt.hh
index 85c0e9429..fd335b811 100644
--- a/src/libutil/fmt.hh
+++ b/src/libutil/fmt.hh
@@ -82,7 +82,7 @@ struct yellowtxt
 template <class T>
 std::ostream & operator<<(std::ostream & out, const yellowtxt<T> & y)
 {
-    return out << ANSI_YELLOW << y.value << ANSI_NORMAL;
+    return out << ANSI_WARNING << y.value << ANSI_NORMAL;
 }
 
 template <class T>
diff --git a/src/libutil/local.mk b/src/libutil/local.mk
index 3a6415ee3..f880c0fc5 100644
--- a/src/libutil/local.mk
+++ b/src/libutil/local.mk
@@ -6,7 +6,7 @@ libutil_DIR := $(d)
 
 libutil_SOURCES := $(wildcard $(d)/*.cc)
 
-libutil_LDFLAGS = -pthread $(OPENSSL_LIBS) $(LIBBROTLI_LIBS) $(LIBARCHIVE_LIBS) $(BOOST_LDFLAGS) -lboost_context
+libutil_LDFLAGS += -pthread $(OPENSSL_LIBS) $(LIBBROTLI_LIBS) $(LIBARCHIVE_LIBS) $(BOOST_LDFLAGS) -lboost_context
 
 ifeq ($(HAVE_LIBCPUID), 1)
 	libutil_LDFLAGS += -lcpuid
diff --git a/src/libutil/logging.cc b/src/libutil/logging.cc
index d2e801175..f8a121ed1 100644
--- a/src/libutil/logging.cc
+++ b/src/libutil/logging.cc
@@ -27,7 +27,7 @@ Logger * logger = makeSimpleLogger(true);
 
 void Logger::warn(const std::string & msg)
 {
-    log(lvlWarn, ANSI_YELLOW "warning:" ANSI_NORMAL " " + msg);
+    log(lvlWarn, ANSI_WARNING "warning:" ANSI_NORMAL " " + msg);
 }
 
 void Logger::writeToStdout(std::string_view s)
@@ -46,7 +46,7 @@ public:
         : printBuildLogs(printBuildLogs)
     {
         systemd = getEnv("IN_SYSTEMD") == "1";
-        tty = isatty(STDERR_FILENO);
+        tty = shouldANSI();
     }
 
     bool isVerbose() override {
@@ -163,7 +163,7 @@ struct JSONLogger : Logger {
 
     void write(const nlohmann::json & json)
     {
-        prevLogger.log(lvlError, "@nix " + json.dump());
+        prevLogger.log(lvlError, "@nix " + json.dump(-1, ' ', false, nlohmann::json::error_handler_t::replace));
     }
 
     void log(Verbosity lvl, const FormatOrString & fs) override
diff --git a/src/libutil/ref.hh b/src/libutil/ref.hh
index 0be2a7e74..347b81f73 100644
--- a/src/libutil/ref.hh
+++ b/src/libutil/ref.hh
@@ -17,7 +17,7 @@ private:
 
 public:
 
-    ref<T>(const ref<T> & r)
+    ref(const ref<T> & r)
         : p(r.p)
     { }
 
@@ -73,6 +73,16 @@ public:
         return ref<T2>((std::shared_ptr<T2>) p);
     }
 
+    bool operator == (const ref<T> & other) const
+    {
+        return p == other.p;
+    }
+
+    bool operator != (const ref<T> & other) const
+    {
+        return p != other.p;
+    }
+
 private:
 
     template<typename T2, typename... Args>
@@ -89,4 +99,47 @@ make_ref(Args&&... args)
     return ref<T>(p);
 }
 
+
+/* A non-nullable pointer.
+   This is similar to a C++ "& reference", but mutable.
+   This is similar to ref<T> but backed by a regular pointer instead of a smart pointer.
+ */
+template<typename T>
+class ptr {
+private:
+    T * p;
+
+public:
+    ptr<T>(const ptr<T> & r)
+        : p(r.p)
+    { }
+
+    explicit ptr<T>(T * p)
+        : p(p)
+    {
+        if (!p)
+            throw std::invalid_argument("null pointer cast to ptr");
+    }
+
+    T* operator ->() const
+    {
+        return &*p;
+    }
+
+    T& operator *() const
+    {
+        return *p;
+    }
+
+    bool operator == (const ptr<T> & other) const
+    {
+        return p == other.p;
+    }
+
+    bool operator != (const ptr<T> & other) const
+    {
+        return p != other.p;
+    }
+};
+
 }
diff --git a/src/libutil/serialise.cc b/src/libutil/serialise.cc
index 374b48d79..16f3476c2 100644
--- a/src/libutil/serialise.cc
+++ b/src/libutil/serialise.cc
@@ -244,7 +244,8 @@ std::unique_ptr<FinishSink> sourceToSink(std::function<void(Source &)> fun)
             if (!cur.empty()) (*coro)(false);
         }
 
-        void finish() {
+        void finish() override
+        {
             if (!coro) return;
             if (!*coro) abort();
             (*coro)(true);
diff --git a/src/libutil/tarfile.cc b/src/libutil/tarfile.cc
index 24905130d..50e691a3d 100644
--- a/src/libutil/tarfile.cc
+++ b/src/libutil/tarfile.cc
@@ -39,32 +39,30 @@ void TarArchive::check(int err, const std::string & reason)
         throw Error(reason, archive_error_string(this->archive));
 }
 
-TarArchive::TarArchive(Source & source, bool raw) : buffer(4096)
+TarArchive::TarArchive(Source & source, bool raw)
+    : source(&source), buffer(4096)
 {
-    this->archive = archive_read_new();
-    this->source = &source;
-
-    if (!raw) {
-        archive_read_support_filter_all(archive);
+    init();
+    if (!raw)
         archive_read_support_format_all(archive);
-    } else {
-        archive_read_support_filter_all(archive);
+    else
         archive_read_support_format_raw(archive);
-        archive_read_support_format_empty(archive);
-    }
     check(archive_read_open(archive, (void *)this, callback_open, callback_read, callback_close), "Failed to open archive (%s)");
 }
 
-
 TarArchive::TarArchive(const Path & path)
 {
-    this->archive = archive_read_new();
-
-    archive_read_support_filter_all(archive);
+    init();
     archive_read_support_format_all(archive);
     check(archive_read_open_filename(archive, path.c_str(), 16384), "failed to open archive: %s");
 }
 
+void TarArchive::init()
+{
+    archive = archive_read_new();
+    archive_read_support_filter_all(archive);
+}
+
 void TarArchive::close()
 {
     check(archive_read_close(this->archive), "Failed to close archive (%s)");
@@ -87,13 +85,16 @@ static void extract_archive(TarArchive & archive, const Path & destDir)
         struct archive_entry * entry;
         int r = archive_read_next_header(archive.archive, &entry);
         if (r == ARCHIVE_EOF) break;
-        else if (r == ARCHIVE_WARN)
+        auto name = archive_entry_pathname(entry);
+        if (!name)
+            throw Error("cannot get archive member name: %s", archive_error_string(archive.archive));
+        if (r == ARCHIVE_WARN)
             warn(archive_error_string(archive.archive));
         else
             archive.check(r);
 
         archive_entry_set_pathname(entry,
-            (destDir + "/" + archive_entry_pathname(entry)).c_str());
+            (destDir + "/" + name).c_str());
 
         archive.check(archive_read_extract(archive.archive, entry, flags));
     }
diff --git a/src/libutil/tarfile.hh b/src/libutil/tarfile.hh
index 4d9141fd4..f107a7e2e 100644
--- a/src/libutil/tarfile.hh
+++ b/src/libutil/tarfile.hh
@@ -17,10 +17,13 @@ struct TarArchive {
     // disable copy constructor
     TarArchive(const TarArchive &) = delete;
 
+    void init();
+
     void close();
 
     ~TarArchive();
 };
+
 void unpackTarfile(Source & source, const Path & destDir);
 
 void unpackTarfile(const Path & tarFile, const Path & destDir);
diff --git a/src/libutil/tests/closure.cc b/src/libutil/tests/closure.cc
new file mode 100644
index 000000000..7597e7807
--- /dev/null
+++ b/src/libutil/tests/closure.cc
@@ -0,0 +1,70 @@
+#include "closure.hh"
+#include <gtest/gtest.h>
+
+namespace nix {
+
+using namespace std;
+
+map<string, set<string>> testGraph = {
+    { "A", { "B", "C", "G" } },
+    { "B", { "A" } }, // Loops back to A
+    { "C", { "F" } }, // Indirect reference
+    { "D", { "A" } }, // Not reachable, but has backreferences
+    { "E", {} }, // Just not reachable
+    { "F", {} },
+    { "G", { "G" } }, // Self reference
+};
+
+TEST(closure, correctClosure) {
+    set<string> aClosure;
+    set<string> expectedClosure = {"A", "B", "C", "F", "G"};
+    computeClosure<string>(
+        {"A"},
+        aClosure,
+        [&](const string currentNode, function<void(promise<set<string>> &)> processEdges) {
+            promise<set<string>> promisedNodes;
+            promisedNodes.set_value(testGraph[currentNode]);
+            processEdges(promisedNodes);
+        }
+    );
+
+    ASSERT_EQ(aClosure, expectedClosure);
+}
+
+TEST(closure, properlyHandlesDirectExceptions) {
+    struct TestExn {};
+    set<string> aClosure;
+    EXPECT_THROW(
+        computeClosure<string>(
+            {"A"},
+            aClosure,
+            [&](const string currentNode, function<void(promise<set<string>> &)> processEdges) {
+                throw TestExn();
+            }
+        ),
+        TestExn
+    );
+}
+
+TEST(closure, properlyHandlesExceptionsInPromise) {
+    struct TestExn {};
+    set<string> aClosure;
+    EXPECT_THROW(
+        computeClosure<string>(
+            {"A"},
+            aClosure,
+            [&](const string currentNode, function<void(promise<set<string>> &)> processEdges) {
+                promise<set<string>> promise;
+                try {
+                    throw TestExn();
+                } catch (...) {
+                    promise.set_exception(std::current_exception());
+                }
+                processEdges(promise);
+            }
+        ),
+        TestExn
+    );
+}
+
+}
diff --git a/src/libutil/tests/logging.cc b/src/libutil/tests/logging.cc
index d990e5499..cef3bd481 100644
--- a/src/libutil/tests/logging.cc
+++ b/src/libutil/tests/logging.cc
@@ -336,7 +336,7 @@ namespace nix {
 
         ASSERT_STREQ(
             hintfmt("only one arg %1% %2%", "fulfilled").str().c_str(),
-            "only one arg " ANSI_YELLOW "fulfilled" ANSI_NORMAL " ");
+            "only one arg " ANSI_WARNING "fulfilled" ANSI_NORMAL " ");
 
     }
 
@@ -344,7 +344,7 @@ namespace nix {
 
         ASSERT_STREQ(
             hintfmt("what about this %1% %2%", "%3%", "one", "two").str().c_str(),
-            "what about this " ANSI_YELLOW "%3%" ANSI_NORMAL " " ANSI_YELLOW "one" ANSI_NORMAL);
+            "what about this " ANSI_WARNING "%3%" ANSI_NORMAL " " ANSI_YELLOW "one" ANSI_NORMAL);
 
     }
 
diff --git a/src/libutil/tests/tests.cc b/src/libutil/tests/tests.cc
index 58df9c5ac..92972ed14 100644
--- a/src/libutil/tests/tests.cc
+++ b/src/libutil/tests/tests.cc
@@ -4,6 +4,8 @@
 #include <limits.h>
 #include <gtest/gtest.h>
 
+#include <numeric>
+
 namespace nix {
 
 /* ----------- tests for util.hh ------------------------------------------------*/
@@ -282,6 +284,17 @@ namespace nix {
         ASSERT_EQ(decoded, s);
     }
 
+    TEST(base64Encode, encodeAndDecodeNonPrintable) {
+        char s[256];
+        std::iota(std::rbegin(s), std::rend(s), 0);
+
+        auto encoded = base64Encode(s);
+        auto decoded = base64Decode(encoded);
+
+        EXPECT_EQ(decoded.length(), 255);
+        ASSERT_EQ(decoded, s);
+    }
+
     /* ----------------------------------------------------------------------------
      * base64Decode
      * --------------------------------------------------------------------------*/
@@ -294,6 +307,10 @@ namespace nix {
         ASSERT_EQ(base64Decode("cXVvZCBlcmF0IGRlbW9uc3RyYW5kdW0="), "quod erat demonstrandum");
     }
 
+    TEST(base64Decode, decodeThrowsOnInvalidChar) {
+        ASSERT_THROW(base64Decode("cXVvZCBlcm_0IGRlbW9uc3RyYW5kdW0="), Error);
+    }
+
     /* ----------------------------------------------------------------------------
      * toLower
      * --------------------------------------------------------------------------*/
diff --git a/src/libutil/url.cc b/src/libutil/url.cc
index c1bab866c..f6232d255 100644
--- a/src/libutil/url.cc
+++ b/src/libutil/url.cc
@@ -32,7 +32,7 @@ ParsedURL parseURL(const std::string & url)
         auto isFile = scheme.find("file") != std::string::npos;
 
         if (authority && *authority != "" && isFile)
-            throw Error("file:// URL '%s' has unexpected authority '%s'",
+            throw BadURL("file:// URL '%s' has unexpected authority '%s'",
                 url, *authority);
 
         if (isFile && path.empty())
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 5f597bf06..defb77a10 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -4,16 +4,18 @@
 #include "finally.hh"
 #include "serialise.hh"
 
+#include <array>
 #include <cctype>
 #include <cerrno>
+#include <climits>
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
-#include <climits>
+#include <future>
 #include <iostream>
+#include <mutex>
 #include <sstream>
 #include <thread>
-#include <future>
 
 #include <fcntl.h>
 #include <grp.h>
@@ -155,6 +157,9 @@ Path canonPath(const Path & path, bool resolveSymlinks)
                     s.clear();  /* restart for symlinks pointing to absolute path */
                 } else {
                     s = dirOf(s);
+                    if (s == "/") {  // we don’t want trailing slashes here, which dirOf only produces if s = /
+                        s.clear();
+                    }
                 }
             }
         }
@@ -410,7 +415,7 @@ static void _deletePath(int parentfd, const Path & path, uint64_t & bytesFreed)
         }
 
         int fd = openat(parentfd, path.c_str(), O_RDONLY);
-        if (!fd)
+        if (fd == -1)
             throw SysError("opening directory '%1%'", path);
         AutoCloseDir dir(fdopendir(fd));
         if (!dir)
@@ -432,12 +437,9 @@ static void _deletePath(const Path & path, uint64_t & bytesFreed)
     if (dir == "")
         dir = "/";
 
-    AutoCloseFD dirfd(open(dir.c_str(), O_RDONLY));
+    AutoCloseFD dirfd{open(dir.c_str(), O_RDONLY)};
     if (!dirfd) {
-        // This really shouldn't fail silently, but it's left this way
-        // for backwards compatibility.
         if (errno == ENOENT) return;
-
         throw SysError("opening directory '%1%'", path);
     }
 
@@ -560,7 +562,7 @@ Path getConfigDir()
 std::vector<Path> getConfigDirs()
 {
     Path configHome = getConfigDir();
-    string configDirs = getEnv("XDG_CONFIG_DIRS").value_or("");
+    string configDirs = getEnv("XDG_CONFIG_DIRS").value_or("/etc/xdg");
     std::vector<Path> result = tokenizeString<std::vector<string>>(configDirs, ":");
     result.insert(result.begin(), configHome);
     return result;
@@ -901,7 +903,7 @@ int Pid::wait()
             return status;
         }
         if (errno != EINTR)
-            throw SysError("cannot get child exit status");
+            throw SysError("cannot get exit status of PID %d", pid);
         checkInterrupt();
     }
 }
@@ -937,9 +939,6 @@ void killUser(uid_t uid)
        users to which the current process can send signals.  So we
        fork a process, switch to uid, and send a mass kill. */
 
-    ProcessOptions options;
-    options.allowVfork = false;
-
     Pid pid = startProcess([&]() {
 
         if (setuid(uid) == -1)
@@ -962,7 +961,7 @@ void killUser(uid_t uid)
         }
 
         _exit(0);
-    }, options);
+    });
 
     int status = pid.wait();
     if (status != 0)
@@ -1032,17 +1031,10 @@ std::vector<char *> stringsToCharPtrs(const Strings & ss)
     return res;
 }
 
-// Output = "standard out" output stream
 string runProgram(Path program, bool searchPath, const Strings & args,
     const std::optional<std::string> & input)
 {
-    RunOptions opts(program, args);
-    opts.searchPath = searchPath;
-    // This allows you to refer to a program with a pathname relative to the
-    // PATH variable.
-    opts.input = input;
-
-    auto res = runProgram(opts);
+    auto res = runProgram(RunOptions {.program = program, .searchPath = searchPath, .args = args, .input = input});
 
     if (!statusOk(res.first))
         throw ExecError(res.first, fmt("program '%1%' %2%", program, statusToString(res.first)));
@@ -1051,9 +1043,8 @@ string runProgram(Path program, bool searchPath, const Strings & args,
 }
 
 // Output = error code + "standard out" output stream
-std::pair<int, std::string> runProgram(const RunOptions & options_)
+std::pair<int, std::string> runProgram(RunOptions && options)
 {
-    RunOptions options(options_);
     StringSink sink;
     options.standardOut = &sink;
 
@@ -1091,8 +1082,7 @@ void runProgram2(const RunOptions & options)
     // vfork implies that the environment of the main process and the fork will
     // be shared (technically this is undefined, but in practice that's the
     // case), so we can't use it if we alter the environment
-    if (options.environment)
-        processOptions.allowVfork = false;
+    processOptions.allowVfork = !options.environment;
 
     /* Fork. */
     Pid pid = startProcess([&]() {
@@ -1215,7 +1205,7 @@ void closeOnExec(int fd)
 //////////////////////////////////////////////////////////////////////
 
 
-bool _isInterrupted = false;
+std::atomic<bool> _isInterrupted = false;
 
 static thread_local bool interruptThrown = false;
 thread_local std::function<bool()> interruptCheck;
@@ -1369,6 +1359,12 @@ void ignoreException()
     }
 }
 
+bool shouldANSI()
+{
+    return isatty(STDERR_FILENO)
+        && getEnv("TERM").value_or("dumb") != "dumb"
+        && !getEnv("NO_COLOR").has_value();
+}
 
 std::string filterANSIEscapes(const std::string & s, bool filterAll, unsigned int width)
 {
@@ -1440,8 +1436,7 @@ std::string filterANSIEscapes(const std::string & s, bool filterAll, unsigned in
 }
 
 
-static char base64Chars[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
-
+constexpr char base64Chars[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 
 string base64Encode(std::string_view s)
 {
@@ -1466,15 +1461,15 @@ string base64Encode(std::string_view s)
 
 string base64Decode(std::string_view s)
 {
-    bool init = false;
-    char decode[256];
-    if (!init) {
-        // FIXME: not thread-safe.
-        memset(decode, -1, sizeof(decode));
+    constexpr char npos = -1;
+    constexpr std::array<char, 256> base64DecodeChars = [&]() {
+        std::array<char, 256>  result{};
+        for (auto& c : result)
+            c = npos;
         for (int i = 0; i < 64; i++)
-            decode[(int) base64Chars[i]] = i;
-        init = true;
-    }
+            result[base64Chars[i]] = i;
+        return result;
+    }();
 
     string res;
     unsigned int d = 0, bits = 0;
@@ -1483,8 +1478,8 @@ string base64Decode(std::string_view s)
         if (c == '=') break;
         if (c == '\n') continue;
 
-        char digit = decode[(unsigned char) c];
-        if (digit == -1)
+        char digit = base64DecodeChars[(unsigned char) c];
+        if (digit == npos)
             throw Error("invalid character in Base64 string: '%c'", c);
 
         bits += 6;
@@ -1637,9 +1632,39 @@ void setStackSize(size_t stackSize)
     #endif
 }
 
-void restoreProcessContext()
+static AutoCloseFD fdSavedMountNamespace;
+
+void saveMountNamespace()
+{
+#if __linux__
+    static std::once_flag done;
+    std::call_once(done, []() {
+        AutoCloseFD fd = open("/proc/self/ns/mnt", O_RDONLY);
+        if (!fd)
+            throw SysError("saving parent mount namespace");
+        fdSavedMountNamespace = std::move(fd);
+    });
+#endif
+}
+
+void restoreMountNamespace()
+{
+#if __linux__
+    try {
+        if (fdSavedMountNamespace && setns(fdSavedMountNamespace.get(), CLONE_NEWNS) == -1)
+            throw SysError("restoring parent mount namespace");
+    } catch (Error & e) {
+        debug(e.msg());
+    }
+#endif
+}
+
+void restoreProcessContext(bool restoreMounts)
 {
     restoreSignals();
+    if (restoreMounts) {
+        restoreMountNamespace();
+    }
 
     restoreAffinity();
 
@@ -1677,7 +1702,7 @@ std::unique_ptr<InterruptCallback> createInterruptCallback(std::function<void()>
 }
 
 
-AutoCloseFD createUnixDomainSocket(const Path & path, mode_t mode)
+AutoCloseFD createUnixDomainSocket()
 {
     AutoCloseFD fdSocket = socket(PF_UNIX, SOCK_STREAM
         #ifdef SOCK_CLOEXEC
@@ -1686,19 +1711,16 @@ AutoCloseFD createUnixDomainSocket(const Path & path, mode_t mode)
         , 0);
     if (!fdSocket)
         throw SysError("cannot create Unix domain socket");
-
     closeOnExec(fdSocket.get());
+    return fdSocket;
+}
 
-    struct sockaddr_un addr;
-    addr.sun_family = AF_UNIX;
-    if (path.size() + 1 >= sizeof(addr.sun_path))
-        throw Error("socket path '%1%' is too long", path);
-    strcpy(addr.sun_path, path.c_str());
 
-    unlink(path.c_str());
+AutoCloseFD createUnixDomainSocket(const Path & path, mode_t mode)
+{
+    auto fdSocket = nix::createUnixDomainSocket();
 
-    if (bind(fdSocket.get(), (struct sockaddr *) &addr, sizeof(addr)) == -1)
-        throw SysError("cannot bind to socket '%1%'", path);
+    bind(fdSocket.get(), path);
 
     if (chmod(path.c_str(), mode) == -1)
         throw SysError("changing permissions on '%1%'", path);
@@ -1710,6 +1732,66 @@ AutoCloseFD createUnixDomainSocket(const Path & path, mode_t mode)
 }
 
 
+void bind(int fd, const std::string & path)
+{
+    unlink(path.c_str());
+
+    struct sockaddr_un addr;
+    addr.sun_family = AF_UNIX;
+
+    if (path.size() + 1 >= sizeof(addr.sun_path)) {
+        Pid pid = startProcess([&]() {
+            auto dir = dirOf(path);
+            if (chdir(dir.c_str()) == -1)
+                throw SysError("chdir to '%s' failed", dir);
+            std::string base(baseNameOf(path));
+            if (base.size() + 1 >= sizeof(addr.sun_path))
+                throw Error("socket path '%s' is too long", base);
+            memcpy(addr.sun_path, base.c_str(), base.size() + 1);
+            if (bind(fd, (struct sockaddr *) &addr, sizeof(addr)) == -1)
+                throw SysError("cannot bind to socket '%s'", path);
+            _exit(0);
+        });
+        int status = pid.wait();
+        if (status != 0)
+            throw Error("cannot bind to socket '%s'", path);
+    } else {
+        memcpy(addr.sun_path, path.c_str(), path.size() + 1);
+        if (bind(fd, (struct sockaddr *) &addr, sizeof(addr)) == -1)
+            throw SysError("cannot bind to socket '%s'", path);
+    }
+}
+
+
+void connect(int fd, const std::string & path)
+{
+    struct sockaddr_un addr;
+    addr.sun_family = AF_UNIX;
+
+    if (path.size() + 1 >= sizeof(addr.sun_path)) {
+        Pid pid = startProcess([&]() {
+            auto dir = dirOf(path);
+            if (chdir(dir.c_str()) == -1)
+                throw SysError("chdir to '%s' failed", dir);
+            std::string base(baseNameOf(path));
+            if (base.size() + 1 >= sizeof(addr.sun_path))
+                throw Error("socket path '%s' is too long", base);
+            memcpy(addr.sun_path, base.c_str(), base.size() + 1);
+            if (connect(fd, (struct sockaddr *) &addr, sizeof(addr)) == -1)
+                throw SysError("cannot connect to socket at '%s'", path);
+            _exit(0);
+        });
+        int status = pid.wait();
+        if (status != 0)
+            throw Error("cannot connect to socket at '%s'", path);
+    } else {
+        memcpy(addr.sun_path, path.c_str(), path.size() + 1);
+        if (connect(fd, (struct sockaddr *) &addr, sizeof(addr)) == -1)
+            throw SysError("cannot connect to socket at '%s'", path);
+    }
+}
+
+
 string showBytes(uint64_t bytes)
 {
     return fmt("%.2f MiB", bytes / (1024.0 * 1024.0));
@@ -1719,8 +1801,10 @@ string showBytes(uint64_t bytes)
 // FIXME: move to libstore/build
 void commonChildInit(Pipe & logPipe)
 {
+    logger = makeSimpleLogger();
+
     const static string pathNullDevice = "/dev/null";
-    restoreProcessContext();
+    restoreProcessContext(false);
 
     /* Put the child in a separate session (and thus a separate
        process group) so that it has no controlling terminal (meaning
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index f84d0fb31..0bdb37a79 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -259,10 +259,10 @@ void killUser(uid_t uid);
    pid to the caller. */
 struct ProcessOptions
 {
-    string errorPrefix = "error: ";
+    string errorPrefix = "";
     bool dieWithParent = true;
     bool runExitHandlers = false;
-    bool allowVfork = true;
+    bool allowVfork = false;
 };
 
 pid_t startProcess(std::function<void()> fun, const ProcessOptions & options = ProcessOptions());
@@ -276,26 +276,20 @@ string runProgram(Path program, bool searchPath = false,
 
 struct RunOptions
 {
+    Path program;
+    bool searchPath = true;
+    Strings args;
     std::optional<uid_t> uid;
     std::optional<uid_t> gid;
     std::optional<Path> chdir;
     std::optional<std::map<std::string, std::string>> environment;
-    Path program;
-    bool searchPath = true;
-    Strings args;
     std::optional<std::string> input;
     Source * standardIn = nullptr;
     Sink * standardOut = nullptr;
     bool mergeStderrToStdout = false;
-    bool _killStderr = false;
-
-    RunOptions(const Path & program, const Strings & args)
-        : program(program), args(args) { };
-
-    RunOptions & killStderr(bool v) { _killStderr = true; return *this; }
 };
 
-std::pair<int, std::string> runProgram(const RunOptions & options);
+std::pair<int, std::string> runProgram(RunOptions && options);
 
 void runProgram2(const RunOptions & options);
 
@@ -306,7 +300,15 @@ void setStackSize(size_t stackSize);
 
 /* Restore the original inherited Unix process context (such as signal
    masks, stack size, CPU affinity). */
-void restoreProcessContext();
+void restoreProcessContext(bool restoreMounts = true);
+
+/* Save the current mount namespace. Ignored if called more than
+   once. */
+void saveMountNamespace();
+
+/* Restore the mount namespace saved by saveMountNamespace(). Ignored
+   if saveMountNamespace() was never called. */
+void restoreMountNamespace();
 
 
 class ExecError : public Error
@@ -335,7 +337,7 @@ void closeOnExec(int fd);
 
 /* User interruption. */
 
-extern bool _isInterrupted;
+extern std::atomic<bool> _isInterrupted;
 
 extern thread_local std::function<bool()> interruptCheck;
 
@@ -482,6 +484,9 @@ constexpr char treeLast[] = "└───";
 constexpr char treeLine[] = "│   ";
 constexpr char treeNull[] = "    ";
 
+/* Determine whether ANSI escape sequences are appropriate for the
+   present output. */
+bool shouldANSI();
 
 /* Truncate a string to 'width' printable characters. If 'filterAll'
    is true, all ANSI escape sequences are filtered out. Otherwise,
@@ -514,6 +519,29 @@ std::optional<typename T::mapped_type> get(const T & map, const typename T::key_
 }
 
 
+/* Remove and return the first item from a container. */
+template <class T>
+std::optional<typename T::value_type> remove_begin(T & c)
+{
+    auto i = c.begin();
+    if (i == c.end()) return {};
+    auto v = std::move(*i);
+    c.erase(i);
+    return v;
+}
+
+
+/* Remove and return the first item from a container. */
+template <class T>
+std::optional<typename T::value_type> pop(T & c)
+{
+    if (c.empty()) return {};
+    auto v = std::move(c.front());
+    c.pop();
+    return v;
+}
+
+
 template<typename T>
 class Callback;
 
@@ -574,9 +602,18 @@ extern PathFilter defaultPathFilter;
 /* Common initialisation performed in child processes. */
 void commonChildInit(Pipe & logPipe);
 
+/* Create a Unix domain socket. */
+AutoCloseFD createUnixDomainSocket();
+
 /* Create a Unix domain socket in listen mode. */
 AutoCloseFD createUnixDomainSocket(const Path & path, mode_t mode);
 
+/* Bind a Unix domain socket to a path. */
+void bind(int fd, const std::string & path);
+
+/* Connect to a Unix domain socket. */
+void connect(int fd, const std::string & path);
+
 
 // A Rust/Python-like enumerate() iterator adapter.
 // Borrowed from http://reedbeta.com/blog/python-like-enumerate-in-cpp17.
diff --git a/src/nix-build/nix-build.cc b/src/nix-build/nix-build.cc
index 9acbedda2..75576ef8a 100755
--- a/src/nix-build/nix-build.cc
+++ b/src/nix-build/nix-build.cc
@@ -1,10 +1,15 @@
 #include <cstring>
 #include <fstream>
 #include <iostream>
+#include <filesystem>
 #include <regex>
 #include <sstream>
 #include <vector>
+#include <map>
 
+#include <nlohmann/json.hpp>
+
+#include "parsed-derivations.hh"
 #include "store-api.hh"
 #include "local-fs-store.hh"
 #include "globals.hh"
@@ -100,7 +105,8 @@ static void main_nix_build(int argc, char * * argv)
 
     // List of environment variables kept for --pure
     std::set<string> keepVars{
-        "HOME", "USER", "LOGNAME", "DISPLAY", "PATH", "TERM", "IN_NIX_SHELL",
+        "HOME", "XDG_RUNTIME_DIR", "USER", "LOGNAME", "DISPLAY",
+        "WAYLAND_DISPLAY", "WAYLAND_SOCKET", "PATH", "TERM", "IN_NIX_SHELL",
         "NIX_SHELL_PRESERVE_PROMPT", "TZ", "PAGER", "NIX_BUILD_SHELL", "SHLVL",
         "http_proxy", "https_proxy", "ftp_proxy", "all_proxy", "no_proxy"
     };
@@ -245,8 +251,9 @@ static void main_nix_build(int argc, char * * argv)
         throw UsageError("'-p' and '-E' are mutually exclusive");
 
     auto store = openStore();
+    auto evalStore = myArgs.evalStoreUrl ? openStore(*myArgs.evalStoreUrl) : store;
 
-    auto state = std::make_unique<EvalState>(myArgs.searchPath, store);
+    auto state = std::make_unique<EvalState>(myArgs.searchPath, evalStore, store);
     state->repair = repair;
 
     auto autoArgs = myArgs.getAutoArgs(*state);
@@ -263,7 +270,7 @@ static void main_nix_build(int argc, char * * argv)
 
     if (packages) {
         std::ostringstream joined;
-        joined << "with import <nixpkgs> { }; (pkgs.runCommandCC or pkgs.runCommand) \"shell\" { buildInputs = [ ";
+        joined << "{...}@args: with import <nixpkgs> args; (pkgs.runCommandCC or pkgs.runCommand) \"shell\" { buildInputs = [ ";
         for (const auto & i : left)
             joined << '(' << i << ") ";
         joined << "]; } \"\"";
@@ -296,8 +303,8 @@ static void main_nix_build(int argc, char * * argv)
                     absolute = canonPath(absPath(i), true);
                 } catch (Error & e) {};
                 auto [path, outputNames] = parsePathWithOutputs(absolute);
-                if (store->isStorePath(path) && hasSuffix(path, ".drv"))
-                    drvs.push_back(DrvInfo(*state, store, absolute));
+                if (evalStore->isStorePath(path) && hasSuffix(path, ".drv"))
+                    drvs.push_back(DrvInfo(*state, evalStore, absolute));
                 else
                     /* If we're in a #! script, interpret filenames
                        relative to the script. */
@@ -335,7 +342,7 @@ static void main_nix_build(int argc, char * * argv)
             printMissing(ref<Store>(store), willBuild, willSubstitute, unknown, downloadSize, narSize);
 
         if (!dryRun)
-            store->buildPaths(paths, buildMode);
+            store->buildPaths(paths, buildMode, evalStore);
     };
 
     if (runEnv) {
@@ -343,9 +350,10 @@ static void main_nix_build(int argc, char * * argv)
             throw UsageError("nix-shell requires a single derivation");
 
         auto & drvInfo = drvs.front();
-        auto drv = store->derivationFromPath(store->parseStorePath(drvInfo.queryDrvPath()));
+        auto drv = evalStore->derivationFromPath(evalStore->parseStorePath(drvInfo.queryDrvPath()));
 
         std::vector<StorePathWithOutputs> pathsToBuild;
+        RealisedPath::Set pathsToCopy;
 
         /* Figure out what bash shell to use. If $NIX_BUILD_SHELL
            is not set, then build bashInteractive from
@@ -364,7 +372,9 @@ static void main_nix_build(int argc, char * * argv)
                 if (!drv)
                     throw Error("the 'bashInteractive' attribute in <nixpkgs> did not evaluate to a derivation");
 
-                pathsToBuild.push_back({store->parseStorePath(drv->queryDrvPath())});
+                auto bashDrv = store->parseStorePath(drv->queryDrvPath());
+                pathsToBuild.push_back({bashDrv});
+                pathsToCopy.insert(bashDrv);
 
                 shell = drv->queryOutPath() + "/bin/bash";
 
@@ -379,14 +389,25 @@ static void main_nix_build(int argc, char * * argv)
         for (const auto & input : drv.inputDrvs)
             if (std::all_of(envExclude.cbegin(), envExclude.cend(),
                     [&](const string & exclude) { return !std::regex_search(store->printStorePath(input.first), std::regex(exclude)); }))
+            {
                 pathsToBuild.push_back({input.first, input.second});
-        for (const auto & src : drv.inputSrcs)
+                pathsToCopy.insert(input.first);
+            }
+        for (const auto & src : drv.inputSrcs) {
             pathsToBuild.push_back({src});
+            pathsToCopy.insert(src);
+        }
 
         buildPaths(pathsToBuild);
 
         if (dryRun) return;
 
+        if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations)) {
+            auto resolvedDrv = drv.tryResolve(*store);
+            assert(resolvedDrv && "Successfully resolved the derivation");
+            drv = *resolvedDrv;
+        }
+
         // Set the environment.
         auto env = getEnv();
 
@@ -422,12 +443,45 @@ static void main_nix_build(int argc, char * * argv)
             } else
                 env[var.first] = var.second;
 
+        std::string structuredAttrsRC;
+
+        if (env.count("__json")) {
+            StorePathSet inputs;
+            for (auto & [depDrvPath, wantedDepOutputs] : drv.inputDrvs) {
+                auto outputs = evalStore->queryPartialDerivationOutputMap(depDrvPath);
+                for (auto & i : wantedDepOutputs) {
+                    auto o = outputs.at(i);
+                    store->computeFSClosure(*o, inputs);
+                }
+            }
+
+            ParsedDerivation parsedDrv(
+                StorePath(store->parseStorePath(drvInfo.queryDrvPath())),
+                drv
+            );
+
+            if (auto structAttrs = parsedDrv.prepareStructuredAttrs(*store, inputs)) {
+                auto json = structAttrs.value();
+                structuredAttrsRC = writeStructuredAttrsShell(json);
+
+                auto attrsJSON = (Path) tmpDir + "/.attrs.json";
+                writeFile(attrsJSON, json.dump());
+
+                auto attrsSH = (Path) tmpDir + "/.attrs.sh";
+                writeFile(attrsSH, structuredAttrsRC);
+
+                env["NIX_ATTRS_SH_FILE"] = attrsSH;
+                env["NIX_ATTRS_JSON_FILE"] = attrsJSON;
+                keepTmp = true;
+            }
+        }
+
         /* Run a shell using the derivation's environment.  For
            convenience, source $stdenv/setup to setup additional
            environment variables and shell functions.  Also don't
            lose the current $PATH directories. */
         auto rcfile = (Path) tmpDir + "/rc";
-        writeFile(rcfile, fmt(
+        std::string rc = fmt(
                 R"(_nix_shell_clean_tmpdir() { rm -rf %1%; }; )"s +
                 (keepTmp ?
                     "trap _nix_shell_clean_tmpdir EXIT; "
@@ -436,8 +490,12 @@ static void main_nix_build(int argc, char * * argv)
                     "_nix_shell_clean_tmpdir; ") +
                 (pure ? "" : "[ -n \"$PS1\" ] && [ -e ~/.bashrc ] && source ~/.bashrc;") +
                 "%2%"
-                "dontAddDisableDepTrack=1; "
-                "[ -e $stdenv/setup ] && source $stdenv/setup; "
+                // always clear PATH.
+                // when nix-shell is run impure, we rehydrate it with the `p=$PATH` above
+                "unset PATH;"
+                "dontAddDisableDepTrack=1;\n"
+                + structuredAttrsRC +
+                "\n[ -e $stdenv/setup ] && source $stdenv/setup; "
                 "%3%"
                 "PATH=%4%:\"$PATH\"; "
                 "SHELL=%5%; "
@@ -455,7 +513,9 @@ static void main_nix_build(int argc, char * * argv)
                 shellEscape(dirOf(*shell)),
                 shellEscape(*shell),
                 (getenv("TZ") ? (string("export TZ=") + shellEscape(getenv("TZ")) + "; ") : ""),
-                envCommand));
+                envCommand);
+        vomit("Sourcing nix-shell with file %s and contents:\n%s", rcfile, rc);
+        writeFile(rcfile, rc);
 
         Strings envStrs;
         for (auto & i : env)
@@ -484,6 +544,7 @@ static void main_nix_build(int argc, char * * argv)
 
         std::vector<StorePathWithOutputs> pathsToBuild;
         std::vector<std::pair<StorePath, std::string>> pathsToBuildOrdered;
+        RealisedPath::Set drvsToCopy;
 
         std::map<StorePath, std::pair<size_t, StringSet>> drvMap;
 
@@ -496,13 +557,13 @@ static void main_nix_build(int argc, char * * argv)
 
             pathsToBuild.push_back({drvPath, {outputName}});
             pathsToBuildOrdered.push_back({drvPath, {outputName}});
+            drvsToCopy.insert(drvPath);
 
             auto i = drvMap.find(drvPath);
             if (i != drvMap.end())
                 i->second.second.insert(outputName);
-            else {
+            else
                 drvMap[drvPath] = {drvMap.size(), {outputName}};
-            }
         }
 
         buildPaths(pathsToBuild);
@@ -517,7 +578,7 @@ static void main_nix_build(int argc, char * * argv)
             if (counter)
                 drvPrefix += fmt("-%d", counter + 1);
 
-            auto builtOutputs = store->queryPartialDerivationOutputMap(drvPath);
+            auto builtOutputs = evalStore->queryPartialDerivationOutputMap(drvPath);
 
             auto maybeOutputPath = builtOutputs.at(outputName);
             assert(maybeOutputPath);
diff --git a/src/nix-copy-closure/nix-copy-closure.cc b/src/nix-copy-closure/nix-copy-closure.cc
index 02ccbe541..841d50fd3 100755
--- a/src/nix-copy-closure/nix-copy-closure.cc
+++ b/src/nix-copy-closure/nix-copy-closure.cc
@@ -54,10 +54,7 @@ static int main_nix_copy_closure(int argc, char ** argv)
         for (auto & path : storePaths)
             storePaths2.insert(from->followLinksToStorePath(path));
 
-        RealisedPath::Set closure;
-        RealisedPath::closure(*from, storePaths2, closure);
-
-        copyPaths(from, to, closure, NoRepair, NoCheckSigs, useSubstitutes);
+        copyClosure(*from, *to, storePaths2, NoRepair, NoCheckSigs, useSubstitutes);
 
         return 0;
     }
diff --git a/src/nix-env/nix-env.cc b/src/nix-env/nix-env.cc
index e04954d45..4056d973d 100644
--- a/src/nix-env/nix-env.cc
+++ b/src/nix-env/nix-env.cc
@@ -879,7 +879,7 @@ static void queryJSON(Globals & globals, vector<DrvInfo> & elems)
                 placeholder.write(nullptr);
             } else {
                 PathSet context;
-                printValueAsJSON(*globals.state, true, *v, placeholder, context);
+                printValueAsJSON(*globals.state, true, *v, noPos, placeholder, context);
             }
         }
     }
@@ -1204,37 +1204,6 @@ static void opSwitchProfile(Globals & globals, Strings opFlags, Strings opArgs)
 }
 
 
-static constexpr GenerationNumber prevGen = std::numeric_limits<GenerationNumber>::max();
-
-
-static void switchGeneration(Globals & globals, GenerationNumber dstGen)
-{
-    PathLocks lock;
-    lockProfile(lock, globals.profile);
-
-    auto [gens, curGen] = findGenerations(globals.profile);
-
-    std::optional<Generation> dst;
-    for (auto & i : gens)
-        if ((dstGen == prevGen && i.number < curGen) ||
-            (dstGen >= 0 && i.number == dstGen))
-            dst = i;
-
-    if (!dst) {
-        if (dstGen == prevGen)
-            throw Error("no generation older than the current (%1%) exists", curGen.value_or(0));
-        else
-            throw Error("generation %1% does not exist", dstGen);
-    }
-
-    printInfo("switching from generation %1% to %2%", curGen.value_or(0), dst->number);
-
-    if (globals.dryRun) return;
-
-    switchLink(globals.profile, dst->path);
-}
-
-
 static void opSwitchGeneration(Globals & globals, Strings opFlags, Strings opArgs)
 {
     if (opFlags.size() > 0)
@@ -1243,7 +1212,7 @@ static void opSwitchGeneration(Globals & globals, Strings opFlags, Strings opArg
         throw UsageError("exactly one argument expected");
 
     if (auto dstGen = string2Int<GenerationNumber>(opArgs.front()))
-        switchGeneration(globals, *dstGen);
+        switchGeneration(globals.profile, *dstGen, globals.dryRun);
     else
         throw UsageError("expected a generation number");
 }
@@ -1256,7 +1225,7 @@ static void opRollback(Globals & globals, Strings opFlags, Strings opArgs)
     if (opArgs.size() != 0)
         throw UsageError("no arguments expected");
 
-    switchGeneration(globals, prevGen);
+    switchGeneration(globals.profile, {}, globals.dryRun);
 }
 
 
@@ -1296,12 +1265,12 @@ static void opDeleteGenerations(Globals & globals, Strings opFlags, Strings opAr
     } else if (opArgs.size() == 1 && opArgs.front().find('d') != string::npos) {
         deleteGenerationsOlderThan(globals.profile, opArgs.front(), globals.dryRun);
     } else if (opArgs.size() == 1 && opArgs.front().find('+') != string::npos) {
-        if(opArgs.front().size() < 2)
-            throw Error("invalid number of generations ‘%1%’", opArgs.front());
+        if (opArgs.front().size() < 2)
+            throw Error("invalid number of generations '%1%'", opArgs.front());
         string str_max = string(opArgs.front(), 1, opArgs.front().size());
         auto max = string2Int<GenerationNumber>(str_max);
         if (!max || *max == 0)
-            throw Error("invalid number of generations to keep ‘%1%’", opArgs.front());
+            throw Error("invalid number of generations to keep '%1%'", opArgs.front());
         deleteGenerationsGreaterThan(globals.profile, *max, globals.dryRun);
     } else {
         std::set<GenerationNumber> gens;
diff --git a/src/nix-env/user-env.cc b/src/nix-env/user-env.cc
index 5ceb2ae67..1fd4bcbd3 100644
--- a/src/nix-env/user-env.cc
+++ b/src/nix-env/user-env.cc
@@ -131,9 +131,9 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
     state.forceValue(topLevel);
     PathSet context;
     Attr & aDrvPath(*topLevel.attrs->find(state.sDrvPath));
-    auto topLevelDrv = state.store->parseStorePath(state.coerceToPath(aDrvPath.pos ? *(aDrvPath.pos) : noPos, *(aDrvPath.value), context));
+    auto topLevelDrv = state.store->parseStorePath(state.coerceToPath(*aDrvPath.pos, *aDrvPath.value, context));
     Attr & aOutPath(*topLevel.attrs->find(state.sOutPath));
-    Path topLevelOut = state.coerceToPath(aOutPath.pos ? *(aOutPath.pos) : noPos, *(aOutPath.value), context);
+    Path topLevelOut = state.coerceToPath(*aOutPath.pos, *aOutPath.value, context);
 
     /* Realise the resulting store expression. */
     debug("building user environment");
diff --git a/src/nix-instantiate/nix-instantiate.cc b/src/nix-instantiate/nix-instantiate.cc
index 95903d882..19a954ddd 100644
--- a/src/nix-instantiate/nix-instantiate.cc
+++ b/src/nix-instantiate/nix-instantiate.cc
@@ -50,9 +50,9 @@ void processExpr(EvalState & state, const Strings & attrPaths,
             else
                 state.autoCallFunction(autoArgs, v, vRes);
             if (output == okXML)
-                printValueAsXML(state, strict, location, vRes, std::cout, context);
+                printValueAsXML(state, strict, location, vRes, std::cout, context, noPos);
             else if (output == okJSON)
-                printValueAsJSON(state, strict, vRes, std::cout, context);
+                printValueAsJSON(state, strict, vRes, v.determinePos(noPos), std::cout, context);
             else {
                 if (strict) state.forceValueDeep(vRes);
                 std::cout << vRes << std::endl;
@@ -153,8 +153,9 @@ static int main_nix_instantiate(int argc, char * * argv)
             settings.readOnlyMode = true;
 
         auto store = openStore();
+        auto evalStore = myArgs.evalStoreUrl ? openStore(*myArgs.evalStoreUrl) : store;
 
-        auto state = std::make_unique<EvalState>(myArgs.searchPath, store);
+        auto state = std::make_unique<EvalState>(myArgs.searchPath, evalStore, store);
         state->repair = repair;
 
         Bindings & autoArgs = *myArgs.getAutoArgs(*state);
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index b327793e7..f0ce0368a 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -801,6 +801,9 @@ static void opServe(Strings opFlags, Strings opArgs)
             settings.enforceDeterminism = readInt(in);
             settings.runDiffHook = true;
         }
+        if (GET_PROTOCOL_MINOR(clientVersion) >= 7) {
+            settings.keepFailed = (bool) readInt(in);
+        }
         settings.printRepeatedBuilds = false;
     };
 
diff --git a/src/nix/app.cc b/src/nix/app.cc
index cf147c631..9719a65dd 100644
--- a/src/nix/app.cc
+++ b/src/nix/app.cc
@@ -3,34 +3,79 @@
 #include "eval-inline.hh"
 #include "eval-cache.hh"
 #include "names.hh"
+#include "command.hh"
 
 namespace nix {
 
-App Installable::toApp(EvalState & state)
+struct InstallableDerivedPath : Installable
 {
-    auto [cursor, attrPath] = getCursor(state);
+    ref<Store> store;
+    const DerivedPath derivedPath;
 
-    auto type = cursor->getAttr("type")->getString();
+    InstallableDerivedPath(ref<Store> store, const DerivedPath & derivedPath)
+        : store(store)
+        , derivedPath(derivedPath)
+    {
+    }
+
+
+    std::string what() override { return derivedPath.to_string(*store); }
+
+    DerivedPaths toDerivedPaths() override
+    {
+        return {derivedPath};
+    }
 
-    auto checkProgram = [&](const Path & program)
+    std::optional<StorePath> getStorePath() override
     {
-        if (!state.store->isInStore(program))
-            throw Error("app program '%s' is not in the Nix store", program);
-    };
+        return std::nullopt;
+    }
+};
+
+/**
+ * Return the rewrites that are needed to resolve a string whose context is
+ * included in `dependencies`
+ */
+StringPairs resolveRewrites(Store & store, const BuiltPaths dependencies)
+{
+    StringPairs res;
+    for (auto & dep : dependencies)
+        if (auto drvDep = std::get_if<BuiltPathBuilt>(&dep))
+            for (auto & [ outputName, outputPath ] : drvDep->outputs)
+                res.emplace(
+                    downstreamPlaceholder(store, drvDep->drvPath, outputName),
+                    store.printStorePath(outputPath)
+                );
+    return res;
+}
+
+/**
+ * Resolve the given string assuming the given context
+ */
+std::string resolveString(Store & store, const std::string & toResolve, const BuiltPaths dependencies)
+{
+    auto rewrites = resolveRewrites(store, dependencies);
+    return rewriteStrings(toResolve, rewrites);
+}
+
+UnresolvedApp Installable::toApp(EvalState & state)
+{
+    auto [cursor, attrPath] = getCursor(state);
+
+    auto type = cursor->getAttr("type")->getString();
 
     if (type == "app") {
         auto [program, context] = cursor->getAttr("program")->getStringWithContext();
 
-        checkProgram(program);
 
         std::vector<StorePathWithOutputs> context2;
         for (auto & [path, name] : context)
             context2.push_back({state.store->parseStorePath(path), {name}});
 
-        return App {
+        return UnresolvedApp{App {
             .context = std::move(context2),
             .program = program,
-        };
+        }};
     }
 
     else if (type == "derivation") {
@@ -45,15 +90,33 @@ App Installable::toApp(EvalState & state)
             ? aMainProgram->getString()
             : DrvName(name).name;
         auto program = outPath + "/bin/" + mainProgram;
-        checkProgram(program);
-        return App {
+        return UnresolvedApp { App {
             .context = { { drvPath, {outputName} } },
             .program = program,
-        };
+        }};
     }
 
     else
         throw Error("attribute '%s' has unsupported type '%s'", attrPath, type);
 }
 
+// FIXME: move to libcmd
+App UnresolvedApp::resolve(ref<Store> evalStore, ref<Store> store)
+{
+    auto res = unresolved;
+
+    std::vector<std::shared_ptr<Installable>> installableContext;
+
+    for (auto & ctxElt : unresolved.context)
+        installableContext.push_back(
+            std::make_shared<InstallableDerivedPath>(store, ctxElt.toDerivedPath()));
+
+    auto builtContext = build(evalStore, store, Realise::Outputs, installableContext);
+    res.program = resolveString(*store, unresolved.program, builtContext);
+    if (!store->isInStore(res.program))
+        throw Error("app program '%s' is not in the Nix store", res.program);
+
+    return res;
+}
+
 }
diff --git a/src/nix/build.cc b/src/nix/build.cc
index 03159b6cc..6e31757a2 100644
--- a/src/nix/build.cc
+++ b/src/nix/build.cc
@@ -52,7 +52,12 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
 
     void run(ref<Store> store) override
     {
-        auto buildables = build(store, dryRun ? Realise::Nothing : Realise::Outputs, installables, buildMode);
+        auto buildables = build(
+            getEvalStore(), store,
+            dryRun ? Realise::Derivation : Realise::Outputs,
+            installables, buildMode);
+
+        if (json) logger->cout("%s", derivedPathsWithHintsToJSON(buildables, store).dump());
 
         if (dryRun) return;
 
@@ -61,14 +66,13 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
                 for (const auto & [_i, buildable] : enumerate(buildables)) {
                     auto i = _i;
                     std::visit(overloaded {
-                        [&](DerivedPathWithHints::Opaque bo) {
+                        [&](const BuiltPath::Opaque & bo) {
                             std::string symlink = outLink;
                             if (i) symlink += fmt("-%d", i);
                             store2->addPermRoot(bo.path, absPath(symlink));
                         },
-                        [&](DerivedPathWithHints::Built bfd) {
-                            auto builtOutputs = store->queryDerivationOutputMap(bfd.drvPath);
-                            for (auto & output : builtOutputs) {
+                        [&](const BuiltPath::Built & bfd) {
+                            for (auto & output : bfd.outputs) {
                                 std::string symlink = outLink;
                                 if (i) symlink += fmt("-%d", i);
                                 if (output.first != "out") symlink += fmt("-%s", output.first);
@@ -79,8 +83,6 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
                 }
 
         updateProfile(buildables);
-
-        if (json) logger->cout("%s", derivedPathsWithHintsToJSON(buildables, store).dump());
     }
 };
 
diff --git a/src/nix/bundle.cc b/src/nix/bundle.cc
index 53dccc63a..aca024bca 100644
--- a/src/nix/bundle.cc
+++ b/src/nix/bundle.cc
@@ -59,7 +59,7 @@ struct CmdBundle : InstallableCommand
 
     Strings getDefaultFlakeAttrPathPrefixes() override
     {
-        Strings res{"apps." + settings.thisSystem.get() + ".", "packages"};
+        Strings res{"apps." + settings.thisSystem.get() + "."};
         for (auto & s : SourceExprCommand::getDefaultFlakeAttrPathPrefixes())
             res.push_back(s);
         return res;
@@ -69,8 +69,7 @@ struct CmdBundle : InstallableCommand
     {
         auto evalState = getEvalState();
 
-        auto app = installable->toApp(*evalState);
-        store->buildPaths(toDerivedPaths(app.context));
+        auto app = installable->toApp(*evalState).resolve(getEvalStore(), store);
 
         auto [bundlerFlakeRef, bundlerName] = parseFlakeRefWithFragment(bundler, absPath("."));
         const flake::LockFlags lockFlags{ .writeLockFile = false };
diff --git a/src/nix/copy.cc b/src/nix/copy.cc
index f59f7c76b..197c85316 100644
--- a/src/nix/copy.cc
+++ b/src/nix/copy.cc
@@ -8,7 +8,7 @@
 
 using namespace nix;
 
-struct CmdCopy : RealisedPathsCommand
+struct CmdCopy : BuiltPathsCommand
 {
     std::string srcUri, dstUri;
 
@@ -16,10 +16,10 @@ struct CmdCopy : RealisedPathsCommand
 
     SubstituteFlag substitute = NoSubstitute;
 
-    using RealisedPathsCommand::run;
+    using BuiltPathsCommand::run;
 
     CmdCopy()
-        : RealisedPathsCommand(true)
+        : BuiltPathsCommand(true)
     {
         addFlag({
             .longName = "from",
@@ -75,16 +75,22 @@ struct CmdCopy : RealisedPathsCommand
         if (srcUri.empty() && dstUri.empty())
             throw UsageError("you must pass '--from' and/or '--to'");
 
-        RealisedPathsCommand::run(store);
+        BuiltPathsCommand::run(store);
     }
 
-    void run(ref<Store> srcStore, std::vector<RealisedPath> paths) override
+    void run(ref<Store> srcStore, BuiltPaths && paths) override
     {
         ref<Store> dstStore = dstUri.empty() ? openStore() : openStore(dstUri);
 
+        RealisedPath::Set stuffToCopy;
+
+        for (auto & builtPath : paths) {
+            auto theseRealisations = builtPath.toRealisedPaths(*srcStore);
+            stuffToCopy.insert(theseRealisations.begin(), theseRealisations.end());
+        }
+
         copyPaths(
-            srcStore, dstStore, RealisedPath::Set(paths.begin(), paths.end()),
-            NoRepair, checkSigs, substitute);
+            *srcStore, *dstStore, stuffToCopy, NoRepair, checkSigs, substitute);
     }
 };
 
diff --git a/src/nix/daemon.cc b/src/nix/daemon.cc
index 2cf2a04c9..6a40a0bd3 100644
--- a/src/nix/daemon.cc
+++ b/src/nix/daemon.cc
@@ -156,9 +156,6 @@ static void daemonLoop()
     if (chdir("/") == -1)
         throw SysError("cannot change current directory");
 
-    //  Get rid of children automatically; don't let them become zombies.
-    setSigChldAction(true);
-
     AutoCloseFD fdSocket;
 
     //  Handle socket-based activation by systemd.
@@ -176,6 +173,9 @@ static void daemonLoop()
         fdSocket = createUnixDomainSocket(settings.nixDaemonSocketFile, 0666);
     }
 
+    //  Get rid of children automatically; don't let them become zombies.
+    setSigChldAction(true);
+
     //  Loop accepting connections.
     while (1) {
 
diff --git a/src/nix/develop.cc b/src/nix/develop.cc
index 498a7b45c..5aad53919 100644
--- a/src/nix/develop.cc
+++ b/src/nix/develop.cc
@@ -7,8 +7,10 @@
 #include "derivations.hh"
 #include "affinity.hh"
 #include "progress-bar.hh"
+#include "run.hh"
 
-#include <regex>
+#include <memory>
+#include <nlohmann/json.hpp>
 
 using namespace nix;
 
@@ -25,94 +27,142 @@ static DevelopSettings developSettings;
 
 static GlobalConfig::Register rDevelopSettings(&developSettings);
 
-struct Var
-{
-    bool exported = true;
-    bool associative = false;
-    std::string quoted; // quoted string or array
-};
-
 struct BuildEnvironment
 {
-    std::map<std::string, Var> env;
-    std::string bashFunctions;
-};
+    struct String
+    {
+        bool exported;
+        std::string value;
 
-BuildEnvironment readEnvironment(const Path & path)
-{
-    BuildEnvironment res;
+        bool operator == (const String & other) const
+        {
+            return exported == other.exported && value == other.value;
+        }
+    };
 
-    std::set<std::string> exported;
+    using Array = std::vector<std::string>;
 
-    debug("reading environment file '%s'", path);
+    using Associative = std::map<std::string, std::string>;
 
-    auto file = readFile(path);
+    using Value = std::variant<String, Array, Associative>;
 
-    auto pos = file.cbegin();
+    std::map<std::string, Value> vars;
+    std::map<std::string, std::string> bashFunctions;
 
-    static std::string varNameRegex =
-        R"re((?:[a-zA-Z_][a-zA-Z0-9_]*))re";
+    static BuildEnvironment fromJSON(std::string_view in)
+    {
+        BuildEnvironment res;
 
-    static std::string simpleStringRegex =
-        R"re((?:[a-zA-Z0-9_/:\.\-\+=]*))re";
+        std::set<std::string> exported;
 
-    static std::string dquotedStringRegex =
-        R"re((?:\$?"(?:[^"\\]|\\[$`"\\\n])*"))re";
+        auto json = nlohmann::json::parse(in);
 
-    static std::string squotedStringRegex =
-        R"re((?:\$?(?:'(?:[^'\\]|\\[abeEfnrtv\\'"?])*'|\\')+))re";
+        for (auto & [name, info] : json["variables"].items()) {
+            std::string type = info["type"];
+            if (type == "var" || type == "exported")
+                res.vars.insert({name, BuildEnvironment::String { .exported = type == "exported", .value = info["value"] }});
+            else if (type == "array")
+                res.vars.insert({name, (Array) info["value"]});
+            else if (type == "associative")
+                res.vars.insert({name, (Associative) info["value"]});
+        }
 
-    static std::string indexedArrayRegex =
-        R"re((?:\(( *\[[0-9]+\]="(?:[^"\\]|\\.)*")*\)))re";
+        for (auto & [name, def] : json["bashFunctions"].items()) {
+            res.bashFunctions.insert({name, def});
+        }
 
-    static std::regex declareRegex(
-        "^declare -a?x (" + varNameRegex + ")(=(" +
-        dquotedStringRegex + "|" + indexedArrayRegex + "))?\n");
+        return res;
+    }
 
-    static std::regex varRegex(
-        "^(" + varNameRegex + ")=(" + simpleStringRegex + "|" + squotedStringRegex + "|" + indexedArrayRegex + ")\n");
+    std::string toJSON() const
+    {
+        auto res = nlohmann::json::object();
+
+        auto vars2 = nlohmann::json::object();
+        for (auto & [name, value] : vars) {
+            auto info = nlohmann::json::object();
+            if (auto str = std::get_if<String>(&value)) {
+                info["type"] = str->exported ? "exported" : "var";
+                info["value"] = str->value;
+            }
+            else if (auto arr = std::get_if<Array>(&value)) {
+                info["type"] = "array";
+                info["value"] = *arr;
+            }
+            else if (auto arr = std::get_if<Associative>(&value)) {
+                info["type"] = "associative";
+                info["value"] = *arr;
+            }
+            vars2[name] = std::move(info);
+        }
+        res["variables"] = std::move(vars2);
 
-    /* Note: we distinguish between an indexed and associative array
-       using the space before the closing parenthesis. Will
-       undoubtedly regret this some day. */
-    static std::regex assocArrayRegex(
-        "^(" + varNameRegex + ")=" + R"re((?:\(( *\[[^\]]+\]="(?:[^"\\]|\\.)*")* *\)))re" + "\n");
+        res["bashFunctions"] = bashFunctions;
 
-    static std::regex functionRegex(
-        "^" + varNameRegex + " \\(\\) *\n");
+        auto json = res.dump();
 
-    while (pos != file.end()) {
+        assert(BuildEnvironment::fromJSON(json) == *this);
 
-        std::smatch match;
+        return json;
+    }
 
-        if (std::regex_search(pos, file.cend(), match, declareRegex, std::regex_constants::match_continuous)) {
-            pos = match[0].second;
-            exported.insert(match[1]);
+    void toBash(std::ostream & out, const std::set<std::string> & ignoreVars) const
+    {
+        for (auto & [name, value] : vars) {
+            if (!ignoreVars.count(name)) {
+                if (auto str = std::get_if<String>(&value)) {
+                    out << fmt("%s=%s\n", name, shellEscape(str->value));
+                    if (str->exported)
+                        out << fmt("export %s\n", name);
+                }
+                else if (auto arr = std::get_if<Array>(&value)) {
+                    out << "declare -a " << name << "=(";
+                    for (auto & s : *arr)
+                        out << shellEscape(s) << " ";
+                    out << ")\n";
+                }
+                else if (auto arr = std::get_if<Associative>(&value)) {
+                    out << "declare -A " << name << "=(";
+                    for (auto & [n, v] : *arr)
+                        out << "[" << shellEscape(n) << "]=" << shellEscape(v) << " ";
+                    out << ")\n";
+                }
+            }
         }
 
-        else if (std::regex_search(pos, file.cend(), match, varRegex, std::regex_constants::match_continuous)) {
-            pos = match[0].second;
-            res.env.insert({match[1], Var { .exported = exported.count(match[1]) > 0, .quoted = match[2] }});
+        for (auto & [name, def] : bashFunctions) {
+            out << name << " ()\n{\n" << def << "}\n";
         }
+    }
 
-        else if (std::regex_search(pos, file.cend(), match, assocArrayRegex, std::regex_constants::match_continuous)) {
-            pos = match[0].second;
-            res.env.insert({match[1], Var { .associative = true, .quoted = match[2] }});
-        }
+    static std::string getString(const Value & value)
+    {
+        if (auto str = std::get_if<String>(&value))
+            return str->value;
+        else
+            throw Error("bash variable is not a string");
+    }
 
-        else if (std::regex_search(pos, file.cend(), match, functionRegex, std::regex_constants::match_continuous)) {
-            res.bashFunctions = std::string(pos, file.cend());
-            break;
+    static Array getStrings(const Value & value)
+    {
+        if (auto str = std::get_if<String>(&value))
+            return tokenizeString<Array>(str->value);
+        else if (auto arr = std::get_if<Array>(&value)) {
+            return *arr;
+        } else if (auto assoc = std::get_if<Associative>(&value)) {
+            Array assocKeys;
+            std::for_each(assoc->begin(), assoc->end(), [&](auto & n) { assocKeys.push_back(n.first); });
+            return assocKeys;
         }
-
-        else throw Error("shell environment '%s' has unexpected line '%s'",
-            path, file.substr(pos - file.cbegin(), 60));
+        else
+            throw Error("bash variable is not a string or array");
     }
 
-    res.env.erase("__output");
-
-    return res;
-}
+    bool operator == (const BuildEnvironment & other) const
+    {
+        return vars == other.vars && bashFunctions == other.bashFunctions;
+    }
+};
 
 const static std::string getEnvSh =
     #include "get-env.sh.gen.hh"
@@ -123,15 +173,15 @@ const static std::string getEnvSh =
    modified derivation with the same dependencies and nearly the same
    initial environment variables, that just writes the resulting
    environment to a file and exits. */
-StorePath getDerivationEnvironment(ref<Store> store, const StorePath & drvPath)
+static StorePath getDerivationEnvironment(ref<Store> store, ref<Store> evalStore, const StorePath & drvPath)
 {
-    auto drv = store->derivationFromPath(drvPath);
+    auto drv = evalStore->derivationFromPath(drvPath);
 
     auto builder = baseNameOf(drv.builder);
     if (builder != "bash")
         throw Error("'nix develop' only works on derivations that use 'bash' as their builder");
 
-    auto getEnvShPath = store->addTextToStore("get-env.sh", getEnvSh, {});
+    auto getEnvShPath = evalStore->addTextToStore("get-env.sh", getEnvSh, {});
 
     drv.args = {store->printStorePath(getEnvShPath)};
 
@@ -144,26 +194,34 @@ StorePath getDerivationEnvironment(ref<Store> store, const StorePath & drvPath)
     /* Rehash and write the derivation. FIXME: would be nice to use
        'buildDerivation', but that's privileged. */
     drv.name += "-env";
-    for (auto & output : drv.outputs) {
-        output.second = { .output = DerivationOutputInputAddressed { .path = StorePath::dummy } };
-        drv.env[output.first] = "";
-    }
     drv.inputSrcs.insert(std::move(getEnvShPath));
-    Hash h = std::get<0>(hashDerivationModulo(*store, drv, true));
+    if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations)) {
+        for (auto & output : drv.outputs) {
+            output.second = {
+                .output = DerivationOutputDeferred{},
+            };
+            drv.env[output.first] = hashPlaceholder(output.first);
+        }
+    } else {
+        for (auto & output : drv.outputs) {
+            output.second = { .output = DerivationOutputInputAddressed { .path = StorePath::dummy } };
+            drv.env[output.first] = "";
+        }
+        Hash h = std::get<0>(hashDerivationModulo(*evalStore, drv, true));
 
-    for (auto & output : drv.outputs) {
-        auto outPath = store->makeOutputPath(output.first, h, drv.name);
-        output.second = { .output = DerivationOutputInputAddressed { .path = outPath } };
-        drv.env[output.first] = store->printStorePath(outPath);
+        for (auto & output : drv.outputs) {
+            auto outPath = store->makeOutputPath(output.first, h, drv.name);
+            output.second = { .output = DerivationOutputInputAddressed { .path = outPath } };
+            drv.env[output.first] = store->printStorePath(outPath);
+        }
     }
 
-    auto shellDrvPath = writeDerivation(*store, drv);
+    auto shellDrvPath = writeDerivation(*evalStore, drv);
 
     /* Build the derivation. */
-    store->buildPaths({DerivedPath::Built{shellDrvPath}});
+    store->buildPaths({DerivedPath::Built{shellDrvPath}}, bmNormal, evalStore);
 
-    for (auto & [_0, outputAndOptPath] : drv.outputsAndOptPaths(*store)) {
-        auto & [_1, optPath] = outputAndOptPath;
+    for (auto & [_0, optPath] : evalStore->queryPartialDerivationOutputMap(shellDrvPath)) {
         assert(optPath);
         auto & outPath = *optPath;
         assert(store->isValidPath(outPath));
@@ -177,18 +235,15 @@ StorePath getDerivationEnvironment(ref<Store> store, const StorePath & drvPath)
 
 struct Common : InstallableCommand, MixProfile
 {
-    std::set<string> ignoreVars{
+    std::set<std::string> ignoreVars{
         "BASHOPTS",
-        "EUID",
         "HOME", // FIXME: don't ignore in pure mode?
-        "HOSTNAME",
         "NIX_BUILD_TOP",
         "NIX_ENFORCE_PURITY",
         "NIX_LOG_FD",
+        "NIX_REMOTE",
         "PPID",
-        "PWD",
         "SHELLOPTS",
-        "SHLVL",
         "SSL_CERT_FILE", // FIXME: only want to ignore /no-cert-file.crt
         "TEMP",
         "TEMPDIR",
@@ -224,22 +279,10 @@ struct Common : InstallableCommand, MixProfile
 
         out << "nix_saved_PATH=\"$PATH\"\n";
 
-        for (auto & i : buildEnvironment.env) {
-            if (!ignoreVars.count(i.first) && !hasPrefix(i.first, "BASH_")) {
-                if (i.second.associative)
-                    out << fmt("declare -A %s=(%s)\n", i.first, i.second.quoted);
-                else {
-                    out << fmt("%s=%s\n", i.first, i.second.quoted);
-                    if (i.second.exported)
-                        out << fmt("export %s\n", i.first);
-                }
-            }
-        }
+        buildEnvironment.toBash(out, ignoreVars);
 
         out << "PATH=\"$PATH:$nix_saved_PATH\"\n";
 
-        out << buildEnvironment.bashFunctions << "\n";
-
         out << "export NIX_BUILD_TOP=\"$(mktemp -d -t nix-shell.XXXXXX)\"\n";
         for (auto & i : {"TMP", "TMPDIR", "TEMP", "TEMPDIR"})
             out << fmt("export %s=\"$NIX_BUILD_TOP\"\n", i);
@@ -249,25 +292,25 @@ struct Common : InstallableCommand, MixProfile
         auto script = out.str();
 
         /* Substitute occurrences of output paths. */
-        auto outputs = buildEnvironment.env.find("outputs");
-        assert(outputs != buildEnvironment.env.end());
+        auto outputs = buildEnvironment.vars.find("outputs");
+        assert(outputs != buildEnvironment.vars.end());
 
         // FIXME: properly unquote 'outputs'.
         StringMap rewrites;
-        for (auto & outputName : tokenizeString<std::vector<std::string>>(replaceStrings(outputs->second.quoted, "'", ""))) {
-            auto from = buildEnvironment.env.find(outputName);
-            assert(from != buildEnvironment.env.end());
+        for (auto & outputName : BuildEnvironment::getStrings(outputs->second)) {
+            auto from = buildEnvironment.vars.find(outputName);
+            assert(from != buildEnvironment.vars.end());
             // FIXME: unquote
-            rewrites.insert({from->second.quoted, outputsDir + "/" + outputName});
+            rewrites.insert({BuildEnvironment::getString(from->second), outputsDir + "/" + outputName});
         }
 
         /* Substitute redirects. */
         for (auto & [installable_, dir_] : redirects) {
             auto dir = absPath(dir_);
             auto installable = parseInstallable(store, installable_);
-            auto buildable = installable->toDerivedPathWithHints();
-            auto doRedirect = [&](const StorePath & path)
-            {
+            auto builtPaths = toStorePaths(
+                getEvalStore(), store, Realise::Nothing, OperateOn::Output, {installable});
+            for (auto & path: builtPaths) {
                 auto from = store->printStorePath(path);
                 if (script.find(from) == std::string::npos)
                     warn("'%s' (path '%s') is not used by this build environment", installable->what(), from);
@@ -275,16 +318,7 @@ struct Common : InstallableCommand, MixProfile
                     printInfo("redirecting '%s' to '%s'", from, dir);
                     rewrites.insert({from, dir});
                 }
-            };
-            std::visit(overloaded {
-                [&](const DerivedPathWithHints::Opaque & bo) {
-                    doRedirect(bo.path);
-                },
-                [&](const DerivedPathWithHints::Built & bfd) {
-                    for (auto & [outputName, path] : bfd.outputs)
-                        if (path) doRedirect(*path);
-                },
-            }, buildable.raw());
+            }
         }
 
         return rewriteStrings(script, rewrites);
@@ -294,6 +328,12 @@ struct Common : InstallableCommand, MixProfile
     {
         return {"devShell." + settings.thisSystem.get(), "defaultPackage." + settings.thisSystem.get()};
     }
+    Strings getDefaultFlakeAttrPathPrefixes() override
+    {
+        auto res = SourceExprCommand::getDefaultFlakeAttrPathPrefixes();
+        res.emplace_front("devShells." + settings.thisSystem.get() + ".");
+        return res;
+    }
 
     StorePath getShellOutPath(ref<Store> store)
     {
@@ -309,7 +349,7 @@ struct Common : InstallableCommand, MixProfile
 
             auto & drvPath = *drvs.begin();
 
-            return getDerivationEnvironment(store, drvPath);
+            return getDerivationEnvironment(store, getEvalStore(), drvPath);
         }
     }
 
@@ -321,7 +361,9 @@ struct Common : InstallableCommand, MixProfile
 
         updateProfile(shellOutPath);
 
-        return {readEnvironment(strPath), strPath};
+        debug("reading environment file '%s'", strPath);
+
+        return {BuildEnvironment::fromJSON(readFile(store->toRealPath(shellOutPath))), strPath};
     }
 };
 
@@ -351,6 +393,12 @@ struct CmdDevelop : Common, MixEnvironment
         });
 
         addFlag({
+            .longName = "unpack",
+            .description = "Run the `unpack` phase.",
+            .handler = {&phase, {"unpack"}},
+        });
+
+        addFlag({
             .longName = "configure",
             .description = "Run the `configure` phase.",
             .handler = {&phase, {"configure"}},
@@ -404,7 +452,7 @@ struct CmdDevelop : Common, MixEnvironment
         if (verbosity >= lvlDebug)
             script += "set -x\n";
 
-        script += fmt("rm -f '%s'\n", rcFilePath);
+        script += fmt("command rm -f '%s'\n", rcFilePath);
 
         if (phase) {
             if (!command.empty())
@@ -423,7 +471,7 @@ struct CmdDevelop : Common, MixEnvironment
         }
 
         else {
-            script += "[ -n \"$PS1\" ] && [ -e ~/.bashrc ] && source ~/.bashrc;\n";
+            script = "[ -n \"$PS1\" ] && [ -e ~/.bashrc ] && source ~/.bashrc;\n" + script;
             if (developSettings.bashPrompt != "")
                 script += fmt("[ -n \"$PS1\" ] && PS1=%s;\n", shellEscape(developSettings.bashPrompt));
             if (developSettings.bashPromptSuffix != "")
@@ -432,8 +480,6 @@ struct CmdDevelop : Common, MixEnvironment
 
         writeFull(rcFileFd.get(), script);
 
-        stopProgressBar();
-
         setEnviron();
         // prevent garbage collection until shell exits
         setenv("NIX_GCROOT", gcroot.data(), 1);
@@ -443,16 +489,20 @@ struct CmdDevelop : Common, MixEnvironment
         try {
             auto state = getEvalState();
 
+            auto nixpkgsLockFlags = lockFlags;
+            nixpkgsLockFlags.inputOverrides = {};
+            nixpkgsLockFlags.inputUpdates = {};
+
             auto bashInstallable = std::make_shared<InstallableFlake>(
                 this,
                 state,
                 installable->nixpkgsFlakeRef(),
                 Strings{"bashInteractive"},
                 Strings{"legacyPackages." + settings.thisSystem.get() + "."},
-                lockFlags);
+                nixpkgsLockFlags);
 
-            shell = state->store->printStorePath(
-                toStorePath(state->store, Realise::Outputs, OperateOn::Output, bashInstallable)) + "/bin/bash";
+            shell = store->printStorePath(
+                toStorePath(getEvalStore(), store, Realise::Outputs, OperateOn::Output, bashInstallable)) + "/bin/bash";
         } catch (Error &) {
             ignoreException();
         }
@@ -462,15 +512,25 @@ struct CmdDevelop : Common, MixEnvironment
         auto args = phase || !command.empty() ? Strings{std::string(baseNameOf(shell)), rcFilePath}
             : Strings{std::string(baseNameOf(shell)), "--rcfile", rcFilePath};
 
-        restoreProcessContext();
-
-        execvp(shell.c_str(), stringsToCharPtrs(args).data());
+        // Need to chdir since phases assume in flake directory
+        if (phase) {
+            // chdir if installable is a flake of type git+file or path
+            auto installableFlake = std::dynamic_pointer_cast<InstallableFlake>(installable);
+            if (installableFlake) {
+                auto sourcePath = installableFlake->getLockedFlake()->flake.resolvedRef.input.getSourcePath();
+                if (sourcePath) {
+                    if (chdir(sourcePath->c_str()) == -1) {
+                        throw SysError("chdir to '%s' failed", *sourcePath);
+                    }
+                }
+            }
+        }
 
-        throw SysError("executing shell '%s'", shell);
+        runProgramInStore(store, shell, args);
     }
 };
 
-struct CmdPrintDevEnv : Common
+struct CmdPrintDevEnv : Common, MixJSON
 {
     std::string description() override
     {
@@ -492,7 +552,10 @@ struct CmdPrintDevEnv : Common
 
         stopProgressBar();
 
-        std::cout << makeRcScript(store, buildEnvironment);
+        logger->writeToStdout(
+            json
+            ? buildEnvironment.toJSON()
+            : makeRcScript(store, buildEnvironment));
     }
 };
 
diff --git a/src/nix/develop.md b/src/nix/develop.md
index e71d9f8aa..1f214966a 100644
--- a/src/nix/develop.md
+++ b/src/nix/develop.md
@@ -29,6 +29,7 @@ R""(
 * Run a particular build phase directly:
 
   ```console
+  # nix develop --unpack
   # nix develop --configure
   # nix develop --build
   # nix develop --check
@@ -84,11 +85,20 @@ the flake's `nixConfig` attribute.
 
 # Flake output attributes
 
-If no flake output attribute is given, `nix run` tries the following
+If no flake output attribute is given, `nix develop` tries the following
 flake output attributes:
 
 * `devShell.<system>`
 
 * `defaultPackage.<system>`
 
+If a flake output *name* is given, `nix develop` tries the following flake
+output attributes:
+
+* `devShells.<system>.<name>`
+
+* `packages.<system>.<name>`
+
+* `legacyPackages.<system>.<name>`
+
 )""
diff --git a/src/nix/diff-closures.cc b/src/nix/diff-closures.cc
index 0c7d531c1..734c41e0e 100644
--- a/src/nix/diff-closures.cc
+++ b/src/nix/diff-closures.cc
@@ -131,9 +131,9 @@ struct CmdDiffClosures : SourceExprCommand
     void run(ref<Store> store) override
     {
         auto before = parseInstallable(store, _before);
-        auto beforePath = toStorePath(store, Realise::Outputs, operateOn, before);
+        auto beforePath = toStorePath(getEvalStore(), store, Realise::Outputs, operateOn, before);
         auto after = parseInstallable(store, _after);
-        auto afterPath = toStorePath(store, Realise::Outputs, operateOn, after);
+        auto afterPath = toStorePath(getEvalStore(), store, Realise::Outputs, operateOn, after);
         printClosureDiff(store, beforePath, afterPath, "");
     }
 };
diff --git a/src/nix/edit.cc b/src/nix/edit.cc
index b26417b18..fc48db0d7 100644
--- a/src/nix/edit.cc
+++ b/src/nix/edit.cc
@@ -31,7 +31,7 @@ struct CmdEdit : InstallableCommand
         auto [v, pos] = installable->toValue(*state);
 
         try {
-            pos = findDerivationFilename(*state, *v, installable->what());
+            pos = findPackageFilename(*state, *v, installable->what());
         } catch (NoPositionInfo &) {
         }
 
diff --git a/src/nix/eval.cc b/src/nix/eval.cc
index 65d61e005..c7517cf79 100644
--- a/src/nix/eval.cc
+++ b/src/nix/eval.cc
@@ -112,7 +112,7 @@ struct CmdEval : MixJSON, InstallableCommand
 
         else if (json) {
             JSONPlaceholder jsonOut(std::cout);
-            printValueAsJSON(*state, true, *v, jsonOut, context);
+            printValueAsJSON(*state, true, *v, pos, jsonOut, context);
         }
 
         else {
diff --git a/src/nix/flake-check.md b/src/nix/flake-check.md
index dc079ba0c..07031c909 100644
--- a/src/nix/flake-check.md
+++ b/src/nix/flake-check.md
@@ -22,42 +22,47 @@ This command verifies that the flake specified by flake reference
 that the derivations specified by the flake's `checks` output can be
 built successfully.
 
+If the `keep-going` option is set to `true`, Nix will keep evaluating as much
+as it can and report the errors as it encounters them. Otherwise it will stop
+at the first error.
+
 # Evaluation checks
 
-This following flake output attributes must be derivations:
+The following flake output attributes must be derivations:
 
 * `checks.`*system*`.`*name*
-* `defaultPackage.`*system*`
-* `devShell.`*system*`
-* `nixosConfigurations.`*name*`.config.system.build.toplevel
+* `defaultPackage.`*system*
+* `devShell.`*system*
+* `devShells.`*system*`.`*name*
+* `nixosConfigurations.`*name*`.config.system.build.toplevel`
 * `packages.`*system*`.`*name*
 
 The following flake output attributes must be [app
 definitions](./nix3-run.md):
 
 * `apps.`*system*`.`*name*
-* `defaultApp.`*system*`
+* `defaultApp.`*system*
 
 The following flake output attributes must be [template
 definitions](./nix3-flake-init.md):
 
 * `defaultTemplate`
-* `templates`.`*name*
+* `templates.`*name*
 
 The following flake output attributes must be *Nixpkgs overlays*:
 
 * `overlay`
-* `overlays`.`*name*
+* `overlays.`*name*
 
 The following flake output attributes must be *NixOS modules*:
 
 * `nixosModule`
-* `nixosModules`.`*name*
+* `nixosModules.`*name*
 
 The following flake output attributes must be
 [bundlers](./nix3-bundle.md):
 
-* `bundlers`.`*name*
+* `bundlers.`*name*
 * `defaultBundler`
 
 In addition, the `hydraJobs` output is evaluated in the same way as
diff --git a/src/nix/flake-show.md b/src/nix/flake-show.md
index 1a42c44a0..e484cf47e 100644
--- a/src/nix/flake-show.md
+++ b/src/nix/flake-show.md
@@ -35,4 +35,7 @@ specified by flake reference *flake-url*. These are the top-level
 attributes in the `outputs` of the flake, as well as lower-level
 attributes for some standard outputs (e.g. `packages` or `checks`).
 
+With `--json`, the output is in a JSON representation suitable for automatic
+processing by other tools.
+
 )""
diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index 62a413e27..97f4d911c 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -84,6 +84,7 @@ struct CmdFlakeUpdate : FlakeCommand
 
         lockFlags.recreateLockFile = true;
         lockFlags.writeLockFile = true;
+        lockFlags.applyNixConfig = true;
 
         lockFlake();
     }
@@ -114,6 +115,7 @@ struct CmdFlakeLock : FlakeCommand
         settings.tarballTtl = 0;
 
         lockFlags.writeLockFile = true;
+        lockFlags.applyNixConfig = true;
 
         lockFlake();
     }
@@ -129,8 +131,18 @@ static void enumerateOutputs(EvalState & state, Value & vFlake,
 
     state.forceAttrs(*aOutputs->value);
 
-    for (auto & attr : *aOutputs->value->attrs)
-        callback(attr.name, *attr.value, *attr.pos);
+    auto sHydraJobs = state.symbols.create("hydraJobs");
+
+    /* Hack: ensure that hydraJobs is evaluated before anything
+       else. This way we can disable IFD for hydraJobs and then enable
+       it for other outputs. */
+    if (auto attr = aOutputs->value->attrs->get(sHydraJobs))
+        callback(attr->name, *attr->value, *attr->pos);
+
+    for (auto & attr : *aOutputs->value->attrs) {
+        if (attr.name != sHydraJobs)
+            callback(attr.name, *attr.value, *attr.pos);
+    }
 }
 
 struct CmdFlakeMetadata : FlakeCommand, MixJSON
@@ -240,6 +252,14 @@ struct CmdFlakeInfo : CmdFlakeMetadata
     }
 };
 
+static bool argHasName(std::string_view arg, std::string_view expected)
+{
+    return
+        arg == expected
+        || arg == "_"
+        || (hasPrefix(arg, "_") && arg.substr(1) == expected);
+}
+
 struct CmdFlakeCheck : FlakeCommand
 {
     bool build = true;
@@ -267,30 +287,50 @@ struct CmdFlakeCheck : FlakeCommand
 
     void run(nix::ref<nix::Store> store) override
     {
-        settings.readOnlyMode = !build;
+        if (!build) {
+            settings.readOnlyMode = true;
+            evalSettings.enableImportFromDerivation.setDefault(false);
+        }
 
         auto state = getEvalState();
+
+        lockFlags.applyNixConfig = true;
         auto flake = lockFlake();
 
+        bool hasErrors = false;
+        auto reportError = [&](const Error & e) {
+            try {
+                throw e;
+            } catch (Error & e) {
+                if (settings.keepGoing) {
+                    ignoreException();
+                    hasErrors = true;
+                }
+                else
+                    throw;
+            }
+        };
+
         // FIXME: rewrite to use EvalCache.
 
         auto checkSystemName = [&](const std::string & system, const Pos & pos) {
             // FIXME: what's the format of "system"?
             if (system.find('-') == std::string::npos)
-                throw Error("'%s' is not a valid system type, at %s", system, pos);
+                reportError(Error("'%s' is not a valid system type, at %s", system, pos));
         };
 
-        auto checkDerivation = [&](const std::string & attrPath, Value & v, const Pos & pos) {
+        auto checkDerivation = [&](const std::string & attrPath, Value & v, const Pos & pos) -> std::optional<StorePath> {
             try {
                 auto drvInfo = getDerivation(*state, v, false);
                 if (!drvInfo)
                     throw Error("flake attribute '%s' is not a derivation", attrPath);
                 // FIXME: check meta attributes
-                return store->parseStorePath(drvInfo->queryDrvPath());
+                return std::make_optional(store->parseStorePath(drvInfo->queryDrvPath()));
             } catch (Error & e) {
                 e.addTrace(pos, hintfmt("while checking the derivation '%s'", attrPath));
-                throw;
+                reportError(e);
             }
+            return std::nullopt;
         };
 
         std::vector<DerivedPath> drvPaths;
@@ -307,23 +347,27 @@ struct CmdFlakeCheck : FlakeCommand
                 #endif
             } catch (Error & e) {
                 e.addTrace(pos, hintfmt("while checking the app definition '%s'", attrPath));
-                throw;
+                reportError(e);
             }
         };
 
         auto checkOverlay = [&](const std::string & attrPath, Value & v, const Pos & pos) {
             try {
                 state->forceValue(v, pos);
-                if (!v.isLambda() || v.lambda.fun->matchAttrs || std::string(v.lambda.fun->arg) != "final")
+                if (!v.isLambda()
+                    || v.lambda.fun->hasFormals()
+                    || !argHasName(v.lambda.fun->arg, "final"))
                     throw Error("overlay does not take an argument named 'final'");
                 auto body = dynamic_cast<ExprLambda *>(v.lambda.fun->body);
-                if (!body || body->matchAttrs || std::string(body->arg) != "prev")
+                if (!body
+                    || body->hasFormals()
+                    || !argHasName(body->arg, "prev"))
                     throw Error("overlay does not take an argument named 'prev'");
                 // FIXME: if we have a 'nixpkgs' input, use it to
                 // evaluate the overlay.
             } catch (Error & e) {
                 e.addTrace(pos, hintfmt("while checking the overlay '%s'", attrPath));
-                throw;
+                reportError(e);
             }
         };
 
@@ -331,7 +375,7 @@ struct CmdFlakeCheck : FlakeCommand
             try {
                 state->forceValue(v, pos);
                 if (v.isLambda()) {
-                    if (!v.lambda.fun->matchAttrs || !v.lambda.fun->formals->ellipsis)
+                    if (!v.lambda.fun->hasFormals() || !v.lambda.fun->formals->ellipsis)
                         throw Error("module must match an open attribute set ('{ config, ... }')");
                 } else if (v.type() == nAttrs) {
                     for (auto & attr : *v.attrs)
@@ -347,7 +391,7 @@ struct CmdFlakeCheck : FlakeCommand
                 // check the module.
             } catch (Error & e) {
                 e.addTrace(pos, hintfmt("while checking the NixOS module '%s'", attrPath));
-                throw;
+                reportError(e);
             }
         };
 
@@ -362,14 +406,18 @@ struct CmdFlakeCheck : FlakeCommand
 
                 for (auto & attr : *v.attrs) {
                     state->forceAttrs(*attr.value, *attr.pos);
-                    if (!state->isDerivation(*attr.value))
-                        checkHydraJobs(attrPath + "." + (std::string) attr.name,
-                            *attr.value, *attr.pos);
+                    auto attrPath2 = attrPath + "." + (std::string) attr.name;
+                    if (state->isDerivation(*attr.value)) {
+                        Activity act(*logger, lvlChatty, actUnknown,
+                            fmt("checking Hydra job '%s'", attrPath2));
+                        checkDerivation(attrPath2, *attr.value, *attr.pos);
+                    } else
+                        checkHydraJobs(attrPath2, *attr.value, *attr.pos);
                 }
 
             } catch (Error & e) {
                 e.addTrace(pos, hintfmt("while checking the Hydra jobset '%s'", attrPath));
-                throw;
+                reportError(e);
             }
         };
 
@@ -384,7 +432,7 @@ struct CmdFlakeCheck : FlakeCommand
                     throw Error("attribute 'config.system.build.toplevel' is not a derivation");
             } catch (Error & e) {
                 e.addTrace(pos, hintfmt("while checking the NixOS configuration '%s'", attrPath));
-                throw;
+                reportError(e);
             }
         };
 
@@ -418,7 +466,7 @@ struct CmdFlakeCheck : FlakeCommand
                 }
             } catch (Error & e) {
                 e.addTrace(pos, hintfmt("while checking the template '%s'", attrPath));
-                throw;
+                reportError(e);
             }
         };
 
@@ -428,12 +476,12 @@ struct CmdFlakeCheck : FlakeCommand
                 if (!v.isLambda())
                     throw Error("bundler must be a function");
                 if (!v.lambda.fun->formals ||
-                    v.lambda.fun->formals->argNames.find(state->symbols.create("program")) == v.lambda.fun->formals->argNames.end() ||
-                    v.lambda.fun->formals->argNames.find(state->symbols.create("system")) == v.lambda.fun->formals->argNames.end())
+                    !v.lambda.fun->formals->argNames.count(state->symbols.create("program")) ||
+                    !v.lambda.fun->formals->argNames.count(state->symbols.create("system")))
                     throw Error("bundler must take formal arguments 'program' and 'system'");
             } catch (Error & e) {
                 e.addTrace(pos, hintfmt("while checking the template '%s'", attrPath));
-                throw;
+                reportError(e);
             }
         };
 
@@ -450,6 +498,8 @@ struct CmdFlakeCheck : FlakeCommand
                         fmt("checking flake output '%s'", name));
 
                     try {
+                        evalSettings.enableImportFromDerivation.setDefault(name != "hydraJobs");
+
                         state->forceValue(vOutput, pos);
 
                         if (name == "checks") {
@@ -461,13 +511,13 @@ struct CmdFlakeCheck : FlakeCommand
                                     auto drvPath = checkDerivation(
                                         fmt("%s.%s.%s", name, attr.name, attr2.name),
                                         *attr2.value, *attr2.pos);
-                                    if ((std::string) attr.name == settings.thisSystem.get())
-                                        drvPaths.push_back(DerivedPath::Built{drvPath});
+                                    if (drvPath && (std::string) attr.name == settings.thisSystem.get())
+                                        drvPaths.push_back(DerivedPath::Built{*drvPath});
                                 }
                             }
                         }
 
-                        else if (name == "packages") {
+                        else if (name == "packages" || name == "devShells") {
                             state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
                                 checkSystemName(attr.name, *attr.pos);
@@ -574,7 +624,7 @@ struct CmdFlakeCheck : FlakeCommand
 
                     } catch (Error & e) {
                         e.addTrace(pos, hintfmt("while checking flake output '%s'", name));
-                        throw;
+                        reportError(e);
                     }
                 });
         }
@@ -583,6 +633,8 @@ struct CmdFlakeCheck : FlakeCommand
             Activity act(*logger, lvlInfo, actUnknown, "running flake checks");
             store->buildPaths(drvPaths);
         }
+        if (hasErrors)
+            throw Error("some errors were encountered during the evaluation");
     }
 };
 
@@ -820,12 +872,12 @@ struct CmdFlakeArchive : FlakeCommand, MixJSON, MixDryRun
 
         if (!dryRun && !dstUri.empty()) {
             ref<Store> dstStore = dstUri.empty() ? openStore() : openStore(dstUri);
-            copyPaths(store, dstStore, sources);
+            copyPaths(*store, *dstStore, sources);
         }
     }
 };
 
-struct CmdFlakeShow : FlakeCommand
+struct CmdFlakeShow : FlakeCommand, MixJSON
 {
     bool showLegacy = false;
 
@@ -852,51 +904,69 @@ struct CmdFlakeShow : FlakeCommand
 
     void run(nix::ref<nix::Store> store) override
     {
+        evalSettings.enableImportFromDerivation.setDefault(false);
+
         auto state = getEvalState();
         auto flake = std::make_shared<LockedFlake>(lockFlake());
 
-        std::function<void(eval_cache::AttrCursor & visitor, const std::vector<Symbol> & attrPath, const std::string & headerPrefix, const std::string & nextPrefix)> visit;
-
-        visit = [&](eval_cache::AttrCursor & visitor, const std::vector<Symbol> & attrPath, const std::string & headerPrefix, const std::string & nextPrefix)
+        std::function<nlohmann::json(
+            eval_cache::AttrCursor & visitor,
+            const std::vector<Symbol> & attrPath,
+            const std::string & headerPrefix,
+            const std::string & nextPrefix)> visit;
+
+        visit = [&](
+            eval_cache::AttrCursor & visitor,
+            const std::vector<Symbol> & attrPath,
+            const std::string & headerPrefix,
+            const std::string & nextPrefix)
+            -> nlohmann::json
         {
+            auto j = nlohmann::json::object();
+
             Activity act(*logger, lvlInfo, actUnknown,
                 fmt("evaluating '%s'", concatStringsSep(".", attrPath)));
             try {
                 auto recurse = [&]()
                 {
-                    logger->cout("%s", headerPrefix);
+                    if (!json)
+                        logger->cout("%s", headerPrefix);
                     auto attrs = visitor.getAttrs();
                     for (const auto & [i, attr] : enumerate(attrs)) {
                         bool last = i + 1 == attrs.size();
                         auto visitor2 = visitor.getAttr(attr);
                         auto attrPath2(attrPath);
                         attrPath2.push_back(attr);
-                        visit(*visitor2, attrPath2,
+                        auto j2 = visit(*visitor2, attrPath2,
                             fmt(ANSI_GREEN "%s%s" ANSI_NORMAL ANSI_BOLD "%s" ANSI_NORMAL, nextPrefix, last ? treeLast : treeConn, attr),
                             nextPrefix + (last ? treeNull : treeLine));
+                        if (json) j.emplace(attr, std::move(j2));
                     }
                 };
 
                 auto showDerivation = [&]()
                 {
                     auto name = visitor.getAttr(state->sName)->getString();
-
-                    /*
-                    std::string description;
-
-                    if (auto aMeta = visitor.maybeGetAttr("meta")) {
-                        if (auto aDescription = aMeta->maybeGetAttr("description"))
-                            description = aDescription->getString();
+                    if (json) {
+                        std::optional<std::string> description;
+                        if (auto aMeta = visitor.maybeGetAttr("meta")) {
+                            if (auto aDescription = aMeta->maybeGetAttr("description"))
+                                description = aDescription->getString();
+                        }
+                        j.emplace("type", "derivation");
+                        j.emplace("name", name);
+                        if (description)
+                            j.emplace("description", *description);
+                    } else {
+                        logger->cout("%s: %s '%s'",
+                            headerPrefix,
+                            attrPath.size() == 2 && attrPath[0] == "devShell" ? "development environment" :
+                            attrPath.size() >= 2 && attrPath[0] == "devShells" ? "development environment" :
+                            attrPath.size() == 3 && attrPath[0] == "checks" ? "derivation" :
+                            attrPath.size() >= 1 && attrPath[0] == "hydraJobs" ? "derivation" :
+                            "package",
+                            name);
                     }
-                    */
-
-                    logger->cout("%s: %s '%s'",
-                        headerPrefix,
-                        attrPath.size() == 2 && attrPath[0] == "devShell" ? "development environment" :
-                        attrPath.size() == 3 && attrPath[0] == "checks" ? "derivation" :
-                        attrPath.size() >= 1 && attrPath[0] == "hydraJobs" ? "derivation" :
-                        "package",
-                        name);
                 };
 
                 if (attrPath.size() == 0
@@ -911,6 +981,7 @@ struct CmdFlakeShow : FlakeCommand
                     || ((attrPath.size() == 1 || attrPath.size() == 2)
                         && (attrPath[0] == "checks"
                             || attrPath[0] == "packages"
+                            || attrPath[0] == "devShells"
                             || attrPath[0] == "apps"))
                     )
                 {
@@ -919,7 +990,7 @@ struct CmdFlakeShow : FlakeCommand
 
                 else if (
                     (attrPath.size() == 2 && (attrPath[0] == "defaultPackage" || attrPath[0] == "devShell"))
-                    || (attrPath.size() == 3 && (attrPath[0] == "checks" || attrPath[0] == "packages"))
+                    || (attrPath.size() == 3 && (attrPath[0] == "checks" || attrPath[0] == "packages" || attrPath[0] == "devShells"))
                     )
                 {
                     if (visitor.isDerivation())
@@ -939,7 +1010,7 @@ struct CmdFlakeShow : FlakeCommand
                     if (attrPath.size() == 1)
                         recurse();
                     else if (!showLegacy)
-                        logger->cout("%s: " ANSI_YELLOW "omitted" ANSI_NORMAL " (use '--legacy' to show)", headerPrefix);
+                        logger->warn(fmt("%s: " ANSI_WARNING "omitted" ANSI_NORMAL " (use '--legacy' to show)", headerPrefix));
                     else {
                         if (visitor.isDerivation())
                             showDerivation();
@@ -956,7 +1027,11 @@ struct CmdFlakeShow : FlakeCommand
                     auto aType = visitor.maybeGetAttr("type");
                     if (!aType || aType->getString() != "app")
                         throw EvalError("not an app definition");
-                    logger->cout("%s: app", headerPrefix);
+                    if (json) {
+                        j.emplace("type", "app");
+                    } else {
+                        logger->cout("%s: app", headerPrefix);
+                    }
                 }
 
                 else if (
@@ -964,27 +1039,41 @@ struct CmdFlakeShow : FlakeCommand
                     (attrPath.size() == 2 && attrPath[0] == "templates"))
                 {
                     auto description = visitor.getAttr("description")->getString();
-                    logger->cout("%s: template: " ANSI_BOLD "%s" ANSI_NORMAL, headerPrefix, description);
+                    if (json) {
+                        j.emplace("type", "template");
+                        j.emplace("description", description);
+                    } else {
+                        logger->cout("%s: template: " ANSI_BOLD "%s" ANSI_NORMAL, headerPrefix, description);
+                    }
                 }
 
                 else {
-                    logger->cout("%s: %s",
-                        headerPrefix,
+                    auto [type, description] =
                         (attrPath.size() == 1 && attrPath[0] == "overlay")
-                        || (attrPath.size() == 2 && attrPath[0] == "overlays") ? "Nixpkgs overlay" :
-                        attrPath.size() == 2 && attrPath[0] == "nixosConfigurations" ? "NixOS configuration" :
-                        attrPath.size() == 2 && attrPath[0] == "nixosModules" ? "NixOS module" :
-                        ANSI_YELLOW "unknown" ANSI_NORMAL);
+                        || (attrPath.size() == 2 && attrPath[0] == "overlays") ? std::make_pair("nixpkgs-overlay", "Nixpkgs overlay") :
+                        attrPath.size() == 2 && attrPath[0] == "nixosConfigurations" ? std::make_pair("nixos-configuration", "NixOS configuration") :
+                        (attrPath.size() == 1 && attrPath[0] == "nixosModule")
+                        || (attrPath.size() == 2 && attrPath[0] == "nixosModules") ? std::make_pair("nixos-module", "NixOS module") :
+                        std::make_pair("unknown", "unknown");
+                    if (json) {
+                        j.emplace("type", type);
+                    } else {
+                        logger->cout("%s: " ANSI_WARNING "%s" ANSI_NORMAL, headerPrefix, description);
+                    }
                 }
             } catch (EvalError & e) {
                 if (!(attrPath.size() > 0 && attrPath[0] == "legacyPackages"))
                     throw;
             }
+
+            return j;
         };
 
         auto cache = openEvalCache(*state, flake);
 
-        visit(*cache->getRoot(), {}, fmt(ANSI_BOLD "%s" ANSI_NORMAL, flake->flake.lockedRef), "");
+        auto j = visit(*cache->getRoot(), {}, fmt(ANSI_BOLD "%s" ANSI_NORMAL, flake->flake.lockedRef), "");
+        if (json)
+            logger->cout("%s", j.dump());
     }
 };
 
@@ -1062,7 +1151,7 @@ struct CmdFlake : NixMultiCommand
     {
         if (!command)
             throw UsageError("'nix flake' requires a sub-command.");
-        settings.requireExperimentalFeature("flakes");
+        settings.requireExperimentalFeature(Xp::Flakes);
         command->second->prepare();
         command->second->run();
     }
diff --git a/src/nix/flake.md b/src/nix/flake.md
index 9e936a049..3b5812a0a 100644
--- a/src/nix/flake.md
+++ b/src/nix/flake.md
@@ -186,8 +186,8 @@ Currently the `type` attribute can be one of the following:
   attribute `url`.
 
   In URL form, the schema must be `http://`, `https://` or `file://`
-  URLs and the extension must be `.zip`, `.tar`, `.tar.gz`, `.tar.xz`
-  or `.tar.bz2`.
+  URLs and the extension must be `.zip`, `.tar`, `.tar.gz`, `.tar.xz`,
+  `.tar.bz2` or `.tar.zst`.
 
 * `github`: A more efficient way to fetch repositories from
   GitHub. The following attributes are required:
@@ -225,7 +225,7 @@ Currently the `type` attribute can be one of the following:
   [flake:]<flake-id>(/<rev-or-ref>(/rev)?)?
   ```
 
-  These perform a lookup of `<flake-id>` in the flake registry. or
+  These perform a lookup of `<flake-id>` in the flake registry. For
   example, `nixpkgs` and `nixpkgs/release-20.09` are indirect flake
   references. The specified `rev` and/or `ref` are merged with the
   entry in the registry; see [nix registry](./nix3-registry.md) for
diff --git a/src/nix/get-env.sh b/src/nix/get-env.sh
index 091c0f573..42c806450 100644
--- a/src/nix/get-env.sh
+++ b/src/nix/get-env.sh
@@ -8,12 +8,123 @@ if [[ -n $stdenv ]]; then
     source $stdenv/setup
 fi
 
-for __output in $outputs; do
+# Better to use compgen, but stdenv bash doesn't have it.
+__vars="$(declare -p)"
+__functions="$(declare -F)"
+
+__dumpEnv() {
+    printf '{\n'
+
+    printf '  "bashFunctions": {\n'
+    local __first=1
+    while read __line; do
+        if ! [[ $__line =~ ^declare\ -f\ (.*) ]]; then continue; fi
+        __fun_name="${BASH_REMATCH[1]}"
+        __fun_body="$(type $__fun_name)"
+        if [[ $__fun_body =~ \{(.*)\} ]]; then
+            if [[ -z $__first ]]; then printf ',\n'; else __first=; fi
+            __fun_body="${BASH_REMATCH[1]}"
+            printf "    "
+            __escapeString "$__fun_name"
+            printf ':'
+            __escapeString "$__fun_body"
+        else
+            printf "Cannot parse definition of function '%s'.\n" "$__fun_name" >&2
+            return 1
+        fi
+    done < <(printf "%s\n" "$__functions")
+    printf '\n  },\n'
+
+    printf '  "variables": {\n'
+    local __first=1
+    while read __line; do
+        if ! [[ $__line =~ ^declare\ (-[^ ])\ ([^=]*) ]]; then continue; fi
+        local type="${BASH_REMATCH[1]}"
+        local __var_name="${BASH_REMATCH[2]}"
+
+        if [[ $__var_name =~ ^BASH_ || \
+              $__var_name = _ || \
+              $__var_name = DIRSTACK || \
+              $__var_name = EUID || \
+              $__var_name = FUNCNAME || \
+              $__var_name = HISTCMD || \
+              $__var_name = HOSTNAME || \
+              $__var_name = GROUPS || \
+              $__var_name = PIPESTATUS || \
+              $__var_name = PWD || \
+              $__var_name = RANDOM || \
+              $__var_name = SHLVL || \
+              $__var_name = SECONDS \
+            ]]; then continue; fi
+
+        if [[ -z $__first ]]; then printf ',\n'; else __first=; fi
+
+        printf "    "
+        __escapeString "$__var_name"
+        printf ': {'
+
+        # FIXME: handle -i, -r, -n.
+        if [[ $type == -x ]]; then
+            printf '"type": "exported", "value": '
+            __escapeString "${!__var_name}"
+        elif [[ $type == -- ]]; then
+            printf '"type": "var", "value": '
+            __escapeString "${!__var_name}"
+        elif [[ $type == -a ]]; then
+            printf '"type": "array", "value": ['
+            local __first2=1
+            __var_name="$__var_name[@]"
+            for __i in "${!__var_name}"; do
+                if [[ -z $__first2 ]]; then printf ', '; else __first2=; fi
+                __escapeString "$__i"
+                printf ' '
+            done
+            printf ']'
+        elif [[ $type == -A ]]; then
+            printf '"type": "associative", "value": {\n'
+            local __first2=1
+            declare -n __var_name2="$__var_name"
+            for __i in "${!__var_name2[@]}"; do
+                if [[ -z $__first2 ]]; then printf ',\n'; else __first2=; fi
+                printf "      "
+                __escapeString "$__i"
+                printf ": "
+                __escapeString "${__var_name2[$__i]}"
+            done
+            printf '\n    }'
+        else
+            printf '"type": "unknown"'
+        fi
+
+        printf "}"
+    done < <(printf "%s\n" "$__vars")
+    printf '\n  }\n}'
+}
+
+__escapeString() {
+    local __s="$1"
+    __s="${__s//\\/\\\\}"
+    __s="${__s//\"/\\\"}"
+    __s="${__s//$'\n'/\\n}"
+    __s="${__s//$'\r'/\\r}"
+    __s="${__s//$'\t'/\\t}"
+    printf '"%s"' "$__s"
+}
+
+# In case of `__structuredAttrs = true;` the list of outputs is an associative
+# array with a format like `outname => /nix/store/hash-drvname-outname`, so `__olist`
+# must contain the array's keys (hence `${!...[@]}`) in this case.
+if [ -e .attrs.sh ]; then
+    __olist="${!outputs[@]}"
+else
+    __olist=$outputs
+fi
+
+for __output in $__olist; do
     if [[ -z $__done ]]; then
-        export > ${!__output}
-        set >> ${!__output}
+        __dumpEnv > ${!__output}
         __done=1
     else
-        echo -n >> ${!__output}
+        echo -n >> "${!__output}"
     fi
 done
diff --git a/src/nix/local.mk b/src/nix/local.mk
index 83b6dd08b..e4ec7634d 100644
--- a/src/nix/local.mk
+++ b/src/nix/local.mk
@@ -14,7 +14,7 @@ nix_SOURCES := \
   $(wildcard src/nix-instantiate/*.cc) \
   $(wildcard src/nix-store/*.cc) \
 
-nix_CXXFLAGS += -I src/libutil -I src/libstore -I src/libfetchers -I src/libexpr -I src/libmain -I src/libcmd
+nix_CXXFLAGS += -I src/libutil -I src/libstore -I src/libfetchers -I src/libexpr -I src/libmain -I src/libcmd -I doc/manual
 
 nix_LIBS = libexpr libmain libfetchers libstore libutil libcmd
 
@@ -30,3 +30,5 @@ src/nix-env/user-env.cc: src/nix-env/buildenv.nix.gen.hh
 src/nix/develop.cc: src/nix/get-env.sh.gen.hh
 
 src/nix-channel/nix-channel.cc: src/nix-channel/unpack-channel.nix.gen.hh
+
+src/nix/main.cc: doc/manual/generate-manpage.nix.gen.hh doc/manual/utils.nix.gen.hh
diff --git a/src/nix/log.cc b/src/nix/log.cc
index 638bb5073..fd3c1d787 100644
--- a/src/nix/log.cc
+++ b/src/nix/log.cc
@@ -30,15 +30,15 @@ struct CmdLog : InstallableCommand
 
         subs.push_front(store);
 
-        auto b = installable->toDerivedPathWithHints();
+        auto b = installable->toDerivedPath();
 
         RunPager pager;
         for (auto & sub : subs) {
             auto log = std::visit(overloaded {
-                [&](DerivedPathWithHints::Opaque bo) {
+                [&](const DerivedPath::Opaque & bo) {
                     return sub->getBuildLog(bo.path);
                 },
-                [&](DerivedPathWithHints::Built bfd) {
+                [&](const DerivedPath::Built & bfd) {
                     return sub->getBuildLog(bfd.drvPath);
                 },
             }, b.raw());
diff --git a/src/nix/main.cc b/src/nix/main.cc
index 008482be3..60b0aa410 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -10,6 +10,7 @@
 #include "filetransfer.hh"
 #include "finally.hh"
 #include "loggers.hh"
+#include "markdown.hh"
 
 #include <sys/types.h>
 #include <sys/socket.h>
@@ -163,9 +164,46 @@ struct NixArgs : virtual MultiCommand, virtual MixCommonArgs
     }
 };
 
-static void showHelp(std::vector<std::string> subcommand)
+/* Render the help for the specified subcommand to stdout using
+   lowdown. */
+static void showHelp(std::vector<std::string> subcommand, MultiCommand & toplevel)
 {
-    showManPage(subcommand.empty() ? "nix" : fmt("nix3-%s", concatStringsSep("-", subcommand)));
+    auto mdName = subcommand.empty() ? "nix" : fmt("nix3-%s", concatStringsSep("-", subcommand));
+
+    evalSettings.restrictEval = false;
+    evalSettings.pureEval = false;
+    EvalState state({}, openStore("dummy://"));
+
+    auto vGenerateManpage = state.allocValue();
+    state.eval(state.parseExprFromString(
+        #include "generate-manpage.nix.gen.hh"
+        , "/"), *vGenerateManpage);
+
+    auto vUtils = state.allocValue();
+    state.cacheFile(
+        "/utils.nix", "/utils.nix",
+        state.parseExprFromString(
+            #include "utils.nix.gen.hh"
+            , "/"),
+        *vUtils);
+
+    auto vArgs = state.allocValue();
+    state.mkAttrs(*vArgs, 16);
+    auto vJson = state.allocAttr(*vArgs, state.symbols.create("command"));
+    mkString(*vJson, toplevel.toJSON().dump());
+    vArgs->attrs->sort();
+
+    auto vRes = state.allocValue();
+    state.callFunction(*vGenerateManpage, *vArgs, *vRes, noPos);
+
+    auto attr = vRes->attrs->get(state.symbols.create(mdName + ".md"));
+    if (!attr)
+        throw UsageError("Nix has no subcommand '%s'", concatStringsSep("", subcommand));
+
+    auto markdown = state.forceString(*attr->value);
+
+    RunPager pager;
+    std::cout << renderMarkdownToTerminal(markdown) << "\n";
 }
 
 struct CmdHelp : Command
@@ -194,7 +232,10 @@ struct CmdHelp : Command
 
     void run() override
     {
-        showHelp(subcommand);
+        assert(parent);
+        MultiCommand * toplevel = parent;
+        while (toplevel->parent) toplevel = toplevel->parent;
+        showHelp(subcommand, *toplevel);
     }
 };
 
@@ -214,6 +255,16 @@ void mainWrapped(int argc, char * * argv)
     initNix();
     initGC();
 
+    #if __linux__
+    if (getuid() == 0) {
+        try {
+            saveMountNamespace();
+            if (unshare(CLONE_NEWNS) == -1)
+                throw SysError("setting up a private mount namespace");
+        } catch (Error & e) { }
+    }
+    #endif
+
     programPath = argv[0];
     auto programName = std::string(baseNameOf(programPath));
 
@@ -277,7 +328,7 @@ void mainWrapped(int argc, char * * argv)
             } else
                 break;
         }
-        showHelp(subcommand);
+        showHelp(subcommand, args);
         return;
     } catch (UsageError &) {
         if (!completions) throw;
@@ -296,7 +347,7 @@ void mainWrapped(int argc, char * * argv)
     if (args.command->first != "repl"
         && args.command->first != "doctor"
         && args.command->first != "upgrade-nix")
-        settings.requireExperimentalFeature("nix-command");
+        settings.requireExperimentalFeature(Xp::NixCommand);
 
     if (args.useNet && !haveInternet()) {
         warn("you don't have Internet access; disabling some network-dependent features");
diff --git a/src/nix/make-content-addressable.cc b/src/nix/make-content-addressable.cc
index f5bdc7e65..12f303a10 100644
--- a/src/nix/make-content-addressable.cc
+++ b/src/nix/make-content-addressable.cc
@@ -25,7 +25,7 @@ struct CmdMakeContentAddressable : StorePathsCommand, MixJSON
           ;
     }
 
-    void run(ref<Store> store, StorePaths storePaths) override
+    void run(ref<Store> store, StorePaths && storePaths) override
     {
         auto paths = store->topoSortPaths(StorePathSet(storePaths.begin(), storePaths.end()));
 
diff --git a/src/nix/path-info.cc b/src/nix/path-info.cc
index 518cd5568..3743d7504 100644
--- a/src/nix/path-info.cc
+++ b/src/nix/path-info.cc
@@ -79,7 +79,7 @@ struct CmdPathInfo : StorePathsCommand, MixJSON
         std::cout << fmt("\t%6.1f%c", res, idents.at(power));
     }
 
-    void run(ref<Store> store, StorePaths storePaths) override
+    void run(ref<Store> store, StorePaths && storePaths) override
     {
         size_t pathLen = 0;
         for (auto & storePath : storePaths)
diff --git a/src/nix/path-info.md b/src/nix/path-info.md
index 76a83e39d..7a1714ba4 100644
--- a/src/nix/path-info.md
+++ b/src/nix/path-info.md
@@ -82,7 +82,7 @@ This command shows information about the store paths produced by
 
 By default, this command only prints the store paths. You can get
 additional information by passing flags such as `--closure-size`,
---size`, `--sigs` or `--json`.
+`--size`, `--sigs` or `--json`.
 
 > **Warning**
 >
diff --git a/src/nix/prefetch.cc b/src/nix/prefetch.cc
index b7da3ea5a..768d37595 100644
--- a/src/nix/prefetch.cc
+++ b/src/nix/prefetch.cc
@@ -199,26 +199,24 @@ static int main_nix_prefetch_url(int argc, char * * argv)
             state->forceAttrs(v);
 
             /* Extract the URL. */
-            auto attr = v.attrs->find(state->symbols.create("urls"));
-            if (attr == v.attrs->end())
-                throw Error("attribute set does not contain a 'urls' attribute");
-            state->forceList(*attr->value);
-            if (attr->value->listSize() < 1)
+            auto & attr = v.attrs->need(state->symbols.create("urls"));
+            state->forceList(*attr.value);
+            if (attr.value->listSize() < 1)
                 throw Error("'urls' list is empty");
-            url = state->forceString(*attr->value->listElems()[0]);
+            url = state->forceString(*attr.value->listElems()[0]);
 
             /* Extract the hash mode. */
-            attr = v.attrs->find(state->symbols.create("outputHashMode"));
-            if (attr == v.attrs->end())
+            auto attr2 = v.attrs->get(state->symbols.create("outputHashMode"));
+            if (!attr2)
                 printInfo("warning: this does not look like a fetchurl call");
             else
-                unpack = state->forceString(*attr->value) == "recursive";
+                unpack = state->forceString(*attr2->value) == "recursive";
 
             /* Extract the name. */
             if (!name) {
-                attr = v.attrs->find(state->symbols.create("name"));
-                if (attr != v.attrs->end())
-                    name = state->forceString(*attr->value);
+                auto attr3 = v.attrs->get(state->symbols.create("name"));
+                if (!attr3)
+                    name = state->forceString(*attr3->value);
             }
         }
 
@@ -283,8 +281,6 @@ struct CmdStorePrefetchFile : StoreCommand, MixJSON
         expectArg("url", &url);
     }
 
-    Category category() override { return catUtility; }
-
     std::string description() override
     {
         return "download a file into the Nix store";
diff --git a/src/nix/print-dev-env.md b/src/nix/print-dev-env.md
index b80252acf..2aad491de 100644
--- a/src/nix/print-dev-env.md
+++ b/src/nix/print-dev-env.md
@@ -8,12 +8,43 @@ R""(
   # . <(nix print-dev-env nixpkgs#hello)
   ```
 
+* Get the build environment in JSON format:
+
+  ```console
+  # nix print-dev-env nixpkgs#hello --json
+  ```
+
+  The output will look like this:
+
+  ```json
+  {
+    "bashFunctions": {
+      "buildPhase": " \n    runHook preBuild;\n...",
+      ...
+    },
+    "variables": {
+      "src": {
+        "type": "exported",
+        "value": "/nix/store/3x7dwzq014bblazs7kq20p9hyzz0qh8g-hello-2.10.tar.gz"
+      },
+      "postUnpackHooks": {
+        "type": "array",
+        "value": ["_updateSourceDateEpochFromSourceRoot"]
+      },
+      ...
+    }
+  }
+  ```
+
 # Description
 
-This command prints a shell script that can be sourced by `b`ash and
-that sets the environment variables and shell functions defined by the
-build process of *installable*. This allows you to get a similar build
+This command prints a shell script that can be sourced by `bash` and
+that sets the variables and shell functions defined by the build
+process of *installable*. This allows you to get a similar build
 environment in your current shell rather than in a subshell (as with
 `nix develop`).
 
+With `--json`, the output is a JSON serialisation of the variables and
+functions defined by the build process.
+
 )""
diff --git a/src/nix/profile-history.md b/src/nix/profile-history.md
index d0fe40c82..f0bfe5037 100644
--- a/src/nix/profile-history.md
+++ b/src/nix/profile-history.md
@@ -6,10 +6,10 @@ R""(
 
   ```console
   # nix profile history
-  Version 508 -> 509:
+  Version 508 (2020-04-10):
     flake:nixpkgs#legacyPackages.x86_64-linux.awscli: ∅ -> 1.17.13
 
-  Version 509 -> 510:
+  Version 509 (2020-05-16) <- 508:
     flake:nixpkgs#legacyPackages.x86_64-linux.awscli: 1.17.13 -> 1.18.211
   ```
 
diff --git a/src/nix/profile-remove.md b/src/nix/profile-remove.md
index dcf825da9..ba85441d8 100644
--- a/src/nix/profile-remove.md
+++ b/src/nix/profile-remove.md
@@ -15,6 +15,7 @@ R""(
   ```
 
 * Remove all packages:
+
   ```console
   # nix profile remove '.*'
   ```
diff --git a/src/nix/profile-rollback.md b/src/nix/profile-rollback.md
new file mode 100644
index 000000000..6bb75aa5e
--- /dev/null
+++ b/src/nix/profile-rollback.md
@@ -0,0 +1,26 @@
+R""(
+
+# Examples
+
+* Roll back your default profile to the previous version:
+
+  ```console
+  # nix profile rollback
+  switching profile from version 519 to 518
+  ```
+
+* Switch your default profile to version 510:
+
+  ```console
+  # nix profile rollback --to 510
+  switching profile from version 518 to 510
+  ```
+
+# Description
+
+This command switches a profile to the most recent version older
+than the currently active version, or if `--to` *N* is given, to
+version *N* of the profile. To see the available versions of a
+profile, use `nix profile history`.
+
+)""
diff --git a/src/nix/profile-upgrade.md b/src/nix/profile-upgrade.md
index 2bd5d256d..e06e74abe 100644
--- a/src/nix/profile-upgrade.md
+++ b/src/nix/profile-upgrade.md
@@ -18,7 +18,7 @@ R""(
 * Upgrade a specific profile element by number:
 
   ```console
-  # nix profile info
+  # nix profile list
   0 flake:nixpkgs#legacyPackages.x86_64-linux.spotify …
 
   # nix profile upgrade 0
diff --git a/src/nix/profile-wipe-history.md b/src/nix/profile-wipe-history.md
new file mode 100644
index 000000000..b4b262864
--- /dev/null
+++ b/src/nix/profile-wipe-history.md
@@ -0,0 +1,20 @@
+R""(
+
+# Examples
+
+* Delete all versions of the default profile older than 100 days:
+
+  ```console
+  # nix profile wipe-history --profile /tmp/profile --older-than 100d
+  removing profile version 515
+  removing profile version 514
+  ```
+
+# Description
+
+This command deletes non-current versions of a profile, making it
+impossible to roll back to these versions. By default, all non-current
+versions are deleted. With `--older-than` *N*`d`, all non-current
+versions older than *N* days are deleted.
+
+)""
diff --git a/src/nix/profile.cc b/src/nix/profile.cc
index 667904cd2..96a20f673 100644
--- a/src/nix/profile.cc
+++ b/src/nix/profile.cc
@@ -12,6 +12,7 @@
 
 #include <nlohmann/json.hpp>
 #include <regex>
+#include <iomanip>
 
 using namespace nix;
 
@@ -97,10 +98,8 @@ struct ProfileManifest
 
         else if (pathExists(profile + "/manifest.nix")) {
             // FIXME: needed because of pure mode; ugly.
-            if (state.allowedPaths) {
-                state.allowedPaths->insert(state.store->followLinksToStore(profile));
-                state.allowedPaths->insert(state.store->followLinksToStore(profile + "/manifest.nix"));
-            }
+            state.allowPath(state.store->followLinksToStore(profile));
+            state.allowPath(state.store->followLinksToStore(profile + "/manifest.nix"));
 
             auto drvInfos = queryInstalled(state, state.store->followLinksToStore(profile));
 
@@ -253,17 +252,17 @@ struct CmdProfileInstall : InstallablesCommand, MixDefaultProfile
 
                 manifest.elements.emplace_back(std::move(element));
             } else {
-                auto buildables = build(store, Realise::Outputs, {installable}, bmNormal);
+                auto buildables = build(getEvalStore(), store, Realise::Outputs, {installable}, bmNormal);
 
                 for (auto & buildable : buildables) {
                     ProfileElement element;
 
                     std::visit(overloaded {
-                        [&](DerivedPathWithHints::Opaque bo) {
+                        [&](const BuiltPath::Opaque & bo) {
                             pathsToBuild.push_back(bo);
                             element.storePaths.insert(bo.path);
                         },
-                        [&](DerivedPathWithHints::Built bfd) {
+                        [&](const BuiltPath::Built & bfd) {
                             // TODO: Why are we querying if we know the output
                             // names already? Is it just to figure out what the
                             // default one is?
@@ -426,7 +425,7 @@ struct CmdProfileUpgrade : virtual SourceExprCommand, MixDefaultProfile, MixProf
                     attrPath,
                 };
 
-                pathsToBuild.push_back(DerivedPath::Built{drv.drvPath, {"out"}}); // FIXME
+                pathsToBuild.push_back(DerivedPath::Built{drv.drvPath, {drv.outputName}});
             }
         }
 
@@ -528,10 +527,11 @@ struct CmdProfileHistory : virtual StoreCommand, EvalCommand, MixDefaultProfile
             if (!first) std::cout << "\n";
             first = false;
 
-            if (prevGen)
-                std::cout << fmt("Version %d -> %d:\n", prevGen->first.number, gen.number);
-            else
-                std::cout << fmt("Version %d:\n", gen.number);
+            std::cout << fmt("Version %s%d" ANSI_NORMAL " (%s)%s:\n",
+                gen.number == curGen ? ANSI_GREEN : ANSI_BOLD,
+                gen.number,
+                std::put_time(std::gmtime(&gen.creationTime), "%Y-%m-%d"),
+                prevGen ? fmt(" <- %d", prevGen->first.number) : "");
 
             ProfileManifest::printDiff(
                 prevGen ? prevGen->second : ProfileManifest(),
@@ -543,6 +543,76 @@ struct CmdProfileHistory : virtual StoreCommand, EvalCommand, MixDefaultProfile
     }
 };
 
+struct CmdProfileRollback : virtual StoreCommand, MixDefaultProfile, MixDryRun
+{
+    std::optional<GenerationNumber> version;
+
+    CmdProfileRollback()
+    {
+        addFlag({
+            .longName = "to",
+            .description = "The profile version to roll back to.",
+            .labels = {"version"},
+            .handler = {&version},
+        });
+    }
+
+    std::string description() override
+    {
+        return "roll back to the previous version or a specified version of a profile";
+    }
+
+    std::string doc() override
+    {
+        return
+          #include "profile-rollback.md"
+          ;
+    }
+
+    void run(ref<Store> store) override
+    {
+        switchGeneration(*profile, version, dryRun);
+    }
+};
+
+struct CmdProfileWipeHistory : virtual StoreCommand, MixDefaultProfile, MixDryRun
+{
+    std::optional<std::string> minAge;
+
+    CmdProfileWipeHistory()
+    {
+        addFlag({
+            .longName = "older-than",
+            .description =
+                "Delete versions older than the specified age. *age* "
+                "must be in the format *N*`d`, where *N* denotes a number "
+                "of days.",
+            .labels = {"age"},
+            .handler = {&minAge},
+        });
+    }
+
+    std::string description() override
+    {
+        return "delete non-current versions of a profile";
+    }
+
+    std::string doc() override
+    {
+        return
+          #include "profile-wipe-history.md"
+          ;
+    }
+
+    void run(ref<Store> store) override
+    {
+        if (minAge)
+            deleteGenerationsOlderThan(*profile, *minAge, dryRun);
+        else
+            deleteOldGenerations(*profile, dryRun);
+    }
+};
+
 struct CmdProfile : NixMultiCommand
 {
     CmdProfile()
@@ -553,6 +623,8 @@ struct CmdProfile : NixMultiCommand
               {"list", []() { return make_ref<CmdProfileList>(); }},
               {"diff-closures", []() { return make_ref<CmdProfileDiffClosures>(); }},
               {"history", []() { return make_ref<CmdProfileHistory>(); }},
+              {"rollback", []() { return make_ref<CmdProfileRollback>(); }},
+              {"wipe-history", []() { return make_ref<CmdProfileWipeHistory>(); }},
           })
     { }
 
diff --git a/src/nix/realisation.cc b/src/nix/realisation.cc
index 9ee9ccb91..c9a7157cd 100644
--- a/src/nix/realisation.cc
+++ b/src/nix/realisation.cc
@@ -28,7 +28,7 @@ struct CmdRealisation : virtual NixMultiCommand
 
 static auto rCmdRealisation = registerCommand<CmdRealisation>("realisation");
 
-struct CmdRealisationInfo : RealisedPathsCommand, MixJSON
+struct CmdRealisationInfo : BuiltPathsCommand, MixJSON
 {
     std::string description() override
     {
@@ -44,12 +44,19 @@ struct CmdRealisationInfo : RealisedPathsCommand, MixJSON
 
     Category category() override { return catSecondary; }
 
-    void run(ref<Store> store, std::vector<RealisedPath> paths) override
+    void run(ref<Store> store, BuiltPaths && paths) override
     {
-        settings.requireExperimentalFeature("ca-derivations");
+        settings.requireExperimentalFeature(Xp::CaDerivations);
+        RealisedPath::Set realisations;
+
+        for (auto & builtPath : paths) {
+            auto theseRealisations = builtPath.toRealisedPaths(*store);
+            realisations.insert(theseRealisations.begin(), theseRealisations.end());
+        }
+
         if (json) {
             nlohmann::json res = nlohmann::json::array();
-            for (auto & path : paths) {
+            for (auto & path : realisations) {
                 nlohmann::json currentPath;
                 if (auto realisation = std::get_if<Realisation>(&path.raw))
                     currentPath = realisation->toJSON();
@@ -61,7 +68,7 @@ struct CmdRealisationInfo : RealisedPathsCommand, MixJSON
             std::cout << res.dump();
         }
         else {
-            for (auto & path : paths) {
+            for (auto & path : realisations) {
                 if (auto realisation = std::get_if<Realisation>(&path.raw)) {
                     std::cout <<
                         realisation->id.to_string() << " " <<
diff --git a/src/nix/registry-add.md b/src/nix/registry-add.md
index 80a31996a..a947fa0b3 100644
--- a/src/nix/registry-add.md
+++ b/src/nix/registry-add.md
@@ -21,6 +21,13 @@ R""(
   # nix registry add nixpkgs/nixos-20.03 ~/Dev/nixpkgs
   ```
 
+* Add `nixpkgs` pointing to `github:nixos/nixpkgs` to your custom flake
+  registry:
+
+  ```console
+  nix registry add --registry ./custom-flake-registry.json nixpkgs github:nixos/nixpkgs
+  ```
+
 # Description
 
 This command adds an entry to the user registry that maps flake
diff --git a/src/nix/registry-pin.md b/src/nix/registry-pin.md
index 6e97e003e..ebc0e3eff 100644
--- a/src/nix/registry-pin.md
+++ b/src/nix/registry-pin.md
@@ -24,6 +24,13 @@ R""(
   …
   ```
 
+* Pin `nixpkgs` in a custom registry to its most recent Git revision:
+
+  ```console
+  # nix registry pin --registry ./custom-flake-registry.json nixpkgs
+  ```
+
+
 # Description
 
 This command adds an entry to the user registry that maps flake
diff --git a/src/nix/registry-remove.md b/src/nix/registry-remove.md
index 4c0eb4947..eecd4c6e7 100644
--- a/src/nix/registry-remove.md
+++ b/src/nix/registry-remove.md
@@ -8,6 +8,12 @@ R""(
   # nix registry remove nixpkgs
   ```
 
+* Remove the entry `nixpkgs` from a custom registry:
+
+  ```console
+  # nix registry remove --registry ./custom-flake-registry.json nixpkgs
+  ```
+
 # Description
 
 This command removes from the user registry any entry for flake
diff --git a/src/nix/registry.cc b/src/nix/registry.cc
index f9719600f..c496f94f8 100644
--- a/src/nix/registry.cc
+++ b/src/nix/registry.cc
@@ -10,6 +10,46 @@
 using namespace nix;
 using namespace nix::flake;
 
+
+class RegistryCommand : virtual Args
+{
+    std::string registry_path;
+
+    std::shared_ptr<fetchers::Registry> registry;
+
+public:
+
+    RegistryCommand()
+    {
+        addFlag({
+            .longName = "registry",
+            .description = "The registry to operate on.",
+            .labels = {"registry"},
+            .handler = {&registry_path},
+        });
+    }
+
+    std::shared_ptr<fetchers::Registry> getRegistry()
+    {
+        if (registry) return registry;
+        if (registry_path.empty()) {
+            registry = fetchers::getUserRegistry();
+        } else {
+            registry = fetchers::getCustomRegistry(registry_path);
+        }
+        return registry;
+    }
+
+    Path getRegistryPath()
+    {
+        if (registry_path.empty()) {
+            return fetchers::getUserRegistryPath();
+        } else {
+            return registry_path;
+        }
+    }
+};
+
 struct CmdRegistryList : StoreCommand
 {
     std::string description() override
@@ -45,7 +85,7 @@ struct CmdRegistryList : StoreCommand
     }
 };
 
-struct CmdRegistryAdd : MixEvalArgs, Command
+struct CmdRegistryAdd : MixEvalArgs, Command, RegistryCommand
 {
     std::string fromUrl, toUrl;
 
@@ -71,16 +111,16 @@ struct CmdRegistryAdd : MixEvalArgs, Command
     {
         auto fromRef = parseFlakeRef(fromUrl);
         auto toRef = parseFlakeRef(toUrl);
+        auto registry = getRegistry();
         fetchers::Attrs extraAttrs;
         if (toRef.subdir != "") extraAttrs["dir"] = toRef.subdir;
-        auto userRegistry = fetchers::getUserRegistry();
-        userRegistry->remove(fromRef.input);
-        userRegistry->add(fromRef.input, toRef.input, extraAttrs);
-        userRegistry->write(fetchers::getUserRegistryPath());
+        registry->remove(fromRef.input);
+        registry->add(fromRef.input, toRef.input, extraAttrs);
+        registry->write(getRegistryPath());
     }
 };
 
-struct CmdRegistryRemove : virtual Args, MixEvalArgs, Command
+struct CmdRegistryRemove : RegistryCommand, Command
 {
     std::string url;
 
@@ -103,19 +143,21 @@ struct CmdRegistryRemove : virtual Args, MixEvalArgs, Command
 
     void run() override
     {
-        auto userRegistry = fetchers::getUserRegistry();
-        userRegistry->remove(parseFlakeRef(url).input);
-        userRegistry->write(fetchers::getUserRegistryPath());
+        auto registry = getRegistry();
+        registry->remove(parseFlakeRef(url).input);
+        registry->write(getRegistryPath());
     }
 };
 
-struct CmdRegistryPin : virtual Args, EvalCommand
+struct CmdRegistryPin : RegistryCommand, EvalCommand
 {
     std::string url;
 
+    std::string locked;
+
     std::string description() override
     {
-        return "pin a flake to its current version in user flake registry";
+        return "pin a flake to its current version or to the current version of a flake URL";
     }
 
     std::string doc() override
@@ -128,18 +170,31 @@ struct CmdRegistryPin : virtual Args, EvalCommand
     CmdRegistryPin()
     {
         expectArg("url", &url);
+
+        expectArgs({
+            .label = "locked",
+            .optional = true,
+            .handler = {&locked},
+            .completer = {[&](size_t, std::string_view prefix) {
+                completeFlakeRef(getStore(), prefix);
+            }}
+        });
     }
 
     void run(nix::ref<nix::Store> store) override
     {
+        if (locked.empty()) {
+            locked = url;
+        }
+        auto registry = getRegistry();
         auto ref = parseFlakeRef(url);
-        auto userRegistry = fetchers::getUserRegistry();
-        userRegistry->remove(ref.input);
-        auto [tree, resolved] = ref.resolve(store).input.fetch(store);
+        auto locked_ref = parseFlakeRef(locked);
+        registry->remove(ref.input);
+        auto [tree, resolved] = locked_ref.resolve(store).input.fetch(store);
         fetchers::Attrs extraAttrs;
         if (ref.subdir != "") extraAttrs["dir"] = ref.subdir;
-        userRegistry->add(ref.input, resolved, extraAttrs);
-        userRegistry->write(fetchers::getUserRegistryPath());
+        registry->add(ref.input, resolved, extraAttrs);
+        registry->write(getRegistryPath());
     }
 };
 
@@ -171,6 +226,7 @@ struct CmdRegistry : virtual NixMultiCommand
 
     void run() override
     {
+        settings.requireExperimentalFeature(Xp::Flakes);
         if (!command)
             throw UsageError("'nix registry' requires a sub-command.");
         command->second->prepare();
diff --git a/src/nix/registry.md b/src/nix/registry.md
index 557e5795b..a1674bd2e 100644
--- a/src/nix/registry.md
+++ b/src/nix/registry.md
@@ -41,7 +41,7 @@ A registry is a JSON file with the following format:
 ```json
 {
   "version": 2,
-  [
+  "flakes": [
     {
       "from": {
         "type": "indirect",
diff --git a/src/nix/run.cc b/src/nix/run.cc
index b5d8ab38a..b01fdebaa 100644
--- a/src/nix/run.cc
+++ b/src/nix/run.cc
@@ -1,3 +1,4 @@
+#include "run.hh"
 #include "command.hh"
 #include "common-args.hh"
 #include "shared.hh"
@@ -20,45 +21,43 @@ using namespace nix;
 
 std::string chrootHelperName = "__run_in_chroot";
 
-struct RunCommon : virtual Command
-{
+namespace nix {
 
-    using Command::run;
+void runProgramInStore(ref<Store> store,
+    const std::string & program,
+    const Strings & args)
+{
+    stopProgressBar();
 
-    void runProgram(ref<Store> store,
-        const std::string & program,
-        const Strings & args)
-    {
-        stopProgressBar();
+    restoreProcessContext();
 
-        restoreProcessContext();
+    /* If this is a diverted store (i.e. its "logical" location
+       (typically /nix/store) differs from its "physical" location
+       (e.g. /home/eelco/nix/store), then run the command in a
+       chroot. For non-root users, this requires running it in new
+       mount and user namespaces. Unfortunately,
+       unshare(CLONE_NEWUSER) doesn't work in a multithreaded program
+       (which "nix" is), so we exec() a single-threaded helper program
+       (chrootHelper() below) to do the work. */
+    auto store2 = store.dynamic_pointer_cast<LocalStore>();
 
-        /* If this is a diverted store (i.e. its "logical" location
-           (typically /nix/store) differs from its "physical" location
-           (e.g. /home/eelco/nix/store), then run the command in a
-           chroot. For non-root users, this requires running it in new
-           mount and user namespaces. Unfortunately,
-           unshare(CLONE_NEWUSER) doesn't work in a multithreaded
-           program (which "nix" is), so we exec() a single-threaded
-           helper program (chrootHelper() below) to do the work. */
-        auto store2 = store.dynamic_pointer_cast<LocalStore>();
+    if (store2 && store->storeDir != store2->getRealStoreDir()) {
+        Strings helperArgs = { chrootHelperName, store->storeDir, store2->getRealStoreDir(), program };
+        for (auto & arg : args) helperArgs.push_back(arg);
 
-        if (store2 && store->storeDir != store2->realStoreDir) {
-            Strings helperArgs = { chrootHelperName, store->storeDir, store2->realStoreDir, program };
-            for (auto & arg : args) helperArgs.push_back(arg);
+        execv(readLink("/proc/self/exe").c_str(), stringsToCharPtrs(helperArgs).data());
 
-            execv(readLink("/proc/self/exe").c_str(), stringsToCharPtrs(helperArgs).data());
+        throw SysError("could not execute chroot helper");
+    }
 
-            throw SysError("could not execute chroot helper");
-        }
+    execvp(program.c_str(), stringsToCharPtrs(args).data());
 
-        execvp(program.c_str(), stringsToCharPtrs(args).data());
+    throw SysError("unable to execute '%s'", program);
+}
 
-        throw SysError("unable to execute '%s'", program);
-    }
-};
+}
 
-struct CmdShell : InstallablesCommand, RunCommon, MixEnvironment
+struct CmdShell : InstallablesCommand, MixEnvironment
 {
 
     using InstallablesCommand::run;
@@ -93,7 +92,7 @@ struct CmdShell : InstallablesCommand, RunCommon, MixEnvironment
 
     void run(ref<Store> store) override
     {
-        auto outPaths = toStorePaths(store, Realise::Outputs, OperateOn::Output, installables);
+        auto outPaths = toStorePaths(getEvalStore(), store, Realise::Outputs, OperateOn::Output, installables);
 
         auto accessor = store->getFSAccessor();
 
@@ -125,13 +124,13 @@ struct CmdShell : InstallablesCommand, RunCommon, MixEnvironment
         Strings args;
         for (auto & arg : command) args.push_back(arg);
 
-        runProgram(store, *command.begin(), args);
+        runProgramInStore(store, *command.begin(), args);
     }
 };
 
 static auto rCmdShell = registerCommand<CmdShell>("shell");
 
-struct CmdRun : InstallableCommand, RunCommon
+struct CmdRun : InstallableCommand
 {
     using InstallableCommand::run;
 
@@ -168,7 +167,7 @@ struct CmdRun : InstallableCommand, RunCommon
 
     Strings getDefaultFlakeAttrPathPrefixes() override
     {
-        Strings res{"apps." + settings.thisSystem.get() + ".", "packages"};
+        Strings res{"apps." + settings.thisSystem.get() + "."};
         for (auto & s : SourceExprCommand::getDefaultFlakeAttrPathPrefixes())
             res.push_back(s);
         return res;
@@ -178,14 +177,12 @@ struct CmdRun : InstallableCommand, RunCommon
     {
         auto state = getEvalState();
 
-        auto app = installable->toApp(*state);
-
-        state->store->buildPaths(toDerivedPaths(app.context));
+        auto app = installable->toApp(*state).resolve(getEvalStore(), store);
 
         Strings allArgs{app.program};
         for (auto & i : args) allArgs.push_back(i);
 
-        runProgram(store, app.program, allArgs);
+        runProgramInStore(store, app.program, allArgs);
     }
 };
 
diff --git a/src/nix/run.hh b/src/nix/run.hh
new file mode 100644
index 000000000..6180a87dd
--- /dev/null
+++ b/src/nix/run.hh
@@ -0,0 +1,11 @@
+#pragma once
+
+#include "store-api.hh"
+
+namespace nix {
+
+void runProgramInStore(ref<Store> store,
+    const std::string & program,
+    const Strings & args);
+
+}
diff --git a/src/nix/search.cc b/src/nix/search.cc
index c52a48d4e..0d8fdd5c2 100644
--- a/src/nix/search.cc
+++ b/src/nix/search.cc
@@ -62,6 +62,7 @@ struct CmdSearch : InstallableCommand, MixJSON
     void run(ref<Store> store) override
     {
         settings.readOnlyMode = true;
+        evalSettings.enableImportFromDerivation.setDefault(false);
 
         // Empty search string should match all packages
         // Use "^" here instead of ".*" due to differences in resulting highlighting
diff --git a/src/nix/show-config.cc b/src/nix/show-config.cc
index 91721219b..29944e748 100644
--- a/src/nix/show-config.cc
+++ b/src/nix/show-config.cc
@@ -22,10 +22,7 @@ struct CmdShowConfig : Command, MixJSON
             // FIXME: use appropriate JSON types (bool, ints, etc).
             logger->cout("%s", globalConfig.toJSON().dump());
         } else {
-            std::map<std::string, Config::SettingInfo> settings;
-            globalConfig.getSettings(settings);
-            for (auto & s : settings)
-                logger->cout("%s = %s", s.first, s.second.value);
+            logger->cout("%s", globalConfig.toKeyValue());
         }
     }
 };
diff --git a/src/nix/show-derivation.cc b/src/nix/show-derivation.cc
index 2588a011d..c614be68d 100644
--- a/src/nix/show-derivation.cc
+++ b/src/nix/show-derivation.cc
@@ -65,18 +65,18 @@ struct CmdShowDerivation : InstallablesCommand
                     auto & outputName = _outputName; // work around clang bug
                     auto outputObj { outputsObj.object(outputName) };
                     std::visit(overloaded {
-                        [&](DerivationOutputInputAddressed doi) {
+                        [&](const DerivationOutputInputAddressed & doi) {
                             outputObj.attr("path", store->printStorePath(doi.path));
                         },
-                        [&](DerivationOutputCAFixed dof) {
+                        [&](const DerivationOutputCAFixed & dof) {
                             outputObj.attr("path", store->printStorePath(dof.path(*store, drv.name, outputName)));
                             outputObj.attr("hashAlgo", dof.hash.printMethodAlgo());
                             outputObj.attr("hash", dof.hash.hash.to_string(Base16, false));
                         },
-                        [&](DerivationOutputCAFloating dof) {
+                        [&](const DerivationOutputCAFloating & dof) {
                             outputObj.attr("hashAlgo", makeFileIngestionPrefix(dof.method) + printHashType(dof.hashType));
                         },
-                        [&](DerivationOutputDeferred) {},
+                        [&](const DerivationOutputDeferred &) {},
                     }, output.output);
                 }
             }
diff --git a/src/nix/sigs.cc b/src/nix/sigs.cc
index c64b472b6..3d659d6d2 100644
--- a/src/nix/sigs.cc
+++ b/src/nix/sigs.cc
@@ -27,7 +27,7 @@ struct CmdCopySigs : StorePathsCommand
         return "copy store path signatures from substituters";
     }
 
-    void run(ref<Store> store, StorePaths storePaths) override
+    void run(ref<Store> store, StorePaths && storePaths) override
     {
         if (substituterUris.empty())
             throw UsageError("you must specify at least one substituter using '-s'");
@@ -113,7 +113,7 @@ struct CmdSign : StorePathsCommand
         return "sign store paths";
     }
 
-    void run(ref<Store> store, StorePaths storePaths) override
+    void run(ref<Store> store, StorePaths && storePaths) override
     {
         if (secretKeyFile.empty())
             throw UsageError("you must specify a secret key file using '-k'");
@@ -218,8 +218,7 @@ struct CmdKey : NixMultiCommand
     void run() override
     {
         if (!command)
-            throw UsageError("'nix flake' requires a sub-command.");
-        settings.requireExperimentalFeature("flakes");
+            throw UsageError("'nix key' requires a sub-command.");
         command->second->prepare();
         command->second->run();
     }
diff --git a/src/nix/store-delete.cc b/src/nix/store-delete.cc
index 10245978e..e4a3cb554 100644
--- a/src/nix/store-delete.cc
+++ b/src/nix/store-delete.cc
@@ -30,7 +30,7 @@ struct CmdStoreDelete : StorePathsCommand
           ;
     }
 
-    void run(ref<Store> store, std::vector<StorePath> storePaths) override
+    void run(ref<Store> store, std::vector<StorePath> && storePaths) override
     {
         for (auto & path : storePaths)
             options.pathsToDelete.insert(path);
diff --git a/src/nix/store-repair.cc b/src/nix/store-repair.cc
index 1c7a4392e..8fcb3639a 100644
--- a/src/nix/store-repair.cc
+++ b/src/nix/store-repair.cc
@@ -17,7 +17,7 @@ struct CmdStoreRepair : StorePathsCommand
           ;
     }
 
-    void run(ref<Store> store, std::vector<StorePath> storePaths) override
+    void run(ref<Store> store, std::vector<StorePath> && storePaths) override
     {
         for (auto & path : storePaths)
             store->repairPath(path);
diff --git a/src/nix/verify.cc b/src/nix/verify.cc
index 1721c7f16..e92df1303 100644
--- a/src/nix/verify.cc
+++ b/src/nix/verify.cc
@@ -59,7 +59,7 @@ struct CmdVerify : StorePathsCommand
           ;
     }
 
-    void run(ref<Store> store, StorePaths storePaths) override
+    void run(ref<Store> store, StorePaths && storePaths) override
     {
         std::vector<ref<Store>> substituters;
         for (auto & s : substituterUris)
@@ -97,15 +97,11 @@ struct CmdVerify : StorePathsCommand
 
                 if (!noContents) {
 
-                    std::unique_ptr<AbstractHashSink> hashSink;
-                    if (!info->ca)
-                        hashSink = std::make_unique<HashSink>(info->narHash.type);
-                    else
-                        hashSink = std::make_unique<HashModuloSink>(info->narHash.type, std::string(info->path.hashPart()));
+                    auto hashSink = HashSink(info->narHash.type);
 
-                    store->narFromPath(info->path, *hashSink);
+                    store->narFromPath(info->path, hashSink);
 
-                    auto hash = hashSink->finish();
+                    auto hash = hashSink.finish();
 
                     if (hash.first != info->narHash) {
                         corrupted++;
diff --git a/src/nix/why-depends.cc b/src/nix/why-depends.cc
index 7a4ca5172..2f6b361bb 100644
--- a/src/nix/why-depends.cc
+++ b/src/nix/why-depends.cc
@@ -62,9 +62,9 @@ struct CmdWhyDepends : SourceExprCommand
     void run(ref<Store> store) override
     {
         auto package = parseInstallable(store, _package);
-        auto packagePath = toStorePath(store, Realise::Outputs, operateOn, package);
+        auto packagePath = toStorePath(getEvalStore(), store, Realise::Outputs, operateOn, package);
         auto dependency = parseInstallable(store, _dependency);
-        auto dependencyPath = toStorePath(store, Realise::Derivation, operateOn, dependency);
+        auto dependencyPath = toStorePath(getEvalStore(), store, Realise::Derivation, operateOn, dependency);
         auto dependencyPathHash = dependencyPath.hashPart();
 
         StorePathSet closure;
diff --git a/src/nlohmann/json.hpp b/src/nlohmann/json.hpp
index c9af0bed3..a70aaf8cb 100644
--- a/src/nlohmann/json.hpp
+++ b/src/nlohmann/json.hpp
@@ -1,12 +1,12 @@
 /*
     __ _____ _____ _____
  __|  |   __|     |   | |  JSON for Modern C++
-|  |  |__   |  |  | | | |  version 3.5.0
+|  |  |__   |  |  | | | |  version 3.9.1
 |_____|_____|_____|_|___|  https://github.com/nlohmann/json
 
 Licensed under the MIT License <http://opensource.org/licenses/MIT>.
 SPDX-License-Identifier: MIT
-Copyright (c) 2013-2018 Niels Lohmann <http://nlohmann.me>.
+Copyright (c) 2013-2019 Niels Lohmann <http://nlohmann.me>.
 
 Permission is hereby  granted, free of charge, to any  person obtaining a copy
 of this software and associated  documentation files (the "Software"), to deal
@@ -27,92 +27,1997 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE  OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 */
 
-#ifndef NLOHMANN_JSON_HPP
-#define NLOHMANN_JSON_HPP
+#ifndef INCLUDE_NLOHMANN_JSON_HPP_
+#define INCLUDE_NLOHMANN_JSON_HPP_
 
 #define NLOHMANN_JSON_VERSION_MAJOR 3
-#define NLOHMANN_JSON_VERSION_MINOR 5
-#define NLOHMANN_JSON_VERSION_PATCH 0
+#define NLOHMANN_JSON_VERSION_MINOR 9
+#define NLOHMANN_JSON_VERSION_PATCH 1
 
 #include <algorithm> // all_of, find, for_each
-#include <cassert> // assert
-#include <ciso646> // and, not, or
 #include <cstddef> // nullptr_t, ptrdiff_t, size_t
 #include <functional> // hash, less
 #include <initializer_list> // initializer_list
 #include <iosfwd> // istream, ostream
 #include <iterator> // random_access_iterator_tag
+#include <memory> // unique_ptr
 #include <numeric> // accumulate
 #include <string> // string, stoi, to_string
 #include <utility> // declval, forward, move, pair, swap
+#include <vector> // vector
 
-// #include <nlohmann/json_fwd.hpp>
-#ifndef NLOHMANN_JSON_FWD_HPP
-#define NLOHMANN_JSON_FWD_HPP
+// #include <nlohmann/adl_serializer.hpp>
 
-#include <cstdint> // int64_t, uint64_t
+
+#include <utility>
+
+// #include <nlohmann/detail/conversions/from_json.hpp>
+
+
+#include <algorithm> // transform
+#include <array> // array
+#include <forward_list> // forward_list
+#include <iterator> // inserter, front_inserter, end
 #include <map> // map
-#include <memory> // allocator
 #include <string> // string
-#include <vector> // vector
+#include <tuple> // tuple, make_tuple
+#include <type_traits> // is_arithmetic, is_same, is_enum, underlying_type, is_convertible
+#include <unordered_map> // unordered_map
+#include <utility> // pair, declval
+#include <valarray> // valarray
+
+// #include <nlohmann/detail/exceptions.hpp>
+
+
+#include <exception> // exception
+#include <stdexcept> // runtime_error
+#include <string> // to_string
+
+// #include <nlohmann/detail/input/position_t.hpp>
+
+
+#include <cstddef> // size_t
 
-/*!
-@brief namespace for Niels Lohmann
-@see https://github.com/nlohmann
-@since version 1.0.0
-*/
 namespace nlohmann
 {
-/*!
-@brief default JSONSerializer template argument
+namespace detail
+{
+/// struct to capture the start position of the current token
+struct position_t
+{
+    /// the total number of characters read
+    std::size_t chars_read_total = 0;
+    /// the number of characters read in the current line
+    std::size_t chars_read_current_line = 0;
+    /// the number of lines read
+    std::size_t lines_read = 0;
 
-This serializer ignores the template arguments and uses ADL
-([argument-dependent lookup](https://en.cppreference.com/w/cpp/language/adl))
-for serialization.
-*/
-template<typename T = void, typename SFINAE = void>
-struct adl_serializer;
+    /// conversion to size_t to preserve SAX interface
+    constexpr operator size_t() const
+    {
+        return chars_read_total;
+    }
+};
 
-template<template<typename U, typename V, typename... Args> class ObjectType =
-         std::map,
-         template<typename U, typename... Args> class ArrayType = std::vector,
-         class StringType = std::string, class BooleanType = bool,
-         class NumberIntegerType = std::int64_t,
-         class NumberUnsignedType = std::uint64_t,
-         class NumberFloatType = double,
-         template<typename U> class AllocatorType = std::allocator,
-         template<typename T, typename SFINAE = void> class JSONSerializer =
-         adl_serializer>
-class basic_json;
+} // namespace detail
+} // namespace nlohmann
 
-/*!
-@brief JSON Pointer
+// #include <nlohmann/detail/macro_scope.hpp>
 
-A JSON pointer defines a string syntax for identifying a specific value
-within a JSON document. It can be used with functions `at` and
-`operator[]`. Furthermore, JSON pointers are the base for JSON patches.
 
-@sa [RFC 6901](https://tools.ietf.org/html/rfc6901)
+#include <utility> // pair
+// #include <nlohmann/thirdparty/hedley/hedley.hpp>
+/* Hedley - https://nemequ.github.io/hedley
+ * Created by Evan Nemerson <evan@nemerson.com>
+ *
+ * To the extent possible under law, the author(s) have dedicated all
+ * copyright and related and neighboring rights to this software to
+ * the public domain worldwide. This software is distributed without
+ * any warranty.
+ *
+ * For details, see <http://creativecommons.org/publicdomain/zero/1.0/>.
+ * SPDX-License-Identifier: CC0-1.0
+ */
+
+#if !defined(JSON_HEDLEY_VERSION) || (JSON_HEDLEY_VERSION < 13)
+#if defined(JSON_HEDLEY_VERSION)
+    #undef JSON_HEDLEY_VERSION
+#endif
+#define JSON_HEDLEY_VERSION 13
 
-@since version 2.0.0
-*/
-template<typename BasicJsonType>
-class json_pointer;
+#if defined(JSON_HEDLEY_STRINGIFY_EX)
+    #undef JSON_HEDLEY_STRINGIFY_EX
+#endif
+#define JSON_HEDLEY_STRINGIFY_EX(x) #x
 
-/*!
-@brief default JSON class
+#if defined(JSON_HEDLEY_STRINGIFY)
+    #undef JSON_HEDLEY_STRINGIFY
+#endif
+#define JSON_HEDLEY_STRINGIFY(x) JSON_HEDLEY_STRINGIFY_EX(x)
 
-This type is the default specialization of the @ref basic_json class which
-uses the standard template types.
+#if defined(JSON_HEDLEY_CONCAT_EX)
+    #undef JSON_HEDLEY_CONCAT_EX
+#endif
+#define JSON_HEDLEY_CONCAT_EX(a,b) a##b
 
-@since version 1.0.0
-*/
-using json = basic_json<>;
-}  // namespace nlohmann
+#if defined(JSON_HEDLEY_CONCAT)
+    #undef JSON_HEDLEY_CONCAT
+#endif
+#define JSON_HEDLEY_CONCAT(a,b) JSON_HEDLEY_CONCAT_EX(a,b)
 
+#if defined(JSON_HEDLEY_CONCAT3_EX)
+    #undef JSON_HEDLEY_CONCAT3_EX
 #endif
+#define JSON_HEDLEY_CONCAT3_EX(a,b,c) a##b##c
 
-// #include <nlohmann/detail/macro_scope.hpp>
+#if defined(JSON_HEDLEY_CONCAT3)
+    #undef JSON_HEDLEY_CONCAT3
+#endif
+#define JSON_HEDLEY_CONCAT3(a,b,c) JSON_HEDLEY_CONCAT3_EX(a,b,c)
+
+#if defined(JSON_HEDLEY_VERSION_ENCODE)
+    #undef JSON_HEDLEY_VERSION_ENCODE
+#endif
+#define JSON_HEDLEY_VERSION_ENCODE(major,minor,revision) (((major) * 1000000) + ((minor) * 1000) + (revision))
+
+#if defined(JSON_HEDLEY_VERSION_DECODE_MAJOR)
+    #undef JSON_HEDLEY_VERSION_DECODE_MAJOR
+#endif
+#define JSON_HEDLEY_VERSION_DECODE_MAJOR(version) ((version) / 1000000)
+
+#if defined(JSON_HEDLEY_VERSION_DECODE_MINOR)
+    #undef JSON_HEDLEY_VERSION_DECODE_MINOR
+#endif
+#define JSON_HEDLEY_VERSION_DECODE_MINOR(version) (((version) % 1000000) / 1000)
+
+#if defined(JSON_HEDLEY_VERSION_DECODE_REVISION)
+    #undef JSON_HEDLEY_VERSION_DECODE_REVISION
+#endif
+#define JSON_HEDLEY_VERSION_DECODE_REVISION(version) ((version) % 1000)
+
+#if defined(JSON_HEDLEY_GNUC_VERSION)
+    #undef JSON_HEDLEY_GNUC_VERSION
+#endif
+#if defined(__GNUC__) && defined(__GNUC_PATCHLEVEL__)
+    #define JSON_HEDLEY_GNUC_VERSION JSON_HEDLEY_VERSION_ENCODE(__GNUC__, __GNUC_MINOR__, __GNUC_PATCHLEVEL__)
+#elif defined(__GNUC__)
+    #define JSON_HEDLEY_GNUC_VERSION JSON_HEDLEY_VERSION_ENCODE(__GNUC__, __GNUC_MINOR__, 0)
+#endif
+
+#if defined(JSON_HEDLEY_GNUC_VERSION_CHECK)
+    #undef JSON_HEDLEY_GNUC_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_GNUC_VERSION)
+    #define JSON_HEDLEY_GNUC_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_GNUC_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_GNUC_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_MSVC_VERSION)
+    #undef JSON_HEDLEY_MSVC_VERSION
+#endif
+#if defined(_MSC_FULL_VER) && (_MSC_FULL_VER >= 140000000)
+    #define JSON_HEDLEY_MSVC_VERSION JSON_HEDLEY_VERSION_ENCODE(_MSC_FULL_VER / 10000000, (_MSC_FULL_VER % 10000000) / 100000, (_MSC_FULL_VER % 100000) / 100)
+#elif defined(_MSC_FULL_VER)
+    #define JSON_HEDLEY_MSVC_VERSION JSON_HEDLEY_VERSION_ENCODE(_MSC_FULL_VER / 1000000, (_MSC_FULL_VER % 1000000) / 10000, (_MSC_FULL_VER % 10000) / 10)
+#elif defined(_MSC_VER)
+    #define JSON_HEDLEY_MSVC_VERSION JSON_HEDLEY_VERSION_ENCODE(_MSC_VER / 100, _MSC_VER % 100, 0)
+#endif
+
+#if defined(JSON_HEDLEY_MSVC_VERSION_CHECK)
+    #undef JSON_HEDLEY_MSVC_VERSION_CHECK
+#endif
+#if !defined(_MSC_VER)
+    #define JSON_HEDLEY_MSVC_VERSION_CHECK(major,minor,patch) (0)
+#elif defined(_MSC_VER) && (_MSC_VER >= 1400)
+    #define JSON_HEDLEY_MSVC_VERSION_CHECK(major,minor,patch) (_MSC_FULL_VER >= ((major * 10000000) + (minor * 100000) + (patch)))
+#elif defined(_MSC_VER) && (_MSC_VER >= 1200)
+    #define JSON_HEDLEY_MSVC_VERSION_CHECK(major,minor,patch) (_MSC_FULL_VER >= ((major * 1000000) + (minor * 10000) + (patch)))
+#else
+    #define JSON_HEDLEY_MSVC_VERSION_CHECK(major,minor,patch) (_MSC_VER >= ((major * 100) + (minor)))
+#endif
+
+#if defined(JSON_HEDLEY_INTEL_VERSION)
+    #undef JSON_HEDLEY_INTEL_VERSION
+#endif
+#if defined(__INTEL_COMPILER) && defined(__INTEL_COMPILER_UPDATE)
+    #define JSON_HEDLEY_INTEL_VERSION JSON_HEDLEY_VERSION_ENCODE(__INTEL_COMPILER / 100, __INTEL_COMPILER % 100, __INTEL_COMPILER_UPDATE)
+#elif defined(__INTEL_COMPILER)
+    #define JSON_HEDLEY_INTEL_VERSION JSON_HEDLEY_VERSION_ENCODE(__INTEL_COMPILER / 100, __INTEL_COMPILER % 100, 0)
+#endif
+
+#if defined(JSON_HEDLEY_INTEL_VERSION_CHECK)
+    #undef JSON_HEDLEY_INTEL_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_INTEL_VERSION)
+    #define JSON_HEDLEY_INTEL_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_INTEL_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_INTEL_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_PGI_VERSION)
+    #undef JSON_HEDLEY_PGI_VERSION
+#endif
+#if defined(__PGI) && defined(__PGIC__) && defined(__PGIC_MINOR__) && defined(__PGIC_PATCHLEVEL__)
+    #define JSON_HEDLEY_PGI_VERSION JSON_HEDLEY_VERSION_ENCODE(__PGIC__, __PGIC_MINOR__, __PGIC_PATCHLEVEL__)
+#endif
+
+#if defined(JSON_HEDLEY_PGI_VERSION_CHECK)
+    #undef JSON_HEDLEY_PGI_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_PGI_VERSION)
+    #define JSON_HEDLEY_PGI_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_PGI_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_PGI_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_SUNPRO_VERSION)
+    #undef JSON_HEDLEY_SUNPRO_VERSION
+#endif
+#if defined(__SUNPRO_C) && (__SUNPRO_C > 0x1000)
+    #define JSON_HEDLEY_SUNPRO_VERSION JSON_HEDLEY_VERSION_ENCODE((((__SUNPRO_C >> 16) & 0xf) * 10) + ((__SUNPRO_C >> 12) & 0xf), (((__SUNPRO_C >> 8) & 0xf) * 10) + ((__SUNPRO_C >> 4) & 0xf), (__SUNPRO_C & 0xf) * 10)
+#elif defined(__SUNPRO_C)
+    #define JSON_HEDLEY_SUNPRO_VERSION JSON_HEDLEY_VERSION_ENCODE((__SUNPRO_C >> 8) & 0xf, (__SUNPRO_C >> 4) & 0xf, (__SUNPRO_C) & 0xf)
+#elif defined(__SUNPRO_CC) && (__SUNPRO_CC > 0x1000)
+    #define JSON_HEDLEY_SUNPRO_VERSION JSON_HEDLEY_VERSION_ENCODE((((__SUNPRO_CC >> 16) & 0xf) * 10) + ((__SUNPRO_CC >> 12) & 0xf), (((__SUNPRO_CC >> 8) & 0xf) * 10) + ((__SUNPRO_CC >> 4) & 0xf), (__SUNPRO_CC & 0xf) * 10)
+#elif defined(__SUNPRO_CC)
+    #define JSON_HEDLEY_SUNPRO_VERSION JSON_HEDLEY_VERSION_ENCODE((__SUNPRO_CC >> 8) & 0xf, (__SUNPRO_CC >> 4) & 0xf, (__SUNPRO_CC) & 0xf)
+#endif
+
+#if defined(JSON_HEDLEY_SUNPRO_VERSION_CHECK)
+    #undef JSON_HEDLEY_SUNPRO_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_SUNPRO_VERSION)
+    #define JSON_HEDLEY_SUNPRO_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_SUNPRO_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_SUNPRO_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_EMSCRIPTEN_VERSION)
+    #undef JSON_HEDLEY_EMSCRIPTEN_VERSION
+#endif
+#if defined(__EMSCRIPTEN__)
+    #define JSON_HEDLEY_EMSCRIPTEN_VERSION JSON_HEDLEY_VERSION_ENCODE(__EMSCRIPTEN_major__, __EMSCRIPTEN_minor__, __EMSCRIPTEN_tiny__)
+#endif
+
+#if defined(JSON_HEDLEY_EMSCRIPTEN_VERSION_CHECK)
+    #undef JSON_HEDLEY_EMSCRIPTEN_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_EMSCRIPTEN_VERSION)
+    #define JSON_HEDLEY_EMSCRIPTEN_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_EMSCRIPTEN_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_EMSCRIPTEN_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_ARM_VERSION)
+    #undef JSON_HEDLEY_ARM_VERSION
+#endif
+#if defined(__CC_ARM) && defined(__ARMCOMPILER_VERSION)
+    #define JSON_HEDLEY_ARM_VERSION JSON_HEDLEY_VERSION_ENCODE(__ARMCOMPILER_VERSION / 1000000, (__ARMCOMPILER_VERSION % 1000000) / 10000, (__ARMCOMPILER_VERSION % 10000) / 100)
+#elif defined(__CC_ARM) && defined(__ARMCC_VERSION)
+    #define JSON_HEDLEY_ARM_VERSION JSON_HEDLEY_VERSION_ENCODE(__ARMCC_VERSION / 1000000, (__ARMCC_VERSION % 1000000) / 10000, (__ARMCC_VERSION % 10000) / 100)
+#endif
+
+#if defined(JSON_HEDLEY_ARM_VERSION_CHECK)
+    #undef JSON_HEDLEY_ARM_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_ARM_VERSION)
+    #define JSON_HEDLEY_ARM_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_ARM_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_ARM_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_IBM_VERSION)
+    #undef JSON_HEDLEY_IBM_VERSION
+#endif
+#if defined(__ibmxl__)
+    #define JSON_HEDLEY_IBM_VERSION JSON_HEDLEY_VERSION_ENCODE(__ibmxl_version__, __ibmxl_release__, __ibmxl_modification__)
+#elif defined(__xlC__) && defined(__xlC_ver__)
+    #define JSON_HEDLEY_IBM_VERSION JSON_HEDLEY_VERSION_ENCODE(__xlC__ >> 8, __xlC__ & 0xff, (__xlC_ver__ >> 8) & 0xff)
+#elif defined(__xlC__)
+    #define JSON_HEDLEY_IBM_VERSION JSON_HEDLEY_VERSION_ENCODE(__xlC__ >> 8, __xlC__ & 0xff, 0)
+#endif
+
+#if defined(JSON_HEDLEY_IBM_VERSION_CHECK)
+    #undef JSON_HEDLEY_IBM_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_IBM_VERSION)
+    #define JSON_HEDLEY_IBM_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_IBM_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_IBM_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_TI_VERSION)
+    #undef JSON_HEDLEY_TI_VERSION
+#endif
+#if \
+    defined(__TI_COMPILER_VERSION__) && \
+    ( \
+      defined(__TMS470__) || defined(__TI_ARM__) || \
+      defined(__MSP430__) || \
+      defined(__TMS320C2000__) \
+    )
+#if (__TI_COMPILER_VERSION__ >= 16000000)
+    #define JSON_HEDLEY_TI_VERSION JSON_HEDLEY_VERSION_ENCODE(__TI_COMPILER_VERSION__ / 1000000, (__TI_COMPILER_VERSION__ % 1000000) / 1000, (__TI_COMPILER_VERSION__ % 1000))
+#endif
+#endif
+
+#if defined(JSON_HEDLEY_TI_VERSION_CHECK)
+    #undef JSON_HEDLEY_TI_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_TI_VERSION)
+    #define JSON_HEDLEY_TI_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_TI_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_TI_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_TI_CL2000_VERSION)
+    #undef JSON_HEDLEY_TI_CL2000_VERSION
+#endif
+#if defined(__TI_COMPILER_VERSION__) && defined(__TMS320C2000__)
+    #define JSON_HEDLEY_TI_CL2000_VERSION JSON_HEDLEY_VERSION_ENCODE(__TI_COMPILER_VERSION__ / 1000000, (__TI_COMPILER_VERSION__ % 1000000) / 1000, (__TI_COMPILER_VERSION__ % 1000))
+#endif
+
+#if defined(JSON_HEDLEY_TI_CL2000_VERSION_CHECK)
+    #undef JSON_HEDLEY_TI_CL2000_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_TI_CL2000_VERSION)
+    #define JSON_HEDLEY_TI_CL2000_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_TI_CL2000_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_TI_CL2000_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_TI_CL430_VERSION)
+    #undef JSON_HEDLEY_TI_CL430_VERSION
+#endif
+#if defined(__TI_COMPILER_VERSION__) && defined(__MSP430__)
+    #define JSON_HEDLEY_TI_CL430_VERSION JSON_HEDLEY_VERSION_ENCODE(__TI_COMPILER_VERSION__ / 1000000, (__TI_COMPILER_VERSION__ % 1000000) / 1000, (__TI_COMPILER_VERSION__ % 1000))
+#endif
+
+#if defined(JSON_HEDLEY_TI_CL430_VERSION_CHECK)
+    #undef JSON_HEDLEY_TI_CL430_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_TI_CL430_VERSION)
+    #define JSON_HEDLEY_TI_CL430_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_TI_CL430_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_TI_CL430_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_TI_ARMCL_VERSION)
+    #undef JSON_HEDLEY_TI_ARMCL_VERSION
+#endif
+#if defined(__TI_COMPILER_VERSION__) && (defined(__TMS470__) || defined(__TI_ARM__))
+    #define JSON_HEDLEY_TI_ARMCL_VERSION JSON_HEDLEY_VERSION_ENCODE(__TI_COMPILER_VERSION__ / 1000000, (__TI_COMPILER_VERSION__ % 1000000) / 1000, (__TI_COMPILER_VERSION__ % 1000))
+#endif
+
+#if defined(JSON_HEDLEY_TI_ARMCL_VERSION_CHECK)
+    #undef JSON_HEDLEY_TI_ARMCL_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_TI_ARMCL_VERSION)
+    #define JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_TI_ARMCL_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_TI_CL6X_VERSION)
+    #undef JSON_HEDLEY_TI_CL6X_VERSION
+#endif
+#if defined(__TI_COMPILER_VERSION__) && defined(__TMS320C6X__)
+    #define JSON_HEDLEY_TI_CL6X_VERSION JSON_HEDLEY_VERSION_ENCODE(__TI_COMPILER_VERSION__ / 1000000, (__TI_COMPILER_VERSION__ % 1000000) / 1000, (__TI_COMPILER_VERSION__ % 1000))
+#endif
+
+#if defined(JSON_HEDLEY_TI_CL6X_VERSION_CHECK)
+    #undef JSON_HEDLEY_TI_CL6X_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_TI_CL6X_VERSION)
+    #define JSON_HEDLEY_TI_CL6X_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_TI_CL6X_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_TI_CL6X_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_TI_CL7X_VERSION)
+    #undef JSON_HEDLEY_TI_CL7X_VERSION
+#endif
+#if defined(__TI_COMPILER_VERSION__) && defined(__C7000__)
+    #define JSON_HEDLEY_TI_CL7X_VERSION JSON_HEDLEY_VERSION_ENCODE(__TI_COMPILER_VERSION__ / 1000000, (__TI_COMPILER_VERSION__ % 1000000) / 1000, (__TI_COMPILER_VERSION__ % 1000))
+#endif
+
+#if defined(JSON_HEDLEY_TI_CL7X_VERSION_CHECK)
+    #undef JSON_HEDLEY_TI_CL7X_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_TI_CL7X_VERSION)
+    #define JSON_HEDLEY_TI_CL7X_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_TI_CL7X_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_TI_CL7X_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_TI_CLPRU_VERSION)
+    #undef JSON_HEDLEY_TI_CLPRU_VERSION
+#endif
+#if defined(__TI_COMPILER_VERSION__) && defined(__PRU__)
+    #define JSON_HEDLEY_TI_CLPRU_VERSION JSON_HEDLEY_VERSION_ENCODE(__TI_COMPILER_VERSION__ / 1000000, (__TI_COMPILER_VERSION__ % 1000000) / 1000, (__TI_COMPILER_VERSION__ % 1000))
+#endif
+
+#if defined(JSON_HEDLEY_TI_CLPRU_VERSION_CHECK)
+    #undef JSON_HEDLEY_TI_CLPRU_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_TI_CLPRU_VERSION)
+    #define JSON_HEDLEY_TI_CLPRU_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_TI_CLPRU_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_TI_CLPRU_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_CRAY_VERSION)
+    #undef JSON_HEDLEY_CRAY_VERSION
+#endif
+#if defined(_CRAYC)
+    #if defined(_RELEASE_PATCHLEVEL)
+        #define JSON_HEDLEY_CRAY_VERSION JSON_HEDLEY_VERSION_ENCODE(_RELEASE_MAJOR, _RELEASE_MINOR, _RELEASE_PATCHLEVEL)
+    #else
+        #define JSON_HEDLEY_CRAY_VERSION JSON_HEDLEY_VERSION_ENCODE(_RELEASE_MAJOR, _RELEASE_MINOR, 0)
+    #endif
+#endif
+
+#if defined(JSON_HEDLEY_CRAY_VERSION_CHECK)
+    #undef JSON_HEDLEY_CRAY_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_CRAY_VERSION)
+    #define JSON_HEDLEY_CRAY_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_CRAY_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_CRAY_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_IAR_VERSION)
+    #undef JSON_HEDLEY_IAR_VERSION
+#endif
+#if defined(__IAR_SYSTEMS_ICC__)
+    #if __VER__ > 1000
+        #define JSON_HEDLEY_IAR_VERSION JSON_HEDLEY_VERSION_ENCODE((__VER__ / 1000000), ((__VER__ / 1000) % 1000), (__VER__ % 1000))
+    #else
+        #define JSON_HEDLEY_IAR_VERSION JSON_HEDLEY_VERSION_ENCODE(VER / 100, __VER__ % 100, 0)
+    #endif
+#endif
+
+#if defined(JSON_HEDLEY_IAR_VERSION_CHECK)
+    #undef JSON_HEDLEY_IAR_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_IAR_VERSION)
+    #define JSON_HEDLEY_IAR_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_IAR_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_IAR_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_TINYC_VERSION)
+    #undef JSON_HEDLEY_TINYC_VERSION
+#endif
+#if defined(__TINYC__)
+    #define JSON_HEDLEY_TINYC_VERSION JSON_HEDLEY_VERSION_ENCODE(__TINYC__ / 1000, (__TINYC__ / 100) % 10, __TINYC__ % 100)
+#endif
+
+#if defined(JSON_HEDLEY_TINYC_VERSION_CHECK)
+    #undef JSON_HEDLEY_TINYC_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_TINYC_VERSION)
+    #define JSON_HEDLEY_TINYC_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_TINYC_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_TINYC_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_DMC_VERSION)
+    #undef JSON_HEDLEY_DMC_VERSION
+#endif
+#if defined(__DMC__)
+    #define JSON_HEDLEY_DMC_VERSION JSON_HEDLEY_VERSION_ENCODE(__DMC__ >> 8, (__DMC__ >> 4) & 0xf, __DMC__ & 0xf)
+#endif
+
+#if defined(JSON_HEDLEY_DMC_VERSION_CHECK)
+    #undef JSON_HEDLEY_DMC_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_DMC_VERSION)
+    #define JSON_HEDLEY_DMC_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_DMC_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_DMC_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_COMPCERT_VERSION)
+    #undef JSON_HEDLEY_COMPCERT_VERSION
+#endif
+#if defined(__COMPCERT_VERSION__)
+    #define JSON_HEDLEY_COMPCERT_VERSION JSON_HEDLEY_VERSION_ENCODE(__COMPCERT_VERSION__ / 10000, (__COMPCERT_VERSION__ / 100) % 100, __COMPCERT_VERSION__ % 100)
+#endif
+
+#if defined(JSON_HEDLEY_COMPCERT_VERSION_CHECK)
+    #undef JSON_HEDLEY_COMPCERT_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_COMPCERT_VERSION)
+    #define JSON_HEDLEY_COMPCERT_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_COMPCERT_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_COMPCERT_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_PELLES_VERSION)
+    #undef JSON_HEDLEY_PELLES_VERSION
+#endif
+#if defined(__POCC__)
+    #define JSON_HEDLEY_PELLES_VERSION JSON_HEDLEY_VERSION_ENCODE(__POCC__ / 100, __POCC__ % 100, 0)
+#endif
+
+#if defined(JSON_HEDLEY_PELLES_VERSION_CHECK)
+    #undef JSON_HEDLEY_PELLES_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_PELLES_VERSION)
+    #define JSON_HEDLEY_PELLES_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_PELLES_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_PELLES_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_GCC_VERSION)
+    #undef JSON_HEDLEY_GCC_VERSION
+#endif
+#if \
+    defined(JSON_HEDLEY_GNUC_VERSION) && \
+    !defined(__clang__) && \
+    !defined(JSON_HEDLEY_INTEL_VERSION) && \
+    !defined(JSON_HEDLEY_PGI_VERSION) && \
+    !defined(JSON_HEDLEY_ARM_VERSION) && \
+    !defined(JSON_HEDLEY_TI_VERSION) && \
+    !defined(JSON_HEDLEY_TI_ARMCL_VERSION) && \
+    !defined(JSON_HEDLEY_TI_CL430_VERSION) && \
+    !defined(JSON_HEDLEY_TI_CL2000_VERSION) && \
+    !defined(JSON_HEDLEY_TI_CL6X_VERSION) && \
+    !defined(JSON_HEDLEY_TI_CL7X_VERSION) && \
+    !defined(JSON_HEDLEY_TI_CLPRU_VERSION) && \
+    !defined(__COMPCERT__)
+    #define JSON_HEDLEY_GCC_VERSION JSON_HEDLEY_GNUC_VERSION
+#endif
+
+#if defined(JSON_HEDLEY_GCC_VERSION_CHECK)
+    #undef JSON_HEDLEY_GCC_VERSION_CHECK
+#endif
+#if defined(JSON_HEDLEY_GCC_VERSION)
+    #define JSON_HEDLEY_GCC_VERSION_CHECK(major,minor,patch) (JSON_HEDLEY_GCC_VERSION >= JSON_HEDLEY_VERSION_ENCODE(major, minor, patch))
+#else
+    #define JSON_HEDLEY_GCC_VERSION_CHECK(major,minor,patch) (0)
+#endif
+
+#if defined(JSON_HEDLEY_HAS_ATTRIBUTE)
+    #undef JSON_HEDLEY_HAS_ATTRIBUTE
+#endif
+#if defined(__has_attribute)
+    #define JSON_HEDLEY_HAS_ATTRIBUTE(attribute) __has_attribute(attribute)
+#else
+    #define JSON_HEDLEY_HAS_ATTRIBUTE(attribute) (0)
+#endif
+
+#if defined(JSON_HEDLEY_GNUC_HAS_ATTRIBUTE)
+    #undef JSON_HEDLEY_GNUC_HAS_ATTRIBUTE
+#endif
+#if defined(__has_attribute)
+    #define JSON_HEDLEY_GNUC_HAS_ATTRIBUTE(attribute,major,minor,patch) __has_attribute(attribute)
+#else
+    #define JSON_HEDLEY_GNUC_HAS_ATTRIBUTE(attribute,major,minor,patch) JSON_HEDLEY_GNUC_VERSION_CHECK(major,minor,patch)
+#endif
+
+#if defined(JSON_HEDLEY_GCC_HAS_ATTRIBUTE)
+    #undef JSON_HEDLEY_GCC_HAS_ATTRIBUTE
+#endif
+#if defined(__has_attribute)
+    #define JSON_HEDLEY_GCC_HAS_ATTRIBUTE(attribute,major,minor,patch) __has_attribute(attribute)
+#else
+    #define JSON_HEDLEY_GCC_HAS_ATTRIBUTE(attribute,major,minor,patch) JSON_HEDLEY_GCC_VERSION_CHECK(major,minor,patch)
+#endif
+
+#if defined(JSON_HEDLEY_HAS_CPP_ATTRIBUTE)
+    #undef JSON_HEDLEY_HAS_CPP_ATTRIBUTE
+#endif
+#if \
+    defined(__has_cpp_attribute) && \
+    defined(__cplusplus) && \
+    (!defined(JSON_HEDLEY_SUNPRO_VERSION) || JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,15,0))
+    #define JSON_HEDLEY_HAS_CPP_ATTRIBUTE(attribute) __has_cpp_attribute(attribute)
+#else
+    #define JSON_HEDLEY_HAS_CPP_ATTRIBUTE(attribute) (0)
+#endif
+
+#if defined(JSON_HEDLEY_HAS_CPP_ATTRIBUTE_NS)
+    #undef JSON_HEDLEY_HAS_CPP_ATTRIBUTE_NS
+#endif
+#if !defined(__cplusplus) || !defined(__has_cpp_attribute)
+    #define JSON_HEDLEY_HAS_CPP_ATTRIBUTE_NS(ns,attribute) (0)
+#elif \
+    !defined(JSON_HEDLEY_PGI_VERSION) && \
+    !defined(JSON_HEDLEY_IAR_VERSION) && \
+    (!defined(JSON_HEDLEY_SUNPRO_VERSION) || JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,15,0)) && \
+    (!defined(JSON_HEDLEY_MSVC_VERSION) || JSON_HEDLEY_MSVC_VERSION_CHECK(19,20,0))
+    #define JSON_HEDLEY_HAS_CPP_ATTRIBUTE_NS(ns,attribute) JSON_HEDLEY_HAS_CPP_ATTRIBUTE(ns::attribute)
+#else
+    #define JSON_HEDLEY_HAS_CPP_ATTRIBUTE_NS(ns,attribute) (0)
+#endif
+
+#if defined(JSON_HEDLEY_GNUC_HAS_CPP_ATTRIBUTE)
+    #undef JSON_HEDLEY_GNUC_HAS_CPP_ATTRIBUTE
+#endif
+#if defined(__has_cpp_attribute) && defined(__cplusplus)
+    #define JSON_HEDLEY_GNUC_HAS_CPP_ATTRIBUTE(attribute,major,minor,patch) __has_cpp_attribute(attribute)
+#else
+    #define JSON_HEDLEY_GNUC_HAS_CPP_ATTRIBUTE(attribute,major,minor,patch) JSON_HEDLEY_GNUC_VERSION_CHECK(major,minor,patch)
+#endif
+
+#if defined(JSON_HEDLEY_GCC_HAS_CPP_ATTRIBUTE)
+    #undef JSON_HEDLEY_GCC_HAS_CPP_ATTRIBUTE
+#endif
+#if defined(__has_cpp_attribute) && defined(__cplusplus)
+    #define JSON_HEDLEY_GCC_HAS_CPP_ATTRIBUTE(attribute,major,minor,patch) __has_cpp_attribute(attribute)
+#else
+    #define JSON_HEDLEY_GCC_HAS_CPP_ATTRIBUTE(attribute,major,minor,patch) JSON_HEDLEY_GCC_VERSION_CHECK(major,minor,patch)
+#endif
+
+#if defined(JSON_HEDLEY_HAS_BUILTIN)
+    #undef JSON_HEDLEY_HAS_BUILTIN
+#endif
+#if defined(__has_builtin)
+    #define JSON_HEDLEY_HAS_BUILTIN(builtin) __has_builtin(builtin)
+#else
+    #define JSON_HEDLEY_HAS_BUILTIN(builtin) (0)
+#endif
+
+#if defined(JSON_HEDLEY_GNUC_HAS_BUILTIN)
+    #undef JSON_HEDLEY_GNUC_HAS_BUILTIN
+#endif
+#if defined(__has_builtin)
+    #define JSON_HEDLEY_GNUC_HAS_BUILTIN(builtin,major,minor,patch) __has_builtin(builtin)
+#else
+    #define JSON_HEDLEY_GNUC_HAS_BUILTIN(builtin,major,minor,patch) JSON_HEDLEY_GNUC_VERSION_CHECK(major,minor,patch)
+#endif
+
+#if defined(JSON_HEDLEY_GCC_HAS_BUILTIN)
+    #undef JSON_HEDLEY_GCC_HAS_BUILTIN
+#endif
+#if defined(__has_builtin)
+    #define JSON_HEDLEY_GCC_HAS_BUILTIN(builtin,major,minor,patch) __has_builtin(builtin)
+#else
+    #define JSON_HEDLEY_GCC_HAS_BUILTIN(builtin,major,minor,patch) JSON_HEDLEY_GCC_VERSION_CHECK(major,minor,patch)
+#endif
+
+#if defined(JSON_HEDLEY_HAS_FEATURE)
+    #undef JSON_HEDLEY_HAS_FEATURE
+#endif
+#if defined(__has_feature)
+    #define JSON_HEDLEY_HAS_FEATURE(feature) __has_feature(feature)
+#else
+    #define JSON_HEDLEY_HAS_FEATURE(feature) (0)
+#endif
+
+#if defined(JSON_HEDLEY_GNUC_HAS_FEATURE)
+    #undef JSON_HEDLEY_GNUC_HAS_FEATURE
+#endif
+#if defined(__has_feature)
+    #define JSON_HEDLEY_GNUC_HAS_FEATURE(feature,major,minor,patch) __has_feature(feature)
+#else
+    #define JSON_HEDLEY_GNUC_HAS_FEATURE(feature,major,minor,patch) JSON_HEDLEY_GNUC_VERSION_CHECK(major,minor,patch)
+#endif
+
+#if defined(JSON_HEDLEY_GCC_HAS_FEATURE)
+    #undef JSON_HEDLEY_GCC_HAS_FEATURE
+#endif
+#if defined(__has_feature)
+    #define JSON_HEDLEY_GCC_HAS_FEATURE(feature,major,minor,patch) __has_feature(feature)
+#else
+    #define JSON_HEDLEY_GCC_HAS_FEATURE(feature,major,minor,patch) JSON_HEDLEY_GCC_VERSION_CHECK(major,minor,patch)
+#endif
+
+#if defined(JSON_HEDLEY_HAS_EXTENSION)
+    #undef JSON_HEDLEY_HAS_EXTENSION
+#endif
+#if defined(__has_extension)
+    #define JSON_HEDLEY_HAS_EXTENSION(extension) __has_extension(extension)
+#else
+    #define JSON_HEDLEY_HAS_EXTENSION(extension) (0)
+#endif
+
+#if defined(JSON_HEDLEY_GNUC_HAS_EXTENSION)
+    #undef JSON_HEDLEY_GNUC_HAS_EXTENSION
+#endif
+#if defined(__has_extension)
+    #define JSON_HEDLEY_GNUC_HAS_EXTENSION(extension,major,minor,patch) __has_extension(extension)
+#else
+    #define JSON_HEDLEY_GNUC_HAS_EXTENSION(extension,major,minor,patch) JSON_HEDLEY_GNUC_VERSION_CHECK(major,minor,patch)
+#endif
+
+#if defined(JSON_HEDLEY_GCC_HAS_EXTENSION)
+    #undef JSON_HEDLEY_GCC_HAS_EXTENSION
+#endif
+#if defined(__has_extension)
+    #define JSON_HEDLEY_GCC_HAS_EXTENSION(extension,major,minor,patch) __has_extension(extension)
+#else
+    #define JSON_HEDLEY_GCC_HAS_EXTENSION(extension,major,minor,patch) JSON_HEDLEY_GCC_VERSION_CHECK(major,minor,patch)
+#endif
+
+#if defined(JSON_HEDLEY_HAS_DECLSPEC_ATTRIBUTE)
+    #undef JSON_HEDLEY_HAS_DECLSPEC_ATTRIBUTE
+#endif
+#if defined(__has_declspec_attribute)
+    #define JSON_HEDLEY_HAS_DECLSPEC_ATTRIBUTE(attribute) __has_declspec_attribute(attribute)
+#else
+    #define JSON_HEDLEY_HAS_DECLSPEC_ATTRIBUTE(attribute) (0)
+#endif
+
+#if defined(JSON_HEDLEY_GNUC_HAS_DECLSPEC_ATTRIBUTE)
+    #undef JSON_HEDLEY_GNUC_HAS_DECLSPEC_ATTRIBUTE
+#endif
+#if defined(__has_declspec_attribute)
+    #define JSON_HEDLEY_GNUC_HAS_DECLSPEC_ATTRIBUTE(attribute,major,minor,patch) __has_declspec_attribute(attribute)
+#else
+    #define JSON_HEDLEY_GNUC_HAS_DECLSPEC_ATTRIBUTE(attribute,major,minor,patch) JSON_HEDLEY_GNUC_VERSION_CHECK(major,minor,patch)
+#endif
+
+#if defined(JSON_HEDLEY_GCC_HAS_DECLSPEC_ATTRIBUTE)
+    #undef JSON_HEDLEY_GCC_HAS_DECLSPEC_ATTRIBUTE
+#endif
+#if defined(__has_declspec_attribute)
+    #define JSON_HEDLEY_GCC_HAS_DECLSPEC_ATTRIBUTE(attribute,major,minor,patch) __has_declspec_attribute(attribute)
+#else
+    #define JSON_HEDLEY_GCC_HAS_DECLSPEC_ATTRIBUTE(attribute,major,minor,patch) JSON_HEDLEY_GCC_VERSION_CHECK(major,minor,patch)
+#endif
+
+#if defined(JSON_HEDLEY_HAS_WARNING)
+    #undef JSON_HEDLEY_HAS_WARNING
+#endif
+#if defined(__has_warning)
+    #define JSON_HEDLEY_HAS_WARNING(warning) __has_warning(warning)
+#else
+    #define JSON_HEDLEY_HAS_WARNING(warning) (0)
+#endif
+
+#if defined(JSON_HEDLEY_GNUC_HAS_WARNING)
+    #undef JSON_HEDLEY_GNUC_HAS_WARNING
+#endif
+#if defined(__has_warning)
+    #define JSON_HEDLEY_GNUC_HAS_WARNING(warning,major,minor,patch) __has_warning(warning)
+#else
+    #define JSON_HEDLEY_GNUC_HAS_WARNING(warning,major,minor,patch) JSON_HEDLEY_GNUC_VERSION_CHECK(major,minor,patch)
+#endif
+
+#if defined(JSON_HEDLEY_GCC_HAS_WARNING)
+    #undef JSON_HEDLEY_GCC_HAS_WARNING
+#endif
+#if defined(__has_warning)
+    #define JSON_HEDLEY_GCC_HAS_WARNING(warning,major,minor,patch) __has_warning(warning)
+#else
+    #define JSON_HEDLEY_GCC_HAS_WARNING(warning,major,minor,patch) JSON_HEDLEY_GCC_VERSION_CHECK(major,minor,patch)
+#endif
+
+/* JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_ is for
+   HEDLEY INTERNAL USE ONLY.  API subject to change without notice. */
+#if defined(JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_)
+    #undef JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_
+#endif
+#if defined(__cplusplus)
+#  if JSON_HEDLEY_HAS_WARNING("-Wc++98-compat")
+#    if JSON_HEDLEY_HAS_WARNING("-Wc++17-extensions")
+#      define JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_(xpr) \
+    JSON_HEDLEY_DIAGNOSTIC_PUSH \
+    _Pragma("clang diagnostic ignored \"-Wc++98-compat\"") \
+    _Pragma("clang diagnostic ignored \"-Wc++17-extensions\"") \
+    xpr \
+    JSON_HEDLEY_DIAGNOSTIC_POP
+#    else
+#      define JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_(xpr) \
+    JSON_HEDLEY_DIAGNOSTIC_PUSH \
+    _Pragma("clang diagnostic ignored \"-Wc++98-compat\"") \
+    xpr \
+    JSON_HEDLEY_DIAGNOSTIC_POP
+#    endif
+#  endif
+#endif
+#if !defined(JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_(x) x
+#endif
+
+#if defined(JSON_HEDLEY_CONST_CAST)
+    #undef JSON_HEDLEY_CONST_CAST
+#endif
+#if defined(__cplusplus)
+#  define JSON_HEDLEY_CONST_CAST(T, expr) (const_cast<T>(expr))
+#elif \
+  JSON_HEDLEY_HAS_WARNING("-Wcast-qual") || \
+  JSON_HEDLEY_GCC_VERSION_CHECK(4,6,0) || \
+  JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0)
+#  define JSON_HEDLEY_CONST_CAST(T, expr) (__extension__ ({ \
+        JSON_HEDLEY_DIAGNOSTIC_PUSH \
+        JSON_HEDLEY_DIAGNOSTIC_DISABLE_CAST_QUAL \
+        ((T) (expr)); \
+        JSON_HEDLEY_DIAGNOSTIC_POP \
+    }))
+#else
+#  define JSON_HEDLEY_CONST_CAST(T, expr) ((T) (expr))
+#endif
+
+#if defined(JSON_HEDLEY_REINTERPRET_CAST)
+    #undef JSON_HEDLEY_REINTERPRET_CAST
+#endif
+#if defined(__cplusplus)
+    #define JSON_HEDLEY_REINTERPRET_CAST(T, expr) (reinterpret_cast<T>(expr))
+#else
+    #define JSON_HEDLEY_REINTERPRET_CAST(T, expr) ((T) (expr))
+#endif
+
+#if defined(JSON_HEDLEY_STATIC_CAST)
+    #undef JSON_HEDLEY_STATIC_CAST
+#endif
+#if defined(__cplusplus)
+    #define JSON_HEDLEY_STATIC_CAST(T, expr) (static_cast<T>(expr))
+#else
+    #define JSON_HEDLEY_STATIC_CAST(T, expr) ((T) (expr))
+#endif
+
+#if defined(JSON_HEDLEY_CPP_CAST)
+    #undef JSON_HEDLEY_CPP_CAST
+#endif
+#if defined(__cplusplus)
+#  if JSON_HEDLEY_HAS_WARNING("-Wold-style-cast")
+#    define JSON_HEDLEY_CPP_CAST(T, expr) \
+    JSON_HEDLEY_DIAGNOSTIC_PUSH \
+    _Pragma("clang diagnostic ignored \"-Wold-style-cast\"") \
+    ((T) (expr)) \
+    JSON_HEDLEY_DIAGNOSTIC_POP
+#  elif JSON_HEDLEY_IAR_VERSION_CHECK(8,3,0)
+#    define JSON_HEDLEY_CPP_CAST(T, expr) \
+    JSON_HEDLEY_DIAGNOSTIC_PUSH \
+    _Pragma("diag_suppress=Pe137") \
+    JSON_HEDLEY_DIAGNOSTIC_POP \
+#  else
+#    define JSON_HEDLEY_CPP_CAST(T, expr) ((T) (expr))
+#  endif
+#else
+#  define JSON_HEDLEY_CPP_CAST(T, expr) (expr)
+#endif
+
+#if \
+    (defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 199901L)) || \
+    defined(__clang__) || \
+    JSON_HEDLEY_GCC_VERSION_CHECK(3,0,0) || \
+    JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0) || \
+    JSON_HEDLEY_IAR_VERSION_CHECK(8,0,0) || \
+    JSON_HEDLEY_PGI_VERSION_CHECK(18,4,0) || \
+    JSON_HEDLEY_ARM_VERSION_CHECK(4,1,0) || \
+    JSON_HEDLEY_TI_VERSION_CHECK(15,12,0) || \
+    JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(4,7,0) || \
+    JSON_HEDLEY_TI_CL430_VERSION_CHECK(2,0,1) || \
+    JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,1,0) || \
+    JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,0,0) || \
+    JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0) || \
+    JSON_HEDLEY_TI_CLPRU_VERSION_CHECK(2,1,0) || \
+    JSON_HEDLEY_CRAY_VERSION_CHECK(5,0,0) || \
+    JSON_HEDLEY_TINYC_VERSION_CHECK(0,9,17) || \
+    JSON_HEDLEY_SUNPRO_VERSION_CHECK(8,0,0) || \
+    (JSON_HEDLEY_IBM_VERSION_CHECK(10,1,0) && defined(__C99_PRAGMA_OPERATOR))
+    #define JSON_HEDLEY_PRAGMA(value) _Pragma(#value)
+#elif JSON_HEDLEY_MSVC_VERSION_CHECK(15,0,0)
+    #define JSON_HEDLEY_PRAGMA(value) __pragma(value)
+#else
+    #define JSON_HEDLEY_PRAGMA(value)
+#endif
+
+#if defined(JSON_HEDLEY_DIAGNOSTIC_PUSH)
+    #undef JSON_HEDLEY_DIAGNOSTIC_PUSH
+#endif
+#if defined(JSON_HEDLEY_DIAGNOSTIC_POP)
+    #undef JSON_HEDLEY_DIAGNOSTIC_POP
+#endif
+#if defined(__clang__)
+    #define JSON_HEDLEY_DIAGNOSTIC_PUSH _Pragma("clang diagnostic push")
+    #define JSON_HEDLEY_DIAGNOSTIC_POP _Pragma("clang diagnostic pop")
+#elif JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_PUSH _Pragma("warning(push)")
+    #define JSON_HEDLEY_DIAGNOSTIC_POP _Pragma("warning(pop)")
+#elif JSON_HEDLEY_GCC_VERSION_CHECK(4,6,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_PUSH _Pragma("GCC diagnostic push")
+    #define JSON_HEDLEY_DIAGNOSTIC_POP _Pragma("GCC diagnostic pop")
+#elif JSON_HEDLEY_MSVC_VERSION_CHECK(15,0,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_PUSH __pragma(warning(push))
+    #define JSON_HEDLEY_DIAGNOSTIC_POP __pragma(warning(pop))
+#elif JSON_HEDLEY_ARM_VERSION_CHECK(5,6,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_PUSH _Pragma("push")
+    #define JSON_HEDLEY_DIAGNOSTIC_POP _Pragma("pop")
+#elif \
+    JSON_HEDLEY_TI_VERSION_CHECK(15,12,0) || \
+    JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(5,2,0) || \
+    JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,4,0) || \
+    JSON_HEDLEY_TI_CL6X_VERSION_CHECK(8,1,0) || \
+    JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0) || \
+    JSON_HEDLEY_TI_CLPRU_VERSION_CHECK(2,1,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_PUSH _Pragma("diag_push")
+    #define JSON_HEDLEY_DIAGNOSTIC_POP _Pragma("diag_pop")
+#elif JSON_HEDLEY_PELLES_VERSION_CHECK(2,90,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_PUSH _Pragma("warning(push)")
+    #define JSON_HEDLEY_DIAGNOSTIC_POP _Pragma("warning(pop)")
+#else
+    #define JSON_HEDLEY_DIAGNOSTIC_PUSH
+    #define JSON_HEDLEY_DIAGNOSTIC_POP
+#endif
+
+#if defined(JSON_HEDLEY_DIAGNOSTIC_DISABLE_DEPRECATED)
+    #undef JSON_HEDLEY_DIAGNOSTIC_DISABLE_DEPRECATED
+#endif
+#if JSON_HEDLEY_HAS_WARNING("-Wdeprecated-declarations")
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_DEPRECATED _Pragma("clang diagnostic ignored \"-Wdeprecated-declarations\"")
+#elif JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_DEPRECATED _Pragma("warning(disable:1478 1786)")
+#elif JSON_HEDLEY_PGI_VERSION_CHECK(17,10,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_DEPRECATED _Pragma("diag_suppress 1215,1444")
+#elif JSON_HEDLEY_GCC_VERSION_CHECK(4,3,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_DEPRECATED _Pragma("GCC diagnostic ignored \"-Wdeprecated-declarations\"")
+#elif JSON_HEDLEY_MSVC_VERSION_CHECK(15,0,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_DEPRECATED __pragma(warning(disable:4996))
+#elif \
+    JSON_HEDLEY_TI_VERSION_CHECK(15,12,0) || \
+    (JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(4,8,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(5,2,0) || \
+    (JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,4,0) || \
+    (JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,3,0) || \
+    (JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,2,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,5,0) || \
+    JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0) || \
+    JSON_HEDLEY_TI_CLPRU_VERSION_CHECK(2,1,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_DEPRECATED _Pragma("diag_suppress 1291,1718")
+#elif JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,13,0) && !defined(__cplusplus)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_DEPRECATED _Pragma("error_messages(off,E_DEPRECATED_ATT,E_DEPRECATED_ATT_MESS)")
+#elif JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,13,0) && defined(__cplusplus)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_DEPRECATED _Pragma("error_messages(off,symdeprecated,symdeprecated2)")
+#elif JSON_HEDLEY_IAR_VERSION_CHECK(8,0,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_DEPRECATED _Pragma("diag_suppress=Pe1444,Pe1215")
+#elif JSON_HEDLEY_PELLES_VERSION_CHECK(2,90,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_DEPRECATED _Pragma("warn(disable:2241)")
+#else
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_DEPRECATED
+#endif
+
+#if defined(JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_PRAGMAS)
+    #undef JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_PRAGMAS
+#endif
+#if JSON_HEDLEY_HAS_WARNING("-Wunknown-pragmas")
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_PRAGMAS _Pragma("clang diagnostic ignored \"-Wunknown-pragmas\"")
+#elif JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_PRAGMAS _Pragma("warning(disable:161)")
+#elif JSON_HEDLEY_PGI_VERSION_CHECK(17,10,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_PRAGMAS _Pragma("diag_suppress 1675")
+#elif JSON_HEDLEY_GCC_VERSION_CHECK(4,3,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_PRAGMAS _Pragma("GCC diagnostic ignored \"-Wunknown-pragmas\"")
+#elif JSON_HEDLEY_MSVC_VERSION_CHECK(15,0,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_PRAGMAS __pragma(warning(disable:4068))
+#elif \
+    JSON_HEDLEY_TI_VERSION_CHECK(16,9,0) || \
+    JSON_HEDLEY_TI_CL6X_VERSION_CHECK(8,0,0) || \
+    JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0) || \
+    JSON_HEDLEY_TI_CLPRU_VERSION_CHECK(2,3,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_PRAGMAS _Pragma("diag_suppress 163")
+#elif JSON_HEDLEY_TI_CL6X_VERSION_CHECK(8,0,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_PRAGMAS _Pragma("diag_suppress 163")
+#elif JSON_HEDLEY_IAR_VERSION_CHECK(8,0,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_PRAGMAS _Pragma("diag_suppress=Pe161")
+#else
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_PRAGMAS
+#endif
+
+#if defined(JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_CPP_ATTRIBUTES)
+    #undef JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_CPP_ATTRIBUTES
+#endif
+#if JSON_HEDLEY_HAS_WARNING("-Wunknown-attributes")
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_CPP_ATTRIBUTES _Pragma("clang diagnostic ignored \"-Wunknown-attributes\"")
+#elif JSON_HEDLEY_GCC_VERSION_CHECK(4,6,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_CPP_ATTRIBUTES _Pragma("GCC diagnostic ignored \"-Wdeprecated-declarations\"")
+#elif JSON_HEDLEY_INTEL_VERSION_CHECK(17,0,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_CPP_ATTRIBUTES _Pragma("warning(disable:1292)")
+#elif JSON_HEDLEY_MSVC_VERSION_CHECK(19,0,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_CPP_ATTRIBUTES __pragma(warning(disable:5030))
+#elif JSON_HEDLEY_PGI_VERSION_CHECK(17,10,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_CPP_ATTRIBUTES _Pragma("diag_suppress 1097")
+#elif JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,14,0) && defined(__cplusplus)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_CPP_ATTRIBUTES _Pragma("error_messages(off,attrskipunsup)")
+#elif \
+    JSON_HEDLEY_TI_VERSION_CHECK(18,1,0) || \
+    JSON_HEDLEY_TI_CL6X_VERSION_CHECK(8,3,0) || \
+    JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_CPP_ATTRIBUTES _Pragma("diag_suppress 1173")
+#elif JSON_HEDLEY_IAR_VERSION_CHECK(8,0,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_CPP_ATTRIBUTES _Pragma("diag_suppress=Pe1097")
+#else
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_CPP_ATTRIBUTES
+#endif
+
+#if defined(JSON_HEDLEY_DIAGNOSTIC_DISABLE_CAST_QUAL)
+    #undef JSON_HEDLEY_DIAGNOSTIC_DISABLE_CAST_QUAL
+#endif
+#if JSON_HEDLEY_HAS_WARNING("-Wcast-qual")
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_CAST_QUAL _Pragma("clang diagnostic ignored \"-Wcast-qual\"")
+#elif JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_CAST_QUAL _Pragma("warning(disable:2203 2331)")
+#elif JSON_HEDLEY_GCC_VERSION_CHECK(3,0,0)
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_CAST_QUAL _Pragma("GCC diagnostic ignored \"-Wcast-qual\"")
+#else
+    #define JSON_HEDLEY_DIAGNOSTIC_DISABLE_CAST_QUAL
+#endif
+
+#if defined(JSON_HEDLEY_DEPRECATED)
+    #undef JSON_HEDLEY_DEPRECATED
+#endif
+#if defined(JSON_HEDLEY_DEPRECATED_FOR)
+    #undef JSON_HEDLEY_DEPRECATED_FOR
+#endif
+#if JSON_HEDLEY_MSVC_VERSION_CHECK(14,0,0)
+    #define JSON_HEDLEY_DEPRECATED(since) __declspec(deprecated("Since " # since))
+    #define JSON_HEDLEY_DEPRECATED_FOR(since, replacement) __declspec(deprecated("Since " #since "; use " #replacement))
+#elif defined(__cplusplus) && (__cplusplus >= 201402L)
+    #define JSON_HEDLEY_DEPRECATED(since) JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_([[deprecated("Since " #since)]])
+    #define JSON_HEDLEY_DEPRECATED_FOR(since, replacement) JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_([[deprecated("Since " #since "; use " #replacement)]])
+#elif \
+    JSON_HEDLEY_HAS_EXTENSION(attribute_deprecated_with_message) || \
+    JSON_HEDLEY_GCC_VERSION_CHECK(4,5,0) || \
+    JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0) || \
+    JSON_HEDLEY_ARM_VERSION_CHECK(5,6,0) || \
+    JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,13,0) || \
+    JSON_HEDLEY_PGI_VERSION_CHECK(17,10,0) || \
+    JSON_HEDLEY_TI_VERSION_CHECK(18,1,0) || \
+    JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(18,1,0) || \
+    JSON_HEDLEY_TI_CL6X_VERSION_CHECK(8,3,0) || \
+    JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0) || \
+    JSON_HEDLEY_TI_CLPRU_VERSION_CHECK(2,3,0)
+    #define JSON_HEDLEY_DEPRECATED(since) __attribute__((__deprecated__("Since " #since)))
+    #define JSON_HEDLEY_DEPRECATED_FOR(since, replacement) __attribute__((__deprecated__("Since " #since "; use " #replacement)))
+#elif \
+    JSON_HEDLEY_HAS_ATTRIBUTE(deprecated) || \
+    JSON_HEDLEY_GCC_VERSION_CHECK(3,1,0) || \
+    JSON_HEDLEY_ARM_VERSION_CHECK(4,1,0) || \
+    JSON_HEDLEY_TI_VERSION_CHECK(15,12,0) || \
+    (JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(4,8,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(5,2,0) || \
+    (JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,4,0) || \
+    (JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,3,0) || \
+    (JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,2,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,5,0) || \
+    JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0) || \
+    JSON_HEDLEY_TI_CLPRU_VERSION_CHECK(2,1,0)
+    #define JSON_HEDLEY_DEPRECATED(since) __attribute__((__deprecated__))
+    #define JSON_HEDLEY_DEPRECATED_FOR(since, replacement) __attribute__((__deprecated__))
+#elif \
+    JSON_HEDLEY_MSVC_VERSION_CHECK(13,10,0) || \
+    JSON_HEDLEY_PELLES_VERSION_CHECK(6,50,0)
+    #define JSON_HEDLEY_DEPRECATED(since) __declspec(deprecated)
+    #define JSON_HEDLEY_DEPRECATED_FOR(since, replacement) __declspec(deprecated)
+#elif JSON_HEDLEY_IAR_VERSION_CHECK(8,0,0)
+    #define JSON_HEDLEY_DEPRECATED(since) _Pragma("deprecated")
+    #define JSON_HEDLEY_DEPRECATED_FOR(since, replacement) _Pragma("deprecated")
+#else
+    #define JSON_HEDLEY_DEPRECATED(since)
+    #define JSON_HEDLEY_DEPRECATED_FOR(since, replacement)
+#endif
+
+#if defined(JSON_HEDLEY_UNAVAILABLE)
+    #undef JSON_HEDLEY_UNAVAILABLE
+#endif
+#if \
+    JSON_HEDLEY_HAS_ATTRIBUTE(warning) || \
+    JSON_HEDLEY_GCC_VERSION_CHECK(4,3,0) || \
+    JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0)
+    #define JSON_HEDLEY_UNAVAILABLE(available_since) __attribute__((__warning__("Not available until " #available_since)))
+#else
+    #define JSON_HEDLEY_UNAVAILABLE(available_since)
+#endif
+
+#if defined(JSON_HEDLEY_WARN_UNUSED_RESULT)
+    #undef JSON_HEDLEY_WARN_UNUSED_RESULT
+#endif
+#if defined(JSON_HEDLEY_WARN_UNUSED_RESULT_MSG)
+    #undef JSON_HEDLEY_WARN_UNUSED_RESULT_MSG
+#endif
+#if (JSON_HEDLEY_HAS_CPP_ATTRIBUTE(nodiscard) >= 201907L)
+    #define JSON_HEDLEY_WARN_UNUSED_RESULT JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_([[nodiscard]])
+    #define JSON_HEDLEY_WARN_UNUSED_RESULT_MSG(msg) JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_([[nodiscard(msg)]])
+#elif JSON_HEDLEY_HAS_CPP_ATTRIBUTE(nodiscard)
+    #define JSON_HEDLEY_WARN_UNUSED_RESULT JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_([[nodiscard]])
+    #define JSON_HEDLEY_WARN_UNUSED_RESULT_MSG(msg) JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_([[nodiscard]])
+#elif \
+    JSON_HEDLEY_HAS_ATTRIBUTE(warn_unused_result) || \
+    JSON_HEDLEY_GCC_VERSION_CHECK(3,4,0) || \
+    JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0) || \
+    JSON_HEDLEY_TI_VERSION_CHECK(15,12,0) || \
+    (JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(4,8,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(5,2,0) || \
+    (JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,4,0) || \
+    (JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,3,0) || \
+    (JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,2,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,5,0) || \
+    JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0) || \
+    JSON_HEDLEY_TI_CLPRU_VERSION_CHECK(2,1,0) || \
+    (JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,15,0) && defined(__cplusplus)) || \
+    JSON_HEDLEY_PGI_VERSION_CHECK(17,10,0)
+    #define JSON_HEDLEY_WARN_UNUSED_RESULT __attribute__((__warn_unused_result__))
+    #define JSON_HEDLEY_WARN_UNUSED_RESULT_MSG(msg) __attribute__((__warn_unused_result__))
+#elif defined(_Check_return_) /* SAL */
+    #define JSON_HEDLEY_WARN_UNUSED_RESULT _Check_return_
+    #define JSON_HEDLEY_WARN_UNUSED_RESULT_MSG(msg) _Check_return_
+#else
+    #define JSON_HEDLEY_WARN_UNUSED_RESULT
+    #define JSON_HEDLEY_WARN_UNUSED_RESULT_MSG(msg)
+#endif
+
+#if defined(JSON_HEDLEY_SENTINEL)
+    #undef JSON_HEDLEY_SENTINEL
+#endif
+#if \
+    JSON_HEDLEY_HAS_ATTRIBUTE(sentinel) || \
+    JSON_HEDLEY_GCC_VERSION_CHECK(4,0,0) || \
+    JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0) || \
+    JSON_HEDLEY_ARM_VERSION_CHECK(5,4,0)
+    #define JSON_HEDLEY_SENTINEL(position) __attribute__((__sentinel__(position)))
+#else
+    #define JSON_HEDLEY_SENTINEL(position)
+#endif
+
+#if defined(JSON_HEDLEY_NO_RETURN)
+    #undef JSON_HEDLEY_NO_RETURN
+#endif
+#if JSON_HEDLEY_IAR_VERSION_CHECK(8,0,0)
+    #define JSON_HEDLEY_NO_RETURN __noreturn
+#elif JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0)
+    #define JSON_HEDLEY_NO_RETURN __attribute__((__noreturn__))
+#elif defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
+    #define JSON_HEDLEY_NO_RETURN _Noreturn
+#elif defined(__cplusplus) && (__cplusplus >= 201103L)
+    #define JSON_HEDLEY_NO_RETURN JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_([[noreturn]])
+#elif \
+    JSON_HEDLEY_HAS_ATTRIBUTE(noreturn) || \
+    JSON_HEDLEY_GCC_VERSION_CHECK(3,2,0) || \
+    JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,11,0) || \
+    JSON_HEDLEY_ARM_VERSION_CHECK(4,1,0) || \
+    JSON_HEDLEY_IBM_VERSION_CHECK(10,1,0) || \
+    JSON_HEDLEY_TI_VERSION_CHECK(15,12,0) || \
+    (JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(4,8,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(5,2,0) || \
+    (JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,4,0) || \
+    (JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,3,0) || \
+    (JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,2,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,5,0) || \
+    JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0) || \
+    JSON_HEDLEY_TI_CLPRU_VERSION_CHECK(2,1,0)
+    #define JSON_HEDLEY_NO_RETURN __attribute__((__noreturn__))
+#elif JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,10,0)
+    #define JSON_HEDLEY_NO_RETURN _Pragma("does_not_return")
+#elif JSON_HEDLEY_MSVC_VERSION_CHECK(13,10,0)
+    #define JSON_HEDLEY_NO_RETURN __declspec(noreturn)
+#elif JSON_HEDLEY_TI_CL6X_VERSION_CHECK(6,0,0) && defined(__cplusplus)
+    #define JSON_HEDLEY_NO_RETURN _Pragma("FUNC_NEVER_RETURNS;")
+#elif JSON_HEDLEY_COMPCERT_VERSION_CHECK(3,2,0)
+    #define JSON_HEDLEY_NO_RETURN __attribute((noreturn))
+#elif JSON_HEDLEY_PELLES_VERSION_CHECK(9,0,0)
+    #define JSON_HEDLEY_NO_RETURN __declspec(noreturn)
+#else
+    #define JSON_HEDLEY_NO_RETURN
+#endif
+
+#if defined(JSON_HEDLEY_NO_ESCAPE)
+    #undef JSON_HEDLEY_NO_ESCAPE
+#endif
+#if JSON_HEDLEY_HAS_ATTRIBUTE(noescape)
+    #define JSON_HEDLEY_NO_ESCAPE __attribute__((__noescape__))
+#else
+    #define JSON_HEDLEY_NO_ESCAPE
+#endif
+
+#if defined(JSON_HEDLEY_UNREACHABLE)
+    #undef JSON_HEDLEY_UNREACHABLE
+#endif
+#if defined(JSON_HEDLEY_UNREACHABLE_RETURN)
+    #undef JSON_HEDLEY_UNREACHABLE_RETURN
+#endif
+#if defined(JSON_HEDLEY_ASSUME)
+    #undef JSON_HEDLEY_ASSUME
+#endif
+#if \
+    JSON_HEDLEY_MSVC_VERSION_CHECK(13,10,0) || \
+    JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0)
+    #define JSON_HEDLEY_ASSUME(expr) __assume(expr)
+#elif JSON_HEDLEY_HAS_BUILTIN(__builtin_assume)
+    #define JSON_HEDLEY_ASSUME(expr) __builtin_assume(expr)
+#elif \
+    JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,2,0) || \
+    JSON_HEDLEY_TI_CL6X_VERSION_CHECK(4,0,0)
+    #if defined(__cplusplus)
+        #define JSON_HEDLEY_ASSUME(expr) std::_nassert(expr)
+    #else
+        #define JSON_HEDLEY_ASSUME(expr) _nassert(expr)
+    #endif
+#endif
+#if \
+    (JSON_HEDLEY_HAS_BUILTIN(__builtin_unreachable) && (!defined(JSON_HEDLEY_ARM_VERSION))) || \
+    JSON_HEDLEY_GCC_VERSION_CHECK(4,5,0) || \
+    JSON_HEDLEY_PGI_VERSION_CHECK(18,10,0) || \
+    JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0) || \
+    JSON_HEDLEY_IBM_VERSION_CHECK(13,1,5)
+    #define JSON_HEDLEY_UNREACHABLE() __builtin_unreachable()
+#elif defined(JSON_HEDLEY_ASSUME)
+    #define JSON_HEDLEY_UNREACHABLE() JSON_HEDLEY_ASSUME(0)
+#endif
+#if !defined(JSON_HEDLEY_ASSUME)
+    #if defined(JSON_HEDLEY_UNREACHABLE)
+        #define JSON_HEDLEY_ASSUME(expr) JSON_HEDLEY_STATIC_CAST(void, ((expr) ? 1 : (JSON_HEDLEY_UNREACHABLE(), 1)))
+    #else
+        #define JSON_HEDLEY_ASSUME(expr) JSON_HEDLEY_STATIC_CAST(void, expr)
+    #endif
+#endif
+#if defined(JSON_HEDLEY_UNREACHABLE)
+    #if  \
+        JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,2,0) || \
+        JSON_HEDLEY_TI_CL6X_VERSION_CHECK(4,0,0)
+        #define JSON_HEDLEY_UNREACHABLE_RETURN(value) return (JSON_HEDLEY_STATIC_CAST(void, JSON_HEDLEY_ASSUME(0)), (value))
+    #else
+        #define JSON_HEDLEY_UNREACHABLE_RETURN(value) JSON_HEDLEY_UNREACHABLE()
+    #endif
+#else
+    #define JSON_HEDLEY_UNREACHABLE_RETURN(value) return (value)
+#endif
+#if !defined(JSON_HEDLEY_UNREACHABLE)
+    #define JSON_HEDLEY_UNREACHABLE() JSON_HEDLEY_ASSUME(0)
+#endif
+
+JSON_HEDLEY_DIAGNOSTIC_PUSH
+#if JSON_HEDLEY_HAS_WARNING("-Wpedantic")
+    #pragma clang diagnostic ignored "-Wpedantic"
+#endif
+#if JSON_HEDLEY_HAS_WARNING("-Wc++98-compat-pedantic") && defined(__cplusplus)
+    #pragma clang diagnostic ignored "-Wc++98-compat-pedantic"
+#endif
+#if JSON_HEDLEY_GCC_HAS_WARNING("-Wvariadic-macros",4,0,0)
+    #if defined(__clang__)
+        #pragma clang diagnostic ignored "-Wvariadic-macros"
+    #elif defined(JSON_HEDLEY_GCC_VERSION)
+        #pragma GCC diagnostic ignored "-Wvariadic-macros"
+    #endif
+#endif
+#if defined(JSON_HEDLEY_NON_NULL)
+    #undef JSON_HEDLEY_NON_NULL
+#endif
+#if \
+    JSON_HEDLEY_HAS_ATTRIBUTE(nonnull) || \
+    JSON_HEDLEY_GCC_VERSION_CHECK(3,3,0) || \
+    JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0) || \
+    JSON_HEDLEY_ARM_VERSION_CHECK(4,1,0)
+    #define JSON_HEDLEY_NON_NULL(...) __attribute__((__nonnull__(__VA_ARGS__)))
+#else
+    #define JSON_HEDLEY_NON_NULL(...)
+#endif
+JSON_HEDLEY_DIAGNOSTIC_POP
+
+#if defined(JSON_HEDLEY_PRINTF_FORMAT)
+    #undef JSON_HEDLEY_PRINTF_FORMAT
+#endif
+#if defined(__MINGW32__) && JSON_HEDLEY_GCC_HAS_ATTRIBUTE(format,4,4,0) && !defined(__USE_MINGW_ANSI_STDIO)
+    #define JSON_HEDLEY_PRINTF_FORMAT(string_idx,first_to_check) __attribute__((__format__(ms_printf, string_idx, first_to_check)))
+#elif defined(__MINGW32__) && JSON_HEDLEY_GCC_HAS_ATTRIBUTE(format,4,4,0) && defined(__USE_MINGW_ANSI_STDIO)
+    #define JSON_HEDLEY_PRINTF_FORMAT(string_idx,first_to_check) __attribute__((__format__(gnu_printf, string_idx, first_to_check)))
+#elif \
+    JSON_HEDLEY_HAS_ATTRIBUTE(format) || \
+    JSON_HEDLEY_GCC_VERSION_CHECK(3,1,0) || \
+    JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0) || \
+    JSON_HEDLEY_ARM_VERSION_CHECK(5,6,0) || \
+    JSON_HEDLEY_IBM_VERSION_CHECK(10,1,0) || \
+    JSON_HEDLEY_TI_VERSION_CHECK(15,12,0) || \
+    (JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(4,8,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(5,2,0) || \
+    (JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,4,0) || \
+    (JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,3,0) || \
+    (JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,2,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,5,0) || \
+    JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0) || \
+    JSON_HEDLEY_TI_CLPRU_VERSION_CHECK(2,1,0)
+    #define JSON_HEDLEY_PRINTF_FORMAT(string_idx,first_to_check) __attribute__((__format__(__printf__, string_idx, first_to_check)))
+#elif JSON_HEDLEY_PELLES_VERSION_CHECK(6,0,0)
+    #define JSON_HEDLEY_PRINTF_FORMAT(string_idx,first_to_check) __declspec(vaformat(printf,string_idx,first_to_check))
+#else
+    #define JSON_HEDLEY_PRINTF_FORMAT(string_idx,first_to_check)
+#endif
+
+#if defined(JSON_HEDLEY_CONSTEXPR)
+    #undef JSON_HEDLEY_CONSTEXPR
+#endif
+#if defined(__cplusplus)
+    #if __cplusplus >= 201103L
+        #define JSON_HEDLEY_CONSTEXPR JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_(constexpr)
+    #endif
+#endif
+#if !defined(JSON_HEDLEY_CONSTEXPR)
+    #define JSON_HEDLEY_CONSTEXPR
+#endif
+
+#if defined(JSON_HEDLEY_PREDICT)
+    #undef JSON_HEDLEY_PREDICT
+#endif
+#if defined(JSON_HEDLEY_LIKELY)
+    #undef JSON_HEDLEY_LIKELY
+#endif
+#if defined(JSON_HEDLEY_UNLIKELY)
+    #undef JSON_HEDLEY_UNLIKELY
+#endif
+#if defined(JSON_HEDLEY_UNPREDICTABLE)
+    #undef JSON_HEDLEY_UNPREDICTABLE
+#endif
+#if JSON_HEDLEY_HAS_BUILTIN(__builtin_unpredictable)
+    #define JSON_HEDLEY_UNPREDICTABLE(expr) __builtin_unpredictable((expr))
+#endif
+#if \
+  JSON_HEDLEY_HAS_BUILTIN(__builtin_expect_with_probability) || \
+  JSON_HEDLEY_GCC_VERSION_CHECK(9,0,0)
+#  define JSON_HEDLEY_PREDICT(expr, value, probability) __builtin_expect_with_probability(  (expr), (value), (probability))
+#  define JSON_HEDLEY_PREDICT_TRUE(expr, probability)   __builtin_expect_with_probability(!!(expr),    1   , (probability))
+#  define JSON_HEDLEY_PREDICT_FALSE(expr, probability)  __builtin_expect_with_probability(!!(expr),    0   , (probability))
+#  define JSON_HEDLEY_LIKELY(expr)                      __builtin_expect                 (!!(expr),    1                  )
+#  define JSON_HEDLEY_UNLIKELY(expr)                    __builtin_expect                 (!!(expr),    0                  )
+#elif \
+  JSON_HEDLEY_HAS_BUILTIN(__builtin_expect) || \
+  JSON_HEDLEY_GCC_VERSION_CHECK(3,0,0) || \
+  JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0) || \
+  (JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,15,0) && defined(__cplusplus)) || \
+  JSON_HEDLEY_ARM_VERSION_CHECK(4,1,0) || \
+  JSON_HEDLEY_IBM_VERSION_CHECK(10,1,0) || \
+  JSON_HEDLEY_TI_VERSION_CHECK(15,12,0) || \
+  JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(4,7,0) || \
+  JSON_HEDLEY_TI_CL430_VERSION_CHECK(3,1,0) || \
+  JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,1,0) || \
+  JSON_HEDLEY_TI_CL6X_VERSION_CHECK(6,1,0) || \
+  JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0) || \
+  JSON_HEDLEY_TI_CLPRU_VERSION_CHECK(2,1,0) || \
+  JSON_HEDLEY_TINYC_VERSION_CHECK(0,9,27) || \
+  JSON_HEDLEY_CRAY_VERSION_CHECK(8,1,0)
+#  define JSON_HEDLEY_PREDICT(expr, expected, probability) \
+    (((probability) >= 0.9) ? __builtin_expect((expr), (expected)) : (JSON_HEDLEY_STATIC_CAST(void, expected), (expr)))
+#  define JSON_HEDLEY_PREDICT_TRUE(expr, probability) \
+    (__extension__ ({ \
+        double hedley_probability_ = (probability); \
+        ((hedley_probability_ >= 0.9) ? __builtin_expect(!!(expr), 1) : ((hedley_probability_ <= 0.1) ? __builtin_expect(!!(expr), 0) : !!(expr))); \
+    }))
+#  define JSON_HEDLEY_PREDICT_FALSE(expr, probability) \
+    (__extension__ ({ \
+        double hedley_probability_ = (probability); \
+        ((hedley_probability_ >= 0.9) ? __builtin_expect(!!(expr), 0) : ((hedley_probability_ <= 0.1) ? __builtin_expect(!!(expr), 1) : !!(expr))); \
+    }))
+#  define JSON_HEDLEY_LIKELY(expr)   __builtin_expect(!!(expr), 1)
+#  define JSON_HEDLEY_UNLIKELY(expr) __builtin_expect(!!(expr), 0)
+#else
+#  define JSON_HEDLEY_PREDICT(expr, expected, probability) (JSON_HEDLEY_STATIC_CAST(void, expected), (expr))
+#  define JSON_HEDLEY_PREDICT_TRUE(expr, probability) (!!(expr))
+#  define JSON_HEDLEY_PREDICT_FALSE(expr, probability) (!!(expr))
+#  define JSON_HEDLEY_LIKELY(expr) (!!(expr))
+#  define JSON_HEDLEY_UNLIKELY(expr) (!!(expr))
+#endif
+#if !defined(JSON_HEDLEY_UNPREDICTABLE)
+    #define JSON_HEDLEY_UNPREDICTABLE(expr) JSON_HEDLEY_PREDICT(expr, 1, 0.5)
+#endif
+
+#if defined(JSON_HEDLEY_MALLOC)
+    #undef JSON_HEDLEY_MALLOC
+#endif
+#if \
+    JSON_HEDLEY_HAS_ATTRIBUTE(malloc) || \
+    JSON_HEDLEY_GCC_VERSION_CHECK(3,1,0) || \
+    JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0) || \
+    JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,11,0) || \
+    JSON_HEDLEY_ARM_VERSION_CHECK(4,1,0) || \
+    JSON_HEDLEY_IBM_VERSION_CHECK(12,1,0) || \
+    JSON_HEDLEY_TI_VERSION_CHECK(15,12,0) || \
+    (JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(4,8,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(5,2,0) || \
+    (JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,4,0) || \
+    (JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,3,0) || \
+    (JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,2,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,5,0) || \
+    JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0) || \
+    JSON_HEDLEY_TI_CLPRU_VERSION_CHECK(2,1,0)
+    #define JSON_HEDLEY_MALLOC __attribute__((__malloc__))
+#elif JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,10,0)
+    #define JSON_HEDLEY_MALLOC _Pragma("returns_new_memory")
+#elif JSON_HEDLEY_MSVC_VERSION_CHECK(14, 0, 0)
+    #define JSON_HEDLEY_MALLOC __declspec(restrict)
+#else
+    #define JSON_HEDLEY_MALLOC
+#endif
+
+#if defined(JSON_HEDLEY_PURE)
+    #undef JSON_HEDLEY_PURE
+#endif
+#if \
+  JSON_HEDLEY_HAS_ATTRIBUTE(pure) || \
+  JSON_HEDLEY_GCC_VERSION_CHECK(2,96,0) || \
+  JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0) || \
+  JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,11,0) || \
+  JSON_HEDLEY_ARM_VERSION_CHECK(4,1,0) || \
+  JSON_HEDLEY_IBM_VERSION_CHECK(10,1,0) || \
+  JSON_HEDLEY_TI_VERSION_CHECK(15,12,0) || \
+  (JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(4,8,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+  JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(5,2,0) || \
+  (JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+  JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,4,0) || \
+  (JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+  JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,3,0) || \
+  (JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,2,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+  JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,5,0) || \
+  JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0) || \
+  JSON_HEDLEY_TI_CLPRU_VERSION_CHECK(2,1,0) || \
+  JSON_HEDLEY_PGI_VERSION_CHECK(17,10,0)
+#  define JSON_HEDLEY_PURE __attribute__((__pure__))
+#elif JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,10,0)
+#  define JSON_HEDLEY_PURE _Pragma("does_not_write_global_data")
+#elif defined(__cplusplus) && \
+    ( \
+      JSON_HEDLEY_TI_CL430_VERSION_CHECK(2,0,1) || \
+      JSON_HEDLEY_TI_CL6X_VERSION_CHECK(4,0,0) || \
+      JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0) \
+    )
+#  define JSON_HEDLEY_PURE _Pragma("FUNC_IS_PURE;")
+#else
+#  define JSON_HEDLEY_PURE
+#endif
+
+#if defined(JSON_HEDLEY_CONST)
+    #undef JSON_HEDLEY_CONST
+#endif
+#if \
+    JSON_HEDLEY_HAS_ATTRIBUTE(const) || \
+    JSON_HEDLEY_GCC_VERSION_CHECK(2,5,0) || \
+    JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0) || \
+    JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,11,0) || \
+    JSON_HEDLEY_ARM_VERSION_CHECK(4,1,0) || \
+    JSON_HEDLEY_IBM_VERSION_CHECK(10,1,0) || \
+    JSON_HEDLEY_TI_VERSION_CHECK(15,12,0) || \
+    (JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(4,8,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(5,2,0) || \
+    (JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,4,0) || \
+    (JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,3,0) || \
+    (JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,2,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,5,0) || \
+    JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0) || \
+    JSON_HEDLEY_TI_CLPRU_VERSION_CHECK(2,1,0) || \
+    JSON_HEDLEY_PGI_VERSION_CHECK(17,10,0)
+    #define JSON_HEDLEY_CONST __attribute__((__const__))
+#elif \
+    JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,10,0)
+    #define JSON_HEDLEY_CONST _Pragma("no_side_effect")
+#else
+    #define JSON_HEDLEY_CONST JSON_HEDLEY_PURE
+#endif
+
+#if defined(JSON_HEDLEY_RESTRICT)
+    #undef JSON_HEDLEY_RESTRICT
+#endif
+#if defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 199901L) && !defined(__cplusplus)
+    #define JSON_HEDLEY_RESTRICT restrict
+#elif \
+    JSON_HEDLEY_GCC_VERSION_CHECK(3,1,0) || \
+    JSON_HEDLEY_MSVC_VERSION_CHECK(14,0,0) || \
+    JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0) || \
+    JSON_HEDLEY_ARM_VERSION_CHECK(4,1,0) || \
+    JSON_HEDLEY_IBM_VERSION_CHECK(10,1,0) || \
+    JSON_HEDLEY_PGI_VERSION_CHECK(17,10,0) || \
+    JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,3,0) || \
+    JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,2,4) || \
+    JSON_HEDLEY_TI_CL6X_VERSION_CHECK(8,1,0) || \
+    JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0) || \
+    (JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,14,0) && defined(__cplusplus)) || \
+    JSON_HEDLEY_IAR_VERSION_CHECK(8,0,0) || \
+    defined(__clang__)
+    #define JSON_HEDLEY_RESTRICT __restrict
+#elif JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,3,0) && !defined(__cplusplus)
+    #define JSON_HEDLEY_RESTRICT _Restrict
+#else
+    #define JSON_HEDLEY_RESTRICT
+#endif
+
+#if defined(JSON_HEDLEY_INLINE)
+    #undef JSON_HEDLEY_INLINE
+#endif
+#if \
+    (defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 199901L)) || \
+    (defined(__cplusplus) && (__cplusplus >= 199711L))
+    #define JSON_HEDLEY_INLINE inline
+#elif \
+    defined(JSON_HEDLEY_GCC_VERSION) || \
+    JSON_HEDLEY_ARM_VERSION_CHECK(6,2,0)
+    #define JSON_HEDLEY_INLINE __inline__
+#elif \
+    JSON_HEDLEY_MSVC_VERSION_CHECK(12,0,0) || \
+    JSON_HEDLEY_ARM_VERSION_CHECK(4,1,0) || \
+    JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(5,1,0) || \
+    JSON_HEDLEY_TI_CL430_VERSION_CHECK(3,1,0) || \
+    JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,2,0) || \
+    JSON_HEDLEY_TI_CL6X_VERSION_CHECK(8,0,0) || \
+    JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0) || \
+    JSON_HEDLEY_TI_CLPRU_VERSION_CHECK(2,1,0)
+    #define JSON_HEDLEY_INLINE __inline
+#else
+    #define JSON_HEDLEY_INLINE
+#endif
+
+#if defined(JSON_HEDLEY_ALWAYS_INLINE)
+    #undef JSON_HEDLEY_ALWAYS_INLINE
+#endif
+#if \
+  JSON_HEDLEY_HAS_ATTRIBUTE(always_inline) || \
+  JSON_HEDLEY_GCC_VERSION_CHECK(4,0,0) || \
+  JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0) || \
+  JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,11,0) || \
+  JSON_HEDLEY_ARM_VERSION_CHECK(4,1,0) || \
+  JSON_HEDLEY_IBM_VERSION_CHECK(10,1,0) || \
+  JSON_HEDLEY_TI_VERSION_CHECK(15,12,0) || \
+  (JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(4,8,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+  JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(5,2,0) || \
+  (JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+  JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,4,0) || \
+  (JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+  JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,3,0) || \
+  (JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,2,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+  JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,5,0) || \
+  JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0) || \
+  JSON_HEDLEY_TI_CLPRU_VERSION_CHECK(2,1,0)
+#  define JSON_HEDLEY_ALWAYS_INLINE __attribute__((__always_inline__)) JSON_HEDLEY_INLINE
+#elif JSON_HEDLEY_MSVC_VERSION_CHECK(12,0,0)
+#  define JSON_HEDLEY_ALWAYS_INLINE __forceinline
+#elif defined(__cplusplus) && \
+    ( \
+      JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(5,2,0) || \
+      JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,3,0) || \
+      JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,4,0) || \
+      JSON_HEDLEY_TI_CL6X_VERSION_CHECK(6,1,0) || \
+      JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0) || \
+      JSON_HEDLEY_TI_CLPRU_VERSION_CHECK(2,1,0) \
+    )
+#  define JSON_HEDLEY_ALWAYS_INLINE _Pragma("FUNC_ALWAYS_INLINE;")
+#elif JSON_HEDLEY_IAR_VERSION_CHECK(8,0,0)
+#  define JSON_HEDLEY_ALWAYS_INLINE _Pragma("inline=forced")
+#else
+#  define JSON_HEDLEY_ALWAYS_INLINE JSON_HEDLEY_INLINE
+#endif
+
+#if defined(JSON_HEDLEY_NEVER_INLINE)
+    #undef JSON_HEDLEY_NEVER_INLINE
+#endif
+#if \
+    JSON_HEDLEY_HAS_ATTRIBUTE(noinline) || \
+    JSON_HEDLEY_GCC_VERSION_CHECK(4,0,0) || \
+    JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0) || \
+    JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,11,0) || \
+    JSON_HEDLEY_ARM_VERSION_CHECK(4,1,0) || \
+    JSON_HEDLEY_IBM_VERSION_CHECK(10,1,0) || \
+    JSON_HEDLEY_TI_VERSION_CHECK(15,12,0) || \
+    (JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(4,8,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_ARMCL_VERSION_CHECK(5,2,0) || \
+    (JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL2000_VERSION_CHECK(6,4,0) || \
+    (JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,0,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL430_VERSION_CHECK(4,3,0) || \
+    (JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,2,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+    JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,5,0) || \
+    JSON_HEDLEY_TI_CL7X_VERSION_CHECK(1,2,0) || \
+    JSON_HEDLEY_TI_CLPRU_VERSION_CHECK(2,1,0)
+    #define JSON_HEDLEY_NEVER_INLINE __attribute__((__noinline__))
+#elif JSON_HEDLEY_MSVC_VERSION_CHECK(13,10,0)
+    #define JSON_HEDLEY_NEVER_INLINE __declspec(noinline)
+#elif JSON_HEDLEY_PGI_VERSION_CHECK(10,2,0)
+    #define JSON_HEDLEY_NEVER_INLINE _Pragma("noinline")
+#elif JSON_HEDLEY_TI_CL6X_VERSION_CHECK(6,0,0) && defined(__cplusplus)
+    #define JSON_HEDLEY_NEVER_INLINE _Pragma("FUNC_CANNOT_INLINE;")
+#elif JSON_HEDLEY_IAR_VERSION_CHECK(8,0,0)
+    #define JSON_HEDLEY_NEVER_INLINE _Pragma("inline=never")
+#elif JSON_HEDLEY_COMPCERT_VERSION_CHECK(3,2,0)
+    #define JSON_HEDLEY_NEVER_INLINE __attribute((noinline))
+#elif JSON_HEDLEY_PELLES_VERSION_CHECK(9,0,0)
+    #define JSON_HEDLEY_NEVER_INLINE __declspec(noinline)
+#else
+    #define JSON_HEDLEY_NEVER_INLINE
+#endif
+
+#if defined(JSON_HEDLEY_PRIVATE)
+    #undef JSON_HEDLEY_PRIVATE
+#endif
+#if defined(JSON_HEDLEY_PUBLIC)
+    #undef JSON_HEDLEY_PUBLIC
+#endif
+#if defined(JSON_HEDLEY_IMPORT)
+    #undef JSON_HEDLEY_IMPORT
+#endif
+#if defined(_WIN32) || defined(__CYGWIN__)
+#  define JSON_HEDLEY_PRIVATE
+#  define JSON_HEDLEY_PUBLIC   __declspec(dllexport)
+#  define JSON_HEDLEY_IMPORT   __declspec(dllimport)
+#else
+#  if \
+    JSON_HEDLEY_HAS_ATTRIBUTE(visibility) || \
+    JSON_HEDLEY_GCC_VERSION_CHECK(3,3,0) || \
+    JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,11,0) || \
+    JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0) || \
+    JSON_HEDLEY_ARM_VERSION_CHECK(4,1,0) || \
+    JSON_HEDLEY_IBM_VERSION_CHECK(13,1,0) || \
+    ( \
+      defined(__TI_EABI__) && \
+      ( \
+        (JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,2,0) && defined(__TI_GNU_ATTRIBUTE_SUPPORT__)) || \
+        JSON_HEDLEY_TI_CL6X_VERSION_CHECK(7,5,0) \
+      ) \
+    )
+#    define JSON_HEDLEY_PRIVATE __attribute__((__visibility__("hidden")))
+#    define JSON_HEDLEY_PUBLIC  __attribute__((__visibility__("default")))
+#  else
+#    define JSON_HEDLEY_PRIVATE
+#    define JSON_HEDLEY_PUBLIC
+#  endif
+#  define JSON_HEDLEY_IMPORT    extern
+#endif
+
+#if defined(JSON_HEDLEY_NO_THROW)
+    #undef JSON_HEDLEY_NO_THROW
+#endif
+#if \
+    JSON_HEDLEY_HAS_ATTRIBUTE(nothrow) || \
+    JSON_HEDLEY_GCC_VERSION_CHECK(3,3,0) || \
+    JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0)
+    #define JSON_HEDLEY_NO_THROW __attribute__((__nothrow__))
+#elif \
+    JSON_HEDLEY_MSVC_VERSION_CHECK(13,1,0) || \
+    JSON_HEDLEY_ARM_VERSION_CHECK(4,1,0)
+    #define JSON_HEDLEY_NO_THROW __declspec(nothrow)
+#else
+    #define JSON_HEDLEY_NO_THROW
+#endif
+
+#if defined(JSON_HEDLEY_FALL_THROUGH)
+    #undef JSON_HEDLEY_FALL_THROUGH
+#endif
+#if \
+    JSON_HEDLEY_HAS_ATTRIBUTE(fallthrough) || \
+    JSON_HEDLEY_GCC_VERSION_CHECK(7,0,0)
+    #define JSON_HEDLEY_FALL_THROUGH __attribute__((__fallthrough__))
+#elif JSON_HEDLEY_HAS_CPP_ATTRIBUTE_NS(clang,fallthrough)
+    #define JSON_HEDLEY_FALL_THROUGH JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_([[clang::fallthrough]])
+#elif JSON_HEDLEY_HAS_CPP_ATTRIBUTE(fallthrough)
+    #define JSON_HEDLEY_FALL_THROUGH JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_([[fallthrough]])
+#elif defined(__fallthrough) /* SAL */
+    #define JSON_HEDLEY_FALL_THROUGH __fallthrough
+#else
+    #define JSON_HEDLEY_FALL_THROUGH
+#endif
+
+#if defined(JSON_HEDLEY_RETURNS_NON_NULL)
+    #undef JSON_HEDLEY_RETURNS_NON_NULL
+#endif
+#if \
+    JSON_HEDLEY_HAS_ATTRIBUTE(returns_nonnull) || \
+    JSON_HEDLEY_GCC_VERSION_CHECK(4,9,0)
+    #define JSON_HEDLEY_RETURNS_NON_NULL __attribute__((__returns_nonnull__))
+#elif defined(_Ret_notnull_) /* SAL */
+    #define JSON_HEDLEY_RETURNS_NON_NULL _Ret_notnull_
+#else
+    #define JSON_HEDLEY_RETURNS_NON_NULL
+#endif
+
+#if defined(JSON_HEDLEY_ARRAY_PARAM)
+    #undef JSON_HEDLEY_ARRAY_PARAM
+#endif
+#if \
+    defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 199901L) && \
+    !defined(__STDC_NO_VLA__) && \
+    !defined(__cplusplus) && \
+    !defined(JSON_HEDLEY_PGI_VERSION) && \
+    !defined(JSON_HEDLEY_TINYC_VERSION)
+    #define JSON_HEDLEY_ARRAY_PARAM(name) (name)
+#else
+    #define JSON_HEDLEY_ARRAY_PARAM(name)
+#endif
+
+#if defined(JSON_HEDLEY_IS_CONSTANT)
+    #undef JSON_HEDLEY_IS_CONSTANT
+#endif
+#if defined(JSON_HEDLEY_REQUIRE_CONSTEXPR)
+    #undef JSON_HEDLEY_REQUIRE_CONSTEXPR
+#endif
+/* JSON_HEDLEY_IS_CONSTEXPR_ is for
+   HEDLEY INTERNAL USE ONLY.  API subject to change without notice. */
+#if defined(JSON_HEDLEY_IS_CONSTEXPR_)
+    #undef JSON_HEDLEY_IS_CONSTEXPR_
+#endif
+#if \
+    JSON_HEDLEY_HAS_BUILTIN(__builtin_constant_p) || \
+    JSON_HEDLEY_GCC_VERSION_CHECK(3,4,0) || \
+    JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0) || \
+    JSON_HEDLEY_TINYC_VERSION_CHECK(0,9,19) || \
+    JSON_HEDLEY_ARM_VERSION_CHECK(4,1,0) || \
+    JSON_HEDLEY_IBM_VERSION_CHECK(13,1,0) || \
+    JSON_HEDLEY_TI_CL6X_VERSION_CHECK(6,1,0) || \
+    (JSON_HEDLEY_SUNPRO_VERSION_CHECK(5,10,0) && !defined(__cplusplus)) || \
+    JSON_HEDLEY_CRAY_VERSION_CHECK(8,1,0)
+    #define JSON_HEDLEY_IS_CONSTANT(expr) __builtin_constant_p(expr)
+#endif
+#if !defined(__cplusplus)
+#  if \
+       JSON_HEDLEY_HAS_BUILTIN(__builtin_types_compatible_p) || \
+       JSON_HEDLEY_GCC_VERSION_CHECK(3,4,0) || \
+       JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0) || \
+       JSON_HEDLEY_IBM_VERSION_CHECK(13,1,0) || \
+       JSON_HEDLEY_CRAY_VERSION_CHECK(8,1,0) || \
+       JSON_HEDLEY_ARM_VERSION_CHECK(5,4,0) || \
+       JSON_HEDLEY_TINYC_VERSION_CHECK(0,9,24)
+#if defined(__INTPTR_TYPE__)
+    #define JSON_HEDLEY_IS_CONSTEXPR_(expr) __builtin_types_compatible_p(__typeof__((1 ? (void*) ((__INTPTR_TYPE__) ((expr) * 0)) : (int*) 0)), int*)
+#else
+    #include <stdint.h>
+    #define JSON_HEDLEY_IS_CONSTEXPR_(expr) __builtin_types_compatible_p(__typeof__((1 ? (void*) ((intptr_t) ((expr) * 0)) : (int*) 0)), int*)
+#endif
+#  elif \
+       ( \
+          defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 201112L) && \
+          !defined(JSON_HEDLEY_SUNPRO_VERSION) && \
+          !defined(JSON_HEDLEY_PGI_VERSION) && \
+          !defined(JSON_HEDLEY_IAR_VERSION)) || \
+       JSON_HEDLEY_HAS_EXTENSION(c_generic_selections) || \
+       JSON_HEDLEY_GCC_VERSION_CHECK(4,9,0) || \
+       JSON_HEDLEY_INTEL_VERSION_CHECK(17,0,0) || \
+       JSON_HEDLEY_IBM_VERSION_CHECK(12,1,0) || \
+       JSON_HEDLEY_ARM_VERSION_CHECK(5,3,0)
+#if defined(__INTPTR_TYPE__)
+    #define JSON_HEDLEY_IS_CONSTEXPR_(expr) _Generic((1 ? (void*) ((__INTPTR_TYPE__) ((expr) * 0)) : (int*) 0), int*: 1, void*: 0)
+#else
+    #include <stdint.h>
+    #define JSON_HEDLEY_IS_CONSTEXPR_(expr) _Generic((1 ? (void*) ((intptr_t) * 0) : (int*) 0), int*: 1, void*: 0)
+#endif
+#  elif \
+       defined(JSON_HEDLEY_GCC_VERSION) || \
+       defined(JSON_HEDLEY_INTEL_VERSION) || \
+       defined(JSON_HEDLEY_TINYC_VERSION) || \
+       defined(JSON_HEDLEY_TI_ARMCL_VERSION) || \
+       JSON_HEDLEY_TI_CL430_VERSION_CHECK(18,12,0) || \
+       defined(JSON_HEDLEY_TI_CL2000_VERSION) || \
+       defined(JSON_HEDLEY_TI_CL6X_VERSION) || \
+       defined(JSON_HEDLEY_TI_CL7X_VERSION) || \
+       defined(JSON_HEDLEY_TI_CLPRU_VERSION) || \
+       defined(__clang__)
+#    define JSON_HEDLEY_IS_CONSTEXPR_(expr) ( \
+        sizeof(void) != \
+        sizeof(*( \
+                  1 ? \
+                  ((void*) ((expr) * 0L) ) : \
+((struct { char v[sizeof(void) * 2]; } *) 1) \
+                ) \
+              ) \
+                                            )
+#  endif
+#endif
+#if defined(JSON_HEDLEY_IS_CONSTEXPR_)
+    #if !defined(JSON_HEDLEY_IS_CONSTANT)
+        #define JSON_HEDLEY_IS_CONSTANT(expr) JSON_HEDLEY_IS_CONSTEXPR_(expr)
+    #endif
+    #define JSON_HEDLEY_REQUIRE_CONSTEXPR(expr) (JSON_HEDLEY_IS_CONSTEXPR_(expr) ? (expr) : (-1))
+#else
+    #if !defined(JSON_HEDLEY_IS_CONSTANT)
+        #define JSON_HEDLEY_IS_CONSTANT(expr) (0)
+    #endif
+    #define JSON_HEDLEY_REQUIRE_CONSTEXPR(expr) (expr)
+#endif
+
+#if defined(JSON_HEDLEY_BEGIN_C_DECLS)
+    #undef JSON_HEDLEY_BEGIN_C_DECLS
+#endif
+#if defined(JSON_HEDLEY_END_C_DECLS)
+    #undef JSON_HEDLEY_END_C_DECLS
+#endif
+#if defined(JSON_HEDLEY_C_DECL)
+    #undef JSON_HEDLEY_C_DECL
+#endif
+#if defined(__cplusplus)
+    #define JSON_HEDLEY_BEGIN_C_DECLS extern "C" {
+    #define JSON_HEDLEY_END_C_DECLS }
+    #define JSON_HEDLEY_C_DECL extern "C"
+#else
+    #define JSON_HEDLEY_BEGIN_C_DECLS
+    #define JSON_HEDLEY_END_C_DECLS
+    #define JSON_HEDLEY_C_DECL
+#endif
+
+#if defined(JSON_HEDLEY_STATIC_ASSERT)
+    #undef JSON_HEDLEY_STATIC_ASSERT
+#endif
+#if \
+  !defined(__cplusplus) && ( \
+      (defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 201112L)) || \
+      JSON_HEDLEY_HAS_FEATURE(c_static_assert) || \
+      JSON_HEDLEY_GCC_VERSION_CHECK(6,0,0) || \
+      JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0) || \
+      defined(_Static_assert) \
+    )
+#  define JSON_HEDLEY_STATIC_ASSERT(expr, message) _Static_assert(expr, message)
+#elif \
+  (defined(__cplusplus) && (__cplusplus >= 201103L)) || \
+  JSON_HEDLEY_MSVC_VERSION_CHECK(16,0,0)
+#  define JSON_HEDLEY_STATIC_ASSERT(expr, message) JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_(static_assert(expr, message))
+#else
+#  define JSON_HEDLEY_STATIC_ASSERT(expr, message)
+#endif
+
+#if defined(JSON_HEDLEY_NULL)
+    #undef JSON_HEDLEY_NULL
+#endif
+#if defined(__cplusplus)
+    #if __cplusplus >= 201103L
+        #define JSON_HEDLEY_NULL JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_(nullptr)
+    #elif defined(NULL)
+        #define JSON_HEDLEY_NULL NULL
+    #else
+        #define JSON_HEDLEY_NULL JSON_HEDLEY_STATIC_CAST(void*, 0)
+    #endif
+#elif defined(NULL)
+    #define JSON_HEDLEY_NULL NULL
+#else
+    #define JSON_HEDLEY_NULL ((void*) 0)
+#endif
+
+#if defined(JSON_HEDLEY_MESSAGE)
+    #undef JSON_HEDLEY_MESSAGE
+#endif
+#if JSON_HEDLEY_HAS_WARNING("-Wunknown-pragmas")
+#  define JSON_HEDLEY_MESSAGE(msg) \
+    JSON_HEDLEY_DIAGNOSTIC_PUSH \
+    JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_PRAGMAS \
+    JSON_HEDLEY_PRAGMA(message msg) \
+    JSON_HEDLEY_DIAGNOSTIC_POP
+#elif \
+  JSON_HEDLEY_GCC_VERSION_CHECK(4,4,0) || \
+  JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0)
+#  define JSON_HEDLEY_MESSAGE(msg) JSON_HEDLEY_PRAGMA(message msg)
+#elif JSON_HEDLEY_CRAY_VERSION_CHECK(5,0,0)
+#  define JSON_HEDLEY_MESSAGE(msg) JSON_HEDLEY_PRAGMA(_CRI message msg)
+#elif JSON_HEDLEY_IAR_VERSION_CHECK(8,0,0)
+#  define JSON_HEDLEY_MESSAGE(msg) JSON_HEDLEY_PRAGMA(message(msg))
+#elif JSON_HEDLEY_PELLES_VERSION_CHECK(2,0,0)
+#  define JSON_HEDLEY_MESSAGE(msg) JSON_HEDLEY_PRAGMA(message(msg))
+#else
+#  define JSON_HEDLEY_MESSAGE(msg)
+#endif
+
+#if defined(JSON_HEDLEY_WARNING)
+    #undef JSON_HEDLEY_WARNING
+#endif
+#if JSON_HEDLEY_HAS_WARNING("-Wunknown-pragmas")
+#  define JSON_HEDLEY_WARNING(msg) \
+    JSON_HEDLEY_DIAGNOSTIC_PUSH \
+    JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_PRAGMAS \
+    JSON_HEDLEY_PRAGMA(clang warning msg) \
+    JSON_HEDLEY_DIAGNOSTIC_POP
+#elif \
+  JSON_HEDLEY_GCC_VERSION_CHECK(4,8,0) || \
+  JSON_HEDLEY_PGI_VERSION_CHECK(18,4,0) || \
+  JSON_HEDLEY_INTEL_VERSION_CHECK(13,0,0)
+#  define JSON_HEDLEY_WARNING(msg) JSON_HEDLEY_PRAGMA(GCC warning msg)
+#elif JSON_HEDLEY_MSVC_VERSION_CHECK(15,0,0)
+#  define JSON_HEDLEY_WARNING(msg) JSON_HEDLEY_PRAGMA(message(msg))
+#else
+#  define JSON_HEDLEY_WARNING(msg) JSON_HEDLEY_MESSAGE(msg)
+#endif
+
+#if defined(JSON_HEDLEY_REQUIRE)
+    #undef JSON_HEDLEY_REQUIRE
+#endif
+#if defined(JSON_HEDLEY_REQUIRE_MSG)
+    #undef JSON_HEDLEY_REQUIRE_MSG
+#endif
+#if JSON_HEDLEY_HAS_ATTRIBUTE(diagnose_if)
+#  if JSON_HEDLEY_HAS_WARNING("-Wgcc-compat")
+#    define JSON_HEDLEY_REQUIRE(expr) \
+    JSON_HEDLEY_DIAGNOSTIC_PUSH \
+    _Pragma("clang diagnostic ignored \"-Wgcc-compat\"") \
+    __attribute__((diagnose_if(!(expr), #expr, "error"))) \
+    JSON_HEDLEY_DIAGNOSTIC_POP
+#    define JSON_HEDLEY_REQUIRE_MSG(expr,msg) \
+    JSON_HEDLEY_DIAGNOSTIC_PUSH \
+    _Pragma("clang diagnostic ignored \"-Wgcc-compat\"") \
+    __attribute__((diagnose_if(!(expr), msg, "error"))) \
+    JSON_HEDLEY_DIAGNOSTIC_POP
+#  else
+#    define JSON_HEDLEY_REQUIRE(expr) __attribute__((diagnose_if(!(expr), #expr, "error")))
+#    define JSON_HEDLEY_REQUIRE_MSG(expr,msg) __attribute__((diagnose_if(!(expr), msg, "error")))
+#  endif
+#else
+#  define JSON_HEDLEY_REQUIRE(expr)
+#  define JSON_HEDLEY_REQUIRE_MSG(expr,msg)
+#endif
+
+#if defined(JSON_HEDLEY_FLAGS)
+    #undef JSON_HEDLEY_FLAGS
+#endif
+#if JSON_HEDLEY_HAS_ATTRIBUTE(flag_enum)
+    #define JSON_HEDLEY_FLAGS __attribute__((__flag_enum__))
+#endif
+
+#if defined(JSON_HEDLEY_FLAGS_CAST)
+    #undef JSON_HEDLEY_FLAGS_CAST
+#endif
+#if JSON_HEDLEY_INTEL_VERSION_CHECK(19,0,0)
+#  define JSON_HEDLEY_FLAGS_CAST(T, expr) (__extension__ ({ \
+        JSON_HEDLEY_DIAGNOSTIC_PUSH \
+        _Pragma("warning(disable:188)") \
+        ((T) (expr)); \
+        JSON_HEDLEY_DIAGNOSTIC_POP \
+    }))
+#else
+#  define JSON_HEDLEY_FLAGS_CAST(T, expr) JSON_HEDLEY_STATIC_CAST(T, expr)
+#endif
+
+#if defined(JSON_HEDLEY_EMPTY_BASES)
+    #undef JSON_HEDLEY_EMPTY_BASES
+#endif
+#if JSON_HEDLEY_MSVC_VERSION_CHECK(19,0,23918) && !JSON_HEDLEY_MSVC_VERSION_CHECK(20,0,0)
+    #define JSON_HEDLEY_EMPTY_BASES __declspec(empty_bases)
+#else
+    #define JSON_HEDLEY_EMPTY_BASES
+#endif
+
+/* Remaining macros are deprecated. */
+
+#if defined(JSON_HEDLEY_GCC_NOT_CLANG_VERSION_CHECK)
+    #undef JSON_HEDLEY_GCC_NOT_CLANG_VERSION_CHECK
+#endif
+#if defined(__clang__)
+    #define JSON_HEDLEY_GCC_NOT_CLANG_VERSION_CHECK(major,minor,patch) (0)
+#else
+    #define JSON_HEDLEY_GCC_NOT_CLANG_VERSION_CHECK(major,minor,patch) JSON_HEDLEY_GCC_VERSION_CHECK(major,minor,patch)
+#endif
+
+#if defined(JSON_HEDLEY_CLANG_HAS_ATTRIBUTE)
+    #undef JSON_HEDLEY_CLANG_HAS_ATTRIBUTE
+#endif
+#define JSON_HEDLEY_CLANG_HAS_ATTRIBUTE(attribute) JSON_HEDLEY_HAS_ATTRIBUTE(attribute)
+
+#if defined(JSON_HEDLEY_CLANG_HAS_CPP_ATTRIBUTE)
+    #undef JSON_HEDLEY_CLANG_HAS_CPP_ATTRIBUTE
+#endif
+#define JSON_HEDLEY_CLANG_HAS_CPP_ATTRIBUTE(attribute) JSON_HEDLEY_HAS_CPP_ATTRIBUTE(attribute)
+
+#if defined(JSON_HEDLEY_CLANG_HAS_BUILTIN)
+    #undef JSON_HEDLEY_CLANG_HAS_BUILTIN
+#endif
+#define JSON_HEDLEY_CLANG_HAS_BUILTIN(builtin) JSON_HEDLEY_HAS_BUILTIN(builtin)
+
+#if defined(JSON_HEDLEY_CLANG_HAS_FEATURE)
+    #undef JSON_HEDLEY_CLANG_HAS_FEATURE
+#endif
+#define JSON_HEDLEY_CLANG_HAS_FEATURE(feature) JSON_HEDLEY_HAS_FEATURE(feature)
+
+#if defined(JSON_HEDLEY_CLANG_HAS_EXTENSION)
+    #undef JSON_HEDLEY_CLANG_HAS_EXTENSION
+#endif
+#define JSON_HEDLEY_CLANG_HAS_EXTENSION(extension) JSON_HEDLEY_HAS_EXTENSION(extension)
+
+#if defined(JSON_HEDLEY_CLANG_HAS_DECLSPEC_DECLSPEC_ATTRIBUTE)
+    #undef JSON_HEDLEY_CLANG_HAS_DECLSPEC_DECLSPEC_ATTRIBUTE
+#endif
+#define JSON_HEDLEY_CLANG_HAS_DECLSPEC_ATTRIBUTE(attribute) JSON_HEDLEY_HAS_DECLSPEC_ATTRIBUTE(attribute)
+
+#if defined(JSON_HEDLEY_CLANG_HAS_WARNING)
+    #undef JSON_HEDLEY_CLANG_HAS_WARNING
+#endif
+#define JSON_HEDLEY_CLANG_HAS_WARNING(warning) JSON_HEDLEY_HAS_WARNING(warning)
+
+#endif /* !defined(JSON_HEDLEY_VERSION) || (JSON_HEDLEY_VERSION < X) */
 
 
 // This file contains all internal macro definitions
@@ -131,6 +2036,18 @@ using json = basic_json<>;
     #endif
 #endif
 
+// C++ language standard detection
+#if (defined(__cplusplus) && __cplusplus >= 202002L) || (defined(_MSVC_LANG) && _MSVC_LANG >= 202002L)
+    #define JSON_HAS_CPP_20
+    #define JSON_HAS_CPP_17
+    #define JSON_HAS_CPP_14
+#elif (defined(__cplusplus) && __cplusplus >= 201703L) || (defined(_HAS_CXX17) && _HAS_CXX17 == 1) // fix for issue #464
+    #define JSON_HAS_CPP_17
+    #define JSON_HAS_CPP_14
+#elif (defined(__cplusplus) && __cplusplus >= 201402L) || (defined(_HAS_CXX14) && _HAS_CXX14 == 1)
+    #define JSON_HAS_CPP_14
+#endif
+
 // disable float-equal warnings on GCC/clang
 #if defined(__clang__) || defined(__GNUC__) || defined(__GNUG__)
     #pragma GCC diagnostic push
@@ -143,15 +2060,6 @@ using json = basic_json<>;
     #pragma GCC diagnostic ignored "-Wdocumentation"
 #endif
 
-// allow for portable deprecation warnings
-#if defined(__clang__) || defined(__GNUC__) || defined(__GNUG__)
-    #define JSON_DEPRECATED __attribute__((deprecated))
-#elif defined(_MSC_VER)
-    #define JSON_DEPRECATED __declspec(deprecated)
-#else
-    #define JSON_DEPRECATED
-#endif
-
 // allow to disable exceptions
 #if (defined(__cpp_exceptions) || defined(__EXCEPTIONS) || defined(_CPPUNWIND)) && !defined(JSON_NOEXCEPTION)
     #define JSON_THROW(exception) throw exception
@@ -159,6 +2067,7 @@ using json = basic_json<>;
     #define JSON_CATCH(exception) catch(exception)
     #define JSON_INTERNAL_CATCH(exception) catch(exception)
 #else
+    #include <cstdlib>
     #define JSON_THROW(exception) std::abort()
     #define JSON_TRY if(true)
     #define JSON_CATCH(exception) if(false)
@@ -185,21 +2094,10 @@ using json = basic_json<>;
     #define JSON_INTERNAL_CATCH JSON_INTERNAL_CATCH_USER
 #endif
 
-// manual branch prediction
-#if defined(__clang__) || defined(__GNUC__) || defined(__GNUG__)
-    #define JSON_LIKELY(x)      __builtin_expect(!!(x), 1)
-    #define JSON_UNLIKELY(x)    __builtin_expect(!!(x), 0)
-#else
-    #define JSON_LIKELY(x)      x
-    #define JSON_UNLIKELY(x)    x
-#endif
-
-// C++ language standard detection
-#if (defined(__cplusplus) && __cplusplus >= 201703L) || (defined(_HAS_CXX17) && _HAS_CXX17 == 1) // fix for issue #464
-    #define JSON_HAS_CPP_17
-    #define JSON_HAS_CPP_14
-#elif (defined(__cplusplus) && __cplusplus >= 201402L) || (defined(_HAS_CXX14) && _HAS_CXX14 == 1)
-    #define JSON_HAS_CPP_14
+// allow to override assert
+#if !defined(JSON_ASSERT)
+    #include <cassert> // assert
+    #define JSON_ASSERT(x) assert(x)
 #endif
 
 /*!
@@ -207,30 +2105,30 @@ using json = basic_json<>;
 @def NLOHMANN_JSON_SERIALIZE_ENUM
 @since version 3.4.0
 */
-#define NLOHMANN_JSON_SERIALIZE_ENUM(ENUM_TYPE, ...)                                           \
-    template<typename BasicJsonType>                                                           \
-    inline void to_json(BasicJsonType& j, const ENUM_TYPE& e)                                  \
-    {                                                                                          \
-        static_assert(std::is_enum<ENUM_TYPE>::value, #ENUM_TYPE " must be an enum!");         \
-        static const std::pair<ENUM_TYPE, BasicJsonType> m[] = __VA_ARGS__;                    \
-        auto it = std::find_if(std::begin(m), std::end(m),                                     \
-                               [e](const std::pair<ENUM_TYPE, BasicJsonType>& ej_pair) -> bool \
-        {                                                                                      \
-            return ej_pair.first == e;                                                         \
-        });                                                                                    \
-        j = ((it != std::end(m)) ? it : std::begin(m))->second;                                \
-    }                                                                                          \
-    template<typename BasicJsonType>                                                           \
-    inline void from_json(const BasicJsonType& j, ENUM_TYPE& e)                                \
-    {                                                                                          \
-        static_assert(std::is_enum<ENUM_TYPE>::value, #ENUM_TYPE " must be an enum!");         \
-        static const std::pair<ENUM_TYPE, BasicJsonType> m[] = __VA_ARGS__;                    \
-        auto it = std::find_if(std::begin(m), std::end(m),                                     \
-                               [j](const std::pair<ENUM_TYPE, BasicJsonType>& ej_pair) -> bool \
-        {                                                                                      \
-            return ej_pair.second == j;                                                        \
-        });                                                                                    \
-        e = ((it != std::end(m)) ? it : std::begin(m))->first;                                 \
+#define NLOHMANN_JSON_SERIALIZE_ENUM(ENUM_TYPE, ...)                                            \
+    template<typename BasicJsonType>                                                            \
+    inline void to_json(BasicJsonType& j, const ENUM_TYPE& e)                                   \
+    {                                                                                           \
+        static_assert(std::is_enum<ENUM_TYPE>::value, #ENUM_TYPE " must be an enum!");          \
+        static const std::pair<ENUM_TYPE, BasicJsonType> m[] = __VA_ARGS__;                     \
+        auto it = std::find_if(std::begin(m), std::end(m),                                      \
+                               [e](const std::pair<ENUM_TYPE, BasicJsonType>& ej_pair) -> bool  \
+        {                                                                                       \
+            return ej_pair.first == e;                                                          \
+        });                                                                                     \
+        j = ((it != std::end(m)) ? it : std::begin(m))->second;                                 \
+    }                                                                                           \
+    template<typename BasicJsonType>                                                            \
+    inline void from_json(const BasicJsonType& j, ENUM_TYPE& e)                                 \
+    {                                                                                           \
+        static_assert(std::is_enum<ENUM_TYPE>::value, #ENUM_TYPE " must be an enum!");          \
+        static const std::pair<ENUM_TYPE, BasicJsonType> m[] = __VA_ARGS__;                     \
+        auto it = std::find_if(std::begin(m), std::end(m),                                      \
+                               [&j](const std::pair<ENUM_TYPE, BasicJsonType>& ej_pair) -> bool \
+        {                                                                                       \
+            return ej_pair.second == j;                                                         \
+        });                                                                                     \
+        e = ((it != std::end(m)) ? it : std::begin(m))->first;                                  \
     }
 
 // Ugly macros to avoid uglier copy-paste when specializing basic_json. They
@@ -242,17 +2140,533 @@ using json = basic_json<>;
              class StringType, class BooleanType, class NumberIntegerType, \
              class NumberUnsignedType, class NumberFloatType,              \
              template<typename> class AllocatorType,                       \
-             template<typename, typename = void> class JSONSerializer>
+             template<typename, typename = void> class JSONSerializer,     \
+             class BinaryType>
 
 #define NLOHMANN_BASIC_JSON_TPL                                            \
     basic_json<ObjectType, ArrayType, StringType, BooleanType,             \
     NumberIntegerType, NumberUnsignedType, NumberFloatType,                \
-    AllocatorType, JSONSerializer>
+    AllocatorType, JSONSerializer, BinaryType>
+
+// Macros to simplify conversion from/to types
+
+#define NLOHMANN_JSON_EXPAND( x ) x
+#define NLOHMANN_JSON_GET_MACRO(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, _17, _18, _19, _20, _21, _22, _23, _24, _25, _26, _27, _28, _29, _30, _31, _32, _33, _34, _35, _36, _37, _38, _39, _40, _41, _42, _43, _44, _45, _46, _47, _48, _49, _50, _51, _52, _53, _54, _55, _56, _57, _58, _59, _60, _61, _62, _63, _64, NAME,...) NAME
+#define NLOHMANN_JSON_PASTE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_GET_MACRO(__VA_ARGS__, \
+        NLOHMANN_JSON_PASTE64, \
+        NLOHMANN_JSON_PASTE63, \
+        NLOHMANN_JSON_PASTE62, \
+        NLOHMANN_JSON_PASTE61, \
+        NLOHMANN_JSON_PASTE60, \
+        NLOHMANN_JSON_PASTE59, \
+        NLOHMANN_JSON_PASTE58, \
+        NLOHMANN_JSON_PASTE57, \
+        NLOHMANN_JSON_PASTE56, \
+        NLOHMANN_JSON_PASTE55, \
+        NLOHMANN_JSON_PASTE54, \
+        NLOHMANN_JSON_PASTE53, \
+        NLOHMANN_JSON_PASTE52, \
+        NLOHMANN_JSON_PASTE51, \
+        NLOHMANN_JSON_PASTE50, \
+        NLOHMANN_JSON_PASTE49, \
+        NLOHMANN_JSON_PASTE48, \
+        NLOHMANN_JSON_PASTE47, \
+        NLOHMANN_JSON_PASTE46, \
+        NLOHMANN_JSON_PASTE45, \
+        NLOHMANN_JSON_PASTE44, \
+        NLOHMANN_JSON_PASTE43, \
+        NLOHMANN_JSON_PASTE42, \
+        NLOHMANN_JSON_PASTE41, \
+        NLOHMANN_JSON_PASTE40, \
+        NLOHMANN_JSON_PASTE39, \
+        NLOHMANN_JSON_PASTE38, \
+        NLOHMANN_JSON_PASTE37, \
+        NLOHMANN_JSON_PASTE36, \
+        NLOHMANN_JSON_PASTE35, \
+        NLOHMANN_JSON_PASTE34, \
+        NLOHMANN_JSON_PASTE33, \
+        NLOHMANN_JSON_PASTE32, \
+        NLOHMANN_JSON_PASTE31, \
+        NLOHMANN_JSON_PASTE30, \
+        NLOHMANN_JSON_PASTE29, \
+        NLOHMANN_JSON_PASTE28, \
+        NLOHMANN_JSON_PASTE27, \
+        NLOHMANN_JSON_PASTE26, \
+        NLOHMANN_JSON_PASTE25, \
+        NLOHMANN_JSON_PASTE24, \
+        NLOHMANN_JSON_PASTE23, \
+        NLOHMANN_JSON_PASTE22, \
+        NLOHMANN_JSON_PASTE21, \
+        NLOHMANN_JSON_PASTE20, \
+        NLOHMANN_JSON_PASTE19, \
+        NLOHMANN_JSON_PASTE18, \
+        NLOHMANN_JSON_PASTE17, \
+        NLOHMANN_JSON_PASTE16, \
+        NLOHMANN_JSON_PASTE15, \
+        NLOHMANN_JSON_PASTE14, \
+        NLOHMANN_JSON_PASTE13, \
+        NLOHMANN_JSON_PASTE12, \
+        NLOHMANN_JSON_PASTE11, \
+        NLOHMANN_JSON_PASTE10, \
+        NLOHMANN_JSON_PASTE9, \
+        NLOHMANN_JSON_PASTE8, \
+        NLOHMANN_JSON_PASTE7, \
+        NLOHMANN_JSON_PASTE6, \
+        NLOHMANN_JSON_PASTE5, \
+        NLOHMANN_JSON_PASTE4, \
+        NLOHMANN_JSON_PASTE3, \
+        NLOHMANN_JSON_PASTE2, \
+        NLOHMANN_JSON_PASTE1)(__VA_ARGS__))
+#define NLOHMANN_JSON_PASTE2(func, v1) func(v1)
+#define NLOHMANN_JSON_PASTE3(func, v1, v2) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE2(func, v2)
+#define NLOHMANN_JSON_PASTE4(func, v1, v2, v3) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE3(func, v2, v3)
+#define NLOHMANN_JSON_PASTE5(func, v1, v2, v3, v4) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE4(func, v2, v3, v4)
+#define NLOHMANN_JSON_PASTE6(func, v1, v2, v3, v4, v5) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE5(func, v2, v3, v4, v5)
+#define NLOHMANN_JSON_PASTE7(func, v1, v2, v3, v4, v5, v6) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE6(func, v2, v3, v4, v5, v6)
+#define NLOHMANN_JSON_PASTE8(func, v1, v2, v3, v4, v5, v6, v7) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE7(func, v2, v3, v4, v5, v6, v7)
+#define NLOHMANN_JSON_PASTE9(func, v1, v2, v3, v4, v5, v6, v7, v8) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE8(func, v2, v3, v4, v5, v6, v7, v8)
+#define NLOHMANN_JSON_PASTE10(func, v1, v2, v3, v4, v5, v6, v7, v8, v9) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE9(func, v2, v3, v4, v5, v6, v7, v8, v9)
+#define NLOHMANN_JSON_PASTE11(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE10(func, v2, v3, v4, v5, v6, v7, v8, v9, v10)
+#define NLOHMANN_JSON_PASTE12(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE11(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11)
+#define NLOHMANN_JSON_PASTE13(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE12(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12)
+#define NLOHMANN_JSON_PASTE14(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE13(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13)
+#define NLOHMANN_JSON_PASTE15(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE14(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14)
+#define NLOHMANN_JSON_PASTE16(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE15(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15)
+#define NLOHMANN_JSON_PASTE17(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE16(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16)
+#define NLOHMANN_JSON_PASTE18(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE17(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17)
+#define NLOHMANN_JSON_PASTE19(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE18(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18)
+#define NLOHMANN_JSON_PASTE20(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE19(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19)
+#define NLOHMANN_JSON_PASTE21(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE20(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20)
+#define NLOHMANN_JSON_PASTE22(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE21(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21)
+#define NLOHMANN_JSON_PASTE23(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE22(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22)
+#define NLOHMANN_JSON_PASTE24(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE23(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23)
+#define NLOHMANN_JSON_PASTE25(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE24(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24)
+#define NLOHMANN_JSON_PASTE26(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE25(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25)
+#define NLOHMANN_JSON_PASTE27(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE26(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26)
+#define NLOHMANN_JSON_PASTE28(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE27(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27)
+#define NLOHMANN_JSON_PASTE29(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE28(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28)
+#define NLOHMANN_JSON_PASTE30(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE29(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29)
+#define NLOHMANN_JSON_PASTE31(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE30(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30)
+#define NLOHMANN_JSON_PASTE32(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE31(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31)
+#define NLOHMANN_JSON_PASTE33(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE32(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32)
+#define NLOHMANN_JSON_PASTE34(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE33(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33)
+#define NLOHMANN_JSON_PASTE35(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE34(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34)
+#define NLOHMANN_JSON_PASTE36(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE35(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35)
+#define NLOHMANN_JSON_PASTE37(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE36(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36)
+#define NLOHMANN_JSON_PASTE38(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE37(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37)
+#define NLOHMANN_JSON_PASTE39(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE38(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38)
+#define NLOHMANN_JSON_PASTE40(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE39(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39)
+#define NLOHMANN_JSON_PASTE41(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE40(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40)
+#define NLOHMANN_JSON_PASTE42(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE41(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41)
+#define NLOHMANN_JSON_PASTE43(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE42(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42)
+#define NLOHMANN_JSON_PASTE44(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE43(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43)
+#define NLOHMANN_JSON_PASTE45(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE44(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44)
+#define NLOHMANN_JSON_PASTE46(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE45(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45)
+#define NLOHMANN_JSON_PASTE47(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE46(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46)
+#define NLOHMANN_JSON_PASTE48(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE47(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47)
+#define NLOHMANN_JSON_PASTE49(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE48(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48)
+#define NLOHMANN_JSON_PASTE50(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE49(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49)
+#define NLOHMANN_JSON_PASTE51(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE50(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50)
+#define NLOHMANN_JSON_PASTE52(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE51(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51)
+#define NLOHMANN_JSON_PASTE53(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE52(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52)
+#define NLOHMANN_JSON_PASTE54(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE53(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53)
+#define NLOHMANN_JSON_PASTE55(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE54(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54)
+#define NLOHMANN_JSON_PASTE56(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54, v55) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE55(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54, v55)
+#define NLOHMANN_JSON_PASTE57(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54, v55, v56) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE56(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54, v55, v56)
+#define NLOHMANN_JSON_PASTE58(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54, v55, v56, v57) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE57(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54, v55, v56, v57)
+#define NLOHMANN_JSON_PASTE59(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54, v55, v56, v57, v58) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE58(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54, v55, v56, v57, v58)
+#define NLOHMANN_JSON_PASTE60(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54, v55, v56, v57, v58, v59) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE59(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54, v55, v56, v57, v58, v59)
+#define NLOHMANN_JSON_PASTE61(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54, v55, v56, v57, v58, v59, v60) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE60(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54, v55, v56, v57, v58, v59, v60)
+#define NLOHMANN_JSON_PASTE62(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54, v55, v56, v57, v58, v59, v60, v61) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE61(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54, v55, v56, v57, v58, v59, v60, v61)
+#define NLOHMANN_JSON_PASTE63(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54, v55, v56, v57, v58, v59, v60, v61, v62) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE62(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54, v55, v56, v57, v58, v59, v60, v61, v62)
+#define NLOHMANN_JSON_PASTE64(func, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54, v55, v56, v57, v58, v59, v60, v61, v62, v63) NLOHMANN_JSON_PASTE2(func, v1) NLOHMANN_JSON_PASTE63(func, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23, v24, v25, v26, v27, v28, v29, v30, v31, v32, v33, v34, v35, v36, v37, v38, v39, v40, v41, v42, v43, v44, v45, v46, v47, v48, v49, v50, v51, v52, v53, v54, v55, v56, v57, v58, v59, v60, v61, v62, v63)
+
+#define NLOHMANN_JSON_TO(v1) nlohmann_json_j[#v1] = nlohmann_json_t.v1;
+#define NLOHMANN_JSON_FROM(v1) nlohmann_json_j.at(#v1).get_to(nlohmann_json_t.v1);
+
+/*!
+@brief macro
+@def NLOHMANN_DEFINE_TYPE_INTRUSIVE
+@since version 3.9.0
+*/
+#define NLOHMANN_DEFINE_TYPE_INTRUSIVE(Type, ...)  \
+    friend void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
+    friend void from_json(const nlohmann::json& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) }
+
+/*!
+@brief macro
+@def NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE
+@since version 3.9.0
+*/
+#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(Type, ...)  \
+    inline void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
+    inline void from_json(const nlohmann::json& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) }
+
+#ifndef JSON_USE_IMPLICIT_CONVERSIONS
+    #define JSON_USE_IMPLICIT_CONVERSIONS 1
+#endif
+
+#if JSON_USE_IMPLICIT_CONVERSIONS
+    #define JSON_EXPLICIT
+#else
+    #define JSON_EXPLICIT explicit
+#endif
+
+
+namespace nlohmann
+{
+namespace detail
+{
+////////////////
+// exceptions //
+////////////////
+
+/*!
+@brief general exception of the @ref basic_json class
+
+This class is an extension of `std::exception` objects with a member @a id for
+exception ids. It is used as the base class for all exceptions thrown by the
+@ref basic_json class. This class can hence be used as "wildcard" to catch
+exceptions.
+
+Subclasses:
+- @ref parse_error for exceptions indicating a parse error
+- @ref invalid_iterator for exceptions indicating errors with iterators
+- @ref type_error for exceptions indicating executing a member function with
+                  a wrong type
+- @ref out_of_range for exceptions indicating access out of the defined range
+- @ref other_error for exceptions indicating other library errors
+
+@internal
+@note To have nothrow-copy-constructible exceptions, we internally use
+      `std::runtime_error` which can cope with arbitrary-length error messages.
+      Intermediate strings are built with static functions and then passed to
+      the actual constructor.
+@endinternal
+
+@liveexample{The following code shows how arbitrary library exceptions can be
+caught.,exception}
+
+@since version 3.0.0
+*/
+class exception : public std::exception
+{
+  public:
+    /// returns the explanatory string
+    JSON_HEDLEY_RETURNS_NON_NULL
+    const char* what() const noexcept override
+    {
+        return m.what();
+    }
+
+    /// the id of the exception
+    const int id;
+
+  protected:
+    JSON_HEDLEY_NON_NULL(3)
+    exception(int id_, const char* what_arg) : id(id_), m(what_arg) {}
+
+    static std::string name(const std::string& ename, int id_)
+    {
+        return "[json.exception." + ename + "." + std::to_string(id_) + "] ";
+    }
+
+  private:
+    /// an exception object as storage for error messages
+    std::runtime_error m;
+};
+
+/*!
+@brief exception indicating a parse error
+
+This exception is thrown by the library when a parse error occurs. Parse errors
+can occur during the deserialization of JSON text, CBOR, MessagePack, as well
+as when using JSON Patch.
+
+Member @a byte holds the byte index of the last read character in the input
+file.
+
+Exceptions have ids 1xx.
+
+name / id                      | example message | description
+------------------------------ | --------------- | -------------------------
+json.exception.parse_error.101 | parse error at 2: unexpected end of input; expected string literal | This error indicates a syntax error while deserializing a JSON text. The error message describes that an unexpected token (character) was encountered, and the member @a byte indicates the error position.
+json.exception.parse_error.102 | parse error at 14: missing or wrong low surrogate | JSON uses the `\uxxxx` format to describe Unicode characters. Code points above above 0xFFFF are split into two `\uxxxx` entries ("surrogate pairs"). This error indicates that the surrogate pair is incomplete or contains an invalid code point.
+json.exception.parse_error.103 | parse error: code points above 0x10FFFF are invalid | Unicode supports code points up to 0x10FFFF. Code points above 0x10FFFF are invalid.
+json.exception.parse_error.104 | parse error: JSON patch must be an array of objects | [RFC 6902](https://tools.ietf.org/html/rfc6902) requires a JSON Patch document to be a JSON document that represents an array of objects.
+json.exception.parse_error.105 | parse error: operation must have string member 'op' | An operation of a JSON Patch document must contain exactly one "op" member, whose value indicates the operation to perform. Its value must be one of "add", "remove", "replace", "move", "copy", or "test"; other values are errors.
+json.exception.parse_error.106 | parse error: array index '01' must not begin with '0' | An array index in a JSON Pointer ([RFC 6901](https://tools.ietf.org/html/rfc6901)) may be `0` or any number without a leading `0`.
+json.exception.parse_error.107 | parse error: JSON pointer must be empty or begin with '/' - was: 'foo' | A JSON Pointer must be a Unicode string containing a sequence of zero or more reference tokens, each prefixed by a `/` character.
+json.exception.parse_error.108 | parse error: escape character '~' must be followed with '0' or '1' | In a JSON Pointer, only `~0` and `~1` are valid escape sequences.
+json.exception.parse_error.109 | parse error: array index 'one' is not a number | A JSON Pointer array index must be a number.
+json.exception.parse_error.110 | parse error at 1: cannot read 2 bytes from vector | When parsing CBOR or MessagePack, the byte vector ends before the complete value has been read.
+json.exception.parse_error.112 | parse error at 1: error reading CBOR; last byte: 0xF8 | Not all types of CBOR or MessagePack are supported. This exception occurs if an unsupported byte was read.
+json.exception.parse_error.113 | parse error at 2: expected a CBOR string; last byte: 0x98 | While parsing a map key, a value that is not a string has been read.
+json.exception.parse_error.114 | parse error: Unsupported BSON record type 0x0F | The parsing of the corresponding BSON record type is not implemented (yet).
+json.exception.parse_error.115 | parse error at byte 5: syntax error while parsing UBJSON high-precision number: invalid number text: 1A | A UBJSON high-precision number could not be parsed.
+
+@note For an input with n bytes, 1 is the index of the first character and n+1
+      is the index of the terminating null byte or the end of file. This also
+      holds true when reading a byte vector (CBOR or MessagePack).
+
+@liveexample{The following code shows how a `parse_error` exception can be
+caught.,parse_error}
+
+@sa - @ref exception for the base class of the library exceptions
+@sa - @ref invalid_iterator for exceptions indicating errors with iterators
+@sa - @ref type_error for exceptions indicating executing a member function with
+                    a wrong type
+@sa - @ref out_of_range for exceptions indicating access out of the defined range
+@sa - @ref other_error for exceptions indicating other library errors
+
+@since version 3.0.0
+*/
+class parse_error : public exception
+{
+  public:
+    /*!
+    @brief create a parse error exception
+    @param[in] id_       the id of the exception
+    @param[in] pos       the position where the error occurred (or with
+                         chars_read_total=0 if the position cannot be
+                         determined)
+    @param[in] what_arg  the explanatory string
+    @return parse_error object
+    */
+    static parse_error create(int id_, const position_t& pos, const std::string& what_arg)
+    {
+        std::string w = exception::name("parse_error", id_) + "parse error" +
+                        position_string(pos) + ": " + what_arg;
+        return parse_error(id_, pos.chars_read_total, w.c_str());
+    }
+
+    static parse_error create(int id_, std::size_t byte_, const std::string& what_arg)
+    {
+        std::string w = exception::name("parse_error", id_) + "parse error" +
+                        (byte_ != 0 ? (" at byte " + std::to_string(byte_)) : "") +
+                        ": " + what_arg;
+        return parse_error(id_, byte_, w.c_str());
+    }
+
+    /*!
+    @brief byte index of the parse error
+
+    The byte index of the last read character in the input file.
+
+    @note For an input with n bytes, 1 is the index of the first character and
+          n+1 is the index of the terminating null byte or the end of file.
+          This also holds true when reading a byte vector (CBOR or MessagePack).
+    */
+    const std::size_t byte;
+
+  private:
+    parse_error(int id_, std::size_t byte_, const char* what_arg)
+        : exception(id_, what_arg), byte(byte_) {}
+
+    static std::string position_string(const position_t& pos)
+    {
+        return " at line " + std::to_string(pos.lines_read + 1) +
+               ", column " + std::to_string(pos.chars_read_current_line);
+    }
+};
+
+/*!
+@brief exception indicating errors with iterators
+
+This exception is thrown if iterators passed to a library function do not match
+the expected semantics.
+
+Exceptions have ids 2xx.
+
+name / id                           | example message | description
+----------------------------------- | --------------- | -------------------------
+json.exception.invalid_iterator.201 | iterators are not compatible | The iterators passed to constructor @ref basic_json(InputIT first, InputIT last) are not compatible, meaning they do not belong to the same container. Therefore, the range (@a first, @a last) is invalid.
+json.exception.invalid_iterator.202 | iterator does not fit current value | In an erase or insert function, the passed iterator @a pos does not belong to the JSON value for which the function was called. It hence does not define a valid position for the deletion/insertion.
+json.exception.invalid_iterator.203 | iterators do not fit current value | Either iterator passed to function @ref erase(IteratorType first, IteratorType last) does not belong to the JSON value from which values shall be erased. It hence does not define a valid range to delete values from.
+json.exception.invalid_iterator.204 | iterators out of range | When an iterator range for a primitive type (number, boolean, or string) is passed to a constructor or an erase function, this range has to be exactly (@ref begin(), @ref end()), because this is the only way the single stored value is expressed. All other ranges are invalid.
+json.exception.invalid_iterator.205 | iterator out of range | When an iterator for a primitive type (number, boolean, or string) is passed to an erase function, the iterator has to be the @ref begin() iterator, because it is the only way to address the stored value. All other iterators are invalid.
+json.exception.invalid_iterator.206 | cannot construct with iterators from null | The iterators passed to constructor @ref basic_json(InputIT first, InputIT last) belong to a JSON null value and hence to not define a valid range.
+json.exception.invalid_iterator.207 | cannot use key() for non-object iterators | The key() member function can only be used on iterators belonging to a JSON object, because other types do not have a concept of a key.
+json.exception.invalid_iterator.208 | cannot use operator[] for object iterators | The operator[] to specify a concrete offset cannot be used on iterators belonging to a JSON object, because JSON objects are unordered.
+json.exception.invalid_iterator.209 | cannot use offsets with object iterators | The offset operators (+, -, +=, -=) cannot be used on iterators belonging to a JSON object, because JSON objects are unordered.
+json.exception.invalid_iterator.210 | iterators do not fit | The iterator range passed to the insert function are not compatible, meaning they do not belong to the same container. Therefore, the range (@a first, @a last) is invalid.
+json.exception.invalid_iterator.211 | passed iterators may not belong to container | The iterator range passed to the insert function must not be a subrange of the container to insert to.
+json.exception.invalid_iterator.212 | cannot compare iterators of different containers | When two iterators are compared, they must belong to the same container.
+json.exception.invalid_iterator.213 | cannot compare order of object iterators | The order of object iterators cannot be compared, because JSON objects are unordered.
+json.exception.invalid_iterator.214 | cannot get value | Cannot get value for iterator: Either the iterator belongs to a null value or it is an iterator to a primitive type (number, boolean, or string), but the iterator is different to @ref begin().
+
+@liveexample{The following code shows how an `invalid_iterator` exception can be
+caught.,invalid_iterator}
+
+@sa - @ref exception for the base class of the library exceptions
+@sa - @ref parse_error for exceptions indicating a parse error
+@sa - @ref type_error for exceptions indicating executing a member function with
+                    a wrong type
+@sa - @ref out_of_range for exceptions indicating access out of the defined range
+@sa - @ref other_error for exceptions indicating other library errors
+
+@since version 3.0.0
+*/
+class invalid_iterator : public exception
+{
+  public:
+    static invalid_iterator create(int id_, const std::string& what_arg)
+    {
+        std::string w = exception::name("invalid_iterator", id_) + what_arg;
+        return invalid_iterator(id_, w.c_str());
+    }
+
+  private:
+    JSON_HEDLEY_NON_NULL(3)
+    invalid_iterator(int id_, const char* what_arg)
+        : exception(id_, what_arg) {}
+};
+
+/*!
+@brief exception indicating executing a member function with a wrong type
+
+This exception is thrown in case of a type error; that is, a library function is
+executed on a JSON value whose type does not match the expected semantics.
+
+Exceptions have ids 3xx.
+
+name / id                     | example message | description
+----------------------------- | --------------- | -------------------------
+json.exception.type_error.301 | cannot create object from initializer list | To create an object from an initializer list, the initializer list must consist only of a list of pairs whose first element is a string. When this constraint is violated, an array is created instead.
+json.exception.type_error.302 | type must be object, but is array | During implicit or explicit value conversion, the JSON type must be compatible to the target type. For instance, a JSON string can only be converted into string types, but not into numbers or boolean types.
+json.exception.type_error.303 | incompatible ReferenceType for get_ref, actual type is object | To retrieve a reference to a value stored in a @ref basic_json object with @ref get_ref, the type of the reference must match the value type. For instance, for a JSON array, the @a ReferenceType must be @ref array_t &.
+json.exception.type_error.304 | cannot use at() with string | The @ref at() member functions can only be executed for certain JSON types.
+json.exception.type_error.305 | cannot use operator[] with string | The @ref operator[] member functions can only be executed for certain JSON types.
+json.exception.type_error.306 | cannot use value() with string | The @ref value() member functions can only be executed for certain JSON types.
+json.exception.type_error.307 | cannot use erase() with string | The @ref erase() member functions can only be executed for certain JSON types.
+json.exception.type_error.308 | cannot use push_back() with string | The @ref push_back() and @ref operator+= member functions can only be executed for certain JSON types.
+json.exception.type_error.309 | cannot use insert() with | The @ref insert() member functions can only be executed for certain JSON types.
+json.exception.type_error.310 | cannot use swap() with number | The @ref swap() member functions can only be executed for certain JSON types.
+json.exception.type_error.311 | cannot use emplace_back() with string | The @ref emplace_back() member function can only be executed for certain JSON types.
+json.exception.type_error.312 | cannot use update() with string | The @ref update() member functions can only be executed for certain JSON types.
+json.exception.type_error.313 | invalid value to unflatten | The @ref unflatten function converts an object whose keys are JSON Pointers back into an arbitrary nested JSON value. The JSON Pointers must not overlap, because then the resulting value would not be well defined.
+json.exception.type_error.314 | only objects can be unflattened | The @ref unflatten function only works for an object whose keys are JSON Pointers.
+json.exception.type_error.315 | values in object must be primitive | The @ref unflatten function only works for an object whose keys are JSON Pointers and whose values are primitive.
+json.exception.type_error.316 | invalid UTF-8 byte at index 10: 0x7E | The @ref dump function only works with UTF-8 encoded strings; that is, if you assign a `std::string` to a JSON value, make sure it is UTF-8 encoded. |
+json.exception.type_error.317 | JSON value cannot be serialized to requested format | The dynamic type of the object cannot be represented in the requested serialization format (e.g. a raw `true` or `null` JSON object cannot be serialized to BSON) |
+
+@liveexample{The following code shows how a `type_error` exception can be
+caught.,type_error}
+
+@sa - @ref exception for the base class of the library exceptions
+@sa - @ref parse_error for exceptions indicating a parse error
+@sa - @ref invalid_iterator for exceptions indicating errors with iterators
+@sa - @ref out_of_range for exceptions indicating access out of the defined range
+@sa - @ref other_error for exceptions indicating other library errors
+
+@since version 3.0.0
+*/
+class type_error : public exception
+{
+  public:
+    static type_error create(int id_, const std::string& what_arg)
+    {
+        std::string w = exception::name("type_error", id_) + what_arg;
+        return type_error(id_, w.c_str());
+    }
+
+  private:
+    JSON_HEDLEY_NON_NULL(3)
+    type_error(int id_, const char* what_arg) : exception(id_, what_arg) {}
+};
+
+/*!
+@brief exception indicating access out of the defined range
+
+This exception is thrown in case a library function is called on an input
+parameter that exceeds the expected range, for instance in case of array
+indices or nonexisting object keys.
+
+Exceptions have ids 4xx.
+
+name / id                       | example message | description
+------------------------------- | --------------- | -------------------------
+json.exception.out_of_range.401 | array index 3 is out of range | The provided array index @a i is larger than @a size-1.
+json.exception.out_of_range.402 | array index '-' (3) is out of range | The special array index `-` in a JSON Pointer never describes a valid element of the array, but the index past the end. That is, it can only be used to add elements at this position, but not to read it.
+json.exception.out_of_range.403 | key 'foo' not found | The provided key was not found in the JSON object.
+json.exception.out_of_range.404 | unresolved reference token 'foo' | A reference token in a JSON Pointer could not be resolved.
+json.exception.out_of_range.405 | JSON pointer has no parent | The JSON Patch operations 'remove' and 'add' can not be applied to the root element of the JSON value.
+json.exception.out_of_range.406 | number overflow parsing '10E1000' | A parsed number could not be stored as without changing it to NaN or INF.
+json.exception.out_of_range.407 | number overflow serializing '9223372036854775808' | UBJSON and BSON only support integer numbers up to 9223372036854775807. (until version 3.8.0) |
+json.exception.out_of_range.408 | excessive array size: 8658170730974374167 | The size (following `#`) of an UBJSON array or object exceeds the maximal capacity. |
+json.exception.out_of_range.409 | BSON key cannot contain code point U+0000 (at byte 2) | Key identifiers to be serialized to BSON cannot contain code point U+0000, since the key is stored as zero-terminated c-string |
+
+@liveexample{The following code shows how an `out_of_range` exception can be
+caught.,out_of_range}
+
+@sa - @ref exception for the base class of the library exceptions
+@sa - @ref parse_error for exceptions indicating a parse error
+@sa - @ref invalid_iterator for exceptions indicating errors with iterators
+@sa - @ref type_error for exceptions indicating executing a member function with
+                    a wrong type
+@sa - @ref other_error for exceptions indicating other library errors
+
+@since version 3.0.0
+*/
+class out_of_range : public exception
+{
+  public:
+    static out_of_range create(int id_, const std::string& what_arg)
+    {
+        std::string w = exception::name("out_of_range", id_) + what_arg;
+        return out_of_range(id_, w.c_str());
+    }
+
+  private:
+    JSON_HEDLEY_NON_NULL(3)
+    out_of_range(int id_, const char* what_arg) : exception(id_, what_arg) {}
+};
+
+/*!
+@brief exception indicating other library errors
+
+This exception is thrown in case of errors that cannot be classified with the
+other exception types.
+
+Exceptions have ids 5xx.
+
+name / id                      | example message | description
+------------------------------ | --------------- | -------------------------
+json.exception.other_error.501 | unsuccessful: {"op":"test","path":"/baz", "value":"bar"} | A JSON Patch operation 'test' failed. The unsuccessful operation is also printed.
+
+@sa - @ref exception for the base class of the library exceptions
+@sa - @ref parse_error for exceptions indicating a parse error
+@sa - @ref invalid_iterator for exceptions indicating errors with iterators
+@sa - @ref type_error for exceptions indicating executing a member function with
+                    a wrong type
+@sa - @ref out_of_range for exceptions indicating access out of the defined range
+
+@liveexample{The following code shows how an `other_error` exception can be
+caught.,other_error}
+
+@since version 3.0.0
+*/
+class other_error : public exception
+{
+  public:
+    static other_error create(int id_, const std::string& what_arg)
+    {
+        std::string w = exception::name("other_error", id_) + what_arg;
+        return other_error(id_, w.c_str());
+    }
+
+  private:
+    JSON_HEDLEY_NON_NULL(3)
+    other_error(int id_, const char* what_arg) : exception(id_, what_arg) {}
+};
+}  // namespace detail
+}  // namespace nlohmann
+
+// #include <nlohmann/detail/macro_scope.hpp>
 
 // #include <nlohmann/detail/meta/cpp_future.hpp>
 
 
-#include <ciso646> // not
 #include <cstddef> // size_t
 #include <type_traits> // conditional, enable_if, false_type, integral_constant, is_constructible, is_integral, is_same, remove_cv, remove_reference, true_type
 
@@ -317,13 +2731,10 @@ constexpr T static_const<T>::value;
 // #include <nlohmann/detail/meta/type_traits.hpp>
 
 
-#include <ciso646> // not
 #include <limits> // numeric_limits
 #include <type_traits> // false_type, is_constructible, is_integral, is_same, true_type
 #include <utility> // declval
 
-// #include <nlohmann/json_fwd.hpp>
-
 // #include <nlohmann/detail/iterators/iterator_traits.hpp>
 
 
@@ -336,11 +2747,11 @@ namespace nlohmann
 {
 namespace detail
 {
-template <typename ...Ts> struct make_void
+template<typename ...Ts> struct make_void
 {
     using type = void;
 };
-template <typename ...Ts> using void_t = typename make_void<Ts...>::type;
+template<typename ...Ts> using void_t = typename make_void<Ts...>::type;
 } // namespace detail
 }  // namespace nlohmann
 
@@ -351,10 +2762,10 @@ namespace nlohmann
 {
 namespace detail
 {
-template <typename It, typename = void>
+template<typename It, typename = void>
 struct iterator_types {};
 
-template <typename It>
+template<typename It>
 struct iterator_types <
     It,
     void_t<typename It::difference_type, typename It::value_type, typename It::pointer,
@@ -369,18 +2780,18 @@ struct iterator_types <
 
 // This is required as some compilers implement std::iterator_traits in a way that
 // doesn't work with SFINAE. See https://github.com/nlohmann/json/issues/1341.
-template <typename T, typename = void>
+template<typename T, typename = void>
 struct iterator_traits
 {
 };
 
-template <typename T>
+template<typename T>
 struct iterator_traits < T, enable_if_t < !std::is_pointer<T>::value >>
             : iterator_types<T>
 {
 };
 
-template <typename T>
+template<typename T>
 struct iterator_traits<T*, enable_if_t<std::is_object<T>::value>>
 {
     using iterator_category = std::random_access_iterator_tag;
@@ -389,8 +2800,10 @@ struct iterator_traits<T*, enable_if_t<std::is_object<T>::value>>
     using pointer = T*;
     using reference = T&;
 };
-}
-}
+} // namespace detail
+} // namespace nlohmann
+
+// #include <nlohmann/detail/macro_scope.hpp>
 
 // #include <nlohmann/detail/meta/cpp_future.hpp>
 
@@ -402,7 +2815,7 @@ struct iterator_traits<T*, enable_if_t<std::is_object<T>::value>>
 // #include <nlohmann/detail/meta/void_t.hpp>
 
 
-// http://en.cppreference.com/w/cpp/experimental/is_detected
+// https://en.cppreference.com/w/cpp/experimental/is_detected
 namespace nlohmann
 {
 namespace detail
@@ -412,48 +2825,128 @@ struct nonesuch
     nonesuch() = delete;
     ~nonesuch() = delete;
     nonesuch(nonesuch const&) = delete;
+    nonesuch(nonesuch const&&) = delete;
     void operator=(nonesuch const&) = delete;
+    void operator=(nonesuch&&) = delete;
 };
 
-template <class Default,
-          class AlwaysVoid,
-          template <class...> class Op,
-          class... Args>
+template<class Default,
+         class AlwaysVoid,
+         template<class...> class Op,
+         class... Args>
 struct detector
 {
     using value_t = std::false_type;
     using type = Default;
 };
 
-template <class Default, template <class...> class Op, class... Args>
+template<class Default, template<class...> class Op, class... Args>
 struct detector<Default, void_t<Op<Args...>>, Op, Args...>
 {
     using value_t = std::true_type;
     using type = Op<Args...>;
 };
 
-template <template <class...> class Op, class... Args>
+template<template<class...> class Op, class... Args>
 using is_detected = typename detector<nonesuch, void, Op, Args...>::value_t;
 
-template <template <class...> class Op, class... Args>
+template<template<class...> class Op, class... Args>
 using detected_t = typename detector<nonesuch, void, Op, Args...>::type;
 
-template <class Default, template <class...> class Op, class... Args>
+template<class Default, template<class...> class Op, class... Args>
 using detected_or = detector<Default, void, Op, Args...>;
 
-template <class Default, template <class...> class Op, class... Args>
+template<class Default, template<class...> class Op, class... Args>
 using detected_or_t = typename detected_or<Default, Op, Args...>::type;
 
-template <class Expected, template <class...> class Op, class... Args>
+template<class Expected, template<class...> class Op, class... Args>
 using is_detected_exact = std::is_same<Expected, detected_t<Op, Args...>>;
 
-template <class To, template <class...> class Op, class... Args>
+template<class To, template<class...> class Op, class... Args>
 using is_detected_convertible =
     std::is_convertible<detected_t<Op, Args...>, To>;
 }  // namespace detail
 }  // namespace nlohmann
 
-// #include <nlohmann/detail/macro_scope.hpp>
+// #include <nlohmann/json_fwd.hpp>
+#ifndef INCLUDE_NLOHMANN_JSON_FWD_HPP_
+#define INCLUDE_NLOHMANN_JSON_FWD_HPP_
+
+#include <cstdint> // int64_t, uint64_t
+#include <map> // map
+#include <memory> // allocator
+#include <string> // string
+#include <vector> // vector
+
+/*!
+@brief namespace for Niels Lohmann
+@see https://github.com/nlohmann
+@since version 1.0.0
+*/
+namespace nlohmann
+{
+/*!
+@brief default JSONSerializer template argument
+
+This serializer ignores the template arguments and uses ADL
+([argument-dependent lookup](https://en.cppreference.com/w/cpp/language/adl))
+for serialization.
+*/
+template<typename T = void, typename SFINAE = void>
+struct adl_serializer;
+
+template<template<typename U, typename V, typename... Args> class ObjectType =
+         std::map,
+         template<typename U, typename... Args> class ArrayType = std::vector,
+         class StringType = std::string, class BooleanType = bool,
+         class NumberIntegerType = std::int64_t,
+         class NumberUnsignedType = std::uint64_t,
+         class NumberFloatType = double,
+         template<typename U> class AllocatorType = std::allocator,
+         template<typename T, typename SFINAE = void> class JSONSerializer =
+         adl_serializer,
+         class BinaryType = std::vector<std::uint8_t>>
+class basic_json;
+
+/*!
+@brief JSON Pointer
+
+A JSON pointer defines a string syntax for identifying a specific value
+within a JSON document. It can be used with functions `at` and
+`operator[]`. Furthermore, JSON pointers are the base for JSON patches.
+
+@sa [RFC 6901](https://tools.ietf.org/html/rfc6901)
+
+@since version 2.0.0
+*/
+template<typename BasicJsonType>
+class json_pointer;
+
+/*!
+@brief default JSON class
+
+This type is the default specialization of the @ref basic_json class which
+uses the standard template types.
+
+@since version 1.0.0
+*/
+using json = basic_json<>;
+
+template<class Key, class T, class IgnoredLess, class Allocator>
+struct ordered_map;
+
+/*!
+@brief ordered JSON class
+
+This type preserves the insertion order of object keys.
+
+@since version 3.9.0
+*/
+using ordered_json = basic_json<nlohmann::ordered_map>;
+
+}  // namespace nlohmann
+
+#endif  // INCLUDE_NLOHMANN_JSON_FWD_HPP_
 
 
 namespace nlohmann
@@ -486,50 +2979,73 @@ template<typename> struct is_basic_json : std::false_type {};
 NLOHMANN_BASIC_JSON_TPL_DECLARATION
 struct is_basic_json<NLOHMANN_BASIC_JSON_TPL> : std::true_type {};
 
+//////////////////////
+// json_ref helpers //
+//////////////////////
+
+template<typename>
+class json_ref;
+
+template<typename>
+struct is_json_ref : std::false_type {};
+
+template<typename T>
+struct is_json_ref<json_ref<T>> : std::true_type {};
+
 //////////////////////////
 // aliases for detected //
 //////////////////////////
 
-template <typename T>
+template<typename T>
 using mapped_type_t = typename T::mapped_type;
 
-template <typename T>
+template<typename T>
 using key_type_t = typename T::key_type;
 
-template <typename T>
+template<typename T>
 using value_type_t = typename T::value_type;
 
-template <typename T>
+template<typename T>
 using difference_type_t = typename T::difference_type;
 
-template <typename T>
+template<typename T>
 using pointer_t = typename T::pointer;
 
-template <typename T>
+template<typename T>
 using reference_t = typename T::reference;
 
-template <typename T>
+template<typename T>
 using iterator_category_t = typename T::iterator_category;
 
-template <typename T>
+template<typename T>
 using iterator_t = typename T::iterator;
 
-template <typename T, typename... Args>
+template<typename T, typename... Args>
 using to_json_function = decltype(T::to_json(std::declval<Args>()...));
 
-template <typename T, typename... Args>
+template<typename T, typename... Args>
 using from_json_function = decltype(T::from_json(std::declval<Args>()...));
 
-template <typename T, typename U>
+template<typename T, typename U>
 using get_template_function = decltype(std::declval<T>().template get<U>());
 
 // trait checking if JSONSerializer<T>::from_json(json const&, udt&) exists
-template <typename BasicJsonType, typename T, typename = void>
+template<typename BasicJsonType, typename T, typename = void>
 struct has_from_json : std::false_type {};
 
+// trait checking if j.get<T> is valid
+// use this trait instead of std::is_constructible or std::is_convertible,
+// both rely on, or make use of implicit conversions, and thus fail when T
+// has several constructors/operator= (see https://github.com/nlohmann/json/issues/958)
 template <typename BasicJsonType, typename T>
-struct has_from_json<BasicJsonType, T,
-           enable_if_t<not is_basic_json<T>::value>>
+struct is_getable
+{
+    static constexpr bool value = is_detected<get_template_function, const BasicJsonType&, T>::value;
+};
+
+template<typename BasicJsonType, typename T>
+struct has_from_json < BasicJsonType, T,
+           enable_if_t < !is_basic_json<T>::value >>
 {
     using serializer = typename BasicJsonType::template json_serializer<T, void>;
 
@@ -540,11 +3056,11 @@ struct has_from_json<BasicJsonType, T,
 
 // This trait checks if JSONSerializer<T>::from_json(json const&) exists
 // this overload is used for non-default-constructible user-defined-types
-template <typename BasicJsonType, typename T, typename = void>
+template<typename BasicJsonType, typename T, typename = void>
 struct has_non_default_from_json : std::false_type {};
 
 template<typename BasicJsonType, typename T>
-struct has_non_default_from_json<BasicJsonType, T, enable_if_t<not is_basic_json<T>::value>>
+struct has_non_default_from_json < BasicJsonType, T, enable_if_t < !is_basic_json<T>::value >>
 {
     using serializer = typename BasicJsonType::template json_serializer<T, void>;
 
@@ -555,11 +3071,11 @@ struct has_non_default_from_json<BasicJsonType, T, enable_if_t<not is_basic_json
 
 // This trait checks if BasicJsonType::json_serializer<T>::to_json exists
 // Do not evaluate the trait when T is a basic_json type, to avoid template instantiation infinite recursion.
-template <typename BasicJsonType, typename T, typename = void>
+template<typename BasicJsonType, typename T, typename = void>
 struct has_to_json : std::false_type {};
 
-template <typename BasicJsonType, typename T>
-struct has_to_json<BasicJsonType, T, enable_if_t<not is_basic_json<T>::value>>
+template<typename BasicJsonType, typename T>
+struct has_to_json < BasicJsonType, T, enable_if_t < !is_basic_json<T>::value >>
 {
     using serializer = typename BasicJsonType::template json_serializer<T, void>;
 
@@ -573,10 +3089,10 @@ struct has_to_json<BasicJsonType, T, enable_if_t<not is_basic_json<T>::value>>
 // is_ functions //
 ///////////////////
 
-template <typename T, typename = void>
+template<typename T, typename = void>
 struct is_iterator_traits : std::false_type {};
 
-template <typename T>
+template<typename T>
 struct is_iterator_traits<iterator_traits<T>>
 {
   private:
@@ -593,20 +3109,20 @@ struct is_iterator_traits<iterator_traits<T>>
 
 // source: https://stackoverflow.com/a/37193089/4116453
 
-template <typename T, typename = void>
+template<typename T, typename = void>
 struct is_complete_type : std::false_type {};
 
-template <typename T>
+template<typename T>
 struct is_complete_type<T, decltype(void(sizeof(T)))> : std::true_type {};
 
-template <typename BasicJsonType, typename CompatibleObjectType,
-          typename = void>
+template<typename BasicJsonType, typename CompatibleObjectType,
+         typename = void>
 struct is_compatible_object_type_impl : std::false_type {};
 
-template <typename BasicJsonType, typename CompatibleObjectType>
+template<typename BasicJsonType, typename CompatibleObjectType>
 struct is_compatible_object_type_impl <
     BasicJsonType, CompatibleObjectType,
-    enable_if_t<is_detected<mapped_type_t, CompatibleObjectType>::value and
+    enable_if_t < is_detected<mapped_type_t, CompatibleObjectType>::value&&
     is_detected<key_type_t, CompatibleObjectType>::value >>
 {
 
@@ -615,44 +3131,53 @@ struct is_compatible_object_type_impl <
     // macOS's is_constructible does not play well with nonesuch...
     static constexpr bool value =
         std::is_constructible<typename object_t::key_type,
-        typename CompatibleObjectType::key_type>::value and
+        typename CompatibleObjectType::key_type>::value &&
         std::is_constructible<typename object_t::mapped_type,
         typename CompatibleObjectType::mapped_type>::value;
 };
 
-template <typename BasicJsonType, typename CompatibleObjectType>
+template<typename BasicJsonType, typename CompatibleObjectType>
 struct is_compatible_object_type
     : is_compatible_object_type_impl<BasicJsonType, CompatibleObjectType> {};
 
-template <typename BasicJsonType, typename ConstructibleObjectType,
-          typename = void>
+template<typename BasicJsonType, typename ConstructibleObjectType,
+         typename = void>
 struct is_constructible_object_type_impl : std::false_type {};
 
-template <typename BasicJsonType, typename ConstructibleObjectType>
+template<typename BasicJsonType, typename ConstructibleObjectType>
 struct is_constructible_object_type_impl <
     BasicJsonType, ConstructibleObjectType,
-    enable_if_t<is_detected<mapped_type_t, ConstructibleObjectType>::value and
+    enable_if_t < is_detected<mapped_type_t, ConstructibleObjectType>::value&&
     is_detected<key_type_t, ConstructibleObjectType>::value >>
 {
     using object_t = typename BasicJsonType::object_t;
 
     static constexpr bool value =
-        (std::is_constructible<typename ConstructibleObjectType::key_type, typename object_t::key_type>::value and
-         std::is_same<typename object_t::mapped_type, typename ConstructibleObjectType::mapped_type>::value) or
-        (has_from_json<BasicJsonType, typename ConstructibleObjectType::mapped_type>::value or
-         has_non_default_from_json<BasicJsonType, typename ConstructibleObjectType::mapped_type >::value);
+        (std::is_default_constructible<ConstructibleObjectType>::value &&
+         (std::is_move_assignable<ConstructibleObjectType>::value ||
+          std::is_copy_assignable<ConstructibleObjectType>::value) &&
+         (std::is_constructible<typename ConstructibleObjectType::key_type,
+          typename object_t::key_type>::value &&
+          std::is_same <
+          typename object_t::mapped_type,
+          typename ConstructibleObjectType::mapped_type >::value)) ||
+        (has_from_json<BasicJsonType,
+         typename ConstructibleObjectType::mapped_type>::value ||
+         has_non_default_from_json <
+         BasicJsonType,
+         typename ConstructibleObjectType::mapped_type >::value);
 };
 
-template <typename BasicJsonType, typename ConstructibleObjectType>
+template<typename BasicJsonType, typename ConstructibleObjectType>
 struct is_constructible_object_type
     : is_constructible_object_type_impl<BasicJsonType,
       ConstructibleObjectType> {};
 
-template <typename BasicJsonType, typename CompatibleStringType,
-          typename = void>
+template<typename BasicJsonType, typename CompatibleStringType,
+         typename = void>
 struct is_compatible_string_type_impl : std::false_type {};
 
-template <typename BasicJsonType, typename CompatibleStringType>
+template<typename BasicJsonType, typename CompatibleStringType>
 struct is_compatible_string_type_impl <
     BasicJsonType, CompatibleStringType,
     enable_if_t<is_detected_exact<typename BasicJsonType::string_t::value_type,
@@ -662,15 +3187,15 @@ struct is_compatible_string_type_impl <
         std::is_constructible<typename BasicJsonType::string_t, CompatibleStringType>::value;
 };
 
-template <typename BasicJsonType, typename ConstructibleStringType>
+template<typename BasicJsonType, typename ConstructibleStringType>
 struct is_compatible_string_type
     : is_compatible_string_type_impl<BasicJsonType, ConstructibleStringType> {};
 
-template <typename BasicJsonType, typename ConstructibleStringType,
-          typename = void>
+template<typename BasicJsonType, typename ConstructibleStringType,
+         typename = void>
 struct is_constructible_string_type_impl : std::false_type {};
 
-template <typename BasicJsonType, typename ConstructibleStringType>
+template<typename BasicJsonType, typename ConstructibleStringType>
 struct is_constructible_string_type_impl <
     BasicJsonType, ConstructibleStringType,
     enable_if_t<is_detected_exact<typename BasicJsonType::string_t::value_type,
@@ -681,82 +3206,86 @@ struct is_constructible_string_type_impl <
         typename BasicJsonType::string_t>::value;
 };
 
-template <typename BasicJsonType, typename ConstructibleStringType>
+template<typename BasicJsonType, typename ConstructibleStringType>
 struct is_constructible_string_type
     : is_constructible_string_type_impl<BasicJsonType, ConstructibleStringType> {};
 
-template <typename BasicJsonType, typename CompatibleArrayType, typename = void>
+template<typename BasicJsonType, typename CompatibleArrayType, typename = void>
 struct is_compatible_array_type_impl : std::false_type {};
 
-template <typename BasicJsonType, typename CompatibleArrayType>
+template<typename BasicJsonType, typename CompatibleArrayType>
 struct is_compatible_array_type_impl <
     BasicJsonType, CompatibleArrayType,
-    enable_if_t<is_detected<value_type_t, CompatibleArrayType>::value and
-    is_detected<iterator_t, CompatibleArrayType>::value and
+    enable_if_t < is_detected<value_type_t, CompatibleArrayType>::value&&
+    is_detected<iterator_t, CompatibleArrayType>::value&&
 // This is needed because json_reverse_iterator has a ::iterator type...
 // Therefore it is detected as a CompatibleArrayType.
 // The real fix would be to have an Iterable concept.
-    not is_iterator_traits<
-    iterator_traits<CompatibleArrayType>>::value >>
+    !is_iterator_traits <
+    iterator_traits<CompatibleArrayType >>::value >>
 {
     static constexpr bool value =
         std::is_constructible<BasicJsonType,
         typename CompatibleArrayType::value_type>::value;
 };
 
-template <typename BasicJsonType, typename CompatibleArrayType>
+template<typename BasicJsonType, typename CompatibleArrayType>
 struct is_compatible_array_type
     : is_compatible_array_type_impl<BasicJsonType, CompatibleArrayType> {};
 
-template <typename BasicJsonType, typename ConstructibleArrayType, typename = void>
+template<typename BasicJsonType, typename ConstructibleArrayType, typename = void>
 struct is_constructible_array_type_impl : std::false_type {};
 
-template <typename BasicJsonType, typename ConstructibleArrayType>
+template<typename BasicJsonType, typename ConstructibleArrayType>
 struct is_constructible_array_type_impl <
     BasicJsonType, ConstructibleArrayType,
     enable_if_t<std::is_same<ConstructibleArrayType,
     typename BasicJsonType::value_type>::value >>
             : std::true_type {};
 
-template <typename BasicJsonType, typename ConstructibleArrayType>
+template<typename BasicJsonType, typename ConstructibleArrayType>
 struct is_constructible_array_type_impl <
     BasicJsonType, ConstructibleArrayType,
-    enable_if_t<not std::is_same<ConstructibleArrayType,
-    typename BasicJsonType::value_type>::value and
-    is_detected<value_type_t, ConstructibleArrayType>::value and
-    is_detected<iterator_t, ConstructibleArrayType>::value and
-    is_complete_type<
-    detected_t<value_type_t, ConstructibleArrayType>>::value >>
+    enable_if_t < !std::is_same<ConstructibleArrayType,
+    typename BasicJsonType::value_type>::value&&
+    std::is_default_constructible<ConstructibleArrayType>::value&&
+(std::is_move_assignable<ConstructibleArrayType>::value ||
+ std::is_copy_assignable<ConstructibleArrayType>::value)&&
+is_detected<value_type_t, ConstructibleArrayType>::value&&
+is_detected<iterator_t, ConstructibleArrayType>::value&&
+is_complete_type <
+detected_t<value_type_t, ConstructibleArrayType >>::value >>
 {
     static constexpr bool value =
         // This is needed because json_reverse_iterator has a ::iterator type,
-        // furthermore, std::back_insert_iterator (and other iterators) have a base class `iterator`...
-        // Therefore it is detected as a ConstructibleArrayType.
-        // The real fix would be to have an Iterable concept.
-        not is_iterator_traits <
-        iterator_traits<ConstructibleArrayType >>::value and
-
-        (std::is_same<typename ConstructibleArrayType::value_type, typename BasicJsonType::array_t::value_type>::value or
+        // furthermore, std::back_insert_iterator (and other iterators) have a
+        // base class `iterator`... Therefore it is detected as a
+        // ConstructibleArrayType. The real fix would be to have an Iterable
+        // concept.
+        !is_iterator_traits<iterator_traits<ConstructibleArrayType>>::value &&
+
+        (std::is_same<typename ConstructibleArrayType::value_type,
+         typename BasicJsonType::array_t::value_type>::value ||
          has_from_json<BasicJsonType,
-         typename ConstructibleArrayType::value_type>::value or
+         typename ConstructibleArrayType::value_type>::value ||
          has_non_default_from_json <
          BasicJsonType, typename ConstructibleArrayType::value_type >::value);
 };
 
-template <typename BasicJsonType, typename ConstructibleArrayType>
+template<typename BasicJsonType, typename ConstructibleArrayType>
 struct is_constructible_array_type
     : is_constructible_array_type_impl<BasicJsonType, ConstructibleArrayType> {};
 
-template <typename RealIntegerType, typename CompatibleNumberIntegerType,
-          typename = void>
+template<typename RealIntegerType, typename CompatibleNumberIntegerType,
+         typename = void>
 struct is_compatible_integer_type_impl : std::false_type {};
 
-template <typename RealIntegerType, typename CompatibleNumberIntegerType>
+template<typename RealIntegerType, typename CompatibleNumberIntegerType>
 struct is_compatible_integer_type_impl <
     RealIntegerType, CompatibleNumberIntegerType,
-    enable_if_t<std::is_integral<RealIntegerType>::value and
-    std::is_integral<CompatibleNumberIntegerType>::value and
-    not std::is_same<bool, CompatibleNumberIntegerType>::value >>
+    enable_if_t < std::is_integral<RealIntegerType>::value&&
+    std::is_integral<CompatibleNumberIntegerType>::value&&
+    !std::is_same<bool, CompatibleNumberIntegerType>::value >>
 {
     // is there an assert somewhere on overflows?
     using RealLimits = std::numeric_limits<RealIntegerType>;
@@ -764,20 +3293,20 @@ struct is_compatible_integer_type_impl <
 
     static constexpr auto value =
         std::is_constructible<RealIntegerType,
-        CompatibleNumberIntegerType>::value and
-        CompatibleLimits::is_integer and
+        CompatibleNumberIntegerType>::value &&
+        CompatibleLimits::is_integer &&
         RealLimits::is_signed == CompatibleLimits::is_signed;
 };
 
-template <typename RealIntegerType, typename CompatibleNumberIntegerType>
+template<typename RealIntegerType, typename CompatibleNumberIntegerType>
 struct is_compatible_integer_type
     : is_compatible_integer_type_impl<RealIntegerType,
       CompatibleNumberIntegerType> {};
 
-template <typename BasicJsonType, typename CompatibleType, typename = void>
+template<typename BasicJsonType, typename CompatibleType, typename = void>
 struct is_compatible_type_impl: std::false_type {};
 
-template <typename BasicJsonType, typename CompatibleType>
+template<typename BasicJsonType, typename CompatibleType>
 struct is_compatible_type_impl <
     BasicJsonType, CompatibleType,
     enable_if_t<is_complete_type<CompatibleType>::value >>
@@ -786,388 +3315,22 @@ struct is_compatible_type_impl <
         has_to_json<BasicJsonType, CompatibleType>::value;
 };
 
-template <typename BasicJsonType, typename CompatibleType>
+template<typename BasicJsonType, typename CompatibleType>
 struct is_compatible_type
     : is_compatible_type_impl<BasicJsonType, CompatibleType> {};
-}  // namespace detail
-}  // namespace nlohmann
-
-// #include <nlohmann/detail/exceptions.hpp>
-
-
-#include <exception> // exception
-#include <stdexcept> // runtime_error
-#include <string> // to_string
-
-// #include <nlohmann/detail/input/position_t.hpp>
-
-
-#include <cstddef> // size_t
-
-namespace nlohmann
-{
-namespace detail
-{
-/// struct to capture the start position of the current token
-struct position_t
-{
-    /// the total number of characters read
-    std::size_t chars_read_total = 0;
-    /// the number of characters read in the current line
-    std::size_t chars_read_current_line = 0;
-    /// the number of lines read
-    std::size_t lines_read = 0;
-
-    /// conversion to size_t to preserve SAX interface
-    constexpr operator size_t() const
-    {
-        return chars_read_total;
-    }
-};
-
-}
-}
-
-
-namespace nlohmann
-{
-namespace detail
-{
-////////////////
-// exceptions //
-////////////////
-
-/*!
-@brief general exception of the @ref basic_json class
-
-This class is an extension of `std::exception` objects with a member @a id for
-exception ids. It is used as the base class for all exceptions thrown by the
-@ref basic_json class. This class can hence be used as "wildcard" to catch
-exceptions.
-
-Subclasses:
-- @ref parse_error for exceptions indicating a parse error
-- @ref invalid_iterator for exceptions indicating errors with iterators
-- @ref type_error for exceptions indicating executing a member function with
-                  a wrong type
-- @ref out_of_range for exceptions indicating access out of the defined range
-- @ref other_error for exceptions indicating other library errors
-
-@internal
-@note To have nothrow-copy-constructible exceptions, we internally use
-      `std::runtime_error` which can cope with arbitrary-length error messages.
-      Intermediate strings are built with static functions and then passed to
-      the actual constructor.
-@endinternal
-
-@liveexample{The following code shows how arbitrary library exceptions can be
-caught.,exception}
-
-@since version 3.0.0
-*/
-class exception : public std::exception
-{
-  public:
-    /// returns the explanatory string
-    const char* what() const noexcept override
-    {
-        return m.what();
-    }
-
-    /// the id of the exception
-    const int id;
-
-  protected:
-    exception(int id_, const char* what_arg) : id(id_), m(what_arg) {}
-
-    static std::string name(const std::string& ename, int id_)
-    {
-        return "[json.exception." + ename + "." + std::to_string(id_) + "] ";
-    }
-
-  private:
-    /// an exception object as storage for error messages
-    std::runtime_error m;
-};
-
-/*!
-@brief exception indicating a parse error
-
-This exception is thrown by the library when a parse error occurs. Parse errors
-can occur during the deserialization of JSON text, CBOR, MessagePack, as well
-as when using JSON Patch.
-
-Member @a byte holds the byte index of the last read character in the input
-file.
-
-Exceptions have ids 1xx.
-
-name / id                      | example message | description
------------------------------- | --------------- | -------------------------
-json.exception.parse_error.101 | parse error at 2: unexpected end of input; expected string literal | This error indicates a syntax error while deserializing a JSON text. The error message describes that an unexpected token (character) was encountered, and the member @a byte indicates the error position.
-json.exception.parse_error.102 | parse error at 14: missing or wrong low surrogate | JSON uses the `\uxxxx` format to describe Unicode characters. Code points above above 0xFFFF are split into two `\uxxxx` entries ("surrogate pairs"). This error indicates that the surrogate pair is incomplete or contains an invalid code point.
-json.exception.parse_error.103 | parse error: code points above 0x10FFFF are invalid | Unicode supports code points up to 0x10FFFF. Code points above 0x10FFFF are invalid.
-json.exception.parse_error.104 | parse error: JSON patch must be an array of objects | [RFC 6902](https://tools.ietf.org/html/rfc6902) requires a JSON Patch document to be a JSON document that represents an array of objects.
-json.exception.parse_error.105 | parse error: operation must have string member 'op' | An operation of a JSON Patch document must contain exactly one "op" member, whose value indicates the operation to perform. Its value must be one of "add", "remove", "replace", "move", "copy", or "test"; other values are errors.
-json.exception.parse_error.106 | parse error: array index '01' must not begin with '0' | An array index in a JSON Pointer ([RFC 6901](https://tools.ietf.org/html/rfc6901)) may be `0` or any number without a leading `0`.
-json.exception.parse_error.107 | parse error: JSON pointer must be empty or begin with '/' - was: 'foo' | A JSON Pointer must be a Unicode string containing a sequence of zero or more reference tokens, each prefixed by a `/` character.
-json.exception.parse_error.108 | parse error: escape character '~' must be followed with '0' or '1' | In a JSON Pointer, only `~0` and `~1` are valid escape sequences.
-json.exception.parse_error.109 | parse error: array index 'one' is not a number | A JSON Pointer array index must be a number.
-json.exception.parse_error.110 | parse error at 1: cannot read 2 bytes from vector | When parsing CBOR or MessagePack, the byte vector ends before the complete value has been read.
-json.exception.parse_error.112 | parse error at 1: error reading CBOR; last byte: 0xF8 | Not all types of CBOR or MessagePack are supported. This exception occurs if an unsupported byte was read.
-json.exception.parse_error.113 | parse error at 2: expected a CBOR string; last byte: 0x98 | While parsing a map key, a value that is not a string has been read.
-json.exception.parse_error.114 | parse error: Unsupported BSON record type 0x0F | The parsing of the corresponding BSON record type is not implemented (yet).
-
-@note For an input with n bytes, 1 is the index of the first character and n+1
-      is the index of the terminating null byte or the end of file. This also
-      holds true when reading a byte vector (CBOR or MessagePack).
-
-@liveexample{The following code shows how a `parse_error` exception can be
-caught.,parse_error}
-
-@sa @ref exception for the base class of the library exceptions
-@sa @ref invalid_iterator for exceptions indicating errors with iterators
-@sa @ref type_error for exceptions indicating executing a member function with
-                    a wrong type
-@sa @ref out_of_range for exceptions indicating access out of the defined range
-@sa @ref other_error for exceptions indicating other library errors
-
-@since version 3.0.0
-*/
-class parse_error : public exception
-{
-  public:
-    /*!
-    @brief create a parse error exception
-    @param[in] id_       the id of the exception
-    @param[in] position  the position where the error occurred (or with
-                         chars_read_total=0 if the position cannot be
-                         determined)
-    @param[in] what_arg  the explanatory string
-    @return parse_error object
-    */
-    static parse_error create(int id_, const position_t& pos, const std::string& what_arg)
-    {
-        std::string w = exception::name("parse_error", id_) + "parse error" +
-                        position_string(pos) + ": " + what_arg;
-        return parse_error(id_, pos.chars_read_total, w.c_str());
-    }
-
-    static parse_error create(int id_, std::size_t byte_, const std::string& what_arg)
-    {
-        std::string w = exception::name("parse_error", id_) + "parse error" +
-                        (byte_ != 0 ? (" at byte " + std::to_string(byte_)) : "") +
-                        ": " + what_arg;
-        return parse_error(id_, byte_, w.c_str());
-    }
-
-    /*!
-    @brief byte index of the parse error
-
-    The byte index of the last read character in the input file.
-
-    @note For an input with n bytes, 1 is the index of the first character and
-          n+1 is the index of the terminating null byte or the end of file.
-          This also holds true when reading a byte vector (CBOR or MessagePack).
-    */
-    const std::size_t byte;
-
-  private:
-    parse_error(int id_, std::size_t byte_, const char* what_arg)
-        : exception(id_, what_arg), byte(byte_) {}
-
-    static std::string position_string(const position_t& pos)
-    {
-        return " at line " + std::to_string(pos.lines_read + 1) +
-               ", column " + std::to_string(pos.chars_read_current_line);
-    }
-};
-
-/*!
-@brief exception indicating errors with iterators
-
-This exception is thrown if iterators passed to a library function do not match
-the expected semantics.
-
-Exceptions have ids 2xx.
-
-name / id                           | example message | description
------------------------------------ | --------------- | -------------------------
-json.exception.invalid_iterator.201 | iterators are not compatible | The iterators passed to constructor @ref basic_json(InputIT first, InputIT last) are not compatible, meaning they do not belong to the same container. Therefore, the range (@a first, @a last) is invalid.
-json.exception.invalid_iterator.202 | iterator does not fit current value | In an erase or insert function, the passed iterator @a pos does not belong to the JSON value for which the function was called. It hence does not define a valid position for the deletion/insertion.
-json.exception.invalid_iterator.203 | iterators do not fit current value | Either iterator passed to function @ref erase(IteratorType first, IteratorType last) does not belong to the JSON value from which values shall be erased. It hence does not define a valid range to delete values from.
-json.exception.invalid_iterator.204 | iterators out of range | When an iterator range for a primitive type (number, boolean, or string) is passed to a constructor or an erase function, this range has to be exactly (@ref begin(), @ref end()), because this is the only way the single stored value is expressed. All other ranges are invalid.
-json.exception.invalid_iterator.205 | iterator out of range | When an iterator for a primitive type (number, boolean, or string) is passed to an erase function, the iterator has to be the @ref begin() iterator, because it is the only way to address the stored value. All other iterators are invalid.
-json.exception.invalid_iterator.206 | cannot construct with iterators from null | The iterators passed to constructor @ref basic_json(InputIT first, InputIT last) belong to a JSON null value and hence to not define a valid range.
-json.exception.invalid_iterator.207 | cannot use key() for non-object iterators | The key() member function can only be used on iterators belonging to a JSON object, because other types do not have a concept of a key.
-json.exception.invalid_iterator.208 | cannot use operator[] for object iterators | The operator[] to specify a concrete offset cannot be used on iterators belonging to a JSON object, because JSON objects are unordered.
-json.exception.invalid_iterator.209 | cannot use offsets with object iterators | The offset operators (+, -, +=, -=) cannot be used on iterators belonging to a JSON object, because JSON objects are unordered.
-json.exception.invalid_iterator.210 | iterators do not fit | The iterator range passed to the insert function are not compatible, meaning they do not belong to the same container. Therefore, the range (@a first, @a last) is invalid.
-json.exception.invalid_iterator.211 | passed iterators may not belong to container | The iterator range passed to the insert function must not be a subrange of the container to insert to.
-json.exception.invalid_iterator.212 | cannot compare iterators of different containers | When two iterators are compared, they must belong to the same container.
-json.exception.invalid_iterator.213 | cannot compare order of object iterators | The order of object iterators cannot be compared, because JSON objects are unordered.
-json.exception.invalid_iterator.214 | cannot get value | Cannot get value for iterator: Either the iterator belongs to a null value or it is an iterator to a primitive type (number, boolean, or string), but the iterator is different to @ref begin().
-
-@liveexample{The following code shows how an `invalid_iterator` exception can be
-caught.,invalid_iterator}
-
-@sa @ref exception for the base class of the library exceptions
-@sa @ref parse_error for exceptions indicating a parse error
-@sa @ref type_error for exceptions indicating executing a member function with
-                    a wrong type
-@sa @ref out_of_range for exceptions indicating access out of the defined range
-@sa @ref other_error for exceptions indicating other library errors
-
-@since version 3.0.0
-*/
-class invalid_iterator : public exception
-{
-  public:
-    static invalid_iterator create(int id_, const std::string& what_arg)
-    {
-        std::string w = exception::name("invalid_iterator", id_) + what_arg;
-        return invalid_iterator(id_, w.c_str());
-    }
-
-  private:
-    invalid_iterator(int id_, const char* what_arg)
-        : exception(id_, what_arg) {}
-};
 
-/*!
-@brief exception indicating executing a member function with a wrong type
-
-This exception is thrown in case of a type error; that is, a library function is
-executed on a JSON value whose type does not match the expected semantics.
-
-Exceptions have ids 3xx.
-
-name / id                     | example message | description
------------------------------ | --------------- | -------------------------
-json.exception.type_error.301 | cannot create object from initializer list | To create an object from an initializer list, the initializer list must consist only of a list of pairs whose first element is a string. When this constraint is violated, an array is created instead.
-json.exception.type_error.302 | type must be object, but is array | During implicit or explicit value conversion, the JSON type must be compatible to the target type. For instance, a JSON string can only be converted into string types, but not into numbers or boolean types.
-json.exception.type_error.303 | incompatible ReferenceType for get_ref, actual type is object | To retrieve a reference to a value stored in a @ref basic_json object with @ref get_ref, the type of the reference must match the value type. For instance, for a JSON array, the @a ReferenceType must be @ref array_t&.
-json.exception.type_error.304 | cannot use at() with string | The @ref at() member functions can only be executed for certain JSON types.
-json.exception.type_error.305 | cannot use operator[] with string | The @ref operator[] member functions can only be executed for certain JSON types.
-json.exception.type_error.306 | cannot use value() with string | The @ref value() member functions can only be executed for certain JSON types.
-json.exception.type_error.307 | cannot use erase() with string | The @ref erase() member functions can only be executed for certain JSON types.
-json.exception.type_error.308 | cannot use push_back() with string | The @ref push_back() and @ref operator+= member functions can only be executed for certain JSON types.
-json.exception.type_error.309 | cannot use insert() with | The @ref insert() member functions can only be executed for certain JSON types.
-json.exception.type_error.310 | cannot use swap() with number | The @ref swap() member functions can only be executed for certain JSON types.
-json.exception.type_error.311 | cannot use emplace_back() with string | The @ref emplace_back() member function can only be executed for certain JSON types.
-json.exception.type_error.312 | cannot use update() with string | The @ref update() member functions can only be executed for certain JSON types.
-json.exception.type_error.313 | invalid value to unflatten | The @ref unflatten function converts an object whose keys are JSON Pointers back into an arbitrary nested JSON value. The JSON Pointers must not overlap, because then the resulting value would not be well defined.
-json.exception.type_error.314 | only objects can be unflattened | The @ref unflatten function only works for an object whose keys are JSON Pointers.
-json.exception.type_error.315 | values in object must be primitive | The @ref unflatten function only works for an object whose keys are JSON Pointers and whose values are primitive.
-json.exception.type_error.316 | invalid UTF-8 byte at index 10: 0x7E | The @ref dump function only works with UTF-8 encoded strings; that is, if you assign a `std::string` to a JSON value, make sure it is UTF-8 encoded. |
-json.exception.type_error.317 | JSON value cannot be serialized to requested format | The dynamic type of the object cannot be represented in the requested serialization format (e.g. a raw `true` or `null` JSON object cannot be serialized to BSON) |
-
-@liveexample{The following code shows how a `type_error` exception can be
-caught.,type_error}
+// https://en.cppreference.com/w/cpp/types/conjunction
+template<class...> struct conjunction : std::true_type { };
+template<class B1> struct conjunction<B1> : B1 { };
+template<class B1, class... Bn>
+struct conjunction<B1, Bn...>
+: std::conditional<bool(B1::value), conjunction<Bn...>, B1>::type {};
 
-@sa @ref exception for the base class of the library exceptions
-@sa @ref parse_error for exceptions indicating a parse error
-@sa @ref invalid_iterator for exceptions indicating errors with iterators
-@sa @ref out_of_range for exceptions indicating access out of the defined range
-@sa @ref other_error for exceptions indicating other library errors
+template<typename T1, typename T2>
+struct is_constructible_tuple : std::false_type {};
 
-@since version 3.0.0
-*/
-class type_error : public exception
-{
-  public:
-    static type_error create(int id_, const std::string& what_arg)
-    {
-        std::string w = exception::name("type_error", id_) + what_arg;
-        return type_error(id_, w.c_str());
-    }
-
-  private:
-    type_error(int id_, const char* what_arg) : exception(id_, what_arg) {}
-};
-
-/*!
-@brief exception indicating access out of the defined range
-
-This exception is thrown in case a library function is called on an input
-parameter that exceeds the expected range, for instance in case of array
-indices or nonexisting object keys.
-
-Exceptions have ids 4xx.
-
-name / id                       | example message | description
-------------------------------- | --------------- | -------------------------
-json.exception.out_of_range.401 | array index 3 is out of range | The provided array index @a i is larger than @a size-1.
-json.exception.out_of_range.402 | array index '-' (3) is out of range | The special array index `-` in a JSON Pointer never describes a valid element of the array, but the index past the end. That is, it can only be used to add elements at this position, but not to read it.
-json.exception.out_of_range.403 | key 'foo' not found | The provided key was not found in the JSON object.
-json.exception.out_of_range.404 | unresolved reference token 'foo' | A reference token in a JSON Pointer could not be resolved.
-json.exception.out_of_range.405 | JSON pointer has no parent | The JSON Patch operations 'remove' and 'add' can not be applied to the root element of the JSON value.
-json.exception.out_of_range.406 | number overflow parsing '10E1000' | A parsed number could not be stored as without changing it to NaN or INF.
-json.exception.out_of_range.407 | number overflow serializing '9223372036854775808' | UBJSON and BSON only support integer numbers up to 9223372036854775807. |
-json.exception.out_of_range.408 | excessive array size: 8658170730974374167 | The size (following `#`) of an UBJSON array or object exceeds the maximal capacity. |
-json.exception.out_of_range.409 | BSON key cannot contain code point U+0000 (at byte 2) | Key identifiers to be serialized to BSON cannot contain code point U+0000, since the key is stored as zero-terminated c-string |
-
-@liveexample{The following code shows how an `out_of_range` exception can be
-caught.,out_of_range}
-
-@sa @ref exception for the base class of the library exceptions
-@sa @ref parse_error for exceptions indicating a parse error
-@sa @ref invalid_iterator for exceptions indicating errors with iterators
-@sa @ref type_error for exceptions indicating executing a member function with
-                    a wrong type
-@sa @ref other_error for exceptions indicating other library errors
-
-@since version 3.0.0
-*/
-class out_of_range : public exception
-{
-  public:
-    static out_of_range create(int id_, const std::string& what_arg)
-    {
-        std::string w = exception::name("out_of_range", id_) + what_arg;
-        return out_of_range(id_, w.c_str());
-    }
-
-  private:
-    out_of_range(int id_, const char* what_arg) : exception(id_, what_arg) {}
-};
-
-/*!
-@brief exception indicating other library errors
-
-This exception is thrown in case of errors that cannot be classified with the
-other exception types.
-
-Exceptions have ids 5xx.
-
-name / id                      | example message | description
------------------------------- | --------------- | -------------------------
-json.exception.other_error.501 | unsuccessful: {"op":"test","path":"/baz", "value":"bar"} | A JSON Patch operation 'test' failed. The unsuccessful operation is also printed.
-
-@sa @ref exception for the base class of the library exceptions
-@sa @ref parse_error for exceptions indicating a parse error
-@sa @ref invalid_iterator for exceptions indicating errors with iterators
-@sa @ref type_error for exceptions indicating executing a member function with
-                    a wrong type
-@sa @ref out_of_range for exceptions indicating access out of the defined range
-
-@liveexample{The following code shows how an `other_error` exception can be
-caught.,other_error}
-
-@since version 3.0.0
-*/
-class other_error : public exception
-{
-  public:
-    static other_error create(int id_, const std::string& what_arg)
-    {
-        std::string w = exception::name("other_error", id_) + what_arg;
-        return other_error(id_, w.c_str());
-    }
-
-  private:
-    other_error(int id_, const char* what_arg) : exception(id_, what_arg) {}
-};
+template<typename T1, typename... Args>
+struct is_constructible_tuple<T1, std::tuple<Args...>> : conjunction<std::is_constructible<T1, Args>...> {};
 }  // namespace detail
 }  // namespace nlohmann
 
@@ -1175,9 +3338,9 @@ class other_error : public exception
 
 
 #include <array> // array
-#include <ciso646> // and
 #include <cstddef> // size_t
 #include <cstdint> // uint8_t
+#include <string> // string
 
 namespace nlohmann
 {
@@ -1221,60 +3384,39 @@ enum class value_t : std::uint8_t
     number_integer,   ///< number value (signed integer)
     number_unsigned,  ///< number value (unsigned integer)
     number_float,     ///< number value (floating-point)
-    discarded         ///< discarded by the the parser callback function
+    binary,           ///< binary array (ordered collection of bytes)
+    discarded         ///< discarded by the parser callback function
 };
 
 /*!
 @brief comparison operator for JSON types
 
 Returns an ordering that is similar to Python:
-- order: null < boolean < number < object < array < string
+- order: null < boolean < number < object < array < string < binary
 - furthermore, each type is not smaller than itself
 - discarded values are not comparable
+- binary is represented as a b"" string in python and directly comparable to a
+  string; however, making a binary array directly comparable with a string would
+  be surprising behavior in a JSON file.
 
 @since version 1.0.0
 */
 inline bool operator<(const value_t lhs, const value_t rhs) noexcept
 {
-    static constexpr std::array<std::uint8_t, 8> order = {{
+    static constexpr std::array<std::uint8_t, 9> order = {{
             0 /* null */, 3 /* object */, 4 /* array */, 5 /* string */,
-            1 /* boolean */, 2 /* integer */, 2 /* unsigned */, 2 /* float */
+            1 /* boolean */, 2 /* integer */, 2 /* unsigned */, 2 /* float */,
+            6 /* binary */
         }
     };
 
     const auto l_index = static_cast<std::size_t>(lhs);
     const auto r_index = static_cast<std::size_t>(rhs);
-    return l_index < order.size() and r_index < order.size() and order[l_index] < order[r_index];
+    return l_index < order.size() && r_index < order.size() && order[l_index] < order[r_index];
 }
 }  // namespace detail
 }  // namespace nlohmann
 
-// #include <nlohmann/detail/conversions/from_json.hpp>
-
-
-#include <algorithm> // transform
-#include <array> // array
-#include <ciso646> // and, not
-#include <forward_list> // forward_list
-#include <iterator> // inserter, front_inserter, end
-#include <map> // map
-#include <string> // string
-#include <tuple> // tuple, make_tuple
-#include <type_traits> // is_arithmetic, is_same, is_enum, underlying_type, is_convertible
-#include <unordered_map> // unordered_map
-#include <utility> // pair, declval
-#include <valarray> // valarray
-
-// #include <nlohmann/detail/exceptions.hpp>
-
-// #include <nlohmann/detail/macro_scope.hpp>
-
-// #include <nlohmann/detail/meta/cpp_future.hpp>
-
-// #include <nlohmann/detail/meta/type_traits.hpp>
-
-// #include <nlohmann/detail/value_t.hpp>
-
 
 namespace nlohmann
 {
@@ -1283,7 +3425,7 @@ namespace detail
 template<typename BasicJsonType>
 void from_json(const BasicJsonType& j, typename std::nullptr_t& n)
 {
-    if (JSON_UNLIKELY(not j.is_null()))
+    if (JSON_HEDLEY_UNLIKELY(!j.is_null()))
     {
         JSON_THROW(type_error::create(302, "type must be null, but is " + std::string(j.type_name())));
     }
@@ -1291,10 +3433,10 @@ void from_json(const BasicJsonType& j, typename std::nullptr_t& n)
 }
 
 // overloads for basic_json template parameters
-template<typename BasicJsonType, typename ArithmeticType,
-         enable_if_t<std::is_arithmetic<ArithmeticType>::value and
-                     not std::is_same<ArithmeticType, typename BasicJsonType::boolean_t>::value,
-                     int> = 0>
+template < typename BasicJsonType, typename ArithmeticType,
+           enable_if_t < std::is_arithmetic<ArithmeticType>::value&&
+                         !std::is_same<ArithmeticType, typename BasicJsonType::boolean_t>::value,
+                         int > = 0 >
 void get_arithmetic_value(const BasicJsonType& j, ArithmeticType& val)
 {
     switch (static_cast<value_t>(j))
@@ -1323,7 +3465,7 @@ void get_arithmetic_value(const BasicJsonType& j, ArithmeticType& val)
 template<typename BasicJsonType>
 void from_json(const BasicJsonType& j, typename BasicJsonType::boolean_t& b)
 {
-    if (JSON_UNLIKELY(not j.is_boolean()))
+    if (JSON_HEDLEY_UNLIKELY(!j.is_boolean()))
     {
         JSON_THROW(type_error::create(302, "type must be boolean, but is " + std::string(j.type_name())));
     }
@@ -1333,7 +3475,7 @@ void from_json(const BasicJsonType& j, typename BasicJsonType::boolean_t& b)
 template<typename BasicJsonType>
 void from_json(const BasicJsonType& j, typename BasicJsonType::string_t& s)
 {
-    if (JSON_UNLIKELY(not j.is_string()))
+    if (JSON_HEDLEY_UNLIKELY(!j.is_string()))
     {
         JSON_THROW(type_error::create(302, "type must be string, but is " + std::string(j.type_name())));
     }
@@ -1343,13 +3485,13 @@ void from_json(const BasicJsonType& j, typename BasicJsonType::string_t& s)
 template <
     typename BasicJsonType, typename ConstructibleStringType,
     enable_if_t <
-        is_constructible_string_type<BasicJsonType, ConstructibleStringType>::value and
-        not std::is_same<typename BasicJsonType::string_t,
-                         ConstructibleStringType>::value,
+        is_constructible_string_type<BasicJsonType, ConstructibleStringType>::value&&
+        !std::is_same<typename BasicJsonType::string_t,
+                      ConstructibleStringType>::value,
         int > = 0 >
 void from_json(const BasicJsonType& j, ConstructibleStringType& s)
 {
-    if (JSON_UNLIKELY(not j.is_string()))
+    if (JSON_HEDLEY_UNLIKELY(!j.is_string()))
     {
         JSON_THROW(type_error::create(302, "type must be string, but is " + std::string(j.type_name())));
     }
@@ -1386,13 +3528,14 @@ void from_json(const BasicJsonType& j, EnumType& e)
 
 // forward_list doesn't have an insert method
 template<typename BasicJsonType, typename T, typename Allocator,
-         enable_if_t<std::is_convertible<BasicJsonType, T>::value, int> = 0>
+         enable_if_t<is_getable<BasicJsonType, T>::value, int> = 0>
 void from_json(const BasicJsonType& j, std::forward_list<T, Allocator>& l)
 {
-    if (JSON_UNLIKELY(not j.is_array()))
+    if (JSON_HEDLEY_UNLIKELY(!j.is_array()))
     {
         JSON_THROW(type_error::create(302, "type must be array, but is " + std::string(j.type_name())));
     }
+    l.clear();
     std::transform(j.rbegin(), j.rend(),
                    std::front_inserter(l), [](const BasicJsonType & i)
     {
@@ -1402,15 +3545,29 @@ void from_json(const BasicJsonType& j, std::forward_list<T, Allocator>& l)
 
 // valarray doesn't have an insert method
 template<typename BasicJsonType, typename T,
-         enable_if_t<std::is_convertible<BasicJsonType, T>::value, int> = 0>
+         enable_if_t<is_getable<BasicJsonType, T>::value, int> = 0>
 void from_json(const BasicJsonType& j, std::valarray<T>& l)
 {
-    if (JSON_UNLIKELY(not j.is_array()))
+    if (JSON_HEDLEY_UNLIKELY(!j.is_array()))
     {
         JSON_THROW(type_error::create(302, "type must be array, but is " + std::string(j.type_name())));
     }
     l.resize(j.size());
-    std::copy(j.m_value.array->begin(), j.m_value.array->end(), std::begin(l));
+    std::transform(j.begin(), j.end(), std::begin(l),
+                   [](const BasicJsonType & elem)
+    {
+        return elem.template get<T>();
+    });
+}
+
+template<typename BasicJsonType, typename T, std::size_t N>
+auto from_json(const BasicJsonType& j, T (&arr)[N])
+-> decltype(j.template get<T>(), void())
+{
+    for (std::size_t i = 0; i < N; ++i)
+    {
+        arr[i] = j.at(i).template get<T>();
+    }
 }
 
 template<typename BasicJsonType>
@@ -1419,7 +3576,7 @@ void from_json_array_impl(const BasicJsonType& j, typename BasicJsonType::array_
     arr = *j.template get_ptr<const typename BasicJsonType::array_t*>();
 }
 
-template <typename BasicJsonType, typename T, std::size_t N>
+template<typename BasicJsonType, typename T, std::size_t N>
 auto from_json_array_impl(const BasicJsonType& j, std::array<T, N>& arr,
                           priority_tag<2> /*unused*/)
 -> decltype(j.template get<T>(), void())
@@ -1439,46 +3596,50 @@ auto from_json_array_impl(const BasicJsonType& j, ConstructibleArrayType& arr, p
 {
     using std::end;
 
-    arr.reserve(j.size());
+    ConstructibleArrayType ret;
+    ret.reserve(j.size());
     std::transform(j.begin(), j.end(),
-                   std::inserter(arr, end(arr)), [](const BasicJsonType & i)
+                   std::inserter(ret, end(ret)), [](const BasicJsonType & i)
     {
         // get<BasicJsonType>() returns *this, this won't call a from_json
         // method when value_type is BasicJsonType
         return i.template get<typename ConstructibleArrayType::value_type>();
     });
+    arr = std::move(ret);
 }
 
-template <typename BasicJsonType, typename ConstructibleArrayType>
+template<typename BasicJsonType, typename ConstructibleArrayType>
 void from_json_array_impl(const BasicJsonType& j, ConstructibleArrayType& arr,
                           priority_tag<0> /*unused*/)
 {
     using std::end;
 
+    ConstructibleArrayType ret;
     std::transform(
-        j.begin(), j.end(), std::inserter(arr, end(arr)),
+        j.begin(), j.end(), std::inserter(ret, end(ret)),
         [](const BasicJsonType & i)
     {
         // get<BasicJsonType>() returns *this, this won't call a from_json
         // method when value_type is BasicJsonType
         return i.template get<typename ConstructibleArrayType::value_type>();
     });
+    arr = std::move(ret);
 }
 
-template <typename BasicJsonType, typename ConstructibleArrayType,
-          enable_if_t <
-              is_constructible_array_type<BasicJsonType, ConstructibleArrayType>::value and
-              not is_constructible_object_type<BasicJsonType, ConstructibleArrayType>::value and
-              not is_constructible_string_type<BasicJsonType, ConstructibleArrayType>::value and
-              not is_basic_json<ConstructibleArrayType>::value,
-              int > = 0 >
-
+template < typename BasicJsonType, typename ConstructibleArrayType,
+           enable_if_t <
+               is_constructible_array_type<BasicJsonType, ConstructibleArrayType>::value&&
+               !is_constructible_object_type<BasicJsonType, ConstructibleArrayType>::value&&
+               !is_constructible_string_type<BasicJsonType, ConstructibleArrayType>::value&&
+               !std::is_same<ConstructibleArrayType, typename BasicJsonType::binary_t>::value&&
+               !is_basic_json<ConstructibleArrayType>::value,
+               int > = 0 >
 auto from_json(const BasicJsonType& j, ConstructibleArrayType& arr)
 -> decltype(from_json_array_impl(j, arr, priority_tag<3> {}),
 j.template get<typename ConstructibleArrayType::value_type>(),
 void())
 {
-    if (JSON_UNLIKELY(not j.is_array()))
+    if (JSON_HEDLEY_UNLIKELY(!j.is_array()))
     {
         JSON_THROW(type_error::create(302, "type must be array, but is " +
                                       std::string(j.type_name())));
@@ -1487,38 +3648,51 @@ void())
     from_json_array_impl(j, arr, priority_tag<3> {});
 }
 
+template<typename BasicJsonType>
+void from_json(const BasicJsonType& j, typename BasicJsonType::binary_t& bin)
+{
+    if (JSON_HEDLEY_UNLIKELY(!j.is_binary()))
+    {
+        JSON_THROW(type_error::create(302, "type must be binary, but is " + std::string(j.type_name())));
+    }
+
+    bin = *j.template get_ptr<const typename BasicJsonType::binary_t*>();
+}
+
 template<typename BasicJsonType, typename ConstructibleObjectType,
          enable_if_t<is_constructible_object_type<BasicJsonType, ConstructibleObjectType>::value, int> = 0>
 void from_json(const BasicJsonType& j, ConstructibleObjectType& obj)
 {
-    if (JSON_UNLIKELY(not j.is_object()))
+    if (JSON_HEDLEY_UNLIKELY(!j.is_object()))
     {
         JSON_THROW(type_error::create(302, "type must be object, but is " + std::string(j.type_name())));
     }
 
+    ConstructibleObjectType ret;
     auto inner_object = j.template get_ptr<const typename BasicJsonType::object_t*>();
     using value_type = typename ConstructibleObjectType::value_type;
     std::transform(
         inner_object->begin(), inner_object->end(),
-        std::inserter(obj, obj.begin()),
+        std::inserter(ret, ret.begin()),
         [](typename BasicJsonType::object_t::value_type const & p)
     {
         return value_type(p.first, p.second.template get<typename ConstructibleObjectType::mapped_type>());
     });
+    obj = std::move(ret);
 }
 
 // overload for arithmetic types, not chosen for basic_json template arguments
 // (BooleanType, etc..); note: Is it really necessary to provide explicit
 // overloads for boolean_t etc. in case of a custom BooleanType which is not
 // an arithmetic type?
-template<typename BasicJsonType, typename ArithmeticType,
-         enable_if_t <
-             std::is_arithmetic<ArithmeticType>::value and
-             not std::is_same<ArithmeticType, typename BasicJsonType::number_unsigned_t>::value and
-             not std::is_same<ArithmeticType, typename BasicJsonType::number_integer_t>::value and
-             not std::is_same<ArithmeticType, typename BasicJsonType::number_float_t>::value and
-             not std::is_same<ArithmeticType, typename BasicJsonType::boolean_t>::value,
-             int> = 0>
+template < typename BasicJsonType, typename ArithmeticType,
+           enable_if_t <
+               std::is_arithmetic<ArithmeticType>::value&&
+               !std::is_same<ArithmeticType, typename BasicJsonType::number_unsigned_t>::value&&
+               !std::is_same<ArithmeticType, typename BasicJsonType::number_integer_t>::value&&
+               !std::is_same<ArithmeticType, typename BasicJsonType::number_float_t>::value&&
+               !std::is_same<ArithmeticType, typename BasicJsonType::boolean_t>::value,
+               int > = 0 >
 void from_json(const BasicJsonType& j, ArithmeticType& val)
 {
     switch (static_cast<value_t>(j))
@@ -1567,18 +3741,19 @@ void from_json(const BasicJsonType& j, std::tuple<Args...>& t)
     from_json_tuple_impl(j, t, index_sequence_for<Args...> {});
 }
 
-template <typename BasicJsonType, typename Key, typename Value, typename Compare, typename Allocator,
-          typename = enable_if_t<not std::is_constructible<
-                                     typename BasicJsonType::string_t, Key>::value>>
+template < typename BasicJsonType, typename Key, typename Value, typename Compare, typename Allocator,
+           typename = enable_if_t < !std::is_constructible <
+                                        typename BasicJsonType::string_t, Key >::value >>
 void from_json(const BasicJsonType& j, std::map<Key, Value, Compare, Allocator>& m)
 {
-    if (JSON_UNLIKELY(not j.is_array()))
+    if (JSON_HEDLEY_UNLIKELY(!j.is_array()))
     {
         JSON_THROW(type_error::create(302, "type must be array, but is " + std::string(j.type_name())));
     }
+    m.clear();
     for (const auto& p : j)
     {
-        if (JSON_UNLIKELY(not p.is_array()))
+        if (JSON_HEDLEY_UNLIKELY(!p.is_array()))
         {
             JSON_THROW(type_error::create(302, "type must be array, but is " + std::string(p.type_name())));
         }
@@ -1586,18 +3761,19 @@ void from_json(const BasicJsonType& j, std::map<Key, Value, Compare, Allocator>&
     }
 }
 
-template <typename BasicJsonType, typename Key, typename Value, typename Hash, typename KeyEqual, typename Allocator,
-          typename = enable_if_t<not std::is_constructible<
-                                     typename BasicJsonType::string_t, Key>::value>>
+template < typename BasicJsonType, typename Key, typename Value, typename Hash, typename KeyEqual, typename Allocator,
+           typename = enable_if_t < !std::is_constructible <
+                                        typename BasicJsonType::string_t, Key >::value >>
 void from_json(const BasicJsonType& j, std::unordered_map<Key, Value, Hash, KeyEqual, Allocator>& m)
 {
-    if (JSON_UNLIKELY(not j.is_array()))
+    if (JSON_HEDLEY_UNLIKELY(!j.is_array()))
     {
         JSON_THROW(type_error::create(302, "type must be array, but is " + std::string(j.type_name())));
     }
+    m.clear();
     for (const auto& p : j)
     {
-        if (JSON_UNLIKELY(not p.is_array()))
+        if (JSON_HEDLEY_UNLIKELY(!p.is_array()))
         {
             JSON_THROW(type_error::create(302, "type must be array, but is " + std::string(p.type_name())));
         }
@@ -1624,43 +3800,45 @@ namespace
 {
 constexpr const auto& from_json = detail::static_const<detail::from_json_fn>::value;
 } // namespace
-}  // namespace nlohmann
+} // namespace nlohmann
 
 // #include <nlohmann/detail/conversions/to_json.hpp>
 
 
-#include <ciso646> // or, and, not
+#include <algorithm> // copy
 #include <iterator> // begin, end
+#include <string> // string
 #include <tuple> // tuple, get
 #include <type_traits> // is_same, is_constructible, is_floating_point, is_enum, underlying_type
 #include <utility> // move, forward, declval, pair
 #include <valarray> // valarray
 #include <vector> // vector
 
-// #include <nlohmann/detail/meta/cpp_future.hpp>
-
-// #include <nlohmann/detail/meta/type_traits.hpp>
-
-// #include <nlohmann/detail/value_t.hpp>
-
 // #include <nlohmann/detail/iterators/iteration_proxy.hpp>
 
 
 #include <cstddef> // size_t
-#include <string> // string, to_string
 #include <iterator> // input_iterator_tag
+#include <string> // string, to_string
 #include <tuple> // tuple_size, get, tuple_element
 
-// #include <nlohmann/detail/value_t.hpp>
-
 // #include <nlohmann/detail/meta/type_traits.hpp>
 
+// #include <nlohmann/detail/value_t.hpp>
+
 
 namespace nlohmann
 {
 namespace detail
 {
-template <typename IteratorType> class iteration_proxy_value
+template<typename string_type>
+void int_to_string( string_type& target, std::size_t value )
+{
+    // For ADL
+    using std::to_string;
+    target = to_string(value);
+}
+template<typename IteratorType> class iteration_proxy_value
 {
   public:
     using difference_type = std::ptrdiff_t;
@@ -1668,6 +3846,7 @@ template <typename IteratorType> class iteration_proxy_value
     using pointer = value_type * ;
     using reference = value_type & ;
     using iterator_category = std::input_iterator_tag;
+    using string_type = typename std::remove_cv< typename std::remove_reference<decltype( std::declval<IteratorType>().key() ) >::type >::type;
 
   private:
     /// the iterator
@@ -1677,9 +3856,9 @@ template <typename IteratorType> class iteration_proxy_value
     /// last stringified array index
     mutable std::size_t array_index_last = 0;
     /// a string representation of the array index
-    mutable std::string array_index_str = "0";
+    mutable string_type array_index_str = "0";
     /// an empty string (to return a reference for primitive values)
-    const std::string empty_str = "";
+    const string_type empty_str = "";
 
   public:
     explicit iteration_proxy_value(IteratorType it) noexcept : anchor(it) {}
@@ -1700,21 +3879,21 @@ template <typename IteratorType> class iteration_proxy_value
     }
 
     /// equality operator (needed for InputIterator)
-    bool operator==(const iteration_proxy_value& o) const noexcept
+    bool operator==(const iteration_proxy_value& o) const
     {
         return anchor == o.anchor;
     }
 
     /// inequality operator (needed for range-based for)
-    bool operator!=(const iteration_proxy_value& o) const noexcept
+    bool operator!=(const iteration_proxy_value& o) const
     {
         return anchor != o.anchor;
     }
 
     /// return key of the iterator
-    const std::string& key() const
+    const string_type& key() const
     {
-        assert(anchor.m_object != nullptr);
+        JSON_ASSERT(anchor.m_object != nullptr);
 
         switch (anchor.m_object->type())
         {
@@ -1723,7 +3902,7 @@ template <typename IteratorType> class iteration_proxy_value
             {
                 if (array_index != array_index_last)
                 {
-                    array_index_str = std::to_string(array_index);
+                    int_to_string( array_index_str, array_index );
                     array_index_last = array_index;
                 }
                 return array_index_str;
@@ -1773,7 +3952,7 @@ template<typename IteratorType> class iteration_proxy
 // Structured Bindings Support
 // For further reference see https://blog.tartanllama.xyz/structured-bindings/
 // And see https://github.com/nlohmann/json/pull/1391
-template <std::size_t N, typename IteratorType, enable_if_t<N == 0, int> = 0>
+template<std::size_t N, typename IteratorType, enable_if_t<N == 0, int> = 0>
 auto get(const nlohmann::detail::iteration_proxy_value<IteratorType>& i) -> decltype(i.key())
 {
     return i.key();
@@ -1781,7 +3960,7 @@ auto get(const nlohmann::detail::iteration_proxy_value<IteratorType>& i) -> decl
 // Structured Bindings Support
 // For further reference see https://blog.tartanllama.xyz/structured-bindings/
 // And see https://github.com/nlohmann/json/pull/1391
-template <std::size_t N, typename IteratorType, enable_if_t<N == 1, int> = 0>
+template<std::size_t N, typename IteratorType, enable_if_t<N == 1, int> = 0>
 auto get(const nlohmann::detail::iteration_proxy_value<IteratorType>& i) -> decltype(i.value())
 {
     return i.value();
@@ -1795,11 +3974,16 @@ auto get(const nlohmann::detail::iteration_proxy_value<IteratorType>& i) -> decl
 // And see https://github.com/nlohmann/json/pull/1391
 namespace std
 {
-template <typename IteratorType>
+#if defined(__clang__)
+    // Fix: https://github.com/nlohmann/json/issues/1401
+    #pragma clang diagnostic push
+    #pragma clang diagnostic ignored "-Wmismatched-tags"
+#endif
+template<typename IteratorType>
 class tuple_size<::nlohmann::detail::iteration_proxy_value<IteratorType>>
             : public std::integral_constant<std::size_t, 2> {};
 
-template <std::size_t N, typename IteratorType>
+template<std::size_t N, typename IteratorType>
 class tuple_element<N, ::nlohmann::detail::iteration_proxy_value<IteratorType >>
 {
   public:
@@ -1807,7 +3991,17 @@ class tuple_element<N, ::nlohmann::detail::iteration_proxy_value<IteratorType >>
                      get<N>(std::declval <
                             ::nlohmann::detail::iteration_proxy_value<IteratorType >> ()));
 };
-}
+#if defined(__clang__)
+    #pragma clang diagnostic pop
+#endif
+} // namespace std
+
+// #include <nlohmann/detail/meta/cpp_future.hpp>
+
+// #include <nlohmann/detail/meta/type_traits.hpp>
+
+// #include <nlohmann/detail/value_t.hpp>
+
 
 namespace nlohmann
 {
@@ -1850,9 +4044,9 @@ struct external_constructor<value_t::string>
         j.assert_invariant();
     }
 
-    template<typename BasicJsonType, typename CompatibleStringType,
-             enable_if_t<not std::is_same<CompatibleStringType, typename BasicJsonType::string_t>::value,
-                         int> = 0>
+    template < typename BasicJsonType, typename CompatibleStringType,
+               enable_if_t < !std::is_same<CompatibleStringType, typename BasicJsonType::string_t>::value,
+                             int > = 0 >
     static void construct(BasicJsonType& j, const CompatibleStringType& str)
     {
         j.m_type = value_t::string;
@@ -1862,6 +4056,28 @@ struct external_constructor<value_t::string>
 };
 
 template<>
+struct external_constructor<value_t::binary>
+{
+    template<typename BasicJsonType>
+    static void construct(BasicJsonType& j, const typename BasicJsonType::binary_t& b)
+    {
+        j.m_type = value_t::binary;
+        typename BasicJsonType::binary_t value{b};
+        j.m_value = value;
+        j.assert_invariant();
+    }
+
+    template<typename BasicJsonType>
+    static void construct(BasicJsonType& j, typename BasicJsonType::binary_t&& b)
+    {
+        j.m_type = value_t::binary;
+        typename BasicJsonType::binary_t value{std::move(b)};
+        j.m_value = value;
+        j.assert_invariant();
+    }
+};
+
+template<>
 struct external_constructor<value_t::number_float>
 {
     template<typename BasicJsonType>
@@ -1916,9 +4132,9 @@ struct external_constructor<value_t::array>
         j.assert_invariant();
     }
 
-    template<typename BasicJsonType, typename CompatibleArrayType,
-             enable_if_t<not std::is_same<CompatibleArrayType, typename BasicJsonType::array_t>::value,
-                         int> = 0>
+    template < typename BasicJsonType, typename CompatibleArrayType,
+               enable_if_t < !std::is_same<CompatibleArrayType, typename BasicJsonType::array_t>::value,
+                             int > = 0 >
     static void construct(BasicJsonType& j, const CompatibleArrayType& arr)
     {
         using std::begin;
@@ -1948,7 +4164,10 @@ struct external_constructor<value_t::array>
         j.m_type = value_t::array;
         j.m_value = value_t::array;
         j.m_value.array->resize(arr.size());
-        std::copy(std::begin(arr), std::end(arr), j.m_value.array->begin());
+        if (arr.size() > 0)
+        {
+            std::copy(std::begin(arr), std::end(arr), j.m_value.array->begin());
+        }
         j.assert_invariant();
     }
 };
@@ -1972,8 +4191,8 @@ struct external_constructor<value_t::object>
         j.assert_invariant();
     }
 
-    template<typename BasicJsonType, typename CompatibleObjectType,
-             enable_if_t<not std::is_same<CompatibleObjectType, typename BasicJsonType::object_t>::value, int> = 0>
+    template < typename BasicJsonType, typename CompatibleObjectType,
+               enable_if_t < !std::is_same<CompatibleObjectType, typename BasicJsonType::object_t>::value, int > = 0 >
     static void construct(BasicJsonType& j, const CompatibleObjectType& obj)
     {
         using std::begin;
@@ -2044,19 +4263,25 @@ void to_json(BasicJsonType& j, const std::vector<bool>& e)
     external_constructor<value_t::array>::construct(j, e);
 }
 
-template <typename BasicJsonType, typename CompatibleArrayType,
-          enable_if_t<is_compatible_array_type<BasicJsonType,
-                      CompatibleArrayType>::value and
-                      not is_compatible_object_type<
-                          BasicJsonType, CompatibleArrayType>::value and
-                      not is_compatible_string_type<BasicJsonType, CompatibleArrayType>::value and
-                      not is_basic_json<CompatibleArrayType>::value,
-                      int> = 0>
+template < typename BasicJsonType, typename CompatibleArrayType,
+           enable_if_t < is_compatible_array_type<BasicJsonType,
+                         CompatibleArrayType>::value&&
+                         !is_compatible_object_type<BasicJsonType, CompatibleArrayType>::value&&
+                         !is_compatible_string_type<BasicJsonType, CompatibleArrayType>::value&&
+                         !std::is_same<typename BasicJsonType::binary_t, CompatibleArrayType>::value&&
+                         !is_basic_json<CompatibleArrayType>::value,
+                         int > = 0 >
 void to_json(BasicJsonType& j, const CompatibleArrayType& arr)
 {
     external_constructor<value_t::array>::construct(j, arr);
 }
 
+template<typename BasicJsonType>
+void to_json(BasicJsonType& j, const typename BasicJsonType::binary_t& bin)
+{
+    external_constructor<value_t::binary>::construct(j, bin);
+}
+
 template<typename BasicJsonType, typename T,
          enable_if_t<std::is_convertible<T, BasicJsonType>::value, int> = 0>
 void to_json(BasicJsonType& j, const std::valarray<T>& arr)
@@ -2070,8 +4295,8 @@ void to_json(BasicJsonType& j, typename BasicJsonType::array_t&& arr)
     external_constructor<value_t::array>::construct(j, std::move(arr));
 }
 
-template<typename BasicJsonType, typename CompatibleObjectType,
-         enable_if_t<is_compatible_object_type<BasicJsonType, CompatibleObjectType>::value and not is_basic_json<CompatibleObjectType>::value, int> = 0>
+template < typename BasicJsonType, typename CompatibleObjectType,
+           enable_if_t < is_compatible_object_type<BasicJsonType, CompatibleObjectType>::value&& !is_basic_json<CompatibleObjectType>::value, int > = 0 >
 void to_json(BasicJsonType& j, const CompatibleObjectType& obj)
 {
     external_constructor<value_t::object>::construct(j, obj);
@@ -2085,23 +4310,23 @@ void to_json(BasicJsonType& j, typename BasicJsonType::object_t&& obj)
 
 template <
     typename BasicJsonType, typename T, std::size_t N,
-    enable_if_t<not std::is_constructible<typename BasicJsonType::string_t,
-                const T(&)[N]>::value,
-                int> = 0 >
+    enable_if_t < !std::is_constructible<typename BasicJsonType::string_t,
+                  const T(&)[N]>::value,
+                  int > = 0 >
 void to_json(BasicJsonType& j, const T(&arr)[N])
 {
     external_constructor<value_t::array>::construct(j, arr);
 }
 
-template<typename BasicJsonType, typename... Args>
-void to_json(BasicJsonType& j, const std::pair<Args...>& p)
+template < typename BasicJsonType, typename T1, typename T2, enable_if_t < std::is_constructible<BasicJsonType, T1>::value&& std::is_constructible<BasicJsonType, T2>::value, int > = 0 >
+void to_json(BasicJsonType& j, const std::pair<T1, T2>& p)
 {
     j = { p.first, p.second };
 }
 
 // for https://github.com/nlohmann/json/pull/1134
-template < typename BasicJsonType, typename T,
-           enable_if_t<std::is_same<T, iteration_proxy_value<typename BasicJsonType::iterator>>::value, int> = 0>
+template<typename BasicJsonType, typename T,
+         enable_if_t<std::is_same<T, iteration_proxy_value<typename BasicJsonType::iterator>>::value, int> = 0>
 void to_json(BasicJsonType& j, const T& b)
 {
     j = { {b.key(), b.value()} };
@@ -2113,10 +4338,10 @@ void to_json_tuple_impl(BasicJsonType& j, const Tuple& t, index_sequence<Idx...>
     j = { std::get<Idx>(t)... };
 }
 
-template<typename BasicJsonType, typename... Args>
-void to_json(BasicJsonType& j, const std::tuple<Args...>& t)
+template<typename BasicJsonType, typename T, enable_if_t<is_constructible_tuple<BasicJsonType, T>::value, int > = 0>
+void to_json(BasicJsonType& j, const T& t)
 {
-    to_json_tuple_impl(j, t, index_sequence_for<Args...> {});
+    to_json_tuple_impl(j, t, make_index_sequence<std::tuple_size<T>::value> {});
 }
 
 struct to_json_fn
@@ -2135,13 +4360,368 @@ namespace
 {
 constexpr const auto& to_json = detail::static_const<detail::to_json_fn>::value;
 } // namespace
+} // namespace nlohmann
+
+
+namespace nlohmann
+{
+
+template<typename, typename>
+struct adl_serializer
+{
+    /*!
+    @brief convert a JSON value to any value type
+
+    This function is usually called by the `get()` function of the
+    @ref basic_json class (either explicit or via conversion operators).
+
+    @param[in] j        JSON value to read from
+    @param[in,out] val  value to write to
+    */
+    template<typename BasicJsonType, typename ValueType>
+    static auto from_json(BasicJsonType&& j, ValueType& val) noexcept(
+        noexcept(::nlohmann::from_json(std::forward<BasicJsonType>(j), val)))
+    -> decltype(::nlohmann::from_json(std::forward<BasicJsonType>(j), val), void())
+    {
+        ::nlohmann::from_json(std::forward<BasicJsonType>(j), val);
+    }
+
+    /*!
+    @brief convert any value type to a JSON value
+
+    This function is usually called by the constructors of the @ref basic_json
+    class.
+
+    @param[in,out] j  JSON value to write to
+    @param[in] val    value to read from
+    */
+    template<typename BasicJsonType, typename ValueType>
+    static auto to_json(BasicJsonType& j, ValueType&& val) noexcept(
+        noexcept(::nlohmann::to_json(j, std::forward<ValueType>(val))))
+    -> decltype(::nlohmann::to_json(j, std::forward<ValueType>(val)), void())
+    {
+        ::nlohmann::to_json(j, std::forward<ValueType>(val));
+    }
+};
+
 }  // namespace nlohmann
 
+// #include <nlohmann/byte_container_with_subtype.hpp>
+
+
+#include <cstdint> // uint8_t
+#include <tuple> // tie
+#include <utility> // move
+
+namespace nlohmann
+{
+
+/*!
+@brief an internal type for a backed binary type
+
+This type extends the template parameter @a BinaryType provided to `basic_json`
+with a subtype used by BSON and MessagePack. This type exists so that the user
+does not have to specify a type themselves with a specific naming scheme in
+order to override the binary type.
+
+@tparam BinaryType container to store bytes (`std::vector<std::uint8_t>` by
+                   default)
+
+@since version 3.8.0
+*/
+template<typename BinaryType>
+class byte_container_with_subtype : public BinaryType
+{
+  public:
+    /// the type of the underlying container
+    using container_type = BinaryType;
+
+    byte_container_with_subtype() noexcept(noexcept(container_type()))
+        : container_type()
+    {}
+
+    byte_container_with_subtype(const container_type& b) noexcept(noexcept(container_type(b)))
+        : container_type(b)
+    {}
+
+    byte_container_with_subtype(container_type&& b) noexcept(noexcept(container_type(std::move(b))))
+        : container_type(std::move(b))
+    {}
+
+    byte_container_with_subtype(const container_type& b, std::uint8_t subtype) noexcept(noexcept(container_type(b)))
+        : container_type(b)
+        , m_subtype(subtype)
+        , m_has_subtype(true)
+    {}
+
+    byte_container_with_subtype(container_type&& b, std::uint8_t subtype) noexcept(noexcept(container_type(std::move(b))))
+        : container_type(std::move(b))
+        , m_subtype(subtype)
+        , m_has_subtype(true)
+    {}
+
+    bool operator==(const byte_container_with_subtype& rhs) const
+    {
+        return std::tie(static_cast<const BinaryType&>(*this), m_subtype, m_has_subtype) ==
+               std::tie(static_cast<const BinaryType&>(rhs), rhs.m_subtype, rhs.m_has_subtype);
+    }
+
+    bool operator!=(const byte_container_with_subtype& rhs) const
+    {
+        return !(rhs == *this);
+    }
+
+    /*!
+    @brief sets the binary subtype
+
+    Sets the binary subtype of the value, also flags a binary JSON value as
+    having a subtype, which has implications for serialization.
+
+    @complexity Constant.
+
+    @exceptionsafety No-throw guarantee: this member function never throws
+    exceptions.
+
+    @sa @ref subtype() -- return the binary subtype
+    @sa @ref clear_subtype() -- clears the binary subtype
+    @sa @ref has_subtype() -- returns whether or not the binary value has a
+    subtype
+
+    @since version 3.8.0
+    */
+    void set_subtype(std::uint8_t subtype) noexcept
+    {
+        m_subtype = subtype;
+        m_has_subtype = true;
+    }
+
+    /*!
+    @brief return the binary subtype
+
+    Returns the numerical subtype of the value if it has a subtype. If it does
+    not have a subtype, this function will return size_t(-1) as a sentinel
+    value.
+
+    @return the numerical subtype of the binary value
+
+    @complexity Constant.
+
+    @exceptionsafety No-throw guarantee: this member function never throws
+    exceptions.
+
+    @sa @ref set_subtype() -- sets the binary subtype
+    @sa @ref clear_subtype() -- clears the binary subtype
+    @sa @ref has_subtype() -- returns whether or not the binary value has a
+    subtype
+
+    @since version 3.8.0
+    */
+    constexpr std::uint8_t subtype() const noexcept
+    {
+        return m_subtype;
+    }
+
+    /*!
+    @brief return whether the value has a subtype
+
+    @return whether the value has a subtype
+
+    @complexity Constant.
+
+    @exceptionsafety No-throw guarantee: this member function never throws
+    exceptions.
+
+    @sa @ref subtype() -- return the binary subtype
+    @sa @ref set_subtype() -- sets the binary subtype
+    @sa @ref clear_subtype() -- clears the binary subtype
+
+    @since version 3.8.0
+    */
+    constexpr bool has_subtype() const noexcept
+    {
+        return m_has_subtype;
+    }
+
+    /*!
+    @brief clears the binary subtype
+
+    Clears the binary subtype and flags the value as not having a subtype, which
+    has implications for serialization; for instance MessagePack will prefer the
+    bin family over the ext family.
+
+    @complexity Constant.
+
+    @exceptionsafety No-throw guarantee: this member function never throws
+    exceptions.
+
+    @sa @ref subtype() -- return the binary subtype
+    @sa @ref set_subtype() -- sets the binary subtype
+    @sa @ref has_subtype() -- returns whether or not the binary value has a
+    subtype
+
+    @since version 3.8.0
+    */
+    void clear_subtype() noexcept
+    {
+        m_subtype = 0;
+        m_has_subtype = false;
+    }
+
+  private:
+    std::uint8_t m_subtype = 0;
+    bool m_has_subtype = false;
+};
+
+}  // namespace nlohmann
+
+// #include <nlohmann/detail/conversions/from_json.hpp>
+
+// #include <nlohmann/detail/conversions/to_json.hpp>
+
+// #include <nlohmann/detail/exceptions.hpp>
+
+// #include <nlohmann/detail/hash.hpp>
+
+
+#include <cstddef> // size_t, uint8_t
+#include <functional> // hash
+
+namespace nlohmann
+{
+namespace detail
+{
+
+// boost::hash_combine
+inline std::size_t combine(std::size_t seed, std::size_t h) noexcept
+{
+    seed ^= h + 0x9e3779b9 + (seed << 6U) + (seed >> 2U);
+    return seed;
+}
+
+/*!
+@brief hash a JSON value
+
+The hash function tries to rely on std::hash where possible. Furthermore, the
+type of the JSON value is taken into account to have different hash values for
+null, 0, 0U, and false, etc.
+
+@tparam BasicJsonType basic_json specialization
+@param j JSON value to hash
+@return hash value of j
+*/
+template<typename BasicJsonType>
+std::size_t hash(const BasicJsonType& j)
+{
+    using string_t = typename BasicJsonType::string_t;
+    using number_integer_t = typename BasicJsonType::number_integer_t;
+    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+    using number_float_t = typename BasicJsonType::number_float_t;
+
+    const auto type = static_cast<std::size_t>(j.type());
+    switch (j.type())
+    {
+        case BasicJsonType::value_t::null:
+        case BasicJsonType::value_t::discarded:
+        {
+            return combine(type, 0);
+        }
+
+        case BasicJsonType::value_t::object:
+        {
+            auto seed = combine(type, j.size());
+            for (const auto& element : j.items())
+            {
+                const auto h = std::hash<string_t> {}(element.key());
+                seed = combine(seed, h);
+                seed = combine(seed, hash(element.value()));
+            }
+            return seed;
+        }
+
+        case BasicJsonType::value_t::array:
+        {
+            auto seed = combine(type, j.size());
+            for (const auto& element : j)
+            {
+                seed = combine(seed, hash(element));
+            }
+            return seed;
+        }
+
+        case BasicJsonType::value_t::string:
+        {
+            const auto h = std::hash<string_t> {}(j.template get_ref<const string_t&>());
+            return combine(type, h);
+        }
+
+        case BasicJsonType::value_t::boolean:
+        {
+            const auto h = std::hash<bool> {}(j.template get<bool>());
+            return combine(type, h);
+        }
+
+        case BasicJsonType::value_t::number_integer:
+        {
+            const auto h = std::hash<number_integer_t> {}(j.template get<number_integer_t>());
+            return combine(type, h);
+        }
+
+        case nlohmann::detail::value_t::number_unsigned:
+        {
+            const auto h = std::hash<number_unsigned_t> {}(j.template get<number_unsigned_t>());
+            return combine(type, h);
+        }
+
+        case nlohmann::detail::value_t::number_float:
+        {
+            const auto h = std::hash<number_float_t> {}(j.template get<number_float_t>());
+            return combine(type, h);
+        }
+
+        case nlohmann::detail::value_t::binary:
+        {
+            auto seed = combine(type, j.get_binary().size());
+            const auto h = std::hash<bool> {}(j.get_binary().has_subtype());
+            seed = combine(seed, h);
+            seed = combine(seed, j.get_binary().subtype());
+            for (const auto byte : j.get_binary())
+            {
+                seed = combine(seed, std::hash<std::uint8_t> {}(byte));
+            }
+            return seed;
+        }
+
+        default: // LCOV_EXCL_LINE
+            JSON_ASSERT(false); // LCOV_EXCL_LINE
+    }
+}
+
+}  // namespace detail
+}  // namespace nlohmann
+
+// #include <nlohmann/detail/input/binary_reader.hpp>
+
+
+#include <algorithm> // generate_n
+#include <array> // array
+#include <cmath> // ldexp
+#include <cstddef> // size_t
+#include <cstdint> // uint8_t, uint16_t, uint32_t, uint64_t
+#include <cstdio> // snprintf
+#include <cstring> // memcpy
+#include <iterator> // back_inserter
+#include <limits> // numeric_limits
+#include <string> // char_traits, string
+#include <utility> // make_pair, move
+
+// #include <nlohmann/detail/exceptions.hpp>
+
 // #include <nlohmann/detail/input/input_adapters.hpp>
 
 
-#include <cassert> // assert
+#include <array> // array
 #include <cstddef> // size_t
+#include <cstdio> //FILE *
 #include <cstring> // strlen
 #include <istream> // istream
 #include <iterator> // begin, end, iterator_traits, random_access_iterator_tag, distance, next
@@ -2150,7 +4730,8 @@ constexpr const auto& to_json = detail::static_const<detail::to_json_fn>::value;
 #include <string> // string, char_traits
 #include <type_traits> // enable_if, is_base_of, is_pointer, is_integral, remove_pointer
 #include <utility> // pair, declval
-#include <cstdio> //FILE *
+
+// #include <nlohmann/detail/iterators/iterator_traits.hpp>
 
 // #include <nlohmann/detail/macro_scope.hpp>
 
@@ -2167,41 +4748,30 @@ enum class input_format_t { json, cbor, msgpack, ubjson, bson };
 ////////////////////
 
 /*!
-@brief abstract input adapter interface
-
-Produces a stream of std::char_traits<char>::int_type characters from a
-std::istream, a buffer, or some other input type. Accepts the return of
-exactly one non-EOF character for future input. The int_type characters
-returned consist of all valid char values as positive values (typically
-unsigned char), plus an EOF value outside that range, specified by the value
-of the function std::char_traits<char>::eof(). This value is typically -1, but
-could be any arbitrary value which is not a valid char value.
-*/
-struct input_adapter_protocol
-{
-    /// get a character [0,255] or std::char_traits<char>::eof().
-    virtual std::char_traits<char>::int_type get_character() = 0;
-    virtual ~input_adapter_protocol() = default;
-};
-
-/// a type to simplify interfaces
-using input_adapter_t = std::shared_ptr<input_adapter_protocol>;
-
-/*!
 Input adapter for stdio file access. This adapter read only 1 byte and do not use any
  buffer. This adapter is a very low level adapter.
 */
-class file_input_adapter : public input_adapter_protocol
+class file_input_adapter
 {
   public:
-    explicit file_input_adapter(std::FILE* f)  noexcept
+    using char_type = char;
+
+    JSON_HEDLEY_NON_NULL(2)
+    explicit file_input_adapter(std::FILE* f) noexcept
         : m_file(f)
     {}
 
-    std::char_traits<char>::int_type get_character() noexcept override
+    // make class move-only
+    file_input_adapter(const file_input_adapter&) = delete;
+    file_input_adapter(file_input_adapter&&) = default;
+    file_input_adapter& operator=(const file_input_adapter&) = delete;
+    file_input_adapter& operator=(file_input_adapter&&) = delete;
+
+    std::char_traits<char>::int_type get_character() noexcept
     {
         return std::fgetc(m_file);
     }
+
   private:
     /// the file pointer to read from
     std::FILE* m_file;
@@ -2217,87 +4787,111 @@ characters following those used in parsing the JSON input.  Clears the
 std::istream flags; any input errors (e.g., EOF) will be detected by the first
 subsequent call for input from the std::istream.
 */
-class input_stream_adapter : public input_adapter_protocol
+class input_stream_adapter
 {
   public:
-    ~input_stream_adapter() override
+    using char_type = char;
+
+    ~input_stream_adapter()
     {
         // clear stream flags; we use underlying streambuf I/O, do not
         // maintain ifstream flags, except eof
-        is.clear(is.rdstate() & std::ios::eofbit);
+        if (is != nullptr)
+        {
+            is->clear(is->rdstate() & std::ios::eofbit);
+        }
     }
 
     explicit input_stream_adapter(std::istream& i)
-        : is(i), sb(*i.rdbuf())
+        : is(&i), sb(i.rdbuf())
     {}
 
     // delete because of pointer members
     input_stream_adapter(const input_stream_adapter&) = delete;
     input_stream_adapter& operator=(input_stream_adapter&) = delete;
-    input_stream_adapter(input_stream_adapter&&) = delete;
-    input_stream_adapter& operator=(input_stream_adapter&&) = delete;
+    input_stream_adapter& operator=(input_stream_adapter&& rhs) = delete;
+
+    input_stream_adapter(input_stream_adapter&& rhs) noexcept : is(rhs.is), sb(rhs.sb)
+    {
+        rhs.is = nullptr;
+        rhs.sb = nullptr;
+    }
 
     // std::istream/std::streambuf use std::char_traits<char>::to_int_type, to
     // ensure that std::char_traits<char>::eof() and the character 0xFF do not
     // end up as the same value, eg. 0xFFFFFFFF.
-    std::char_traits<char>::int_type get_character() override
+    std::char_traits<char>::int_type get_character()
     {
-        auto res = sb.sbumpc();
+        auto res = sb->sbumpc();
         // set eof manually, as we don't use the istream interface.
-        if (res == EOF)
+        if (JSON_HEDLEY_UNLIKELY(res == EOF))
         {
-            is.clear(is.rdstate() | std::ios::eofbit);
+            is->clear(is->rdstate() | std::ios::eofbit);
         }
         return res;
     }
 
   private:
     /// the associated input stream
-    std::istream& is;
-    std::streambuf& sb;
+    std::istream* is = nullptr;
+    std::streambuf* sb = nullptr;
 };
 
-/// input adapter for buffer input
-class input_buffer_adapter : public input_adapter_protocol
+// General-purpose iterator-based adapter. It might not be as fast as
+// theoretically possible for some containers, but it is extremely versatile.
+template<typename IteratorType>
+class iterator_input_adapter
 {
   public:
-    input_buffer_adapter(const char* b, const std::size_t l) noexcept
-        : cursor(b), limit(b + l)
-    {}
+    using char_type = typename std::iterator_traits<IteratorType>::value_type;
 
-    // delete because of pointer members
-    input_buffer_adapter(const input_buffer_adapter&) = delete;
-    input_buffer_adapter& operator=(input_buffer_adapter&) = delete;
-    input_buffer_adapter(input_buffer_adapter&&) = delete;
-    input_buffer_adapter& operator=(input_buffer_adapter&&) = delete;
-    ~input_buffer_adapter() override = default;
+    iterator_input_adapter(IteratorType first, IteratorType last)
+        : current(std::move(first)), end(std::move(last)) {}
 
-    std::char_traits<char>::int_type get_character() noexcept override
+    typename std::char_traits<char_type>::int_type get_character()
     {
-        if (JSON_LIKELY(cursor < limit))
+        if (JSON_HEDLEY_LIKELY(current != end))
         {
-            return std::char_traits<char>::to_int_type(*(cursor++));
+            auto result = std::char_traits<char_type>::to_int_type(*current);
+            std::advance(current, 1);
+            return result;
+        }
+        else
+        {
+            return std::char_traits<char_type>::eof();
         }
-
-        return std::char_traits<char>::eof();
     }
 
   private:
-    /// pointer to the current character
-    const char* cursor;
-    /// pointer past the last character
-    const char* const limit;
+    IteratorType current;
+    IteratorType end;
+
+    template<typename BaseInputAdapter, size_t T>
+    friend struct wide_string_input_helper;
+
+    bool empty() const
+    {
+        return current == end;
+    }
+
 };
 
-template<typename WideStringType, size_t T>
-struct wide_string_input_helper
+
+template<typename BaseInputAdapter, size_t T>
+struct wide_string_input_helper;
+
+template<typename BaseInputAdapter>
+struct wide_string_input_helper<BaseInputAdapter, 4>
 {
     // UTF-32
-    static void fill_buffer(const WideStringType& str, size_t& current_wchar, std::array<std::char_traits<char>::int_type, 4>& utf8_bytes, size_t& utf8_bytes_index, size_t& utf8_bytes_filled)
+    static void fill_buffer(BaseInputAdapter& input,
+                            std::array<std::char_traits<char>::int_type, 4>& utf8_bytes,
+                            size_t& utf8_bytes_index,
+                            size_t& utf8_bytes_filled)
     {
         utf8_bytes_index = 0;
 
-        if (current_wchar == str.size())
+        if (JSON_HEDLEY_UNLIKELY(input.empty()))
         {
             utf8_bytes[0] = std::char_traits<char>::eof();
             utf8_bytes_filled = 1;
@@ -2305,54 +4899,57 @@ struct wide_string_input_helper
         else
         {
             // get the current character
-            const auto wc = static_cast<int>(str[current_wchar++]);
+            const auto wc = input.get_character();
 
             // UTF-32 to UTF-8 encoding
             if (wc < 0x80)
             {
-                utf8_bytes[0] = wc;
+                utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(wc);
                 utf8_bytes_filled = 1;
             }
             else if (wc <= 0x7FF)
             {
-                utf8_bytes[0] = 0xC0 | ((wc >> 6) & 0x1F);
-                utf8_bytes[1] = 0x80 | (wc & 0x3F);
+                utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(0xC0u | ((static_cast<unsigned int>(wc) >> 6u) & 0x1Fu));
+                utf8_bytes[1] = static_cast<std::char_traits<char>::int_type>(0x80u | (static_cast<unsigned int>(wc) & 0x3Fu));
                 utf8_bytes_filled = 2;
             }
             else if (wc <= 0xFFFF)
             {
-                utf8_bytes[0] = 0xE0 | ((wc >> 12) & 0x0F);
-                utf8_bytes[1] = 0x80 | ((wc >> 6) & 0x3F);
-                utf8_bytes[2] = 0x80 | (wc & 0x3F);
+                utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(0xE0u | ((static_cast<unsigned int>(wc) >> 12u) & 0x0Fu));
+                utf8_bytes[1] = static_cast<std::char_traits<char>::int_type>(0x80u | ((static_cast<unsigned int>(wc) >> 6u) & 0x3Fu));
+                utf8_bytes[2] = static_cast<std::char_traits<char>::int_type>(0x80u | (static_cast<unsigned int>(wc) & 0x3Fu));
                 utf8_bytes_filled = 3;
             }
             else if (wc <= 0x10FFFF)
             {
-                utf8_bytes[0] = 0xF0 | ((wc >> 18) & 0x07);
-                utf8_bytes[1] = 0x80 | ((wc >> 12) & 0x3F);
-                utf8_bytes[2] = 0x80 | ((wc >> 6) & 0x3F);
-                utf8_bytes[3] = 0x80 | (wc & 0x3F);
+                utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(0xF0u | ((static_cast<unsigned int>(wc) >> 18u) & 0x07u));
+                utf8_bytes[1] = static_cast<std::char_traits<char>::int_type>(0x80u | ((static_cast<unsigned int>(wc) >> 12u) & 0x3Fu));
+                utf8_bytes[2] = static_cast<std::char_traits<char>::int_type>(0x80u | ((static_cast<unsigned int>(wc) >> 6u) & 0x3Fu));
+                utf8_bytes[3] = static_cast<std::char_traits<char>::int_type>(0x80u | (static_cast<unsigned int>(wc) & 0x3Fu));
                 utf8_bytes_filled = 4;
             }
             else
             {
                 // unknown character
-                utf8_bytes[0] = wc;
+                utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(wc);
                 utf8_bytes_filled = 1;
             }
         }
     }
 };
 
-template<typename WideStringType>
-struct wide_string_input_helper<WideStringType, 2>
+template<typename BaseInputAdapter>
+struct wide_string_input_helper<BaseInputAdapter, 2>
 {
     // UTF-16
-    static void fill_buffer(const WideStringType& str, size_t& current_wchar, std::array<std::char_traits<char>::int_type, 4>& utf8_bytes, size_t& utf8_bytes_index, size_t& utf8_bytes_filled)
+    static void fill_buffer(BaseInputAdapter& input,
+                            std::array<std::char_traits<char>::int_type, 4>& utf8_bytes,
+                            size_t& utf8_bytes_index,
+                            size_t& utf8_bytes_filled)
     {
         utf8_bytes_index = 0;
 
-        if (current_wchar == str.size())
+        if (JSON_HEDLEY_UNLIKELY(input.empty()))
         {
             utf8_bytes[0] = std::char_traits<char>::eof();
             utf8_bytes_filled = 1;
@@ -2360,44 +4957,42 @@ struct wide_string_input_helper<WideStringType, 2>
         else
         {
             // get the current character
-            const auto wc = static_cast<int>(str[current_wchar++]);
+            const auto wc = input.get_character();
 
             // UTF-16 to UTF-8 encoding
             if (wc < 0x80)
             {
-                utf8_bytes[0] = wc;
+                utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(wc);
                 utf8_bytes_filled = 1;
             }
             else if (wc <= 0x7FF)
             {
-                utf8_bytes[0] = 0xC0 | ((wc >> 6));
-                utf8_bytes[1] = 0x80 | (wc & 0x3F);
+                utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(0xC0u | ((static_cast<unsigned int>(wc) >> 6u)));
+                utf8_bytes[1] = static_cast<std::char_traits<char>::int_type>(0x80u | (static_cast<unsigned int>(wc) & 0x3Fu));
                 utf8_bytes_filled = 2;
             }
-            else if (0xD800 > wc or wc >= 0xE000)
+            else if (0xD800 > wc || wc >= 0xE000)
             {
-                utf8_bytes[0] = 0xE0 | ((wc >> 12));
-                utf8_bytes[1] = 0x80 | ((wc >> 6) & 0x3F);
-                utf8_bytes[2] = 0x80 | (wc & 0x3F);
+                utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(0xE0u | ((static_cast<unsigned int>(wc) >> 12u)));
+                utf8_bytes[1] = static_cast<std::char_traits<char>::int_type>(0x80u | ((static_cast<unsigned int>(wc) >> 6u) & 0x3Fu));
+                utf8_bytes[2] = static_cast<std::char_traits<char>::int_type>(0x80u | (static_cast<unsigned int>(wc) & 0x3Fu));
                 utf8_bytes_filled = 3;
             }
             else
             {
-                if (current_wchar < str.size())
+                if (JSON_HEDLEY_UNLIKELY(!input.empty()))
                 {
-                    const auto wc2 = static_cast<int>(str[current_wchar++]);
-                    const int charcode = 0x10000 + (((wc & 0x3FF) << 10) | (wc2 & 0x3FF));
-                    utf8_bytes[0] = 0xf0 | (charcode >> 18);
-                    utf8_bytes[1] = 0x80 | ((charcode >> 12) & 0x3F);
-                    utf8_bytes[2] = 0x80 | ((charcode >> 6) & 0x3F);
-                    utf8_bytes[3] = 0x80 | (charcode & 0x3F);
+                    const auto wc2 = static_cast<unsigned int>(input.get_character());
+                    const auto charcode = 0x10000u + (((static_cast<unsigned int>(wc) & 0x3FFu) << 10u) | (wc2 & 0x3FFu));
+                    utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(0xF0u | (charcode >> 18u));
+                    utf8_bytes[1] = static_cast<std::char_traits<char>::int_type>(0x80u | ((charcode >> 12u) & 0x3Fu));
+                    utf8_bytes[2] = static_cast<std::char_traits<char>::int_type>(0x80u | ((charcode >> 6u) & 0x3Fu));
+                    utf8_bytes[3] = static_cast<std::char_traits<char>::int_type>(0x80u | (charcode & 0x3Fu));
                     utf8_bytes_filled = 4;
                 }
                 else
                 {
-                    // unknown character
-                    ++current_wchar;
-                    utf8_bytes[0] = wc;
+                    utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(wc);
                     utf8_bytes_filled = 1;
                 }
             }
@@ -2405,44 +5000,42 @@ struct wide_string_input_helper<WideStringType, 2>
     }
 };
 
-template<typename WideStringType>
-class wide_string_input_adapter : public input_adapter_protocol
+// Wraps another input apdater to convert wide character types into individual bytes.
+template<typename BaseInputAdapter, typename WideCharType>
+class wide_string_input_adapter
 {
   public:
-    explicit wide_string_input_adapter(const WideStringType& w)  noexcept
-        : str(w)
-    {}
+    using char_type = char;
 
-    std::char_traits<char>::int_type get_character() noexcept override
+    wide_string_input_adapter(BaseInputAdapter base)
+        : base_adapter(base) {}
+
+    typename std::char_traits<char>::int_type get_character() noexcept
     {
         // check if buffer needs to be filled
         if (utf8_bytes_index == utf8_bytes_filled)
         {
-            fill_buffer<sizeof(typename WideStringType::value_type)>();
+            fill_buffer<sizeof(WideCharType)>();
 
-            assert(utf8_bytes_filled > 0);
-            assert(utf8_bytes_index == 0);
+            JSON_ASSERT(utf8_bytes_filled > 0);
+            JSON_ASSERT(utf8_bytes_index == 0);
         }
 
         // use buffer
-        assert(utf8_bytes_filled > 0);
-        assert(utf8_bytes_index < utf8_bytes_filled);
+        JSON_ASSERT(utf8_bytes_filled > 0);
+        JSON_ASSERT(utf8_bytes_index < utf8_bytes_filled);
         return utf8_bytes[utf8_bytes_index++];
     }
 
   private:
+    BaseInputAdapter base_adapter;
+
     template<size_t T>
     void fill_buffer()
     {
-        wide_string_input_helper<WideStringType, T>::fill_buffer(str, current_wchar, utf8_bytes, utf8_bytes_index, utf8_bytes_filled);
+        wide_string_input_helper<BaseInputAdapter, T>::fill_buffer(base_adapter, utf8_bytes, utf8_bytes_index, utf8_bytes_filled);
     }
 
-    /// the wstring to process
-    const WideStringType& str;
-
-    /// index of the current wchar in str
-    std::size_t current_wchar = 0;
-
     /// a buffer for UTF-8 bytes
     std::array<std::char_traits<char>::int_type, 4> utf8_bytes = {{0, 0, 0, 0}};
 
@@ -2452,132 +5045,853 @@ class wide_string_input_adapter : public input_adapter_protocol
     std::size_t utf8_bytes_filled = 0;
 };
 
-class input_adapter
+
+template<typename IteratorType, typename Enable = void>
+struct iterator_input_adapter_factory
 {
-  public:
-    // native support
-    input_adapter(std::FILE* file)
-        : ia(std::make_shared<file_input_adapter>(file)) {}
-    /// input adapter for input stream
-    input_adapter(std::istream& i)
-        : ia(std::make_shared<input_stream_adapter>(i)) {}
+    using iterator_type = IteratorType;
+    using char_type = typename std::iterator_traits<iterator_type>::value_type;
+    using adapter_type = iterator_input_adapter<iterator_type>;
 
-    /// input adapter for input stream
-    input_adapter(std::istream&& i)
-        : ia(std::make_shared<input_stream_adapter>(i)) {}
+    static adapter_type create(IteratorType first, IteratorType last)
+    {
+        return adapter_type(std::move(first), std::move(last));
+    }
+};
 
-    input_adapter(const std::wstring& ws)
-        : ia(std::make_shared<wide_string_input_adapter<std::wstring>>(ws)) {}
+template<typename T>
+struct is_iterator_of_multibyte
+{
+    using value_type = typename std::iterator_traits<T>::value_type;
+    enum
+    {
+        value = sizeof(value_type) > 1
+    };
+};
 
-    input_adapter(const std::u16string& ws)
-        : ia(std::make_shared<wide_string_input_adapter<std::u16string>>(ws)) {}
+template<typename IteratorType>
+struct iterator_input_adapter_factory<IteratorType, enable_if_t<is_iterator_of_multibyte<IteratorType>::value>>
+{
+    using iterator_type = IteratorType;
+    using char_type = typename std::iterator_traits<iterator_type>::value_type;
+    using base_adapter_type = iterator_input_adapter<iterator_type>;
+    using adapter_type = wide_string_input_adapter<base_adapter_type, char_type>;
 
-    input_adapter(const std::u32string& ws)
-        : ia(std::make_shared<wide_string_input_adapter<std::u32string>>(ws)) {}
+    static adapter_type create(IteratorType first, IteratorType last)
+    {
+        return adapter_type(base_adapter_type(std::move(first), std::move(last)));
+    }
+};
 
-    /// input adapter for buffer
-    template<typename CharT,
-             typename std::enable_if<
-                 std::is_pointer<CharT>::value and
-                 std::is_integral<typename std::remove_pointer<CharT>::type>::value and
-                 sizeof(typename std::remove_pointer<CharT>::type) == 1,
-                 int>::type = 0>
-    input_adapter(CharT b, std::size_t l)
-        : ia(std::make_shared<input_buffer_adapter>(reinterpret_cast<const char*>(b), l)) {}
+// General purpose iterator-based input
+template<typename IteratorType>
+typename iterator_input_adapter_factory<IteratorType>::adapter_type input_adapter(IteratorType first, IteratorType last)
+{
+    using factory_type = iterator_input_adapter_factory<IteratorType>;
+    return factory_type::create(first, last);
+}
 
-    // derived support
+// Convenience shorthand from container to iterator
+template<typename ContainerType>
+auto input_adapter(const ContainerType& container) -> decltype(input_adapter(begin(container), end(container)))
+{
+    // Enable ADL
+    using std::begin;
+    using std::end;
 
-    /// input adapter for string literal
-    template<typename CharT,
-             typename std::enable_if<
-                 std::is_pointer<CharT>::value and
-                 std::is_integral<typename std::remove_pointer<CharT>::type>::value and
-                 sizeof(typename std::remove_pointer<CharT>::type) == 1,
-                 int>::type = 0>
-    input_adapter(CharT b)
-        : input_adapter(reinterpret_cast<const char*>(b),
-                        std::strlen(reinterpret_cast<const char*>(b))) {}
+    return input_adapter(begin(container), end(container));
+}
+
+// Special cases with fast paths
+inline file_input_adapter input_adapter(std::FILE* file)
+{
+    return file_input_adapter(file);
+}
+
+inline input_stream_adapter input_adapter(std::istream& stream)
+{
+    return input_stream_adapter(stream);
+}
+
+inline input_stream_adapter input_adapter(std::istream&& stream)
+{
+    return input_stream_adapter(stream);
+}
+
+using contiguous_bytes_input_adapter = decltype(input_adapter(std::declval<const char*>(), std::declval<const char*>()));
+
+// Null-delimited strings, and the like.
+template < typename CharT,
+           typename std::enable_if <
+               std::is_pointer<CharT>::value&&
+               !std::is_array<CharT>::value&&
+               std::is_integral<typename std::remove_pointer<CharT>::type>::value&&
+               sizeof(typename std::remove_pointer<CharT>::type) == 1,
+               int >::type = 0 >
+contiguous_bytes_input_adapter input_adapter(CharT b)
+{
+    auto length = std::strlen(reinterpret_cast<const char*>(b));
+    const auto* ptr = reinterpret_cast<const char*>(b);
+    return input_adapter(ptr, ptr + length);
+}
+
+template<typename T, std::size_t N>
+auto input_adapter(T (&array)[N]) -> decltype(input_adapter(array, array + N))
+{
+    return input_adapter(array, array + N);
+}
+
+// This class only handles inputs of input_buffer_adapter type.
+// It's required so that expressions like {ptr, len} can be implicitely casted
+// to the correct adapter.
+class span_input_adapter
+{
+  public:
+    template < typename CharT,
+               typename std::enable_if <
+                   std::is_pointer<CharT>::value&&
+                   std::is_integral<typename std::remove_pointer<CharT>::type>::value&&
+                   sizeof(typename std::remove_pointer<CharT>::type) == 1,
+                   int >::type = 0 >
+    span_input_adapter(CharT b, std::size_t l)
+        : ia(reinterpret_cast<const char*>(b), reinterpret_cast<const char*>(b) + l) {}
 
-    /// input adapter for iterator range with contiguous storage
     template<class IteratorType,
              typename std::enable_if<
                  std::is_same<typename iterator_traits<IteratorType>::iterator_category, std::random_access_iterator_tag>::value,
                  int>::type = 0>
-    input_adapter(IteratorType first, IteratorType last)
+    span_input_adapter(IteratorType first, IteratorType last)
+        : ia(input_adapter(first, last)) {}
+
+    contiguous_bytes_input_adapter&& get()
+    {
+        return std::move(ia);
+    }
+
+  private:
+    contiguous_bytes_input_adapter ia;
+};
+}  // namespace detail
+}  // namespace nlohmann
+
+// #include <nlohmann/detail/input/json_sax.hpp>
+
+
+#include <cstddef>
+#include <string> // string
+#include <utility> // move
+#include <vector> // vector
+
+// #include <nlohmann/detail/exceptions.hpp>
+
+// #include <nlohmann/detail/macro_scope.hpp>
+
+
+namespace nlohmann
+{
+
+/*!
+@brief SAX interface
+
+This class describes the SAX interface used by @ref nlohmann::json::sax_parse.
+Each function is called in different situations while the input is parsed. The
+boolean return value informs the parser whether to continue processing the
+input.
+*/
+template<typename BasicJsonType>
+struct json_sax
+{
+    using number_integer_t = typename BasicJsonType::number_integer_t;
+    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+    using number_float_t = typename BasicJsonType::number_float_t;
+    using string_t = typename BasicJsonType::string_t;
+    using binary_t = typename BasicJsonType::binary_t;
+
+    /*!
+    @brief a null value was read
+    @return whether parsing should proceed
+    */
+    virtual bool null() = 0;
+
+    /*!
+    @brief a boolean value was read
+    @param[in] val  boolean value
+    @return whether parsing should proceed
+    */
+    virtual bool boolean(bool val) = 0;
+
+    /*!
+    @brief an integer number was read
+    @param[in] val  integer value
+    @return whether parsing should proceed
+    */
+    virtual bool number_integer(number_integer_t val) = 0;
+
+    /*!
+    @brief an unsigned integer number was read
+    @param[in] val  unsigned integer value
+    @return whether parsing should proceed
+    */
+    virtual bool number_unsigned(number_unsigned_t val) = 0;
+
+    /*!
+    @brief an floating-point number was read
+    @param[in] val  floating-point value
+    @param[in] s    raw token value
+    @return whether parsing should proceed
+    */
+    virtual bool number_float(number_float_t val, const string_t& s) = 0;
+
+    /*!
+    @brief a string was read
+    @param[in] val  string value
+    @return whether parsing should proceed
+    @note It is safe to move the passed string.
+    */
+    virtual bool string(string_t& val) = 0;
+
+    /*!
+    @brief a binary string was read
+    @param[in] val  binary value
+    @return whether parsing should proceed
+    @note It is safe to move the passed binary.
+    */
+    virtual bool binary(binary_t& val) = 0;
+
+    /*!
+    @brief the beginning of an object was read
+    @param[in] elements  number of object elements or -1 if unknown
+    @return whether parsing should proceed
+    @note binary formats may report the number of elements
+    */
+    virtual bool start_object(std::size_t elements) = 0;
+
+    /*!
+    @brief an object key was read
+    @param[in] val  object key
+    @return whether parsing should proceed
+    @note It is safe to move the passed string.
+    */
+    virtual bool key(string_t& val) = 0;
+
+    /*!
+    @brief the end of an object was read
+    @return whether parsing should proceed
+    */
+    virtual bool end_object() = 0;
+
+    /*!
+    @brief the beginning of an array was read
+    @param[in] elements  number of array elements or -1 if unknown
+    @return whether parsing should proceed
+    @note binary formats may report the number of elements
+    */
+    virtual bool start_array(std::size_t elements) = 0;
+
+    /*!
+    @brief the end of an array was read
+    @return whether parsing should proceed
+    */
+    virtual bool end_array() = 0;
+
+    /*!
+    @brief a parse error occurred
+    @param[in] position    the position in the input where the error occurs
+    @param[in] last_token  the last read token
+    @param[in] ex          an exception object describing the error
+    @return whether parsing should proceed (must return false)
+    */
+    virtual bool parse_error(std::size_t position,
+                             const std::string& last_token,
+                             const detail::exception& ex) = 0;
+
+    virtual ~json_sax() = default;
+};
+
+
+namespace detail
+{
+/*!
+@brief SAX implementation to create a JSON value from SAX events
+
+This class implements the @ref json_sax interface and processes the SAX events
+to create a JSON value which makes it basically a DOM parser. The structure or
+hierarchy of the JSON value is managed by the stack `ref_stack` which contains
+a pointer to the respective array or object for each recursion depth.
+
+After successful parsing, the value that is passed by reference to the
+constructor contains the parsed value.
+
+@tparam BasicJsonType  the JSON type
+*/
+template<typename BasicJsonType>
+class json_sax_dom_parser
+{
+  public:
+    using number_integer_t = typename BasicJsonType::number_integer_t;
+    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+    using number_float_t = typename BasicJsonType::number_float_t;
+    using string_t = typename BasicJsonType::string_t;
+    using binary_t = typename BasicJsonType::binary_t;
+
+    /*!
+    @param[in, out] r  reference to a JSON value that is manipulated while
+                       parsing
+    @param[in] allow_exceptions_  whether parse errors yield exceptions
+    */
+    explicit json_sax_dom_parser(BasicJsonType& r, const bool allow_exceptions_ = true)
+        : root(r), allow_exceptions(allow_exceptions_)
+    {}
+
+    // make class move-only
+    json_sax_dom_parser(const json_sax_dom_parser&) = delete;
+    json_sax_dom_parser(json_sax_dom_parser&&) = default;
+    json_sax_dom_parser& operator=(const json_sax_dom_parser&) = delete;
+    json_sax_dom_parser& operator=(json_sax_dom_parser&&) = default;
+    ~json_sax_dom_parser() = default;
+
+    bool null()
+    {
+        handle_value(nullptr);
+        return true;
+    }
+
+    bool boolean(bool val)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool number_integer(number_integer_t val)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool number_unsigned(number_unsigned_t val)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool number_float(number_float_t val, const string_t& /*unused*/)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool string(string_t& val)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool binary(binary_t& val)
+    {
+        handle_value(std::move(val));
+        return true;
+    }
+
+    bool start_object(std::size_t len)
     {
-#ifndef NDEBUG
-        // assertion to check that the iterator range is indeed contiguous,
-        // see http://stackoverflow.com/a/35008842/266378 for more discussion
-        const auto is_contiguous = std::accumulate(
-                                       first, last, std::pair<bool, int>(true, 0),
-                                       [&first](std::pair<bool, int> res, decltype(*first) val)
+        ref_stack.push_back(handle_value(BasicJsonType::value_t::object));
+
+        if (JSON_HEDLEY_UNLIKELY(len != std::size_t(-1) && len > ref_stack.back()->max_size()))
         {
-            res.first &= (val == *(std::next(std::addressof(*first), res.second++)));
-            return res;
-        }).first;
-        assert(is_contiguous);
-#endif
+            JSON_THROW(out_of_range::create(408,
+                                            "excessive object size: " + std::to_string(len)));
+        }
 
-        // assertion to check that each element is 1 byte long
-        static_assert(
-            sizeof(typename iterator_traits<IteratorType>::value_type) == 1,
-            "each element in the iterator range must have the size of 1 byte");
+        return true;
+    }
+
+    bool key(string_t& val)
+    {
+        // add null at given key and store the reference for later
+        object_element = &(ref_stack.back()->m_value.object->operator[](val));
+        return true;
+    }
 
-        const auto len = static_cast<size_t>(std::distance(first, last));
-        if (JSON_LIKELY(len > 0))
+    bool end_object()
+    {
+        ref_stack.pop_back();
+        return true;
+    }
+
+    bool start_array(std::size_t len)
+    {
+        ref_stack.push_back(handle_value(BasicJsonType::value_t::array));
+
+        if (JSON_HEDLEY_UNLIKELY(len != std::size_t(-1) && len > ref_stack.back()->max_size()))
         {
-            // there is at least one element: use the address of first
-            ia = std::make_shared<input_buffer_adapter>(reinterpret_cast<const char*>(&(*first)), len);
+            JSON_THROW(out_of_range::create(408,
+                                            "excessive array size: " + std::to_string(len)));
         }
-        else
+
+        return true;
+    }
+
+    bool end_array()
+    {
+        ref_stack.pop_back();
+        return true;
+    }
+
+    template<class Exception>
+    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/,
+                     const Exception& ex)
+    {
+        errored = true;
+        static_cast<void>(ex);
+        if (allow_exceptions)
+        {
+            JSON_THROW(ex);
+        }
+        return false;
+    }
+
+    constexpr bool is_errored() const
+    {
+        return errored;
+    }
+
+  private:
+    /*!
+    @invariant If the ref stack is empty, then the passed value will be the new
+               root.
+    @invariant If the ref stack contains a value, then it is an array or an
+               object to which we can add elements
+    */
+    template<typename Value>
+    JSON_HEDLEY_RETURNS_NON_NULL
+    BasicJsonType* handle_value(Value&& v)
+    {
+        if (ref_stack.empty())
+        {
+            root = BasicJsonType(std::forward<Value>(v));
+            return &root;
+        }
+
+        JSON_ASSERT(ref_stack.back()->is_array() || ref_stack.back()->is_object());
+
+        if (ref_stack.back()->is_array())
+        {
+            ref_stack.back()->m_value.array->emplace_back(std::forward<Value>(v));
+            return &(ref_stack.back()->m_value.array->back());
+        }
+
+        JSON_ASSERT(ref_stack.back()->is_object());
+        JSON_ASSERT(object_element);
+        *object_element = BasicJsonType(std::forward<Value>(v));
+        return object_element;
+    }
+
+    /// the parsed JSON value
+    BasicJsonType& root;
+    /// stack to model hierarchy of values
+    std::vector<BasicJsonType*> ref_stack {};
+    /// helper to hold the reference for the next object element
+    BasicJsonType* object_element = nullptr;
+    /// whether a syntax error occurred
+    bool errored = false;
+    /// whether to throw exceptions in case of errors
+    const bool allow_exceptions = true;
+};
+
+template<typename BasicJsonType>
+class json_sax_dom_callback_parser
+{
+  public:
+    using number_integer_t = typename BasicJsonType::number_integer_t;
+    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+    using number_float_t = typename BasicJsonType::number_float_t;
+    using string_t = typename BasicJsonType::string_t;
+    using binary_t = typename BasicJsonType::binary_t;
+    using parser_callback_t = typename BasicJsonType::parser_callback_t;
+    using parse_event_t = typename BasicJsonType::parse_event_t;
+
+    json_sax_dom_callback_parser(BasicJsonType& r,
+                                 const parser_callback_t cb,
+                                 const bool allow_exceptions_ = true)
+        : root(r), callback(cb), allow_exceptions(allow_exceptions_)
+    {
+        keep_stack.push_back(true);
+    }
+
+    // make class move-only
+    json_sax_dom_callback_parser(const json_sax_dom_callback_parser&) = delete;
+    json_sax_dom_callback_parser(json_sax_dom_callback_parser&&) = default;
+    json_sax_dom_callback_parser& operator=(const json_sax_dom_callback_parser&) = delete;
+    json_sax_dom_callback_parser& operator=(json_sax_dom_callback_parser&&) = default;
+    ~json_sax_dom_callback_parser() = default;
+
+    bool null()
+    {
+        handle_value(nullptr);
+        return true;
+    }
+
+    bool boolean(bool val)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool number_integer(number_integer_t val)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool number_unsigned(number_unsigned_t val)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool number_float(number_float_t val, const string_t& /*unused*/)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool string(string_t& val)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool binary(binary_t& val)
+    {
+        handle_value(std::move(val));
+        return true;
+    }
+
+    bool start_object(std::size_t len)
+    {
+        // check callback for object start
+        const bool keep = callback(static_cast<int>(ref_stack.size()), parse_event_t::object_start, discarded);
+        keep_stack.push_back(keep);
+
+        auto val = handle_value(BasicJsonType::value_t::object, true);
+        ref_stack.push_back(val.second);
+
+        // check object limit
+        if (ref_stack.back() && JSON_HEDLEY_UNLIKELY(len != std::size_t(-1) && len > ref_stack.back()->max_size()))
+        {
+            JSON_THROW(out_of_range::create(408, "excessive object size: " + std::to_string(len)));
+        }
+
+        return true;
+    }
+
+    bool key(string_t& val)
+    {
+        BasicJsonType k = BasicJsonType(val);
+
+        // check callback for key
+        const bool keep = callback(static_cast<int>(ref_stack.size()), parse_event_t::key, k);
+        key_keep_stack.push_back(keep);
+
+        // add discarded value at given key and store the reference for later
+        if (keep && ref_stack.back())
+        {
+            object_element = &(ref_stack.back()->m_value.object->operator[](val) = discarded);
+        }
+
+        return true;
+    }
+
+    bool end_object()
+    {
+        if (ref_stack.back() && !callback(static_cast<int>(ref_stack.size()) - 1, parse_event_t::object_end, *ref_stack.back()))
+        {
+            // discard object
+            *ref_stack.back() = discarded;
+        }
+
+        JSON_ASSERT(!ref_stack.empty());
+        JSON_ASSERT(!keep_stack.empty());
+        ref_stack.pop_back();
+        keep_stack.pop_back();
+
+        if (!ref_stack.empty() && ref_stack.back() && ref_stack.back()->is_structured())
         {
-            // the address of first cannot be used: use nullptr
-            ia = std::make_shared<input_buffer_adapter>(nullptr, len);
+            // remove discarded value
+            for (auto it = ref_stack.back()->begin(); it != ref_stack.back()->end(); ++it)
+            {
+                if (it->is_discarded())
+                {
+                    ref_stack.back()->erase(it);
+                    break;
+                }
+            }
         }
+
+        return true;
     }
 
-    /// input adapter for array
-    template<class T, std::size_t N>
-    input_adapter(T (&array)[N])
-        : input_adapter(std::begin(array), std::end(array)) {}
+    bool start_array(std::size_t len)
+    {
+        const bool keep = callback(static_cast<int>(ref_stack.size()), parse_event_t::array_start, discarded);
+        keep_stack.push_back(keep);
+
+        auto val = handle_value(BasicJsonType::value_t::array, true);
+        ref_stack.push_back(val.second);
+
+        // check array limit
+        if (ref_stack.back() && JSON_HEDLEY_UNLIKELY(len != std::size_t(-1) && len > ref_stack.back()->max_size()))
+        {
+            JSON_THROW(out_of_range::create(408, "excessive array size: " + std::to_string(len)));
+        }
+
+        return true;
+    }
+
+    bool end_array()
+    {
+        bool keep = true;
+
+        if (ref_stack.back())
+        {
+            keep = callback(static_cast<int>(ref_stack.size()) - 1, parse_event_t::array_end, *ref_stack.back());
+            if (!keep)
+            {
+                // discard array
+                *ref_stack.back() = discarded;
+            }
+        }
+
+        JSON_ASSERT(!ref_stack.empty());
+        JSON_ASSERT(!keep_stack.empty());
+        ref_stack.pop_back();
+        keep_stack.pop_back();
 
-    /// input adapter for contiguous container
-    template<class ContiguousContainer, typename
-             std::enable_if<not std::is_pointer<ContiguousContainer>::value and
-                            std::is_base_of<std::random_access_iterator_tag, typename iterator_traits<decltype(std::begin(std::declval<ContiguousContainer const>()))>::iterator_category>::value,
-                            int>::type = 0>
-    input_adapter(const ContiguousContainer& c)
-        : input_adapter(std::begin(c), std::end(c)) {}
+        // remove discarded value
+        if (!keep && !ref_stack.empty() && ref_stack.back()->is_array())
+        {
+            ref_stack.back()->m_value.array->pop_back();
+        }
 
-    operator input_adapter_t()
+        return true;
+    }
+
+    template<class Exception>
+    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/,
+                     const Exception& ex)
     {
-        return ia;
+        errored = true;
+        static_cast<void>(ex);
+        if (allow_exceptions)
+        {
+            JSON_THROW(ex);
+        }
+        return false;
+    }
+
+    constexpr bool is_errored() const
+    {
+        return errored;
     }
 
   private:
-    /// the actual adapter
-    input_adapter_t ia = nullptr;
+    /*!
+    @param[in] v  value to add to the JSON value we build during parsing
+    @param[in] skip_callback  whether we should skip calling the callback
+               function; this is required after start_array() and
+               start_object() SAX events, because otherwise we would call the
+               callback function with an empty array or object, respectively.
+
+    @invariant If the ref stack is empty, then the passed value will be the new
+               root.
+    @invariant If the ref stack contains a value, then it is an array or an
+               object to which we can add elements
+
+    @return pair of boolean (whether value should be kept) and pointer (to the
+            passed value in the ref_stack hierarchy; nullptr if not kept)
+    */
+    template<typename Value>
+    std::pair<bool, BasicJsonType*> handle_value(Value&& v, const bool skip_callback = false)
+    {
+        JSON_ASSERT(!keep_stack.empty());
+
+        // do not handle this value if we know it would be added to a discarded
+        // container
+        if (!keep_stack.back())
+        {
+            return {false, nullptr};
+        }
+
+        // create value
+        auto value = BasicJsonType(std::forward<Value>(v));
+
+        // check callback
+        const bool keep = skip_callback || callback(static_cast<int>(ref_stack.size()), parse_event_t::value, value);
+
+        // do not handle this value if we just learnt it shall be discarded
+        if (!keep)
+        {
+            return {false, nullptr};
+        }
+
+        if (ref_stack.empty())
+        {
+            root = std::move(value);
+            return {true, &root};
+        }
+
+        // skip this value if we already decided to skip the parent
+        // (https://github.com/nlohmann/json/issues/971#issuecomment-413678360)
+        if (!ref_stack.back())
+        {
+            return {false, nullptr};
+        }
+
+        // we now only expect arrays and objects
+        JSON_ASSERT(ref_stack.back()->is_array() || ref_stack.back()->is_object());
+
+        // array
+        if (ref_stack.back()->is_array())
+        {
+            ref_stack.back()->m_value.array->push_back(std::move(value));
+            return {true, &(ref_stack.back()->m_value.array->back())};
+        }
+
+        // object
+        JSON_ASSERT(ref_stack.back()->is_object());
+        // check if we should store an element for the current key
+        JSON_ASSERT(!key_keep_stack.empty());
+        const bool store_element = key_keep_stack.back();
+        key_keep_stack.pop_back();
+
+        if (!store_element)
+        {
+            return {false, nullptr};
+        }
+
+        JSON_ASSERT(object_element);
+        *object_element = std::move(value);
+        return {true, object_element};
+    }
+
+    /// the parsed JSON value
+    BasicJsonType& root;
+    /// stack to model hierarchy of values
+    std::vector<BasicJsonType*> ref_stack {};
+    /// stack to manage which values to keep
+    std::vector<bool> keep_stack {};
+    /// stack to manage which object keys to keep
+    std::vector<bool> key_keep_stack {};
+    /// helper to hold the reference for the next object element
+    BasicJsonType* object_element = nullptr;
+    /// whether a syntax error occurred
+    bool errored = false;
+    /// callback function
+    const parser_callback_t callback = nullptr;
+    /// whether to throw exceptions in case of errors
+    const bool allow_exceptions = true;
+    /// a discarded value for the callback
+    BasicJsonType discarded = BasicJsonType::value_t::discarded;
+};
+
+template<typename BasicJsonType>
+class json_sax_acceptor
+{
+  public:
+    using number_integer_t = typename BasicJsonType::number_integer_t;
+    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+    using number_float_t = typename BasicJsonType::number_float_t;
+    using string_t = typename BasicJsonType::string_t;
+    using binary_t = typename BasicJsonType::binary_t;
+
+    bool null()
+    {
+        return true;
+    }
+
+    bool boolean(bool /*unused*/)
+    {
+        return true;
+    }
+
+    bool number_integer(number_integer_t /*unused*/)
+    {
+        return true;
+    }
+
+    bool number_unsigned(number_unsigned_t /*unused*/)
+    {
+        return true;
+    }
+
+    bool number_float(number_float_t /*unused*/, const string_t& /*unused*/)
+    {
+        return true;
+    }
+
+    bool string(string_t& /*unused*/)
+    {
+        return true;
+    }
+
+    bool binary(binary_t& /*unused*/)
+    {
+        return true;
+    }
+
+    bool start_object(std::size_t /*unused*/ = std::size_t(-1))
+    {
+        return true;
+    }
+
+    bool key(string_t& /*unused*/)
+    {
+        return true;
+    }
+
+    bool end_object()
+    {
+        return true;
+    }
+
+    bool start_array(std::size_t /*unused*/ = std::size_t(-1))
+    {
+        return true;
+    }
+
+    bool end_array()
+    {
+        return true;
+    }
+
+    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/, const detail::exception& /*unused*/)
+    {
+        return false;
+    }
 };
 }  // namespace detail
+
 }  // namespace nlohmann
 
 // #include <nlohmann/detail/input/lexer.hpp>
 
 
+#include <array> // array
 #include <clocale> // localeconv
 #include <cstddef> // size_t
-#include <cstdlib> // strtof, strtod, strtold, strtoll, strtoull
 #include <cstdio> // snprintf
+#include <cstdlib> // strtof, strtod, strtold, strtoll, strtoull
 #include <initializer_list> // initializer_list
 #include <string> // char_traits, string
+#include <utility> // move
 #include <vector> // vector
 
-// #include <nlohmann/detail/macro_scope.hpp>
-
 // #include <nlohmann/detail/input/input_adapters.hpp>
 
 // #include <nlohmann/detail/input/position_t.hpp>
 
+// #include <nlohmann/detail/macro_scope.hpp>
+
 
 namespace nlohmann
 {
@@ -2587,19 +5901,9 @@ namespace detail
 // lexer //
 ///////////
 
-/*!
-@brief lexical analysis
-
-This class organizes the lexical analysis during JSON deserialization.
-*/
 template<typename BasicJsonType>
-class lexer
+class lexer_base
 {
-    using number_integer_t = typename BasicJsonType::number_integer_t;
-    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
-    using number_float_t = typename BasicJsonType::number_float_t;
-    using string_t = typename BasicJsonType::string_t;
-
   public:
     /// token types for the parser
     enum class token_type
@@ -2624,6 +5928,8 @@ class lexer
     };
 
     /// return name of values of type token_type (only used for errors)
+    JSON_HEDLEY_RETURNS_NON_NULL
+    JSON_HEDLEY_CONST
     static const char* token_type_name(const token_type t) noexcept
     {
         switch (t)
@@ -2638,9 +5944,9 @@ class lexer
                 return "null literal";
             case token_type::value_string:
                 return "string literal";
-            case lexer::token_type::value_unsigned:
-            case lexer::token_type::value_integer:
-            case lexer::token_type::value_float:
+            case token_type::value_unsigned:
+            case token_type::value_integer:
+            case token_type::value_float:
                 return "number literal";
             case token_type::begin_array:
                 return "'['";
@@ -2666,15 +5972,36 @@ class lexer
                 // LCOV_EXCL_STOP
         }
     }
+};
+/*!
+@brief lexical analysis
+
+This class organizes the lexical analysis during JSON deserialization.
+*/
+template<typename BasicJsonType, typename InputAdapterType>
+class lexer : public lexer_base<BasicJsonType>
+{
+    using number_integer_t = typename BasicJsonType::number_integer_t;
+    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+    using number_float_t = typename BasicJsonType::number_float_t;
+    using string_t = typename BasicJsonType::string_t;
+    using char_type = typename InputAdapterType::char_type;
+    using char_int_type = typename std::char_traits<char_type>::int_type;
 
-    explicit lexer(detail::input_adapter_t&& adapter)
-        : ia(std::move(adapter)), decimal_point_char(get_decimal_point()) {}
+  public:
+    using token_type = typename lexer_base<BasicJsonType>::token_type;
+
+    explicit lexer(InputAdapterType&& adapter, bool ignore_comments_ = false)
+        : ia(std::move(adapter))
+        , ignore_comments(ignore_comments_)
+        , decimal_point_char(static_cast<char_int_type>(get_decimal_point()))
+    {}
 
     // delete because of pointer members
     lexer(const lexer&) = delete;
-    lexer(lexer&&) = delete;
+    lexer(lexer&&) = default;
     lexer& operator=(lexer&) = delete;
-    lexer& operator=(lexer&&) = delete;
+    lexer& operator=(lexer&&) = default;
     ~lexer() = default;
 
   private:
@@ -2683,10 +6010,11 @@ class lexer
     /////////////////////
 
     /// return the locale-dependent decimal point
+    JSON_HEDLEY_PURE
     static char get_decimal_point() noexcept
     {
-        const auto loc = localeconv();
-        assert(loc != nullptr);
+        const auto* loc = localeconv();
+        JSON_ASSERT(loc != nullptr);
         return (loc->decimal_point == nullptr) ? '.' : *(loc->decimal_point);
     }
 
@@ -2712,25 +6040,25 @@ class lexer
     int get_codepoint()
     {
         // this function only makes sense after reading `\u`
-        assert(current == 'u');
+        JSON_ASSERT(current == 'u');
         int codepoint = 0;
 
-        const auto factors = { 12, 8, 4, 0 };
+        const auto factors = { 12u, 8u, 4u, 0u };
         for (const auto factor : factors)
         {
             get();
 
-            if (current >= '0' and current <= '9')
+            if (current >= '0' && current <= '9')
             {
-                codepoint += ((current - 0x30) << factor);
+                codepoint += static_cast<int>((static_cast<unsigned int>(current) - 0x30u) << factor);
             }
-            else if (current >= 'A' and current <= 'F')
+            else if (current >= 'A' && current <= 'F')
             {
-                codepoint += ((current - 0x37) << factor);
+                codepoint += static_cast<int>((static_cast<unsigned int>(current) - 0x37u) << factor);
             }
-            else if (current >= 'a' and current <= 'f')
+            else if (current >= 'a' && current <= 'f')
             {
-                codepoint += ((current - 0x57) << factor);
+                codepoint += static_cast<int>((static_cast<unsigned int>(current) - 0x57u) << factor);
             }
             else
             {
@@ -2738,7 +6066,7 @@ class lexer
             }
         }
 
-        assert(0x0000 <= codepoint and codepoint <= 0xFFFF);
+        JSON_ASSERT(0x0000 <= codepoint && codepoint <= 0xFFFF);
         return codepoint;
     }
 
@@ -2757,15 +6085,15 @@ class lexer
 
     @return true if and only if no range violation was detected
     */
-    bool next_byte_in_range(std::initializer_list<int> ranges)
+    bool next_byte_in_range(std::initializer_list<char_int_type> ranges)
     {
-        assert(ranges.size() == 2 or ranges.size() == 4 or ranges.size() == 6);
+        JSON_ASSERT(ranges.size() == 2 || ranges.size() == 4 || ranges.size() == 6);
         add(current);
 
         for (auto range = ranges.begin(); range != ranges.end(); ++range)
         {
             get();
-            if (JSON_LIKELY(*range <= current and current <= *(++range)))
+            if (JSON_HEDLEY_LIKELY(*range <= current && current <= *(++range)))
             {
                 add(current);
             }
@@ -2800,7 +6128,7 @@ class lexer
         reset();
 
         // we entered the function by reading an open quote
-        assert(current == '\"');
+        JSON_ASSERT(current == '\"');
 
         while (true)
         {
@@ -2808,7 +6136,7 @@ class lexer
             switch (get())
             {
                 // end of file while parsing string
-                case std::char_traits<char>::eof():
+                case std::char_traits<char_type>::eof():
                 {
                     error_message = "invalid string: missing closing quote";
                     return token_type::parse_error;
@@ -2864,55 +6192,55 @@ class lexer
                             const int codepoint1 = get_codepoint();
                             int codepoint = codepoint1; // start with codepoint1
 
-                            if (JSON_UNLIKELY(codepoint1 == -1))
+                            if (JSON_HEDLEY_UNLIKELY(codepoint1 == -1))
                             {
                                 error_message = "invalid string: '\\u' must be followed by 4 hex digits";
                                 return token_type::parse_error;
                             }
 
                             // check if code point is a high surrogate
-                            if (0xD800 <= codepoint1 and codepoint1 <= 0xDBFF)
+                            if (0xD800 <= codepoint1 && codepoint1 <= 0xDBFF)
                             {
                                 // expect next \uxxxx entry
-                                if (JSON_LIKELY(get() == '\\' and get() == 'u'))
+                                if (JSON_HEDLEY_LIKELY(get() == '\\' && get() == 'u'))
                                 {
                                     const int codepoint2 = get_codepoint();
 
-                                    if (JSON_UNLIKELY(codepoint2 == -1))
+                                    if (JSON_HEDLEY_UNLIKELY(codepoint2 == -1))
                                     {
                                         error_message = "invalid string: '\\u' must be followed by 4 hex digits";
                                         return token_type::parse_error;
                                     }
 
                                     // check if codepoint2 is a low surrogate
-                                    if (JSON_LIKELY(0xDC00 <= codepoint2 and codepoint2 <= 0xDFFF))
+                                    if (JSON_HEDLEY_LIKELY(0xDC00 <= codepoint2 && codepoint2 <= 0xDFFF))
                                     {
                                         // overwrite codepoint
-                                        codepoint =
-                                            // high surrogate occupies the most significant 22 bits
-                                            (codepoint1 << 10)
-                                            // low surrogate occupies the least significant 15 bits
-                                            + codepoint2
-                                            // there is still the 0xD800, 0xDC00 and 0x10000 noise
-                                            // in the result so we have to subtract with:
-                                            // (0xD800 << 10) + DC00 - 0x10000 = 0x35FDC00
-                                            - 0x35FDC00;
+                                        codepoint = static_cast<int>(
+                                                        // high surrogate occupies the most significant 22 bits
+                                                        (static_cast<unsigned int>(codepoint1) << 10u)
+                                                        // low surrogate occupies the least significant 15 bits
+                                                        + static_cast<unsigned int>(codepoint2)
+                                                        // there is still the 0xD800, 0xDC00 and 0x10000 noise
+                                                        // in the result so we have to subtract with:
+                                                        // (0xD800 << 10) + DC00 - 0x10000 = 0x35FDC00
+                                                        - 0x35FDC00u);
                                     }
                                     else
                                     {
-                                        error_message = "invalid string: surrogate U+DC00..U+DFFF must be followed by U+DC00..U+DFFF";
+                                        error_message = "invalid string: surrogate U+D800..U+DBFF must be followed by U+DC00..U+DFFF";
                                         return token_type::parse_error;
                                     }
                                 }
                                 else
                                 {
-                                    error_message = "invalid string: surrogate U+DC00..U+DFFF must be followed by U+DC00..U+DFFF";
+                                    error_message = "invalid string: surrogate U+D800..U+DBFF must be followed by U+DC00..U+DFFF";
                                     return token_type::parse_error;
                                 }
                             }
                             else
                             {
-                                if (JSON_UNLIKELY(0xDC00 <= codepoint1 and codepoint1 <= 0xDFFF))
+                                if (JSON_HEDLEY_UNLIKELY(0xDC00 <= codepoint1 && codepoint1 <= 0xDFFF))
                                 {
                                     error_message = "invalid string: surrogate U+DC00..U+DFFF must follow U+D800..U+DBFF";
                                     return token_type::parse_error;
@@ -2920,34 +6248,34 @@ class lexer
                             }
 
                             // result of the above calculation yields a proper codepoint
-                            assert(0x00 <= codepoint and codepoint <= 0x10FFFF);
+                            JSON_ASSERT(0x00 <= codepoint && codepoint <= 0x10FFFF);
 
                             // translate codepoint into bytes
                             if (codepoint < 0x80)
                             {
                                 // 1-byte characters: 0xxxxxxx (ASCII)
-                                add(codepoint);
+                                add(static_cast<char_int_type>(codepoint));
                             }
                             else if (codepoint <= 0x7FF)
                             {
                                 // 2-byte characters: 110xxxxx 10xxxxxx
-                                add(0xC0 | (codepoint >> 6));
-                                add(0x80 | (codepoint & 0x3F));
+                                add(static_cast<char_int_type>(0xC0u | (static_cast<unsigned int>(codepoint) >> 6u)));
+                                add(static_cast<char_int_type>(0x80u | (static_cast<unsigned int>(codepoint) & 0x3Fu)));
                             }
                             else if (codepoint <= 0xFFFF)
                             {
                                 // 3-byte characters: 1110xxxx 10xxxxxx 10xxxxxx
-                                add(0xE0 | (codepoint >> 12));
-                                add(0x80 | ((codepoint >> 6) & 0x3F));
-                                add(0x80 | (codepoint & 0x3F));
+                                add(static_cast<char_int_type>(0xE0u | (static_cast<unsigned int>(codepoint) >> 12u)));
+                                add(static_cast<char_int_type>(0x80u | ((static_cast<unsigned int>(codepoint) >> 6u) & 0x3Fu)));
+                                add(static_cast<char_int_type>(0x80u | (static_cast<unsigned int>(codepoint) & 0x3Fu)));
                             }
                             else
                             {
                                 // 4-byte characters: 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
-                                add(0xF0 | (codepoint >> 18));
-                                add(0x80 | ((codepoint >> 12) & 0x3F));
-                                add(0x80 | ((codepoint >> 6) & 0x3F));
-                                add(0x80 | (codepoint & 0x3F));
+                                add(static_cast<char_int_type>(0xF0u | (static_cast<unsigned int>(codepoint) >> 18u)));
+                                add(static_cast<char_int_type>(0x80u | ((static_cast<unsigned int>(codepoint) >> 12u) & 0x3Fu)));
+                                add(static_cast<char_int_type>(0x80u | ((static_cast<unsigned int>(codepoint) >> 6u) & 0x3Fu)));
+                                add(static_cast<char_int_type>(0x80u | (static_cast<unsigned int>(codepoint) & 0x3Fu)));
                             }
 
                             break;
@@ -3287,7 +6615,7 @@ class lexer
                 case 0xDE:
                 case 0xDF:
                 {
-                    if (JSON_UNLIKELY(not next_byte_in_range({0x80, 0xBF})))
+                    if (JSON_HEDLEY_UNLIKELY(!next_byte_in_range({0x80, 0xBF})))
                     {
                         return token_type::parse_error;
                     }
@@ -3297,7 +6625,7 @@ class lexer
                 // U+0800..U+0FFF: bytes E0 A0..BF 80..BF
                 case 0xE0:
                 {
-                    if (JSON_UNLIKELY(not (next_byte_in_range({0xA0, 0xBF, 0x80, 0xBF}))))
+                    if (JSON_HEDLEY_UNLIKELY(!(next_byte_in_range({0xA0, 0xBF, 0x80, 0xBF}))))
                     {
                         return token_type::parse_error;
                     }
@@ -3321,7 +6649,7 @@ class lexer
                 case 0xEE:
                 case 0xEF:
                 {
-                    if (JSON_UNLIKELY(not (next_byte_in_range({0x80, 0xBF, 0x80, 0xBF}))))
+                    if (JSON_HEDLEY_UNLIKELY(!(next_byte_in_range({0x80, 0xBF, 0x80, 0xBF}))))
                     {
                         return token_type::parse_error;
                     }
@@ -3331,7 +6659,7 @@ class lexer
                 // U+D000..U+D7FF: bytes ED 80..9F 80..BF
                 case 0xED:
                 {
-                    if (JSON_UNLIKELY(not (next_byte_in_range({0x80, 0x9F, 0x80, 0xBF}))))
+                    if (JSON_HEDLEY_UNLIKELY(!(next_byte_in_range({0x80, 0x9F, 0x80, 0xBF}))))
                     {
                         return token_type::parse_error;
                     }
@@ -3341,7 +6669,7 @@ class lexer
                 // U+10000..U+3FFFF F0 90..BF 80..BF 80..BF
                 case 0xF0:
                 {
-                    if (JSON_UNLIKELY(not (next_byte_in_range({0x90, 0xBF, 0x80, 0xBF, 0x80, 0xBF}))))
+                    if (JSON_HEDLEY_UNLIKELY(!(next_byte_in_range({0x90, 0xBF, 0x80, 0xBF, 0x80, 0xBF}))))
                     {
                         return token_type::parse_error;
                     }
@@ -3353,7 +6681,7 @@ class lexer
                 case 0xF2:
                 case 0xF3:
                 {
-                    if (JSON_UNLIKELY(not (next_byte_in_range({0x80, 0xBF, 0x80, 0xBF, 0x80, 0xBF}))))
+                    if (JSON_HEDLEY_UNLIKELY(!(next_byte_in_range({0x80, 0xBF, 0x80, 0xBF, 0x80, 0xBF}))))
                     {
                         return token_type::parse_error;
                     }
@@ -3363,7 +6691,7 @@ class lexer
                 // U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
                 case 0xF4:
                 {
-                    if (JSON_UNLIKELY(not (next_byte_in_range({0x80, 0x8F, 0x80, 0xBF, 0x80, 0xBF}))))
+                    if (JSON_HEDLEY_UNLIKELY(!(next_byte_in_range({0x80, 0x8F, 0x80, 0xBF, 0x80, 0xBF}))))
                     {
                         return token_type::parse_error;
                     }
@@ -3380,16 +6708,90 @@ class lexer
         }
     }
 
+    /*!
+     * @brief scan a comment
+     * @return whether comment could be scanned successfully
+     */
+    bool scan_comment()
+    {
+        switch (get())
+        {
+            // single-line comments skip input until a newline or EOF is read
+            case '/':
+            {
+                while (true)
+                {
+                    switch (get())
+                    {
+                        case '\n':
+                        case '\r':
+                        case std::char_traits<char_type>::eof():
+                        case '\0':
+                            return true;
+
+                        default:
+                            break;
+                    }
+                }
+            }
+
+            // multi-line comments skip input until */ is read
+            case '*':
+            {
+                while (true)
+                {
+                    switch (get())
+                    {
+                        case std::char_traits<char_type>::eof():
+                        case '\0':
+                        {
+                            error_message = "invalid comment; missing closing '*/'";
+                            return false;
+                        }
+
+                        case '*':
+                        {
+                            switch (get())
+                            {
+                                case '/':
+                                    return true;
+
+                                default:
+                                {
+                                    unget();
+                                    continue;
+                                }
+                            }
+                        }
+
+                        default:
+                            continue;
+                    }
+                }
+            }
+
+            // unexpected character after reading '/'
+            default:
+            {
+                error_message = "invalid comment; expecting '/' or '*' after '/'";
+                return false;
+            }
+        }
+    }
+
+    JSON_HEDLEY_NON_NULL(2)
     static void strtof(float& f, const char* str, char** endptr) noexcept
     {
         f = std::strtof(str, endptr);
     }
 
+    JSON_HEDLEY_NON_NULL(2)
     static void strtof(double& f, const char* str, char** endptr) noexcept
     {
         f = std::strtod(str, endptr);
     }
 
+    JSON_HEDLEY_NON_NULL(2)
     static void strtof(long double& f, const char* str, char** endptr) noexcept
     {
         f = std::strtold(str, endptr);
@@ -3412,7 +6814,7 @@ class lexer
     minus    | zero     | any1     | [error]  | [error] | [error] | [error]  | [error]
     zero     | done     | done     | exponent | done    | done    | decimal1 | done
     any1     | any1     | any1     | exponent | done    | done    | decimal1 | done
-    decimal1 | decimal2 | [error]  | [error]  | [error] | [error] | [error]  | [error]
+    decimal1 | decimal2 | decimal2 | [error]  | [error] | [error] | [error]  | [error]
     decimal2 | decimal2 | decimal2 | exponent | done    | done    | done     | done
     exponent | any2     | any2     | [error]  | sign    | sign    | [error]  | [error]
     sign     | any2     | any2     | [error]  | [error] | [error] | [error]  | [error]
@@ -3473,13 +6875,9 @@ class lexer
                 goto scan_number_any1;
             }
 
-            // LCOV_EXCL_START
-            default:
-            {
-                // all other characters are rejected outside scan_number()
-                assert(false);
-            }
-                // LCOV_EXCL_STOP
+            // all other characters are rejected outside scan_number()
+            default:            // LCOV_EXCL_LINE
+                JSON_ASSERT(false);  // LCOV_EXCL_LINE
         }
 
 scan_number_minus:
@@ -3726,7 +7124,7 @@ scan_number_done:
             const auto x = std::strtoull(token_buffer.data(), &endptr, 10);
 
             // we checked the number format before
-            assert(endptr == token_buffer.data() + token_buffer.size());
+            JSON_ASSERT(endptr == token_buffer.data() + token_buffer.size());
 
             if (errno == 0)
             {
@@ -3742,7 +7140,7 @@ scan_number_done:
             const auto x = std::strtoll(token_buffer.data(), &endptr, 10);
 
             // we checked the number format before
-            assert(endptr == token_buffer.data() + token_buffer.size());
+            JSON_ASSERT(endptr == token_buffer.data() + token_buffer.size());
 
             if (errno == 0)
             {
@@ -3759,7 +7157,7 @@ scan_number_done:
         strtof(value_float, token_buffer.data(), &endptr);
 
         // we checked the number format before
-        assert(endptr == token_buffer.data() + token_buffer.size());
+        JSON_ASSERT(endptr == token_buffer.data() + token_buffer.size());
 
         return token_type::value_float;
     }
@@ -3769,13 +7167,14 @@ scan_number_done:
     @param[in] length        the length of the passed literal text
     @param[in] return_type   the token type to return on success
     */
-    token_type scan_literal(const char* literal_text, const std::size_t length,
+    JSON_HEDLEY_NON_NULL(2)
+    token_type scan_literal(const char_type* literal_text, const std::size_t length,
                             token_type return_type)
     {
-        assert(current == literal_text[0]);
+        JSON_ASSERT(std::char_traits<char_type>::to_char_type(current) == literal_text[0]);
         for (std::size_t i = 1; i < length; ++i)
         {
-            if (JSON_UNLIKELY(get() != literal_text[i]))
+            if (JSON_HEDLEY_UNLIKELY(std::char_traits<char_type>::to_char_type(get()) != literal_text[i]))
             {
                 error_message = "invalid literal";
                 return token_type::parse_error;
@@ -3793,7 +7192,7 @@ scan_number_done:
     {
         token_buffer.clear();
         token_string.clear();
-        token_string.push_back(std::char_traits<char>::to_char_type(current));
+        token_string.push_back(std::char_traits<char_type>::to_char_type(current));
     }
 
     /*
@@ -3806,7 +7205,7 @@ scan_number_done:
 
     @return character read from the input
     */
-    std::char_traits<char>::int_type get()
+    char_int_type get()
     {
         ++position.chars_read_total;
         ++position.chars_read_current_line;
@@ -3818,18 +7217,18 @@ scan_number_done:
         }
         else
         {
-            current = ia->get_character();
+            current = ia.get_character();
         }
 
-        if (JSON_LIKELY(current != std::char_traits<char>::eof()))
+        if (JSON_HEDLEY_LIKELY(current != std::char_traits<char_type>::eof()))
         {
-            token_string.push_back(std::char_traits<char>::to_char_type(current));
+            token_string.push_back(std::char_traits<char_type>::to_char_type(current));
         }
 
         if (current == '\n')
         {
             ++position.lines_read;
-            ++position.chars_read_current_line = 0;
+            position.chars_read_current_line = 0;
         }
 
         return current;
@@ -3862,17 +7261,17 @@ scan_number_done:
             --position.chars_read_current_line;
         }
 
-        if (JSON_LIKELY(current != std::char_traits<char>::eof()))
+        if (JSON_HEDLEY_LIKELY(current != std::char_traits<char_type>::eof()))
         {
-            assert(token_string.size() != 0);
+            JSON_ASSERT(!token_string.empty());
             token_string.pop_back();
         }
     }
 
     /// add a character to token_buffer
-    void add(int c)
+    void add(char_int_type c)
     {
-        token_buffer.push_back(std::char_traits<char>::to_char_type(c));
+        token_buffer.push_back(static_cast<typename string_t::value_type>(c));
     }
 
   public:
@@ -3923,17 +7322,17 @@ scan_number_done:
         std::string result;
         for (const auto c : token_string)
         {
-            if ('\x00' <= c and c <= '\x1F')
+            if (static_cast<unsigned char>(c) <= '\x1F')
             {
                 // escape control characters
-                char cs[9];
-                (std::snprintf)(cs, 9, "<U+%.4X>", static_cast<unsigned char>(c));
-                result += cs;
+                std::array<char, 9> cs{{}};
+                (std::snprintf)(cs.data(), cs.size(), "<U+%.4X>", static_cast<unsigned char>(c));
+                result += cs.data();
             }
             else
             {
                 // add character as is
-                result.push_back(c);
+                result.push_back(static_cast<std::string::value_type>(c));
             }
         }
 
@@ -3941,6 +7340,7 @@ scan_number_done:
     }
 
     /// return syntax error message
+    JSON_HEDLEY_RETURNS_NON_NULL
     constexpr const char* get_error_message() const noexcept
     {
         return error_message;
@@ -3959,7 +7359,7 @@ scan_number_done:
         if (get() == 0xEF)
         {
             // check if we completely parse the BOM
-            return get() == 0xBB and get() == 0xBF;
+            return get() == 0xBB && get() == 0xBF;
         }
 
         // the first character is not the beginning of the BOM; unget it to
@@ -3968,21 +7368,38 @@ scan_number_done:
         return true;
     }
 
+    void skip_whitespace()
+    {
+        do
+        {
+            get();
+        }
+        while (current == ' ' || current == '\t' || current == '\n' || current == '\r');
+    }
+
     token_type scan()
     {
         // initially, skip the BOM
-        if (position.chars_read_total == 0 and not skip_bom())
+        if (position.chars_read_total == 0 && !skip_bom())
         {
             error_message = "invalid BOM; must be 0xEF 0xBB 0xBF if given";
             return token_type::parse_error;
         }
 
         // read next character and ignore whitespace
-        do
+        skip_whitespace();
+
+        // ignore comments
+        while (ignore_comments && current == '/')
         {
-            get();
+            if (!scan_comment())
+            {
+                return token_type::parse_error;
+            }
+
+            // skip following whitespace
+            skip_whitespace();
         }
-        while (current == ' ' or current == '\t' or current == '\n' or current == '\r');
 
         switch (current)
         {
@@ -4002,11 +7419,20 @@ scan_number_done:
 
             // literals
             case 't':
-                return scan_literal("true", 4, token_type::literal_true);
+            {
+                std::array<char_type, 4> true_literal = {{'t', 'r', 'u', 'e'}};
+                return scan_literal(true_literal.data(), true_literal.size(), token_type::literal_true);
+            }
             case 'f':
-                return scan_literal("false", 5, token_type::literal_false);
+            {
+                std::array<char_type, 5> false_literal = {{'f', 'a', 'l', 's', 'e'}};
+                return scan_literal(false_literal.data(), false_literal.size(), token_type::literal_false);
+            }
             case 'n':
-                return scan_literal("null", 4, token_type::literal_null);
+            {
+                std::array<char_type, 4> null_literal = {{'n', 'u', 'l', 'l'}};
+                return scan_literal(null_literal.data(), null_literal.size(), token_type::literal_null);
+            }
 
             // string
             case '\"':
@@ -4029,7 +7455,7 @@ scan_number_done:
             // end of input (the null byte is needed when parsing from
             // string literals)
             case '\0':
-            case std::char_traits<char>::eof():
+            case std::char_traits<char_type>::eof():
                 return token_type::end_of_input;
 
             // error
@@ -4041,19 +7467,22 @@ scan_number_done:
 
   private:
     /// input adapter
-    detail::input_adapter_t ia = nullptr;
+    InputAdapterType ia;
+
+    /// whether comments should be ignored (true) or signaled as errors (false)
+    const bool ignore_comments = false;
 
     /// the current character
-    std::char_traits<char>::int_type current = std::char_traits<char>::eof();
+    char_int_type current = std::char_traits<char_type>::eof();
 
     /// whether the next get() call should just return current
     bool next_unget = false;
 
     /// the start position of the current token
-    position_t position;
+    position_t position {};
 
     /// raw input token string (for error messages)
-    std::vector<char> token_string {};
+    std::vector<char_type> token_string {};
 
     /// buffer for variable-length tokens (numbers, strings)
     string_t token_buffer {};
@@ -4067,23 +7496,11 @@ scan_number_done:
     number_float_t value_float = 0;
 
     /// the decimal point
-    const char decimal_point_char = '.';
+    const char_int_type decimal_point_char = '.';
 };
 }  // namespace detail
 }  // namespace nlohmann
 
-// #include <nlohmann/detail/input/parser.hpp>
-
-
-#include <cassert> // assert
-#include <cmath> // isfinite
-#include <cstdint> // uint8_t
-#include <functional> // function
-#include <string> // string
-#include <utility> // move
-
-// #include <nlohmann/detail/exceptions.hpp>
-
 // #include <nlohmann/detail/macro_scope.hpp>
 
 // #include <nlohmann/detail/meta/is_sax.hpp>
@@ -4091,6 +7508,7 @@ scan_number_done:
 
 #include <cstdint> // size_t
 #include <utility> // declval
+#include <string> // string
 
 // #include <nlohmann/detail/meta/detected.hpp>
 
@@ -4101,53 +7519,57 @@ namespace nlohmann
 {
 namespace detail
 {
-template <typename T>
+template<typename T>
 using null_function_t = decltype(std::declval<T&>().null());
 
-template <typename T>
+template<typename T>
 using boolean_function_t =
     decltype(std::declval<T&>().boolean(std::declval<bool>()));
 
-template <typename T, typename Integer>
+template<typename T, typename Integer>
 using number_integer_function_t =
     decltype(std::declval<T&>().number_integer(std::declval<Integer>()));
 
-template <typename T, typename Unsigned>
+template<typename T, typename Unsigned>
 using number_unsigned_function_t =
     decltype(std::declval<T&>().number_unsigned(std::declval<Unsigned>()));
 
-template <typename T, typename Float, typename String>
+template<typename T, typename Float, typename String>
 using number_float_function_t = decltype(std::declval<T&>().number_float(
                                     std::declval<Float>(), std::declval<const String&>()));
 
-template <typename T, typename String>
+template<typename T, typename String>
 using string_function_t =
     decltype(std::declval<T&>().string(std::declval<String&>()));
 
-template <typename T>
+template<typename T, typename Binary>
+using binary_function_t =
+    decltype(std::declval<T&>().binary(std::declval<Binary&>()));
+
+template<typename T>
 using start_object_function_t =
     decltype(std::declval<T&>().start_object(std::declval<std::size_t>()));
 
-template <typename T, typename String>
+template<typename T, typename String>
 using key_function_t =
     decltype(std::declval<T&>().key(std::declval<String&>()));
 
-template <typename T>
+template<typename T>
 using end_object_function_t = decltype(std::declval<T&>().end_object());
 
-template <typename T>
+template<typename T>
 using start_array_function_t =
     decltype(std::declval<T&>().start_array(std::declval<std::size_t>()));
 
-template <typename T>
+template<typename T>
 using end_array_function_t = decltype(std::declval<T&>().end_array());
 
-template <typename T, typename Exception>
+template<typename T, typename Exception>
 using parse_error_function_t = decltype(std::declval<T&>().parse_error(
         std::declval<std::size_t>(), std::declval<const std::string&>(),
         std::declval<const Exception&>()));
 
-template <typename SAX, typename BasicJsonType>
+template<typename SAX, typename BasicJsonType>
 struct is_sax
 {
   private:
@@ -4158,19 +7580,18 @@ struct is_sax
     using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
     using number_float_t = typename BasicJsonType::number_float_t;
     using string_t = typename BasicJsonType::string_t;
+    using binary_t = typename BasicJsonType::binary_t;
     using exception_t = typename BasicJsonType::exception;
 
   public:
     static constexpr bool value =
         is_detected_exact<bool, null_function_t, SAX>::value &&
         is_detected_exact<bool, boolean_function_t, SAX>::value &&
-        is_detected_exact<bool, number_integer_function_t, SAX,
-        number_integer_t>::value &&
-        is_detected_exact<bool, number_unsigned_function_t, SAX,
-        number_unsigned_t>::value &&
-        is_detected_exact<bool, number_float_function_t, SAX, number_float_t,
-        string_t>::value &&
+        is_detected_exact<bool, number_integer_function_t, SAX, number_integer_t>::value &&
+        is_detected_exact<bool, number_unsigned_function_t, SAX, number_unsigned_t>::value &&
+        is_detected_exact<bool, number_float_function_t, SAX, number_float_t, string_t>::value &&
         is_detected_exact<bool, string_function_t, SAX, string_t>::value &&
+        is_detected_exact<bool, binary_function_t, SAX, binary_t>::value &&
         is_detected_exact<bool, start_object_function_t, SAX>::value &&
         is_detected_exact<bool, key_function_t, SAX, string_t>::value &&
         is_detected_exact<bool, end_object_function_t, SAX>::value &&
@@ -4179,7 +7600,7 @@ struct is_sax
         is_detected_exact<bool, parse_error_function_t, SAX, exception_t>::value;
 };
 
-template <typename SAX, typename BasicJsonType>
+template<typename SAX, typename BasicJsonType>
 struct is_sax_static_asserts
 {
   private:
@@ -4190,6 +7611,7 @@ struct is_sax_static_asserts
     using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
     using number_float_t = typename BasicJsonType::number_float_t;
     using string_t = typename BasicJsonType::string_t;
+    using binary_t = typename BasicJsonType::binary_t;
     using exception_t = typename BasicJsonType::exception;
 
   public:
@@ -4213,6 +7635,9 @@ struct is_sax_static_asserts
     static_assert(
         is_detected_exact<bool, string_function_t, SAX, string_t>::value,
         "Missing/invalid function: bool string(string_t&)");
+    static_assert(
+        is_detected_exact<bool, binary_function_t, SAX, binary_t>::value,
+        "Missing/invalid function: bool binary(binary_t&)");
     static_assert(is_detected_exact<bool, start_object_function_t, SAX>::value,
                   "Missing/invalid function: bool start_object(std::size_t)");
     static_assert(is_detected_exact<bool, key_function_t, SAX, string_t>::value,
@@ -4231,715 +7656,2473 @@ struct is_sax_static_asserts
 }  // namespace detail
 }  // namespace nlohmann
 
-// #include <nlohmann/detail/input/input_adapters.hpp>
-
-// #include <nlohmann/detail/input/json_sax.hpp>
+// #include <nlohmann/detail/value_t.hpp>
 
 
-#include <cstddef>
-#include <string>
-#include <vector>
+namespace nlohmann
+{
+namespace detail
+{
 
-// #include <nlohmann/detail/input/parser.hpp>
+/// how to treat CBOR tags
+enum class cbor_tag_handler_t
+{
+    error,  ///< throw a parse_error exception in case of a tag
+    ignore   ///< ignore tags
+};
 
-// #include <nlohmann/detail/exceptions.hpp>
+/*!
+@brief determine system byte order
 
+@return true if and only if system's byte order is little endian
 
-namespace nlohmann
+@note from https://stackoverflow.com/a/1001328/266378
+*/
+static inline bool little_endianess(int num = 1) noexcept
 {
+    return *reinterpret_cast<char*>(&num) == 1;
+}
 
-/*!
-@brief SAX interface
 
-This class describes the SAX interface used by @ref nlohmann::json::sax_parse.
-Each function is called in different situations while the input is parsed. The
-boolean return value informs the parser whether to continue processing the
-input.
+///////////////////
+// binary reader //
+///////////////////
+
+/*!
+@brief deserialization of CBOR, MessagePack, and UBJSON values
 */
-template<typename BasicJsonType>
-struct json_sax
+template<typename BasicJsonType, typename InputAdapterType, typename SAX = json_sax_dom_parser<BasicJsonType>>
+class binary_reader
 {
-    /// type for (signed) integers
     using number_integer_t = typename BasicJsonType::number_integer_t;
-    /// type for unsigned integers
     using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
-    /// type for floating-point numbers
     using number_float_t = typename BasicJsonType::number_float_t;
-    /// type for strings
     using string_t = typename BasicJsonType::string_t;
+    using binary_t = typename BasicJsonType::binary_t;
+    using json_sax_t = SAX;
+    using char_type = typename InputAdapterType::char_type;
+    using char_int_type = typename std::char_traits<char_type>::int_type;
 
+  public:
     /*!
-    @brief a null value was read
-    @return whether parsing should proceed
-    */
-    virtual bool null() = 0;
+    @brief create a binary reader
 
-    /*!
-    @brief a boolean value was read
-    @param[in] val  boolean value
-    @return whether parsing should proceed
+    @param[in] adapter  input adapter to read from
     */
-    virtual bool boolean(bool val) = 0;
+    explicit binary_reader(InputAdapterType&& adapter) : ia(std::move(adapter))
+    {
+        (void)detail::is_sax_static_asserts<SAX, BasicJsonType> {};
+    }
 
-    /*!
-    @brief an integer number was read
-    @param[in] val  integer value
-    @return whether parsing should proceed
-    */
-    virtual bool number_integer(number_integer_t val) = 0;
+    // make class move-only
+    binary_reader(const binary_reader&) = delete;
+    binary_reader(binary_reader&&) = default;
+    binary_reader& operator=(const binary_reader&) = delete;
+    binary_reader& operator=(binary_reader&&) = default;
+    ~binary_reader() = default;
 
     /*!
-    @brief an unsigned integer number was read
-    @param[in] val  unsigned integer value
-    @return whether parsing should proceed
-    */
-    virtual bool number_unsigned(number_unsigned_t val) = 0;
+    @param[in] format  the binary format to parse
+    @param[in] sax_    a SAX event processor
+    @param[in] strict  whether to expect the input to be consumed completed
+    @param[in] tag_handler  how to treat CBOR tags
 
-    /*!
-    @brief an floating-point number was read
-    @param[in] val  floating-point value
-    @param[in] s    raw token value
-    @return whether parsing should proceed
+    @return
     */
-    virtual bool number_float(number_float_t val, const string_t& s) = 0;
+    JSON_HEDLEY_NON_NULL(3)
+    bool sax_parse(const input_format_t format,
+                   json_sax_t* sax_,
+                   const bool strict = true,
+                   const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error)
+    {
+        sax = sax_;
+        bool result = false;
 
-    /*!
-    @brief a string was read
-    @param[in] val  string value
-    @return whether parsing should proceed
-    @note It is safe to move the passed string.
-    */
-    virtual bool string(string_t& val) = 0;
+        switch (format)
+        {
+            case input_format_t::bson:
+                result = parse_bson_internal();
+                break;
 
-    /*!
-    @brief the beginning of an object was read
-    @param[in] elements  number of object elements or -1 if unknown
-    @return whether parsing should proceed
-    @note binary formats may report the number of elements
-    */
-    virtual bool start_object(std::size_t elements) = 0;
+            case input_format_t::cbor:
+                result = parse_cbor_internal(true, tag_handler);
+                break;
+
+            case input_format_t::msgpack:
+                result = parse_msgpack_internal();
+                break;
+
+            case input_format_t::ubjson:
+                result = parse_ubjson_internal();
+                break;
+
+            default:            // LCOV_EXCL_LINE
+                JSON_ASSERT(false);  // LCOV_EXCL_LINE
+        }
+
+        // strict mode: next byte must be EOF
+        if (result && strict)
+        {
+            if (format == input_format_t::ubjson)
+            {
+                get_ignore_noop();
+            }
+            else
+            {
+                get();
+            }
+
+            if (JSON_HEDLEY_UNLIKELY(current != std::char_traits<char_type>::eof()))
+            {
+                return sax->parse_error(chars_read, get_token_string(),
+                                        parse_error::create(110, chars_read, exception_message(format, "expected end of input; last byte: 0x" + get_token_string(), "value")));
+            }
+        }
+
+        return result;
+    }
+
+  private:
+    //////////
+    // BSON //
+    //////////
 
     /*!
-    @brief an object key was read
-    @param[in] val  object key
-    @return whether parsing should proceed
-    @note It is safe to move the passed string.
+    @brief Reads in a BSON-object and passes it to the SAX-parser.
+    @return whether a valid BSON-value was passed to the SAX parser
     */
-    virtual bool key(string_t& val) = 0;
+    bool parse_bson_internal()
+    {
+        std::int32_t document_size{};
+        get_number<std::int32_t, true>(input_format_t::bson, document_size);
+
+        if (JSON_HEDLEY_UNLIKELY(!sax->start_object(std::size_t(-1))))
+        {
+            return false;
+        }
+
+        if (JSON_HEDLEY_UNLIKELY(!parse_bson_element_list(/*is_array*/false)))
+        {
+            return false;
+        }
+
+        return sax->end_object();
+    }
 
     /*!
-    @brief the end of an object was read
-    @return whether parsing should proceed
+    @brief Parses a C-style string from the BSON input.
+    @param[in, out] result  A reference to the string variable where the read
+                            string is to be stored.
+    @return `true` if the \x00-byte indicating the end of the string was
+             encountered before the EOF; false` indicates an unexpected EOF.
     */
-    virtual bool end_object() = 0;
+    bool get_bson_cstr(string_t& result)
+    {
+        auto out = std::back_inserter(result);
+        while (true)
+        {
+            get();
+            if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::bson, "cstring")))
+            {
+                return false;
+            }
+            if (current == 0x00)
+            {
+                return true;
+            }
+            *out++ = static_cast<typename string_t::value_type>(current);
+        }
+    }
 
     /*!
-    @brief the beginning of an array was read
-    @param[in] elements  number of array elements or -1 if unknown
-    @return whether parsing should proceed
-    @note binary formats may report the number of elements
+    @brief Parses a zero-terminated string of length @a len from the BSON
+           input.
+    @param[in] len  The length (including the zero-byte at the end) of the
+                    string to be read.
+    @param[in, out] result  A reference to the string variable where the read
+                            string is to be stored.
+    @tparam NumberType The type of the length @a len
+    @pre len >= 1
+    @return `true` if the string was successfully parsed
     */
-    virtual bool start_array(std::size_t elements) = 0;
+    template<typename NumberType>
+    bool get_bson_string(const NumberType len, string_t& result)
+    {
+        if (JSON_HEDLEY_UNLIKELY(len < 1))
+        {
+            auto last_token = get_token_string();
+            return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read, exception_message(input_format_t::bson, "string length must be at least 1, is " + std::to_string(len), "string")));
+        }
+
+        return get_string(input_format_t::bson, len - static_cast<NumberType>(1), result) && get() != std::char_traits<char_type>::eof();
+    }
 
     /*!
-    @brief the end of an array was read
-    @return whether parsing should proceed
+    @brief Parses a byte array input of length @a len from the BSON input.
+    @param[in] len  The length of the byte array to be read.
+    @param[in, out] result  A reference to the binary variable where the read
+                            array is to be stored.
+    @tparam NumberType The type of the length @a len
+    @pre len >= 0
+    @return `true` if the byte array was successfully parsed
     */
-    virtual bool end_array() = 0;
+    template<typename NumberType>
+    bool get_bson_binary(const NumberType len, binary_t& result)
+    {
+        if (JSON_HEDLEY_UNLIKELY(len < 0))
+        {
+            auto last_token = get_token_string();
+            return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read, exception_message(input_format_t::bson, "byte array length cannot be negative, is " + std::to_string(len), "binary")));
+        }
+
+        // All BSON binary values have a subtype
+        std::uint8_t subtype{};
+        get_number<std::uint8_t>(input_format_t::bson, subtype);
+        result.set_subtype(subtype);
+
+        return get_binary(input_format_t::bson, len, result);
+    }
 
     /*!
-    @brief a parse error occurred
-    @param[in] position    the position in the input where the error occurs
-    @param[in] last_token  the last read token
-    @param[in] ex          an exception object describing the error
-    @return whether parsing should proceed (must return false)
+    @brief Read a BSON document element of the given @a element_type.
+    @param[in] element_type The BSON element type, c.f. http://bsonspec.org/spec.html
+    @param[in] element_type_parse_position The position in the input stream,
+               where the `element_type` was read.
+    @warning Not all BSON element types are supported yet. An unsupported
+             @a element_type will give rise to a parse_error.114:
+             Unsupported BSON record type 0x...
+    @return whether a valid BSON-object/array was passed to the SAX parser
     */
-    virtual bool parse_error(std::size_t position,
-                             const std::string& last_token,
-                             const detail::exception& ex) = 0;
+    bool parse_bson_element_internal(const char_int_type element_type,
+                                     const std::size_t element_type_parse_position)
+    {
+        switch (element_type)
+        {
+            case 0x01: // double
+            {
+                double number{};
+                return get_number<double, true>(input_format_t::bson, number) && sax->number_float(static_cast<number_float_t>(number), "");
+            }
 
-    virtual ~json_sax() = default;
-};
+            case 0x02: // string
+            {
+                std::int32_t len{};
+                string_t value;
+                return get_number<std::int32_t, true>(input_format_t::bson, len) && get_bson_string(len, value) && sax->string(value);
+            }
 
+            case 0x03: // object
+            {
+                return parse_bson_internal();
+            }
 
-namespace detail
-{
-/*!
-@brief SAX implementation to create a JSON value from SAX events
+            case 0x04: // array
+            {
+                return parse_bson_array();
+            }
 
-This class implements the @ref json_sax interface and processes the SAX events
-to create a JSON value which makes it basically a DOM parser. The structure or
-hierarchy of the JSON value is managed by the stack `ref_stack` which contains
-a pointer to the respective array or object for each recursion depth.
+            case 0x05: // binary
+            {
+                std::int32_t len{};
+                binary_t value;
+                return get_number<std::int32_t, true>(input_format_t::bson, len) && get_bson_binary(len, value) && sax->binary(value);
+            }
 
-After successful parsing, the value that is passed by reference to the
-constructor contains the parsed value.
+            case 0x08: // boolean
+            {
+                return sax->boolean(get() != 0);
+            }
 
-@tparam BasicJsonType  the JSON type
-*/
-template<typename BasicJsonType>
-class json_sax_dom_parser
-{
-  public:
-    using number_integer_t = typename BasicJsonType::number_integer_t;
-    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
-    using number_float_t = typename BasicJsonType::number_float_t;
-    using string_t = typename BasicJsonType::string_t;
+            case 0x0A: // null
+            {
+                return sax->null();
+            }
 
-    /*!
-    @param[in, out] r  reference to a JSON value that is manipulated while
-                       parsing
-    @param[in] allow_exceptions_  whether parse errors yield exceptions
-    */
-    explicit json_sax_dom_parser(BasicJsonType& r, const bool allow_exceptions_ = true)
-        : root(r), allow_exceptions(allow_exceptions_)
-    {}
+            case 0x10: // int32
+            {
+                std::int32_t value{};
+                return get_number<std::int32_t, true>(input_format_t::bson, value) && sax->number_integer(value);
+            }
 
-    bool null()
-    {
-        handle_value(nullptr);
-        return true;
-    }
+            case 0x12: // int64
+            {
+                std::int64_t value{};
+                return get_number<std::int64_t, true>(input_format_t::bson, value) && sax->number_integer(value);
+            }
 
-    bool boolean(bool val)
-    {
-        handle_value(val);
-        return true;
+            default: // anything else not supported (yet)
+            {
+                std::array<char, 3> cr{{}};
+                (std::snprintf)(cr.data(), cr.size(), "%.2hhX", static_cast<unsigned char>(element_type));
+                return sax->parse_error(element_type_parse_position, std::string(cr.data()), parse_error::create(114, element_type_parse_position, "Unsupported BSON record type 0x" + std::string(cr.data())));
+            }
+        }
     }
 
-    bool number_integer(number_integer_t val)
-    {
-        handle_value(val);
-        return true;
-    }
+    /*!
+    @brief Read a BSON element list (as specified in the BSON-spec)
 
-    bool number_unsigned(number_unsigned_t val)
-    {
-        handle_value(val);
-        return true;
-    }
+    The same binary layout is used for objects and arrays, hence it must be
+    indicated with the argument @a is_array which one is expected
+    (true --> array, false --> object).
 
-    bool number_float(number_float_t val, const string_t& /*unused*/)
+    @param[in] is_array Determines if the element list being read is to be
+                        treated as an object (@a is_array == false), or as an
+                        array (@a is_array == true).
+    @return whether a valid BSON-object/array was passed to the SAX parser
+    */
+    bool parse_bson_element_list(const bool is_array)
     {
-        handle_value(val);
-        return true;
-    }
+        string_t key;
+
+        while (auto element_type = get())
+        {
+            if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::bson, "element list")))
+            {
+                return false;
+            }
+
+            const std::size_t element_type_parse_position = chars_read;
+            if (JSON_HEDLEY_UNLIKELY(!get_bson_cstr(key)))
+            {
+                return false;
+            }
+
+            if (!is_array && !sax->key(key))
+            {
+                return false;
+            }
+
+            if (JSON_HEDLEY_UNLIKELY(!parse_bson_element_internal(element_type, element_type_parse_position)))
+            {
+                return false;
+            }
+
+            // get_bson_cstr only appends
+            key.clear();
+        }
 
-    bool string(string_t& val)
-    {
-        handle_value(val);
         return true;
     }
 
-    bool start_object(std::size_t len)
+    /*!
+    @brief Reads an array from the BSON input and passes it to the SAX-parser.
+    @return whether a valid BSON-array was passed to the SAX parser
+    */
+    bool parse_bson_array()
     {
-        ref_stack.push_back(handle_value(BasicJsonType::value_t::object));
+        std::int32_t document_size{};
+        get_number<std::int32_t, true>(input_format_t::bson, document_size);
 
-        if (JSON_UNLIKELY(len != std::size_t(-1) and len > ref_stack.back()->max_size()))
+        if (JSON_HEDLEY_UNLIKELY(!sax->start_array(std::size_t(-1))))
         {
-            JSON_THROW(out_of_range::create(408,
-                                            "excessive object size: " + std::to_string(len)));
+            return false;
         }
 
-        return true;
-    }
+        if (JSON_HEDLEY_UNLIKELY(!parse_bson_element_list(/*is_array*/true)))
+        {
+            return false;
+        }
 
-    bool key(string_t& val)
-    {
-        // add null at given key and store the reference for later
-        object_element = &(ref_stack.back()->m_value.object->operator[](val));
-        return true;
+        return sax->end_array();
     }
 
-    bool end_object()
+    //////////
+    // CBOR //
+    //////////
+
+    /*!
+    @param[in] get_char  whether a new character should be retrieved from the
+                         input (true) or whether the last read character should
+                         be considered instead (false)
+    @param[in] tag_handler how CBOR tags should be treated
+
+    @return whether a valid CBOR value was passed to the SAX parser
+    */
+    bool parse_cbor_internal(const bool get_char,
+                             const cbor_tag_handler_t tag_handler)
     {
-        ref_stack.pop_back();
-        return true;
+        switch (get_char ? get() : current)
+        {
+            // EOF
+            case std::char_traits<char_type>::eof():
+                return unexpect_eof(input_format_t::cbor, "value");
+
+            // Integer 0x00..0x17 (0..23)
+            case 0x00:
+            case 0x01:
+            case 0x02:
+            case 0x03:
+            case 0x04:
+            case 0x05:
+            case 0x06:
+            case 0x07:
+            case 0x08:
+            case 0x09:
+            case 0x0A:
+            case 0x0B:
+            case 0x0C:
+            case 0x0D:
+            case 0x0E:
+            case 0x0F:
+            case 0x10:
+            case 0x11:
+            case 0x12:
+            case 0x13:
+            case 0x14:
+            case 0x15:
+            case 0x16:
+            case 0x17:
+                return sax->number_unsigned(static_cast<number_unsigned_t>(current));
+
+            case 0x18: // Unsigned integer (one-byte uint8_t follows)
+            {
+                std::uint8_t number{};
+                return get_number(input_format_t::cbor, number) && sax->number_unsigned(number);
+            }
+
+            case 0x19: // Unsigned integer (two-byte uint16_t follows)
+            {
+                std::uint16_t number{};
+                return get_number(input_format_t::cbor, number) && sax->number_unsigned(number);
+            }
+
+            case 0x1A: // Unsigned integer (four-byte uint32_t follows)
+            {
+                std::uint32_t number{};
+                return get_number(input_format_t::cbor, number) && sax->number_unsigned(number);
+            }
+
+            case 0x1B: // Unsigned integer (eight-byte uint64_t follows)
+            {
+                std::uint64_t number{};
+                return get_number(input_format_t::cbor, number) && sax->number_unsigned(number);
+            }
+
+            // Negative integer -1-0x00..-1-0x17 (-1..-24)
+            case 0x20:
+            case 0x21:
+            case 0x22:
+            case 0x23:
+            case 0x24:
+            case 0x25:
+            case 0x26:
+            case 0x27:
+            case 0x28:
+            case 0x29:
+            case 0x2A:
+            case 0x2B:
+            case 0x2C:
+            case 0x2D:
+            case 0x2E:
+            case 0x2F:
+            case 0x30:
+            case 0x31:
+            case 0x32:
+            case 0x33:
+            case 0x34:
+            case 0x35:
+            case 0x36:
+            case 0x37:
+                return sax->number_integer(static_cast<std::int8_t>(0x20 - 1 - current));
+
+            case 0x38: // Negative integer (one-byte uint8_t follows)
+            {
+                std::uint8_t number{};
+                return get_number(input_format_t::cbor, number) && sax->number_integer(static_cast<number_integer_t>(-1) - number);
+            }
+
+            case 0x39: // Negative integer -1-n (two-byte uint16_t follows)
+            {
+                std::uint16_t number{};
+                return get_number(input_format_t::cbor, number) && sax->number_integer(static_cast<number_integer_t>(-1) - number);
+            }
+
+            case 0x3A: // Negative integer -1-n (four-byte uint32_t follows)
+            {
+                std::uint32_t number{};
+                return get_number(input_format_t::cbor, number) && sax->number_integer(static_cast<number_integer_t>(-1) - number);
+            }
+
+            case 0x3B: // Negative integer -1-n (eight-byte uint64_t follows)
+            {
+                std::uint64_t number{};
+                return get_number(input_format_t::cbor, number) && sax->number_integer(static_cast<number_integer_t>(-1)
+                        - static_cast<number_integer_t>(number));
+            }
+
+            // Binary data (0x00..0x17 bytes follow)
+            case 0x40:
+            case 0x41:
+            case 0x42:
+            case 0x43:
+            case 0x44:
+            case 0x45:
+            case 0x46:
+            case 0x47:
+            case 0x48:
+            case 0x49:
+            case 0x4A:
+            case 0x4B:
+            case 0x4C:
+            case 0x4D:
+            case 0x4E:
+            case 0x4F:
+            case 0x50:
+            case 0x51:
+            case 0x52:
+            case 0x53:
+            case 0x54:
+            case 0x55:
+            case 0x56:
+            case 0x57:
+            case 0x58: // Binary data (one-byte uint8_t for n follows)
+            case 0x59: // Binary data (two-byte uint16_t for n follow)
+            case 0x5A: // Binary data (four-byte uint32_t for n follow)
+            case 0x5B: // Binary data (eight-byte uint64_t for n follow)
+            case 0x5F: // Binary data (indefinite length)
+            {
+                binary_t b;
+                return get_cbor_binary(b) && sax->binary(b);
+            }
+
+            // UTF-8 string (0x00..0x17 bytes follow)
+            case 0x60:
+            case 0x61:
+            case 0x62:
+            case 0x63:
+            case 0x64:
+            case 0x65:
+            case 0x66:
+            case 0x67:
+            case 0x68:
+            case 0x69:
+            case 0x6A:
+            case 0x6B:
+            case 0x6C:
+            case 0x6D:
+            case 0x6E:
+            case 0x6F:
+            case 0x70:
+            case 0x71:
+            case 0x72:
+            case 0x73:
+            case 0x74:
+            case 0x75:
+            case 0x76:
+            case 0x77:
+            case 0x78: // UTF-8 string (one-byte uint8_t for n follows)
+            case 0x79: // UTF-8 string (two-byte uint16_t for n follow)
+            case 0x7A: // UTF-8 string (four-byte uint32_t for n follow)
+            case 0x7B: // UTF-8 string (eight-byte uint64_t for n follow)
+            case 0x7F: // UTF-8 string (indefinite length)
+            {
+                string_t s;
+                return get_cbor_string(s) && sax->string(s);
+            }
+
+            // array (0x00..0x17 data items follow)
+            case 0x80:
+            case 0x81:
+            case 0x82:
+            case 0x83:
+            case 0x84:
+            case 0x85:
+            case 0x86:
+            case 0x87:
+            case 0x88:
+            case 0x89:
+            case 0x8A:
+            case 0x8B:
+            case 0x8C:
+            case 0x8D:
+            case 0x8E:
+            case 0x8F:
+            case 0x90:
+            case 0x91:
+            case 0x92:
+            case 0x93:
+            case 0x94:
+            case 0x95:
+            case 0x96:
+            case 0x97:
+                return get_cbor_array(static_cast<std::size_t>(static_cast<unsigned int>(current) & 0x1Fu), tag_handler);
+
+            case 0x98: // array (one-byte uint8_t for n follows)
+            {
+                std::uint8_t len{};
+                return get_number(input_format_t::cbor, len) && get_cbor_array(static_cast<std::size_t>(len), tag_handler);
+            }
+
+            case 0x99: // array (two-byte uint16_t for n follow)
+            {
+                std::uint16_t len{};
+                return get_number(input_format_t::cbor, len) && get_cbor_array(static_cast<std::size_t>(len), tag_handler);
+            }
+
+            case 0x9A: // array (four-byte uint32_t for n follow)
+            {
+                std::uint32_t len{};
+                return get_number(input_format_t::cbor, len) && get_cbor_array(static_cast<std::size_t>(len), tag_handler);
+            }
+
+            case 0x9B: // array (eight-byte uint64_t for n follow)
+            {
+                std::uint64_t len{};
+                return get_number(input_format_t::cbor, len) && get_cbor_array(static_cast<std::size_t>(len), tag_handler);
+            }
+
+            case 0x9F: // array (indefinite length)
+                return get_cbor_array(std::size_t(-1), tag_handler);
+
+            // map (0x00..0x17 pairs of data items follow)
+            case 0xA0:
+            case 0xA1:
+            case 0xA2:
+            case 0xA3:
+            case 0xA4:
+            case 0xA5:
+            case 0xA6:
+            case 0xA7:
+            case 0xA8:
+            case 0xA9:
+            case 0xAA:
+            case 0xAB:
+            case 0xAC:
+            case 0xAD:
+            case 0xAE:
+            case 0xAF:
+            case 0xB0:
+            case 0xB1:
+            case 0xB2:
+            case 0xB3:
+            case 0xB4:
+            case 0xB5:
+            case 0xB6:
+            case 0xB7:
+                return get_cbor_object(static_cast<std::size_t>(static_cast<unsigned int>(current) & 0x1Fu), tag_handler);
+
+            case 0xB8: // map (one-byte uint8_t for n follows)
+            {
+                std::uint8_t len{};
+                return get_number(input_format_t::cbor, len) && get_cbor_object(static_cast<std::size_t>(len), tag_handler);
+            }
+
+            case 0xB9: // map (two-byte uint16_t for n follow)
+            {
+                std::uint16_t len{};
+                return get_number(input_format_t::cbor, len) && get_cbor_object(static_cast<std::size_t>(len), tag_handler);
+            }
+
+            case 0xBA: // map (four-byte uint32_t for n follow)
+            {
+                std::uint32_t len{};
+                return get_number(input_format_t::cbor, len) && get_cbor_object(static_cast<std::size_t>(len), tag_handler);
+            }
+
+            case 0xBB: // map (eight-byte uint64_t for n follow)
+            {
+                std::uint64_t len{};
+                return get_number(input_format_t::cbor, len) && get_cbor_object(static_cast<std::size_t>(len), tag_handler);
+            }
+
+            case 0xBF: // map (indefinite length)
+                return get_cbor_object(std::size_t(-1), tag_handler);
+
+            case 0xC6: // tagged item
+            case 0xC7:
+            case 0xC8:
+            case 0xC9:
+            case 0xCA:
+            case 0xCB:
+            case 0xCC:
+            case 0xCD:
+            case 0xCE:
+            case 0xCF:
+            case 0xD0:
+            case 0xD1:
+            case 0xD2:
+            case 0xD3:
+            case 0xD4:
+            case 0xD8: // tagged item (1 bytes follow)
+            case 0xD9: // tagged item (2 bytes follow)
+            case 0xDA: // tagged item (4 bytes follow)
+            case 0xDB: // tagged item (8 bytes follow)
+            {
+                switch (tag_handler)
+                {
+                    case cbor_tag_handler_t::error:
+                    {
+                        auto last_token = get_token_string();
+                        return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read, exception_message(input_format_t::cbor, "invalid byte: 0x" + last_token, "value")));
+                    }
+
+                    case cbor_tag_handler_t::ignore:
+                    {
+                        switch (current)
+                        {
+                            case 0xD8:
+                            {
+                                std::uint8_t len{};
+                                get_number(input_format_t::cbor, len);
+                                break;
+                            }
+                            case 0xD9:
+                            {
+                                std::uint16_t len{};
+                                get_number(input_format_t::cbor, len);
+                                break;
+                            }
+                            case 0xDA:
+                            {
+                                std::uint32_t len{};
+                                get_number(input_format_t::cbor, len);
+                                break;
+                            }
+                            case 0xDB:
+                            {
+                                std::uint64_t len{};
+                                get_number(input_format_t::cbor, len);
+                                break;
+                            }
+                            default:
+                                break;
+                        }
+                        return parse_cbor_internal(true, tag_handler);
+                    }
+
+                    default:            // LCOV_EXCL_LINE
+                        JSON_ASSERT(false);  // LCOV_EXCL_LINE
+                }
+            }
+
+            case 0xF4: // false
+                return sax->boolean(false);
+
+            case 0xF5: // true
+                return sax->boolean(true);
+
+            case 0xF6: // null
+                return sax->null();
+
+            case 0xF9: // Half-Precision Float (two-byte IEEE 754)
+            {
+                const auto byte1_raw = get();
+                if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::cbor, "number")))
+                {
+                    return false;
+                }
+                const auto byte2_raw = get();
+                if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::cbor, "number")))
+                {
+                    return false;
+                }
+
+                const auto byte1 = static_cast<unsigned char>(byte1_raw);
+                const auto byte2 = static_cast<unsigned char>(byte2_raw);
+
+                // code from RFC 7049, Appendix D, Figure 3:
+                // As half-precision floating-point numbers were only added
+                // to IEEE 754 in 2008, today's programming platforms often
+                // still only have limited support for them. It is very
+                // easy to include at least decoding support for them even
+                // without such support. An example of a small decoder for
+                // half-precision floating-point numbers in the C language
+                // is shown in Fig. 3.
+                const auto half = static_cast<unsigned int>((byte1 << 8u) + byte2);
+                const double val = [&half]
+                {
+                    const int exp = (half >> 10u) & 0x1Fu;
+                    const unsigned int mant = half & 0x3FFu;
+                    JSON_ASSERT(0 <= exp&& exp <= 32);
+                    JSON_ASSERT(mant <= 1024);
+                    switch (exp)
+                    {
+                        case 0:
+                            return std::ldexp(mant, -24);
+                        case 31:
+                            return (mant == 0)
+                            ? std::numeric_limits<double>::infinity()
+                            : std::numeric_limits<double>::quiet_NaN();
+                        default:
+                            return std::ldexp(mant + 1024, exp - 25);
+                    }
+                }();
+                return sax->number_float((half & 0x8000u) != 0
+                                         ? static_cast<number_float_t>(-val)
+                                         : static_cast<number_float_t>(val), "");
+            }
+
+            case 0xFA: // Single-Precision Float (four-byte IEEE 754)
+            {
+                float number{};
+                return get_number(input_format_t::cbor, number) && sax->number_float(static_cast<number_float_t>(number), "");
+            }
+
+            case 0xFB: // Double-Precision Float (eight-byte IEEE 754)
+            {
+                double number{};
+                return get_number(input_format_t::cbor, number) && sax->number_float(static_cast<number_float_t>(number), "");
+            }
+
+            default: // anything else (0xFF is handled inside the other types)
+            {
+                auto last_token = get_token_string();
+                return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read, exception_message(input_format_t::cbor, "invalid byte: 0x" + last_token, "value")));
+            }
+        }
     }
 
-    bool start_array(std::size_t len)
-    {
-        ref_stack.push_back(handle_value(BasicJsonType::value_t::array));
+    /*!
+    @brief reads a CBOR string
+
+    This function first reads starting bytes to determine the expected
+    string length and then copies this number of bytes into a string.
+    Additionally, CBOR's strings with indefinite lengths are supported.
 
-        if (JSON_UNLIKELY(len != std::size_t(-1) and len > ref_stack.back()->max_size()))
+    @param[out] result  created string
+
+    @return whether string creation completed
+    */
+    bool get_cbor_string(string_t& result)
+    {
+        if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::cbor, "string")))
         {
-            JSON_THROW(out_of_range::create(408,
-                                            "excessive array size: " + std::to_string(len)));
+            return false;
         }
 
-        return true;
-    }
+        switch (current)
+        {
+            // UTF-8 string (0x00..0x17 bytes follow)
+            case 0x60:
+            case 0x61:
+            case 0x62:
+            case 0x63:
+            case 0x64:
+            case 0x65:
+            case 0x66:
+            case 0x67:
+            case 0x68:
+            case 0x69:
+            case 0x6A:
+            case 0x6B:
+            case 0x6C:
+            case 0x6D:
+            case 0x6E:
+            case 0x6F:
+            case 0x70:
+            case 0x71:
+            case 0x72:
+            case 0x73:
+            case 0x74:
+            case 0x75:
+            case 0x76:
+            case 0x77:
+            {
+                return get_string(input_format_t::cbor, static_cast<unsigned int>(current) & 0x1Fu, result);
+            }
 
-    bool end_array()
-    {
-        ref_stack.pop_back();
-        return true;
+            case 0x78: // UTF-8 string (one-byte uint8_t for n follows)
+            {
+                std::uint8_t len{};
+                return get_number(input_format_t::cbor, len) && get_string(input_format_t::cbor, len, result);
+            }
+
+            case 0x79: // UTF-8 string (two-byte uint16_t for n follow)
+            {
+                std::uint16_t len{};
+                return get_number(input_format_t::cbor, len) && get_string(input_format_t::cbor, len, result);
+            }
+
+            case 0x7A: // UTF-8 string (four-byte uint32_t for n follow)
+            {
+                std::uint32_t len{};
+                return get_number(input_format_t::cbor, len) && get_string(input_format_t::cbor, len, result);
+            }
+
+            case 0x7B: // UTF-8 string (eight-byte uint64_t for n follow)
+            {
+                std::uint64_t len{};
+                return get_number(input_format_t::cbor, len) && get_string(input_format_t::cbor, len, result);
+            }
+
+            case 0x7F: // UTF-8 string (indefinite length)
+            {
+                while (get() != 0xFF)
+                {
+                    string_t chunk;
+                    if (!get_cbor_string(chunk))
+                    {
+                        return false;
+                    }
+                    result.append(chunk);
+                }
+                return true;
+            }
+
+            default:
+            {
+                auto last_token = get_token_string();
+                return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read, exception_message(input_format_t::cbor, "expected length specification (0x60-0x7B) or indefinite string type (0x7F); last byte: 0x" + last_token, "string")));
+            }
+        }
     }
 
-    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/,
-                     const detail::exception& ex)
+    /*!
+    @brief reads a CBOR byte array
+
+    This function first reads starting bytes to determine the expected
+    byte array length and then copies this number of bytes into the byte array.
+    Additionally, CBOR's byte arrays with indefinite lengths are supported.
+
+    @param[out] result  created byte array
+
+    @return whether byte array creation completed
+    */
+    bool get_cbor_binary(binary_t& result)
     {
-        errored = true;
-        if (allow_exceptions)
+        if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::cbor, "binary")))
         {
-            // determine the proper exception type from the id
-            switch ((ex.id / 100) % 100)
+            return false;
+        }
+
+        switch (current)
+        {
+            // Binary data (0x00..0x17 bytes follow)
+            case 0x40:
+            case 0x41:
+            case 0x42:
+            case 0x43:
+            case 0x44:
+            case 0x45:
+            case 0x46:
+            case 0x47:
+            case 0x48:
+            case 0x49:
+            case 0x4A:
+            case 0x4B:
+            case 0x4C:
+            case 0x4D:
+            case 0x4E:
+            case 0x4F:
+            case 0x50:
+            case 0x51:
+            case 0x52:
+            case 0x53:
+            case 0x54:
+            case 0x55:
+            case 0x56:
+            case 0x57:
             {
-                case 1:
-                    JSON_THROW(*reinterpret_cast<const detail::parse_error*>(&ex));
-                case 4:
-                    JSON_THROW(*reinterpret_cast<const detail::out_of_range*>(&ex));
-                // LCOV_EXCL_START
-                case 2:
-                    JSON_THROW(*reinterpret_cast<const detail::invalid_iterator*>(&ex));
-                case 3:
-                    JSON_THROW(*reinterpret_cast<const detail::type_error*>(&ex));
-                case 5:
-                    JSON_THROW(*reinterpret_cast<const detail::other_error*>(&ex));
-                default:
-                    assert(false);
-                    // LCOV_EXCL_STOP
+                return get_binary(input_format_t::cbor, static_cast<unsigned int>(current) & 0x1Fu, result);
+            }
+
+            case 0x58: // Binary data (one-byte uint8_t for n follows)
+            {
+                std::uint8_t len{};
+                return get_number(input_format_t::cbor, len) &&
+                       get_binary(input_format_t::cbor, len, result);
+            }
+
+            case 0x59: // Binary data (two-byte uint16_t for n follow)
+            {
+                std::uint16_t len{};
+                return get_number(input_format_t::cbor, len) &&
+                       get_binary(input_format_t::cbor, len, result);
+            }
+
+            case 0x5A: // Binary data (four-byte uint32_t for n follow)
+            {
+                std::uint32_t len{};
+                return get_number(input_format_t::cbor, len) &&
+                       get_binary(input_format_t::cbor, len, result);
+            }
+
+            case 0x5B: // Binary data (eight-byte uint64_t for n follow)
+            {
+                std::uint64_t len{};
+                return get_number(input_format_t::cbor, len) &&
+                       get_binary(input_format_t::cbor, len, result);
+            }
+
+            case 0x5F: // Binary data (indefinite length)
+            {
+                while (get() != 0xFF)
+                {
+                    binary_t chunk;
+                    if (!get_cbor_binary(chunk))
+                    {
+                        return false;
+                    }
+                    result.insert(result.end(), chunk.begin(), chunk.end());
+                }
+                return true;
+            }
+
+            default:
+            {
+                auto last_token = get_token_string();
+                return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read, exception_message(input_format_t::cbor, "expected length specification (0x40-0x5B) or indefinite binary array type (0x5F); last byte: 0x" + last_token, "binary")));
             }
         }
-        return false;
     }
 
-    constexpr bool is_errored() const
+    /*!
+    @param[in] len  the length of the array or std::size_t(-1) for an
+                    array of indefinite size
+    @param[in] tag_handler how CBOR tags should be treated
+    @return whether array creation completed
+    */
+    bool get_cbor_array(const std::size_t len,
+                        const cbor_tag_handler_t tag_handler)
     {
-        return errored;
+        if (JSON_HEDLEY_UNLIKELY(!sax->start_array(len)))
+        {
+            return false;
+        }
+
+        if (len != std::size_t(-1))
+        {
+            for (std::size_t i = 0; i < len; ++i)
+            {
+                if (JSON_HEDLEY_UNLIKELY(!parse_cbor_internal(true, tag_handler)))
+                {
+                    return false;
+                }
+            }
+        }
+        else
+        {
+            while (get() != 0xFF)
+            {
+                if (JSON_HEDLEY_UNLIKELY(!parse_cbor_internal(false, tag_handler)))
+                {
+                    return false;
+                }
+            }
+        }
+
+        return sax->end_array();
     }
 
-  private:
     /*!
-    @invariant If the ref stack is empty, then the passed value will be the new
-               root.
-    @invariant If the ref stack contains a value, then it is an array or an
-               object to which we can add elements
+    @param[in] len  the length of the object or std::size_t(-1) for an
+                    object of indefinite size
+    @param[in] tag_handler how CBOR tags should be treated
+    @return whether object creation completed
     */
-    template<typename Value>
-    BasicJsonType* handle_value(Value&& v)
+    bool get_cbor_object(const std::size_t len,
+                         const cbor_tag_handler_t tag_handler)
     {
-        if (ref_stack.empty())
+        if (JSON_HEDLEY_UNLIKELY(!sax->start_object(len)))
         {
-            root = BasicJsonType(std::forward<Value>(v));
-            return &root;
+            return false;
         }
 
-        assert(ref_stack.back()->is_array() or ref_stack.back()->is_object());
-
-        if (ref_stack.back()->is_array())
+        string_t key;
+        if (len != std::size_t(-1))
         {
-            ref_stack.back()->m_value.array->emplace_back(std::forward<Value>(v));
-            return &(ref_stack.back()->m_value.array->back());
+            for (std::size_t i = 0; i < len; ++i)
+            {
+                get();
+                if (JSON_HEDLEY_UNLIKELY(!get_cbor_string(key) || !sax->key(key)))
+                {
+                    return false;
+                }
+
+                if (JSON_HEDLEY_UNLIKELY(!parse_cbor_internal(true, tag_handler)))
+                {
+                    return false;
+                }
+                key.clear();
+            }
         }
         else
         {
-            assert(object_element);
-            *object_element = BasicJsonType(std::forward<Value>(v));
-            return object_element;
+            while (get() != 0xFF)
+            {
+                if (JSON_HEDLEY_UNLIKELY(!get_cbor_string(key) || !sax->key(key)))
+                {
+                    return false;
+                }
+
+                if (JSON_HEDLEY_UNLIKELY(!parse_cbor_internal(true, tag_handler)))
+                {
+                    return false;
+                }
+                key.clear();
+            }
         }
-    }
 
-    /// the parsed JSON value
-    BasicJsonType& root;
-    /// stack to model hierarchy of values
-    std::vector<BasicJsonType*> ref_stack;
-    /// helper to hold the reference for the next object element
-    BasicJsonType* object_element = nullptr;
-    /// whether a syntax error occurred
-    bool errored = false;
-    /// whether to throw exceptions in case of errors
-    const bool allow_exceptions = true;
-};
+        return sax->end_object();
+    }
 
-template<typename BasicJsonType>
-class json_sax_dom_callback_parser
-{
-  public:
-    using number_integer_t = typename BasicJsonType::number_integer_t;
-    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
-    using number_float_t = typename BasicJsonType::number_float_t;
-    using string_t = typename BasicJsonType::string_t;
-    using parser_callback_t = typename BasicJsonType::parser_callback_t;
-    using parse_event_t = typename BasicJsonType::parse_event_t;
+    /////////////
+    // MsgPack //
+    /////////////
 
-    json_sax_dom_callback_parser(BasicJsonType& r,
-                                 const parser_callback_t cb,
-                                 const bool allow_exceptions_ = true)
-        : root(r), callback(cb), allow_exceptions(allow_exceptions_)
+    /*!
+    @return whether a valid MessagePack value was passed to the SAX parser
+    */
+    bool parse_msgpack_internal()
     {
-        keep_stack.push_back(true);
-    }
+        switch (get())
+        {
+            // EOF
+            case std::char_traits<char_type>::eof():
+                return unexpect_eof(input_format_t::msgpack, "value");
 
-    bool null()
-    {
-        handle_value(nullptr);
-        return true;
-    }
+            // positive fixint
+            case 0x00:
+            case 0x01:
+            case 0x02:
+            case 0x03:
+            case 0x04:
+            case 0x05:
+            case 0x06:
+            case 0x07:
+            case 0x08:
+            case 0x09:
+            case 0x0A:
+            case 0x0B:
+            case 0x0C:
+            case 0x0D:
+            case 0x0E:
+            case 0x0F:
+            case 0x10:
+            case 0x11:
+            case 0x12:
+            case 0x13:
+            case 0x14:
+            case 0x15:
+            case 0x16:
+            case 0x17:
+            case 0x18:
+            case 0x19:
+            case 0x1A:
+            case 0x1B:
+            case 0x1C:
+            case 0x1D:
+            case 0x1E:
+            case 0x1F:
+            case 0x20:
+            case 0x21:
+            case 0x22:
+            case 0x23:
+            case 0x24:
+            case 0x25:
+            case 0x26:
+            case 0x27:
+            case 0x28:
+            case 0x29:
+            case 0x2A:
+            case 0x2B:
+            case 0x2C:
+            case 0x2D:
+            case 0x2E:
+            case 0x2F:
+            case 0x30:
+            case 0x31:
+            case 0x32:
+            case 0x33:
+            case 0x34:
+            case 0x35:
+            case 0x36:
+            case 0x37:
+            case 0x38:
+            case 0x39:
+            case 0x3A:
+            case 0x3B:
+            case 0x3C:
+            case 0x3D:
+            case 0x3E:
+            case 0x3F:
+            case 0x40:
+            case 0x41:
+            case 0x42:
+            case 0x43:
+            case 0x44:
+            case 0x45:
+            case 0x46:
+            case 0x47:
+            case 0x48:
+            case 0x49:
+            case 0x4A:
+            case 0x4B:
+            case 0x4C:
+            case 0x4D:
+            case 0x4E:
+            case 0x4F:
+            case 0x50:
+            case 0x51:
+            case 0x52:
+            case 0x53:
+            case 0x54:
+            case 0x55:
+            case 0x56:
+            case 0x57:
+            case 0x58:
+            case 0x59:
+            case 0x5A:
+            case 0x5B:
+            case 0x5C:
+            case 0x5D:
+            case 0x5E:
+            case 0x5F:
+            case 0x60:
+            case 0x61:
+            case 0x62:
+            case 0x63:
+            case 0x64:
+            case 0x65:
+            case 0x66:
+            case 0x67:
+            case 0x68:
+            case 0x69:
+            case 0x6A:
+            case 0x6B:
+            case 0x6C:
+            case 0x6D:
+            case 0x6E:
+            case 0x6F:
+            case 0x70:
+            case 0x71:
+            case 0x72:
+            case 0x73:
+            case 0x74:
+            case 0x75:
+            case 0x76:
+            case 0x77:
+            case 0x78:
+            case 0x79:
+            case 0x7A:
+            case 0x7B:
+            case 0x7C:
+            case 0x7D:
+            case 0x7E:
+            case 0x7F:
+                return sax->number_unsigned(static_cast<number_unsigned_t>(current));
 
-    bool boolean(bool val)
-    {
-        handle_value(val);
-        return true;
-    }
+            // fixmap
+            case 0x80:
+            case 0x81:
+            case 0x82:
+            case 0x83:
+            case 0x84:
+            case 0x85:
+            case 0x86:
+            case 0x87:
+            case 0x88:
+            case 0x89:
+            case 0x8A:
+            case 0x8B:
+            case 0x8C:
+            case 0x8D:
+            case 0x8E:
+            case 0x8F:
+                return get_msgpack_object(static_cast<std::size_t>(static_cast<unsigned int>(current) & 0x0Fu));
 
-    bool number_integer(number_integer_t val)
-    {
-        handle_value(val);
-        return true;
+            // fixarray
+            case 0x90:
+            case 0x91:
+            case 0x92:
+            case 0x93:
+            case 0x94:
+            case 0x95:
+            case 0x96:
+            case 0x97:
+            case 0x98:
+            case 0x99:
+            case 0x9A:
+            case 0x9B:
+            case 0x9C:
+            case 0x9D:
+            case 0x9E:
+            case 0x9F:
+                return get_msgpack_array(static_cast<std::size_t>(static_cast<unsigned int>(current) & 0x0Fu));
+
+            // fixstr
+            case 0xA0:
+            case 0xA1:
+            case 0xA2:
+            case 0xA3:
+            case 0xA4:
+            case 0xA5:
+            case 0xA6:
+            case 0xA7:
+            case 0xA8:
+            case 0xA9:
+            case 0xAA:
+            case 0xAB:
+            case 0xAC:
+            case 0xAD:
+            case 0xAE:
+            case 0xAF:
+            case 0xB0:
+            case 0xB1:
+            case 0xB2:
+            case 0xB3:
+            case 0xB4:
+            case 0xB5:
+            case 0xB6:
+            case 0xB7:
+            case 0xB8:
+            case 0xB9:
+            case 0xBA:
+            case 0xBB:
+            case 0xBC:
+            case 0xBD:
+            case 0xBE:
+            case 0xBF:
+            case 0xD9: // str 8
+            case 0xDA: // str 16
+            case 0xDB: // str 32
+            {
+                string_t s;
+                return get_msgpack_string(s) && sax->string(s);
+            }
+
+            case 0xC0: // nil
+                return sax->null();
+
+            case 0xC2: // false
+                return sax->boolean(false);
+
+            case 0xC3: // true
+                return sax->boolean(true);
+
+            case 0xC4: // bin 8
+            case 0xC5: // bin 16
+            case 0xC6: // bin 32
+            case 0xC7: // ext 8
+            case 0xC8: // ext 16
+            case 0xC9: // ext 32
+            case 0xD4: // fixext 1
+            case 0xD5: // fixext 2
+            case 0xD6: // fixext 4
+            case 0xD7: // fixext 8
+            case 0xD8: // fixext 16
+            {
+                binary_t b;
+                return get_msgpack_binary(b) && sax->binary(b);
+            }
+
+            case 0xCA: // float 32
+            {
+                float number{};
+                return get_number(input_format_t::msgpack, number) && sax->number_float(static_cast<number_float_t>(number), "");
+            }
+
+            case 0xCB: // float 64
+            {
+                double number{};
+                return get_number(input_format_t::msgpack, number) && sax->number_float(static_cast<number_float_t>(number), "");
+            }
+
+            case 0xCC: // uint 8
+            {
+                std::uint8_t number{};
+                return get_number(input_format_t::msgpack, number) && sax->number_unsigned(number);
+            }
+
+            case 0xCD: // uint 16
+            {
+                std::uint16_t number{};
+                return get_number(input_format_t::msgpack, number) && sax->number_unsigned(number);
+            }
+
+            case 0xCE: // uint 32
+            {
+                std::uint32_t number{};
+                return get_number(input_format_t::msgpack, number) && sax->number_unsigned(number);
+            }
+
+            case 0xCF: // uint 64
+            {
+                std::uint64_t number{};
+                return get_number(input_format_t::msgpack, number) && sax->number_unsigned(number);
+            }
+
+            case 0xD0: // int 8
+            {
+                std::int8_t number{};
+                return get_number(input_format_t::msgpack, number) && sax->number_integer(number);
+            }
+
+            case 0xD1: // int 16
+            {
+                std::int16_t number{};
+                return get_number(input_format_t::msgpack, number) && sax->number_integer(number);
+            }
+
+            case 0xD2: // int 32
+            {
+                std::int32_t number{};
+                return get_number(input_format_t::msgpack, number) && sax->number_integer(number);
+            }
+
+            case 0xD3: // int 64
+            {
+                std::int64_t number{};
+                return get_number(input_format_t::msgpack, number) && sax->number_integer(number);
+            }
+
+            case 0xDC: // array 16
+            {
+                std::uint16_t len{};
+                return get_number(input_format_t::msgpack, len) && get_msgpack_array(static_cast<std::size_t>(len));
+            }
+
+            case 0xDD: // array 32
+            {
+                std::uint32_t len{};
+                return get_number(input_format_t::msgpack, len) && get_msgpack_array(static_cast<std::size_t>(len));
+            }
+
+            case 0xDE: // map 16
+            {
+                std::uint16_t len{};
+                return get_number(input_format_t::msgpack, len) && get_msgpack_object(static_cast<std::size_t>(len));
+            }
+
+            case 0xDF: // map 32
+            {
+                std::uint32_t len{};
+                return get_number(input_format_t::msgpack, len) && get_msgpack_object(static_cast<std::size_t>(len));
+            }
+
+            // negative fixint
+            case 0xE0:
+            case 0xE1:
+            case 0xE2:
+            case 0xE3:
+            case 0xE4:
+            case 0xE5:
+            case 0xE6:
+            case 0xE7:
+            case 0xE8:
+            case 0xE9:
+            case 0xEA:
+            case 0xEB:
+            case 0xEC:
+            case 0xED:
+            case 0xEE:
+            case 0xEF:
+            case 0xF0:
+            case 0xF1:
+            case 0xF2:
+            case 0xF3:
+            case 0xF4:
+            case 0xF5:
+            case 0xF6:
+            case 0xF7:
+            case 0xF8:
+            case 0xF9:
+            case 0xFA:
+            case 0xFB:
+            case 0xFC:
+            case 0xFD:
+            case 0xFE:
+            case 0xFF:
+                return sax->number_integer(static_cast<std::int8_t>(current));
+
+            default: // anything else
+            {
+                auto last_token = get_token_string();
+                return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read, exception_message(input_format_t::msgpack, "invalid byte: 0x" + last_token, "value")));
+            }
+        }
     }
 
-    bool number_unsigned(number_unsigned_t val)
+    /*!
+    @brief reads a MessagePack string
+
+    This function first reads starting bytes to determine the expected
+    string length and then copies this number of bytes into a string.
+
+    @param[out] result  created string
+
+    @return whether string creation completed
+    */
+    bool get_msgpack_string(string_t& result)
     {
-        handle_value(val);
-        return true;
+        if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::msgpack, "string")))
+        {
+            return false;
+        }
+
+        switch (current)
+        {
+            // fixstr
+            case 0xA0:
+            case 0xA1:
+            case 0xA2:
+            case 0xA3:
+            case 0xA4:
+            case 0xA5:
+            case 0xA6:
+            case 0xA7:
+            case 0xA8:
+            case 0xA9:
+            case 0xAA:
+            case 0xAB:
+            case 0xAC:
+            case 0xAD:
+            case 0xAE:
+            case 0xAF:
+            case 0xB0:
+            case 0xB1:
+            case 0xB2:
+            case 0xB3:
+            case 0xB4:
+            case 0xB5:
+            case 0xB6:
+            case 0xB7:
+            case 0xB8:
+            case 0xB9:
+            case 0xBA:
+            case 0xBB:
+            case 0xBC:
+            case 0xBD:
+            case 0xBE:
+            case 0xBF:
+            {
+                return get_string(input_format_t::msgpack, static_cast<unsigned int>(current) & 0x1Fu, result);
+            }
+
+            case 0xD9: // str 8
+            {
+                std::uint8_t len{};
+                return get_number(input_format_t::msgpack, len) && get_string(input_format_t::msgpack, len, result);
+            }
+
+            case 0xDA: // str 16
+            {
+                std::uint16_t len{};
+                return get_number(input_format_t::msgpack, len) && get_string(input_format_t::msgpack, len, result);
+            }
+
+            case 0xDB: // str 32
+            {
+                std::uint32_t len{};
+                return get_number(input_format_t::msgpack, len) && get_string(input_format_t::msgpack, len, result);
+            }
+
+            default:
+            {
+                auto last_token = get_token_string();
+                return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read, exception_message(input_format_t::msgpack, "expected length specification (0xA0-0xBF, 0xD9-0xDB); last byte: 0x" + last_token, "string")));
+            }
+        }
     }
 
-    bool number_float(number_float_t val, const string_t& /*unused*/)
+    /*!
+    @brief reads a MessagePack byte array
+
+    This function first reads starting bytes to determine the expected
+    byte array length and then copies this number of bytes into a byte array.
+
+    @param[out] result  created byte array
+
+    @return whether byte array creation completed
+    */
+    bool get_msgpack_binary(binary_t& result)
     {
-        handle_value(val);
-        return true;
+        // helper function to set the subtype
+        auto assign_and_return_true = [&result](std::int8_t subtype)
+        {
+            result.set_subtype(static_cast<std::uint8_t>(subtype));
+            return true;
+        };
+
+        switch (current)
+        {
+            case 0xC4: // bin 8
+            {
+                std::uint8_t len{};
+                return get_number(input_format_t::msgpack, len) &&
+                       get_binary(input_format_t::msgpack, len, result);
+            }
+
+            case 0xC5: // bin 16
+            {
+                std::uint16_t len{};
+                return get_number(input_format_t::msgpack, len) &&
+                       get_binary(input_format_t::msgpack, len, result);
+            }
+
+            case 0xC6: // bin 32
+            {
+                std::uint32_t len{};
+                return get_number(input_format_t::msgpack, len) &&
+                       get_binary(input_format_t::msgpack, len, result);
+            }
+
+            case 0xC7: // ext 8
+            {
+                std::uint8_t len{};
+                std::int8_t subtype{};
+                return get_number(input_format_t::msgpack, len) &&
+                       get_number(input_format_t::msgpack, subtype) &&
+                       get_binary(input_format_t::msgpack, len, result) &&
+                       assign_and_return_true(subtype);
+            }
+
+            case 0xC8: // ext 16
+            {
+                std::uint16_t len{};
+                std::int8_t subtype{};
+                return get_number(input_format_t::msgpack, len) &&
+                       get_number(input_format_t::msgpack, subtype) &&
+                       get_binary(input_format_t::msgpack, len, result) &&
+                       assign_and_return_true(subtype);
+            }
+
+            case 0xC9: // ext 32
+            {
+                std::uint32_t len{};
+                std::int8_t subtype{};
+                return get_number(input_format_t::msgpack, len) &&
+                       get_number(input_format_t::msgpack, subtype) &&
+                       get_binary(input_format_t::msgpack, len, result) &&
+                       assign_and_return_true(subtype);
+            }
+
+            case 0xD4: // fixext 1
+            {
+                std::int8_t subtype{};
+                return get_number(input_format_t::msgpack, subtype) &&
+                       get_binary(input_format_t::msgpack, 1, result) &&
+                       assign_and_return_true(subtype);
+            }
+
+            case 0xD5: // fixext 2
+            {
+                std::int8_t subtype{};
+                return get_number(input_format_t::msgpack, subtype) &&
+                       get_binary(input_format_t::msgpack, 2, result) &&
+                       assign_and_return_true(subtype);
+            }
+
+            case 0xD6: // fixext 4
+            {
+                std::int8_t subtype{};
+                return get_number(input_format_t::msgpack, subtype) &&
+                       get_binary(input_format_t::msgpack, 4, result) &&
+                       assign_and_return_true(subtype);
+            }
+
+            case 0xD7: // fixext 8
+            {
+                std::int8_t subtype{};
+                return get_number(input_format_t::msgpack, subtype) &&
+                       get_binary(input_format_t::msgpack, 8, result) &&
+                       assign_and_return_true(subtype);
+            }
+
+            case 0xD8: // fixext 16
+            {
+                std::int8_t subtype{};
+                return get_number(input_format_t::msgpack, subtype) &&
+                       get_binary(input_format_t::msgpack, 16, result) &&
+                       assign_and_return_true(subtype);
+            }
+
+            default:           // LCOV_EXCL_LINE
+                return false;  // LCOV_EXCL_LINE
+        }
     }
 
-    bool string(string_t& val)
+    /*!
+    @param[in] len  the length of the array
+    @return whether array creation completed
+    */
+    bool get_msgpack_array(const std::size_t len)
     {
-        handle_value(val);
-        return true;
+        if (JSON_HEDLEY_UNLIKELY(!sax->start_array(len)))
+        {
+            return false;
+        }
+
+        for (std::size_t i = 0; i < len; ++i)
+        {
+            if (JSON_HEDLEY_UNLIKELY(!parse_msgpack_internal()))
+            {
+                return false;
+            }
+        }
+
+        return sax->end_array();
     }
 
-    bool start_object(std::size_t len)
+    /*!
+    @param[in] len  the length of the object
+    @return whether object creation completed
+    */
+    bool get_msgpack_object(const std::size_t len)
     {
-        // check callback for object start
-        const bool keep = callback(static_cast<int>(ref_stack.size()), parse_event_t::object_start, discarded);
-        keep_stack.push_back(keep);
-
-        auto val = handle_value(BasicJsonType::value_t::object, true);
-        ref_stack.push_back(val.second);
+        if (JSON_HEDLEY_UNLIKELY(!sax->start_object(len)))
+        {
+            return false;
+        }
 
-        // check object limit
-        if (ref_stack.back())
+        string_t key;
+        for (std::size_t i = 0; i < len; ++i)
         {
-            if (JSON_UNLIKELY(len != std::size_t(-1) and len > ref_stack.back()->max_size()))
+            get();
+            if (JSON_HEDLEY_UNLIKELY(!get_msgpack_string(key) || !sax->key(key)))
+            {
+                return false;
+            }
+
+            if (JSON_HEDLEY_UNLIKELY(!parse_msgpack_internal()))
             {
-                JSON_THROW(out_of_range::create(408,
-                                                "excessive object size: " + std::to_string(len)));
+                return false;
             }
+            key.clear();
         }
 
-        return true;
+        return sax->end_object();
     }
 
-    bool key(string_t& val)
+    ////////////
+    // UBJSON //
+    ////////////
+
+    /*!
+    @param[in] get_char  whether a new character should be retrieved from the
+                         input (true, default) or whether the last read
+                         character should be considered instead
+
+    @return whether a valid UBJSON value was passed to the SAX parser
+    */
+    bool parse_ubjson_internal(const bool get_char = true)
     {
-        BasicJsonType k = BasicJsonType(val);
+        return get_ubjson_value(get_char ? get_ignore_noop() : current);
+    }
 
-        // check callback for key
-        const bool keep = callback(static_cast<int>(ref_stack.size()), parse_event_t::key, k);
-        key_keep_stack.push_back(keep);
+    /*!
+    @brief reads a UBJSON string
 
-        // add discarded value at given key and store the reference for later
-        if (keep and ref_stack.back())
+    This function is either called after reading the 'S' byte explicitly
+    indicating a string, or in case of an object key where the 'S' byte can be
+    left out.
+
+    @param[out] result   created string
+    @param[in] get_char  whether a new character should be retrieved from the
+                         input (true, default) or whether the last read
+                         character should be considered instead
+
+    @return whether string creation completed
+    */
+    bool get_ubjson_string(string_t& result, const bool get_char = true)
+    {
+        if (get_char)
         {
-            object_element = &(ref_stack.back()->m_value.object->operator[](val) = discarded);
+            get();  // TODO(niels): may we ignore N here?
         }
 
-        return true;
+        if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::ubjson, "value")))
+        {
+            return false;
+        }
+
+        switch (current)
+        {
+            case 'U':
+            {
+                std::uint8_t len{};
+                return get_number(input_format_t::ubjson, len) && get_string(input_format_t::ubjson, len, result);
+            }
+
+            case 'i':
+            {
+                std::int8_t len{};
+                return get_number(input_format_t::ubjson, len) && get_string(input_format_t::ubjson, len, result);
+            }
+
+            case 'I':
+            {
+                std::int16_t len{};
+                return get_number(input_format_t::ubjson, len) && get_string(input_format_t::ubjson, len, result);
+            }
+
+            case 'l':
+            {
+                std::int32_t len{};
+                return get_number(input_format_t::ubjson, len) && get_string(input_format_t::ubjson, len, result);
+            }
+
+            case 'L':
+            {
+                std::int64_t len{};
+                return get_number(input_format_t::ubjson, len) && get_string(input_format_t::ubjson, len, result);
+            }
+
+            default:
+                auto last_token = get_token_string();
+                return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read, exception_message(input_format_t::ubjson, "expected length type specification (U, i, I, l, L); last byte: 0x" + last_token, "string")));
+        }
     }
 
-    bool end_object()
+    /*!
+    @param[out] result  determined size
+    @return whether size determination completed
+    */
+    bool get_ubjson_size_value(std::size_t& result)
     {
-        if (ref_stack.back())
+        switch (get_ignore_noop())
         {
-            if (not callback(static_cast<int>(ref_stack.size()) - 1, parse_event_t::object_end, *ref_stack.back()))
+            case 'U':
             {
-                // discard object
-                *ref_stack.back() = discarded;
+                std::uint8_t number{};
+                if (JSON_HEDLEY_UNLIKELY(!get_number(input_format_t::ubjson, number)))
+                {
+                    return false;
+                }
+                result = static_cast<std::size_t>(number);
+                return true;
             }
-        }
 
-        assert(not ref_stack.empty());
-        assert(not keep_stack.empty());
-        ref_stack.pop_back();
-        keep_stack.pop_back();
+            case 'i':
+            {
+                std::int8_t number{};
+                if (JSON_HEDLEY_UNLIKELY(!get_number(input_format_t::ubjson, number)))
+                {
+                    return false;
+                }
+                result = static_cast<std::size_t>(number);
+                return true;
+            }
 
-        if (not ref_stack.empty() and ref_stack.back())
-        {
-            // remove discarded value
-            if (ref_stack.back()->is_object())
+            case 'I':
             {
-                for (auto it = ref_stack.back()->begin(); it != ref_stack.back()->end(); ++it)
+                std::int16_t number{};
+                if (JSON_HEDLEY_UNLIKELY(!get_number(input_format_t::ubjson, number)))
                 {
-                    if (it->is_discarded())
-                    {
-                        ref_stack.back()->erase(it);
-                        break;
-                    }
+                    return false;
                 }
+                result = static_cast<std::size_t>(number);
+                return true;
             }
-        }
 
-        return true;
+            case 'l':
+            {
+                std::int32_t number{};
+                if (JSON_HEDLEY_UNLIKELY(!get_number(input_format_t::ubjson, number)))
+                {
+                    return false;
+                }
+                result = static_cast<std::size_t>(number);
+                return true;
+            }
+
+            case 'L':
+            {
+                std::int64_t number{};
+                if (JSON_HEDLEY_UNLIKELY(!get_number(input_format_t::ubjson, number)))
+                {
+                    return false;
+                }
+                result = static_cast<std::size_t>(number);
+                return true;
+            }
+
+            default:
+            {
+                auto last_token = get_token_string();
+                return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read, exception_message(input_format_t::ubjson, "expected length type specification (U, i, I, l, L) after '#'; last byte: 0x" + last_token, "size")));
+            }
+        }
     }
 
-    bool start_array(std::size_t len)
+    /*!
+    @brief determine the type and size for a container
+
+    In the optimized UBJSON format, a type and a size can be provided to allow
+    for a more compact representation.
+
+    @param[out] result  pair of the size and the type
+
+    @return whether pair creation completed
+    */
+    bool get_ubjson_size_type(std::pair<std::size_t, char_int_type>& result)
     {
-        const bool keep = callback(static_cast<int>(ref_stack.size()), parse_event_t::array_start, discarded);
-        keep_stack.push_back(keep);
+        result.first = string_t::npos; // size
+        result.second = 0; // type
 
-        auto val = handle_value(BasicJsonType::value_t::array, true);
-        ref_stack.push_back(val.second);
+        get_ignore_noop();
 
-        // check array limit
-        if (ref_stack.back())
+        if (current == '$')
         {
-            if (JSON_UNLIKELY(len != std::size_t(-1) and len > ref_stack.back()->max_size()))
+            result.second = get();  // must not ignore 'N', because 'N' maybe the type
+            if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::ubjson, "type")))
             {
-                JSON_THROW(out_of_range::create(408,
-                                                "excessive array size: " + std::to_string(len)));
+                return false;
             }
+
+            get_ignore_noop();
+            if (JSON_HEDLEY_UNLIKELY(current != '#'))
+            {
+                if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::ubjson, "value")))
+                {
+                    return false;
+                }
+                auto last_token = get_token_string();
+                return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read, exception_message(input_format_t::ubjson, "expected '#' after type information; last byte: 0x" + last_token, "size")));
+            }
+
+            return get_ubjson_size_value(result.first);
+        }
+
+        if (current == '#')
+        {
+            return get_ubjson_size_value(result.first);
         }
 
         return true;
     }
 
-    bool end_array()
+    /*!
+    @param prefix  the previously read or set type prefix
+    @return whether value creation completed
+    */
+    bool get_ubjson_value(const char_int_type prefix)
     {
-        bool keep = true;
-
-        if (ref_stack.back())
+        switch (prefix)
         {
-            keep = callback(static_cast<int>(ref_stack.size()) - 1, parse_event_t::array_end, *ref_stack.back());
-            if (not keep)
+            case std::char_traits<char_type>::eof():  // EOF
+                return unexpect_eof(input_format_t::ubjson, "value");
+
+            case 'T':  // true
+                return sax->boolean(true);
+            case 'F':  // false
+                return sax->boolean(false);
+
+            case 'Z':  // null
+                return sax->null();
+
+            case 'U':
             {
-                // discard array
-                *ref_stack.back() = discarded;
+                std::uint8_t number{};
+                return get_number(input_format_t::ubjson, number) && sax->number_unsigned(number);
             }
-        }
 
-        assert(not ref_stack.empty());
-        assert(not keep_stack.empty());
-        ref_stack.pop_back();
-        keep_stack.pop_back();
+            case 'i':
+            {
+                std::int8_t number{};
+                return get_number(input_format_t::ubjson, number) && sax->number_integer(number);
+            }
 
-        // remove discarded value
-        if (not keep and not ref_stack.empty())
-        {
-            if (ref_stack.back()->is_array())
+            case 'I':
             {
-                ref_stack.back()->m_value.array->pop_back();
+                std::int16_t number{};
+                return get_number(input_format_t::ubjson, number) && sax->number_integer(number);
             }
-        }
 
-        return true;
-    }
+            case 'l':
+            {
+                std::int32_t number{};
+                return get_number(input_format_t::ubjson, number) && sax->number_integer(number);
+            }
 
-    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/,
-                     const detail::exception& ex)
-    {
-        errored = true;
-        if (allow_exceptions)
-        {
-            // determine the proper exception type from the id
-            switch ((ex.id / 100) % 100)
+            case 'L':
             {
-                case 1:
-                    JSON_THROW(*reinterpret_cast<const detail::parse_error*>(&ex));
-                case 4:
-                    JSON_THROW(*reinterpret_cast<const detail::out_of_range*>(&ex));
-                // LCOV_EXCL_START
-                case 2:
-                    JSON_THROW(*reinterpret_cast<const detail::invalid_iterator*>(&ex));
-                case 3:
-                    JSON_THROW(*reinterpret_cast<const detail::type_error*>(&ex));
-                case 5:
-                    JSON_THROW(*reinterpret_cast<const detail::other_error*>(&ex));
-                default:
-                    assert(false);
-                    // LCOV_EXCL_STOP
+                std::int64_t number{};
+                return get_number(input_format_t::ubjson, number) && sax->number_integer(number);
             }
-        }
-        return false;
-    }
 
-    constexpr bool is_errored() const
-    {
-        return errored;
-    }
+            case 'd':
+            {
+                float number{};
+                return get_number(input_format_t::ubjson, number) && sax->number_float(static_cast<number_float_t>(number), "");
+            }
 
-  private:
-    /*!
-    @param[in] v  value to add to the JSON value we build during parsing
-    @param[in] skip_callback  whether we should skip calling the callback
-               function; this is required after start_array() and
-               start_object() SAX events, because otherwise we would call the
-               callback function with an empty array or object, respectively.
+            case 'D':
+            {
+                double number{};
+                return get_number(input_format_t::ubjson, number) && sax->number_float(static_cast<number_float_t>(number), "");
+            }
 
-    @invariant If the ref stack is empty, then the passed value will be the new
-               root.
-    @invariant If the ref stack contains a value, then it is an array or an
-               object to which we can add elements
+            case 'H':
+            {
+                return get_ubjson_high_precision_number();
+            }
 
-    @return pair of boolean (whether value should be kept) and pointer (to the
-            passed value in the ref_stack hierarchy; nullptr if not kept)
+            case 'C':  // char
+            {
+                get();
+                if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::ubjson, "char")))
+                {
+                    return false;
+                }
+                if (JSON_HEDLEY_UNLIKELY(current > 127))
+                {
+                    auto last_token = get_token_string();
+                    return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read, exception_message(input_format_t::ubjson, "byte after 'C' must be in range 0x00..0x7F; last byte: 0x" + last_token, "char")));
+                }
+                string_t s(1, static_cast<typename string_t::value_type>(current));
+                return sax->string(s);
+            }
+
+            case 'S':  // string
+            {
+                string_t s;
+                return get_ubjson_string(s) && sax->string(s);
+            }
+
+            case '[':  // array
+                return get_ubjson_array();
+
+            case '{':  // object
+                return get_ubjson_object();
+
+            default: // anything else
+            {
+                auto last_token = get_token_string();
+                return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read, exception_message(input_format_t::ubjson, "invalid byte: 0x" + last_token, "value")));
+            }
+        }
+    }
+
+    /*!
+    @return whether array creation completed
     */
-    template<typename Value>
-    std::pair<bool, BasicJsonType*> handle_value(Value&& v, const bool skip_callback = false)
+    bool get_ubjson_array()
     {
-        assert(not keep_stack.empty());
+        std::pair<std::size_t, char_int_type> size_and_type;
+        if (JSON_HEDLEY_UNLIKELY(!get_ubjson_size_type(size_and_type)))
+        {
+            return false;
+        }
 
-        // do not handle this value if we know it would be added to a discarded
-        // container
-        if (not keep_stack.back())
+        if (size_and_type.first != string_t::npos)
         {
-            return {false, nullptr};
+            if (JSON_HEDLEY_UNLIKELY(!sax->start_array(size_and_type.first)))
+            {
+                return false;
+            }
+
+            if (size_and_type.second != 0)
+            {
+                if (size_and_type.second != 'N')
+                {
+                    for (std::size_t i = 0; i < size_and_type.first; ++i)
+                    {
+                        if (JSON_HEDLEY_UNLIKELY(!get_ubjson_value(size_and_type.second)))
+                        {
+                            return false;
+                        }
+                    }
+                }
+            }
+            else
+            {
+                for (std::size_t i = 0; i < size_and_type.first; ++i)
+                {
+                    if (JSON_HEDLEY_UNLIKELY(!parse_ubjson_internal()))
+                    {
+                        return false;
+                    }
+                }
+            }
         }
+        else
+        {
+            if (JSON_HEDLEY_UNLIKELY(!sax->start_array(std::size_t(-1))))
+            {
+                return false;
+            }
 
-        // create value
-        auto value = BasicJsonType(std::forward<Value>(v));
+            while (current != ']')
+            {
+                if (JSON_HEDLEY_UNLIKELY(!parse_ubjson_internal(false)))
+                {
+                    return false;
+                }
+                get_ignore_noop();
+            }
+        }
 
-        // check callback
-        const bool keep = skip_callback or callback(static_cast<int>(ref_stack.size()), parse_event_t::value, value);
+        return sax->end_array();
+    }
 
-        // do not handle this value if we just learnt it shall be discarded
-        if (not keep)
+    /*!
+    @return whether object creation completed
+    */
+    bool get_ubjson_object()
+    {
+        std::pair<std::size_t, char_int_type> size_and_type;
+        if (JSON_HEDLEY_UNLIKELY(!get_ubjson_size_type(size_and_type)))
         {
-            return {false, nullptr};
+            return false;
         }
 
-        if (ref_stack.empty())
+        string_t key;
+        if (size_and_type.first != string_t::npos)
         {
-            root = std::move(value);
-            return {true, &root};
-        }
+            if (JSON_HEDLEY_UNLIKELY(!sax->start_object(size_and_type.first)))
+            {
+                return false;
+            }
 
-        // skip this value if we already decided to skip the parent
-        // (https://github.com/nlohmann/json/issues/971#issuecomment-413678360)
-        if (not ref_stack.back())
+            if (size_and_type.second != 0)
+            {
+                for (std::size_t i = 0; i < size_and_type.first; ++i)
+                {
+                    if (JSON_HEDLEY_UNLIKELY(!get_ubjson_string(key) || !sax->key(key)))
+                    {
+                        return false;
+                    }
+                    if (JSON_HEDLEY_UNLIKELY(!get_ubjson_value(size_and_type.second)))
+                    {
+                        return false;
+                    }
+                    key.clear();
+                }
+            }
+            else
+            {
+                for (std::size_t i = 0; i < size_and_type.first; ++i)
+                {
+                    if (JSON_HEDLEY_UNLIKELY(!get_ubjson_string(key) || !sax->key(key)))
+                    {
+                        return false;
+                    }
+                    if (JSON_HEDLEY_UNLIKELY(!parse_ubjson_internal()))
+                    {
+                        return false;
+                    }
+                    key.clear();
+                }
+            }
+        }
+        else
         {
-            return {false, nullptr};
+            if (JSON_HEDLEY_UNLIKELY(!sax->start_object(std::size_t(-1))))
+            {
+                return false;
+            }
+
+            while (current != '}')
+            {
+                if (JSON_HEDLEY_UNLIKELY(!get_ubjson_string(key, false) || !sax->key(key)))
+                {
+                    return false;
+                }
+                if (JSON_HEDLEY_UNLIKELY(!parse_ubjson_internal()))
+                {
+                    return false;
+                }
+                get_ignore_noop();
+                key.clear();
+            }
         }
 
-        // we now only expect arrays and objects
-        assert(ref_stack.back()->is_array() or ref_stack.back()->is_object());
+        return sax->end_object();
+    }
 
-        if (ref_stack.back()->is_array())
+    // Note, no reader for UBJSON binary types is implemented because they do
+    // not exist
+
+    bool get_ubjson_high_precision_number()
+    {
+        // get size of following number string
+        std::size_t size{};
+        auto res = get_ubjson_size_value(size);
+        if (JSON_HEDLEY_UNLIKELY(!res))
         {
-            ref_stack.back()->m_value.array->push_back(std::move(value));
-            return {true, &(ref_stack.back()->m_value.array->back())};
+            return res;
         }
-        else
-        {
-            // check if we should store an element for the current key
-            assert(not key_keep_stack.empty());
-            const bool store_element = key_keep_stack.back();
-            key_keep_stack.pop_back();
 
-            if (not store_element)
+        // get number string
+        std::vector<char> number_vector;
+        for (std::size_t i = 0; i < size; ++i)
+        {
+            get();
+            if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::ubjson, "number")))
             {
-                return {false, nullptr};
+                return false;
             }
+            number_vector.push_back(static_cast<char>(current));
+        }
+
+        // parse number string
+        auto number_ia = detail::input_adapter(std::forward<decltype(number_vector)>(number_vector));
+        auto number_lexer = detail::lexer<BasicJsonType, decltype(number_ia)>(std::move(number_ia), false);
+        const auto result_number = number_lexer.scan();
+        const auto number_string = number_lexer.get_token_string();
+        const auto result_remainder = number_lexer.scan();
 
-            assert(object_element);
-            *object_element = std::move(value);
-            return {true, object_element};
+        using token_type = typename detail::lexer_base<BasicJsonType>::token_type;
+
+        if (JSON_HEDLEY_UNLIKELY(result_remainder != token_type::end_of_input))
+        {
+            return sax->parse_error(chars_read, number_string, parse_error::create(115, chars_read, exception_message(input_format_t::ubjson, "invalid number text: " + number_lexer.get_token_string(), "high-precision number")));
+        }
+
+        switch (result_number)
+        {
+            case token_type::value_integer:
+                return sax->number_integer(number_lexer.get_number_integer());
+            case token_type::value_unsigned:
+                return sax->number_unsigned(number_lexer.get_number_unsigned());
+            case token_type::value_float:
+                return sax->number_float(number_lexer.get_number_float(), std::move(number_string));
+            default:
+                return sax->parse_error(chars_read, number_string, parse_error::create(115, chars_read, exception_message(input_format_t::ubjson, "invalid number text: " + number_lexer.get_token_string(), "high-precision number")));
         }
     }
 
-    /// the parsed JSON value
-    BasicJsonType& root;
-    /// stack to model hierarchy of values
-    std::vector<BasicJsonType*> ref_stack;
-    /// stack to manage which values to keep
-    std::vector<bool> keep_stack;
-    /// stack to manage which object keys to keep
-    std::vector<bool> key_keep_stack;
-    /// helper to hold the reference for the next object element
-    BasicJsonType* object_element = nullptr;
-    /// whether a syntax error occurred
-    bool errored = false;
-    /// callback function
-    const parser_callback_t callback = nullptr;
-    /// whether to throw exceptions in case of errors
-    const bool allow_exceptions = true;
-    /// a discarded value for the callback
-    BasicJsonType discarded = BasicJsonType::value_t::discarded;
-};
+    ///////////////////////
+    // Utility functions //
+    ///////////////////////
 
-template<typename BasicJsonType>
-class json_sax_acceptor
-{
-  public:
-    using number_integer_t = typename BasicJsonType::number_integer_t;
-    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
-    using number_float_t = typename BasicJsonType::number_float_t;
-    using string_t = typename BasicJsonType::string_t;
+    /*!
+    @brief get next character from the input
 
-    bool null()
-    {
-        return true;
-    }
+    This function provides the interface to the used input adapter. It does
+    not throw in case the input reached EOF, but returns a -'ve valued
+    `std::char_traits<char_type>::eof()` in that case.
 
-    bool boolean(bool /*unused*/)
+    @return character read from the input
+    */
+    char_int_type get()
     {
-        return true;
+        ++chars_read;
+        return current = ia.get_character();
     }
 
-    bool number_integer(number_integer_t /*unused*/)
+    /*!
+    @return character read from the input after ignoring all 'N' entries
+    */
+    char_int_type get_ignore_noop()
     {
-        return true;
-    }
+        do
+        {
+            get();
+        }
+        while (current == 'N');
 
-    bool number_unsigned(number_unsigned_t /*unused*/)
-    {
-        return true;
+        return current;
     }
 
-    bool number_float(number_float_t /*unused*/, const string_t& /*unused*/)
-    {
-        return true;
-    }
+    /*
+    @brief read a number from the input
 
-    bool string(string_t& /*unused*/)
-    {
-        return true;
-    }
+    @tparam NumberType the type of the number
+    @param[in] format   the current format (for diagnostics)
+    @param[out] result  number of type @a NumberType
 
-    bool start_object(std::size_t  /*unused*/ = std::size_t(-1))
+    @return whether conversion completed
+
+    @note This function needs to respect the system's endianess, because
+          bytes in CBOR, MessagePack, and UBJSON are stored in network order
+          (big endian) and therefore need reordering on little endian systems.
+    */
+    template<typename NumberType, bool InputIsLittleEndian = false>
+    bool get_number(const input_format_t format, NumberType& result)
     {
+        // step 1: read input into array with system's byte order
+        std::array<std::uint8_t, sizeof(NumberType)> vec;
+        for (std::size_t i = 0; i < sizeof(NumberType); ++i)
+        {
+            get();
+            if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(format, "number")))
+            {
+                return false;
+            }
+
+            // reverse byte order prior to conversion if necessary
+            if (is_little_endian != InputIsLittleEndian)
+            {
+                vec[sizeof(NumberType) - i - 1] = static_cast<std::uint8_t>(current);
+            }
+            else
+            {
+                vec[i] = static_cast<std::uint8_t>(current); // LCOV_EXCL_LINE
+            }
+        }
+
+        // step 2: convert array into number of type T and return
+        std::memcpy(&result, vec.data(), sizeof(NumberType));
         return true;
     }
 
-    bool key(string_t& /*unused*/)
+    /*!
+    @brief create a string by reading characters from the input
+
+    @tparam NumberType the type of the number
+    @param[in] format the current format (for diagnostics)
+    @param[in] len number of characters to read
+    @param[out] result string created by reading @a len bytes
+
+    @return whether string creation completed
+
+    @note We can not reserve @a len bytes for the result, because @a len
+          may be too large. Usually, @ref unexpect_eof() detects the end of
+          the input before we run out of string memory.
+    */
+    template<typename NumberType>
+    bool get_string(const input_format_t format,
+                    const NumberType len,
+                    string_t& result)
     {
-        return true;
+        bool success = true;
+        for (NumberType i = 0; i < len; i++)
+        {
+            get();
+            if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(format, "string")))
+            {
+                success = false;
+                break;
+            }
+            result.push_back(static_cast<typename string_t::value_type>(current));
+        };
+        return success;
     }
 
-    bool end_object()
+    /*!
+    @brief create a byte array by reading bytes from the input
+
+    @tparam NumberType the type of the number
+    @param[in] format the current format (for diagnostics)
+    @param[in] len number of bytes to read
+    @param[out] result byte array created by reading @a len bytes
+
+    @return whether byte array creation completed
+
+    @note We can not reserve @a len bytes for the result, because @a len
+          may be too large. Usually, @ref unexpect_eof() detects the end of
+          the input before we run out of memory.
+    */
+    template<typename NumberType>
+    bool get_binary(const input_format_t format,
+                    const NumberType len,
+                    binary_t& result)
     {
-        return true;
+        bool success = true;
+        for (NumberType i = 0; i < len; i++)
+        {
+            get();
+            if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(format, "binary")))
+            {
+                success = false;
+                break;
+            }
+            result.push_back(static_cast<std::uint8_t>(current));
+        }
+        return success;
     }
 
-    bool start_array(std::size_t  /*unused*/ = std::size_t(-1))
+    /*!
+    @param[in] format   the current format (for diagnostics)
+    @param[in] context  further context information (for diagnostics)
+    @return whether the last read character is not EOF
+    */
+    JSON_HEDLEY_NON_NULL(3)
+    bool unexpect_eof(const input_format_t format, const char* context) const
     {
+        if (JSON_HEDLEY_UNLIKELY(current == std::char_traits<char_type>::eof()))
+        {
+            return sax->parse_error(chars_read, "<end of file>",
+                                    parse_error::create(110, chars_read, exception_message(format, "unexpected end of input", context)));
+        }
         return true;
     }
 
-    bool end_array()
+    /*!
+    @return a string representation of the last read byte
+    */
+    std::string get_token_string() const
     {
-        return true;
+        std::array<char, 3> cr{{}};
+        (std::snprintf)(cr.data(), cr.size(), "%.2hhX", static_cast<unsigned char>(current));
+        return std::string{cr.data()};
     }
 
-    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/, const detail::exception& /*unused*/)
+    /*!
+    @param[in] format   the current format
+    @param[in] detail   a detailed error message
+    @param[in] context  further context information
+    @return a message string to use in the parse_error exceptions
+    */
+    std::string exception_message(const input_format_t format,
+                                  const std::string& detail,
+                                  const std::string& context) const
     {
-        return false;
+        std::string error_msg = "syntax error while parsing ";
+
+        switch (format)
+        {
+            case input_format_t::cbor:
+                error_msg += "CBOR";
+                break;
+
+            case input_format_t::msgpack:
+                error_msg += "MessagePack";
+                break;
+
+            case input_format_t::ubjson:
+                error_msg += "UBJSON";
+                break;
+
+            case input_format_t::bson:
+                error_msg += "BSON";
+                break;
+
+            default:            // LCOV_EXCL_LINE
+                JSON_ASSERT(false);  // LCOV_EXCL_LINE
+        }
+
+        return error_msg + " " + context + ": " + detail;
     }
+
+  private:
+    /// input adapter
+    InputAdapterType ia;
+
+    /// the current character
+    char_int_type current = std::char_traits<char_type>::eof();
+
+    /// the number of characters read
+    std::size_t chars_read = 0;
+
+    /// whether we can assume little endianess
+    const bool is_little_endian = little_endianess();
+
+    /// the SAX parser
+    json_sax_t* sax = nullptr;
 };
 }  // namespace detail
-
 }  // namespace nlohmann
 
+// #include <nlohmann/detail/input/input_adapters.hpp>
+
+// #include <nlohmann/detail/input/lexer.hpp>
+
+// #include <nlohmann/detail/input/parser.hpp>
+
+
+#include <cmath> // isfinite
+#include <cstdint> // uint8_t
+#include <functional> // function
+#include <string> // string
+#include <utility> // move
+#include <vector> // vector
+
+// #include <nlohmann/detail/exceptions.hpp>
+
+// #include <nlohmann/detail/input/input_adapters.hpp>
+
+// #include <nlohmann/detail/input/json_sax.hpp>
+
 // #include <nlohmann/detail/input/lexer.hpp>
 
+// #include <nlohmann/detail/macro_scope.hpp>
+
+// #include <nlohmann/detail/meta/is_sax.hpp>
+
 // #include <nlohmann/detail/value_t.hpp>
 
 
@@ -4951,46 +10134,50 @@ namespace detail
 // parser //
 ////////////
 
+enum class parse_event_t : uint8_t
+{
+    /// the parser read `{` and started to process a JSON object
+    object_start,
+    /// the parser read `}` and finished processing a JSON object
+    object_end,
+    /// the parser read `[` and started to process a JSON array
+    array_start,
+    /// the parser read `]` and finished processing a JSON array
+    array_end,
+    /// the parser read a key of a value in an object
+    key,
+    /// the parser finished reading a JSON value
+    value
+};
+
+template<typename BasicJsonType>
+using parser_callback_t =
+    std::function<bool(int depth, parse_event_t event, BasicJsonType& parsed)>;
+
 /*!
 @brief syntax analysis
 
-This class implements a recursive decent parser.
+This class implements a recursive descent parser.
 */
-template<typename BasicJsonType>
+template<typename BasicJsonType, typename InputAdapterType>
 class parser
 {
     using number_integer_t = typename BasicJsonType::number_integer_t;
     using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
     using number_float_t = typename BasicJsonType::number_float_t;
     using string_t = typename BasicJsonType::string_t;
-    using lexer_t = lexer<BasicJsonType>;
+    using lexer_t = lexer<BasicJsonType, InputAdapterType>;
     using token_type = typename lexer_t::token_type;
 
   public:
-    enum class parse_event_t : uint8_t
-    {
-        /// the parser read `{` and started to process a JSON object
-        object_start,
-        /// the parser read `}` and finished processing a JSON object
-        object_end,
-        /// the parser read `[` and started to process a JSON array
-        array_start,
-        /// the parser read `]` and finished processing a JSON array
-        array_end,
-        /// the parser read a key of a value in an object
-        key,
-        /// the parser finished reading a JSON value
-        value
-    };
-
-    using parser_callback_t =
-        std::function<bool(int depth, parse_event_t event, BasicJsonType& parsed)>;
-
     /// a parser reading from an input adapter
-    explicit parser(detail::input_adapter_t&& adapter,
-                    const parser_callback_t cb = nullptr,
-                    const bool allow_exceptions_ = true)
-        : callback(cb), m_lexer(std::move(adapter)), allow_exceptions(allow_exceptions_)
+    explicit parser(InputAdapterType&& adapter,
+                    const parser_callback_t<BasicJsonType> cb = nullptr,
+                    const bool allow_exceptions_ = true,
+                    const bool skip_comments = false)
+        : callback(cb)
+        , m_lexer(std::move(adapter), skip_comments)
+        , allow_exceptions(allow_exceptions_)
     {
         // read first token
         get_token();
@@ -5015,7 +10202,7 @@ class parser
             result.assert_invariant();
 
             // in strict mode, input must be completely read
-            if (strict and (get_token() != token_type::end_of_input))
+            if (strict && (get_token() != token_type::end_of_input))
             {
                 sdp.parse_error(m_lexer.get_position(),
                                 m_lexer.get_token_string(),
@@ -5044,7 +10231,7 @@ class parser
             result.assert_invariant();
 
             // in strict mode, input must be completely read
-            if (strict and (get_token() != token_type::end_of_input))
+            if (strict && (get_token() != token_type::end_of_input))
             {
                 sdp.parse_error(m_lexer.get_position(),
                                 m_lexer.get_token_string(),
@@ -5073,14 +10260,15 @@ class parser
         return sax_parse(&sax_acceptor, strict);
     }
 
-    template <typename SAX>
+    template<typename SAX>
+    JSON_HEDLEY_NON_NULL(2)
     bool sax_parse(SAX* sax, const bool strict = true)
     {
         (void)detail::is_sax_static_asserts<SAX, BasicJsonType> {};
         const bool result = sax_parse_internal(sax);
 
         // strict mode: next byte must be EOF
-        if (result and strict and (get_token() != token_type::end_of_input))
+        if (result && strict && (get_token() != token_type::end_of_input))
         {
             return sax->parse_error(m_lexer.get_position(),
                                     m_lexer.get_token_string(),
@@ -5092,7 +10280,8 @@ class parser
     }
 
   private:
-    template <typename SAX>
+    template<typename SAX>
+    JSON_HEDLEY_NON_NULL(2)
     bool sax_parse_internal(SAX* sax)
     {
         // stack to remember the hierarchy of structured values we are parsing
@@ -5103,14 +10292,14 @@ class parser
 
         while (true)
         {
-            if (not skip_to_state_evaluation)
+            if (!skip_to_state_evaluation)
             {
                 // invariant: get_token() was called before each iteration
                 switch (last_token)
                 {
                     case token_type::begin_object:
                     {
-                        if (JSON_UNLIKELY(not sax->start_object(std::size_t(-1))))
+                        if (JSON_HEDLEY_UNLIKELY(!sax->start_object(std::size_t(-1))))
                         {
                             return false;
                         }
@@ -5118,7 +10307,7 @@ class parser
                         // closing } -> we are done
                         if (get_token() == token_type::end_object)
                         {
-                            if (JSON_UNLIKELY(not sax->end_object()))
+                            if (JSON_HEDLEY_UNLIKELY(!sax->end_object()))
                             {
                                 return false;
                             }
@@ -5126,20 +10315,20 @@ class parser
                         }
 
                         // parse key
-                        if (JSON_UNLIKELY(last_token != token_type::value_string))
+                        if (JSON_HEDLEY_UNLIKELY(last_token != token_type::value_string))
                         {
                             return sax->parse_error(m_lexer.get_position(),
                                                     m_lexer.get_token_string(),
                                                     parse_error::create(101, m_lexer.get_position(),
                                                             exception_message(token_type::value_string, "object key")));
                         }
-                        if (JSON_UNLIKELY(not sax->key(m_lexer.get_string())))
+                        if (JSON_HEDLEY_UNLIKELY(!sax->key(m_lexer.get_string())))
                         {
                             return false;
                         }
 
                         // parse separator (:)
-                        if (JSON_UNLIKELY(get_token() != token_type::name_separator))
+                        if (JSON_HEDLEY_UNLIKELY(get_token() != token_type::name_separator))
                         {
                             return sax->parse_error(m_lexer.get_position(),
                                                     m_lexer.get_token_string(),
@@ -5157,7 +10346,7 @@ class parser
 
                     case token_type::begin_array:
                     {
-                        if (JSON_UNLIKELY(not sax->start_array(std::size_t(-1))))
+                        if (JSON_HEDLEY_UNLIKELY(!sax->start_array(std::size_t(-1))))
                         {
                             return false;
                         }
@@ -5165,7 +10354,7 @@ class parser
                         // closing ] -> we are done
                         if (get_token() == token_type::end_array)
                         {
-                            if (JSON_UNLIKELY(not sax->end_array()))
+                            if (JSON_HEDLEY_UNLIKELY(!sax->end_array()))
                             {
                                 return false;
                             }
@@ -5183,25 +10372,24 @@ class parser
                     {
                         const auto res = m_lexer.get_number_float();
 
-                        if (JSON_UNLIKELY(not std::isfinite(res)))
+                        if (JSON_HEDLEY_UNLIKELY(!std::isfinite(res)))
                         {
                             return sax->parse_error(m_lexer.get_position(),
                                                     m_lexer.get_token_string(),
                                                     out_of_range::create(406, "number overflow parsing '" + m_lexer.get_token_string() + "'"));
                         }
-                        else
+
+                        if (JSON_HEDLEY_UNLIKELY(!sax->number_float(res, m_lexer.get_string())))
                         {
-                            if (JSON_UNLIKELY(not sax->number_float(res, m_lexer.get_string())))
-                            {
-                                return false;
-                            }
-                            break;
+                            return false;
                         }
+
+                        break;
                     }
 
                     case token_type::literal_false:
                     {
-                        if (JSON_UNLIKELY(not sax->boolean(false)))
+                        if (JSON_HEDLEY_UNLIKELY(!sax->boolean(false)))
                         {
                             return false;
                         }
@@ -5210,7 +10398,7 @@ class parser
 
                     case token_type::literal_null:
                     {
-                        if (JSON_UNLIKELY(not sax->null()))
+                        if (JSON_HEDLEY_UNLIKELY(!sax->null()))
                         {
                             return false;
                         }
@@ -5219,7 +10407,7 @@ class parser
 
                     case token_type::literal_true:
                     {
-                        if (JSON_UNLIKELY(not sax->boolean(true)))
+                        if (JSON_HEDLEY_UNLIKELY(!sax->boolean(true)))
                         {
                             return false;
                         }
@@ -5228,7 +10416,7 @@ class parser
 
                     case token_type::value_integer:
                     {
-                        if (JSON_UNLIKELY(not sax->number_integer(m_lexer.get_number_integer())))
+                        if (JSON_HEDLEY_UNLIKELY(!sax->number_integer(m_lexer.get_number_integer())))
                         {
                             return false;
                         }
@@ -5237,7 +10425,7 @@ class parser
 
                     case token_type::value_string:
                     {
-                        if (JSON_UNLIKELY(not sax->string(m_lexer.get_string())))
+                        if (JSON_HEDLEY_UNLIKELY(!sax->string(m_lexer.get_string())))
                         {
                             return false;
                         }
@@ -5246,7 +10434,7 @@ class parser
 
                     case token_type::value_unsigned:
                     {
-                        if (JSON_UNLIKELY(not sax->number_unsigned(m_lexer.get_number_unsigned())))
+                        if (JSON_HEDLEY_UNLIKELY(!sax->number_unsigned(m_lexer.get_number_unsigned())))
                         {
                             return false;
                         }
@@ -5282,103 +10470,95 @@ class parser
                 // empty stack: we reached the end of the hierarchy: done
                 return true;
             }
-            else
+
+            if (states.back())  // array
             {
-                if (states.back())  // array
+                // comma -> next value
+                if (get_token() == token_type::value_separator)
                 {
-                    // comma -> next value
-                    if (get_token() == token_type::value_separator)
+                    // parse a new value
+                    get_token();
+                    continue;
+                }
+
+                // closing ]
+                if (JSON_HEDLEY_LIKELY(last_token == token_type::end_array))
+                {
+                    if (JSON_HEDLEY_UNLIKELY(!sax->end_array()))
                     {
-                        // parse a new value
-                        get_token();
-                        continue;
+                        return false;
                     }
 
-                    // closing ]
-                    if (JSON_LIKELY(last_token == token_type::end_array))
-                    {
-                        if (JSON_UNLIKELY(not sax->end_array()))
-                        {
-                            return false;
-                        }
+                    // We are done with this array. Before we can parse a
+                    // new value, we need to evaluate the new state first.
+                    // By setting skip_to_state_evaluation to false, we
+                    // are effectively jumping to the beginning of this if.
+                    JSON_ASSERT(!states.empty());
+                    states.pop_back();
+                    skip_to_state_evaluation = true;
+                    continue;
+                }
 
-                        // We are done with this array. Before we can parse a
-                        // new value, we need to evaluate the new state first.
-                        // By setting skip_to_state_evaluation to false, we
-                        // are effectively jumping to the beginning of this if.
-                        assert(not states.empty());
-                        states.pop_back();
-                        skip_to_state_evaluation = true;
-                        continue;
-                    }
-                    else
+                return sax->parse_error(m_lexer.get_position(),
+                                        m_lexer.get_token_string(),
+                                        parse_error::create(101, m_lexer.get_position(),
+                                                exception_message(token_type::end_array, "array")));
+            }
+            else  // object
+            {
+                // comma -> next value
+                if (get_token() == token_type::value_separator)
+                {
+                    // parse key
+                    if (JSON_HEDLEY_UNLIKELY(get_token() != token_type::value_string))
                     {
                         return sax->parse_error(m_lexer.get_position(),
                                                 m_lexer.get_token_string(),
                                                 parse_error::create(101, m_lexer.get_position(),
-                                                        exception_message(token_type::end_array, "array")));
+                                                        exception_message(token_type::value_string, "object key")));
                     }
-                }
-                else  // object
-                {
-                    // comma -> next value
-                    if (get_token() == token_type::value_separator)
-                    {
-                        // parse key
-                        if (JSON_UNLIKELY(get_token() != token_type::value_string))
-                        {
-                            return sax->parse_error(m_lexer.get_position(),
-                                                    m_lexer.get_token_string(),
-                                                    parse_error::create(101, m_lexer.get_position(),
-                                                            exception_message(token_type::value_string, "object key")));
-                        }
-                        else
-                        {
-                            if (JSON_UNLIKELY(not sax->key(m_lexer.get_string())))
-                            {
-                                return false;
-                            }
-                        }
 
-                        // parse separator (:)
-                        if (JSON_UNLIKELY(get_token() != token_type::name_separator))
-                        {
-                            return sax->parse_error(m_lexer.get_position(),
-                                                    m_lexer.get_token_string(),
-                                                    parse_error::create(101, m_lexer.get_position(),
-                                                            exception_message(token_type::name_separator, "object separator")));
-                        }
-
-                        // parse values
-                        get_token();
-                        continue;
-                    }
-
-                    // closing }
-                    if (JSON_LIKELY(last_token == token_type::end_object))
+                    if (JSON_HEDLEY_UNLIKELY(!sax->key(m_lexer.get_string())))
                     {
-                        if (JSON_UNLIKELY(not sax->end_object()))
-                        {
-                            return false;
-                        }
-
-                        // We are done with this object. Before we can parse a
-                        // new value, we need to evaluate the new state first.
-                        // By setting skip_to_state_evaluation to false, we
-                        // are effectively jumping to the beginning of this if.
-                        assert(not states.empty());
-                        states.pop_back();
-                        skip_to_state_evaluation = true;
-                        continue;
+                        return false;
                     }
-                    else
+
+                    // parse separator (:)
+                    if (JSON_HEDLEY_UNLIKELY(get_token() != token_type::name_separator))
                     {
                         return sax->parse_error(m_lexer.get_position(),
                                                 m_lexer.get_token_string(),
                                                 parse_error::create(101, m_lexer.get_position(),
-                                                        exception_message(token_type::end_object, "object")));
+                                                        exception_message(token_type::name_separator, "object separator")));
+                    }
+
+                    // parse values
+                    get_token();
+                    continue;
+                }
+
+                // closing }
+                if (JSON_HEDLEY_LIKELY(last_token == token_type::end_object))
+                {
+                    if (JSON_HEDLEY_UNLIKELY(!sax->end_object()))
+                    {
+                        return false;
                     }
+
+                    // We are done with this object. Before we can parse a
+                    // new value, we need to evaluate the new state first.
+                    // By setting skip_to_state_evaluation to false, we
+                    // are effectively jumping to the beginning of this if.
+                    JSON_ASSERT(!states.empty());
+                    states.pop_back();
+                    skip_to_state_evaluation = true;
+                    continue;
                 }
+
+                return sax->parse_error(m_lexer.get_position(),
+                                        m_lexer.get_token_string(),
+                                        parse_error::create(101, m_lexer.get_position(),
+                                                exception_message(token_type::end_object, "object")));
             }
         }
     }
@@ -5386,14 +10566,14 @@ class parser
     /// get next token from lexer
     token_type get_token()
     {
-        return (last_token = m_lexer.scan());
+        return last_token = m_lexer.scan();
     }
 
     std::string exception_message(const token_type expected, const std::string& context)
     {
         std::string error_msg = "syntax error ";
 
-        if (not context.empty())
+        if (!context.empty())
         {
             error_msg += "while parsing " + context + " ";
         }
@@ -5420,7 +10600,7 @@ class parser
 
   private:
     /// callback function
-    const parser_callback_t callback = nullptr;
+    const parser_callback_t<BasicJsonType> callback = nullptr;
     /// the type of the last read token
     token_type last_token = token_type::uninitialized;
     /// the lexer
@@ -5431,6 +10611,9 @@ class parser
 }  // namespace detail
 }  // namespace nlohmann
 
+// #include <nlohmann/detail/iterators/internal_iterator.hpp>
+
+
 // #include <nlohmann/detail/iterators/primitive_iterator.hpp>
 
 
@@ -5553,11 +10736,6 @@ class primitive_iterator_t
 }  // namespace detail
 }  // namespace nlohmann
 
-// #include <nlohmann/detail/iterators/internal_iterator.hpp>
-
-
-// #include <nlohmann/detail/iterators/primitive_iterator.hpp>
-
 
 namespace nlohmann
 {
@@ -5584,7 +10762,6 @@ template<typename BasicJsonType> struct internal_iterator
 // #include <nlohmann/detail/iterators/iter_impl.hpp>
 
 
-#include <ciso646> // not
 #include <iterator> // iterator, random_access_iterator_tag, bidirectional_iterator_tag, advance, next
 #include <type_traits> // conditional, is_const, remove_const
 
@@ -5598,6 +10775,8 @@ template<typename BasicJsonType> struct internal_iterator
 
 // #include <nlohmann/detail/meta/cpp_future.hpp>
 
+// #include <nlohmann/detail/meta/type_traits.hpp>
+
 // #include <nlohmann/detail/value_t.hpp>
 
 
@@ -5674,7 +10853,7 @@ class iter_impl
     */
     explicit iter_impl(pointer object) noexcept : m_object(object)
     {
-        assert(m_object != nullptr);
+        JSON_ASSERT(m_object != nullptr);
 
         switch (m_object->m_type)
         {
@@ -5708,16 +10887,41 @@ class iter_impl
     */
 
     /*!
+    @brief const copy constructor
+    @param[in] other const iterator to copy from
+    @note This copy constructor had to be defined explicitly to circumvent a bug
+          occurring on msvc v19.0 compiler (VS 2015) debug build. For more
+          information refer to: https://github.com/nlohmann/json/issues/1608
+    */
+    iter_impl(const iter_impl<const BasicJsonType>& other) noexcept
+        : m_object(other.m_object), m_it(other.m_it)
+    {}
+
+    /*!
+    @brief converting assignment
+    @param[in] other const iterator to copy from
+    @return const/non-const iterator
+    @note It is not checked whether @a other is initialized.
+    */
+    iter_impl& operator=(const iter_impl<const BasicJsonType>& other) noexcept
+    {
+        m_object = other.m_object;
+        m_it = other.m_it;
+        return *this;
+    }
+
+    /*!
     @brief converting constructor
     @param[in] other  non-const iterator to copy from
     @note It is not checked whether @a other is initialized.
     */
     iter_impl(const iter_impl<typename std::remove_const<BasicJsonType>::type>& other) noexcept
-        : m_object(other.m_object), m_it(other.m_it) {}
+        : m_object(other.m_object), m_it(other.m_it)
+    {}
 
     /*!
     @brief converting assignment
-    @param[in,out] other  non-const iterator to copy from
+    @param[in] other  non-const iterator to copy from
     @return const/non-const iterator
     @note It is not checked whether @a other is initialized.
     */
@@ -5735,7 +10939,7 @@ class iter_impl
     */
     void set_begin() noexcept
     {
-        assert(m_object != nullptr);
+        JSON_ASSERT(m_object != nullptr);
 
         switch (m_object->m_type)
         {
@@ -5772,7 +10976,7 @@ class iter_impl
     */
     void set_end() noexcept
     {
-        assert(m_object != nullptr);
+        JSON_ASSERT(m_object != nullptr);
 
         switch (m_object->m_type)
         {
@@ -5803,19 +11007,19 @@ class iter_impl
     */
     reference operator*() const
     {
-        assert(m_object != nullptr);
+        JSON_ASSERT(m_object != nullptr);
 
         switch (m_object->m_type)
         {
             case value_t::object:
             {
-                assert(m_it.object_iterator != m_object->m_value.object->end());
+                JSON_ASSERT(m_it.object_iterator != m_object->m_value.object->end());
                 return m_it.object_iterator->second;
             }
 
             case value_t::array:
             {
-                assert(m_it.array_iterator != m_object->m_value.array->end());
+                JSON_ASSERT(m_it.array_iterator != m_object->m_value.array->end());
                 return *m_it.array_iterator;
             }
 
@@ -5824,7 +11028,7 @@ class iter_impl
 
             default:
             {
-                if (JSON_LIKELY(m_it.primitive_iterator.is_begin()))
+                if (JSON_HEDLEY_LIKELY(m_it.primitive_iterator.is_begin()))
                 {
                     return *m_object;
                 }
@@ -5840,25 +11044,25 @@ class iter_impl
     */
     pointer operator->() const
     {
-        assert(m_object != nullptr);
+        JSON_ASSERT(m_object != nullptr);
 
         switch (m_object->m_type)
         {
             case value_t::object:
             {
-                assert(m_it.object_iterator != m_object->m_value.object->end());
+                JSON_ASSERT(m_it.object_iterator != m_object->m_value.object->end());
                 return &(m_it.object_iterator->second);
             }
 
             case value_t::array:
             {
-                assert(m_it.array_iterator != m_object->m_value.array->end());
+                JSON_ASSERT(m_it.array_iterator != m_object->m_value.array->end());
                 return &*m_it.array_iterator;
             }
 
             default:
             {
-                if (JSON_LIKELY(m_it.primitive_iterator.is_begin()))
+                if (JSON_HEDLEY_LIKELY(m_it.primitive_iterator.is_begin()))
                 {
                     return m_object;
                 }
@@ -5885,7 +11089,7 @@ class iter_impl
     */
     iter_impl& operator++()
     {
-        assert(m_object != nullptr);
+        JSON_ASSERT(m_object != nullptr);
 
         switch (m_object->m_type)
         {
@@ -5928,7 +11132,7 @@ class iter_impl
     */
     iter_impl& operator--()
     {
-        assert(m_object != nullptr);
+        JSON_ASSERT(m_object != nullptr);
 
         switch (m_object->m_type)
         {
@@ -5961,12 +11165,12 @@ class iter_impl
     bool operator==(const iter_impl& other) const
     {
         // if objects are not the same, the comparison is undefined
-        if (JSON_UNLIKELY(m_object != other.m_object))
+        if (JSON_HEDLEY_UNLIKELY(m_object != other.m_object))
         {
             JSON_THROW(invalid_iterator::create(212, "cannot compare iterators of different containers"));
         }
 
-        assert(m_object != nullptr);
+        JSON_ASSERT(m_object != nullptr);
 
         switch (m_object->m_type)
         {
@@ -5987,7 +11191,7 @@ class iter_impl
     */
     bool operator!=(const iter_impl& other) const
     {
-        return not operator==(other);
+        return !operator==(other);
     }
 
     /*!
@@ -5997,12 +11201,12 @@ class iter_impl
     bool operator<(const iter_impl& other) const
     {
         // if objects are not the same, the comparison is undefined
-        if (JSON_UNLIKELY(m_object != other.m_object))
+        if (JSON_HEDLEY_UNLIKELY(m_object != other.m_object))
         {
             JSON_THROW(invalid_iterator::create(212, "cannot compare iterators of different containers"));
         }
 
-        assert(m_object != nullptr);
+        JSON_ASSERT(m_object != nullptr);
 
         switch (m_object->m_type)
         {
@@ -6023,7 +11227,7 @@ class iter_impl
     */
     bool operator<=(const iter_impl& other) const
     {
-        return not other.operator < (*this);
+        return !other.operator < (*this);
     }
 
     /*!
@@ -6032,7 +11236,7 @@ class iter_impl
     */
     bool operator>(const iter_impl& other) const
     {
-        return not operator<=(other);
+        return !operator<=(other);
     }
 
     /*!
@@ -6041,7 +11245,7 @@ class iter_impl
     */
     bool operator>=(const iter_impl& other) const
     {
-        return not operator<(other);
+        return !operator<(other);
     }
 
     /*!
@@ -6050,7 +11254,7 @@ class iter_impl
     */
     iter_impl& operator+=(difference_type i)
     {
-        assert(m_object != nullptr);
+        JSON_ASSERT(m_object != nullptr);
 
         switch (m_object->m_type)
         {
@@ -6121,7 +11325,7 @@ class iter_impl
     */
     difference_type operator-(const iter_impl& other) const
     {
-        assert(m_object != nullptr);
+        JSON_ASSERT(m_object != nullptr);
 
         switch (m_object->m_type)
         {
@@ -6142,7 +11346,7 @@ class iter_impl
     */
     reference operator[](difference_type n) const
     {
-        assert(m_object != nullptr);
+        JSON_ASSERT(m_object != nullptr);
 
         switch (m_object->m_type)
         {
@@ -6157,7 +11361,7 @@ class iter_impl
 
             default:
             {
-                if (JSON_LIKELY(m_it.primitive_iterator.get_value() == -n))
+                if (JSON_HEDLEY_LIKELY(m_it.primitive_iterator.get_value() == -n))
                 {
                     return *m_object;
                 }
@@ -6173,9 +11377,9 @@ class iter_impl
     */
     const typename object_t::key_type& key() const
     {
-        assert(m_object != nullptr);
+        JSON_ASSERT(m_object != nullptr);
 
-        if (JSON_LIKELY(m_object->is_object()))
+        if (JSON_HEDLEY_LIKELY(m_object->is_object()))
         {
             return m_it.object_iterator->first;
         }
@@ -6196,10 +11400,11 @@ class iter_impl
     /// associated JSON instance
     pointer m_object = nullptr;
     /// the actual iterator of the associated instance
-    internal_iterator<typename std::remove_const<BasicJsonType>::type> m_it;
+    internal_iterator<typename std::remove_const<BasicJsonType>::type> m_it {};
 };
-}  // namespace detail
+} // namespace detail
 } // namespace nlohmann
+
 // #include <nlohmann/detail/iterators/iteration_proxy.hpp>
 
 // #include <nlohmann/detail/iterators/json_reverse_iterator.hpp>
@@ -6323,2132 +11528,1214 @@ class json_reverse_iterator : public std::reverse_iterator<Base>
 }  // namespace detail
 }  // namespace nlohmann
 
-// #include <nlohmann/detail/output/output_adapters.hpp>
+// #include <nlohmann/detail/iterators/primitive_iterator.hpp>
 
+// #include <nlohmann/detail/json_pointer.hpp>
 
-#include <algorithm> // copy
-#include <cstddef> // size_t
-#include <ios> // streamsize
-#include <iterator> // back_inserter
-#include <memory> // shared_ptr, make_shared
-#include <ostream> // basic_ostream
-#include <string> // basic_string
+
+#include <algorithm> // all_of
+#include <cctype> // isdigit
+#include <limits> // max
+#include <numeric> // accumulate
+#include <string> // string
+#include <utility> // move
 #include <vector> // vector
 
+// #include <nlohmann/detail/exceptions.hpp>
+
+// #include <nlohmann/detail/macro_scope.hpp>
+
+// #include <nlohmann/detail/value_t.hpp>
+
+
 namespace nlohmann
 {
-namespace detail
-{
-/// abstract output adapter interface
-template<typename CharType> struct output_adapter_protocol
+template<typename BasicJsonType>
+class json_pointer
 {
-    virtual void write_character(CharType c) = 0;
-    virtual void write_characters(const CharType* s, std::size_t length) = 0;
-    virtual ~output_adapter_protocol() = default;
-};
-
-/// a type to simplify interfaces
-template<typename CharType>
-using output_adapter_t = std::shared_ptr<output_adapter_protocol<CharType>>;
+    // allow basic_json to access private members
+    NLOHMANN_BASIC_JSON_TPL_DECLARATION
+    friend class basic_json;
 
-/// output adapter for byte vectors
-template<typename CharType>
-class output_vector_adapter : public output_adapter_protocol<CharType>
-{
   public:
-    explicit output_vector_adapter(std::vector<CharType>& vec) noexcept
-        : v(vec)
-    {}
+    /*!
+    @brief create JSON pointer
 
-    void write_character(CharType c) override
-    {
-        v.push_back(c);
-    }
+    Create a JSON pointer according to the syntax described in
+    [Section 3 of RFC6901](https://tools.ietf.org/html/rfc6901#section-3).
 
-    void write_characters(const CharType* s, std::size_t length) override
-    {
-        std::copy(s, s + length, std::back_inserter(v));
-    }
+    @param[in] s  string representing the JSON pointer; if omitted, the empty
+                  string is assumed which references the whole JSON value
 
-  private:
-    std::vector<CharType>& v;
-};
+    @throw parse_error.107 if the given JSON pointer @a s is nonempty and does
+                           not begin with a slash (`/`); see example below
 
-/// output adapter for output streams
-template<typename CharType>
-class output_stream_adapter : public output_adapter_protocol<CharType>
-{
-  public:
-    explicit output_stream_adapter(std::basic_ostream<CharType>& s) noexcept
-        : stream(s)
+    @throw parse_error.108 if a tilde (`~`) in the given JSON pointer @a s is
+    not followed by `0` (representing `~`) or `1` (representing `/`); see
+    example below
+
+    @liveexample{The example shows the construction several valid JSON pointers
+    as well as the exceptional behavior.,json_pointer}
+
+    @since version 2.0.0
+    */
+    explicit json_pointer(const std::string& s = "")
+        : reference_tokens(split(s))
     {}
 
-    void write_character(CharType c) override
-    {
-        stream.put(c);
-    }
+    /*!
+    @brief return a string representation of the JSON pointer
 
-    void write_characters(const CharType* s, std::size_t length) override
-    {
-        stream.write(s, static_cast<std::streamsize>(length));
-    }
+    @invariant For each JSON pointer `ptr`, it holds:
+    @code {.cpp}
+    ptr == json_pointer(ptr.to_string());
+    @endcode
 
-  private:
-    std::basic_ostream<CharType>& stream;
-};
+    @return a string representation of the JSON pointer
 
-/// output adapter for basic_string
-template<typename CharType, typename StringType = std::basic_string<CharType>>
-class output_string_adapter : public output_adapter_protocol<CharType>
-{
-  public:
-    explicit output_string_adapter(StringType& s) noexcept
-        : str(s)
-    {}
+    @liveexample{The example shows the result of `to_string`.,json_pointer__to_string}
 
-    void write_character(CharType c) override
+    @since version 2.0.0
+    */
+    std::string to_string() const
     {
-        str.push_back(c);
+        return std::accumulate(reference_tokens.begin(), reference_tokens.end(),
+                               std::string{},
+                               [](const std::string & a, const std::string & b)
+        {
+            return a + "/" + escape(b);
+        });
     }
 
-    void write_characters(const CharType* s, std::size_t length) override
+    /// @copydoc to_string()
+    operator std::string() const
     {
-        str.append(s, length);
+        return to_string();
     }
 
-  private:
-    StringType& str;
-};
+    /*!
+    @brief append another JSON pointer at the end of this JSON pointer
 
-template<typename CharType, typename StringType = std::basic_string<CharType>>
-class output_adapter
-{
-  public:
-    output_adapter(std::vector<CharType>& vec)
-        : oa(std::make_shared<output_vector_adapter<CharType>>(vec)) {}
+    @param[in] ptr  JSON pointer to append
+    @return JSON pointer with @a ptr appended
 
-    output_adapter(std::basic_ostream<CharType>& s)
-        : oa(std::make_shared<output_stream_adapter<CharType>>(s)) {}
+    @liveexample{The example shows the usage of `operator/=`.,json_pointer__operator_add}
 
-    output_adapter(StringType& s)
-        : oa(std::make_shared<output_string_adapter<CharType, StringType>>(s)) {}
+    @complexity Linear in the length of @a ptr.
 
-    operator output_adapter_t<CharType>()
+    @sa @ref operator/=(std::string) to append a reference token
+    @sa @ref operator/=(std::size_t) to append an array index
+    @sa @ref operator/(const json_pointer&, const json_pointer&) for a binary operator
+
+    @since version 3.6.0
+    */
+    json_pointer& operator/=(const json_pointer& ptr)
     {
-        return oa;
+        reference_tokens.insert(reference_tokens.end(),
+                                ptr.reference_tokens.begin(),
+                                ptr.reference_tokens.end());
+        return *this;
     }
 
-  private:
-    output_adapter_t<CharType> oa = nullptr;
-};
-}  // namespace detail
-}  // namespace nlohmann
-
-// #include <nlohmann/detail/input/binary_reader.hpp>
-
-
-#include <algorithm> // generate_n
-#include <array> // array
-#include <cassert> // assert
-#include <cmath> // ldexp
-#include <cstddef> // size_t
-#include <cstdint> // uint8_t, uint16_t, uint32_t, uint64_t
-#include <cstdio> // snprintf
-#include <cstring> // memcpy
-#include <iterator> // back_inserter
-#include <limits> // numeric_limits
-#include <string> // char_traits, string
-#include <utility> // make_pair, move
+    /*!
+    @brief append an unescaped reference token at the end of this JSON pointer
 
-// #include <nlohmann/detail/input/input_adapters.hpp>
+    @param[in] token  reference token to append
+    @return JSON pointer with @a token appended without escaping @a token
 
-// #include <nlohmann/detail/input/json_sax.hpp>
+    @liveexample{The example shows the usage of `operator/=`.,json_pointer__operator_add}
 
-// #include <nlohmann/detail/exceptions.hpp>
+    @complexity Amortized constant.
 
-// #include <nlohmann/detail/macro_scope.hpp>
+    @sa @ref operator/=(const json_pointer&) to append a JSON pointer
+    @sa @ref operator/=(std::size_t) to append an array index
+    @sa @ref operator/(const json_pointer&, std::size_t) for a binary operator
 
-// #include <nlohmann/detail/meta/is_sax.hpp>
+    @since version 3.6.0
+    */
+    json_pointer& operator/=(std::string token)
+    {
+        push_back(std::move(token));
+        return *this;
+    }
 
-// #include <nlohmann/detail/value_t.hpp>
+    /*!
+    @brief append an array index at the end of this JSON pointer
 
+    @param[in] array_idx  array index to append
+    @return JSON pointer with @a array_idx appended
 
-namespace nlohmann
-{
-namespace detail
-{
-///////////////////
-// binary reader //
-///////////////////
+    @liveexample{The example shows the usage of `operator/=`.,json_pointer__operator_add}
 
-/*!
-@brief deserialization of CBOR, MessagePack, and UBJSON values
-*/
-template<typename BasicJsonType, typename SAX = json_sax_dom_parser<BasicJsonType>>
-class binary_reader
-{
-    using number_integer_t = typename BasicJsonType::number_integer_t;
-    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
-    using number_float_t = typename BasicJsonType::number_float_t;
-    using string_t = typename BasicJsonType::string_t;
-    using json_sax_t = SAX;
+    @complexity Amortized constant.
 
-  public:
-    /*!
-    @brief create a binary reader
+    @sa @ref operator/=(const json_pointer&) to append a JSON pointer
+    @sa @ref operator/=(std::string) to append a reference token
+    @sa @ref operator/(const json_pointer&, std::string) for a binary operator
 
-    @param[in] adapter  input adapter to read from
+    @since version 3.6.0
     */
-    explicit binary_reader(input_adapter_t adapter) : ia(std::move(adapter))
+    json_pointer& operator/=(std::size_t array_idx)
     {
-        (void)detail::is_sax_static_asserts<SAX, BasicJsonType> {};
-        assert(ia);
+        return *this /= std::to_string(array_idx);
     }
 
     /*!
-    @param[in] format  the binary format to parse
-    @param[in] sax_    a SAX event processor
-    @param[in] strict  whether to expect the input to be consumed completed
+    @brief create a new JSON pointer by appending the right JSON pointer at the end of the left JSON pointer
 
-    @return
-    */
-    bool sax_parse(const input_format_t format,
-                   json_sax_t* sax_,
-                   const bool strict = true)
-    {
-        sax = sax_;
-        bool result = false;
+    @param[in] lhs  JSON pointer
+    @param[in] rhs  JSON pointer
+    @return a new JSON pointer with @a rhs appended to @a lhs
 
-        switch (format)
-        {
-            case input_format_t::bson:
-                result = parse_bson_internal();
-                break;
+    @liveexample{The example shows the usage of `operator/`.,json_pointer__operator_add_binary}
 
-            case input_format_t::cbor:
-                result = parse_cbor_internal();
-                break;
+    @complexity Linear in the length of @a lhs and @a rhs.
 
-            case input_format_t::msgpack:
-                result = parse_msgpack_internal();
-                break;
+    @sa @ref operator/=(const json_pointer&) to append a JSON pointer
 
-            case input_format_t::ubjson:
-                result = parse_ubjson_internal();
-                break;
-
-            // LCOV_EXCL_START
-            default:
-                assert(false);
-                // LCOV_EXCL_STOP
-        }
+    @since version 3.6.0
+    */
+    friend json_pointer operator/(const json_pointer& lhs,
+                                  const json_pointer& rhs)
+    {
+        return json_pointer(lhs) /= rhs;
+    }
 
-        // strict mode: next byte must be EOF
-        if (result and strict)
-        {
-            if (format == input_format_t::ubjson)
-            {
-                get_ignore_noop();
-            }
-            else
-            {
-                get();
-            }
+    /*!
+    @brief create a new JSON pointer by appending the unescaped token at the end of the JSON pointer
 
-            if (JSON_UNLIKELY(current != std::char_traits<char>::eof()))
-            {
-                return sax->parse_error(chars_read, get_token_string(),
-                                        parse_error::create(110, chars_read, exception_message(format, "expected end of input; last byte: 0x" + get_token_string(), "value")));
-            }
-        }
+    @param[in] ptr  JSON pointer
+    @param[in] token  reference token
+    @return a new JSON pointer with unescaped @a token appended to @a ptr
 
-        return result;
-    }
+    @liveexample{The example shows the usage of `operator/`.,json_pointer__operator_add_binary}
 
-    /*!
-    @brief determine system byte order
+    @complexity Linear in the length of @a ptr.
 
-    @return true if and only if system's byte order is little endian
+    @sa @ref operator/=(std::string) to append a reference token
 
-    @note from http://stackoverflow.com/a/1001328/266378
+    @since version 3.6.0
     */
-    static constexpr bool little_endianess(int num = 1) noexcept
+    friend json_pointer operator/(const json_pointer& ptr, std::string token)
     {
-        return (*reinterpret_cast<char*>(&num) == 1);
+        return json_pointer(ptr) /= std::move(token);
     }
 
-  private:
-    //////////
-    // BSON //
-    //////////
-
     /*!
-    @brief Reads in a BSON-object and passes it to the SAX-parser.
-    @return whether a valid BSON-value was passed to the SAX parser
-    */
-    bool parse_bson_internal()
-    {
-        std::int32_t document_size;
-        get_number<std::int32_t, true>(input_format_t::bson, document_size);
+    @brief create a new JSON pointer by appending the array-index-token at the end of the JSON pointer
 
-        if (JSON_UNLIKELY(not sax->start_object(std::size_t(-1))))
-        {
-            return false;
-        }
+    @param[in] ptr  JSON pointer
+    @param[in] array_idx  array index
+    @return a new JSON pointer with @a array_idx appended to @a ptr
 
-        if (JSON_UNLIKELY(not parse_bson_element_list(/*is_array*/false)))
-        {
-            return false;
-        }
+    @liveexample{The example shows the usage of `operator/`.,json_pointer__operator_add_binary}
 
-        return sax->end_object();
-    }
+    @complexity Linear in the length of @a ptr.
 
-    /*!
-    @brief Parses a C-style string from the BSON input.
-    @param[in, out] result  A reference to the string variable where the read
-                            string is to be stored.
-    @return `true` if the \x00-byte indicating the end of the string was
-             encountered before the EOF; false` indicates an unexpected EOF.
+    @sa @ref operator/=(std::size_t) to append an array index
+
+    @since version 3.6.0
     */
-    bool get_bson_cstr(string_t& result)
+    friend json_pointer operator/(const json_pointer& ptr, std::size_t array_idx)
     {
-        auto out = std::back_inserter(result);
-        while (true)
-        {
-            get();
-            if (JSON_UNLIKELY(not unexpect_eof(input_format_t::bson, "cstring")))
-            {
-                return false;
-            }
-            if (current == 0x00)
-            {
-                return true;
-            }
-            *out++ = static_cast<char>(current);
-        }
-
-        return true;
+        return json_pointer(ptr) /= array_idx;
     }
 
     /*!
-    @brief Parses a zero-terminated string of length @a len from the BSON
-           input.
-    @param[in] len  The length (including the zero-byte at the end) of the
-                    string to be read.
-    @param[in, out] result  A reference to the string variable where the read
-                            string is to be stored.
-    @tparam NumberType The type of the length @a len
-    @pre len >= 1
-    @return `true` if the string was successfully parsed
+    @brief returns the parent of this JSON pointer
+
+    @return parent of this JSON pointer; in case this JSON pointer is the root,
+            the root itself is returned
+
+    @complexity Linear in the length of the JSON pointer.
+
+    @liveexample{The example shows the result of `parent_pointer` for different
+    JSON Pointers.,json_pointer__parent_pointer}
+
+    @since version 3.6.0
     */
-    template<typename NumberType>
-    bool get_bson_string(const NumberType len, string_t& result)
+    json_pointer parent_pointer() const
     {
-        if (JSON_UNLIKELY(len < 1))
+        if (empty())
         {
-            auto last_token = get_token_string();
-            return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read, exception_message(input_format_t::bson, "string length must be at least 1, is " + std::to_string(len), "string")));
+            return *this;
         }
 
-        return get_string(input_format_t::bson, len - static_cast<NumberType>(1), result) and get() != std::char_traits<char>::eof();
+        json_pointer res = *this;
+        res.pop_back();
+        return res;
     }
 
     /*!
-    @brief Read a BSON document element of the given @a element_type.
-    @param[in] element_type The BSON element type, c.f. http://bsonspec.org/spec.html
-    @param[in] element_type_parse_position The position in the input stream,
-               where the `element_type` was read.
-    @warning Not all BSON element types are supported yet. An unsupported
-             @a element_type will give rise to a parse_error.114:
-             Unsupported BSON record type 0x...
-    @return whether a valid BSON-object/array was passed to the SAX parser
-    */
-    bool parse_bson_element_internal(const int element_type,
-                                     const std::size_t element_type_parse_position)
-    {
-        switch (element_type)
-        {
-            case 0x01: // double
-            {
-                double number;
-                return get_number<double, true>(input_format_t::bson, number) and sax->number_float(static_cast<number_float_t>(number), "");
-            }
-
-            case 0x02: // string
-            {
-                std::int32_t len;
-                string_t value;
-                return get_number<std::int32_t, true>(input_format_t::bson, len) and get_bson_string(len, value) and sax->string(value);
-            }
-
-            case 0x03: // object
-            {
-                return parse_bson_internal();
-            }
+    @brief remove last reference token
 
-            case 0x04: // array
-            {
-                return parse_bson_array();
-            }
+    @pre not `empty()`
 
-            case 0x08: // boolean
-            {
-                return sax->boolean(get() != 0);
-            }
+    @liveexample{The example shows the usage of `pop_back`.,json_pointer__pop_back}
 
-            case 0x0A: // null
-            {
-                return sax->null();
-            }
-
-            case 0x10: // int32
-            {
-                std::int32_t value;
-                return get_number<std::int32_t, true>(input_format_t::bson, value) and sax->number_integer(value);
-            }
-
-            case 0x12: // int64
-            {
-                std::int64_t value;
-                return get_number<std::int64_t, true>(input_format_t::bson, value) and sax->number_integer(value);
-            }
-
-            default: // anything else not supported (yet)
-            {
-                char cr[3];
-                (std::snprintf)(cr, sizeof(cr), "%.2hhX", static_cast<unsigned char>(element_type));
-                return sax->parse_error(element_type_parse_position, std::string(cr), parse_error::create(114, element_type_parse_position, "Unsupported BSON record type 0x" + std::string(cr)));
-            }
-        }
-    }
-
-    /*!
-    @brief Read a BSON element list (as specified in the BSON-spec)
+    @complexity Constant.
 
-    The same binary layout is used for objects and arrays, hence it must be
-    indicated with the argument @a is_array which one is expected
-    (true --> array, false --> object).
+    @throw out_of_range.405 if JSON pointer has no parent
 
-    @param[in] is_array Determines if the element list being read is to be
-                        treated as an object (@a is_array == false), or as an
-                        array (@a is_array == true).
-    @return whether a valid BSON-object/array was passed to the SAX parser
+    @since version 3.6.0
     */
-    bool parse_bson_element_list(const bool is_array)
+    void pop_back()
     {
-        string_t key;
-        while (int element_type = get())
+        if (JSON_HEDLEY_UNLIKELY(empty()))
         {
-            if (JSON_UNLIKELY(not unexpect_eof(input_format_t::bson, "element list")))
-            {
-                return false;
-            }
-
-            const std::size_t element_type_parse_position = chars_read;
-            if (JSON_UNLIKELY(not get_bson_cstr(key)))
-            {
-                return false;
-            }
-
-            if (not is_array)
-            {
-                if (not sax->key(key))
-                {
-                    return false;
-                }
-            }
-
-            if (JSON_UNLIKELY(not parse_bson_element_internal(element_type, element_type_parse_position)))
-            {
-                return false;
-            }
-
-            // get_bson_cstr only appends
-            key.clear();
+            JSON_THROW(detail::out_of_range::create(405, "JSON pointer has no parent"));
         }
 
-        return true;
+        reference_tokens.pop_back();
     }
 
     /*!
-    @brief Reads an array from the BSON input and passes it to the SAX-parser.
-    @return whether a valid BSON-array was passed to the SAX parser
-    */
-    bool parse_bson_array()
-    {
-        std::int32_t document_size;
-        get_number<std::int32_t, true>(input_format_t::bson, document_size);
+    @brief return last reference token
 
-        if (JSON_UNLIKELY(not sax->start_array(std::size_t(-1))))
-        {
-            return false;
-        }
+    @pre not `empty()`
+    @return last reference token
 
-        if (JSON_UNLIKELY(not parse_bson_element_list(/*is_array*/true)))
-        {
-            return false;
-        }
-
-        return sax->end_array();
-    }
+    @liveexample{The example shows the usage of `back`.,json_pointer__back}
 
-    //////////
-    // CBOR //
-    //////////
+    @complexity Constant.
 
-    /*!
-    @param[in] get_char  whether a new character should be retrieved from the
-                         input (true, default) or whether the last read
-                         character should be considered instead
+    @throw out_of_range.405 if JSON pointer has no parent
 
-    @return whether a valid CBOR value was passed to the SAX parser
+    @since version 3.6.0
     */
-    bool parse_cbor_internal(const bool get_char = true)
+    const std::string& back() const
     {
-        switch (get_char ? get() : current)
+        if (JSON_HEDLEY_UNLIKELY(empty()))
         {
-            // EOF
-            case std::char_traits<char>::eof():
-                return unexpect_eof(input_format_t::cbor, "value");
+            JSON_THROW(detail::out_of_range::create(405, "JSON pointer has no parent"));
+        }
 
-            // Integer 0x00..0x17 (0..23)
-            case 0x00:
-            case 0x01:
-            case 0x02:
-            case 0x03:
-            case 0x04:
-            case 0x05:
-            case 0x06:
-            case 0x07:
-            case 0x08:
-            case 0x09:
-            case 0x0A:
-            case 0x0B:
-            case 0x0C:
-            case 0x0D:
-            case 0x0E:
-            case 0x0F:
-            case 0x10:
-            case 0x11:
-            case 0x12:
-            case 0x13:
-            case 0x14:
-            case 0x15:
-            case 0x16:
-            case 0x17:
-                return sax->number_unsigned(static_cast<number_unsigned_t>(current));
+        return reference_tokens.back();
+    }
 
-            case 0x18: // Unsigned integer (one-byte uint8_t follows)
-            {
-                uint8_t number;
-                return get_number(input_format_t::cbor, number) and sax->number_unsigned(number);
-            }
+    /*!
+    @brief append an unescaped token at the end of the reference pointer
 
-            case 0x19: // Unsigned integer (two-byte uint16_t follows)
-            {
-                uint16_t number;
-                return get_number(input_format_t::cbor, number) and sax->number_unsigned(number);
-            }
+    @param[in] token  token to add
 
-            case 0x1A: // Unsigned integer (four-byte uint32_t follows)
-            {
-                uint32_t number;
-                return get_number(input_format_t::cbor, number) and sax->number_unsigned(number);
-            }
+    @complexity Amortized constant.
 
-            case 0x1B: // Unsigned integer (eight-byte uint64_t follows)
-            {
-                uint64_t number;
-                return get_number(input_format_t::cbor, number) and sax->number_unsigned(number);
-            }
+    @liveexample{The example shows the result of `push_back` for different
+    JSON Pointers.,json_pointer__push_back}
 
-            // Negative integer -1-0x00..-1-0x17 (-1..-24)
-            case 0x20:
-            case 0x21:
-            case 0x22:
-            case 0x23:
-            case 0x24:
-            case 0x25:
-            case 0x26:
-            case 0x27:
-            case 0x28:
-            case 0x29:
-            case 0x2A:
-            case 0x2B:
-            case 0x2C:
-            case 0x2D:
-            case 0x2E:
-            case 0x2F:
-            case 0x30:
-            case 0x31:
-            case 0x32:
-            case 0x33:
-            case 0x34:
-            case 0x35:
-            case 0x36:
-            case 0x37:
-                return sax->number_integer(static_cast<int8_t>(0x20 - 1 - current));
+    @since version 3.6.0
+    */
+    void push_back(const std::string& token)
+    {
+        reference_tokens.push_back(token);
+    }
 
-            case 0x38: // Negative integer (one-byte uint8_t follows)
-            {
-                uint8_t number;
-                return get_number(input_format_t::cbor, number) and sax->number_integer(static_cast<number_integer_t>(-1) - number);
-            }
+    /// @copydoc push_back(const std::string&)
+    void push_back(std::string&& token)
+    {
+        reference_tokens.push_back(std::move(token));
+    }
 
-            case 0x39: // Negative integer -1-n (two-byte uint16_t follows)
-            {
-                uint16_t number;
-                return get_number(input_format_t::cbor, number) and sax->number_integer(static_cast<number_integer_t>(-1) - number);
-            }
+    /*!
+    @brief return whether pointer points to the root document
 
-            case 0x3A: // Negative integer -1-n (four-byte uint32_t follows)
-            {
-                uint32_t number;
-                return get_number(input_format_t::cbor, number) and sax->number_integer(static_cast<number_integer_t>(-1) - number);
-            }
+    @return true iff the JSON pointer points to the root document
 
-            case 0x3B: // Negative integer -1-n (eight-byte uint64_t follows)
-            {
-                uint64_t number;
-                return get_number(input_format_t::cbor, number) and sax->number_integer(static_cast<number_integer_t>(-1)
-                        - static_cast<number_integer_t>(number));
-            }
+    @complexity Constant.
 
-            // UTF-8 string (0x00..0x17 bytes follow)
-            case 0x60:
-            case 0x61:
-            case 0x62:
-            case 0x63:
-            case 0x64:
-            case 0x65:
-            case 0x66:
-            case 0x67:
-            case 0x68:
-            case 0x69:
-            case 0x6A:
-            case 0x6B:
-            case 0x6C:
-            case 0x6D:
-            case 0x6E:
-            case 0x6F:
-            case 0x70:
-            case 0x71:
-            case 0x72:
-            case 0x73:
-            case 0x74:
-            case 0x75:
-            case 0x76:
-            case 0x77:
-            case 0x78: // UTF-8 string (one-byte uint8_t for n follows)
-            case 0x79: // UTF-8 string (two-byte uint16_t for n follow)
-            case 0x7A: // UTF-8 string (four-byte uint32_t for n follow)
-            case 0x7B: // UTF-8 string (eight-byte uint64_t for n follow)
-            case 0x7F: // UTF-8 string (indefinite length)
-            {
-                string_t s;
-                return get_cbor_string(s) and sax->string(s);
-            }
+    @exceptionsafety No-throw guarantee: this function never throws exceptions.
 
-            // array (0x00..0x17 data items follow)
-            case 0x80:
-            case 0x81:
-            case 0x82:
-            case 0x83:
-            case 0x84:
-            case 0x85:
-            case 0x86:
-            case 0x87:
-            case 0x88:
-            case 0x89:
-            case 0x8A:
-            case 0x8B:
-            case 0x8C:
-            case 0x8D:
-            case 0x8E:
-            case 0x8F:
-            case 0x90:
-            case 0x91:
-            case 0x92:
-            case 0x93:
-            case 0x94:
-            case 0x95:
-            case 0x96:
-            case 0x97:
-                return get_cbor_array(static_cast<std::size_t>(current & 0x1F));
+    @liveexample{The example shows the result of `empty` for different JSON
+    Pointers.,json_pointer__empty}
 
-            case 0x98: // array (one-byte uint8_t for n follows)
-            {
-                uint8_t len;
-                return get_number(input_format_t::cbor, len) and get_cbor_array(static_cast<std::size_t>(len));
-            }
+    @since version 3.6.0
+    */
+    bool empty() const noexcept
+    {
+        return reference_tokens.empty();
+    }
 
-            case 0x99: // array (two-byte uint16_t for n follow)
-            {
-                uint16_t len;
-                return get_number(input_format_t::cbor, len) and get_cbor_array(static_cast<std::size_t>(len));
-            }
+  private:
+    /*!
+    @param[in] s  reference token to be converted into an array index
 
-            case 0x9A: // array (four-byte uint32_t for n follow)
-            {
-                uint32_t len;
-                return get_number(input_format_t::cbor, len) and get_cbor_array(static_cast<std::size_t>(len));
-            }
+    @return integer representation of @a s
 
-            case 0x9B: // array (eight-byte uint64_t for n follow)
-            {
-                uint64_t len;
-                return get_number(input_format_t::cbor, len) and get_cbor_array(static_cast<std::size_t>(len));
-            }
+    @throw parse_error.106  if an array index begins with '0'
+    @throw parse_error.109  if an array index begins not with a digit
+    @throw out_of_range.404 if string @a s could not be converted to an integer
+    @throw out_of_range.410 if an array index exceeds size_type
+    */
+    static typename BasicJsonType::size_type array_index(const std::string& s)
+    {
+        using size_type = typename BasicJsonType::size_type;
 
-            case 0x9F: // array (indefinite length)
-                return get_cbor_array(std::size_t(-1));
+        // error condition (cf. RFC 6901, Sect. 4)
+        if (JSON_HEDLEY_UNLIKELY(s.size() > 1 && s[0] == '0'))
+        {
+            JSON_THROW(detail::parse_error::create(106, 0,
+                                                   "array index '" + s +
+                                                   "' must not begin with '0'"));
+        }
 
-            // map (0x00..0x17 pairs of data items follow)
-            case 0xA0:
-            case 0xA1:
-            case 0xA2:
-            case 0xA3:
-            case 0xA4:
-            case 0xA5:
-            case 0xA6:
-            case 0xA7:
-            case 0xA8:
-            case 0xA9:
-            case 0xAA:
-            case 0xAB:
-            case 0xAC:
-            case 0xAD:
-            case 0xAE:
-            case 0xAF:
-            case 0xB0:
-            case 0xB1:
-            case 0xB2:
-            case 0xB3:
-            case 0xB4:
-            case 0xB5:
-            case 0xB6:
-            case 0xB7:
-                return get_cbor_object(static_cast<std::size_t>(current & 0x1F));
+        // error condition (cf. RFC 6901, Sect. 4)
+        if (JSON_HEDLEY_UNLIKELY(s.size() > 1 && !(s[0] >= '1' && s[0] <= '9')))
+        {
+            JSON_THROW(detail::parse_error::create(109, 0, "array index '" + s + "' is not a number"));
+        }
 
-            case 0xB8: // map (one-byte uint8_t for n follows)
-            {
-                uint8_t len;
-                return get_number(input_format_t::cbor, len) and get_cbor_object(static_cast<std::size_t>(len));
-            }
+        std::size_t processed_chars = 0;
+        unsigned long long res = 0;
+        JSON_TRY
+        {
+            res = std::stoull(s, &processed_chars);
+        }
+        JSON_CATCH(std::out_of_range&)
+        {
+            JSON_THROW(detail::out_of_range::create(404, "unresolved reference token '" + s + "'"));
+        }
 
-            case 0xB9: // map (two-byte uint16_t for n follow)
-            {
-                uint16_t len;
-                return get_number(input_format_t::cbor, len) and get_cbor_object(static_cast<std::size_t>(len));
-            }
+        // check if the string was completely read
+        if (JSON_HEDLEY_UNLIKELY(processed_chars != s.size()))
+        {
+            JSON_THROW(detail::out_of_range::create(404, "unresolved reference token '" + s + "'"));
+        }
 
-            case 0xBA: // map (four-byte uint32_t for n follow)
-            {
-                uint32_t len;
-                return get_number(input_format_t::cbor, len) and get_cbor_object(static_cast<std::size_t>(len));
-            }
+        // only triggered on special platforms (like 32bit), see also
+        // https://github.com/nlohmann/json/pull/2203
+        if (res >= static_cast<unsigned long long>((std::numeric_limits<size_type>::max)()))
+        {
+            JSON_THROW(detail::out_of_range::create(410, "array index " + s + " exceeds size_type")); // LCOV_EXCL_LINE
+        }
 
-            case 0xBB: // map (eight-byte uint64_t for n follow)
-            {
-                uint64_t len;
-                return get_number(input_format_t::cbor, len) and get_cbor_object(static_cast<std::size_t>(len));
-            }
+        return static_cast<size_type>(res);
+    }
 
-            case 0xBF: // map (indefinite length)
-                return get_cbor_object(std::size_t(-1));
+    json_pointer top() const
+    {
+        if (JSON_HEDLEY_UNLIKELY(empty()))
+        {
+            JSON_THROW(detail::out_of_range::create(405, "JSON pointer has no parent"));
+        }
 
-            case 0xF4: // false
-                return sax->boolean(false);
+        json_pointer result = *this;
+        result.reference_tokens = {reference_tokens[0]};
+        return result;
+    }
 
-            case 0xF5: // true
-                return sax->boolean(true);
+    /*!
+    @brief create and return a reference to the pointed to value
 
-            case 0xF6: // null
-                return sax->null();
+    @complexity Linear in the number of reference tokens.
 
-            case 0xF9: // Half-Precision Float (two-byte IEEE 754)
+    @throw parse_error.109 if array index is not a number
+    @throw type_error.313 if value cannot be unflattened
+    */
+    BasicJsonType& get_and_create(BasicJsonType& j) const
+    {
+        auto result = &j;
+
+        // in case no reference tokens exist, return a reference to the JSON value
+        // j which will be overwritten by a primitive value
+        for (const auto& reference_token : reference_tokens)
+        {
+            switch (result->type())
             {
-                const int byte1_raw = get();
-                if (JSON_UNLIKELY(not unexpect_eof(input_format_t::cbor, "number")))
+                case detail::value_t::null:
                 {
-                    return false;
+                    if (reference_token == "0")
+                    {
+                        // start a new array if reference token is 0
+                        result = &result->operator[](0);
+                    }
+                    else
+                    {
+                        // start a new object otherwise
+                        result = &result->operator[](reference_token);
+                    }
+                    break;
                 }
-                const int byte2_raw = get();
-                if (JSON_UNLIKELY(not unexpect_eof(input_format_t::cbor, "number")))
+
+                case detail::value_t::object:
                 {
-                    return false;
+                    // create an entry in the object
+                    result = &result->operator[](reference_token);
+                    break;
                 }
 
-                const auto byte1 = static_cast<unsigned char>(byte1_raw);
-                const auto byte2 = static_cast<unsigned char>(byte2_raw);
-
-                // code from RFC 7049, Appendix D, Figure 3:
-                // As half-precision floating-point numbers were only added
-                // to IEEE 754 in 2008, today's programming platforms often
-                // still only have limited support for them. It is very
-                // easy to include at least decoding support for them even
-                // without such support. An example of a small decoder for
-                // half-precision floating-point numbers in the C language
-                // is shown in Fig. 3.
-                const int half = (byte1 << 8) + byte2;
-                const double val = [&half]
+                case detail::value_t::array:
                 {
-                    const int exp = (half >> 10) & 0x1F;
-                    const int mant = half & 0x3FF;
-                    assert(0 <= exp and exp <= 32);
-                    assert(0 <= mant and mant <= 1024);
-                    switch (exp)
-                    {
-                        case 0:
-                            return std::ldexp(mant, -24);
-                        case 31:
-                            return (mant == 0)
-                            ? std::numeric_limits<double>::infinity()
-                            : std::numeric_limits<double>::quiet_NaN();
-                        default:
-                            return std::ldexp(mant + 1024, exp - 25);
-                    }
-                }();
-                return sax->number_float((half & 0x8000) != 0
-                                         ? static_cast<number_float_t>(-val)
-                                         : static_cast<number_float_t>(val), "");
-            }
-
-            case 0xFA: // Single-Precision Float (four-byte IEEE 754)
-            {
-                float number;
-                return get_number(input_format_t::cbor, number) and sax->number_float(static_cast<number_float_t>(number), "");
-            }
-
-            case 0xFB: // Double-Precision Float (eight-byte IEEE 754)
-            {
-                double number;
-                return get_number(input_format_t::cbor, number) and sax->number_float(static_cast<number_float_t>(number), "");
-            }
+                    // create an entry in the array
+                    result = &result->operator[](array_index(reference_token));
+                    break;
+                }
 
-            default: // anything else (0xFF is handled inside the other types)
-            {
-                auto last_token = get_token_string();
-                return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read, exception_message(input_format_t::cbor, "invalid byte: 0x" + last_token, "value")));
+                /*
+                The following code is only reached if there exists a reference
+                token _and_ the current value is primitive. In this case, we have
+                an error situation, because primitive values may only occur as
+                single value; that is, with an empty list of reference tokens.
+                */
+                default:
+                    JSON_THROW(detail::type_error::create(313, "invalid value to unflatten"));
             }
         }
+
+        return *result;
     }
 
     /*!
-    @brief reads a CBOR string
+    @brief return a reference to the pointed to value
 
-    This function first reads starting bytes to determine the expected
-    string length and then copies this number of bytes into a string.
-    Additionally, CBOR's strings with indefinite lengths are supported.
+    @note This version does not throw if a value is not present, but tries to
+          create nested values instead. For instance, calling this function
+          with pointer `"/this/that"` on a null value is equivalent to calling
+          `operator[]("this").operator[]("that")` on that value, effectively
+          changing the null value to an object.
 
-    @param[out] result  created string
+    @param[in] ptr  a JSON value
 
-    @return whether string creation completed
+    @return reference to the JSON value pointed to by the JSON pointer
+
+    @complexity Linear in the length of the JSON pointer.
+
+    @throw parse_error.106   if an array index begins with '0'
+    @throw parse_error.109   if an array index was not a number
+    @throw out_of_range.404  if the JSON pointer can not be resolved
     */
-    bool get_cbor_string(string_t& result)
+    BasicJsonType& get_unchecked(BasicJsonType* ptr) const
     {
-        if (JSON_UNLIKELY(not unexpect_eof(input_format_t::cbor, "string")))
-        {
-            return false;
-        }
-
-        switch (current)
+        for (const auto& reference_token : reference_tokens)
         {
-            // UTF-8 string (0x00..0x17 bytes follow)
-            case 0x60:
-            case 0x61:
-            case 0x62:
-            case 0x63:
-            case 0x64:
-            case 0x65:
-            case 0x66:
-            case 0x67:
-            case 0x68:
-            case 0x69:
-            case 0x6A:
-            case 0x6B:
-            case 0x6C:
-            case 0x6D:
-            case 0x6E:
-            case 0x6F:
-            case 0x70:
-            case 0x71:
-            case 0x72:
-            case 0x73:
-            case 0x74:
-            case 0x75:
-            case 0x76:
-            case 0x77:
-            {
-                return get_string(input_format_t::cbor, current & 0x1F, result);
-            }
-
-            case 0x78: // UTF-8 string (one-byte uint8_t for n follows)
-            {
-                uint8_t len;
-                return get_number(input_format_t::cbor, len) and get_string(input_format_t::cbor, len, result);
-            }
-
-            case 0x79: // UTF-8 string (two-byte uint16_t for n follow)
+            // convert null values to arrays or objects before continuing
+            if (ptr->is_null())
             {
-                uint16_t len;
-                return get_number(input_format_t::cbor, len) and get_string(input_format_t::cbor, len, result);
-            }
+                // check if reference token is a number
+                const bool nums =
+                    std::all_of(reference_token.begin(), reference_token.end(),
+                                [](const unsigned char x)
+                {
+                    return std::isdigit(x);
+                });
 
-            case 0x7A: // UTF-8 string (four-byte uint32_t for n follow)
-            {
-                uint32_t len;
-                return get_number(input_format_t::cbor, len) and get_string(input_format_t::cbor, len, result);
+                // change value to array for numbers or "-" or to object otherwise
+                *ptr = (nums || reference_token == "-")
+                       ? detail::value_t::array
+                       : detail::value_t::object;
             }
 
-            case 0x7B: // UTF-8 string (eight-byte uint64_t for n follow)
+            switch (ptr->type())
             {
-                uint64_t len;
-                return get_number(input_format_t::cbor, len) and get_string(input_format_t::cbor, len, result);
-            }
+                case detail::value_t::object:
+                {
+                    // use unchecked object access
+                    ptr = &ptr->operator[](reference_token);
+                    break;
+                }
 
-            case 0x7F: // UTF-8 string (indefinite length)
-            {
-                while (get() != 0xFF)
+                case detail::value_t::array:
                 {
-                    string_t chunk;
-                    if (not get_cbor_string(chunk))
+                    if (reference_token == "-")
                     {
-                        return false;
+                        // explicitly treat "-" as index beyond the end
+                        ptr = &ptr->operator[](ptr->m_value.array->size());
                     }
-                    result.append(chunk);
+                    else
+                    {
+                        // convert array index to number; unchecked access
+                        ptr = &ptr->operator[](array_index(reference_token));
+                    }
+                    break;
                 }
-                return true;
-            }
 
-            default:
-            {
-                auto last_token = get_token_string();
-                return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read, exception_message(input_format_t::cbor, "expected length specification (0x60-0x7B) or indefinite string type (0x7F); last byte: 0x" + last_token, "string")));
+                default:
+                    JSON_THROW(detail::out_of_range::create(404, "unresolved reference token '" + reference_token + "'"));
             }
         }
+
+        return *ptr;
     }
 
     /*!
-    @param[in] len  the length of the array or std::size_t(-1) for an
-                    array of indefinite size
-    @return whether array creation completed
+    @throw parse_error.106   if an array index begins with '0'
+    @throw parse_error.109   if an array index was not a number
+    @throw out_of_range.402  if the array index '-' is used
+    @throw out_of_range.404  if the JSON pointer can not be resolved
     */
-    bool get_cbor_array(const std::size_t len)
+    BasicJsonType& get_checked(BasicJsonType* ptr) const
     {
-        if (JSON_UNLIKELY(not sax->start_array(len)))
-        {
-            return false;
-        }
-
-        if (len != std::size_t(-1))
+        for (const auto& reference_token : reference_tokens)
         {
-            for (std::size_t i = 0; i < len; ++i)
+            switch (ptr->type())
             {
-                if (JSON_UNLIKELY(not parse_cbor_internal()))
+                case detail::value_t::object:
                 {
-                    return false;
+                    // note: at performs range check
+                    ptr = &ptr->at(reference_token);
+                    break;
                 }
-            }
-        }
-        else
-        {
-            while (get() != 0xFF)
-            {
-                if (JSON_UNLIKELY(not parse_cbor_internal(false)))
+
+                case detail::value_t::array:
                 {
-                    return false;
+                    if (JSON_HEDLEY_UNLIKELY(reference_token == "-"))
+                    {
+                        // "-" always fails the range check
+                        JSON_THROW(detail::out_of_range::create(402,
+                                                                "array index '-' (" + std::to_string(ptr->m_value.array->size()) +
+                                                                ") is out of range"));
+                    }
+
+                    // note: at performs range check
+                    ptr = &ptr->at(array_index(reference_token));
+                    break;
                 }
+
+                default:
+                    JSON_THROW(detail::out_of_range::create(404, "unresolved reference token '" + reference_token + "'"));
             }
         }
 
-        return sax->end_array();
+        return *ptr;
     }
 
     /*!
-    @param[in] len  the length of the object or std::size_t(-1) for an
-                    object of indefinite size
-    @return whether object creation completed
+    @brief return a const reference to the pointed to value
+
+    @param[in] ptr  a JSON value
+
+    @return const reference to the JSON value pointed to by the JSON
+    pointer
+
+    @throw parse_error.106   if an array index begins with '0'
+    @throw parse_error.109   if an array index was not a number
+    @throw out_of_range.402  if the array index '-' is used
+    @throw out_of_range.404  if the JSON pointer can not be resolved
     */
-    bool get_cbor_object(const std::size_t len)
+    const BasicJsonType& get_unchecked(const BasicJsonType* ptr) const
     {
-        if (not JSON_UNLIKELY(sax->start_object(len)))
-        {
-            return false;
-        }
-
-        string_t key;
-        if (len != std::size_t(-1))
+        for (const auto& reference_token : reference_tokens)
         {
-            for (std::size_t i = 0; i < len; ++i)
+            switch (ptr->type())
             {
-                get();
-                if (JSON_UNLIKELY(not get_cbor_string(key) or not sax->key(key)))
+                case detail::value_t::object:
                 {
-                    return false;
+                    // use unchecked object access
+                    ptr = &ptr->operator[](reference_token);
+                    break;
                 }
 
-                if (JSON_UNLIKELY(not parse_cbor_internal()))
+                case detail::value_t::array:
                 {
-                    return false;
+                    if (JSON_HEDLEY_UNLIKELY(reference_token == "-"))
+                    {
+                        // "-" cannot be used for const access
+                        JSON_THROW(detail::out_of_range::create(402,
+                                                                "array index '-' (" + std::to_string(ptr->m_value.array->size()) +
+                                                                ") is out of range"));
+                    }
+
+                    // use unchecked array access
+                    ptr = &ptr->operator[](array_index(reference_token));
+                    break;
                 }
-                key.clear();
+
+                default:
+                    JSON_THROW(detail::out_of_range::create(404, "unresolved reference token '" + reference_token + "'"));
             }
         }
-        else
+
+        return *ptr;
+    }
+
+    /*!
+    @throw parse_error.106   if an array index begins with '0'
+    @throw parse_error.109   if an array index was not a number
+    @throw out_of_range.402  if the array index '-' is used
+    @throw out_of_range.404  if the JSON pointer can not be resolved
+    */
+    const BasicJsonType& get_checked(const BasicJsonType* ptr) const
+    {
+        for (const auto& reference_token : reference_tokens)
         {
-            while (get() != 0xFF)
+            switch (ptr->type())
             {
-                if (JSON_UNLIKELY(not get_cbor_string(key) or not sax->key(key)))
+                case detail::value_t::object:
                 {
-                    return false;
+                    // note: at performs range check
+                    ptr = &ptr->at(reference_token);
+                    break;
                 }
 
-                if (JSON_UNLIKELY(not parse_cbor_internal()))
+                case detail::value_t::array:
                 {
-                    return false;
+                    if (JSON_HEDLEY_UNLIKELY(reference_token == "-"))
+                    {
+                        // "-" always fails the range check
+                        JSON_THROW(detail::out_of_range::create(402,
+                                                                "array index '-' (" + std::to_string(ptr->m_value.array->size()) +
+                                                                ") is out of range"));
+                    }
+
+                    // note: at performs range check
+                    ptr = &ptr->at(array_index(reference_token));
+                    break;
                 }
-                key.clear();
+
+                default:
+                    JSON_THROW(detail::out_of_range::create(404, "unresolved reference token '" + reference_token + "'"));
             }
         }
 
-        return sax->end_object();
+        return *ptr;
     }
 
-    /////////////
-    // MsgPack //
-    /////////////
-
     /*!
-    @return whether a valid MessagePack value was passed to the SAX parser
+    @throw parse_error.106   if an array index begins with '0'
+    @throw parse_error.109   if an array index was not a number
     */
-    bool parse_msgpack_internal()
+    bool contains(const BasicJsonType* ptr) const
     {
-        switch (get())
+        for (const auto& reference_token : reference_tokens)
         {
-            // EOF
-            case std::char_traits<char>::eof():
-                return unexpect_eof(input_format_t::msgpack, "value");
-
-            // positive fixint
-            case 0x00:
-            case 0x01:
-            case 0x02:
-            case 0x03:
-            case 0x04:
-            case 0x05:
-            case 0x06:
-            case 0x07:
-            case 0x08:
-            case 0x09:
-            case 0x0A:
-            case 0x0B:
-            case 0x0C:
-            case 0x0D:
-            case 0x0E:
-            case 0x0F:
-            case 0x10:
-            case 0x11:
-            case 0x12:
-            case 0x13:
-            case 0x14:
-            case 0x15:
-            case 0x16:
-            case 0x17:
-            case 0x18:
-            case 0x19:
-            case 0x1A:
-            case 0x1B:
-            case 0x1C:
-            case 0x1D:
-            case 0x1E:
-            case 0x1F:
-            case 0x20:
-            case 0x21:
-            case 0x22:
-            case 0x23:
-            case 0x24:
-            case 0x25:
-            case 0x26:
-            case 0x27:
-            case 0x28:
-            case 0x29:
-            case 0x2A:
-            case 0x2B:
-            case 0x2C:
-            case 0x2D:
-            case 0x2E:
-            case 0x2F:
-            case 0x30:
-            case 0x31:
-            case 0x32:
-            case 0x33:
-            case 0x34:
-            case 0x35:
-            case 0x36:
-            case 0x37:
-            case 0x38:
-            case 0x39:
-            case 0x3A:
-            case 0x3B:
-            case 0x3C:
-            case 0x3D:
-            case 0x3E:
-            case 0x3F:
-            case 0x40:
-            case 0x41:
-            case 0x42:
-            case 0x43:
-            case 0x44:
-            case 0x45:
-            case 0x46:
-            case 0x47:
-            case 0x48:
-            case 0x49:
-            case 0x4A:
-            case 0x4B:
-            case 0x4C:
-            case 0x4D:
-            case 0x4E:
-            case 0x4F:
-            case 0x50:
-            case 0x51:
-            case 0x52:
-            case 0x53:
-            case 0x54:
-            case 0x55:
-            case 0x56:
-            case 0x57:
-            case 0x58:
-            case 0x59:
-            case 0x5A:
-            case 0x5B:
-            case 0x5C:
-            case 0x5D:
-            case 0x5E:
-            case 0x5F:
-            case 0x60:
-            case 0x61:
-            case 0x62:
-            case 0x63:
-            case 0x64:
-            case 0x65:
-            case 0x66:
-            case 0x67:
-            case 0x68:
-            case 0x69:
-            case 0x6A:
-            case 0x6B:
-            case 0x6C:
-            case 0x6D:
-            case 0x6E:
-            case 0x6F:
-            case 0x70:
-            case 0x71:
-            case 0x72:
-            case 0x73:
-            case 0x74:
-            case 0x75:
-            case 0x76:
-            case 0x77:
-            case 0x78:
-            case 0x79:
-            case 0x7A:
-            case 0x7B:
-            case 0x7C:
-            case 0x7D:
-            case 0x7E:
-            case 0x7F:
-                return sax->number_unsigned(static_cast<number_unsigned_t>(current));
-
-            // fixmap
-            case 0x80:
-            case 0x81:
-            case 0x82:
-            case 0x83:
-            case 0x84:
-            case 0x85:
-            case 0x86:
-            case 0x87:
-            case 0x88:
-            case 0x89:
-            case 0x8A:
-            case 0x8B:
-            case 0x8C:
-            case 0x8D:
-            case 0x8E:
-            case 0x8F:
-                return get_msgpack_object(static_cast<std::size_t>(current & 0x0F));
-
-            // fixarray
-            case 0x90:
-            case 0x91:
-            case 0x92:
-            case 0x93:
-            case 0x94:
-            case 0x95:
-            case 0x96:
-            case 0x97:
-            case 0x98:
-            case 0x99:
-            case 0x9A:
-            case 0x9B:
-            case 0x9C:
-            case 0x9D:
-            case 0x9E:
-            case 0x9F:
-                return get_msgpack_array(static_cast<std::size_t>(current & 0x0F));
-
-            // fixstr
-            case 0xA0:
-            case 0xA1:
-            case 0xA2:
-            case 0xA3:
-            case 0xA4:
-            case 0xA5:
-            case 0xA6:
-            case 0xA7:
-            case 0xA8:
-            case 0xA9:
-            case 0xAA:
-            case 0xAB:
-            case 0xAC:
-            case 0xAD:
-            case 0xAE:
-            case 0xAF:
-            case 0xB0:
-            case 0xB1:
-            case 0xB2:
-            case 0xB3:
-            case 0xB4:
-            case 0xB5:
-            case 0xB6:
-            case 0xB7:
-            case 0xB8:
-            case 0xB9:
-            case 0xBA:
-            case 0xBB:
-            case 0xBC:
-            case 0xBD:
-            case 0xBE:
-            case 0xBF:
+            switch (ptr->type())
             {
-                string_t s;
-                return get_msgpack_string(s) and sax->string(s);
-            }
-
-            case 0xC0: // nil
-                return sax->null();
-
-            case 0xC2: // false
-                return sax->boolean(false);
-
-            case 0xC3: // true
-                return sax->boolean(true);
-
-            case 0xCA: // float 32
-            {
-                float number;
-                return get_number(input_format_t::msgpack, number) and sax->number_float(static_cast<number_float_t>(number), "");
-            }
-
-            case 0xCB: // float 64
-            {
-                double number;
-                return get_number(input_format_t::msgpack, number) and sax->number_float(static_cast<number_float_t>(number), "");
-            }
-
-            case 0xCC: // uint 8
-            {
-                uint8_t number;
-                return get_number(input_format_t::msgpack, number) and sax->number_unsigned(number);
-            }
-
-            case 0xCD: // uint 16
-            {
-                uint16_t number;
-                return get_number(input_format_t::msgpack, number) and sax->number_unsigned(number);
-            }
-
-            case 0xCE: // uint 32
-            {
-                uint32_t number;
-                return get_number(input_format_t::msgpack, number) and sax->number_unsigned(number);
-            }
-
-            case 0xCF: // uint 64
-            {
-                uint64_t number;
-                return get_number(input_format_t::msgpack, number) and sax->number_unsigned(number);
-            }
-
-            case 0xD0: // int 8
-            {
-                int8_t number;
-                return get_number(input_format_t::msgpack, number) and sax->number_integer(number);
-            }
-
-            case 0xD1: // int 16
-            {
-                int16_t number;
-                return get_number(input_format_t::msgpack, number) and sax->number_integer(number);
-            }
-
-            case 0xD2: // int 32
-            {
-                int32_t number;
-                return get_number(input_format_t::msgpack, number) and sax->number_integer(number);
-            }
-
-            case 0xD3: // int 64
-            {
-                int64_t number;
-                return get_number(input_format_t::msgpack, number) and sax->number_integer(number);
-            }
-
-            case 0xD9: // str 8
-            case 0xDA: // str 16
-            case 0xDB: // str 32
-            {
-                string_t s;
-                return get_msgpack_string(s) and sax->string(s);
-            }
-
-            case 0xDC: // array 16
-            {
-                uint16_t len;
-                return get_number(input_format_t::msgpack, len) and get_msgpack_array(static_cast<std::size_t>(len));
-            }
+                case detail::value_t::object:
+                {
+                    if (!ptr->contains(reference_token))
+                    {
+                        // we did not find the key in the object
+                        return false;
+                    }
 
-            case 0xDD: // array 32
-            {
-                uint32_t len;
-                return get_number(input_format_t::msgpack, len) and get_msgpack_array(static_cast<std::size_t>(len));
-            }
+                    ptr = &ptr->operator[](reference_token);
+                    break;
+                }
 
-            case 0xDE: // map 16
-            {
-                uint16_t len;
-                return get_number(input_format_t::msgpack, len) and get_msgpack_object(static_cast<std::size_t>(len));
-            }
+                case detail::value_t::array:
+                {
+                    if (JSON_HEDLEY_UNLIKELY(reference_token == "-"))
+                    {
+                        // "-" always fails the range check
+                        return false;
+                    }
+                    if (JSON_HEDLEY_UNLIKELY(reference_token.size() == 1 && !("0" <= reference_token && reference_token <= "9")))
+                    {
+                        // invalid char
+                        return false;
+                    }
+                    if (JSON_HEDLEY_UNLIKELY(reference_token.size() > 1))
+                    {
+                        if (JSON_HEDLEY_UNLIKELY(!('1' <= reference_token[0] && reference_token[0] <= '9')))
+                        {
+                            // first char should be between '1' and '9'
+                            return false;
+                        }
+                        for (std::size_t i = 1; i < reference_token.size(); i++)
+                        {
+                            if (JSON_HEDLEY_UNLIKELY(!('0' <= reference_token[i] && reference_token[i] <= '9')))
+                            {
+                                // other char should be between '0' and '9'
+                                return false;
+                            }
+                        }
+                    }
 
-            case 0xDF: // map 32
-            {
-                uint32_t len;
-                return get_number(input_format_t::msgpack, len) and get_msgpack_object(static_cast<std::size_t>(len));
-            }
+                    const auto idx = array_index(reference_token);
+                    if (idx >= ptr->size())
+                    {
+                        // index out of range
+                        return false;
+                    }
 
-            // negative fixint
-            case 0xE0:
-            case 0xE1:
-            case 0xE2:
-            case 0xE3:
-            case 0xE4:
-            case 0xE5:
-            case 0xE6:
-            case 0xE7:
-            case 0xE8:
-            case 0xE9:
-            case 0xEA:
-            case 0xEB:
-            case 0xEC:
-            case 0xED:
-            case 0xEE:
-            case 0xEF:
-            case 0xF0:
-            case 0xF1:
-            case 0xF2:
-            case 0xF3:
-            case 0xF4:
-            case 0xF5:
-            case 0xF6:
-            case 0xF7:
-            case 0xF8:
-            case 0xF9:
-            case 0xFA:
-            case 0xFB:
-            case 0xFC:
-            case 0xFD:
-            case 0xFE:
-            case 0xFF:
-                return sax->number_integer(static_cast<int8_t>(current));
+                    ptr = &ptr->operator[](idx);
+                    break;
+                }
 
-            default: // anything else
-            {
-                auto last_token = get_token_string();
-                return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read, exception_message(input_format_t::msgpack, "invalid byte: 0x" + last_token, "value")));
+                default:
+                {
+                    // we do not expect primitive values if there is still a
+                    // reference token to process
+                    return false;
+                }
             }
         }
+
+        // no reference token left means we found a primitive value
+        return true;
     }
 
     /*!
-    @brief reads a MessagePack string
-
-    This function first reads starting bytes to determine the expected
-    string length and then copies this number of bytes into a string.
+    @brief split the string input to reference tokens
 
-    @param[out] result  created string
+    @note This function is only called by the json_pointer constructor.
+          All exceptions below are documented there.
 
-    @return whether string creation completed
+    @throw parse_error.107  if the pointer is not empty or begins with '/'
+    @throw parse_error.108  if character '~' is not followed by '0' or '1'
     */
-    bool get_msgpack_string(string_t& result)
+    static std::vector<std::string> split(const std::string& reference_string)
     {
-        if (JSON_UNLIKELY(not unexpect_eof(input_format_t::msgpack, "string")))
+        std::vector<std::string> result;
+
+        // special case: empty reference string -> no reference tokens
+        if (reference_string.empty())
         {
-            return false;
+            return result;
         }
 
-        switch (current)
+        // check if nonempty reference string begins with slash
+        if (JSON_HEDLEY_UNLIKELY(reference_string[0] != '/'))
         {
-            // fixstr
-            case 0xA0:
-            case 0xA1:
-            case 0xA2:
-            case 0xA3:
-            case 0xA4:
-            case 0xA5:
-            case 0xA6:
-            case 0xA7:
-            case 0xA8:
-            case 0xA9:
-            case 0xAA:
-            case 0xAB:
-            case 0xAC:
-            case 0xAD:
-            case 0xAE:
-            case 0xAF:
-            case 0xB0:
-            case 0xB1:
-            case 0xB2:
-            case 0xB3:
-            case 0xB4:
-            case 0xB5:
-            case 0xB6:
-            case 0xB7:
-            case 0xB8:
-            case 0xB9:
-            case 0xBA:
-            case 0xBB:
-            case 0xBC:
-            case 0xBD:
-            case 0xBE:
-            case 0xBF:
-            {
-                return get_string(input_format_t::msgpack, current & 0x1F, result);
-            }
+            JSON_THROW(detail::parse_error::create(107, 1,
+                                                   "JSON pointer must be empty or begin with '/' - was: '" +
+                                                   reference_string + "'"));
+        }
 
-            case 0xD9: // str 8
-            {
-                uint8_t len;
-                return get_number(input_format_t::msgpack, len) and get_string(input_format_t::msgpack, len, result);
-            }
+        // extract the reference tokens:
+        // - slash: position of the last read slash (or end of string)
+        // - start: position after the previous slash
+        for (
+            // search for the first slash after the first character
+            std::size_t slash = reference_string.find_first_of('/', 1),
+            // set the beginning of the first reference token
+            start = 1;
+            // we can stop if start == 0 (if slash == std::string::npos)
+            start != 0;
+            // set the beginning of the next reference token
+            // (will eventually be 0 if slash == std::string::npos)
+            start = (slash == std::string::npos) ? 0 : slash + 1,
+            // find next slash
+            slash = reference_string.find_first_of('/', start))
+        {
+            // use the text between the beginning of the reference token
+            // (start) and the last slash (slash).
+            auto reference_token = reference_string.substr(start, slash - start);
 
-            case 0xDA: // str 16
+            // check reference tokens are properly escaped
+            for (std::size_t pos = reference_token.find_first_of('~');
+                    pos != std::string::npos;
+                    pos = reference_token.find_first_of('~', pos + 1))
             {
-                uint16_t len;
-                return get_number(input_format_t::msgpack, len) and get_string(input_format_t::msgpack, len, result);
-            }
+                JSON_ASSERT(reference_token[pos] == '~');
 
-            case 0xDB: // str 32
-            {
-                uint32_t len;
-                return get_number(input_format_t::msgpack, len) and get_string(input_format_t::msgpack, len, result);
+                // ~ must be followed by 0 or 1
+                if (JSON_HEDLEY_UNLIKELY(pos == reference_token.size() - 1 ||
+                                         (reference_token[pos + 1] != '0' &&
+                                          reference_token[pos + 1] != '1')))
+                {
+                    JSON_THROW(detail::parse_error::create(108, 0, "escape character '~' must be followed with '0' or '1'"));
+                }
             }
 
-            default:
-            {
-                auto last_token = get_token_string();
-                return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read, exception_message(input_format_t::msgpack, "expected length specification (0xA0-0xBF, 0xD9-0xDB); last byte: 0x" + last_token, "string")));
-            }
+            // finally, store the reference token
+            unescape(reference_token);
+            result.push_back(reference_token);
         }
+
+        return result;
     }
 
     /*!
-    @param[in] len  the length of the array
-    @return whether array creation completed
-    */
-    bool get_msgpack_array(const std::size_t len)
-    {
-        if (JSON_UNLIKELY(not sax->start_array(len)))
-        {
-            return false;
-        }
+    @brief replace all occurrences of a substring by another string
 
-        for (std::size_t i = 0; i < len; ++i)
-        {
-            if (JSON_UNLIKELY(not parse_msgpack_internal()))
-            {
-                return false;
-            }
-        }
+    @param[in,out] s  the string to manipulate; changed so that all
+                   occurrences of @a f are replaced with @a t
+    @param[in]     f  the substring to replace with @a t
+    @param[in]     t  the string to replace @a f
 
-        return sax->end_array();
-    }
+    @pre The search string @a f must not be empty. **This precondition is
+    enforced with an assertion.**
 
-    /*!
-    @param[in] len  the length of the object
-    @return whether object creation completed
+    @since version 2.0.0
     */
-    bool get_msgpack_object(const std::size_t len)
+    static void replace_substring(std::string& s, const std::string& f,
+                                  const std::string& t)
     {
-        if (JSON_UNLIKELY(not sax->start_object(len)))
-        {
-            return false;
-        }
-
-        string_t key;
-        for (std::size_t i = 0; i < len; ++i)
-        {
-            get();
-            if (JSON_UNLIKELY(not get_msgpack_string(key) or not sax->key(key)))
-            {
-                return false;
-            }
-
-            if (JSON_UNLIKELY(not parse_msgpack_internal()))
-            {
-                return false;
-            }
-            key.clear();
-        }
-
-        return sax->end_object();
+        JSON_ASSERT(!f.empty());
+        for (auto pos = s.find(f);                // find first occurrence of f
+                pos != std::string::npos;         // make sure f was found
+                s.replace(pos, f.size(), t),      // replace with t, and
+                pos = s.find(f, pos + t.size()))  // find next occurrence of f
+        {}
     }
 
-    ////////////
-    // UBJSON //
-    ////////////
-
-    /*!
-    @param[in] get_char  whether a new character should be retrieved from the
-                         input (true, default) or whether the last read
-                         character should be considered instead
-
-    @return whether a valid UBJSON value was passed to the SAX parser
-    */
-    bool parse_ubjson_internal(const bool get_char = true)
+    /// escape "~" to "~0" and "/" to "~1"
+    static std::string escape(std::string s)
     {
-        return get_ubjson_value(get_char ? get_ignore_noop() : current);
+        replace_substring(s, "~", "~0");
+        replace_substring(s, "/", "~1");
+        return s;
     }
 
-    /*!
-    @brief reads a UBJSON string
-
-    This function is either called after reading the 'S' byte explicitly
-    indicating a string, or in case of an object key where the 'S' byte can be
-    left out.
-
-    @param[out] result   created string
-    @param[in] get_char  whether a new character should be retrieved from the
-                         input (true, default) or whether the last read
-                         character should be considered instead
-
-    @return whether string creation completed
-    */
-    bool get_ubjson_string(string_t& result, const bool get_char = true)
+    /// unescape "~1" to tilde and "~0" to slash (order is important!)
+    static void unescape(std::string& s)
     {
-        if (get_char)
-        {
-            get();  // TODO: may we ignore N here?
-        }
-
-        if (JSON_UNLIKELY(not unexpect_eof(input_format_t::ubjson, "value")))
-        {
-            return false;
-        }
-
-        switch (current)
-        {
-            case 'U':
-            {
-                uint8_t len;
-                return get_number(input_format_t::ubjson, len) and get_string(input_format_t::ubjson, len, result);
-            }
-
-            case 'i':
-            {
-                int8_t len;
-                return get_number(input_format_t::ubjson, len) and get_string(input_format_t::ubjson, len, result);
-            }
-
-            case 'I':
-            {
-                int16_t len;
-                return get_number(input_format_t::ubjson, len) and get_string(input_format_t::ubjson, len, result);
-            }
-
-            case 'l':
-            {
-                int32_t len;
-                return get_number(input_format_t::ubjson, len) and get_string(input_format_t::ubjson, len, result);
-            }
-
-            case 'L':
-            {
-                int64_t len;
-                return get_number(input_format_t::ubjson, len) and get_string(input_format_t::ubjson, len, result);
-            }
-
-            default:
-                auto last_token = get_token_string();
-                return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read, exception_message(input_format_t::ubjson, "expected length type specification (U, i, I, l, L); last byte: 0x" + last_token, "string")));
-        }
+        replace_substring(s, "~1", "/");
+        replace_substring(s, "~0", "~");
     }
 
     /*!
-    @param[out] result  determined size
-    @return whether size determination completed
+    @param[in] reference_string  the reference string to the current value
+    @param[in] value             the value to consider
+    @param[in,out] result        the result object to insert values to
+
+    @note Empty objects or arrays are flattened to `null`.
     */
-    bool get_ubjson_size_value(std::size_t& result)
+    static void flatten(const std::string& reference_string,
+                        const BasicJsonType& value,
+                        BasicJsonType& result)
     {
-        switch (get_ignore_noop())
+        switch (value.type())
         {
-            case 'U':
-            {
-                uint8_t number;
-                if (JSON_UNLIKELY(not get_number(input_format_t::ubjson, number)))
-                {
-                    return false;
-                }
-                result = static_cast<std::size_t>(number);
-                return true;
-            }
-
-            case 'i':
+            case detail::value_t::array:
             {
-                int8_t number;
-                if (JSON_UNLIKELY(not get_number(input_format_t::ubjson, number)))
+                if (value.m_value.array->empty())
                 {
-                    return false;
+                    // flatten empty array as null
+                    result[reference_string] = nullptr;
                 }
-                result = static_cast<std::size_t>(number);
-                return true;
-            }
-
-            case 'I':
-            {
-                int16_t number;
-                if (JSON_UNLIKELY(not get_number(input_format_t::ubjson, number)))
+                else
                 {
-                    return false;
+                    // iterate array and use index as reference string
+                    for (std::size_t i = 0; i < value.m_value.array->size(); ++i)
+                    {
+                        flatten(reference_string + "/" + std::to_string(i),
+                                value.m_value.array->operator[](i), result);
+                    }
                 }
-                result = static_cast<std::size_t>(number);
-                return true;
+                break;
             }
 
-            case 'l':
+            case detail::value_t::object:
             {
-                int32_t number;
-                if (JSON_UNLIKELY(not get_number(input_format_t::ubjson, number)))
+                if (value.m_value.object->empty())
                 {
-                    return false;
+                    // flatten empty object as null
+                    result[reference_string] = nullptr;
                 }
-                result = static_cast<std::size_t>(number);
-                return true;
-            }
-
-            case 'L':
-            {
-                int64_t number;
-                if (JSON_UNLIKELY(not get_number(input_format_t::ubjson, number)))
+                else
                 {
-                    return false;
+                    // iterate object and use keys as reference string
+                    for (const auto& element : *value.m_value.object)
+                    {
+                        flatten(reference_string + "/" + escape(element.first), element.second, result);
+                    }
                 }
-                result = static_cast<std::size_t>(number);
-                return true;
+                break;
             }
 
             default:
             {
-                auto last_token = get_token_string();
-                return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read, exception_message(input_format_t::ubjson, "expected length type specification (U, i, I, l, L) after '#'; last byte: 0x" + last_token, "size")));
+                // add primitive value with its reference string
+                result[reference_string] = value;
+                break;
             }
         }
     }
 
     /*!
-    @brief determine the type and size for a container
-
-    In the optimized UBJSON format, a type and a size can be provided to allow
-    for a more compact representation.
+    @param[in] value  flattened JSON
 
-    @param[out] result  pair of the size and the type
+    @return unflattened JSON
 
-    @return whether pair creation completed
+    @throw parse_error.109 if array index is not a number
+    @throw type_error.314  if value is not an object
+    @throw type_error.315  if object values are not primitive
+    @throw type_error.313  if value cannot be unflattened
     */
-    bool get_ubjson_size_type(std::pair<std::size_t, int>& result)
+    static BasicJsonType
+    unflatten(const BasicJsonType& value)
     {
-        result.first = string_t::npos; // size
-        result.second = 0; // type
+        if (JSON_HEDLEY_UNLIKELY(!value.is_object()))
+        {
+            JSON_THROW(detail::type_error::create(314, "only objects can be unflattened"));
+        }
 
-        get_ignore_noop();
+        BasicJsonType result;
 
-        if (current == '$')
+        // iterate the JSON object values
+        for (const auto& element : *value.m_value.object)
         {
-            result.second = get();  // must not ignore 'N', because 'N' maybe the type
-            if (JSON_UNLIKELY(not unexpect_eof(input_format_t::ubjson, "type")))
-            {
-                return false;
-            }
-
-            get_ignore_noop();
-            if (JSON_UNLIKELY(current != '#'))
+            if (JSON_HEDLEY_UNLIKELY(!element.second.is_primitive()))
             {
-                if (JSON_UNLIKELY(not unexpect_eof(input_format_t::ubjson, "value")))
-                {
-                    return false;
-                }
-                auto last_token = get_token_string();
-                return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read, exception_message(input_format_t::ubjson, "expected '#' after type information; last byte: 0x" + last_token, "size")));
+                JSON_THROW(detail::type_error::create(315, "values in object must be primitive"));
             }
 
-            return get_ubjson_size_value(result.first);
-        }
-        else if (current == '#')
-        {
-            return get_ubjson_size_value(result.first);
+            // assign value to reference pointed to by JSON pointer; Note that if
+            // the JSON pointer is "" (i.e., points to the whole value), function
+            // get_and_create returns a reference to result itself. An assignment
+            // will then create a primitive value.
+            json_pointer(element.first).get_and_create(result) = element.second;
         }
-        return true;
+
+        return result;
     }
 
     /*!
-    @param prefix  the previously read or set type prefix
-    @return whether value creation completed
+    @brief compares two JSON pointers for equality
+
+    @param[in] lhs  JSON pointer to compare
+    @param[in] rhs  JSON pointer to compare
+    @return whether @a lhs is equal to @a rhs
+
+    @complexity Linear in the length of the JSON pointer
+
+    @exceptionsafety No-throw guarantee: this function never throws exceptions.
     */
-    bool get_ubjson_value(const int prefix)
+    friend bool operator==(json_pointer const& lhs,
+                           json_pointer const& rhs) noexcept
     {
-        switch (prefix)
-        {
-            case std::char_traits<char>::eof():  // EOF
-                return unexpect_eof(input_format_t::ubjson, "value");
+        return lhs.reference_tokens == rhs.reference_tokens;
+    }
 
-            case 'T':  // true
-                return sax->boolean(true);
-            case 'F':  // false
-                return sax->boolean(false);
+    /*!
+    @brief compares two JSON pointers for inequality
 
-            case 'Z':  // null
-                return sax->null();
+    @param[in] lhs  JSON pointer to compare
+    @param[in] rhs  JSON pointer to compare
+    @return whether @a lhs is not equal @a rhs
 
-            case 'U':
-            {
-                uint8_t number;
-                return get_number(input_format_t::ubjson, number) and sax->number_unsigned(number);
-            }
+    @complexity Linear in the length of the JSON pointer
 
-            case 'i':
-            {
-                int8_t number;
-                return get_number(input_format_t::ubjson, number) and sax->number_integer(number);
-            }
+    @exceptionsafety No-throw guarantee: this function never throws exceptions.
+    */
+    friend bool operator!=(json_pointer const& lhs,
+                           json_pointer const& rhs) noexcept
+    {
+        return !(lhs == rhs);
+    }
 
-            case 'I':
-            {
-                int16_t number;
-                return get_number(input_format_t::ubjson, number) and sax->number_integer(number);
-            }
+    /// the reference tokens
+    std::vector<std::string> reference_tokens;
+};
+}  // namespace nlohmann
 
-            case 'l':
-            {
-                int32_t number;
-                return get_number(input_format_t::ubjson, number) and sax->number_integer(number);
-            }
+// #include <nlohmann/detail/json_ref.hpp>
 
-            case 'L':
-            {
-                int64_t number;
-                return get_number(input_format_t::ubjson, number) and sax->number_integer(number);
-            }
 
-            case 'd':
-            {
-                float number;
-                return get_number(input_format_t::ubjson, number) and sax->number_float(static_cast<number_float_t>(number), "");
-            }
+#include <initializer_list>
+#include <utility>
 
-            case 'D':
-            {
-                double number;
-                return get_number(input_format_t::ubjson, number) and sax->number_float(static_cast<number_float_t>(number), "");
-            }
+// #include <nlohmann/detail/meta/type_traits.hpp>
 
-            case 'C':  // char
-            {
-                get();
-                if (JSON_UNLIKELY(not unexpect_eof(input_format_t::ubjson, "char")))
-                {
-                    return false;
-                }
-                if (JSON_UNLIKELY(current > 127))
-                {
-                    auto last_token = get_token_string();
-                    return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read, exception_message(input_format_t::ubjson, "byte after 'C' must be in range 0x00..0x7F; last byte: 0x" + last_token, "char")));
-                }
-                string_t s(1, static_cast<char>(current));
-                return sax->string(s);
-            }
 
-            case 'S':  // string
-            {
-                string_t s;
-                return get_ubjson_string(s) and sax->string(s);
-            }
+namespace nlohmann
+{
+namespace detail
+{
+template<typename BasicJsonType>
+class json_ref
+{
+  public:
+    using value_type = BasicJsonType;
 
-            case '[':  // array
-                return get_ubjson_array();
+    json_ref(value_type&& value)
+        : owned_value(std::move(value))
+        , value_ref(&owned_value)
+        , is_rvalue(true)
+    {}
 
-            case '{':  // object
-                return get_ubjson_object();
+    json_ref(const value_type& value)
+        : value_ref(const_cast<value_type*>(&value))
+        , is_rvalue(false)
+    {}
 
-            default: // anything else
-            {
-                auto last_token = get_token_string();
-                return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read, exception_message(input_format_t::ubjson, "invalid byte: 0x" + last_token, "value")));
-            }
-        }
-    }
+    json_ref(std::initializer_list<json_ref> init)
+        : owned_value(init)
+        , value_ref(&owned_value)
+        , is_rvalue(true)
+    {}
 
-    /*!
-    @return whether array creation completed
-    */
-    bool get_ubjson_array()
-    {
-        std::pair<std::size_t, int> size_and_type;
-        if (JSON_UNLIKELY(not get_ubjson_size_type(size_and_type)))
-        {
-            return false;
-        }
+    template <
+        class... Args,
+        enable_if_t<std::is_constructible<value_type, Args...>::value, int> = 0 >
+    json_ref(Args && ... args)
+        : owned_value(std::forward<Args>(args)...)
+        , value_ref(&owned_value)
+        , is_rvalue(true)
+    {}
 
-        if (size_and_type.first != string_t::npos)
-        {
-            if (JSON_UNLIKELY(not sax->start_array(size_and_type.first)))
-            {
-                return false;
-            }
+    // class should be movable only
+    json_ref(json_ref&&) = default;
+    json_ref(const json_ref&) = delete;
+    json_ref& operator=(const json_ref&) = delete;
+    json_ref& operator=(json_ref&&) = delete;
+    ~json_ref() = default;
 
-            if (size_and_type.second != 0)
-            {
-                if (size_and_type.second != 'N')
-                {
-                    for (std::size_t i = 0; i < size_and_type.first; ++i)
-                    {
-                        if (JSON_UNLIKELY(not get_ubjson_value(size_and_type.second)))
-                        {
-                            return false;
-                        }
-                    }
-                }
-            }
-            else
-            {
-                for (std::size_t i = 0; i < size_and_type.first; ++i)
-                {
-                    if (JSON_UNLIKELY(not parse_ubjson_internal()))
-                    {
-                        return false;
-                    }
-                }
-            }
-        }
-        else
+    value_type moved_or_copied() const
+    {
+        if (is_rvalue)
         {
-            if (JSON_UNLIKELY(not sax->start_array(std::size_t(-1))))
-            {
-                return false;
-            }
-
-            while (current != ']')
-            {
-                if (JSON_UNLIKELY(not parse_ubjson_internal(false)))
-                {
-                    return false;
-                }
-                get_ignore_noop();
-            }
+            return std::move(*value_ref);
         }
+        return *value_ref;
+    }
 
-        return sax->end_array();
+    value_type const& operator*() const
+    {
+        return *static_cast<value_type const*>(value_ref);
     }
 
-    /*!
-    @return whether object creation completed
-    */
-    bool get_ubjson_object()
+    value_type const* operator->() const
     {
-        std::pair<std::size_t, int> size_and_type;
-        if (JSON_UNLIKELY(not get_ubjson_size_type(size_and_type)))
-        {
-            return false;
-        }
+        return static_cast<value_type const*>(value_ref);
+    }
 
-        string_t key;
-        if (size_and_type.first != string_t::npos)
-        {
-            if (JSON_UNLIKELY(not sax->start_object(size_and_type.first)))
-            {
-                return false;
-            }
+  private:
+    mutable value_type owned_value = nullptr;
+    value_type* value_ref = nullptr;
+    const bool is_rvalue = true;
+};
+}  // namespace detail
+}  // namespace nlohmann
 
-            if (size_and_type.second != 0)
-            {
-                for (std::size_t i = 0; i < size_and_type.first; ++i)
-                {
-                    if (JSON_UNLIKELY(not get_ubjson_string(key) or not sax->key(key)))
-                    {
-                        return false;
-                    }
-                    if (JSON_UNLIKELY(not get_ubjson_value(size_and_type.second)))
-                    {
-                        return false;
-                    }
-                    key.clear();
-                }
-            }
-            else
-            {
-                for (std::size_t i = 0; i < size_and_type.first; ++i)
-                {
-                    if (JSON_UNLIKELY(not get_ubjson_string(key) or not sax->key(key)))
-                    {
-                        return false;
-                    }
-                    if (JSON_UNLIKELY(not parse_ubjson_internal()))
-                    {
-                        return false;
-                    }
-                    key.clear();
-                }
-            }
-        }
-        else
-        {
-            if (JSON_UNLIKELY(not sax->start_object(std::size_t(-1))))
-            {
-                return false;
-            }
+// #include <nlohmann/detail/macro_scope.hpp>
 
-            while (current != '}')
-            {
-                if (JSON_UNLIKELY(not get_ubjson_string(key, false) or not sax->key(key)))
-                {
-                    return false;
-                }
-                if (JSON_UNLIKELY(not parse_ubjson_internal()))
-                {
-                    return false;
-                }
-                get_ignore_noop();
-                key.clear();
-            }
-        }
+// #include <nlohmann/detail/meta/cpp_future.hpp>
 
-        return sax->end_object();
-    }
+// #include <nlohmann/detail/meta/type_traits.hpp>
 
-    ///////////////////////
-    // Utility functions //
-    ///////////////////////
+// #include <nlohmann/detail/output/binary_writer.hpp>
 
-    /*!
-    @brief get next character from the input
 
-    This function provides the interface to the used input adapter. It does
-    not throw in case the input reached EOF, but returns a -'ve valued
-    `std::char_traits<char>::eof()` in that case.
+#include <algorithm> // reverse
+#include <array> // array
+#include <cstdint> // uint8_t, uint16_t, uint32_t, uint64_t
+#include <cstring> // memcpy
+#include <limits> // numeric_limits
+#include <string> // string
+#include <cmath> // isnan, isinf
 
-    @return character read from the input
-    */
-    int get()
-    {
-        ++chars_read;
-        return (current = ia->get_character());
-    }
+// #include <nlohmann/detail/input/binary_reader.hpp>
 
-    /*!
-    @return character read from the input after ignoring all 'N' entries
-    */
-    int get_ignore_noop()
-    {
-        do
-        {
-            get();
-        }
-        while (current == 'N');
+// #include <nlohmann/detail/macro_scope.hpp>
 
-        return current;
-    }
+// #include <nlohmann/detail/output/output_adapters.hpp>
 
-    /*
-    @brief read a number from the input
 
-    @tparam NumberType the type of the number
-    @param[in] format   the current format (for diagnostics)
-    @param[out] result  number of type @a NumberType
+#include <algorithm> // copy
+#include <cstddef> // size_t
+#include <ios> // streamsize
+#include <iterator> // back_inserter
+#include <memory> // shared_ptr, make_shared
+#include <ostream> // basic_ostream
+#include <string> // basic_string
+#include <vector> // vector
+// #include <nlohmann/detail/macro_scope.hpp>
 
-    @return whether conversion completed
 
-    @note This function needs to respect the system's endianess, because
-          bytes in CBOR, MessagePack, and UBJSON are stored in network order
-          (big endian) and therefore need reordering on little endian systems.
-    */
-    template<typename NumberType, bool InputIsLittleEndian = false>
-    bool get_number(const input_format_t format, NumberType& result)
-    {
-        // step 1: read input into array with system's byte order
-        std::array<uint8_t, sizeof(NumberType)> vec;
-        for (std::size_t i = 0; i < sizeof(NumberType); ++i)
-        {
-            get();
-            if (JSON_UNLIKELY(not unexpect_eof(format, "number")))
-            {
-                return false;
-            }
+namespace nlohmann
+{
+namespace detail
+{
+/// abstract output adapter interface
+template<typename CharType> struct output_adapter_protocol
+{
+    virtual void write_character(CharType c) = 0;
+    virtual void write_characters(const CharType* s, std::size_t length) = 0;
+    virtual ~output_adapter_protocol() = default;
+};
 
-            // reverse byte order prior to conversion if necessary
-            if (is_little_endian && !InputIsLittleEndian)
-            {
-                vec[sizeof(NumberType) - i - 1] = static_cast<uint8_t>(current);
-            }
-            else
-            {
-                vec[i] = static_cast<uint8_t>(current); // LCOV_EXCL_LINE
-            }
-        }
+/// a type to simplify interfaces
+template<typename CharType>
+using output_adapter_t = std::shared_ptr<output_adapter_protocol<CharType>>;
 
-        // step 2: convert array into number of type T and return
-        std::memcpy(&result, vec.data(), sizeof(NumberType));
-        return true;
+/// output adapter for byte vectors
+template<typename CharType>
+class output_vector_adapter : public output_adapter_protocol<CharType>
+{
+  public:
+    explicit output_vector_adapter(std::vector<CharType>& vec) noexcept
+        : v(vec)
+    {}
+
+    void write_character(CharType c) override
+    {
+        v.push_back(c);
     }
 
-    /*!
-    @brief create a string by reading characters from the input
+    JSON_HEDLEY_NON_NULL(2)
+    void write_characters(const CharType* s, std::size_t length) override
+    {
+        std::copy(s, s + length, std::back_inserter(v));
+    }
 
-    @tparam NumberType the type of the number
-    @param[in] format the current format (for diagnostics)
-    @param[in] len number of characters to read
-    @param[out] result string created by reading @a len bytes
+  private:
+    std::vector<CharType>& v;
+};
 
-    @return whether string creation completed
+/// output adapter for output streams
+template<typename CharType>
+class output_stream_adapter : public output_adapter_protocol<CharType>
+{
+  public:
+    explicit output_stream_adapter(std::basic_ostream<CharType>& s) noexcept
+        : stream(s)
+    {}
 
-    @note We can not reserve @a len bytes for the result, because @a len
-          may be too large. Usually, @ref unexpect_eof() detects the end of
-          the input before we run out of string memory.
-    */
-    template<typename NumberType>
-    bool get_string(const input_format_t format,
-                    const NumberType len,
-                    string_t& result)
+    void write_character(CharType c) override
     {
-        bool success = true;
-        std::generate_n(std::back_inserter(result), len, [this, &success, &format]()
-        {
-            get();
-            if (JSON_UNLIKELY(not unexpect_eof(format, "string")))
-            {
-                success = false;
-            }
-            return static_cast<char>(current);
-        });
-        return success;
+        stream.put(c);
     }
 
-    /*!
-    @param[in] format   the current format (for diagnostics)
-    @param[in] context  further context information (for diagnostics)
-    @return whether the last read character is not EOF
-    */
-    bool unexpect_eof(const input_format_t format, const char* context) const
+    JSON_HEDLEY_NON_NULL(2)
+    void write_characters(const CharType* s, std::size_t length) override
     {
-        if (JSON_UNLIKELY(current == std::char_traits<char>::eof()))
-        {
-            return sax->parse_error(chars_read, "<end of file>",
-                                    parse_error::create(110, chars_read, exception_message(format, "unexpected end of input", context)));
-        }
-        return true;
+        stream.write(s, static_cast<std::streamsize>(length));
     }
 
-    /*!
-    @return a string representation of the last read byte
-    */
-    std::string get_token_string() const
+  private:
+    std::basic_ostream<CharType>& stream;
+};
+
+/// output adapter for basic_string
+template<typename CharType, typename StringType = std::basic_string<CharType>>
+class output_string_adapter : public output_adapter_protocol<CharType>
+{
+  public:
+    explicit output_string_adapter(StringType& s) noexcept
+        : str(s)
+    {}
+
+    void write_character(CharType c) override
     {
-        char cr[3];
-        (std::snprintf)(cr, 3, "%.2hhX", static_cast<unsigned char>(current));
-        return std::string{cr};
+        str.push_back(c);
     }
 
-    /*!
-    @param[in] format   the current format
-    @param[in] detail   a detailed error message
-    @param[in] context  further contect information
-    @return a message string to use in the parse_error exceptions
-    */
-    std::string exception_message(const input_format_t format,
-                                  const std::string& detail,
-                                  const std::string& context) const
+    JSON_HEDLEY_NON_NULL(2)
+    void write_characters(const CharType* s, std::size_t length) override
     {
-        std::string error_msg = "syntax error while parsing ";
-
-        switch (format)
-        {
-            case input_format_t::cbor:
-                error_msg += "CBOR";
-                break;
+        str.append(s, length);
+    }
 
-            case input_format_t::msgpack:
-                error_msg += "MessagePack";
-                break;
+  private:
+    StringType& str;
+};
 
-            case input_format_t::ubjson:
-                error_msg += "UBJSON";
-                break;
+template<typename CharType, typename StringType = std::basic_string<CharType>>
+class output_adapter
+{
+  public:
+    output_adapter(std::vector<CharType>& vec)
+        : oa(std::make_shared<output_vector_adapter<CharType>>(vec)) {}
 
-            case input_format_t::bson:
-                error_msg += "BSON";
-                break;
+    output_adapter(std::basic_ostream<CharType>& s)
+        : oa(std::make_shared<output_stream_adapter<CharType>>(s)) {}
 
-            // LCOV_EXCL_START
-            default:
-                assert(false);
-                // LCOV_EXCL_STOP
-        }
+    output_adapter(StringType& s)
+        : oa(std::make_shared<output_string_adapter<CharType, StringType>>(s)) {}
 
-        return error_msg + " " + context + ": " + detail;
+    operator output_adapter_t<CharType>()
+    {
+        return oa;
     }
 
   private:
-    /// input adapter
-    input_adapter_t ia = nullptr;
-
-    /// the current character
-    int current = std::char_traits<char>::eof();
-
-    /// the number of characters read
-    std::size_t chars_read = 0;
-
-    /// whether we can assume little endianess
-    const bool is_little_endian = little_endianess();
-
-    /// the SAX parser
-    json_sax_t* sax = nullptr;
+    output_adapter_t<CharType> oa = nullptr;
 };
 }  // namespace detail
 }  // namespace nlohmann
 
-// #include <nlohmann/detail/output/binary_writer.hpp>
-
-
-#include <algorithm> // reverse
-#include <array> // array
-#include <cstdint> // uint8_t, uint16_t, uint32_t, uint64_t
-#include <cstring> // memcpy
-#include <limits> // numeric_limits
-
-// #include <nlohmann/detail/input/binary_reader.hpp>
-
-// #include <nlohmann/detail/output/output_adapters.hpp>
-
 
 namespace nlohmann
 {
@@ -8465,6 +12752,8 @@ template<typename BasicJsonType, typename CharType>
 class binary_writer
 {
     using string_t = typename BasicJsonType::string_t;
+    using binary_t = typename BasicJsonType::binary_t;
+    using number_float_t = typename BasicJsonType::number_float_t;
 
   public:
     /*!
@@ -8474,7 +12763,7 @@ class binary_writer
     */
     explicit binary_writer(output_adapter_t<CharType> adapter) : oa(adapter)
     {
-        assert(oa);
+        JSON_ASSERT(oa);
     }
 
     /*!
@@ -8528,27 +12817,27 @@ class binary_writer
                     // code from the value_t::number_unsigned case here.
                     if (j.m_value.number_integer <= 0x17)
                     {
-                        write_number(static_cast<uint8_t>(j.m_value.number_integer));
+                        write_number(static_cast<std::uint8_t>(j.m_value.number_integer));
                     }
-                    else if (j.m_value.number_integer <= (std::numeric_limits<uint8_t>::max)())
+                    else if (j.m_value.number_integer <= (std::numeric_limits<std::uint8_t>::max)())
                     {
                         oa->write_character(to_char_type(0x18));
-                        write_number(static_cast<uint8_t>(j.m_value.number_integer));
+                        write_number(static_cast<std::uint8_t>(j.m_value.number_integer));
                     }
-                    else if (j.m_value.number_integer <= (std::numeric_limits<uint16_t>::max)())
+                    else if (j.m_value.number_integer <= (std::numeric_limits<std::uint16_t>::max)())
                     {
                         oa->write_character(to_char_type(0x19));
-                        write_number(static_cast<uint16_t>(j.m_value.number_integer));
+                        write_number(static_cast<std::uint16_t>(j.m_value.number_integer));
                     }
-                    else if (j.m_value.number_integer <= (std::numeric_limits<uint32_t>::max)())
+                    else if (j.m_value.number_integer <= (std::numeric_limits<std::uint32_t>::max)())
                     {
                         oa->write_character(to_char_type(0x1A));
-                        write_number(static_cast<uint32_t>(j.m_value.number_integer));
+                        write_number(static_cast<std::uint32_t>(j.m_value.number_integer));
                     }
                     else
                     {
                         oa->write_character(to_char_type(0x1B));
-                        write_number(static_cast<uint64_t>(j.m_value.number_integer));
+                        write_number(static_cast<std::uint64_t>(j.m_value.number_integer));
                     }
                 }
                 else
@@ -8558,27 +12847,27 @@ class binary_writer
                     const auto positive_number = -1 - j.m_value.number_integer;
                     if (j.m_value.number_integer >= -24)
                     {
-                        write_number(static_cast<uint8_t>(0x20 + positive_number));
+                        write_number(static_cast<std::uint8_t>(0x20 + positive_number));
                     }
-                    else if (positive_number <= (std::numeric_limits<uint8_t>::max)())
+                    else if (positive_number <= (std::numeric_limits<std::uint8_t>::max)())
                     {
                         oa->write_character(to_char_type(0x38));
-                        write_number(static_cast<uint8_t>(positive_number));
+                        write_number(static_cast<std::uint8_t>(positive_number));
                     }
-                    else if (positive_number <= (std::numeric_limits<uint16_t>::max)())
+                    else if (positive_number <= (std::numeric_limits<std::uint16_t>::max)())
                     {
                         oa->write_character(to_char_type(0x39));
-                        write_number(static_cast<uint16_t>(positive_number));
+                        write_number(static_cast<std::uint16_t>(positive_number));
                     }
-                    else if (positive_number <= (std::numeric_limits<uint32_t>::max)())
+                    else if (positive_number <= (std::numeric_limits<std::uint32_t>::max)())
                     {
                         oa->write_character(to_char_type(0x3A));
-                        write_number(static_cast<uint32_t>(positive_number));
+                        write_number(static_cast<std::uint32_t>(positive_number));
                     }
                     else
                     {
                         oa->write_character(to_char_type(0x3B));
-                        write_number(static_cast<uint64_t>(positive_number));
+                        write_number(static_cast<std::uint64_t>(positive_number));
                     }
                 }
                 break;
@@ -8588,35 +12877,51 @@ class binary_writer
             {
                 if (j.m_value.number_unsigned <= 0x17)
                 {
-                    write_number(static_cast<uint8_t>(j.m_value.number_unsigned));
+                    write_number(static_cast<std::uint8_t>(j.m_value.number_unsigned));
                 }
-                else if (j.m_value.number_unsigned <= (std::numeric_limits<uint8_t>::max)())
+                else if (j.m_value.number_unsigned <= (std::numeric_limits<std::uint8_t>::max)())
                 {
                     oa->write_character(to_char_type(0x18));
-                    write_number(static_cast<uint8_t>(j.m_value.number_unsigned));
+                    write_number(static_cast<std::uint8_t>(j.m_value.number_unsigned));
                 }
-                else if (j.m_value.number_unsigned <= (std::numeric_limits<uint16_t>::max)())
+                else if (j.m_value.number_unsigned <= (std::numeric_limits<std::uint16_t>::max)())
                 {
                     oa->write_character(to_char_type(0x19));
-                    write_number(static_cast<uint16_t>(j.m_value.number_unsigned));
+                    write_number(static_cast<std::uint16_t>(j.m_value.number_unsigned));
                 }
-                else if (j.m_value.number_unsigned <= (std::numeric_limits<uint32_t>::max)())
+                else if (j.m_value.number_unsigned <= (std::numeric_limits<std::uint32_t>::max)())
                 {
                     oa->write_character(to_char_type(0x1A));
-                    write_number(static_cast<uint32_t>(j.m_value.number_unsigned));
+                    write_number(static_cast<std::uint32_t>(j.m_value.number_unsigned));
                 }
                 else
                 {
                     oa->write_character(to_char_type(0x1B));
-                    write_number(static_cast<uint64_t>(j.m_value.number_unsigned));
+                    write_number(static_cast<std::uint64_t>(j.m_value.number_unsigned));
                 }
                 break;
             }
 
             case value_t::number_float:
             {
-                oa->write_character(get_cbor_float_prefix(j.m_value.number_float));
-                write_number(j.m_value.number_float);
+                if (std::isnan(j.m_value.number_float))
+                {
+                    // NaN is 0xf97e00 in CBOR
+                    oa->write_character(to_char_type(0xF9));
+                    oa->write_character(to_char_type(0x7E));
+                    oa->write_character(to_char_type(0x00));
+                }
+                else if (std::isinf(j.m_value.number_float))
+                {
+                    // Infinity is 0xf97c00, -Infinity is 0xf9fc00
+                    oa->write_character(to_char_type(0xf9));
+                    oa->write_character(j.m_value.number_float > 0 ? to_char_type(0x7C) : to_char_type(0xFC));
+                    oa->write_character(to_char_type(0x00));
+                }
+                else
+                {
+                    write_compact_float(j.m_value.number_float, detail::input_format_t::cbor);
+                }
                 break;
             }
 
@@ -8626,28 +12931,28 @@ class binary_writer
                 const auto N = j.m_value.string->size();
                 if (N <= 0x17)
                 {
-                    write_number(static_cast<uint8_t>(0x60 + N));
+                    write_number(static_cast<std::uint8_t>(0x60 + N));
                 }
-                else if (N <= (std::numeric_limits<uint8_t>::max)())
+                else if (N <= (std::numeric_limits<std::uint8_t>::max)())
                 {
                     oa->write_character(to_char_type(0x78));
-                    write_number(static_cast<uint8_t>(N));
+                    write_number(static_cast<std::uint8_t>(N));
                 }
-                else if (N <= (std::numeric_limits<uint16_t>::max)())
+                else if (N <= (std::numeric_limits<std::uint16_t>::max)())
                 {
                     oa->write_character(to_char_type(0x79));
-                    write_number(static_cast<uint16_t>(N));
+                    write_number(static_cast<std::uint16_t>(N));
                 }
-                else if (N <= (std::numeric_limits<uint32_t>::max)())
+                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
                 {
                     oa->write_character(to_char_type(0x7A));
-                    write_number(static_cast<uint32_t>(N));
+                    write_number(static_cast<std::uint32_t>(N));
                 }
                 // LCOV_EXCL_START
-                else if (N <= (std::numeric_limits<uint64_t>::max)())
+                else if (N <= (std::numeric_limits<std::uint64_t>::max)())
                 {
                     oa->write_character(to_char_type(0x7B));
-                    write_number(static_cast<uint64_t>(N));
+                    write_number(static_cast<std::uint64_t>(N));
                 }
                 // LCOV_EXCL_STOP
 
@@ -8664,28 +12969,28 @@ class binary_writer
                 const auto N = j.m_value.array->size();
                 if (N <= 0x17)
                 {
-                    write_number(static_cast<uint8_t>(0x80 + N));
+                    write_number(static_cast<std::uint8_t>(0x80 + N));
                 }
-                else if (N <= (std::numeric_limits<uint8_t>::max)())
+                else if (N <= (std::numeric_limits<std::uint8_t>::max)())
                 {
                     oa->write_character(to_char_type(0x98));
-                    write_number(static_cast<uint8_t>(N));
+                    write_number(static_cast<std::uint8_t>(N));
                 }
-                else if (N <= (std::numeric_limits<uint16_t>::max)())
+                else if (N <= (std::numeric_limits<std::uint16_t>::max)())
                 {
                     oa->write_character(to_char_type(0x99));
-                    write_number(static_cast<uint16_t>(N));
+                    write_number(static_cast<std::uint16_t>(N));
                 }
-                else if (N <= (std::numeric_limits<uint32_t>::max)())
+                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
                 {
                     oa->write_character(to_char_type(0x9A));
-                    write_number(static_cast<uint32_t>(N));
+                    write_number(static_cast<std::uint32_t>(N));
                 }
                 // LCOV_EXCL_START
-                else if (N <= (std::numeric_limits<uint64_t>::max)())
+                else if (N <= (std::numeric_limits<std::uint64_t>::max)())
                 {
                     oa->write_character(to_char_type(0x9B));
-                    write_number(static_cast<uint64_t>(N));
+                    write_number(static_cast<std::uint64_t>(N));
                 }
                 // LCOV_EXCL_STOP
 
@@ -8697,34 +13002,79 @@ class binary_writer
                 break;
             }
 
+            case value_t::binary:
+            {
+                if (j.m_value.binary->has_subtype())
+                {
+                    write_number(static_cast<std::uint8_t>(0xd8));
+                    write_number(j.m_value.binary->subtype());
+                }
+
+                // step 1: write control byte and the binary array size
+                const auto N = j.m_value.binary->size();
+                if (N <= 0x17)
+                {
+                    write_number(static_cast<std::uint8_t>(0x40 + N));
+                }
+                else if (N <= (std::numeric_limits<std::uint8_t>::max)())
+                {
+                    oa->write_character(to_char_type(0x58));
+                    write_number(static_cast<std::uint8_t>(N));
+                }
+                else if (N <= (std::numeric_limits<std::uint16_t>::max)())
+                {
+                    oa->write_character(to_char_type(0x59));
+                    write_number(static_cast<std::uint16_t>(N));
+                }
+                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
+                {
+                    oa->write_character(to_char_type(0x5A));
+                    write_number(static_cast<std::uint32_t>(N));
+                }
+                // LCOV_EXCL_START
+                else if (N <= (std::numeric_limits<std::uint64_t>::max)())
+                {
+                    oa->write_character(to_char_type(0x5B));
+                    write_number(static_cast<std::uint64_t>(N));
+                }
+                // LCOV_EXCL_STOP
+
+                // step 2: write each element
+                oa->write_characters(
+                    reinterpret_cast<const CharType*>(j.m_value.binary->data()),
+                    N);
+
+                break;
+            }
+
             case value_t::object:
             {
                 // step 1: write control byte and the object size
                 const auto N = j.m_value.object->size();
                 if (N <= 0x17)
                 {
-                    write_number(static_cast<uint8_t>(0xA0 + N));
+                    write_number(static_cast<std::uint8_t>(0xA0 + N));
                 }
-                else if (N <= (std::numeric_limits<uint8_t>::max)())
+                else if (N <= (std::numeric_limits<std::uint8_t>::max)())
                 {
                     oa->write_character(to_char_type(0xB8));
-                    write_number(static_cast<uint8_t>(N));
+                    write_number(static_cast<std::uint8_t>(N));
                 }
-                else if (N <= (std::numeric_limits<uint16_t>::max)())
+                else if (N <= (std::numeric_limits<std::uint16_t>::max)())
                 {
                     oa->write_character(to_char_type(0xB9));
-                    write_number(static_cast<uint16_t>(N));
+                    write_number(static_cast<std::uint16_t>(N));
                 }
-                else if (N <= (std::numeric_limits<uint32_t>::max)())
+                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
                 {
                     oa->write_character(to_char_type(0xBA));
-                    write_number(static_cast<uint32_t>(N));
+                    write_number(static_cast<std::uint32_t>(N));
                 }
                 // LCOV_EXCL_START
-                else if (N <= (std::numeric_limits<uint64_t>::max)())
+                else if (N <= (std::numeric_limits<std::uint64_t>::max)())
                 {
                     oa->write_character(to_char_type(0xBB));
-                    write_number(static_cast<uint64_t>(N));
+                    write_number(static_cast<std::uint64_t>(N));
                 }
                 // LCOV_EXCL_STOP
 
@@ -8773,31 +13123,31 @@ class binary_writer
                     if (j.m_value.number_unsigned < 128)
                     {
                         // positive fixnum
-                        write_number(static_cast<uint8_t>(j.m_value.number_integer));
+                        write_number(static_cast<std::uint8_t>(j.m_value.number_integer));
                     }
-                    else if (j.m_value.number_unsigned <= (std::numeric_limits<uint8_t>::max)())
+                    else if (j.m_value.number_unsigned <= (std::numeric_limits<std::uint8_t>::max)())
                     {
                         // uint 8
                         oa->write_character(to_char_type(0xCC));
-                        write_number(static_cast<uint8_t>(j.m_value.number_integer));
+                        write_number(static_cast<std::uint8_t>(j.m_value.number_integer));
                     }
-                    else if (j.m_value.number_unsigned <= (std::numeric_limits<uint16_t>::max)())
+                    else if (j.m_value.number_unsigned <= (std::numeric_limits<std::uint16_t>::max)())
                     {
                         // uint 16
                         oa->write_character(to_char_type(0xCD));
-                        write_number(static_cast<uint16_t>(j.m_value.number_integer));
+                        write_number(static_cast<std::uint16_t>(j.m_value.number_integer));
                     }
-                    else if (j.m_value.number_unsigned <= (std::numeric_limits<uint32_t>::max)())
+                    else if (j.m_value.number_unsigned <= (std::numeric_limits<std::uint32_t>::max)())
                     {
                         // uint 32
                         oa->write_character(to_char_type(0xCE));
-                        write_number(static_cast<uint32_t>(j.m_value.number_integer));
+                        write_number(static_cast<std::uint32_t>(j.m_value.number_integer));
                     }
-                    else if (j.m_value.number_unsigned <= (std::numeric_limits<uint64_t>::max)())
+                    else if (j.m_value.number_unsigned <= (std::numeric_limits<std::uint64_t>::max)())
                     {
                         // uint 64
                         oa->write_character(to_char_type(0xCF));
-                        write_number(static_cast<uint64_t>(j.m_value.number_integer));
+                        write_number(static_cast<std::uint64_t>(j.m_value.number_integer));
                     }
                 }
                 else
@@ -8805,35 +13155,35 @@ class binary_writer
                     if (j.m_value.number_integer >= -32)
                     {
                         // negative fixnum
-                        write_number(static_cast<int8_t>(j.m_value.number_integer));
+                        write_number(static_cast<std::int8_t>(j.m_value.number_integer));
                     }
-                    else if (j.m_value.number_integer >= (std::numeric_limits<int8_t>::min)() and
-                             j.m_value.number_integer <= (std::numeric_limits<int8_t>::max)())
+                    else if (j.m_value.number_integer >= (std::numeric_limits<std::int8_t>::min)() &&
+                             j.m_value.number_integer <= (std::numeric_limits<std::int8_t>::max)())
                     {
                         // int 8
                         oa->write_character(to_char_type(0xD0));
-                        write_number(static_cast<int8_t>(j.m_value.number_integer));
+                        write_number(static_cast<std::int8_t>(j.m_value.number_integer));
                     }
-                    else if (j.m_value.number_integer >= (std::numeric_limits<int16_t>::min)() and
-                             j.m_value.number_integer <= (std::numeric_limits<int16_t>::max)())
+                    else if (j.m_value.number_integer >= (std::numeric_limits<std::int16_t>::min)() &&
+                             j.m_value.number_integer <= (std::numeric_limits<std::int16_t>::max)())
                     {
                         // int 16
                         oa->write_character(to_char_type(0xD1));
-                        write_number(static_cast<int16_t>(j.m_value.number_integer));
+                        write_number(static_cast<std::int16_t>(j.m_value.number_integer));
                     }
-                    else if (j.m_value.number_integer >= (std::numeric_limits<int32_t>::min)() and
-                             j.m_value.number_integer <= (std::numeric_limits<int32_t>::max)())
+                    else if (j.m_value.number_integer >= (std::numeric_limits<std::int32_t>::min)() &&
+                             j.m_value.number_integer <= (std::numeric_limits<std::int32_t>::max)())
                     {
                         // int 32
                         oa->write_character(to_char_type(0xD2));
-                        write_number(static_cast<int32_t>(j.m_value.number_integer));
+                        write_number(static_cast<std::int32_t>(j.m_value.number_integer));
                     }
-                    else if (j.m_value.number_integer >= (std::numeric_limits<int64_t>::min)() and
-                             j.m_value.number_integer <= (std::numeric_limits<int64_t>::max)())
+                    else if (j.m_value.number_integer >= (std::numeric_limits<std::int64_t>::min)() &&
+                             j.m_value.number_integer <= (std::numeric_limits<std::int64_t>::max)())
                     {
                         // int 64
                         oa->write_character(to_char_type(0xD3));
-                        write_number(static_cast<int64_t>(j.m_value.number_integer));
+                        write_number(static_cast<std::int64_t>(j.m_value.number_integer));
                     }
                 }
                 break;
@@ -8844,39 +13194,38 @@ class binary_writer
                 if (j.m_value.number_unsigned < 128)
                 {
                     // positive fixnum
-                    write_number(static_cast<uint8_t>(j.m_value.number_integer));
+                    write_number(static_cast<std::uint8_t>(j.m_value.number_integer));
                 }
-                else if (j.m_value.number_unsigned <= (std::numeric_limits<uint8_t>::max)())
+                else if (j.m_value.number_unsigned <= (std::numeric_limits<std::uint8_t>::max)())
                 {
                     // uint 8
                     oa->write_character(to_char_type(0xCC));
-                    write_number(static_cast<uint8_t>(j.m_value.number_integer));
+                    write_number(static_cast<std::uint8_t>(j.m_value.number_integer));
                 }
-                else if (j.m_value.number_unsigned <= (std::numeric_limits<uint16_t>::max)())
+                else if (j.m_value.number_unsigned <= (std::numeric_limits<std::uint16_t>::max)())
                 {
                     // uint 16
                     oa->write_character(to_char_type(0xCD));
-                    write_number(static_cast<uint16_t>(j.m_value.number_integer));
+                    write_number(static_cast<std::uint16_t>(j.m_value.number_integer));
                 }
-                else if (j.m_value.number_unsigned <= (std::numeric_limits<uint32_t>::max)())
+                else if (j.m_value.number_unsigned <= (std::numeric_limits<std::uint32_t>::max)())
                 {
                     // uint 32
                     oa->write_character(to_char_type(0xCE));
-                    write_number(static_cast<uint32_t>(j.m_value.number_integer));
+                    write_number(static_cast<std::uint32_t>(j.m_value.number_integer));
                 }
-                else if (j.m_value.number_unsigned <= (std::numeric_limits<uint64_t>::max)())
+                else if (j.m_value.number_unsigned <= (std::numeric_limits<std::uint64_t>::max)())
                 {
                     // uint 64
                     oa->write_character(to_char_type(0xCF));
-                    write_number(static_cast<uint64_t>(j.m_value.number_integer));
+                    write_number(static_cast<std::uint64_t>(j.m_value.number_integer));
                 }
                 break;
             }
 
             case value_t::number_float:
             {
-                oa->write_character(get_msgpack_float_prefix(j.m_value.number_float));
-                write_number(j.m_value.number_float);
+                write_compact_float(j.m_value.number_float, detail::input_format_t::msgpack);
                 break;
             }
 
@@ -8887,25 +13236,25 @@ class binary_writer
                 if (N <= 31)
                 {
                     // fixstr
-                    write_number(static_cast<uint8_t>(0xA0 | N));
+                    write_number(static_cast<std::uint8_t>(0xA0 | N));
                 }
-                else if (N <= (std::numeric_limits<uint8_t>::max)())
+                else if (N <= (std::numeric_limits<std::uint8_t>::max)())
                 {
                     // str 8
                     oa->write_character(to_char_type(0xD9));
-                    write_number(static_cast<uint8_t>(N));
+                    write_number(static_cast<std::uint8_t>(N));
                 }
-                else if (N <= (std::numeric_limits<uint16_t>::max)())
+                else if (N <= (std::numeric_limits<std::uint16_t>::max)())
                 {
                     // str 16
                     oa->write_character(to_char_type(0xDA));
-                    write_number(static_cast<uint16_t>(N));
+                    write_number(static_cast<std::uint16_t>(N));
                 }
-                else if (N <= (std::numeric_limits<uint32_t>::max)())
+                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
                 {
                     // str 32
                     oa->write_character(to_char_type(0xDB));
-                    write_number(static_cast<uint32_t>(N));
+                    write_number(static_cast<std::uint32_t>(N));
                 }
 
                 // step 2: write the string
@@ -8922,19 +13271,19 @@ class binary_writer
                 if (N <= 15)
                 {
                     // fixarray
-                    write_number(static_cast<uint8_t>(0x90 | N));
+                    write_number(static_cast<std::uint8_t>(0x90 | N));
                 }
-                else if (N <= (std::numeric_limits<uint16_t>::max)())
+                else if (N <= (std::numeric_limits<std::uint16_t>::max)())
                 {
                     // array 16
                     oa->write_character(to_char_type(0xDC));
-                    write_number(static_cast<uint16_t>(N));
+                    write_number(static_cast<std::uint16_t>(N));
                 }
-                else if (N <= (std::numeric_limits<uint32_t>::max)())
+                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
                 {
                     // array 32
                     oa->write_character(to_char_type(0xDD));
-                    write_number(static_cast<uint32_t>(N));
+                    write_number(static_cast<std::uint32_t>(N));
                 }
 
                 // step 2: write each element
@@ -8945,6 +13294,89 @@ class binary_writer
                 break;
             }
 
+            case value_t::binary:
+            {
+                // step 0: determine if the binary type has a set subtype to
+                // determine whether or not to use the ext or fixext types
+                const bool use_ext = j.m_value.binary->has_subtype();
+
+                // step 1: write control byte and the byte string length
+                const auto N = j.m_value.binary->size();
+                if (N <= (std::numeric_limits<std::uint8_t>::max)())
+                {
+                    std::uint8_t output_type{};
+                    bool fixed = true;
+                    if (use_ext)
+                    {
+                        switch (N)
+                        {
+                            case 1:
+                                output_type = 0xD4; // fixext 1
+                                break;
+                            case 2:
+                                output_type = 0xD5; // fixext 2
+                                break;
+                            case 4:
+                                output_type = 0xD6; // fixext 4
+                                break;
+                            case 8:
+                                output_type = 0xD7; // fixext 8
+                                break;
+                            case 16:
+                                output_type = 0xD8; // fixext 16
+                                break;
+                            default:
+                                output_type = 0xC7; // ext 8
+                                fixed = false;
+                                break;
+                        }
+
+                    }
+                    else
+                    {
+                        output_type = 0xC4; // bin 8
+                        fixed = false;
+                    }
+
+                    oa->write_character(to_char_type(output_type));
+                    if (!fixed)
+                    {
+                        write_number(static_cast<std::uint8_t>(N));
+                    }
+                }
+                else if (N <= (std::numeric_limits<std::uint16_t>::max)())
+                {
+                    std::uint8_t output_type = use_ext
+                                               ? 0xC8 // ext 16
+                                               : 0xC5; // bin 16
+
+                    oa->write_character(to_char_type(output_type));
+                    write_number(static_cast<std::uint16_t>(N));
+                }
+                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
+                {
+                    std::uint8_t output_type = use_ext
+                                               ? 0xC9 // ext 32
+                                               : 0xC6; // bin 32
+
+                    oa->write_character(to_char_type(output_type));
+                    write_number(static_cast<std::uint32_t>(N));
+                }
+
+                // step 1.5: if this is an ext type, write the subtype
+                if (use_ext)
+                {
+                    write_number(static_cast<std::int8_t>(j.m_value.binary->subtype()));
+                }
+
+                // step 2: write the byte string
+                oa->write_characters(
+                    reinterpret_cast<const CharType*>(j.m_value.binary->data()),
+                    N);
+
+                break;
+            }
+
             case value_t::object:
             {
                 // step 1: write control byte and the object size
@@ -8952,19 +13384,19 @@ class binary_writer
                 if (N <= 15)
                 {
                     // fixmap
-                    write_number(static_cast<uint8_t>(0x80 | (N & 0xF)));
+                    write_number(static_cast<std::uint8_t>(0x80 | (N & 0xF)));
                 }
-                else if (N <= (std::numeric_limits<uint16_t>::max)())
+                else if (N <= (std::numeric_limits<std::uint16_t>::max)())
                 {
                     // map 16
                     oa->write_character(to_char_type(0xDE));
-                    write_number(static_cast<uint16_t>(N));
+                    write_number(static_cast<std::uint16_t>(N));
                 }
-                else if (N <= (std::numeric_limits<uint32_t>::max)())
+                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
                 {
                     // map 32
                     oa->write_character(to_char_type(0xDF));
-                    write_number(static_cast<uint32_t>(N));
+                    write_number(static_cast<std::uint32_t>(N));
                 }
 
                 // step 2: write each element
@@ -9051,9 +13483,9 @@ class binary_writer
                 }
 
                 bool prefix_required = true;
-                if (use_type and not j.m_value.array->empty())
+                if (use_type && !j.m_value.array->empty())
                 {
-                    assert(use_count);
+                    JSON_ASSERT(use_count);
                     const CharType first_prefix = ubjson_prefix(j.front());
                     const bool same_prefix = std::all_of(j.begin() + 1, j.end(),
                                                          [this, first_prefix](const BasicJsonType & v)
@@ -9080,7 +13512,50 @@ class binary_writer
                     write_ubjson(el, use_count, use_type, prefix_required);
                 }
 
-                if (not use_count)
+                if (!use_count)
+                {
+                    oa->write_character(to_char_type(']'));
+                }
+
+                break;
+            }
+
+            case value_t::binary:
+            {
+                if (add_prefix)
+                {
+                    oa->write_character(to_char_type('['));
+                }
+
+                if (use_type && !j.m_value.binary->empty())
+                {
+                    JSON_ASSERT(use_count);
+                    oa->write_character(to_char_type('$'));
+                    oa->write_character('U');
+                }
+
+                if (use_count)
+                {
+                    oa->write_character(to_char_type('#'));
+                    write_number_with_ubjson_prefix(j.m_value.binary->size(), true);
+                }
+
+                if (use_type)
+                {
+                    oa->write_characters(
+                        reinterpret_cast<const CharType*>(j.m_value.binary->data()),
+                        j.m_value.binary->size());
+                }
+                else
+                {
+                    for (size_t i = 0; i < j.m_value.binary->size(); ++i)
+                    {
+                        oa->write_character(to_char_type('U'));
+                        oa->write_character(j.m_value.binary->data()[i]);
+                    }
+                }
+
+                if (!use_count)
                 {
                     oa->write_character(to_char_type(']'));
                 }
@@ -9096,9 +13571,9 @@ class binary_writer
                 }
 
                 bool prefix_required = true;
-                if (use_type and not j.m_value.object->empty())
+                if (use_type && !j.m_value.object->empty())
                 {
-                    assert(use_count);
+                    JSON_ASSERT(use_count);
                     const CharType first_prefix = ubjson_prefix(j.front());
                     const bool same_prefix = std::all_of(j.begin(), j.end(),
                                                          [this, first_prefix](const BasicJsonType & v)
@@ -9129,7 +13604,7 @@ class binary_writer
                     write_ubjson(el.second, use_count, use_type, prefix_required);
                 }
 
-                if (not use_count)
+                if (!use_count)
                 {
                     oa->write_character(to_char_type('}'));
                 }
@@ -9154,7 +13629,7 @@ class binary_writer
     static std::size_t calc_bson_entry_header_size(const string_t& name)
     {
         const auto it = name.find(static_cast<typename string_t::value_type>(0));
-        if (JSON_UNLIKELY(it != BasicJsonType::string_t::npos))
+        if (JSON_HEDLEY_UNLIKELY(it != BasicJsonType::string_t::npos))
         {
             JSON_THROW(out_of_range::create(409,
                                             "BSON key cannot contain code point U+0000 (at byte " + std::to_string(it) + ")"));
@@ -9230,14 +13705,9 @@ class binary_writer
     */
     static std::size_t calc_bson_integer_size(const std::int64_t value)
     {
-        if ((std::numeric_limits<std::int32_t>::min)() <= value and value <= (std::numeric_limits<std::int32_t>::max)())
-        {
-            return sizeof(std::int32_t);
-        }
-        else
-        {
-            return sizeof(std::int64_t);
-        }
+        return (std::numeric_limits<std::int32_t>::min)() <= value && value <= (std::numeric_limits<std::int32_t>::max)()
+               ? sizeof(std::int32_t)
+               : sizeof(std::int64_t);
     }
 
     /*!
@@ -9246,7 +13716,7 @@ class binary_writer
     void write_bson_integer(const string_t& name,
                             const std::int64_t value)
     {
-        if ((std::numeric_limits<std::int32_t>::min)() <= value and value <= (std::numeric_limits<std::int32_t>::max)())
+        if ((std::numeric_limits<std::int32_t>::min)() <= value && value <= (std::numeric_limits<std::int32_t>::max)())
         {
             write_bson_entry_header(name, 0x10); // int32
             write_number<std::int32_t, true>(static_cast<std::int32_t>(value));
@@ -9305,18 +13775,25 @@ class binary_writer
     */
     static std::size_t calc_bson_array_size(const typename BasicJsonType::array_t& value)
     {
-        std::size_t embedded_document_size = 0ul;
         std::size_t array_index = 0ul;
 
-        for (const auto& el : value)
+        const std::size_t embedded_document_size = std::accumulate(std::begin(value), std::end(value), std::size_t(0), [&array_index](std::size_t result, const typename BasicJsonType::array_t::value_type & el)
         {
-            embedded_document_size += calc_bson_element_size(std::to_string(array_index++), el);
-        }
+            return result + calc_bson_element_size(std::to_string(array_index++), el);
+        });
 
         return sizeof(std::int32_t) + embedded_document_size + 1ul;
     }
 
     /*!
+    @return The size of the BSON-encoded binary array @a value
+    */
+    static std::size_t calc_bson_binary_size(const typename BasicJsonType::binary_t& value)
+    {
+        return sizeof(std::int32_t) + value.size() + 1ul;
+    }
+
+    /*!
     @brief Writes a BSON element with key @a name and array @a value
     */
     void write_bson_array(const string_t& name,
@@ -9336,6 +13813,20 @@ class binary_writer
     }
 
     /*!
+    @brief Writes a BSON element with key @a name and binary value @a value
+    */
+    void write_bson_binary(const string_t& name,
+                           const binary_t& value)
+    {
+        write_bson_entry_header(name, 0x05);
+
+        write_number<std::int32_t, true>(static_cast<std::int32_t>(value.size()));
+        write_number(value.has_subtype() ? value.subtype() : std::uint8_t(0x00));
+
+        oa->write_characters(reinterpret_cast<const CharType*>(value.data()), value.size());
+    }
+
+    /*!
     @brief Calculates the size necessary to serialize the JSON value @a j with its @a name
     @return The calculated size for the BSON document entry for @a j with the given @a name.
     */
@@ -9351,6 +13842,9 @@ class binary_writer
             case value_t::array:
                 return header_size + calc_bson_array_size(*j.m_value.array);
 
+            case value_t::binary:
+                return header_size + calc_bson_binary_size(*j.m_value.binary);
+
             case value_t::boolean:
                 return header_size + 1ul;
 
@@ -9371,10 +13865,10 @@ class binary_writer
 
             // LCOV_EXCL_START
             default:
-                assert(false);
+                JSON_ASSERT(false);
                 return 0ul;
                 // LCOV_EXCL_STOP
-        };
+        }
     }
 
     /*!
@@ -9395,6 +13889,9 @@ class binary_writer
             case value_t::array:
                 return write_bson_array(name, *j.m_value.array);
 
+            case value_t::binary:
+                return write_bson_binary(name, *j.m_value.binary);
+
             case value_t::boolean:
                 return write_bson_boolean(name, j.m_value.boolean);
 
@@ -9415,10 +13912,10 @@ class binary_writer
 
             // LCOV_EXCL_START
             default:
-                assert(false);
+                JSON_ASSERT(false);
                 return;
                 // LCOV_EXCL_STOP
-        };
+        }
     }
 
     /*!
@@ -9429,7 +13926,7 @@ class binary_writer
     */
     static std::size_t calc_bson_object_size(const typename BasicJsonType::object_t& value)
     {
-        std::size_t document_size = std::accumulate(value.begin(), value.end(), 0ul,
+        std::size_t document_size = std::accumulate(value.begin(), value.end(), std::size_t(0),
                                     [](size_t result, const typename BasicJsonType::object_t::value_type & el)
         {
             return result += calc_bson_element_size(el.first, el.second);
@@ -9505,115 +14002,129 @@ class binary_writer
     void write_number_with_ubjson_prefix(const NumberType n,
                                          const bool add_prefix)
     {
-        if (n <= static_cast<uint64_t>((std::numeric_limits<int8_t>::max)()))
+        if (n <= static_cast<std::uint64_t>((std::numeric_limits<std::int8_t>::max)()))
         {
             if (add_prefix)
             {
                 oa->write_character(to_char_type('i'));  // int8
             }
-            write_number(static_cast<uint8_t>(n));
+            write_number(static_cast<std::uint8_t>(n));
         }
-        else if (n <= (std::numeric_limits<uint8_t>::max)())
+        else if (n <= (std::numeric_limits<std::uint8_t>::max)())
         {
             if (add_prefix)
             {
                 oa->write_character(to_char_type('U'));  // uint8
             }
-            write_number(static_cast<uint8_t>(n));
+            write_number(static_cast<std::uint8_t>(n));
         }
-        else if (n <= static_cast<uint64_t>((std::numeric_limits<int16_t>::max)()))
+        else if (n <= static_cast<std::uint64_t>((std::numeric_limits<std::int16_t>::max)()))
         {
             if (add_prefix)
             {
                 oa->write_character(to_char_type('I'));  // int16
             }
-            write_number(static_cast<int16_t>(n));
+            write_number(static_cast<std::int16_t>(n));
         }
-        else if (n <= static_cast<uint64_t>((std::numeric_limits<int32_t>::max)()))
+        else if (n <= static_cast<std::uint64_t>((std::numeric_limits<std::int32_t>::max)()))
         {
             if (add_prefix)
             {
                 oa->write_character(to_char_type('l'));  // int32
             }
-            write_number(static_cast<int32_t>(n));
+            write_number(static_cast<std::int32_t>(n));
         }
-        else if (n <= static_cast<uint64_t>((std::numeric_limits<int64_t>::max)()))
+        else if (n <= static_cast<std::uint64_t>((std::numeric_limits<std::int64_t>::max)()))
         {
             if (add_prefix)
             {
                 oa->write_character(to_char_type('L'));  // int64
             }
-            write_number(static_cast<int64_t>(n));
+            write_number(static_cast<std::int64_t>(n));
         }
         else
         {
-            JSON_THROW(out_of_range::create(407, "integer number " + std::to_string(n) + " cannot be represented by UBJSON as it does not fit int64"));
+            if (add_prefix)
+            {
+                oa->write_character(to_char_type('H'));  // high-precision number
+            }
+
+            const auto number = BasicJsonType(n).dump();
+            write_number_with_ubjson_prefix(number.size(), true);
+            for (std::size_t i = 0; i < number.size(); ++i)
+            {
+                oa->write_character(to_char_type(static_cast<std::uint8_t>(number[i])));
+            }
         }
     }
 
     // UBJSON: write number (signed integer)
-    template<typename NumberType, typename std::enable_if<
-                 std::is_signed<NumberType>::value and
-                 not std::is_floating_point<NumberType>::value, int>::type = 0>
+    template < typename NumberType, typename std::enable_if <
+                   std::is_signed<NumberType>::value&&
+                   !std::is_floating_point<NumberType>::value, int >::type = 0 >
     void write_number_with_ubjson_prefix(const NumberType n,
                                          const bool add_prefix)
     {
-        if ((std::numeric_limits<int8_t>::min)() <= n and n <= (std::numeric_limits<int8_t>::max)())
+        if ((std::numeric_limits<std::int8_t>::min)() <= n && n <= (std::numeric_limits<std::int8_t>::max)())
         {
             if (add_prefix)
             {
                 oa->write_character(to_char_type('i'));  // int8
             }
-            write_number(static_cast<int8_t>(n));
+            write_number(static_cast<std::int8_t>(n));
         }
-        else if (static_cast<int64_t>((std::numeric_limits<uint8_t>::min)()) <= n and n <= static_cast<int64_t>((std::numeric_limits<uint8_t>::max)()))
+        else if (static_cast<std::int64_t>((std::numeric_limits<std::uint8_t>::min)()) <= n && n <= static_cast<std::int64_t>((std::numeric_limits<std::uint8_t>::max)()))
         {
             if (add_prefix)
             {
                 oa->write_character(to_char_type('U'));  // uint8
             }
-            write_number(static_cast<uint8_t>(n));
+            write_number(static_cast<std::uint8_t>(n));
         }
-        else if ((std::numeric_limits<int16_t>::min)() <= n and n <= (std::numeric_limits<int16_t>::max)())
+        else if ((std::numeric_limits<std::int16_t>::min)() <= n && n <= (std::numeric_limits<std::int16_t>::max)())
         {
             if (add_prefix)
             {
                 oa->write_character(to_char_type('I'));  // int16
             }
-            write_number(static_cast<int16_t>(n));
+            write_number(static_cast<std::int16_t>(n));
         }
-        else if ((std::numeric_limits<int32_t>::min)() <= n and n <= (std::numeric_limits<int32_t>::max)())
+        else if ((std::numeric_limits<std::int32_t>::min)() <= n && n <= (std::numeric_limits<std::int32_t>::max)())
         {
             if (add_prefix)
             {
                 oa->write_character(to_char_type('l'));  // int32
             }
-            write_number(static_cast<int32_t>(n));
+            write_number(static_cast<std::int32_t>(n));
         }
-        else if ((std::numeric_limits<int64_t>::min)() <= n and n <= (std::numeric_limits<int64_t>::max)())
+        else if ((std::numeric_limits<std::int64_t>::min)() <= n && n <= (std::numeric_limits<std::int64_t>::max)())
         {
             if (add_prefix)
             {
                 oa->write_character(to_char_type('L'));  // int64
             }
-            write_number(static_cast<int64_t>(n));
+            write_number(static_cast<std::int64_t>(n));
         }
         // LCOV_EXCL_START
         else
         {
-            JSON_THROW(out_of_range::create(407, "integer number " + std::to_string(n) + " cannot be represented by UBJSON as it does not fit int64"));
+            if (add_prefix)
+            {
+                oa->write_character(to_char_type('H'));  // high-precision number
+            }
+
+            const auto number = BasicJsonType(n).dump();
+            write_number_with_ubjson_prefix(number.size(), true);
+            for (std::size_t i = 0; i < number.size(); ++i)
+            {
+                oa->write_character(to_char_type(static_cast<std::uint8_t>(number[i])));
+            }
         }
         // LCOV_EXCL_STOP
     }
 
     /*!
     @brief determine the type prefix of container values
-
-    @note This function does not need to be 100% accurate when it comes to
-          integer limits. In case a number exceeds the limits of int64_t,
-          this will be detected by a later call to function
-          write_number_with_ubjson_prefix. Therefore, we return 'L' for any
-          value that does not fit the previous limits.
     */
     CharType ubjson_prefix(const BasicJsonType& j) const noexcept
     {
@@ -9627,46 +14138,54 @@ class binary_writer
 
             case value_t::number_integer:
             {
-                if ((std::numeric_limits<int8_t>::min)() <= j.m_value.number_integer and j.m_value.number_integer <= (std::numeric_limits<int8_t>::max)())
+                if ((std::numeric_limits<std::int8_t>::min)() <= j.m_value.number_integer && j.m_value.number_integer <= (std::numeric_limits<std::int8_t>::max)())
                 {
                     return 'i';
                 }
-                if ((std::numeric_limits<uint8_t>::min)() <= j.m_value.number_integer and j.m_value.number_integer <= (std::numeric_limits<uint8_t>::max)())
+                if ((std::numeric_limits<std::uint8_t>::min)() <= j.m_value.number_integer && j.m_value.number_integer <= (std::numeric_limits<std::uint8_t>::max)())
                 {
                     return 'U';
                 }
-                if ((std::numeric_limits<int16_t>::min)() <= j.m_value.number_integer and j.m_value.number_integer <= (std::numeric_limits<int16_t>::max)())
+                if ((std::numeric_limits<std::int16_t>::min)() <= j.m_value.number_integer && j.m_value.number_integer <= (std::numeric_limits<std::int16_t>::max)())
                 {
                     return 'I';
                 }
-                if ((std::numeric_limits<int32_t>::min)() <= j.m_value.number_integer and j.m_value.number_integer <= (std::numeric_limits<int32_t>::max)())
+                if ((std::numeric_limits<std::int32_t>::min)() <= j.m_value.number_integer && j.m_value.number_integer <= (std::numeric_limits<std::int32_t>::max)())
                 {
                     return 'l';
                 }
-                // no check and assume int64_t (see note above)
-                return 'L';
+                if ((std::numeric_limits<std::int64_t>::min)() <= j.m_value.number_integer && j.m_value.number_integer <= (std::numeric_limits<std::int64_t>::max)())
+                {
+                    return 'L';
+                }
+                // anything else is treated as high-precision number
+                return 'H'; // LCOV_EXCL_LINE
             }
 
             case value_t::number_unsigned:
             {
-                if (j.m_value.number_unsigned <= (std::numeric_limits<int8_t>::max)())
+                if (j.m_value.number_unsigned <= static_cast<std::uint64_t>((std::numeric_limits<std::int8_t>::max)()))
                 {
                     return 'i';
                 }
-                if (j.m_value.number_unsigned <= (std::numeric_limits<uint8_t>::max)())
+                if (j.m_value.number_unsigned <= static_cast<std::uint64_t>((std::numeric_limits<std::uint8_t>::max)()))
                 {
                     return 'U';
                 }
-                if (j.m_value.number_unsigned <= (std::numeric_limits<int16_t>::max)())
+                if (j.m_value.number_unsigned <= static_cast<std::uint64_t>((std::numeric_limits<std::int16_t>::max)()))
                 {
                     return 'I';
                 }
-                if (j.m_value.number_unsigned <= (std::numeric_limits<int32_t>::max)())
+                if (j.m_value.number_unsigned <= static_cast<std::uint64_t>((std::numeric_limits<std::int32_t>::max)()))
                 {
                     return 'l';
                 }
-                // no check and assume int64_t (see note above)
-                return 'L';
+                if (j.m_value.number_unsigned <= static_cast<std::uint64_t>((std::numeric_limits<std::int64_t>::max)()))
+                {
+                    return 'L';
+                }
+                // anything else is treated as high-precision number
+                return 'H'; // LCOV_EXCL_LINE
             }
 
             case value_t::number_float:
@@ -9675,7 +14194,8 @@ class binary_writer
             case value_t::string:
                 return 'S';
 
-            case value_t::array:
+            case value_t::array: // fallthrough
+            case value_t::binary:
                 return '[';
 
             case value_t::object:
@@ -9719,7 +14239,7 @@ class binary_writer
         std::memcpy(vec.data(), &n, sizeof(NumberType));
 
         // step 2: write array to output (with possible reordering)
-        if (is_little_endian and not OutputIsLittleEndian)
+        if (is_little_endian != OutputIsLittleEndian)
         {
             // reverse byte order prior to conversion if necessary
             std::reverse(vec.begin(), vec.end());
@@ -9728,24 +14248,44 @@ class binary_writer
         oa->write_characters(vec.data(), sizeof(NumberType));
     }
 
+    void write_compact_float(const number_float_t n, detail::input_format_t format)
+    {
+        if (static_cast<double>(n) >= static_cast<double>(std::numeric_limits<float>::lowest()) &&
+                static_cast<double>(n) <= static_cast<double>((std::numeric_limits<float>::max)()) &&
+                static_cast<double>(static_cast<float>(n)) == static_cast<double>(n))
+        {
+            oa->write_character(format == detail::input_format_t::cbor
+                                ? get_cbor_float_prefix(static_cast<float>(n))
+                                : get_msgpack_float_prefix(static_cast<float>(n)));
+            write_number(static_cast<float>(n));
+        }
+        else
+        {
+            oa->write_character(format == detail::input_format_t::cbor
+                                ? get_cbor_float_prefix(n)
+                                : get_msgpack_float_prefix(n));
+            write_number(n);
+        }
+    }
+
   public:
     // The following to_char_type functions are implement the conversion
     // between uint8_t and CharType. In case CharType is not unsigned,
     // such a conversion is required to allow values greater than 128.
     // See <https://github.com/nlohmann/json/issues/1286> for a discussion.
     template < typename C = CharType,
-               enable_if_t < std::is_signed<C>::value and std::is_signed<char>::value > * = nullptr >
+               enable_if_t < std::is_signed<C>::value && std::is_signed<char>::value > * = nullptr >
     static constexpr CharType to_char_type(std::uint8_t x) noexcept
     {
         return *reinterpret_cast<char*>(&x);
     }
 
     template < typename C = CharType,
-               enable_if_t < std::is_signed<C>::value and std::is_unsigned<char>::value > * = nullptr >
+               enable_if_t < std::is_signed<C>::value && std::is_unsigned<char>::value > * = nullptr >
     static CharType to_char_type(std::uint8_t x) noexcept
     {
         static_assert(sizeof(std::uint8_t) == sizeof(CharType), "size of CharType must be equal to std::uint8_t");
-        static_assert(std::is_pod<CharType>::value, "CharType must be POD");
+        static_assert(std::is_trivial<CharType>::value, "CharType must be trivial");
         CharType result;
         std::memcpy(&result, &x, sizeof(x));
         return result;
@@ -9760,8 +14300,8 @@ class binary_writer
 
     template < typename InputCharType, typename C = CharType,
                enable_if_t <
-                   std::is_signed<C>::value and
-                   std::is_signed<char>::value and
+                   std::is_signed<C>::value &&
+                   std::is_signed<char>::value &&
                    std::is_same<char, typename std::remove_cv<InputCharType>::type>::value
                    > * = nullptr >
     static constexpr CharType to_char_type(InputCharType x) noexcept
@@ -9771,7 +14311,7 @@ class binary_writer
 
   private:
     /// whether we can assume little endianess
-    const bool is_little_endian = binary_reader<BasicJsonType>::little_endianess();
+    const bool is_little_endian = little_endianess();
 
     /// the output
     output_adapter_t<CharType> oa = nullptr;
@@ -9779,32 +14319,35 @@ class binary_writer
 }  // namespace detail
 }  // namespace nlohmann
 
+// #include <nlohmann/detail/output/output_adapters.hpp>
+
 // #include <nlohmann/detail/output/serializer.hpp>
 
 
 #include <algorithm> // reverse, remove, fill, find, none_of
 #include <array> // array
-#include <cassert> // assert
-#include <ciso646> // and, or
 #include <clocale> // localeconv, lconv
 #include <cmath> // labs, isfinite, isnan, signbit
 #include <cstddef> // size_t, ptrdiff_t
 #include <cstdint> // uint8_t
 #include <cstdio> // snprintf
 #include <limits> // numeric_limits
-#include <string> // string
+#include <string> // string, char_traits
 #include <type_traits> // is_same
-
-// #include <nlohmann/detail/exceptions.hpp>
+#include <utility> // move
 
 // #include <nlohmann/detail/conversions/to_chars.hpp>
 
 
-#include <cassert> // assert
-#include <ciso646> // or, and, not
+#include <array> // array
 #include <cmath>   // signbit, isfinite
 #include <cstdint> // intN_t, uintN_t
 #include <cstring> // memcpy, memmove
+#include <limits> // numeric_limits
+#include <type_traits> // conditional
+
+// #include <nlohmann/detail/macro_scope.hpp>
+
 
 namespace nlohmann
 {
@@ -9833,7 +14376,7 @@ For a detailed description of the algorithm see:
 namespace dtoa_impl
 {
 
-template <typename Target, typename Source>
+template<typename Target, typename Source>
 Target reinterpret_bits(const Source source)
 {
     static_assert(sizeof(Target) == sizeof(Source), "size mismatch");
@@ -9847,10 +14390,10 @@ struct diyfp // f * 2^e
 {
     static constexpr int kPrecision = 64; // = q
 
-    uint64_t f = 0;
+    std::uint64_t f = 0;
     int e = 0;
 
-    constexpr diyfp(uint64_t f_, int e_) noexcept : f(f_), e(e_) {}
+    constexpr diyfp(std::uint64_t f_, int e_) noexcept : f(f_), e(e_) {}
 
     /*!
     @brief returns x - y
@@ -9858,8 +14401,8 @@ struct diyfp // f * 2^e
     */
     static diyfp sub(const diyfp& x, const diyfp& y) noexcept
     {
-        assert(x.e == y.e);
-        assert(x.f >= y.f);
+        JSON_ASSERT(x.e == y.e);
+        JSON_ASSERT(x.f >= y.f);
 
         return {x.f - y.f, x.e};
     }
@@ -9895,23 +14438,23 @@ struct diyfp // f * 2^e
         //
         //   = p_lo + 2^64 p_hi
 
-        const uint64_t u_lo = x.f & 0xFFFFFFFF;
-        const uint64_t u_hi = x.f >> 32;
-        const uint64_t v_lo = y.f & 0xFFFFFFFF;
-        const uint64_t v_hi = y.f >> 32;
+        const std::uint64_t u_lo = x.f & 0xFFFFFFFFu;
+        const std::uint64_t u_hi = x.f >> 32u;
+        const std::uint64_t v_lo = y.f & 0xFFFFFFFFu;
+        const std::uint64_t v_hi = y.f >> 32u;
 
-        const uint64_t p0 = u_lo * v_lo;
-        const uint64_t p1 = u_lo * v_hi;
-        const uint64_t p2 = u_hi * v_lo;
-        const uint64_t p3 = u_hi * v_hi;
+        const std::uint64_t p0 = u_lo * v_lo;
+        const std::uint64_t p1 = u_lo * v_hi;
+        const std::uint64_t p2 = u_hi * v_lo;
+        const std::uint64_t p3 = u_hi * v_hi;
 
-        const uint64_t p0_hi = p0 >> 32;
-        const uint64_t p1_lo = p1 & 0xFFFFFFFF;
-        const uint64_t p1_hi = p1 >> 32;
-        const uint64_t p2_lo = p2 & 0xFFFFFFFF;
-        const uint64_t p2_hi = p2 >> 32;
+        const std::uint64_t p0_hi = p0 >> 32u;
+        const std::uint64_t p1_lo = p1 & 0xFFFFFFFFu;
+        const std::uint64_t p1_hi = p1 >> 32u;
+        const std::uint64_t p2_lo = p2 & 0xFFFFFFFFu;
+        const std::uint64_t p2_hi = p2 >> 32u;
 
-        uint64_t Q = p0_hi + p1_lo + p2_lo;
+        std::uint64_t Q = p0_hi + p1_lo + p2_lo;
 
         // The full product might now be computed as
         //
@@ -9922,9 +14465,9 @@ struct diyfp // f * 2^e
         // Effectively we only need to add the highest bit in p_lo to p_hi (and
         // Q_hi + 1 does not overflow).
 
-        Q += uint64_t{1} << (64 - 32 - 1); // round, ties up
+        Q += std::uint64_t{1} << (64u - 32u - 1u); // round, ties up
 
-        const uint64_t h = p3 + p2_hi + p1_hi + (Q >> 32);
+        const std::uint64_t h = p3 + p2_hi + p1_hi + (Q >> 32u);
 
         return {h, x.e + y.e + 64};
     }
@@ -9935,11 +14478,11 @@ struct diyfp // f * 2^e
     */
     static diyfp normalize(diyfp x) noexcept
     {
-        assert(x.f != 0);
+        JSON_ASSERT(x.f != 0);
 
-        while ((x.f >> 63) == 0)
+        while ((x.f >> 63u) == 0)
         {
-            x.f <<= 1;
+            x.f <<= 1u;
             x.e--;
         }
 
@@ -9954,8 +14497,8 @@ struct diyfp // f * 2^e
     {
         const int delta = x.e - target_exponent;
 
-        assert(delta >= 0);
-        assert(((x.f << delta) >> delta) == x.f);
+        JSON_ASSERT(delta >= 0);
+        JSON_ASSERT(((x.f << delta) >> delta) == x.f);
 
         return {x.f << delta, target_exponent};
     }
@@ -9974,11 +14517,11 @@ boundaries.
 
 @pre value must be finite and positive
 */
-template <typename FloatType>
+template<typename FloatType>
 boundaries compute_boundaries(FloatType value)
 {
-    assert(std::isfinite(value));
-    assert(value > 0);
+    JSON_ASSERT(std::isfinite(value));
+    JSON_ASSERT(value > 0);
 
     // Convert the IEEE representation into a diyfp.
     //
@@ -9993,15 +14536,15 @@ boundaries compute_boundaries(FloatType value)
     constexpr int      kPrecision = std::numeric_limits<FloatType>::digits; // = p (includes the hidden bit)
     constexpr int      kBias      = std::numeric_limits<FloatType>::max_exponent - 1 + (kPrecision - 1);
     constexpr int      kMinExp    = 1 - kBias;
-    constexpr uint64_t kHiddenBit = uint64_t{1} << (kPrecision - 1); // = 2^(p-1)
+    constexpr std::uint64_t kHiddenBit = std::uint64_t{1} << (kPrecision - 1); // = 2^(p-1)
 
-    using bits_type = typename std::conditional< kPrecision == 24, uint32_t, uint64_t >::type;
+    using bits_type = typename std::conditional<kPrecision == 24, std::uint32_t, std::uint64_t >::type;
 
-    const uint64_t bits = reinterpret_bits<bits_type>(value);
-    const uint64_t E = bits >> (kPrecision - 1);
-    const uint64_t F = bits & (kHiddenBit - 1);
+    const std::uint64_t bits = reinterpret_bits<bits_type>(value);
+    const std::uint64_t E = bits >> (kPrecision - 1);
+    const std::uint64_t F = bits & (kHiddenBit - 1);
 
-    const bool is_denormal = (E == 0);
+    const bool is_denormal = E == 0;
     const diyfp v = is_denormal
                     ? diyfp(F, kMinExp)
                     : diyfp(F + kHiddenBit, static_cast<int>(E) - kBias);
@@ -10027,7 +14570,7 @@ boundaries compute_boundaries(FloatType value)
     //      -----------------+------+------+-------------+-------------+---  (B)
     //                       v-     m-     v             m+            v+
 
-    const bool lower_boundary_is_closer = (F == 0 and E > 1);
+    const bool lower_boundary_is_closer = F == 0 && E > 1;
     const diyfp m_plus = diyfp(2 * v.f + 1, v.e - 1);
     const diyfp m_minus = lower_boundary_is_closer
                           ? diyfp(4 * v.f - 1, v.e - 2)  // (B)
@@ -10102,7 +14645,7 @@ constexpr int kGamma = -32;
 
 struct cached_power // c = f * 2^e ~= 10^k
 {
-    uint64_t f;
+    std::uint64_t f;
     int e;
     int k;
 };
@@ -10126,7 +14669,7 @@ inline cached_power get_cached_power_for_binary_exponent(int e)
     //      ==> 2^(q - 1 + alpha) <= c * 2^(e + q)
     //      ==> 2^(alpha - e - 1) <= c
     //
-    // If c were an exakt power of ten, i.e. c = 10^k, one may determine k as
+    // If c were an exact power of ten, i.e. c = 10^k, one may determine k as
     //
     //      k = ceil( log_10( 2^(alpha - e - 1) ) )
     //        = ceil( (alpha - e - 1) * log_10(2) )
@@ -10166,110 +14709,110 @@ inline cached_power get_cached_power_for_binary_exponent(int e)
     // NB:
     // Actually this function returns c, such that -60 <= e_c + e + 64 <= -34.
 
-    constexpr int kCachedPowersSize = 79;
     constexpr int kCachedPowersMinDecExp = -300;
     constexpr int kCachedPowersDecStep = 8;
 
-    static constexpr cached_power kCachedPowers[] =
-    {
-        { 0xAB70FE17C79AC6CA, -1060, -300 },
-        { 0xFF77B1FCBEBCDC4F, -1034, -292 },
-        { 0xBE5691EF416BD60C, -1007, -284 },
-        { 0x8DD01FAD907FFC3C,  -980, -276 },
-        { 0xD3515C2831559A83,  -954, -268 },
-        { 0x9D71AC8FADA6C9B5,  -927, -260 },
-        { 0xEA9C227723EE8BCB,  -901, -252 },
-        { 0xAECC49914078536D,  -874, -244 },
-        { 0x823C12795DB6CE57,  -847, -236 },
-        { 0xC21094364DFB5637,  -821, -228 },
-        { 0x9096EA6F3848984F,  -794, -220 },
-        { 0xD77485CB25823AC7,  -768, -212 },
-        { 0xA086CFCD97BF97F4,  -741, -204 },
-        { 0xEF340A98172AACE5,  -715, -196 },
-        { 0xB23867FB2A35B28E,  -688, -188 },
-        { 0x84C8D4DFD2C63F3B,  -661, -180 },
-        { 0xC5DD44271AD3CDBA,  -635, -172 },
-        { 0x936B9FCEBB25C996,  -608, -164 },
-        { 0xDBAC6C247D62A584,  -582, -156 },
-        { 0xA3AB66580D5FDAF6,  -555, -148 },
-        { 0xF3E2F893DEC3F126,  -529, -140 },
-        { 0xB5B5ADA8AAFF80B8,  -502, -132 },
-        { 0x87625F056C7C4A8B,  -475, -124 },
-        { 0xC9BCFF6034C13053,  -449, -116 },
-        { 0x964E858C91BA2655,  -422, -108 },
-        { 0xDFF9772470297EBD,  -396, -100 },
-        { 0xA6DFBD9FB8E5B88F,  -369,  -92 },
-        { 0xF8A95FCF88747D94,  -343,  -84 },
-        { 0xB94470938FA89BCF,  -316,  -76 },
-        { 0x8A08F0F8BF0F156B,  -289,  -68 },
-        { 0xCDB02555653131B6,  -263,  -60 },
-        { 0x993FE2C6D07B7FAC,  -236,  -52 },
-        { 0xE45C10C42A2B3B06,  -210,  -44 },
-        { 0xAA242499697392D3,  -183,  -36 },
-        { 0xFD87B5F28300CA0E,  -157,  -28 },
-        { 0xBCE5086492111AEB,  -130,  -20 },
-        { 0x8CBCCC096F5088CC,  -103,  -12 },
-        { 0xD1B71758E219652C,   -77,   -4 },
-        { 0x9C40000000000000,   -50,    4 },
-        { 0xE8D4A51000000000,   -24,   12 },
-        { 0xAD78EBC5AC620000,     3,   20 },
-        { 0x813F3978F8940984,    30,   28 },
-        { 0xC097CE7BC90715B3,    56,   36 },
-        { 0x8F7E32CE7BEA5C70,    83,   44 },
-        { 0xD5D238A4ABE98068,   109,   52 },
-        { 0x9F4F2726179A2245,   136,   60 },
-        { 0xED63A231D4C4FB27,   162,   68 },
-        { 0xB0DE65388CC8ADA8,   189,   76 },
-        { 0x83C7088E1AAB65DB,   216,   84 },
-        { 0xC45D1DF942711D9A,   242,   92 },
-        { 0x924D692CA61BE758,   269,  100 },
-        { 0xDA01EE641A708DEA,   295,  108 },
-        { 0xA26DA3999AEF774A,   322,  116 },
-        { 0xF209787BB47D6B85,   348,  124 },
-        { 0xB454E4A179DD1877,   375,  132 },
-        { 0x865B86925B9BC5C2,   402,  140 },
-        { 0xC83553C5C8965D3D,   428,  148 },
-        { 0x952AB45CFA97A0B3,   455,  156 },
-        { 0xDE469FBD99A05FE3,   481,  164 },
-        { 0xA59BC234DB398C25,   508,  172 },
-        { 0xF6C69A72A3989F5C,   534,  180 },
-        { 0xB7DCBF5354E9BECE,   561,  188 },
-        { 0x88FCF317F22241E2,   588,  196 },
-        { 0xCC20CE9BD35C78A5,   614,  204 },
-        { 0x98165AF37B2153DF,   641,  212 },
-        { 0xE2A0B5DC971F303A,   667,  220 },
-        { 0xA8D9D1535CE3B396,   694,  228 },
-        { 0xFB9B7CD9A4A7443C,   720,  236 },
-        { 0xBB764C4CA7A44410,   747,  244 },
-        { 0x8BAB8EEFB6409C1A,   774,  252 },
-        { 0xD01FEF10A657842C,   800,  260 },
-        { 0x9B10A4E5E9913129,   827,  268 },
-        { 0xE7109BFBA19C0C9D,   853,  276 },
-        { 0xAC2820D9623BF429,   880,  284 },
-        { 0x80444B5E7AA7CF85,   907,  292 },
-        { 0xBF21E44003ACDD2D,   933,  300 },
-        { 0x8E679C2F5E44FF8F,   960,  308 },
-        { 0xD433179D9C8CB841,   986,  316 },
-        { 0x9E19DB92B4E31BA9,  1013,  324 },
+    static constexpr std::array<cached_power, 79> kCachedPowers =
+    {
+        {
+            { 0xAB70FE17C79AC6CA, -1060, -300 },
+            { 0xFF77B1FCBEBCDC4F, -1034, -292 },
+            { 0xBE5691EF416BD60C, -1007, -284 },
+            { 0x8DD01FAD907FFC3C,  -980, -276 },
+            { 0xD3515C2831559A83,  -954, -268 },
+            { 0x9D71AC8FADA6C9B5,  -927, -260 },
+            { 0xEA9C227723EE8BCB,  -901, -252 },
+            { 0xAECC49914078536D,  -874, -244 },
+            { 0x823C12795DB6CE57,  -847, -236 },
+            { 0xC21094364DFB5637,  -821, -228 },
+            { 0x9096EA6F3848984F,  -794, -220 },
+            { 0xD77485CB25823AC7,  -768, -212 },
+            { 0xA086CFCD97BF97F4,  -741, -204 },
+            { 0xEF340A98172AACE5,  -715, -196 },
+            { 0xB23867FB2A35B28E,  -688, -188 },
+            { 0x84C8D4DFD2C63F3B,  -661, -180 },
+            { 0xC5DD44271AD3CDBA,  -635, -172 },
+            { 0x936B9FCEBB25C996,  -608, -164 },
+            { 0xDBAC6C247D62A584,  -582, -156 },
+            { 0xA3AB66580D5FDAF6,  -555, -148 },
+            { 0xF3E2F893DEC3F126,  -529, -140 },
+            { 0xB5B5ADA8AAFF80B8,  -502, -132 },
+            { 0x87625F056C7C4A8B,  -475, -124 },
+            { 0xC9BCFF6034C13053,  -449, -116 },
+            { 0x964E858C91BA2655,  -422, -108 },
+            { 0xDFF9772470297EBD,  -396, -100 },
+            { 0xA6DFBD9FB8E5B88F,  -369,  -92 },
+            { 0xF8A95FCF88747D94,  -343,  -84 },
+            { 0xB94470938FA89BCF,  -316,  -76 },
+            { 0x8A08F0F8BF0F156B,  -289,  -68 },
+            { 0xCDB02555653131B6,  -263,  -60 },
+            { 0x993FE2C6D07B7FAC,  -236,  -52 },
+            { 0xE45C10C42A2B3B06,  -210,  -44 },
+            { 0xAA242499697392D3,  -183,  -36 },
+            { 0xFD87B5F28300CA0E,  -157,  -28 },
+            { 0xBCE5086492111AEB,  -130,  -20 },
+            { 0x8CBCCC096F5088CC,  -103,  -12 },
+            { 0xD1B71758E219652C,   -77,   -4 },
+            { 0x9C40000000000000,   -50,    4 },
+            { 0xE8D4A51000000000,   -24,   12 },
+            { 0xAD78EBC5AC620000,     3,   20 },
+            { 0x813F3978F8940984,    30,   28 },
+            { 0xC097CE7BC90715B3,    56,   36 },
+            { 0x8F7E32CE7BEA5C70,    83,   44 },
+            { 0xD5D238A4ABE98068,   109,   52 },
+            { 0x9F4F2726179A2245,   136,   60 },
+            { 0xED63A231D4C4FB27,   162,   68 },
+            { 0xB0DE65388CC8ADA8,   189,   76 },
+            { 0x83C7088E1AAB65DB,   216,   84 },
+            { 0xC45D1DF942711D9A,   242,   92 },
+            { 0x924D692CA61BE758,   269,  100 },
+            { 0xDA01EE641A708DEA,   295,  108 },
+            { 0xA26DA3999AEF774A,   322,  116 },
+            { 0xF209787BB47D6B85,   348,  124 },
+            { 0xB454E4A179DD1877,   375,  132 },
+            { 0x865B86925B9BC5C2,   402,  140 },
+            { 0xC83553C5C8965D3D,   428,  148 },
+            { 0x952AB45CFA97A0B3,   455,  156 },
+            { 0xDE469FBD99A05FE3,   481,  164 },
+            { 0xA59BC234DB398C25,   508,  172 },
+            { 0xF6C69A72A3989F5C,   534,  180 },
+            { 0xB7DCBF5354E9BECE,   561,  188 },
+            { 0x88FCF317F22241E2,   588,  196 },
+            { 0xCC20CE9BD35C78A5,   614,  204 },
+            { 0x98165AF37B2153DF,   641,  212 },
+            { 0xE2A0B5DC971F303A,   667,  220 },
+            { 0xA8D9D1535CE3B396,   694,  228 },
+            { 0xFB9B7CD9A4A7443C,   720,  236 },
+            { 0xBB764C4CA7A44410,   747,  244 },
+            { 0x8BAB8EEFB6409C1A,   774,  252 },
+            { 0xD01FEF10A657842C,   800,  260 },
+            { 0x9B10A4E5E9913129,   827,  268 },
+            { 0xE7109BFBA19C0C9D,   853,  276 },
+            { 0xAC2820D9623BF429,   880,  284 },
+            { 0x80444B5E7AA7CF85,   907,  292 },
+            { 0xBF21E44003ACDD2D,   933,  300 },
+            { 0x8E679C2F5E44FF8F,   960,  308 },
+            { 0xD433179D9C8CB841,   986,  316 },
+            { 0x9E19DB92B4E31BA9,  1013,  324 },
+        }
     };
 
     // This computation gives exactly the same results for k as
     //      k = ceil((kAlpha - e - 1) * 0.30102999566398114)
     // for |e| <= 1500, but doesn't require floating-point operations.
     // NB: log_10(2) ~= 78913 / 2^18
-    assert(e >= -1500);
-    assert(e <=  1500);
+    JSON_ASSERT(e >= -1500);
+    JSON_ASSERT(e <=  1500);
     const int f = kAlpha - e - 1;
     const int k = (f * 78913) / (1 << 18) + static_cast<int>(f > 0);
 
     const int index = (-kCachedPowersMinDecExp + k + (kCachedPowersDecStep - 1)) / kCachedPowersDecStep;
-    assert(index >= 0);
-    assert(index < kCachedPowersSize);
-    static_cast<void>(kCachedPowersSize); // Fix warning.
+    JSON_ASSERT(index >= 0);
+    JSON_ASSERT(static_cast<std::size_t>(index) < kCachedPowers.size());
 
-    const cached_power cached = kCachedPowers[index];
-    assert(kAlpha <= cached.e + e + 64);
-    assert(kGamma >= cached.e + e + 64);
+    const cached_power cached = kCachedPowers[static_cast<std::size_t>(index)];
+    JSON_ASSERT(kAlpha <= cached.e + e + 64);
+    JSON_ASSERT(kGamma >= cached.e + e + 64);
 
     return cached;
 }
@@ -10278,7 +14821,7 @@ inline cached_power get_cached_power_for_binary_exponent(int e)
 For n != 0, returns k, such that pow10 := 10^(k-1) <= n < 10^k.
 For n == 0, returns 1 and sets pow10 := 1.
 */
-inline int find_largest_pow10(const uint32_t n, uint32_t& pow10)
+inline int find_largest_pow10(const std::uint32_t n, std::uint32_t& pow10)
 {
     // LCOV_EXCL_START
     if (n >= 1000000000)
@@ -10334,13 +14877,13 @@ inline int find_largest_pow10(const uint32_t n, uint32_t& pow10)
     }
 }
 
-inline void grisu2_round(char* buf, int len, uint64_t dist, uint64_t delta,
-                         uint64_t rest, uint64_t ten_k)
+inline void grisu2_round(char* buf, int len, std::uint64_t dist, std::uint64_t delta,
+                         std::uint64_t rest, std::uint64_t ten_k)
 {
-    assert(len >= 1);
-    assert(dist <= delta);
-    assert(rest <= delta);
-    assert(ten_k > 0);
+    JSON_ASSERT(len >= 1);
+    JSON_ASSERT(dist <= delta);
+    JSON_ASSERT(rest <= delta);
+    JSON_ASSERT(ten_k > 0);
 
     //               <--------------------------- delta ---->
     //                                  <---- dist --------->
@@ -10362,10 +14905,10 @@ inline void grisu2_round(char* buf, int len, uint64_t dist, uint64_t delta,
     // integer arithmetic.
 
     while (rest < dist
-            and delta - rest >= ten_k
-            and (rest + ten_k < dist or dist - rest > rest + ten_k - dist))
+            && delta - rest >= ten_k
+            && (rest + ten_k < dist || dist - rest > rest + ten_k - dist))
     {
-        assert(buf[len - 1] != '0');
+        JSON_ASSERT(buf[len - 1] != '0');
         buf[len - 1]--;
         rest += ten_k;
     }
@@ -10393,11 +14936,11 @@ inline void grisu2_digit_gen(char* buffer, int& length, int& decimal_exponent,
     // Grisu2 generates the digits of M+ from left to right and stops as soon as
     // V is in [M-,M+].
 
-    assert(M_plus.e >= kAlpha);
-    assert(M_plus.e <= kGamma);
+    JSON_ASSERT(M_plus.e >= kAlpha);
+    JSON_ASSERT(M_plus.e <= kGamma);
 
-    uint64_t delta = diyfp::sub(M_plus, M_minus).f; // (significand of (M+ - M-), implicit exponent is e)
-    uint64_t dist  = diyfp::sub(M_plus, w      ).f; // (significand of (M+ - w ), implicit exponent is e)
+    std::uint64_t delta = diyfp::sub(M_plus, M_minus).f; // (significand of (M+ - M-), implicit exponent is e)
+    std::uint64_t dist  = diyfp::sub(M_plus, w      ).f; // (significand of (M+ - w ), implicit exponent is e)
 
     // Split M+ = f * 2^e into two parts p1 and p2 (note: e < 0):
     //
@@ -10406,18 +14949,18 @@ inline void grisu2_digit_gen(char* buffer, int& length, int& decimal_exponent,
     //         = ((p1        ) * 2^-e + (p2        )) * 2^e
     //         = p1 + p2 * 2^e
 
-    const diyfp one(uint64_t{1} << -M_plus.e, M_plus.e);
+    const diyfp one(std::uint64_t{1} << -M_plus.e, M_plus.e);
 
-    auto p1 = static_cast<uint32_t>(M_plus.f >> -one.e); // p1 = f div 2^-e (Since -e >= 32, p1 fits into a 32-bit int.)
-    uint64_t p2 = M_plus.f & (one.f - 1);                    // p2 = f mod 2^-e
+    auto p1 = static_cast<std::uint32_t>(M_plus.f >> -one.e); // p1 = f div 2^-e (Since -e >= 32, p1 fits into a 32-bit int.)
+    std::uint64_t p2 = M_plus.f & (one.f - 1);                    // p2 = f mod 2^-e
 
     // 1)
     //
     // Generate the digits of the integral part p1 = d[n-1]...d[1]d[0]
 
-    assert(p1 > 0);
+    JSON_ASSERT(p1 > 0);
 
-    uint32_t pow10;
+    std::uint32_t pow10;
     const int k = find_largest_pow10(p1, pow10);
 
     //      10^(k-1) <= p1 < 10^k, pow10 = 10^(k-1)
@@ -10445,13 +14988,13 @@ inline void grisu2_digit_gen(char* buffer, int& length, int& decimal_exponent,
         //      M+ = buffer * 10^n + (p1 + p2 * 2^e)    (buffer = 0 for n = k)
         //      pow10 = 10^(n-1) <= p1 < 10^n
         //
-        const uint32_t d = p1 / pow10;  // d = p1 div 10^(n-1)
-        const uint32_t r = p1 % pow10;  // r = p1 mod 10^(n-1)
+        const std::uint32_t d = p1 / pow10;  // d = p1 div 10^(n-1)
+        const std::uint32_t r = p1 % pow10;  // r = p1 mod 10^(n-1)
         //
         //      M+ = buffer * 10^n + (d * 10^(n-1) + r) + p2 * 2^e
         //         = (buffer * 10 + d) * 10^(n-1) + (r + p2 * 2^e)
         //
-        assert(d <= 9);
+        JSON_ASSERT(d <= 9);
         buffer[length++] = static_cast<char>('0' + d); // buffer := buffer * 10 + d
         //
         //      M+ = buffer * 10^(n-1) + (r + p2 * 2^e)
@@ -10471,7 +15014,7 @@ inline void grisu2_digit_gen(char* buffer, int& length, int& decimal_exponent,
         // Note:
         // Since rest and delta share the same exponent e, it suffices to
         // compare the significands.
-        const uint64_t rest = (uint64_t{p1} << -one.e) + p2;
+        const std::uint64_t rest = (std::uint64_t{p1} << -one.e) + p2;
         if (rest <= delta)
         {
             // V = buffer * 10^n, with M- <= V <= M+.
@@ -10487,7 +15030,7 @@ inline void grisu2_digit_gen(char* buffer, int& length, int& decimal_exponent,
             //
             //      10^n = (10^n * 2^-e) * 2^e = ulp * 2^e
             //
-            const uint64_t ten_n = uint64_t{pow10} << -one.e;
+            const std::uint64_t ten_n = std::uint64_t{pow10} << -one.e;
             grisu2_round(buffer, length, dist, delta, rest, ten_n);
 
             return;
@@ -10538,7 +15081,7 @@ inline void grisu2_digit_gen(char* buffer, int& length, int& decimal_exponent,
     //
     // and stop as soon as 10^-m * r * 2^e <= delta * 2^e
 
-    assert(p2 > delta);
+    JSON_ASSERT(p2 > delta);
 
     int m = 0;
     for (;;)
@@ -10549,16 +15092,16 @@ inline void grisu2_digit_gen(char* buffer, int& length, int& decimal_exponent,
         //         = buffer * 10^-m + 10^-m * (1/10 * (10 * p2)                   ) * 2^e
         //         = buffer * 10^-m + 10^-m * (1/10 * ((10*p2 div 2^-e) * 2^-e + (10*p2 mod 2^-e)) * 2^e
         //
-        assert(p2 <= UINT64_MAX / 10);
+        JSON_ASSERT(p2 <= (std::numeric_limits<std::uint64_t>::max)() / 10);
         p2 *= 10;
-        const uint64_t d = p2 >> -one.e;     // d = (10 * p2) div 2^-e
-        const uint64_t r = p2 & (one.f - 1); // r = (10 * p2) mod 2^-e
+        const std::uint64_t d = p2 >> -one.e;     // d = (10 * p2) div 2^-e
+        const std::uint64_t r = p2 & (one.f - 1); // r = (10 * p2) mod 2^-e
         //
         //      M+ = buffer * 10^-m + 10^-m * (1/10 * (d * 2^-e + r) * 2^e
         //         = buffer * 10^-m + 10^-m * (1/10 * (d + r * 2^e))
         //         = (buffer * 10 + d) * 10^(-m-1) + 10^(-m-1) * r * 2^e
         //
-        assert(d <= 9);
+        JSON_ASSERT(d <= 9);
         buffer[length++] = static_cast<char>('0' + d); // buffer := buffer * 10 + d
         //
         //      M+ = buffer * 10^(-m-1) + 10^(-m-1) * r * 2^e
@@ -10592,7 +15135,7 @@ inline void grisu2_digit_gen(char* buffer, int& length, int& decimal_exponent,
     //
     //      10^m * 10^-m = 1 = 2^-e * 2^e = ten_m * 2^e
     //
-    const uint64_t ten_m = one.f;
+    const std::uint64_t ten_m = one.f;
     grisu2_round(buffer, length, dist, delta, p2, ten_m);
 
     // By construction this algorithm generates the shortest possible decimal
@@ -10615,11 +15158,12 @@ v = buf * 10^decimal_exponent
 len is the length of the buffer (number of decimal digits)
 The buffer must be large enough, i.e. >= max_digits10.
 */
+JSON_HEDLEY_NON_NULL(1)
 inline void grisu2(char* buf, int& len, int& decimal_exponent,
                    diyfp m_minus, diyfp v, diyfp m_plus)
 {
-    assert(m_plus.e == m_minus.e);
-    assert(m_plus.e == v.e);
+    JSON_ASSERT(m_plus.e == m_minus.e);
+    JSON_ASSERT(m_plus.e == v.e);
 
     //  --------(-----------------------+-----------------------)--------    (A)
     //          m-                      v                       m+
@@ -10673,14 +15217,15 @@ v = buf * 10^decimal_exponent
 len is the length of the buffer (number of decimal digits)
 The buffer must be large enough, i.e. >= max_digits10.
 */
-template <typename FloatType>
+template<typename FloatType>
+JSON_HEDLEY_NON_NULL(1)
 void grisu2(char* buf, int& len, int& decimal_exponent, FloatType value)
 {
     static_assert(diyfp::kPrecision >= std::numeric_limits<FloatType>::digits + 3,
                   "internal error: not enough precision");
 
-    assert(std::isfinite(value));
-    assert(value > 0);
+    JSON_ASSERT(std::isfinite(value));
+    JSON_ASSERT(value > 0);
 
     // If the neighbors (and boundaries) of 'value' are always computed for double-precision
     // numbers, all float's can be recovered using strtod (and strtof). However, the resulting
@@ -10712,10 +15257,12 @@ void grisu2(char* buf, int& len, int& decimal_exponent, FloatType value)
 @return a pointer to the element following the exponent.
 @pre -1000 < e < 1000
 */
+JSON_HEDLEY_NON_NULL(1)
+JSON_HEDLEY_RETURNS_NON_NULL
 inline char* append_exponent(char* buf, int e)
 {
-    assert(e > -1000);
-    assert(e <  1000);
+    JSON_ASSERT(e > -1000);
+    JSON_ASSERT(e <  1000);
 
     if (e < 0)
     {
@@ -10727,7 +15274,7 @@ inline char* append_exponent(char* buf, int e)
         *buf++ = '+';
     }
 
-    auto k = static_cast<uint32_t>(e);
+    auto k = static_cast<std::uint32_t>(e);
     if (k < 10)
     {
         // Always print at least two digits in the exponent.
@@ -10762,11 +15309,13 @@ notation. Otherwise it will be printed in exponential notation.
 @pre min_exp < 0
 @pre max_exp > 0
 */
+JSON_HEDLEY_NON_NULL(1)
+JSON_HEDLEY_RETURNS_NON_NULL
 inline char* format_buffer(char* buf, int len, int decimal_exponent,
                            int min_exp, int max_exp)
 {
-    assert(min_exp < 0);
-    assert(max_exp > 0);
+    JSON_ASSERT(min_exp < 0);
+    JSON_ASSERT(max_exp > 0);
 
     const int k = len;
     const int n = len + decimal_exponent;
@@ -10775,40 +15324,40 @@ inline char* format_buffer(char* buf, int len, int decimal_exponent,
     // k is the length of the buffer (number of decimal digits)
     // n is the position of the decimal point relative to the start of the buffer.
 
-    if (k <= n and n <= max_exp)
+    if (k <= n && n <= max_exp)
     {
         // digits[000]
         // len <= max_exp + 2
 
-        std::memset(buf + k, '0', static_cast<size_t>(n - k));
+        std::memset(buf + k, '0', static_cast<size_t>(n) - static_cast<size_t>(k));
         // Make it look like a floating-point number (#362, #378)
         buf[n + 0] = '.';
         buf[n + 1] = '0';
-        return buf + (n + 2);
+        return buf + (static_cast<size_t>(n) + 2);
     }
 
-    if (0 < n and n <= max_exp)
+    if (0 < n && n <= max_exp)
     {
         // dig.its
         // len <= max_digits10 + 1
 
-        assert(k > n);
+        JSON_ASSERT(k > n);
 
-        std::memmove(buf + (n + 1), buf + n, static_cast<size_t>(k - n));
+        std::memmove(buf + (static_cast<size_t>(n) + 1), buf + n, static_cast<size_t>(k) - static_cast<size_t>(n));
         buf[n] = '.';
-        return buf + (k + 1);
+        return buf + (static_cast<size_t>(k) + 1U);
     }
 
-    if (min_exp < n and n <= 0)
+    if (min_exp < n && n <= 0)
     {
         // 0.[000]digits
         // len <= 2 + (-min_exp - 1) + max_digits10
 
-        std::memmove(buf + (2 + -n), buf, static_cast<size_t>(k));
+        std::memmove(buf + (2 + static_cast<size_t>(-n)), buf, static_cast<size_t>(k));
         buf[0] = '0';
         buf[1] = '.';
         std::memset(buf + 2, '0', static_cast<size_t>(-n));
-        return buf + (2 + (-n) + k);
+        return buf + (2U + static_cast<size_t>(-n) + static_cast<size_t>(k));
     }
 
     if (k == 1)
@@ -10823,9 +15372,9 @@ inline char* format_buffer(char* buf, int len, int decimal_exponent,
         // d.igitsE+123
         // len <= max_digits10 + 1 + 5
 
-        std::memmove(buf + 2, buf + 1, static_cast<size_t>(k - 1));
+        std::memmove(buf + 2, buf + 1, static_cast<size_t>(k) - 1);
         buf[1] = '.';
-        buf += 1 + k;
+        buf += 1 + static_cast<size_t>(k);
     }
 
     *buf++ = 'e';
@@ -10844,11 +15393,13 @@ format. Returns an iterator pointing past-the-end of the decimal representation.
 @note The buffer must be large enough.
 @note The result is NOT null-terminated.
 */
-template <typename FloatType>
+template<typename FloatType>
+JSON_HEDLEY_NON_NULL(1, 2)
+JSON_HEDLEY_RETURNS_NON_NULL
 char* to_chars(char* first, const char* last, FloatType value)
 {
     static_cast<void>(last); // maybe unused - fix warning
-    assert(std::isfinite(value));
+    JSON_ASSERT(std::isfinite(value));
 
     // Use signbit(value) instead of (value < 0) since signbit works for -0.
     if (std::signbit(value))
@@ -10866,7 +15417,7 @@ char* to_chars(char* first, const char* last, FloatType value)
         return first;
     }
 
-    assert(last - first >= std::numeric_limits<FloatType>::max_digits10);
+    JSON_ASSERT(last - first >= std::numeric_limits<FloatType>::max_digits10);
 
     // Compute v = buffer * 10^decimal_exponent.
     // The decimal digits are stored in the buffer, which needs to be interpreted
@@ -10876,16 +15427,16 @@ char* to_chars(char* first, const char* last, FloatType value)
     int decimal_exponent = 0;
     dtoa_impl::grisu2(first, len, decimal_exponent, value);
 
-    assert(len <= std::numeric_limits<FloatType>::max_digits10);
+    JSON_ASSERT(len <= std::numeric_limits<FloatType>::max_digits10);
 
     // Format the buffer like printf("%.*g", prec, value)
     constexpr int kMinExp = -4;
     // Use digits10 here to increase compatibility with version 2.
     constexpr int kMaxExp = std::numeric_limits<FloatType>::digits10;
 
-    assert(last - first >= kMaxExp + 2);
-    assert(last - first >= 2 + (-kMinExp - 1) + std::numeric_limits<FloatType>::max_digits10);
-    assert(last - first >= std::numeric_limits<FloatType>::max_digits10 + 6);
+    JSON_ASSERT(last - first >= kMaxExp + 2);
+    JSON_ASSERT(last - first >= 2 + (-kMinExp - 1) + std::numeric_limits<FloatType>::max_digits10);
+    JSON_ASSERT(last - first >= std::numeric_limits<FloatType>::max_digits10 + 6);
 
     return dtoa_impl::format_buffer(first, len, decimal_exponent, kMinExp, kMaxExp);
 }
@@ -10893,6 +15444,8 @@ char* to_chars(char* first, const char* last, FloatType value)
 } // namespace detail
 } // namespace nlohmann
 
+// #include <nlohmann/detail/exceptions.hpp>
+
 // #include <nlohmann/detail/macro_scope.hpp>
 
 // #include <nlohmann/detail/meta/cpp_future.hpp>
@@ -10927,8 +15480,9 @@ class serializer
     using number_float_t = typename BasicJsonType::number_float_t;
     using number_integer_t = typename BasicJsonType::number_integer_t;
     using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
-    static constexpr uint8_t UTF8_ACCEPT = 0;
-    static constexpr uint8_t UTF8_REJECT = 1;
+    using binary_char_t = typename BasicJsonType::binary_t::value_type;
+    static constexpr std::uint8_t UTF8_ACCEPT = 0;
+    static constexpr std::uint8_t UTF8_REJECT = 1;
 
   public:
     /*!
@@ -10940,8 +15494,8 @@ class serializer
                error_handler_t error_handler_ = error_handler_t::strict)
         : o(std::move(s))
         , loc(std::localeconv())
-        , thousands_sep(loc->thousands_sep == nullptr ? '\0' : * (loc->thousands_sep))
-        , decimal_point(loc->decimal_point == nullptr ? '\0' : * (loc->decimal_point))
+        , thousands_sep(loc->thousands_sep == nullptr ? '\0' : std::char_traits<char>::to_char_type(* (loc->thousands_sep)))
+        , decimal_point(loc->decimal_point == nullptr ? '\0' : std::char_traits<char>::to_char_type(* (loc->decimal_point)))
         , indent_char(ichar)
         , indent_string(512, indent_char)
         , error_handler(error_handler_)
@@ -10965,13 +15519,19 @@ class serializer
     - strings and object keys are escaped using `escape_string()`
     - integer numbers are converted implicitly via `operator<<`
     - floating-point numbers are converted to a string using `"%g"` format
+    - binary values are serialized as objects containing the subtype and the
+      byte array
 
-    @param[in] val             value to serialize
-    @param[in] pretty_print    whether the output shall be pretty-printed
-    @param[in] indent_step     the indent level
-    @param[in] current_indent  the current indent level (only used internally)
+    @param[in] val               value to serialize
+    @param[in] pretty_print      whether the output shall be pretty-printed
+    @param[in] ensure_ascii If @a ensure_ascii is true, all non-ASCII characters
+    in the output are escaped with `\uXXXX` sequences, and the result consists
+    of ASCII characters only.
+    @param[in] indent_step       the indent level
+    @param[in] current_indent    the current indent level (only used internally)
     */
-    void dump(const BasicJsonType& val, const bool pretty_print,
+    void dump(const BasicJsonType& val,
+              const bool pretty_print,
               const bool ensure_ascii,
               const unsigned int indent_step,
               const unsigned int current_indent = 0)
@@ -10992,7 +15552,7 @@ class serializer
 
                     // variable to hold indentation for recursive calls
                     const auto new_indent = current_indent + indent_step;
-                    if (JSON_UNLIKELY(indent_string.size() < new_indent))
+                    if (JSON_HEDLEY_UNLIKELY(indent_string.size() < new_indent))
                     {
                         indent_string.resize(indent_string.size() * 2, ' ');
                     }
@@ -11010,8 +15570,8 @@ class serializer
                     }
 
                     // last element
-                    assert(i != val.m_value.object->cend());
-                    assert(std::next(i) == val.m_value.object->cend());
+                    JSON_ASSERT(i != val.m_value.object->cend());
+                    JSON_ASSERT(std::next(i) == val.m_value.object->cend());
                     o->write_characters(indent_string.c_str(), new_indent);
                     o->write_character('\"');
                     dump_escaped(i->first, ensure_ascii);
@@ -11038,8 +15598,8 @@ class serializer
                     }
 
                     // last element
-                    assert(i != val.m_value.object->cend());
-                    assert(std::next(i) == val.m_value.object->cend());
+                    JSON_ASSERT(i != val.m_value.object->cend());
+                    JSON_ASSERT(std::next(i) == val.m_value.object->cend());
                     o->write_character('\"');
                     dump_escaped(i->first, ensure_ascii);
                     o->write_characters("\":", 2);
@@ -11065,7 +15625,7 @@ class serializer
 
                     // variable to hold indentation for recursive calls
                     const auto new_indent = current_indent + indent_step;
-                    if (JSON_UNLIKELY(indent_string.size() < new_indent))
+                    if (JSON_HEDLEY_UNLIKELY(indent_string.size() < new_indent))
                     {
                         indent_string.resize(indent_string.size() * 2, ' ');
                     }
@@ -11080,7 +15640,7 @@ class serializer
                     }
 
                     // last element
-                    assert(not val.m_value.array->empty());
+                    JSON_ASSERT(!val.m_value.array->empty());
                     o->write_characters(indent_string.c_str(), new_indent);
                     dump(val.m_value.array->back(), true, ensure_ascii, indent_step, new_indent);
 
@@ -11101,7 +15661,7 @@ class serializer
                     }
 
                     // last element
-                    assert(not val.m_value.array->empty());
+                    JSON_ASSERT(!val.m_value.array->empty());
                     dump(val.m_value.array->back(), false, ensure_ascii, indent_step, current_indent);
 
                     o->write_character(']');
@@ -11118,6 +15678,79 @@ class serializer
                 return;
             }
 
+            case value_t::binary:
+            {
+                if (pretty_print)
+                {
+                    o->write_characters("{\n", 2);
+
+                    // variable to hold indentation for recursive calls
+                    const auto new_indent = current_indent + indent_step;
+                    if (JSON_HEDLEY_UNLIKELY(indent_string.size() < new_indent))
+                    {
+                        indent_string.resize(indent_string.size() * 2, ' ');
+                    }
+
+                    o->write_characters(indent_string.c_str(), new_indent);
+
+                    o->write_characters("\"bytes\": [", 10);
+
+                    if (!val.m_value.binary->empty())
+                    {
+                        for (auto i = val.m_value.binary->cbegin();
+                                i != val.m_value.binary->cend() - 1; ++i)
+                        {
+                            dump_integer(*i);
+                            o->write_characters(", ", 2);
+                        }
+                        dump_integer(val.m_value.binary->back());
+                    }
+
+                    o->write_characters("],\n", 3);
+                    o->write_characters(indent_string.c_str(), new_indent);
+
+                    o->write_characters("\"subtype\": ", 11);
+                    if (val.m_value.binary->has_subtype())
+                    {
+                        dump_integer(val.m_value.binary->subtype());
+                    }
+                    else
+                    {
+                        o->write_characters("null", 4);
+                    }
+                    o->write_character('\n');
+                    o->write_characters(indent_string.c_str(), current_indent);
+                    o->write_character('}');
+                }
+                else
+                {
+                    o->write_characters("{\"bytes\":[", 10);
+
+                    if (!val.m_value.binary->empty())
+                    {
+                        for (auto i = val.m_value.binary->cbegin();
+                                i != val.m_value.binary->cend() - 1; ++i)
+                        {
+                            dump_integer(*i);
+                            o->write_character(',');
+                        }
+                        dump_integer(val.m_value.binary->back());
+                    }
+
+                    o->write_characters("],\"subtype\":", 12);
+                    if (val.m_value.binary->has_subtype())
+                    {
+                        dump_integer(val.m_value.binary->subtype());
+                        o->write_character('}');
+                    }
+                    else
+                    {
+                        o->write_characters("null}", 5);
+                    }
+                }
+                return;
+            }
+
             case value_t::boolean:
             {
                 if (val.m_value.boolean)
@@ -11160,6 +15793,9 @@ class serializer
                 o->write_characters("null", 4);
                 return;
             }
+
+            default:            // LCOV_EXCL_LINE
+                JSON_ASSERT(false);  // LCOV_EXCL_LINE
         }
     }
 
@@ -11180,8 +15816,8 @@ class serializer
     */
     void dump_escaped(const string_t& s, const bool ensure_ascii)
     {
-        uint32_t codepoint;
-        uint8_t state = UTF8_ACCEPT;
+        std::uint32_t codepoint;
+        std::uint8_t state = UTF8_ACCEPT;
         std::size_t bytes = 0;  // number of bytes written to string_buffer
 
         // number of bytes written at the point of the last valid byte
@@ -11251,19 +15887,19 @@ class serializer
                         {
                             // escape control characters (0x00..0x1F) or, if
                             // ensure_ascii parameter is used, non-ASCII characters
-                            if ((codepoint <= 0x1F) or (ensure_ascii and (codepoint >= 0x7F)))
+                            if ((codepoint <= 0x1F) || (ensure_ascii && (codepoint >= 0x7F)))
                             {
                                 if (codepoint <= 0xFFFF)
                                 {
                                     (std::snprintf)(string_buffer.data() + bytes, 7, "\\u%04x",
-                                                    static_cast<uint16_t>(codepoint));
+                                                    static_cast<std::uint16_t>(codepoint));
                                     bytes += 6;
                                 }
                                 else
                                 {
                                     (std::snprintf)(string_buffer.data() + bytes, 13, "\\u%04x\\u%04x",
-                                                    static_cast<uint16_t>(0xD7C0 + (codepoint >> 10)),
-                                                    static_cast<uint16_t>(0xDC00 + (codepoint & 0x3FF)));
+                                                    static_cast<std::uint16_t>(0xD7C0u + (codepoint >> 10u)),
+                                                    static_cast<std::uint16_t>(0xDC00u + (codepoint & 0x3FFu)));
                                     bytes += 12;
                                 }
                             }
@@ -11337,6 +15973,16 @@ class serializer
                                     string_buffer[bytes++] = detail::binary_writer<BasicJsonType, char>::to_char_type('\xBF');
                                     string_buffer[bytes++] = detail::binary_writer<BasicJsonType, char>::to_char_type('\xBD');
                                 }
+
+                                // write buffer and reset index; there must be 13 bytes
+                                // left, as this is the maximal number of bytes to be
+                                // written ("\uxxxx\uxxxx\0") for one code point
+                                if (string_buffer.size() - bytes < 13)
+                                {
+                                    o->write_characters(string_buffer.data(), bytes);
+                                    bytes = 0;
+                                }
+
                                 bytes_after_last_accept = bytes;
                             }
 
@@ -11346,13 +15992,16 @@ class serializer
                             state = UTF8_ACCEPT;
                             break;
                         }
+
+                        default:            // LCOV_EXCL_LINE
+                            JSON_ASSERT(false);  // LCOV_EXCL_LINE
                     }
                     break;
                 }
 
                 default:  // decode found yet incomplete multi-byte code point
                 {
-                    if (not ensure_ascii)
+                    if (!ensure_ascii)
                     {
                         // code point will not be escaped - copy byte to buffer
                         string_buffer[bytes++] = s[i];
@@ -11364,7 +16013,7 @@ class serializer
         }
 
         // we finished processing the string
-        if (JSON_LIKELY(state == UTF8_ACCEPT))
+        if (JSON_HEDLEY_LIKELY(state == UTF8_ACCEPT))
         {
             // write buffer
             if (bytes > 0)
@@ -11380,7 +16029,7 @@ class serializer
                 case error_handler_t::strict:
                 {
                     std::string sn(3, '\0');
-                    (std::snprintf)(&sn[0], sn.size(), "%.2X", static_cast<uint8_t>(s.back()));
+                    (std::snprintf)(&sn[0], sn.size(), "%.2X", static_cast<std::uint8_t>(s.back()));
                     JSON_THROW(type_error::create(316, "incomplete UTF-8 string; last byte: 0x" + sn));
                 }
 
@@ -11406,7 +16055,44 @@ class serializer
                     }
                     break;
                 }
+
+                default:            // LCOV_EXCL_LINE
+                    JSON_ASSERT(false);  // LCOV_EXCL_LINE
+            }
+        }
+    }
+
+    /*!
+    @brief count digits
+
+    Count the number of decimal (base 10) digits for an input unsigned integer.
+
+    @param[in] x  unsigned integer number to count its digits
+    @return    number of decimal digits
+    */
+    inline unsigned int count_digits(number_unsigned_t x) noexcept
+    {
+        unsigned int n_digits = 1;
+        for (;;)
+        {
+            if (x < 10)
+            {
+                return n_digits;
+            }
+            if (x < 100)
+            {
+                return n_digits + 1;
             }
+            if (x < 1000)
+            {
+                return n_digits + 2;
+            }
+            if (x < 10000)
+            {
+                return n_digits + 3;
+            }
+            x = x / 10000u;
+            n_digits += 4;
         }
     }
 
@@ -11419,12 +16105,29 @@ class serializer
     @param[in] x  integer number (signed or unsigned) to dump
     @tparam NumberType either @a number_integer_t or @a number_unsigned_t
     */
-    template<typename NumberType, detail::enable_if_t<
-                 std::is_same<NumberType, number_unsigned_t>::value or
-                 std::is_same<NumberType, number_integer_t>::value,
-                 int> = 0>
+    template < typename NumberType, detail::enable_if_t <
+                   std::is_same<NumberType, number_unsigned_t>::value ||
+                   std::is_same<NumberType, number_integer_t>::value ||
+                   std::is_same<NumberType, binary_char_t>::value,
+                   int > = 0 >
     void dump_integer(NumberType x)
     {
+        static constexpr std::array<std::array<char, 2>, 100> digits_to_99
+        {
+            {
+                {{'0', '0'}}, {{'0', '1'}}, {{'0', '2'}}, {{'0', '3'}}, {{'0', '4'}}, {{'0', '5'}}, {{'0', '6'}}, {{'0', '7'}}, {{'0', '8'}}, {{'0', '9'}},
+                {{'1', '0'}}, {{'1', '1'}}, {{'1', '2'}}, {{'1', '3'}}, {{'1', '4'}}, {{'1', '5'}}, {{'1', '6'}}, {{'1', '7'}}, {{'1', '8'}}, {{'1', '9'}},
+                {{'2', '0'}}, {{'2', '1'}}, {{'2', '2'}}, {{'2', '3'}}, {{'2', '4'}}, {{'2', '5'}}, {{'2', '6'}}, {{'2', '7'}}, {{'2', '8'}}, {{'2', '9'}},
+                {{'3', '0'}}, {{'3', '1'}}, {{'3', '2'}}, {{'3', '3'}}, {{'3', '4'}}, {{'3', '5'}}, {{'3', '6'}}, {{'3', '7'}}, {{'3', '8'}}, {{'3', '9'}},
+                {{'4', '0'}}, {{'4', '1'}}, {{'4', '2'}}, {{'4', '3'}}, {{'4', '4'}}, {{'4', '5'}}, {{'4', '6'}}, {{'4', '7'}}, {{'4', '8'}}, {{'4', '9'}},
+                {{'5', '0'}}, {{'5', '1'}}, {{'5', '2'}}, {{'5', '3'}}, {{'5', '4'}}, {{'5', '5'}}, {{'5', '6'}}, {{'5', '7'}}, {{'5', '8'}}, {{'5', '9'}},
+                {{'6', '0'}}, {{'6', '1'}}, {{'6', '2'}}, {{'6', '3'}}, {{'6', '4'}}, {{'6', '5'}}, {{'6', '6'}}, {{'6', '7'}}, {{'6', '8'}}, {{'6', '9'}},
+                {{'7', '0'}}, {{'7', '1'}}, {{'7', '2'}}, {{'7', '3'}}, {{'7', '4'}}, {{'7', '5'}}, {{'7', '6'}}, {{'7', '7'}}, {{'7', '8'}}, {{'7', '9'}},
+                {{'8', '0'}}, {{'8', '1'}}, {{'8', '2'}}, {{'8', '3'}}, {{'8', '4'}}, {{'8', '5'}}, {{'8', '6'}}, {{'8', '7'}}, {{'8', '8'}}, {{'8', '9'}},
+                {{'9', '0'}}, {{'9', '1'}}, {{'9', '2'}}, {{'9', '3'}}, {{'9', '4'}}, {{'9', '5'}}, {{'9', '6'}}, {{'9', '7'}}, {{'9', '8'}}, {{'9', '9'}},
+            }
+        };
+
         // special case for "0"
         if (x == 0)
         {
@@ -11432,28 +16135,57 @@ class serializer
             return;
         }
 
-        const bool is_negative = std::is_same<NumberType, number_integer_t>::value and not (x >= 0);  // see issue #755
-        std::size_t i = 0;
+        // use a pointer to fill the buffer
+        auto buffer_ptr = number_buffer.begin();
+
+        const bool is_negative = std::is_same<NumberType, number_integer_t>::value && !(x >= 0); // see issue #755
+        number_unsigned_t abs_value;
 
-        while (x != 0)
+        unsigned int n_chars;
+
+        if (is_negative)
         {
-            // spare 1 byte for '\0'
-            assert(i < number_buffer.size() - 1);
+            *buffer_ptr = '-';
+            abs_value = remove_sign(static_cast<number_integer_t>(x));
 
-            const auto digit = std::labs(static_cast<long>(x % 10));
-            number_buffer[i++] = static_cast<char>('0' + digit);
-            x /= 10;
+            // account one more byte for the minus sign
+            n_chars = 1 + count_digits(abs_value);
+        }
+        else
+        {
+            abs_value = static_cast<number_unsigned_t>(x);
+            n_chars = count_digits(abs_value);
         }
 
-        if (is_negative)
+        // spare 1 byte for '\0'
+        JSON_ASSERT(n_chars < number_buffer.size() - 1);
+
+        // jump to the end to generate the string from backward
+        // so we later avoid reversing the result
+        buffer_ptr += n_chars;
+
+        // Fast int2ascii implementation inspired by "Fastware" talk by Andrei Alexandrescu
+        // See: https://www.youtube.com/watch?v=o4-CwDo2zpg
+        while (abs_value >= 100)
+        {
+            const auto digits_index = static_cast<unsigned>((abs_value % 100));
+            abs_value /= 100;
+            *(--buffer_ptr) = digits_to_99[digits_index][1];
+            *(--buffer_ptr) = digits_to_99[digits_index][0];
+        }
+
+        if (abs_value >= 10)
+        {
+            const auto digits_index = static_cast<unsigned>(abs_value);
+            *(--buffer_ptr) = digits_to_99[digits_index][1];
+            *(--buffer_ptr) = digits_to_99[digits_index][0];
+        }
+        else
         {
-            // make sure there is capacity for the '-'
-            assert(i < number_buffer.size() - 2);
-            number_buffer[i++] = '-';
+            *(--buffer_ptr) = static_cast<char>('0' + abs_value);
         }
 
-        std::reverse(number_buffer.begin(), number_buffer.begin() + i);
-        o->write_characters(number_buffer.data(), i);
+        o->write_characters(number_buffer.data(), n_chars);
     }
 
     /*!
@@ -11467,7 +16199,7 @@ class serializer
     void dump_float(number_float_t x)
     {
         // NaN / inf
-        if (not std::isfinite(x))
+        if (!std::isfinite(x))
         {
             o->write_characters("null", 4);
             return;
@@ -11479,8 +16211,8 @@ class serializer
         //
         // NB: The test below works if <long double> == <double>.
         static constexpr bool is_ieee_single_or_double
-            = (std::numeric_limits<number_float_t>::is_iec559 and std::numeric_limits<number_float_t>::digits == 24 and std::numeric_limits<number_float_t>::max_exponent == 128) or
-              (std::numeric_limits<number_float_t>::is_iec559 and std::numeric_limits<number_float_t>::digits == 53 and std::numeric_limits<number_float_t>::max_exponent == 1024);
+            = (std::numeric_limits<number_float_t>::is_iec559 && std::numeric_limits<number_float_t>::digits == 24 && std::numeric_limits<number_float_t>::max_exponent == 128) ||
+              (std::numeric_limits<number_float_t>::is_iec559 && std::numeric_limits<number_float_t>::digits == 53 && std::numeric_limits<number_float_t>::max_exponent == 1024);
 
         dump_float(x, std::integral_constant<bool, is_ieee_single_or_double>());
     }
@@ -11502,9 +16234,9 @@ class serializer
         std::ptrdiff_t len = (std::snprintf)(number_buffer.data(), number_buffer.size(), "%.*g", d, x);
 
         // negative value indicates an error
-        assert(len > 0);
+        JSON_ASSERT(len > 0);
         // check if buffer was large enough
-        assert(static_cast<std::size_t>(len) < number_buffer.size());
+        JSON_ASSERT(static_cast<std::size_t>(len) < number_buffer.size());
 
         // erase thousands separator
         if (thousands_sep != '\0')
@@ -11512,12 +16244,12 @@ class serializer
             const auto end = std::remove(number_buffer.begin(),
                                          number_buffer.begin() + len, thousands_sep);
             std::fill(end, number_buffer.end(), '\0');
-            assert((end - number_buffer.begin()) <= len);
+            JSON_ASSERT((end - number_buffer.begin()) <= len);
             len = (end - number_buffer.begin());
         }
 
         // convert decimal point to '.'
-        if (decimal_point != '\0' and decimal_point != '.')
+        if (decimal_point != '\0' && decimal_point != '.')
         {
             const auto dec_pos = std::find(number_buffer.begin(), number_buffer.end(), decimal_point);
             if (dec_pos != number_buffer.end())
@@ -11533,7 +16265,7 @@ class serializer
             std::none_of(number_buffer.begin(), number_buffer.begin() + len + 1,
                          [](char c)
         {
-            return (c == '.' or c == 'e');
+            return c == '.' || c == 'e';
         });
 
         if (value_is_int_like)
@@ -11563,9 +16295,9 @@ class serializer
     @copyright Copyright (c) 2008-2009 Bjoern Hoehrmann <bjoern@hoehrmann.de>
     @sa http://bjoern.hoehrmann.de/utf-8/decoder/dfa/
     */
-    static uint8_t decode(uint8_t& state, uint32_t& codep, const uint8_t byte) noexcept
+    static std::uint8_t decode(std::uint8_t& state, std::uint32_t& codep, const std::uint8_t byte) noexcept
     {
-        static const std::array<uint8_t, 400> utf8d =
+        static const std::array<std::uint8_t, 400> utf8d =
         {
             {
                 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 00..1F
@@ -11585,16 +16317,44 @@ class serializer
             }
         };
 
-        const uint8_t type = utf8d[byte];
+        const std::uint8_t type = utf8d[byte];
 
         codep = (state != UTF8_ACCEPT)
-                ? (byte & 0x3fu) | (codep << 6)
-                : static_cast<uint32_t>(0xff >> type) & (byte);
+                ? (byte & 0x3fu) | (codep << 6u)
+                : (0xFFu >> type) & (byte);
 
-        state = utf8d[256u + state * 16u + type];
+        std::size_t index = 256u + static_cast<size_t>(state) * 16u + static_cast<size_t>(type);
+        JSON_ASSERT(index < 400);
+        state = utf8d[index];
         return state;
     }
 
+    /*
+     * Overload to make the compiler happy while it is instantiating
+     * dump_integer for number_unsigned_t.
+     * Must never be called.
+     */
+    number_unsigned_t remove_sign(number_unsigned_t x)
+    {
+        JSON_ASSERT(false); // LCOV_EXCL_LINE
+        return x; // LCOV_EXCL_LINE
+    }
+
+    /*
+     * Helper function for dump_integer
+     *
+     * This function takes a negative signed integer and returns its absolute
+     * value as unsigned integer. The plus/minus shuffling is necessary as we can
+     * not directly remove the sign of an arbitrary signed integer as the
+     * absolute values of INT_MIN and INT_MAX are usually not the same. See
+     * #1708 for details.
+     */
+    inline number_unsigned_t remove_sign(number_integer_t x) noexcept
+    {
+        JSON_ASSERT(x < 0 && x < (std::numeric_limits<number_integer_t>::max)());
+        return static_cast<number_unsigned_t>(-(x + 1)) + 1;
+    }
+
   private:
     /// the output of the serializer
     output_adapter_t<char> o = nullptr;
@@ -11623,827 +16383,178 @@ class serializer
 }  // namespace detail
 }  // namespace nlohmann
 
-// #include <nlohmann/detail/json_ref.hpp>
-
-
-#include <initializer_list>
-#include <utility>
-
-// #include <nlohmann/detail/meta/type_traits.hpp>
-
-
-namespace nlohmann
-{
-namespace detail
-{
-template<typename BasicJsonType>
-class json_ref
-{
-  public:
-    using value_type = BasicJsonType;
-
-    json_ref(value_type&& value)
-        : owned_value(std::move(value)), value_ref(&owned_value), is_rvalue(true)
-    {}
-
-    json_ref(const value_type& value)
-        : value_ref(const_cast<value_type*>(&value)), is_rvalue(false)
-    {}
-
-    json_ref(std::initializer_list<json_ref> init)
-        : owned_value(init), value_ref(&owned_value), is_rvalue(true)
-    {}
-
-    template <
-        class... Args,
-        enable_if_t<std::is_constructible<value_type, Args...>::value, int> = 0 >
-    json_ref(Args && ... args)
-        : owned_value(std::forward<Args>(args)...), value_ref(&owned_value),
-          is_rvalue(true) {}
-
-    // class should be movable only
-    json_ref(json_ref&&) = default;
-    json_ref(const json_ref&) = delete;
-    json_ref& operator=(const json_ref&) = delete;
-    json_ref& operator=(json_ref&&) = delete;
-    ~json_ref() = default;
-
-    value_type moved_or_copied() const
-    {
-        if (is_rvalue)
-        {
-            return std::move(*value_ref);
-        }
-        return *value_ref;
-    }
-
-    value_type const& operator*() const
-    {
-        return *static_cast<value_type const*>(value_ref);
-    }
-
-    value_type const* operator->() const
-    {
-        return static_cast<value_type const*>(value_ref);
-    }
+// #include <nlohmann/detail/value_t.hpp>
 
-  private:
-    mutable value_type owned_value = nullptr;
-    value_type* value_ref = nullptr;
-    const bool is_rvalue;
-};
-}  // namespace detail
-}  // namespace nlohmann
+// #include <nlohmann/json_fwd.hpp>
 
-// #include <nlohmann/detail/json_pointer.hpp>
+// #include <nlohmann/ordered_map.hpp>
 
 
-#include <cassert> // assert
-#include <numeric> // accumulate
-#include <string> // string
+#include <functional> // less
+#include <memory> // allocator
+#include <utility> // pair
 #include <vector> // vector
 
-// #include <nlohmann/detail/macro_scope.hpp>
-
-// #include <nlohmann/detail/exceptions.hpp>
-
-// #include <nlohmann/detail/value_t.hpp>
-
-
 namespace nlohmann
 {
-template<typename BasicJsonType>
-class json_pointer
-{
-    // allow basic_json to access private members
-    NLOHMANN_BASIC_JSON_TPL_DECLARATION
-    friend class basic_json;
 
-  public:
-    /*!
-    @brief create JSON pointer
-
-    Create a JSON pointer according to the syntax described in
-    [Section 3 of RFC6901](https://tools.ietf.org/html/rfc6901#section-3).
-
-    @param[in] s  string representing the JSON pointer; if omitted, the empty
-                  string is assumed which references the whole JSON value
-
-    @throw parse_error.107 if the given JSON pointer @a s is nonempty and does
-                           not begin with a slash (`/`); see example below
-
-    @throw parse_error.108 if a tilde (`~`) in the given JSON pointer @a s is
-    not followed by `0` (representing `~`) or `1` (representing `/`); see
-    example below
-
-    @liveexample{The example shows the construction several valid JSON pointers
-    as well as the exceptional behavior.,json_pointer}
-
-    @since version 2.0.0
-    */
-    explicit json_pointer(const std::string& s = "")
-        : reference_tokens(split(s))
-    {}
-
-    /*!
-    @brief return a string representation of the JSON pointer
-
-    @invariant For each JSON pointer `ptr`, it holds:
-    @code {.cpp}
-    ptr == json_pointer(ptr.to_string());
-    @endcode
-
-    @return a string representation of the JSON pointer
-
-    @liveexample{The example shows the result of `to_string`.,
-    json_pointer__to_string}
-
-    @since version 2.0.0
-    */
-    std::string to_string() const
-    {
-        return std::accumulate(reference_tokens.begin(), reference_tokens.end(),
-                               std::string{},
-                               [](const std::string & a, const std::string & b)
-        {
-            return a + "/" + escape(b);
-        });
-    }
-
-    /// @copydoc to_string()
-    operator std::string() const
-    {
-        return to_string();
-    }
-
-    /*!
-    @param[in] s  reference token to be converted into an array index
-
-    @return integer representation of @a s
-
-    @throw out_of_range.404 if string @a s could not be converted to an integer
-    */
-    static int array_index(const std::string& s)
-    {
-        std::size_t processed_chars = 0;
-        const int res = std::stoi(s, &processed_chars);
-
-        // check if the string was completely read
-        if (JSON_UNLIKELY(processed_chars != s.size()))
-        {
-            JSON_THROW(detail::out_of_range::create(404, "unresolved reference token '" + s + "'"));
-        }
+/// ordered_map: a minimal map-like container that preserves insertion order
+/// for use within nlohmann::basic_json<ordered_map>
+template <class Key, class T, class IgnoredLess = std::less<Key>,
+          class Allocator = std::allocator<std::pair<const Key, T>>>
+                  struct ordered_map : std::vector<std::pair<const Key, T>, Allocator>
+{
+    using key_type = Key;
+    using mapped_type = T;
+    using Container = std::vector<std::pair<const Key, T>, Allocator>;
+    using typename Container::iterator;
+    using typename Container::const_iterator;
+    using typename Container::size_type;
+    using typename Container::value_type;
 
-        return res;
-    }
+    // Explicit constructors instead of `using Container::Container`
+    // otherwise older compilers choke on it (GCC <= 5.5, xcode <= 9.4)
+    ordered_map(const Allocator& alloc = Allocator()) : Container{alloc} {}
+    template <class It>
+    ordered_map(It first, It last, const Allocator& alloc = Allocator())
+        : Container{first, last, alloc} {}
+    ordered_map(std::initializer_list<T> init, const Allocator& alloc = Allocator() )
+        : Container{init, alloc} {}
 
-  private:
-    /*!
-    @brief remove and return last reference pointer
-    @throw out_of_range.405 if JSON pointer has no parent
-    */
-    std::string pop_back()
+    std::pair<iterator, bool> emplace(const key_type& key, T&& t)
     {
-        if (JSON_UNLIKELY(is_root()))
+        for (auto it = this->begin(); it != this->end(); ++it)
         {
-            JSON_THROW(detail::out_of_range::create(405, "JSON pointer has no parent"));
+            if (it->first == key)
+            {
+                return {it, false};
+            }
         }
-
-        auto last = reference_tokens.back();
-        reference_tokens.pop_back();
-        return last;
+        Container::emplace_back(key, t);
+        return {--this->end(), true};
     }
 
-    /// return whether pointer points to the root document
-    bool is_root() const noexcept
+    T& operator[](const Key& key)
     {
-        return reference_tokens.empty();
+        return emplace(key, T{}).first->second;
     }
 
-    json_pointer top() const
+    const T& operator[](const Key& key) const
     {
-        if (JSON_UNLIKELY(is_root()))
-        {
-            JSON_THROW(detail::out_of_range::create(405, "JSON pointer has no parent"));
-        }
-
-        json_pointer result = *this;
-        result.reference_tokens = {reference_tokens[0]};
-        return result;
+        return at(key);
     }
 
-    /*!
-    @brief create and return a reference to the pointed to value
-
-    @complexity Linear in the number of reference tokens.
-
-    @throw parse_error.109 if array index is not a number
-    @throw type_error.313 if value cannot be unflattened
-    */
-    BasicJsonType& get_and_create(BasicJsonType& j) const
+    T& at(const Key& key)
     {
-        using size_type = typename BasicJsonType::size_type;
-        auto result = &j;
-
-        // in case no reference tokens exist, return a reference to the JSON value
-        // j which will be overwritten by a primitive value
-        for (const auto& reference_token : reference_tokens)
+        for (auto it = this->begin(); it != this->end(); ++it)
         {
-            switch (result->m_type)
+            if (it->first == key)
             {
-                case detail::value_t::null:
-                {
-                    if (reference_token == "0")
-                    {
-                        // start a new array if reference token is 0
-                        result = &result->operator[](0);
-                    }
-                    else
-                    {
-                        // start a new object otherwise
-                        result = &result->operator[](reference_token);
-                    }
-                    break;
-                }
-
-                case detail::value_t::object:
-                {
-                    // create an entry in the object
-                    result = &result->operator[](reference_token);
-                    break;
-                }
-
-                case detail::value_t::array:
-                {
-                    // create an entry in the array
-                    JSON_TRY
-                    {
-                        result = &result->operator[](static_cast<size_type>(array_index(reference_token)));
-                    }
-                    JSON_CATCH(std::invalid_argument&)
-                    {
-                        JSON_THROW(detail::parse_error::create(109, 0, "array index '" + reference_token + "' is not a number"));
-                    }
-                    break;
-                }
-
-                /*
-                The following code is only reached if there exists a reference
-                token _and_ the current value is primitive. In this case, we have
-                an error situation, because primitive values may only occur as
-                single value; that is, with an empty list of reference tokens.
-                */
-                default:
-                    JSON_THROW(detail::type_error::create(313, "invalid value to unflatten"));
+                return it->second;
             }
         }
 
-        return *result;
+        throw std::out_of_range("key not found");
     }
 
-    /*!
-    @brief return a reference to the pointed to value
-
-    @note This version does not throw if a value is not present, but tries to
-          create nested values instead. For instance, calling this function
-          with pointer `"/this/that"` on a null value is equivalent to calling
-          `operator[]("this").operator[]("that")` on that value, effectively
-          changing the null value to an object.
-
-    @param[in] ptr  a JSON value
-
-    @return reference to the JSON value pointed to by the JSON pointer
-
-    @complexity Linear in the length of the JSON pointer.
-
-    @throw parse_error.106   if an array index begins with '0'
-    @throw parse_error.109   if an array index was not a number
-    @throw out_of_range.404  if the JSON pointer can not be resolved
-    */
-    BasicJsonType& get_unchecked(BasicJsonType* ptr) const
+    const T& at(const Key& key) const
     {
-        using size_type = typename BasicJsonType::size_type;
-        for (const auto& reference_token : reference_tokens)
+        for (auto it = this->begin(); it != this->end(); ++it)
         {
-            // convert null values to arrays or objects before continuing
-            if (ptr->m_type == detail::value_t::null)
-            {
-                // check if reference token is a number
-                const bool nums =
-                    std::all_of(reference_token.begin(), reference_token.end(),
-                                [](const char x)
-                {
-                    return (x >= '0' and x <= '9');
-                });
-
-                // change value to array for numbers or "-" or to object otherwise
-                *ptr = (nums or reference_token == "-")
-                       ? detail::value_t::array
-                       : detail::value_t::object;
-            }
-
-            switch (ptr->m_type)
+            if (it->first == key)
             {
-                case detail::value_t::object:
-                {
-                    // use unchecked object access
-                    ptr = &ptr->operator[](reference_token);
-                    break;
-                }
-
-                case detail::value_t::array:
-                {
-                    // error condition (cf. RFC 6901, Sect. 4)
-                    if (JSON_UNLIKELY(reference_token.size() > 1 and reference_token[0] == '0'))
-                    {
-                        JSON_THROW(detail::parse_error::create(106, 0,
-                                                               "array index '" + reference_token +
-                                                               "' must not begin with '0'"));
-                    }
-
-                    if (reference_token == "-")
-                    {
-                        // explicitly treat "-" as index beyond the end
-                        ptr = &ptr->operator[](ptr->m_value.array->size());
-                    }
-                    else
-                    {
-                        // convert array index to number; unchecked access
-                        JSON_TRY
-                        {
-                            ptr = &ptr->operator[](
-                                static_cast<size_type>(array_index(reference_token)));
-                        }
-                        JSON_CATCH(std::invalid_argument&)
-                        {
-                            JSON_THROW(detail::parse_error::create(109, 0, "array index '" + reference_token + "' is not a number"));
-                        }
-                    }
-                    break;
-                }
-
-                default:
-                    JSON_THROW(detail::out_of_range::create(404, "unresolved reference token '" + reference_token + "'"));
+                return it->second;
             }
         }
 
-        return *ptr;
+        throw std::out_of_range("key not found");
     }
 
-    /*!
-    @throw parse_error.106   if an array index begins with '0'
-    @throw parse_error.109   if an array index was not a number
-    @throw out_of_range.402  if the array index '-' is used
-    @throw out_of_range.404  if the JSON pointer can not be resolved
-    */
-    BasicJsonType& get_checked(BasicJsonType* ptr) const
+    size_type erase(const Key& key)
     {
-        using size_type = typename BasicJsonType::size_type;
-        for (const auto& reference_token : reference_tokens)
+        for (auto it = this->begin(); it != this->end(); ++it)
         {
-            switch (ptr->m_type)
+            if (it->first == key)
             {
-                case detail::value_t::object:
+                // Since we cannot move const Keys, re-construct them in place
+                for (auto next = it; ++next != this->end(); ++it)
                 {
-                    // note: at performs range check
-                    ptr = &ptr->at(reference_token);
-                    break;
-                }
-
-                case detail::value_t::array:
-                {
-                    if (JSON_UNLIKELY(reference_token == "-"))
-                    {
-                        // "-" always fails the range check
-                        JSON_THROW(detail::out_of_range::create(402,
-                                                                "array index '-' (" + std::to_string(ptr->m_value.array->size()) +
-                                                                ") is out of range"));
-                    }
-
-                    // error condition (cf. RFC 6901, Sect. 4)
-                    if (JSON_UNLIKELY(reference_token.size() > 1 and reference_token[0] == '0'))
-                    {
-                        JSON_THROW(detail::parse_error::create(106, 0,
-                                                               "array index '" + reference_token +
-                                                               "' must not begin with '0'"));
-                    }
-
-                    // note: at performs range check
-                    JSON_TRY
-                    {
-                        ptr = &ptr->at(static_cast<size_type>(array_index(reference_token)));
-                    }
-                    JSON_CATCH(std::invalid_argument&)
-                    {
-                        JSON_THROW(detail::parse_error::create(109, 0, "array index '" + reference_token + "' is not a number"));
-                    }
-                    break;
+                    it->~value_type(); // Destroy but keep allocation
+                    new (&*it) value_type{std::move(*next)};
                 }
-
-                default:
-                    JSON_THROW(detail::out_of_range::create(404, "unresolved reference token '" + reference_token + "'"));
+                Container::pop_back();
+                return 1;
             }
         }
-
-        return *ptr;
+        return 0;
     }
 
-    /*!
-    @brief return a const reference to the pointed to value
-
-    @param[in] ptr  a JSON value
-
-    @return const reference to the JSON value pointed to by the JSON
-    pointer
-
-    @throw parse_error.106   if an array index begins with '0'
-    @throw parse_error.109   if an array index was not a number
-    @throw out_of_range.402  if the array index '-' is used
-    @throw out_of_range.404  if the JSON pointer can not be resolved
-    */
-    const BasicJsonType& get_unchecked(const BasicJsonType* ptr) const
+    iterator erase(iterator pos)
     {
-        using size_type = typename BasicJsonType::size_type;
-        for (const auto& reference_token : reference_tokens)
-        {
-            switch (ptr->m_type)
-            {
-                case detail::value_t::object:
-                {
-                    // use unchecked object access
-                    ptr = &ptr->operator[](reference_token);
-                    break;
-                }
+        auto it = pos;
 
-                case detail::value_t::array:
-                {
-                    if (JSON_UNLIKELY(reference_token == "-"))
-                    {
-                        // "-" cannot be used for const access
-                        JSON_THROW(detail::out_of_range::create(402,
-                                                                "array index '-' (" + std::to_string(ptr->m_value.array->size()) +
-                                                                ") is out of range"));
-                    }
-
-                    // error condition (cf. RFC 6901, Sect. 4)
-                    if (JSON_UNLIKELY(reference_token.size() > 1 and reference_token[0] == '0'))
-                    {
-                        JSON_THROW(detail::parse_error::create(106, 0,
-                                                               "array index '" + reference_token +
-                                                               "' must not begin with '0'"));
-                    }
-
-                    // use unchecked array access
-                    JSON_TRY
-                    {
-                        ptr = &ptr->operator[](
-                            static_cast<size_type>(array_index(reference_token)));
-                    }
-                    JSON_CATCH(std::invalid_argument&)
-                    {
-                        JSON_THROW(detail::parse_error::create(109, 0, "array index '" + reference_token + "' is not a number"));
-                    }
-                    break;
-                }
-
-                default:
-                    JSON_THROW(detail::out_of_range::create(404, "unresolved reference token '" + reference_token + "'"));
-            }
+        // Since we cannot move const Keys, re-construct them in place
+        for (auto next = it; ++next != this->end(); ++it)
+        {
+            it->~value_type(); // Destroy but keep allocation
+            new (&*it) value_type{std::move(*next)};
         }
-
-        return *ptr;
+        Container::pop_back();
+        return pos;
     }
 
-    /*!
-    @throw parse_error.106   if an array index begins with '0'
-    @throw parse_error.109   if an array index was not a number
-    @throw out_of_range.402  if the array index '-' is used
-    @throw out_of_range.404  if the JSON pointer can not be resolved
-    */
-    const BasicJsonType& get_checked(const BasicJsonType* ptr) const
+    size_type count(const Key& key) const
     {
-        using size_type = typename BasicJsonType::size_type;
-        for (const auto& reference_token : reference_tokens)
+        for (auto it = this->begin(); it != this->end(); ++it)
         {
-            switch (ptr->m_type)
+            if (it->first == key)
             {
-                case detail::value_t::object:
-                {
-                    // note: at performs range check
-                    ptr = &ptr->at(reference_token);
-                    break;
-                }
-
-                case detail::value_t::array:
-                {
-                    if (JSON_UNLIKELY(reference_token == "-"))
-                    {
-                        // "-" always fails the range check
-                        JSON_THROW(detail::out_of_range::create(402,
-                                                                "array index '-' (" + std::to_string(ptr->m_value.array->size()) +
-                                                                ") is out of range"));
-                    }
-
-                    // error condition (cf. RFC 6901, Sect. 4)
-                    if (JSON_UNLIKELY(reference_token.size() > 1 and reference_token[0] == '0'))
-                    {
-                        JSON_THROW(detail::parse_error::create(106, 0,
-                                                               "array index '" + reference_token +
-                                                               "' must not begin with '0'"));
-                    }
-
-                    // note: at performs range check
-                    JSON_TRY
-                    {
-                        ptr = &ptr->at(static_cast<size_type>(array_index(reference_token)));
-                    }
-                    JSON_CATCH(std::invalid_argument&)
-                    {
-                        JSON_THROW(detail::parse_error::create(109, 0, "array index '" + reference_token + "' is not a number"));
-                    }
-                    break;
-                }
-
-                default:
-                    JSON_THROW(detail::out_of_range::create(404, "unresolved reference token '" + reference_token + "'"));
+                return 1;
             }
         }
-
-        return *ptr;
+        return 0;
     }
 
-    /*!
-    @brief split the string input to reference tokens
-
-    @note This function is only called by the json_pointer constructor.
-          All exceptions below are documented there.
-
-    @throw parse_error.107  if the pointer is not empty or begins with '/'
-    @throw parse_error.108  if character '~' is not followed by '0' or '1'
-    */
-    static std::vector<std::string> split(const std::string& reference_string)
+    iterator find(const Key& key)
     {
-        std::vector<std::string> result;
-
-        // special case: empty reference string -> no reference tokens
-        if (reference_string.empty())
-        {
-            return result;
-        }
-
-        // check if nonempty reference string begins with slash
-        if (JSON_UNLIKELY(reference_string[0] != '/'))
-        {
-            JSON_THROW(detail::parse_error::create(107, 1,
-                                                   "JSON pointer must be empty or begin with '/' - was: '" +
-                                                   reference_string + "'"));
-        }
-
-        // extract the reference tokens:
-        // - slash: position of the last read slash (or end of string)
-        // - start: position after the previous slash
-        for (
-            // search for the first slash after the first character
-            std::size_t slash = reference_string.find_first_of('/', 1),
-            // set the beginning of the first reference token
-            start = 1;
-            // we can stop if start == 0 (if slash == std::string::npos)
-            start != 0;
-            // set the beginning of the next reference token
-            // (will eventually be 0 if slash == std::string::npos)
-            start = (slash == std::string::npos) ? 0 : slash + 1,
-            // find next slash
-            slash = reference_string.find_first_of('/', start))
+        for (auto it = this->begin(); it != this->end(); ++it)
         {
-            // use the text between the beginning of the reference token
-            // (start) and the last slash (slash).
-            auto reference_token = reference_string.substr(start, slash - start);
-
-            // check reference tokens are properly escaped
-            for (std::size_t pos = reference_token.find_first_of('~');
-                    pos != std::string::npos;
-                    pos = reference_token.find_first_of('~', pos + 1))
+            if (it->first == key)
             {
-                assert(reference_token[pos] == '~');
-
-                // ~ must be followed by 0 or 1
-                if (JSON_UNLIKELY(pos == reference_token.size() - 1 or
-                                  (reference_token[pos + 1] != '0' and
-                                   reference_token[pos + 1] != '1')))
-                {
-                    JSON_THROW(detail::parse_error::create(108, 0, "escape character '~' must be followed with '0' or '1'"));
-                }
+                return it;
             }
-
-            // finally, store the reference token
-            unescape(reference_token);
-            result.push_back(reference_token);
         }
-
-        return result;
-    }
-
-    /*!
-    @brief replace all occurrences of a substring by another string
-
-    @param[in,out] s  the string to manipulate; changed so that all
-                   occurrences of @a f are replaced with @a t
-    @param[in]     f  the substring to replace with @a t
-    @param[in]     t  the string to replace @a f
-
-    @pre The search string @a f must not be empty. **This precondition is
-    enforced with an assertion.**
-
-    @since version 2.0.0
-    */
-    static void replace_substring(std::string& s, const std::string& f,
-                                  const std::string& t)
-    {
-        assert(not f.empty());
-        for (auto pos = s.find(f);                // find first occurrence of f
-                pos != std::string::npos;         // make sure f was found
-                s.replace(pos, f.size(), t),      // replace with t, and
-                pos = s.find(f, pos + t.size()))  // find next occurrence of f
-        {}
-    }
-
-    /// escape "~" to "~0" and "/" to "~1"
-    static std::string escape(std::string s)
-    {
-        replace_substring(s, "~", "~0");
-        replace_substring(s, "/", "~1");
-        return s;
-    }
-
-    /// unescape "~1" to tilde and "~0" to slash (order is important!)
-    static void unescape(std::string& s)
-    {
-        replace_substring(s, "~1", "/");
-        replace_substring(s, "~0", "~");
+        return Container::end();
     }
 
-    /*!
-    @param[in] reference_string  the reference string to the current value
-    @param[in] value             the value to consider
-    @param[in,out] result        the result object to insert values to
-
-    @note Empty objects or arrays are flattened to `null`.
-    */
-    static void flatten(const std::string& reference_string,
-                        const BasicJsonType& value,
-                        BasicJsonType& result)
+    const_iterator find(const Key& key) const
     {
-        switch (value.m_type)
+        for (auto it = this->begin(); it != this->end(); ++it)
         {
-            case detail::value_t::array:
+            if (it->first == key)
             {
-                if (value.m_value.array->empty())
-                {
-                    // flatten empty array as null
-                    result[reference_string] = nullptr;
-                }
-                else
-                {
-                    // iterate array and use index as reference string
-                    for (std::size_t i = 0; i < value.m_value.array->size(); ++i)
-                    {
-                        flatten(reference_string + "/" + std::to_string(i),
-                                value.m_value.array->operator[](i), result);
-                    }
-                }
-                break;
-            }
-
-            case detail::value_t::object:
-            {
-                if (value.m_value.object->empty())
-                {
-                    // flatten empty object as null
-                    result[reference_string] = nullptr;
-                }
-                else
-                {
-                    // iterate object and use keys as reference string
-                    for (const auto& element : *value.m_value.object)
-                    {
-                        flatten(reference_string + "/" + escape(element.first), element.second, result);
-                    }
-                }
-                break;
-            }
-
-            default:
-            {
-                // add primitive value with its reference string
-                result[reference_string] = value;
-                break;
+                return it;
             }
         }
+        return Container::end();
     }
 
-    /*!
-    @param[in] value  flattened JSON
-
-    @return unflattened JSON
-
-    @throw parse_error.109 if array index is not a number
-    @throw type_error.314  if value is not an object
-    @throw type_error.315  if object values are not primitive
-    @throw type_error.313  if value cannot be unflattened
-    */
-    static BasicJsonType
-    unflatten(const BasicJsonType& value)
+    std::pair<iterator, bool> insert( value_type&& value )
     {
-        if (JSON_UNLIKELY(not value.is_object()))
-        {
-            JSON_THROW(detail::type_error::create(314, "only objects can be unflattened"));
-        }
-
-        BasicJsonType result;
+        return emplace(value.first, std::move(value.second));
+    }
 
-        // iterate the JSON object values
-        for (const auto& element : *value.m_value.object)
+    std::pair<iterator, bool> insert( const value_type& value )
+    {
+        for (auto it = this->begin(); it != this->end(); ++it)
         {
-            if (JSON_UNLIKELY(not element.second.is_primitive()))
+            if (it->first == value.first)
             {
-                JSON_THROW(detail::type_error::create(315, "values in object must be primitive"));
+                return {it, false};
             }
-
-            // assign value to reference pointed to by JSON pointer; Note that if
-            // the JSON pointer is "" (i.e., points to the whole value), function
-            // get_and_create returns a reference to result itself. An assignment
-            // will then create a primitive value.
-            json_pointer(element.first).get_and_create(result) = element.second;
         }
-
-        return result;
-    }
-
-    friend bool operator==(json_pointer const& lhs,
-                           json_pointer const& rhs) noexcept
-    {
-        return (lhs.reference_tokens == rhs.reference_tokens);
-    }
-
-    friend bool operator!=(json_pointer const& lhs,
-                           json_pointer const& rhs) noexcept
-    {
-        return not (lhs == rhs);
-    }
-
-    /// the reference tokens
-    std::vector<std::string> reference_tokens;
-};
-}  // namespace nlohmann
-
-// #include <nlohmann/adl_serializer.hpp>
-
-
-#include <utility>
-
-// #include <nlohmann/detail/conversions/from_json.hpp>
-
-// #include <nlohmann/detail/conversions/to_json.hpp>
-
-
-namespace nlohmann
-{
-
-template<typename, typename>
-struct adl_serializer
-{
-    /*!
-    @brief convert a JSON value to any value type
-
-    This function is usually called by the `get()` function of the
-    @ref basic_json class (either explicit or via conversion operators).
-
-    @param[in] j        JSON value to read from
-    @param[in,out] val  value to write to
-    */
-    template<typename BasicJsonType, typename ValueType>
-    static auto from_json(BasicJsonType&& j, ValueType& val) noexcept(
-        noexcept(::nlohmann::from_json(std::forward<BasicJsonType>(j), val)))
-    -> decltype(::nlohmann::from_json(std::forward<BasicJsonType>(j), val), void())
-    {
-        ::nlohmann::from_json(std::forward<BasicJsonType>(j), val);
-    }
-
-    /*!
-    @brief convert any value type to a JSON value
-
-    This function is usually called by the constructors of the @ref basic_json
-    class.
-
-    @param[in,out] j  JSON value to write to
-    @param[in] val    value to read from
-    */
-    template <typename BasicJsonType, typename ValueType>
-    static auto to_json(BasicJsonType& j, ValueType&& val) noexcept(
-        noexcept(::nlohmann::to_json(j, std::forward<ValueType>(val))))
-    -> decltype(::nlohmann::to_json(j, std::forward<ValueType>(val)), void())
-    {
-        ::nlohmann::to_json(j, std::forward<ValueType>(val));
+        Container::push_back(value);
+        return {--this->end(), true};
     }
 };
 
@@ -12475,6 +16586,9 @@ default; will be used in @ref number_integer_t)
 `uint64_t` by default; will be used in @ref number_unsigned_t)
 @tparam NumberFloatType type for JSON floating-point numbers (`double` by
 default; will be used in @ref number_float_t)
+@tparam BinaryType type for packed binary data for compatibility with binary
+serialization formats (`std::vector<std::uint8_t>` by default; will be used in
+@ref binary_t)
 @tparam AllocatorType type of the allocator to use (`std::allocator` by
 default)
 @tparam JSONSerializer the serializer to resolve internal calls to `to_json()`
@@ -12529,7 +16643,7 @@ relationship:
 The invariants are checked by member function assert_invariant().
 
 @internal
-@note ObjectType trick from http://stackoverflow.com/a/9860911
+@note ObjectType trick from https://stackoverflow.com/a/9860911
 @endinternal
 
 @see [RFC 7159: The JavaScript Object Notation (JSON) Data Interchange
@@ -12545,13 +16659,15 @@ class basic_json
   private:
     template<detail::value_t> friend struct detail::external_constructor;
     friend ::nlohmann::json_pointer<basic_json>;
-    friend ::nlohmann::detail::parser<basic_json>;
+
+    template<typename BasicJsonType, typename InputType>
+    friend class ::nlohmann::detail::parser;
     friend ::nlohmann::detail::serializer<basic_json>;
     template<typename BasicJsonType>
     friend class ::nlohmann::detail::iter_impl;
     template<typename BasicJsonType, typename CharType>
     friend class ::nlohmann::detail::binary_writer;
-    template<typename BasicJsonType, typename SAX>
+    template<typename BasicJsonType, typename InputType, typename SAX>
     friend class ::nlohmann::detail::binary_reader;
     template<typename BasicJsonType>
     friend class ::nlohmann::detail::json_sax_dom_parser;
@@ -12562,8 +16678,19 @@ class basic_json
     using basic_json_t = NLOHMANN_BASIC_JSON_TPL;
 
     // convenience aliases for types residing in namespace detail;
-    using lexer = ::nlohmann::detail::lexer<basic_json>;
-    using parser = ::nlohmann::detail::parser<basic_json>;
+    using lexer = ::nlohmann::detail::lexer_base<basic_json>;
+
+    template<typename InputAdapterType>
+    static ::nlohmann::detail::parser<basic_json, InputAdapterType> parser(
+        InputAdapterType adapter,
+        detail::parser_callback_t<basic_json>cb = nullptr,
+        const bool allow_exceptions = true,
+        const bool ignore_comments = false
+                                 )
+    {
+        return ::nlohmann::detail::parser<basic_json, InputAdapterType>(std::move(adapter),
+                std::move(cb), allow_exceptions, ignore_comments);
+    }
 
     using primitive_iterator_t = ::nlohmann::detail::primitive_iterator_t;
     template<typename BasicJsonType>
@@ -12577,7 +16704,8 @@ class basic_json
     template<typename CharType>
     using output_adapter_t = ::nlohmann::detail::output_adapter_t<CharType>;
 
-    using binary_reader = ::nlohmann::detail::binary_reader<basic_json>;
+    template<typename InputType>
+    using binary_reader = ::nlohmann::detail::binary_reader<basic_json, InputType>;
     template<typename CharType> using binary_writer = ::nlohmann::detail::binary_writer<basic_json, CharType>;
 
     using serializer = ::nlohmann::detail::serializer<basic_json>;
@@ -12590,6 +16718,8 @@ class basic_json
     using json_serializer = JSONSerializer<T, SFINAE>;
     /// how to treat decoding errors
     using error_handler_t = detail::error_handler_t;
+    /// how to treat CBOR tags
+    using cbor_tag_handler_t = detail::cbor_tag_handler_t;
     /// helper type for initializer lists of basic_json values
     using initializer_list_t = std::initializer_list<detail::json_ref<basic_json>>;
 
@@ -12697,11 +16827,12 @@ class basic_json
 
     @since 2.1.0
     */
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json meta()
     {
         basic_json result;
 
-        result["copyright"] = "(C) 2013-2017 Niels Lohmann";
+        result["copyright"] = "(C) 2013-2020 Niels Lohmann";
         result["name"] = "JSON for Modern C++";
         result["url"] = "https://github.com/nlohmann/json";
         result["version"]["string"] =
@@ -13195,12 +17326,83 @@ class basic_json
     */
     using number_float_t = NumberFloatType;
 
+    /*!
+    @brief a type for a packed binary type
+
+    This type is a type designed to carry binary data that appears in various
+    serialized formats, such as CBOR's Major Type 2, MessagePack's bin, and
+    BSON's generic binary subtype. This type is NOT a part of standard JSON and
+    exists solely for compatibility with these binary types. As such, it is
+    simply defined as an ordered sequence of zero or more byte values.
+
+    Additionally, as an implementation detail, the subtype of the binary data is
+    carried around as a `std::uint8_t`, which is compatible with both of the
+    binary data formats that use binary subtyping, (though the specific
+    numbering is incompatible with each other, and it is up to the user to
+    translate between them).
+
+    [CBOR's RFC 7049](https://tools.ietf.org/html/rfc7049) describes this type
+    as:
+    > Major type 2: a byte string. The string's length in bytes is represented
+    > following the rules for positive integers (major type 0).
+
+    [MessagePack's documentation on the bin type
+    family](https://github.com/msgpack/msgpack/blob/master/spec.md#bin-format-family)
+    describes this type as:
+    > Bin format family stores an byte array in 2, 3, or 5 bytes of extra bytes
+    > in addition to the size of the byte array.
+
+    [BSON's specifications](http://bsonspec.org/spec.html) describe several
+    binary types; however, this type is intended to represent the generic binary
+    type which has the description:
+    > Generic binary subtype - This is the most commonly used binary subtype and
+    > should be the 'default' for drivers and tools.
+
+    None of these impose any limitations on the internal representation other
+    than the basic unit of storage be some type of array whose parts are
+    decomposable into bytes.
+
+    The default representation of this binary format is a
+    `std::vector<std::uint8_t>`, which is a very common way to represent a byte
+    array in modern C++.
+
+    #### Default type
+
+    The default values for @a BinaryType is `std::vector<std::uint8_t>`
+
+    #### Storage
+
+    Binary Arrays are stored as pointers in a @ref basic_json type. That is,
+    for any access to array values, a pointer of the type `binary_t*` must be
+    dereferenced.
+
+    #### Notes on subtypes
+
+    - CBOR
+       - Binary values are represented as byte strings. No subtypes are
+         supported and will be ignored when CBOR is written.
+    - MessagePack
+       - If a subtype is given and the binary array contains exactly 1, 2, 4, 8,
+         or 16 elements, the fixext family (fixext1, fixext2, fixext4, fixext8)
+         is used. For other sizes, the ext family (ext8, ext16, ext32) is used.
+         The subtype is then added as singed 8-bit integer.
+       - If no subtype is given, the bin family (bin8, bin16, bin32) is used.
+    - BSON
+       - If a subtype is given, it is used and added as unsigned 8-bit integer.
+       - If no subtype is given, the generic binary subtype 0x00 is used.
+
+    @sa @ref binary -- create a binary array
+
+    @since version 3.8.0
+    */
+    using binary_t = nlohmann::byte_container_with_subtype<BinaryType>;
     /// @}
 
   private:
 
     /// helper for exception-safe object creation
     template<typename T, typename... Args>
+    JSON_HEDLEY_RETURNS_NON_NULL
     static T* create(Args&& ... args)
     {
         AllocatorType<T> alloc;
@@ -13212,7 +17414,7 @@ class basic_json
         };
         std::unique_ptr<T, decltype(deleter)> object(AllocatorTraits::allocate(alloc, 1), deleter);
         AllocatorTraits::construct(alloc, object.get(), std::forward<Args>(args)...);
-        assert(object != nullptr);
+        JSON_ASSERT(object != nullptr);
         return object.release();
     }
 
@@ -13236,6 +17438,7 @@ class basic_json
     number    | number_integer  | @ref number_integer_t
     number    | number_unsigned | @ref number_unsigned_t
     number    | number_float    | @ref number_float_t
+    binary    | binary          | pointer to @ref binary_t
     null      | null            | *no value is stored*
 
     @note Variable-length types (objects, arrays, and strings) are stored as
@@ -13252,6 +17455,8 @@ class basic_json
         array_t* array;
         /// string (stored with pointer to save storage)
         string_t* string;
+        /// binary (stored with pointer to save storage)
+        binary_t* binary;
         /// boolean
         boolean_t boolean;
         /// number (integer)
@@ -13294,6 +17499,12 @@ class basic_json
                     break;
                 }
 
+                case value_t::binary:
+                {
+                    binary = create<binary_t>();
+                    break;
+                }
+
                 case value_t::boolean:
                 {
                     boolean = boolean_t(false);
@@ -13327,9 +17538,9 @@ class basic_json
                 default:
                 {
                     object = nullptr;  // silence warning, see #821
-                    if (JSON_UNLIKELY(t == value_t::null))
+                    if (JSON_HEDLEY_UNLIKELY(t == value_t::null))
                     {
-                        JSON_THROW(other_error::create(500, "961c151d2e87f2686a955a9be24d316f1362bf21 3.5.0")); // LCOV_EXCL_LINE
+                        JSON_THROW(other_error::create(500, "961c151d2e87f2686a955a9be24d316f1362bf21 3.9.1")); // LCOV_EXCL_LINE
                     }
                     break;
                 }
@@ -13372,8 +17583,79 @@ class basic_json
             array = create<array_t>(std::move(value));
         }
 
+        /// constructor for binary arrays
+        json_value(const typename binary_t::container_type& value)
+        {
+            binary = create<binary_t>(value);
+        }
+
+        /// constructor for rvalue binary arrays
+        json_value(typename binary_t::container_type&& value)
+        {
+            binary = create<binary_t>(std::move(value));
+        }
+
+        /// constructor for binary arrays (internal type)
+        json_value(const binary_t& value)
+        {
+            binary = create<binary_t>(value);
+        }
+
+        /// constructor for rvalue binary arrays (internal type)
+        json_value(binary_t&& value)
+        {
+            binary = create<binary_t>(std::move(value));
+        }
+
         void destroy(value_t t) noexcept
         {
+            // flatten the current json_value to a heap-allocated stack
+            std::vector<basic_json> stack;
+
+            // move the top-level items to stack
+            if (t == value_t::array)
+            {
+                stack.reserve(array->size());
+                std::move(array->begin(), array->end(), std::back_inserter(stack));
+            }
+            else if (t == value_t::object)
+            {
+                stack.reserve(object->size());
+                for (auto&& it : *object)
+                {
+                    stack.push_back(std::move(it.second));
+                }
+            }
+
+            while (!stack.empty())
+            {
+                // move the last item to local variable to be processed
+                basic_json current_item(std::move(stack.back()));
+                stack.pop_back();
+
+                // if current_item is array/object, move
+                // its children to the stack to be processed later
+                if (current_item.is_array())
+                {
+                    std::move(current_item.m_value.array->begin(), current_item.m_value.array->end(),
+                              std::back_inserter(stack));
+
+                    current_item.m_value.array->clear();
+                }
+                else if (current_item.is_object())
+                {
+                    for (auto&& it : *current_item.m_value.object)
+                    {
+                        stack.push_back(std::move(it.second));
+                    }
+
+                    current_item.m_value.object->clear();
+                }
+
+                // it's now safe that current_item get destructed
+                // since it doesn't have any children
+            }
+
             switch (t)
             {
                 case value_t::object:
@@ -13400,6 +17682,14 @@ class basic_json
                     break;
                 }
 
+                case value_t::binary:
+                {
+                    AllocatorType<binary_t> alloc;
+                    std::allocator_traits<decltype(alloc)>::destroy(alloc, binary);
+                    std::allocator_traits<decltype(alloc)>::deallocate(alloc, binary, 1);
+                    break;
+                }
+
                 default:
                 {
                     break;
@@ -13419,9 +17709,10 @@ class basic_json
     */
     void assert_invariant() const noexcept
     {
-        assert(m_type != value_t::object or m_value.object != nullptr);
-        assert(m_type != value_t::array or m_value.array != nullptr);
-        assert(m_type != value_t::string or m_value.string != nullptr);
+        JSON_ASSERT(m_type != value_t::object || m_value.object != nullptr);
+        JSON_ASSERT(m_type != value_t::array || m_value.array != nullptr);
+        JSON_ASSERT(m_type != value_t::string || m_value.string != nullptr);
+        JSON_ASSERT(m_type != value_t::binary || m_value.binary != nullptr);
     }
 
   public:
@@ -13444,7 +17735,7 @@ class basic_json
 
     @sa @ref parser_callback_t for more information and examples
     */
-    using parse_event_t = typename parser::parse_event_t;
+    using parse_event_t = detail::parse_event_t;
 
     /*!
     @brief per-element parser callback type
@@ -13495,7 +17786,7 @@ class basic_json
 
     @since version 1.0.0
     */
-    using parser_callback_t = typename parser::parser_callback_t;
+    using parser_callback_t = detail::parser_callback_t<basic_json>;
 
     //////////////////
     // constructors //
@@ -13520,6 +17811,7 @@ class basic_json
     number      | `0`
     object      | `{}`
     array       | `[]`
+    binary      | empty array
 
     @param[in] v  the type of the value to create
 
@@ -13591,6 +17883,12 @@ class basic_json
       @ref number_float_t, and all convertible number types such as `int`,
       `size_t`, `int64_t`, `float` or `double` can be used.
     - **boolean**: @ref boolean_t / `bool` can be used.
+    - **binary**: @ref binary_t / `std::vector<uint8_t>` may be used,
+      unfortunately because string literals cannot be distinguished from binary
+      character arrays by the C++ type system, all types compatible with `const
+      char*` will be directed to the string constructor instead.  This is both
+      for backwards compatibility, and due to the fact that a binary type is not
+      a standard JSON type.
 
     See the examples below.
 
@@ -13622,10 +17920,10 @@ class basic_json
 
     @since version 2.1.0
     */
-    template <typename CompatibleType,
-              typename U = detail::uncvref_t<CompatibleType>,
-              detail::enable_if_t<
-                  not detail::is_basic_json<U>::value and detail::is_compatible_type<basic_json_t, U>::value, int> = 0>
+    template < typename CompatibleType,
+               typename U = detail::uncvref_t<CompatibleType>,
+               detail::enable_if_t <
+                   !detail::is_basic_json<U>::value && detail::is_compatible_type<basic_json_t, U>::value, int > = 0 >
     basic_json(CompatibleType && val) noexcept(noexcept(
                 JSONSerializer<U>::to_json(std::declval<basic_json_t&>(),
                                            std::forward<CompatibleType>(val))))
@@ -13660,9 +17958,9 @@ class basic_json
 
     @since version 3.2.0
     */
-    template <typename BasicJsonType,
-              detail::enable_if_t<
-                  detail::is_basic_json<BasicJsonType>::value and not std::is_same<basic_json, BasicJsonType>::value, int> = 0>
+    template < typename BasicJsonType,
+               detail::enable_if_t <
+                   detail::is_basic_json<BasicJsonType>::value&& !std::is_same<basic_json, BasicJsonType>::value, int > = 0 >
     basic_json(const BasicJsonType& val)
     {
         using other_boolean_t = typename BasicJsonType::boolean_t;
@@ -13672,6 +17970,7 @@ class basic_json
         using other_string_t = typename BasicJsonType::string_t;
         using other_object_t = typename BasicJsonType::object_t;
         using other_array_t = typename BasicJsonType::array_t;
+        using other_binary_t = typename BasicJsonType::binary_t;
 
         switch (val.type())
         {
@@ -13696,12 +17995,17 @@ class basic_json
             case value_t::array:
                 JSONSerializer<other_array_t>::to_json(*this, val.template get_ref<const other_array_t&>());
                 break;
+            case value_t::binary:
+                JSONSerializer<other_binary_t>::to_json(*this, val.template get_ref<const other_binary_t&>());
+                break;
             case value_t::null:
                 *this = nullptr;
                 break;
             case value_t::discarded:
                 m_type = value_t::discarded;
                 break;
+            default:            // LCOV_EXCL_LINE
+                JSON_ASSERT(false);  // LCOV_EXCL_LINE
         }
         assert_invariant();
     }
@@ -13789,11 +18093,11 @@ class basic_json
         bool is_an_object = std::all_of(init.begin(), init.end(),
                                         [](const detail::json_ref<basic_json>& element_ref)
         {
-            return (element_ref->is_array() and element_ref->size() == 2 and (*element_ref)[0].is_string());
+            return element_ref->is_array() && element_ref->size() == 2 && (*element_ref)[0].is_string();
         });
 
         // adjust type if type deduction is not wanted
-        if (not type_deduction)
+        if (!type_deduction)
         {
             // if array is wanted, do not create an object though possible
             if (manual_type == value_t::array)
@@ -13802,7 +18106,7 @@ class basic_json
             }
 
             // if object is wanted but impossible, throw an exception
-            if (JSON_UNLIKELY(manual_type == value_t::object and not is_an_object))
+            if (JSON_HEDLEY_UNLIKELY(manual_type == value_t::object && !is_an_object))
             {
                 JSON_THROW(type_error::create(301, "cannot create object from initializer list"));
             }
@@ -13833,6 +18137,99 @@ class basic_json
     }
 
     /*!
+    @brief explicitly create a binary array (without subtype)
+
+    Creates a JSON binary array value from a given binary container. Binary
+    values are part of various binary formats, such as CBOR, MessagePack, and
+    BSON. This constructor is used to create a value for serialization to those
+    formats.
+
+    @note Note, this function exists because of the difficulty in correctly
+    specifying the correct template overload in the standard value ctor, as both
+    JSON arrays and JSON binary arrays are backed with some form of a
+    `std::vector`. Because JSON binary arrays are a non-standard extension it
+    was decided that it would be best to prevent automatic initialization of a
+    binary array type, for backwards compatibility and so it does not happen on
+    accident.
+
+    @param[in] init container containing bytes to use as binary type
+
+    @return JSON binary array value
+
+    @complexity Linear in the size of @a init.
+
+    @exceptionsafety Strong guarantee: if an exception is thrown, there are no
+    changes to any JSON value.
+
+    @since version 3.8.0
+    */
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    static basic_json binary(const typename binary_t::container_type& init)
+    {
+        auto res = basic_json();
+        res.m_type = value_t::binary;
+        res.m_value = init;
+        return res;
+    }
+
+    /*!
+    @brief explicitly create a binary array (with subtype)
+
+    Creates a JSON binary array value from a given binary container. Binary
+    values are part of various binary formats, such as CBOR, MessagePack, and
+    BSON. This constructor is used to create a value for serialization to those
+    formats.
+
+    @note Note, this function exists because of the difficulty in correctly
+    specifying the correct template overload in the standard value ctor, as both
+    JSON arrays and JSON binary arrays are backed with some form of a
+    `std::vector`. Because JSON binary arrays are a non-standard extension it
+    was decided that it would be best to prevent automatic initialization of a
+    binary array type, for backwards compatibility and so it does not happen on
+    accident.
+
+    @param[in] init container containing bytes to use as binary type
+    @param[in] subtype subtype to use in MessagePack and BSON
+
+    @return JSON binary array value
+
+    @complexity Linear in the size of @a init.
+
+    @exceptionsafety Strong guarantee: if an exception is thrown, there are no
+    changes to any JSON value.
+
+    @since version 3.8.0
+    */
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    static basic_json binary(const typename binary_t::container_type& init, std::uint8_t subtype)
+    {
+        auto res = basic_json();
+        res.m_type = value_t::binary;
+        res.m_value = binary_t(init, subtype);
+        return res;
+    }
+
+    /// @copydoc binary(const typename binary_t::container_type&)
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    static basic_json binary(typename binary_t::container_type&& init)
+    {
+        auto res = basic_json();
+        res.m_type = value_t::binary;
+        res.m_value = std::move(init);
+        return res;
+    }
+
+    /// @copydoc binary(const typename binary_t::container_type&, std::uint8_t)
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    static basic_json binary(typename binary_t::container_type&& init, std::uint8_t subtype)
+    {
+        auto res = basic_json();
+        res.m_type = value_t::binary;
+        res.m_value = binary_t(std::move(init), subtype);
+        return res;
+    }
+
+    /*!
     @brief explicitly create an array from an initializer list
 
     Creates a JSON array value from a given initializer list. That is, given a
@@ -13869,6 +18266,7 @@ class basic_json
 
     @since version 1.0.0
     */
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json array(initializer_list_t init = {})
     {
         return basic_json(init, false, value_t::array);
@@ -13912,6 +18310,7 @@ class basic_json
 
     @since version 1.0.0
     */
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json object(initializer_list_t init = {})
     {
         return basic_json(init, false, value_t::object);
@@ -14001,16 +18400,16 @@ class basic_json
 
     @since version 1.0.0
     */
-    template<class InputIT, typename std::enable_if<
-                 std::is_same<InputIT, typename basic_json_t::iterator>::value or
-                 std::is_same<InputIT, typename basic_json_t::const_iterator>::value, int>::type = 0>
+    template < class InputIT, typename std::enable_if <
+                   std::is_same<InputIT, typename basic_json_t::iterator>::value ||
+                   std::is_same<InputIT, typename basic_json_t::const_iterator>::value, int >::type = 0 >
     basic_json(InputIT first, InputIT last)
     {
-        assert(first.m_object != nullptr);
-        assert(last.m_object != nullptr);
+        JSON_ASSERT(first.m_object != nullptr);
+        JSON_ASSERT(last.m_object != nullptr);
 
         // make sure iterator fits the current value
-        if (JSON_UNLIKELY(first.m_object != last.m_object))
+        if (JSON_HEDLEY_UNLIKELY(first.m_object != last.m_object))
         {
             JSON_THROW(invalid_iterator::create(201, "iterators are not compatible"));
         }
@@ -14027,8 +18426,8 @@ class basic_json
             case value_t::number_unsigned:
             case value_t::string:
             {
-                if (JSON_UNLIKELY(not first.m_it.primitive_iterator.is_begin()
-                                  or not last.m_it.primitive_iterator.is_end()))
+                if (JSON_HEDLEY_UNLIKELY(!first.m_it.primitive_iterator.is_begin()
+                                         || !last.m_it.primitive_iterator.is_end()))
                 {
                     JSON_THROW(invalid_iterator::create(204, "iterators out of range"));
                 }
@@ -14085,6 +18484,12 @@ class basic_json
                 break;
             }
 
+            case value_t::binary:
+            {
+                m_value = *first.m_object->m_value.binary;
+                break;
+            }
+
             default:
                 JSON_THROW(invalid_iterator::create(206, "cannot construct with iterators from " +
                                                     std::string(first.m_object->type_name())));
@@ -14098,10 +18503,10 @@ class basic_json
     // other constructors and destructor //
     ///////////////////////////////////////
 
-    /// @private
-    basic_json(const detail::json_ref<basic_json>& ref)
-        : basic_json(ref.moved_or_copied())
-    {}
+    template<typename JsonRef,
+             detail::enable_if_t<detail::conjunction<detail::is_json_ref<JsonRef>,
+                                 std::is_same<typename JsonRef::value_type, basic_json>>::value, int> = 0 >
+    basic_json(const JsonRef& ref) : basic_json(ref.moved_or_copied()) {}
 
     /*!
     @brief copy constructor
@@ -14178,6 +18583,12 @@ class basic_json
                 break;
             }
 
+            case value_t::binary:
+            {
+                m_value = *other.m_value.binary;
+                break;
+            }
+
             default:
                 break;
         }
@@ -14249,9 +18660,9 @@ class basic_json
     @since version 1.0.0
     */
     basic_json& operator=(basic_json other) noexcept (
-        std::is_nothrow_move_constructible<value_t>::value and
-        std::is_nothrow_move_assignable<value_t>::value and
-        std::is_nothrow_move_constructible<json_value>::value and
+        std::is_nothrow_move_constructible<value_t>::value&&
+        std::is_nothrow_move_assignable<value_t>::value&&
+        std::is_nothrow_move_constructible<json_value>::value&&
         std::is_nothrow_move_assignable<json_value>::value
     )
     {
@@ -14317,12 +18728,17 @@ class basic_json
     @param[in] error_handler  how to react on decoding errors; there are three
     possible values: `strict` (throws and exception in case a decoding error
     occurs; default), `replace` (replace invalid UTF-8 sequences with U+FFFD),
-    and `ignore` (ignore invalid UTF-8 sequences during serialization).
+    and `ignore` (ignore invalid UTF-8 sequences during serialization; all
+    bytes are copied to the output unchanged).
 
     @return string containing the serialization of the JSON value
 
     @throw type_error.316 if a string stored inside the JSON value is not
-                          UTF-8 encoded
+                          UTF-8 encoded and @a error_handler is set to strict
+
+    @note Binary values are serialized as object containing two keys:
+      - "bytes": an array of bytes as integers
+      - "subtype": the subtype as integer or "null" if the binary has no subtype
 
     @complexity Linear.
 
@@ -14337,7 +18753,8 @@ class basic_json
 
     @since version 1.0.0; indentation character @a indent_char, option
            @a ensure_ascii and exceptions added in version 3.0.0; error
-           handlers added in version 3.4.0.
+           handlers added in version 3.4.0; serialization of binary values added
+           in version 3.8.0.
     */
     string_t dump(const int indent = -1,
                   const char indent_char = ' ',
@@ -14376,6 +18793,7 @@ class basic_json
             number (floating-point)   | value_t::number_float
             object                    | value_t::object
             array                     | value_t::array
+            binary                    | value_t::binary
             discarded                 | value_t::discarded
 
     @complexity Constant.
@@ -14418,12 +18836,13 @@ class basic_json
     @sa @ref is_string() -- returns whether JSON value is a string
     @sa @ref is_boolean() -- returns whether JSON value is a boolean
     @sa @ref is_number() -- returns whether JSON value is a number
+    @sa @ref is_binary() -- returns whether JSON value is a binary array
 
     @since version 1.0.0
     */
     constexpr bool is_primitive() const noexcept
     {
-        return is_null() or is_string() or is_boolean() or is_number();
+        return is_null() || is_string() || is_boolean() || is_number() || is_binary();
     }
 
     /*!
@@ -14450,7 +18869,7 @@ class basic_json
     */
     constexpr bool is_structured() const noexcept
     {
-        return is_array() or is_object();
+        return is_array() || is_object();
     }
 
     /*!
@@ -14472,7 +18891,7 @@ class basic_json
     */
     constexpr bool is_null() const noexcept
     {
-        return (m_type == value_t::null);
+        return m_type == value_t::null;
     }
 
     /*!
@@ -14494,7 +18913,7 @@ class basic_json
     */
     constexpr bool is_boolean() const noexcept
     {
-        return (m_type == value_t::boolean);
+        return m_type == value_t::boolean;
     }
 
     /*!
@@ -14524,7 +18943,7 @@ class basic_json
     */
     constexpr bool is_number() const noexcept
     {
-        return is_number_integer() or is_number_float();
+        return is_number_integer() || is_number_float();
     }
 
     /*!
@@ -14553,7 +18972,7 @@ class basic_json
     */
     constexpr bool is_number_integer() const noexcept
     {
-        return (m_type == value_t::number_integer or m_type == value_t::number_unsigned);
+        return m_type == value_t::number_integer || m_type == value_t::number_unsigned;
     }
 
     /*!
@@ -14581,7 +19000,7 @@ class basic_json
     */
     constexpr bool is_number_unsigned() const noexcept
     {
-        return (m_type == value_t::number_unsigned);
+        return m_type == value_t::number_unsigned;
     }
 
     /*!
@@ -14609,7 +19028,7 @@ class basic_json
     */
     constexpr bool is_number_float() const noexcept
     {
-        return (m_type == value_t::number_float);
+        return m_type == value_t::number_float;
     }
 
     /*!
@@ -14631,7 +19050,7 @@ class basic_json
     */
     constexpr bool is_object() const noexcept
     {
-        return (m_type == value_t::object);
+        return m_type == value_t::object;
     }
 
     /*!
@@ -14653,7 +19072,7 @@ class basic_json
     */
     constexpr bool is_array() const noexcept
     {
-        return (m_type == value_t::array);
+        return m_type == value_t::array;
     }
 
     /*!
@@ -14675,7 +19094,29 @@ class basic_json
     */
     constexpr bool is_string() const noexcept
     {
-        return (m_type == value_t::string);
+        return m_type == value_t::string;
+    }
+
+    /*!
+    @brief return whether value is a binary array
+
+    This function returns true if and only if the JSON value is a binary array.
+
+    @return `true` if type is binary array, `false` otherwise.
+
+    @complexity Constant.
+
+    @exceptionsafety No-throw guarantee: this member function never throws
+    exceptions.
+
+    @liveexample{The following code exemplifies `is_binary()` for all JSON
+    types.,is_binary}
+
+    @since version 3.8.0
+    */
+    constexpr bool is_binary() const noexcept
+    {
+        return m_type == value_t::binary;
     }
 
     /*!
@@ -14702,7 +19143,7 @@ class basic_json
     */
     constexpr bool is_discarded() const noexcept
     {
-        return (m_type == value_t::discarded);
+        return m_type == value_t::discarded;
     }
 
     /*!
@@ -14741,7 +19182,7 @@ class basic_json
     /// get a boolean (explicit)
     boolean_t get_impl(boolean_t* /*unused*/) const
     {
-        if (JSON_LIKELY(is_boolean()))
+        if (JSON_HEDLEY_LIKELY(is_boolean()))
         {
             return m_value.boolean;
         }
@@ -14833,6 +19274,18 @@ class basic_json
         return is_number_float() ? &m_value.number_float : nullptr;
     }
 
+    /// get a pointer to the value (binary)
+    binary_t* get_impl_ptr(binary_t* /*unused*/) noexcept
+    {
+        return is_binary() ? m_value.binary : nullptr;
+    }
+
+    /// get a pointer to the value (binary)
+    constexpr const binary_t* get_impl_ptr(const binary_t* /*unused*/) const noexcept
+    {
+        return is_binary() ? m_value.binary : nullptr;
+    }
+
     /*!
     @brief helper function to implement get_ref()
 
@@ -14850,7 +19303,7 @@ class basic_json
         // delegate the call to get_ptr<>()
         auto ptr = obj.template get_ptr<typename std::add_pointer<ReferenceType>::type>();
 
-        if (JSON_LIKELY(ptr != nullptr))
+        if (JSON_HEDLEY_LIKELY(ptr != nullptr))
         {
             return *ptr;
         }
@@ -14900,9 +19353,9 @@ class basic_json
 
     @since version 3.2.0
     */
-    template<typename BasicJsonType, detail::enable_if_t<
-                 not std::is_same<BasicJsonType, basic_json>::value and
-                 detail::is_basic_json<BasicJsonType>::value, int> = 0>
+    template < typename BasicJsonType, detail::enable_if_t <
+                   !std::is_same<BasicJsonType, basic_json>::value&&
+                   detail::is_basic_json<BasicJsonType>::value, int > = 0 >
     BasicJsonType get() const
     {
         return *this;
@@ -14947,19 +19400,19 @@ class basic_json
 
     @since version 2.1.0
     */
-    template<typename ValueTypeCV, typename ValueType = detail::uncvref_t<ValueTypeCV>,
-             detail::enable_if_t <
-                 not detail::is_basic_json<ValueType>::value and
-                 detail::has_from_json<basic_json_t, ValueType>::value and
-                 not detail::has_non_default_from_json<basic_json_t, ValueType>::value,
-                 int> = 0>
+    template < typename ValueTypeCV, typename ValueType = detail::uncvref_t<ValueTypeCV>,
+               detail::enable_if_t <
+                   !detail::is_basic_json<ValueType>::value &&
+                   detail::has_from_json<basic_json_t, ValueType>::value &&
+                   !detail::has_non_default_from_json<basic_json_t, ValueType>::value,
+                   int > = 0 >
     ValueType get() const noexcept(noexcept(
                                        JSONSerializer<ValueType>::from_json(std::declval<const basic_json_t&>(), std::declval<ValueType&>())))
     {
         // we cannot static_assert on ValueTypeCV being non-const, because
         // there is support for get<const basic_json_t>(), which is why we
         // still need the uncvref
-        static_assert(not std::is_reference<ValueTypeCV>::value,
+        static_assert(!std::is_reference<ValueTypeCV>::value,
                       "get() cannot be used with reference types, you might want to use get_ref()");
         static_assert(std::is_default_constructible<ValueType>::value,
                       "types must be DefaultConstructible when used with get()");
@@ -15000,16 +19453,16 @@ class basic_json
 
     @since version 2.1.0
     */
-    template<typename ValueTypeCV, typename ValueType = detail::uncvref_t<ValueTypeCV>,
-             detail::enable_if_t<not std::is_same<basic_json_t, ValueType>::value and
-                                 detail::has_non_default_from_json<basic_json_t, ValueType>::value,
-                                 int> = 0>
+    template < typename ValueTypeCV, typename ValueType = detail::uncvref_t<ValueTypeCV>,
+               detail::enable_if_t < !std::is_same<basic_json_t, ValueType>::value &&
+                                     detail::has_non_default_from_json<basic_json_t, ValueType>::value,
+                                     int > = 0 >
     ValueType get() const noexcept(noexcept(
-                                       JSONSerializer<ValueTypeCV>::from_json(std::declval<const basic_json_t&>())))
+                                       JSONSerializer<ValueType>::from_json(std::declval<const basic_json_t&>())))
     {
-        static_assert(not std::is_reference<ValueTypeCV>::value,
+        static_assert(!std::is_reference<ValueTypeCV>::value,
                       "get() cannot be used with reference types, you might want to use get_ref()");
-        return JSONSerializer<ValueTypeCV>::from_json(*this);
+        return JSONSerializer<ValueType>::from_json(*this);
     }
 
     /*!
@@ -15045,11 +19498,11 @@ class basic_json
 
     @since version 3.3.0
     */
-    template<typename ValueType,
-             detail::enable_if_t <
-                 not detail::is_basic_json<ValueType>::value and
-                 detail::has_from_json<basic_json_t, ValueType>::value,
-                 int> = 0>
+    template < typename ValueType,
+               detail::enable_if_t <
+                   !detail::is_basic_json<ValueType>::value&&
+                   detail::has_from_json<basic_json_t, ValueType>::value,
+                   int > = 0 >
     ValueType & get_to(ValueType& v) const noexcept(noexcept(
                 JSONSerializer<ValueType>::from_json(std::declval<const basic_json_t&>(), v)))
     {
@@ -15057,6 +19510,31 @@ class basic_json
         return v;
     }
 
+    // specialization to allow to call get_to with a basic_json value
+    // see https://github.com/nlohmann/json/issues/2175
+    template<typename ValueType,
+             detail::enable_if_t <
+                 detail::is_basic_json<ValueType>::value,
+                 int> = 0>
+    ValueType & get_to(ValueType& v) const
+    {
+        v = *this;
+        return v;
+    }
+
+    template <
+        typename T, std::size_t N,
+        typename Array = T (&)[N],
+        detail::enable_if_t <
+            detail::has_from_json<basic_json_t, Array>::value, int > = 0 >
+    Array get_to(T (&v)[N]) const
+    noexcept(noexcept(JSONSerializer<Array>::from_json(
+                          std::declval<const basic_json_t&>(), v)))
+    {
+        JSONSerializer<Array>::from_json(*this, v);
+        return v;
+    }
+
 
     /*!
     @brief get a pointer value (implicit)
@@ -15096,9 +19574,9 @@ class basic_json
     @brief get a pointer value (implicit)
     @copydoc get_ptr()
     */
-    template<typename PointerType, typename std::enable_if<
-                 std::is_pointer<PointerType>::value and
-                 std::is_const<typename std::remove_pointer<PointerType>::type>::value, int>::type = 0>
+    template < typename PointerType, typename std::enable_if <
+                   std::is_pointer<PointerType>::value&&
+                   std::is_const<typename std::remove_pointer<PointerType>::type>::value, int >::type = 0 >
     constexpr auto get_ptr() const noexcept -> decltype(std::declval<const basic_json_t&>().get_impl_ptr(std::declval<PointerType>()))
     {
         // delegate the call to get_impl_ptr<>() const
@@ -15190,9 +19668,9 @@ class basic_json
     @brief get a reference value (implicit)
     @copydoc get_ref()
     */
-    template<typename ReferenceType, typename std::enable_if<
-                 std::is_reference<ReferenceType>::value and
-                 std::is_const<typename std::remove_reference<ReferenceType>::type>::value, int>::type = 0>
+    template < typename ReferenceType, typename std::enable_if <
+                   std::is_reference<ReferenceType>::value&&
+                   std::is_const<typename std::remove_reference<ReferenceType>::type>::value, int >::type = 0 >
     ReferenceType get_ref() const
     {
         // delegate call to get_ref_impl
@@ -15229,25 +19707,52 @@ class basic_json
     @since version 1.0.0
     */
     template < typename ValueType, typename std::enable_if <
-                   not std::is_pointer<ValueType>::value and
-                   not std::is_same<ValueType, detail::json_ref<basic_json>>::value and
-                   not std::is_same<ValueType, typename string_t::value_type>::value and
-                   not detail::is_basic_json<ValueType>::value
-
-#ifndef _MSC_VER  // fix for issue #167 operator<< ambiguity under VS2015
-                   and not std::is_same<ValueType, std::initializer_list<typename string_t::value_type>>::value
-#if defined(JSON_HAS_CPP_17) && defined(_MSC_VER) and _MSC_VER <= 1914
-                   and not std::is_same<ValueType, typename std::string_view>::value
-#endif
+                   !std::is_pointer<ValueType>::value&&
+                   !std::is_same<ValueType, detail::json_ref<basic_json>>::value&&
+                   !std::is_same<ValueType, typename string_t::value_type>::value&&
+                   !detail::is_basic_json<ValueType>::value
+                   && !std::is_same<ValueType, std::initializer_list<typename string_t::value_type>>::value
+#if defined(JSON_HAS_CPP_17) && (defined(__GNUC__) || (defined(_MSC_VER) && _MSC_VER >= 1910 && _MSC_VER <= 1914))
+                   && !std::is_same<ValueType, typename std::string_view>::value
 #endif
-                   and detail::is_detected<detail::get_template_function, const basic_json_t&, ValueType>::value
+                   && detail::is_detected<detail::get_template_function, const basic_json_t&, ValueType>::value
                    , int >::type = 0 >
-    operator ValueType() const
+    JSON_EXPLICIT operator ValueType() const
     {
         // delegate the call to get<>() const
         return get<ValueType>();
     }
 
+    /*!
+    @return reference to the binary value
+
+    @throw type_error.302 if the value is not binary
+
+    @sa @ref is_binary() to check if the value is binary
+
+    @since version 3.8.0
+    */
+    binary_t& get_binary()
+    {
+        if (!is_binary())
+        {
+            JSON_THROW(type_error::create(302, "type must be binary, but is " + std::string(type_name())));
+        }
+
+        return *get_ptr<binary_t*>();
+    }
+
+    /// @copydoc get_binary()
+    const binary_t& get_binary() const
+    {
+        if (!is_binary())
+        {
+            JSON_THROW(type_error::create(302, "type must be binary, but is " + std::string(type_name())));
+        }
+
+        return *get_ptr<const binary_t*>();
+    }
+
     /// @}
 
 
@@ -15288,7 +19793,7 @@ class basic_json
     reference at(size_type idx)
     {
         // at only works for arrays
-        if (JSON_LIKELY(is_array()))
+        if (JSON_HEDLEY_LIKELY(is_array()))
         {
             JSON_TRY
             {
@@ -15335,7 +19840,7 @@ class basic_json
     const_reference at(size_type idx) const
     {
         // at only works for arrays
-        if (JSON_LIKELY(is_array()))
+        if (JSON_HEDLEY_LIKELY(is_array()))
         {
             JSON_TRY
             {
@@ -15386,7 +19891,7 @@ class basic_json
     reference at(const typename object_t::key_type& key)
     {
         // at only works for objects
-        if (JSON_LIKELY(is_object()))
+        if (JSON_HEDLEY_LIKELY(is_object()))
         {
             JSON_TRY
             {
@@ -15437,7 +19942,7 @@ class basic_json
     const_reference at(const typename object_t::key_type& key) const
     {
         // at only works for objects
-        if (JSON_LIKELY(is_object()))
+        if (JSON_HEDLEY_LIKELY(is_object()))
         {
             JSON_TRY
             {
@@ -15491,7 +19996,7 @@ class basic_json
         }
 
         // operator[] only works for arrays
-        if (JSON_LIKELY(is_array()))
+        if (JSON_HEDLEY_LIKELY(is_array()))
         {
             // fill up array with null values if given idx is outside range
             if (idx >= m_value.array->size())
@@ -15529,7 +20034,7 @@ class basic_json
     const_reference operator[](size_type idx) const
     {
         // const operator[] only works for arrays
-        if (JSON_LIKELY(is_array()))
+        if (JSON_HEDLEY_LIKELY(is_array()))
         {
             return m_value.array->operator[](idx);
         }
@@ -15575,7 +20080,7 @@ class basic_json
         }
 
         // operator[] only works for objects
-        if (JSON_LIKELY(is_object()))
+        if (JSON_HEDLEY_LIKELY(is_object()))
         {
             return m_value.object->operator[](key);
         }
@@ -15616,9 +20121,9 @@ class basic_json
     const_reference operator[](const typename object_t::key_type& key) const
     {
         // const operator[] only works for objects
-        if (JSON_LIKELY(is_object()))
+        if (JSON_HEDLEY_LIKELY(is_object()))
         {
-            assert(m_value.object->find(key) != m_value.object->end());
+            JSON_ASSERT(m_value.object->find(key) != m_value.object->end());
             return m_value.object->find(key)->second;
         }
 
@@ -15653,6 +20158,7 @@ class basic_json
     @since version 1.1.0
     */
     template<typename T>
+    JSON_HEDLEY_NON_NULL(2)
     reference operator[](T* key)
     {
         // implicitly convert null to object
@@ -15664,7 +20170,7 @@ class basic_json
         }
 
         // at only works for objects
-        if (JSON_LIKELY(is_object()))
+        if (JSON_HEDLEY_LIKELY(is_object()))
         {
             return m_value.object->operator[](key);
         }
@@ -15703,12 +20209,13 @@ class basic_json
     @since version 1.1.0
     */
     template<typename T>
+    JSON_HEDLEY_NON_NULL(2)
     const_reference operator[](T* key) const
     {
         // at only works for objects
-        if (JSON_LIKELY(is_object()))
+        if (JSON_HEDLEY_LIKELY(is_object()))
         {
-            assert(m_value.object->find(key) != m_value.object->end());
+            JSON_ASSERT(m_value.object->find(key) != m_value.object->end());
             return m_value.object->find(key)->second;
         }
 
@@ -15748,6 +20255,8 @@ class basic_json
     @return copy of the element at key @a key or @a default_value if @a key
     is not found
 
+    @throw type_error.302 if @a default_value does not match the type of the
+    value at @a key
     @throw type_error.306 if the JSON value is not an object; in that case,
     using `value()` with a key makes no sense.
 
@@ -15763,18 +20272,20 @@ class basic_json
 
     @since version 1.0.0
     */
-    template<class ValueType, typename std::enable_if<
-                 std::is_convertible<basic_json_t, ValueType>::value, int>::type = 0>
+    // using std::is_convertible in a std::enable_if will fail when using explicit conversions
+    template < class ValueType, typename std::enable_if <
+                   detail::is_getable<basic_json_t, ValueType>::value
+                   && !std::is_same<value_t, ValueType>::value, int >::type = 0 >
     ValueType value(const typename object_t::key_type& key, const ValueType& default_value) const
     {
         // at only works for objects
-        if (JSON_LIKELY(is_object()))
+        if (JSON_HEDLEY_LIKELY(is_object()))
         {
             // if key is found, return value and given default value otherwise
             const auto it = find(key);
             if (it != end())
             {
-                return *it;
+                return it->template get<ValueType>();
             }
 
             return default_value;
@@ -15821,6 +20332,8 @@ class basic_json
     @return copy of the element at key @a key or @a default_value if @a key
     is not found
 
+    @throw type_error.302 if @a default_value does not match the type of the
+    value at @a ptr
     @throw type_error.306 if the JSON value is not an object; in that case,
     using `value()` with a key makes no sense.
 
@@ -15834,16 +20347,16 @@ class basic_json
     @since version 2.0.2
     */
     template<class ValueType, typename std::enable_if<
-                 std::is_convertible<basic_json_t, ValueType>::value, int>::type = 0>
+                 detail::is_getable<basic_json_t, ValueType>::value, int>::type = 0>
     ValueType value(const json_pointer& ptr, const ValueType& default_value) const
     {
         // at only works for objects
-        if (JSON_LIKELY(is_object()))
+        if (JSON_HEDLEY_LIKELY(is_object()))
         {
             // if pointer resolves a value, return it or use default value
             JSON_TRY
             {
-                return ptr.get_checked(this);
+                return ptr.get_checked(this).template get<ValueType>();
             }
             JSON_INTERNAL_CATCH (out_of_range&)
             {
@@ -15858,6 +20371,7 @@ class basic_json
     @brief overload for a default value of type const char*
     @copydoc basic_json::value(const json_pointer&, ValueType) const
     */
+    JSON_HEDLEY_NON_NULL(3)
     string_t value(const json_pointer& ptr, const char* default_value) const
     {
         return value(ptr, string_t(default_value));
@@ -15870,8 +20384,8 @@ class basic_json
     container `c`, the expression `c.front()` is equivalent to `*c.begin()`.
 
     @return In case of a structured type (array or object), a reference to the
-    first element is returned. In case of number, string, or boolean values, a
-    reference to the value is returned.
+    first element is returned. In case of number, string, boolean, or binary
+    values, a reference to the value is returned.
 
     @complexity Constant.
 
@@ -15913,8 +20427,8 @@ class basic_json
     @endcode
 
     @return In case of a structured type (array or object), a reference to the
-    last element is returned. In case of number, string, or boolean values, a
-    reference to the value is returned.
+    last element is returned. In case of number, string, boolean, or binary
+    values, a reference to the value is returned.
 
     @complexity Constant.
 
@@ -15980,7 +20494,7 @@ class basic_json
     @complexity The complexity depends on the type:
     - objects: amortized constant
     - arrays: linear in distance between @a pos and the end of the container
-    - strings: linear in the length of the string
+    - strings and binary: linear in the length of the member
     - other types: constant
 
     @liveexample{The example shows the result of `erase()` for different JSON
@@ -15995,14 +20509,14 @@ class basic_json
 
     @since version 1.0.0
     */
-    template<class IteratorType, typename std::enable_if<
-                 std::is_same<IteratorType, typename basic_json_t::iterator>::value or
-                 std::is_same<IteratorType, typename basic_json_t::const_iterator>::value, int>::type
-             = 0>
+    template < class IteratorType, typename std::enable_if <
+                   std::is_same<IteratorType, typename basic_json_t::iterator>::value ||
+                   std::is_same<IteratorType, typename basic_json_t::const_iterator>::value, int >::type
+               = 0 >
     IteratorType erase(IteratorType pos)
     {
         // make sure iterator fits the current value
-        if (JSON_UNLIKELY(this != pos.m_object))
+        if (JSON_HEDLEY_UNLIKELY(this != pos.m_object))
         {
             JSON_THROW(invalid_iterator::create(202, "iterator does not fit current value"));
         }
@@ -16016,8 +20530,9 @@ class basic_json
             case value_t::number_integer:
             case value_t::number_unsigned:
             case value_t::string:
+            case value_t::binary:
             {
-                if (JSON_UNLIKELY(not pos.m_it.primitive_iterator.is_begin()))
+                if (JSON_HEDLEY_UNLIKELY(!pos.m_it.primitive_iterator.is_begin()))
                 {
                     JSON_THROW(invalid_iterator::create(205, "iterator out of range"));
                 }
@@ -16029,6 +20544,13 @@ class basic_json
                     std::allocator_traits<decltype(alloc)>::deallocate(alloc, m_value.string, 1);
                     m_value.string = nullptr;
                 }
+                else if (is_binary())
+                {
+                    AllocatorType<binary_t> alloc;
+                    std::allocator_traits<decltype(alloc)>::destroy(alloc, m_value.binary);
+                    std::allocator_traits<decltype(alloc)>::deallocate(alloc, m_value.binary, 1);
+                    m_value.binary = nullptr;
+                }
 
                 m_type = value_t::null;
                 assert_invariant();
@@ -16086,7 +20608,7 @@ class basic_json
     - objects: `log(size()) + std::distance(first, last)`
     - arrays: linear in the distance between @a first and @a last, plus linear
       in the distance between @a last and end of the container
-    - strings: linear in the length of the string
+    - strings and binary: linear in the length of the member
     - other types: constant
 
     @liveexample{The example shows the result of `erase()` for different JSON
@@ -16100,14 +20622,14 @@ class basic_json
 
     @since version 1.0.0
     */
-    template<class IteratorType, typename std::enable_if<
-                 std::is_same<IteratorType, typename basic_json_t::iterator>::value or
-                 std::is_same<IteratorType, typename basic_json_t::const_iterator>::value, int>::type
-             = 0>
+    template < class IteratorType, typename std::enable_if <
+                   std::is_same<IteratorType, typename basic_json_t::iterator>::value ||
+                   std::is_same<IteratorType, typename basic_json_t::const_iterator>::value, int >::type
+               = 0 >
     IteratorType erase(IteratorType first, IteratorType last)
     {
         // make sure iterator fits the current value
-        if (JSON_UNLIKELY(this != first.m_object or this != last.m_object))
+        if (JSON_HEDLEY_UNLIKELY(this != first.m_object || this != last.m_object))
         {
             JSON_THROW(invalid_iterator::create(203, "iterators do not fit current value"));
         }
@@ -16121,9 +20643,10 @@ class basic_json
             case value_t::number_integer:
             case value_t::number_unsigned:
             case value_t::string:
+            case value_t::binary:
             {
-                if (JSON_LIKELY(not first.m_it.primitive_iterator.is_begin()
-                                or not last.m_it.primitive_iterator.is_end()))
+                if (JSON_HEDLEY_LIKELY(!first.m_it.primitive_iterator.is_begin()
+                                       || !last.m_it.primitive_iterator.is_end()))
                 {
                     JSON_THROW(invalid_iterator::create(204, "iterators out of range"));
                 }
@@ -16135,6 +20658,13 @@ class basic_json
                     std::allocator_traits<decltype(alloc)>::deallocate(alloc, m_value.string, 1);
                     m_value.string = nullptr;
                 }
+                else if (is_binary())
+                {
+                    AllocatorType<binary_t> alloc;
+                    std::allocator_traits<decltype(alloc)>::destroy(alloc, m_value.binary);
+                    std::allocator_traits<decltype(alloc)>::deallocate(alloc, m_value.binary, 1);
+                    m_value.binary = nullptr;
+                }
 
                 m_type = value_t::null;
                 assert_invariant();
@@ -16194,7 +20724,7 @@ class basic_json
     size_type erase(const typename object_t::key_type& key)
     {
         // this erase only works for objects
-        if (JSON_LIKELY(is_object()))
+        if (JSON_HEDLEY_LIKELY(is_object()))
         {
             return m_value.object->erase(key);
         }
@@ -16229,9 +20759,9 @@ class basic_json
     void erase(const size_type idx)
     {
         // this erase only works for arrays
-        if (JSON_LIKELY(is_array()))
+        if (JSON_HEDLEY_LIKELY(is_array()))
         {
-            if (JSON_UNLIKELY(idx >= size()))
+            if (JSON_HEDLEY_UNLIKELY(idx >= size()))
             {
                 JSON_THROW(out_of_range::create(401, "array index " + std::to_string(idx) + " is out of range"));
             }
@@ -16274,6 +20804,8 @@ class basic_json
 
     @liveexample{The example shows how `find()` is used.,find__key_type}
 
+    @sa @ref contains(KeyT&&) const -- checks whether a key exists
+
     @since version 1.0.0
     */
     template<typename KeyT>
@@ -16334,6 +20866,69 @@ class basic_json
         return is_object() ? m_value.object->count(std::forward<KeyT>(key)) : 0;
     }
 
+    /*!
+    @brief check the existence of an element in a JSON object
+
+    Check whether an element exists in a JSON object with key equivalent to
+    @a key. If the element is not found or the JSON value is not an object,
+    false is returned.
+
+    @note This method always returns false when executed on a JSON type
+          that is not an object.
+
+    @param[in] key key value to check its existence.
+
+    @return true if an element with specified @a key exists. If no such
+    element with such key is found or the JSON value is not an object,
+    false is returned.
+
+    @complexity Logarithmic in the size of the JSON object.
+
+    @liveexample{The following code shows an example for `contains()`.,contains}
+
+    @sa @ref find(KeyT&&) -- returns an iterator to an object element
+    @sa @ref contains(const json_pointer&) const -- checks the existence for a JSON pointer
+
+    @since version 3.6.0
+    */
+    template < typename KeyT, typename std::enable_if <
+                   !std::is_same<typename std::decay<KeyT>::type, json_pointer>::value, int >::type = 0 >
+    bool contains(KeyT && key) const
+    {
+        return is_object() && m_value.object->find(std::forward<KeyT>(key)) != m_value.object->end();
+    }
+
+    /*!
+    @brief check the existence of an element in a JSON object given a JSON pointer
+
+    Check whether the given JSON pointer @a ptr can be resolved in the current
+    JSON value.
+
+    @note This method can be executed on any JSON value type.
+
+    @param[in] ptr JSON pointer to check its existence.
+
+    @return true if the JSON pointer can be resolved to a stored value, false
+    otherwise.
+
+    @post If `j.contains(ptr)` returns true, it is safe to call `j[ptr]`.
+
+    @throw parse_error.106   if an array index begins with '0'
+    @throw parse_error.109   if an array index was not a number
+
+    @complexity Logarithmic in the size of the JSON object.
+
+    @liveexample{The following code shows an example for `contains()`.,contains_json_pointer}
+
+    @sa @ref contains(KeyT &&) const -- checks the existence of a key
+
+    @since version 3.7.0
+    */
+    bool contains(const json_pointer& ptr) const
+    {
+        return ptr.contains(this);
+    }
+
     /// @}
 
 
@@ -16675,7 +21270,7 @@ class basic_json
                 future 4.0.0 of the library. Please use @ref items() instead;
                 that is, replace `json::iterator_wrapper(j)` with `j.items()`.
     */
-    JSON_DEPRECATED
+    JSON_HEDLEY_DEPRECATED_FOR(3.1.0, items())
     static iteration_proxy<iterator> iterator_wrapper(reference ref) noexcept
     {
         return ref.items();
@@ -16684,7 +21279,7 @@ class basic_json
     /*!
     @copydoc iterator_wrapper(reference)
     */
-    JSON_DEPRECATED
+    JSON_HEDLEY_DEPRECATED_FOR(3.1.0, items())
     static iteration_proxy<const_iterator> iterator_wrapper(const_reference ref) noexcept
     {
         return ref.items();
@@ -16741,6 +21336,11 @@ class basic_json
           element as string (see example). For primitive types (e.g., numbers),
           `key()` returns an empty string.
 
+    @warning Using `items()` on temporary objects is dangerous. Make sure the
+             object's lifetime exeeds the iteration. See
+             <https://github.com/nlohmann/json/issues/2040> for more
+             information.
+
     @return iteration proxy object wrapping @a ref with an interface to use in
             range-based for loops
 
@@ -16789,6 +21389,7 @@ class basic_json
             boolean     | `false`
             string      | `false`
             number      | `false`
+            binary      | `false`
             object      | result of function `object_t::empty()`
             array       | result of function `array_t::empty()`
 
@@ -16860,6 +21461,7 @@ class basic_json
             boolean     | `1`
             string      | `1`
             number      | `1`
+            binary      | `1`
             object      | result of function object_t::size()
             array       | result of function array_t::size()
 
@@ -16934,6 +21536,7 @@ class basic_json
             boolean     | `1` (same as `size()`)
             string      | `1` (same as `size()`)
             number      | `1` (same as `size()`)
+            binary      | `1` (same as `size()`)
             object      | result of function `object_t::max_size()`
             array       | result of function `array_t::max_size()`
 
@@ -17006,6 +21609,7 @@ class basic_json
     boolean     | `false`
     string      | `""`
     number      | `0`
+    binary      | An empty byte vector
     object      | `{}`
     array       | `[]`
 
@@ -17063,6 +21667,12 @@ class basic_json
                 break;
             }
 
+            case value_t::binary:
+            {
+                m_value.binary->clear();
+                break;
+            }
+
             case value_t::array:
             {
                 m_value.array->clear();
@@ -17103,7 +21713,7 @@ class basic_json
     void push_back(basic_json&& val)
     {
         // push_back only works for null objects or arrays
-        if (JSON_UNLIKELY(not(is_null() or is_array())))
+        if (JSON_HEDLEY_UNLIKELY(!(is_null() || is_array())))
         {
             JSON_THROW(type_error::create(308, "cannot use push_back() with " + std::string(type_name())));
         }
@@ -17118,8 +21728,7 @@ class basic_json
 
         // add element to array (move semantics)
         m_value.array->push_back(std::move(val));
-        // invalidate object
-        val.m_type = value_t::null;
+        // if val is moved from, basic_json move constructor marks it null so we do not call the destructor
     }
 
     /*!
@@ -17139,7 +21748,7 @@ class basic_json
     void push_back(const basic_json& val)
     {
         // push_back only works for null objects or arrays
-        if (JSON_UNLIKELY(not(is_null() or is_array())))
+        if (JSON_HEDLEY_UNLIKELY(!(is_null() || is_array())))
         {
             JSON_THROW(type_error::create(308, "cannot use push_back() with " + std::string(type_name())));
         }
@@ -17189,7 +21798,7 @@ class basic_json
     void push_back(const typename object_t::value_type& val)
     {
         // push_back only works for null objects or objects
-        if (JSON_UNLIKELY(not(is_null() or is_object())))
+        if (JSON_HEDLEY_UNLIKELY(!(is_null() || is_object())))
         {
             JSON_THROW(type_error::create(308, "cannot use push_back() with " + std::string(type_name())));
         }
@@ -17243,7 +21852,7 @@ class basic_json
     */
     void push_back(initializer_list_t init)
     {
-        if (is_object() and init.size() == 2 and (*init.begin())->is_string())
+        if (is_object() && init.size() == 2 && (*init.begin())->is_string())
         {
             basic_json&& key = init.begin()->moved_or_copied();
             push_back(typename object_t::value_type(
@@ -17275,6 +21884,8 @@ class basic_json
     @param[in] args arguments to forward to a constructor of @ref basic_json
     @tparam Args compatible types to create a @ref basic_json object
 
+    @return reference to the inserted element
+
     @throw type_error.311 when called on a type other than JSON array or
     null; example: `"cannot use emplace_back() with number"`
 
@@ -17284,13 +21895,13 @@ class basic_json
     elements to a JSON array. Note how the `null` value was silently converted
     to a JSON array.,emplace_back}
 
-    @since version 2.0.8
+    @since version 2.0.8, returns reference since 3.7.0
     */
     template<class... Args>
-    void emplace_back(Args&& ... args)
+    reference emplace_back(Args&& ... args)
     {
         // emplace_back only works for null objects or arrays
-        if (JSON_UNLIKELY(not(is_null() or is_array())))
+        if (JSON_HEDLEY_UNLIKELY(!(is_null() || is_array())))
         {
             JSON_THROW(type_error::create(311, "cannot use emplace_back() with " + std::string(type_name())));
         }
@@ -17304,7 +21915,12 @@ class basic_json
         }
 
         // add element to array (perfect forwarding)
+#ifdef JSON_HAS_CPP_17
+        return m_value.array->emplace_back(std::forward<Args>(args)...);
+#else
         m_value.array->emplace_back(std::forward<Args>(args)...);
+        return m_value.array->back();
+#endif
     }
 
     /*!
@@ -17338,7 +21954,7 @@ class basic_json
     std::pair<iterator, bool> emplace(Args&& ... args)
     {
         // emplace only works for null objects or arrays
-        if (JSON_UNLIKELY(not(is_null() or is_object())))
+        if (JSON_HEDLEY_UNLIKELY(!(is_null() || is_object())))
         {
             JSON_THROW(type_error::create(311, "cannot use emplace() with " + std::string(type_name())));
         }
@@ -17368,7 +21984,7 @@ class basic_json
     iterator insert_iterator(const_iterator pos, Args&& ... args)
     {
         iterator result(this);
-        assert(m_value.array != nullptr);
+        JSON_ASSERT(m_value.array != nullptr);
 
         auto insert_pos = std::distance(m_value.array->begin(), pos.m_it.array_iterator);
         m_value.array->insert(pos.m_it.array_iterator, std::forward<Args>(args)...);
@@ -17406,10 +22022,10 @@ class basic_json
     iterator insert(const_iterator pos, const basic_json& val)
     {
         // insert only works for arrays
-        if (JSON_LIKELY(is_array()))
+        if (JSON_HEDLEY_LIKELY(is_array()))
         {
             // check if iterator pos fits to this JSON value
-            if (JSON_UNLIKELY(pos.m_object != this))
+            if (JSON_HEDLEY_UNLIKELY(pos.m_object != this))
             {
                 JSON_THROW(invalid_iterator::create(202, "iterator does not fit current value"));
             }
@@ -17457,10 +22073,10 @@ class basic_json
     iterator insert(const_iterator pos, size_type cnt, const basic_json& val)
     {
         // insert only works for arrays
-        if (JSON_LIKELY(is_array()))
+        if (JSON_HEDLEY_LIKELY(is_array()))
         {
             // check if iterator pos fits to this JSON value
-            if (JSON_UNLIKELY(pos.m_object != this))
+            if (JSON_HEDLEY_UNLIKELY(pos.m_object != this))
             {
                 JSON_THROW(invalid_iterator::create(202, "iterator does not fit current value"));
             }
@@ -17505,24 +22121,24 @@ class basic_json
     iterator insert(const_iterator pos, const_iterator first, const_iterator last)
     {
         // insert only works for arrays
-        if (JSON_UNLIKELY(not is_array()))
+        if (JSON_HEDLEY_UNLIKELY(!is_array()))
         {
             JSON_THROW(type_error::create(309, "cannot use insert() with " + std::string(type_name())));
         }
 
         // check if iterator pos fits to this JSON value
-        if (JSON_UNLIKELY(pos.m_object != this))
+        if (JSON_HEDLEY_UNLIKELY(pos.m_object != this))
         {
             JSON_THROW(invalid_iterator::create(202, "iterator does not fit current value"));
         }
 
         // check if range iterators belong to the same JSON object
-        if (JSON_UNLIKELY(first.m_object != last.m_object))
+        if (JSON_HEDLEY_UNLIKELY(first.m_object != last.m_object))
         {
             JSON_THROW(invalid_iterator::create(210, "iterators do not fit"));
         }
 
-        if (JSON_UNLIKELY(first.m_object == this))
+        if (JSON_HEDLEY_UNLIKELY(first.m_object == this))
         {
             JSON_THROW(invalid_iterator::create(211, "passed iterators may not belong to container"));
         }
@@ -17558,13 +22174,13 @@ class basic_json
     iterator insert(const_iterator pos, initializer_list_t ilist)
     {
         // insert only works for arrays
-        if (JSON_UNLIKELY(not is_array()))
+        if (JSON_HEDLEY_UNLIKELY(!is_array()))
         {
             JSON_THROW(type_error::create(309, "cannot use insert() with " + std::string(type_name())));
         }
 
         // check if iterator pos fits to this JSON value
-        if (JSON_UNLIKELY(pos.m_object != this))
+        if (JSON_HEDLEY_UNLIKELY(pos.m_object != this))
         {
             JSON_THROW(invalid_iterator::create(202, "iterator does not fit current value"));
         }
@@ -17599,19 +22215,19 @@ class basic_json
     void insert(const_iterator first, const_iterator last)
     {
         // insert only works for objects
-        if (JSON_UNLIKELY(not is_object()))
+        if (JSON_HEDLEY_UNLIKELY(!is_object()))
         {
             JSON_THROW(type_error::create(309, "cannot use insert() with " + std::string(type_name())));
         }
 
         // check if range iterators belong to the same JSON object
-        if (JSON_UNLIKELY(first.m_object != last.m_object))
+        if (JSON_HEDLEY_UNLIKELY(first.m_object != last.m_object))
         {
             JSON_THROW(invalid_iterator::create(210, "iterators do not fit"));
         }
 
         // passed iterators must belong to objects
-        if (JSON_UNLIKELY(not first.m_object->is_object()))
+        if (JSON_HEDLEY_UNLIKELY(!first.m_object->is_object()))
         {
             JSON_THROW(invalid_iterator::create(202, "iterators first and last must point to objects"));
         }
@@ -17648,11 +22264,11 @@ class basic_json
             assert_invariant();
         }
 
-        if (JSON_UNLIKELY(not is_object()))
+        if (JSON_HEDLEY_UNLIKELY(!is_object()))
         {
             JSON_THROW(type_error::create(312, "cannot use update() with " + std::string(type_name())));
         }
-        if (JSON_UNLIKELY(not j.is_object()))
+        if (JSON_HEDLEY_UNLIKELY(!j.is_object()))
         {
             JSON_THROW(type_error::create(312, "cannot use update() with " + std::string(j.type_name())));
         }
@@ -17699,20 +22315,20 @@ class basic_json
             assert_invariant();
         }
 
-        if (JSON_UNLIKELY(not is_object()))
+        if (JSON_HEDLEY_UNLIKELY(!is_object()))
         {
             JSON_THROW(type_error::create(312, "cannot use update() with " + std::string(type_name())));
         }
 
         // check if range iterators belong to the same JSON object
-        if (JSON_UNLIKELY(first.m_object != last.m_object))
+        if (JSON_HEDLEY_UNLIKELY(first.m_object != last.m_object))
         {
             JSON_THROW(invalid_iterator::create(210, "iterators do not fit"));
         }
 
         // passed iterators must belong to objects
-        if (JSON_UNLIKELY(not first.m_object->is_object()
-                          or not last.m_object->is_object()))
+        if (JSON_HEDLEY_UNLIKELY(!first.m_object->is_object()
+                                 || !last.m_object->is_object()))
         {
             JSON_THROW(invalid_iterator::create(202, "iterators first and last must point to objects"));
         }
@@ -17741,9 +22357,9 @@ class basic_json
     @since version 1.0.0
     */
     void swap(reference other) noexcept (
-        std::is_nothrow_move_constructible<value_t>::value and
-        std::is_nothrow_move_assignable<value_t>::value and
-        std::is_nothrow_move_constructible<json_value>::value and
+        std::is_nothrow_move_constructible<value_t>::value&&
+        std::is_nothrow_move_assignable<value_t>::value&&
+        std::is_nothrow_move_constructible<json_value>::value&&
         std::is_nothrow_move_assignable<json_value>::value
     )
     {
@@ -17755,6 +22371,34 @@ class basic_json
     /*!
     @brief exchanges the values
 
+    Exchanges the contents of the JSON value from @a left with those of @a right. Does not
+    invoke any move, copy, or swap operations on individual elements. All
+    iterators and references remain valid. The past-the-end iterator is
+    invalidated. implemented as a friend function callable via ADL.
+
+    @param[in,out] left JSON value to exchange the contents with
+    @param[in,out] right JSON value to exchange the contents with
+
+    @complexity Constant.
+
+    @liveexample{The example below shows how JSON values can be swapped with
+    `swap()`.,swap__reference}
+
+    @since version 1.0.0
+    */
+    friend void swap(reference left, reference right) noexcept (
+        std::is_nothrow_move_constructible<value_t>::value&&
+        std::is_nothrow_move_assignable<value_t>::value&&
+        std::is_nothrow_move_constructible<json_value>::value&&
+        std::is_nothrow_move_assignable<json_value>::value
+    )
+    {
+        left.swap(right);
+    }
+
+    /*!
+    @brief exchanges the values
+
     Exchanges the contents of a JSON array with those of @a other. Does not
     invoke any move, copy, or swap operations on individual elements. All
     iterators and references remain valid. The past-the-end iterator is
@@ -17775,7 +22419,7 @@ class basic_json
     void swap(array_t& other)
     {
         // swap only works for arrays
-        if (JSON_LIKELY(is_array()))
+        if (JSON_HEDLEY_LIKELY(is_array()))
         {
             std::swap(*(m_value.array), other);
         }
@@ -17808,7 +22452,7 @@ class basic_json
     void swap(object_t& other)
     {
         // swap only works for objects
-        if (JSON_LIKELY(is_object()))
+        if (JSON_HEDLEY_LIKELY(is_object()))
         {
             std::swap(*(m_value.object), other);
         }
@@ -17841,7 +22485,7 @@ class basic_json
     void swap(string_t& other)
     {
         // swap only works for strings
-        if (JSON_LIKELY(is_string()))
+        if (JSON_HEDLEY_LIKELY(is_string()))
         {
             std::swap(*(m_value.string), other);
         }
@@ -17851,6 +22495,53 @@ class basic_json
         }
     }
 
+    /*!
+    @brief exchanges the values
+
+    Exchanges the contents of a JSON string with those of @a other. Does not
+    invoke any move, copy, or swap operations on individual elements. All
+    iterators and references remain valid. The past-the-end iterator is
+    invalidated.
+
+    @param[in,out] other binary to exchange the contents with
+
+    @throw type_error.310 when JSON value is not a string; example: `"cannot
+    use swap() with boolean"`
+
+    @complexity Constant.
+
+    @liveexample{The example below shows how strings can be swapped with
+    `swap()`.,swap__binary_t}
+
+    @since version 3.8.0
+    */
+    void swap(binary_t& other)
+    {
+        // swap only works for strings
+        if (JSON_HEDLEY_LIKELY(is_binary()))
+        {
+            std::swap(*(m_value.binary), other);
+        }
+        else
+        {
+            JSON_THROW(type_error::create(310, "cannot use swap() with " + std::string(type_name())));
+        }
+    }
+
+    /// @copydoc swap(binary_t)
+    void swap(typename binary_t::container_type& other)
+    {
+        // swap only works for strings
+        if (JSON_HEDLEY_LIKELY(is_binary()))
+        {
+            std::swap(*(m_value.binary), other);
+        }
+        else
+        {
+            JSON_THROW(type_error::create(310, "cannot use swap() with " + std::string(type_name())));
+        }
+    }
+
     /// @}
 
   public:
@@ -17869,13 +22560,13 @@ class basic_json
       their stored values are the same according to their respective
       `operator==`.
     - Integer and floating-point numbers are automatically converted before
-      comparison. Note than two NaN values are always treated as unequal.
+      comparison. Note that two NaN values are always treated as unequal.
     - Two JSON null values are equal.
 
     @note Floating-point inside JSON values numbers are compared with
     `json::number_float_t::operator==` which is `double::operator==` by
     default. To compare floating-point while respecting an epsilon, an alternative
-    [comparison function](https://github.com/mariokonrad/marnav/blob/master/src/marnav/math/floatingpoint.hpp#L34-#L39)
+    [comparison function](https://github.com/mariokonrad/marnav/blob/master/include/marnav/math/floatingpoint.hpp#L34-#L39)
     could be used, for instance
     @code {.cpp}
     template<typename T, typename = typename std::enable_if<std::is_floating_point<T>::value, T>::type>
@@ -17884,6 +22575,22 @@ class basic_json
         return std::abs(a - b) <= epsilon;
     }
     @endcode
+    Or you can self-defined operator equal function like this:
+    @code {.cpp}
+    bool my_equal(const_reference lhs, const_reference rhs) {
+    const auto lhs_type lhs.type();
+    const auto rhs_type rhs.type();
+    if (lhs_type == rhs_type) {
+        switch(lhs_type)
+            // self_defined case
+            case value_t::number_float:
+                return std::abs(lhs - rhs) <= std::numeric_limits<float>::epsilon();
+            // other cases remain the same with the original
+            ...
+    }
+    ...
+    }
+    @endcode
 
     @note NaN values never compare equal to themselves or to other NaN values.
 
@@ -17910,56 +22617,59 @@ class basic_json
             switch (lhs_type)
             {
                 case value_t::array:
-                    return (*lhs.m_value.array == *rhs.m_value.array);
+                    return *lhs.m_value.array == *rhs.m_value.array;
 
                 case value_t::object:
-                    return (*lhs.m_value.object == *rhs.m_value.object);
+                    return *lhs.m_value.object == *rhs.m_value.object;
 
                 case value_t::null:
                     return true;
 
                 case value_t::string:
-                    return (*lhs.m_value.string == *rhs.m_value.string);
+                    return *lhs.m_value.string == *rhs.m_value.string;
 
                 case value_t::boolean:
-                    return (lhs.m_value.boolean == rhs.m_value.boolean);
+                    return lhs.m_value.boolean == rhs.m_value.boolean;
 
                 case value_t::number_integer:
-                    return (lhs.m_value.number_integer == rhs.m_value.number_integer);
+                    return lhs.m_value.number_integer == rhs.m_value.number_integer;
 
                 case value_t::number_unsigned:
-                    return (lhs.m_value.number_unsigned == rhs.m_value.number_unsigned);
+                    return lhs.m_value.number_unsigned == rhs.m_value.number_unsigned;
 
                 case value_t::number_float:
-                    return (lhs.m_value.number_float == rhs.m_value.number_float);
+                    return lhs.m_value.number_float == rhs.m_value.number_float;
+
+                case value_t::binary:
+                    return *lhs.m_value.binary == *rhs.m_value.binary;
 
                 default:
                     return false;
             }
         }
-        else if (lhs_type == value_t::number_integer and rhs_type == value_t::number_float)
+        else if (lhs_type == value_t::number_integer && rhs_type == value_t::number_float)
         {
-            return (static_cast<number_float_t>(lhs.m_value.number_integer) == rhs.m_value.number_float);
+            return static_cast<number_float_t>(lhs.m_value.number_integer) == rhs.m_value.number_float;
         }
-        else if (lhs_type == value_t::number_float and rhs_type == value_t::number_integer)
+        else if (lhs_type == value_t::number_float && rhs_type == value_t::number_integer)
         {
-            return (lhs.m_value.number_float == static_cast<number_float_t>(rhs.m_value.number_integer));
+            return lhs.m_value.number_float == static_cast<number_float_t>(rhs.m_value.number_integer);
         }
-        else if (lhs_type == value_t::number_unsigned and rhs_type == value_t::number_float)
+        else if (lhs_type == value_t::number_unsigned && rhs_type == value_t::number_float)
         {
-            return (static_cast<number_float_t>(lhs.m_value.number_unsigned) == rhs.m_value.number_float);
+            return static_cast<number_float_t>(lhs.m_value.number_unsigned) == rhs.m_value.number_float;
         }
-        else if (lhs_type == value_t::number_float and rhs_type == value_t::number_unsigned)
+        else if (lhs_type == value_t::number_float && rhs_type == value_t::number_unsigned)
         {
-            return (lhs.m_value.number_float == static_cast<number_float_t>(rhs.m_value.number_unsigned));
+            return lhs.m_value.number_float == static_cast<number_float_t>(rhs.m_value.number_unsigned);
         }
-        else if (lhs_type == value_t::number_unsigned and rhs_type == value_t::number_integer)
+        else if (lhs_type == value_t::number_unsigned && rhs_type == value_t::number_integer)
         {
-            return (static_cast<number_integer_t>(lhs.m_value.number_unsigned) == rhs.m_value.number_integer);
+            return static_cast<number_integer_t>(lhs.m_value.number_unsigned) == rhs.m_value.number_integer;
         }
-        else if (lhs_type == value_t::number_integer and rhs_type == value_t::number_unsigned)
+        else if (lhs_type == value_t::number_integer && rhs_type == value_t::number_unsigned)
         {
-            return (lhs.m_value.number_integer == static_cast<number_integer_t>(rhs.m_value.number_unsigned));
+            return lhs.m_value.number_integer == static_cast<number_integer_t>(rhs.m_value.number_unsigned);
         }
 
         return false;
@@ -17973,7 +22683,7 @@ class basic_json
                  std::is_scalar<ScalarType>::value, int>::type = 0>
     friend bool operator==(const_reference lhs, const ScalarType rhs) noexcept
     {
-        return (lhs == basic_json(rhs));
+        return lhs == basic_json(rhs);
     }
 
     /*!
@@ -17984,7 +22694,7 @@ class basic_json
                  std::is_scalar<ScalarType>::value, int>::type = 0>
     friend bool operator==(const ScalarType lhs, const_reference rhs) noexcept
     {
-        return (basic_json(lhs) == rhs);
+        return basic_json(lhs) == rhs;
     }
 
     /*!
@@ -18007,7 +22717,7 @@ class basic_json
     */
     friend bool operator!=(const_reference lhs, const_reference rhs) noexcept
     {
-        return not (lhs == rhs);
+        return !(lhs == rhs);
     }
 
     /*!
@@ -18018,7 +22728,7 @@ class basic_json
                  std::is_scalar<ScalarType>::value, int>::type = 0>
     friend bool operator!=(const_reference lhs, const ScalarType rhs) noexcept
     {
-        return (lhs != basic_json(rhs));
+        return lhs != basic_json(rhs);
     }
 
     /*!
@@ -18029,7 +22739,7 @@ class basic_json
                  std::is_scalar<ScalarType>::value, int>::type = 0>
     friend bool operator!=(const ScalarType lhs, const_reference rhs) noexcept
     {
-        return (basic_json(lhs) != rhs);
+        return basic_json(lhs) != rhs;
     }
 
     /*!
@@ -18068,54 +22778,59 @@ class basic_json
             switch (lhs_type)
             {
                 case value_t::array:
+                    // note parentheses are necessary, see
+                    // https://github.com/nlohmann/json/issues/1530
                     return (*lhs.m_value.array) < (*rhs.m_value.array);
 
                 case value_t::object:
-                    return *lhs.m_value.object < *rhs.m_value.object;
+                    return (*lhs.m_value.object) < (*rhs.m_value.object);
 
                 case value_t::null:
                     return false;
 
                 case value_t::string:
-                    return *lhs.m_value.string < *rhs.m_value.string;
+                    return (*lhs.m_value.string) < (*rhs.m_value.string);
 
                 case value_t::boolean:
-                    return lhs.m_value.boolean < rhs.m_value.boolean;
+                    return (lhs.m_value.boolean) < (rhs.m_value.boolean);
 
                 case value_t::number_integer:
-                    return lhs.m_value.number_integer < rhs.m_value.number_integer;
+                    return (lhs.m_value.number_integer) < (rhs.m_value.number_integer);
 
                 case value_t::number_unsigned:
-                    return lhs.m_value.number_unsigned < rhs.m_value.number_unsigned;
+                    return (lhs.m_value.number_unsigned) < (rhs.m_value.number_unsigned);
 
                 case value_t::number_float:
-                    return lhs.m_value.number_float < rhs.m_value.number_float;
+                    return (lhs.m_value.number_float) < (rhs.m_value.number_float);
+
+                case value_t::binary:
+                    return (*lhs.m_value.binary) < (*rhs.m_value.binary);
 
                 default:
                     return false;
             }
         }
-        else if (lhs_type == value_t::number_integer and rhs_type == value_t::number_float)
+        else if (lhs_type == value_t::number_integer && rhs_type == value_t::number_float)
         {
             return static_cast<number_float_t>(lhs.m_value.number_integer) < rhs.m_value.number_float;
         }
-        else if (lhs_type == value_t::number_float and rhs_type == value_t::number_integer)
+        else if (lhs_type == value_t::number_float && rhs_type == value_t::number_integer)
         {
             return lhs.m_value.number_float < static_cast<number_float_t>(rhs.m_value.number_integer);
         }
-        else if (lhs_type == value_t::number_unsigned and rhs_type == value_t::number_float)
+        else if (lhs_type == value_t::number_unsigned && rhs_type == value_t::number_float)
         {
             return static_cast<number_float_t>(lhs.m_value.number_unsigned) < rhs.m_value.number_float;
         }
-        else if (lhs_type == value_t::number_float and rhs_type == value_t::number_unsigned)
+        else if (lhs_type == value_t::number_float && rhs_type == value_t::number_unsigned)
         {
             return lhs.m_value.number_float < static_cast<number_float_t>(rhs.m_value.number_unsigned);
         }
-        else if (lhs_type == value_t::number_integer and rhs_type == value_t::number_unsigned)
+        else if (lhs_type == value_t::number_integer && rhs_type == value_t::number_unsigned)
         {
             return lhs.m_value.number_integer < static_cast<number_integer_t>(rhs.m_value.number_unsigned);
         }
-        else if (lhs_type == value_t::number_unsigned and rhs_type == value_t::number_integer)
+        else if (lhs_type == value_t::number_unsigned && rhs_type == value_t::number_integer)
         {
             return static_cast<number_integer_t>(lhs.m_value.number_unsigned) < rhs.m_value.number_integer;
         }
@@ -18134,7 +22849,7 @@ class basic_json
                  std::is_scalar<ScalarType>::value, int>::type = 0>
     friend bool operator<(const_reference lhs, const ScalarType rhs) noexcept
     {
-        return (lhs < basic_json(rhs));
+        return lhs < basic_json(rhs);
     }
 
     /*!
@@ -18145,7 +22860,7 @@ class basic_json
                  std::is_scalar<ScalarType>::value, int>::type = 0>
     friend bool operator<(const ScalarType lhs, const_reference rhs) noexcept
     {
-        return (basic_json(lhs) < rhs);
+        return basic_json(lhs) < rhs;
     }
 
     /*!
@@ -18169,7 +22884,7 @@ class basic_json
     */
     friend bool operator<=(const_reference lhs, const_reference rhs) noexcept
     {
-        return not (rhs < lhs);
+        return !(rhs < lhs);
     }
 
     /*!
@@ -18180,7 +22895,7 @@ class basic_json
                  std::is_scalar<ScalarType>::value, int>::type = 0>
     friend bool operator<=(const_reference lhs, const ScalarType rhs) noexcept
     {
-        return (lhs <= basic_json(rhs));
+        return lhs <= basic_json(rhs);
     }
 
     /*!
@@ -18191,7 +22906,7 @@ class basic_json
                  std::is_scalar<ScalarType>::value, int>::type = 0>
     friend bool operator<=(const ScalarType lhs, const_reference rhs) noexcept
     {
-        return (basic_json(lhs) <= rhs);
+        return basic_json(lhs) <= rhs;
     }
 
     /*!
@@ -18215,7 +22930,7 @@ class basic_json
     */
     friend bool operator>(const_reference lhs, const_reference rhs) noexcept
     {
-        return not (lhs <= rhs);
+        return !(lhs <= rhs);
     }
 
     /*!
@@ -18226,7 +22941,7 @@ class basic_json
                  std::is_scalar<ScalarType>::value, int>::type = 0>
     friend bool operator>(const_reference lhs, const ScalarType rhs) noexcept
     {
-        return (lhs > basic_json(rhs));
+        return lhs > basic_json(rhs);
     }
 
     /*!
@@ -18237,7 +22952,7 @@ class basic_json
                  std::is_scalar<ScalarType>::value, int>::type = 0>
     friend bool operator>(const ScalarType lhs, const_reference rhs) noexcept
     {
-        return (basic_json(lhs) > rhs);
+        return basic_json(lhs) > rhs;
     }
 
     /*!
@@ -18261,7 +22976,7 @@ class basic_json
     */
     friend bool operator>=(const_reference lhs, const_reference rhs) noexcept
     {
-        return not (lhs < rhs);
+        return !(lhs < rhs);
     }
 
     /*!
@@ -18272,7 +22987,7 @@ class basic_json
                  std::is_scalar<ScalarType>::value, int>::type = 0>
     friend bool operator>=(const_reference lhs, const ScalarType rhs) noexcept
     {
-        return (lhs >= basic_json(rhs));
+        return lhs >= basic_json(rhs);
     }
 
     /*!
@@ -18283,7 +22998,7 @@ class basic_json
                  std::is_scalar<ScalarType>::value, int>::type = 0>
     friend bool operator>=(const ScalarType lhs, const_reference rhs) noexcept
     {
-        return (basic_json(lhs) >= rhs);
+        return basic_json(lhs) >= rhs;
     }
 
     /// @}
@@ -18329,8 +23044,8 @@ class basic_json
     friend std::ostream& operator<<(std::ostream& o, const basic_json& j)
     {
         // read width member and use it as indentation parameter if nonzero
-        const bool pretty_print = (o.width() > 0);
-        const auto indentation = (pretty_print ? o.width() : 0);
+        const bool pretty_print = o.width() > 0;
+        const auto indentation = pretty_print ? o.width() : 0;
 
         // reset width to 0 for subsequent calls to this stream
         o.width(0);
@@ -18349,7 +23064,7 @@ class basic_json
                 instead; that is, replace calls like `j >> o;` with `o << j;`.
     @since version 1.0.0; deprecated since version 3.0.0
     */
-    JSON_DEPRECATED
+    JSON_HEDLEY_DEPRECATED_FOR(3.0.0, operator<<(std::ostream&, const basic_json&))
     friend std::ostream& operator>>(const basic_json& j, std::ostream& o)
     {
         return o << j;
@@ -18368,32 +23083,13 @@ class basic_json
     /*!
     @brief deserialize from a compatible input
 
-    This function reads from a compatible input. Examples are:
-    - an array of 1-byte values
-    - strings with character/literal type with size of 1 byte
-    - input streams
-    - container with contiguous storage of 1-byte values. Compatible container
-      types include `std::vector`, `std::string`, `std::array`,
-      `std::valarray`, and `std::initializer_list`. Furthermore, C-style
-      arrays can be used with `std::begin()`/`std::end()`. User-defined
-      containers can be used as long as they implement random-access iterators
-      and a contiguous storage.
-
-    @pre Each element of the container has a size of 1 byte. Violating this
-    precondition yields undefined behavior. **This precondition is enforced
-    with a static assertion.**
-
-    @pre The container storage is contiguous. Violating this precondition
-    yields undefined behavior. **This precondition is enforced with an
-    assertion.**
-    @pre Each element of the container has a size of 1 byte. Violating this
-    precondition yields undefined behavior. **This precondition is enforced
-    with a static assertion.**
-
-    @warning There is no way to enforce all preconditions at compile-time. If
-             the function is called with a noncompliant container and with
-             assertions switched off, the behavior is undefined and will most
-             likely yield segmentation violation.
+    @tparam InputType A compatible input, for instance
+    - an std::istream object
+    - a FILE pointer
+    - a C-style array of characters
+    - a pointer to a null-terminated string of single byte characters
+    - an object obj for which begin(obj) and end(obj) produces a valid pair of
+      iterators.
 
     @param[in] i  input to read from
     @param[in] cb  a parser callback function of type @ref parser_callback_t
@@ -18401,8 +23097,13 @@ class basic_json
     (optional)
     @param[in] allow_exceptions  whether to throw exceptions in case of a
     parse error (optional, true by default)
+    @param[in] ignore_comments  whether comments should be ignored and treated
+    like whitespace (true) or yield a parse error (true); (optional, false by
+    default)
 
-    @return result of the deserialization
+    @return deserialized JSON value; in case of a parse error and
+            @a allow_exceptions set to `false`, the return value will be
+            value_t::discarded.
 
     @throw parse_error.101 if a parse error occurs; example: `""unexpected end
     of input; expected string literal""`
@@ -18411,7 +23112,7 @@ class basic_json
 
     @complexity Linear in the length of the input. The parser is a predictive
     LL(1) parser. The complexity can be higher if the parser callback function
-    @a cb has a super-linear complexity.
+    @a cb or reading from the input @a i has a super-linear complexity.
 
     @note A UTF-8 byte order mark is silently ignored.
 
@@ -18427,20 +23128,122 @@ class basic_json
     @liveexample{The example below demonstrates the `parse()` function reading
     from a contiguous container.,parse__contiguouscontainer__parser_callback_t}
 
-    @since version 2.0.3 (contiguous containers)
+    @since version 2.0.3 (contiguous containers); version 3.9.0 allowed to
+    ignore comments.
     */
-    static basic_json parse(detail::input_adapter&& i,
+    template<typename InputType>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    static basic_json parse(InputType&& i,
+                            const parser_callback_t cb = nullptr,
+                            const bool allow_exceptions = true,
+                            const bool ignore_comments = false)
+    {
+        basic_json result;
+        parser(detail::input_adapter(std::forward<InputType>(i)), cb, allow_exceptions, ignore_comments).parse(true, result);
+        return result;
+    }
+
+    /*!
+    @brief deserialize from a pair of character iterators
+
+    The value_type of the iterator must be a integral type with size of 1, 2 or
+    4 bytes, which will be interpreted respectively as UTF-8, UTF-16 and UTF-32.
+
+    @param[in] first iterator to start of character range
+    @param[in] last  iterator to end of character range
+    @param[in] cb  a parser callback function of type @ref parser_callback_t
+    which is used to control the deserialization by filtering unwanted values
+    (optional)
+    @param[in] allow_exceptions  whether to throw exceptions in case of a
+    parse error (optional, true by default)
+    @param[in] ignore_comments  whether comments should be ignored and treated
+    like whitespace (true) or yield a parse error (true); (optional, false by
+    default)
+
+    @return deserialized JSON value; in case of a parse error and
+            @a allow_exceptions set to `false`, the return value will be
+            value_t::discarded.
+
+    @throw parse_error.101 if a parse error occurs; example: `""unexpected end
+    of input; expected string literal""`
+    @throw parse_error.102 if to_unicode fails or surrogate error
+    @throw parse_error.103 if to_unicode fails
+    */
+    template<typename IteratorType>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    static basic_json parse(IteratorType first,
+                            IteratorType last,
+                            const parser_callback_t cb = nullptr,
+                            const bool allow_exceptions = true,
+                            const bool ignore_comments = false)
+    {
+        basic_json result;
+        parser(detail::input_adapter(std::move(first), std::move(last)), cb, allow_exceptions, ignore_comments).parse(true, result);
+        return result;
+    }
+
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    JSON_HEDLEY_DEPRECATED_FOR(3.8.0, parse(ptr, ptr + len))
+    static basic_json parse(detail::span_input_adapter&& i,
                             const parser_callback_t cb = nullptr,
-                            const bool allow_exceptions = true)
+                            const bool allow_exceptions = true,
+                            const bool ignore_comments = false)
     {
         basic_json result;
-        parser(i, cb, allow_exceptions).parse(true, result);
+        parser(i.get(), cb, allow_exceptions, ignore_comments).parse(true, result);
         return result;
     }
 
-    static bool accept(detail::input_adapter&& i)
+    /*!
+    @brief check if the input is valid JSON
+
+    Unlike the @ref parse(InputType&&, const parser_callback_t,const bool)
+    function, this function neither throws an exception in case of invalid JSON
+    input (i.e., a parse error) nor creates diagnostic information.
+
+    @tparam InputType A compatible input, for instance
+    - an std::istream object
+    - a FILE pointer
+    - a C-style array of characters
+    - a pointer to a null-terminated string of single byte characters
+    - an object obj for which begin(obj) and end(obj) produces a valid pair of
+      iterators.
+
+    @param[in] i input to read from
+    @param[in] ignore_comments  whether comments should be ignored and treated
+    like whitespace (true) or yield a parse error (true); (optional, false by
+    default)
+
+    @return Whether the input read from @a i is valid JSON.
+
+    @complexity Linear in the length of the input. The parser is a predictive
+    LL(1) parser.
+
+    @note A UTF-8 byte order mark is silently ignored.
+
+    @liveexample{The example below demonstrates the `accept()` function reading
+    from a string.,accept__string}
+    */
+    template<typename InputType>
+    static bool accept(InputType&& i,
+                       const bool ignore_comments = false)
     {
-        return parser(i).accept(true);
+        return parser(detail::input_adapter(std::forward<InputType>(i)), nullptr, false, ignore_comments).accept(true);
+    }
+
+    template<typename IteratorType>
+    static bool accept(IteratorType first, IteratorType last,
+                       const bool ignore_comments = false)
+    {
+        return parser(detail::input_adapter(std::move(first), std::move(last)), nullptr, false, ignore_comments).accept(true);
+    }
+
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    JSON_HEDLEY_DEPRECATED_FOR(3.8.0, accept(ptr, ptr + len))
+    static bool accept(detail::span_input_adapter&& i,
+                       const bool ignore_comments = false)
+    {
+        return parser(i.get(), nullptr, false, ignore_comments).accept(true);
     }
 
     /*!
@@ -18449,36 +23252,20 @@ class basic_json
     The SAX event lister must follow the interface of @ref json_sax.
 
     This function reads from a compatible input. Examples are:
-    - an array of 1-byte values
-    - strings with character/literal type with size of 1 byte
-    - input streams
-    - container with contiguous storage of 1-byte values. Compatible container
-      types include `std::vector`, `std::string`, `std::array`,
-      `std::valarray`, and `std::initializer_list`. Furthermore, C-style
-      arrays can be used with `std::begin()`/`std::end()`. User-defined
-      containers can be used as long as they implement random-access iterators
-      and a contiguous storage.
-
-    @pre Each element of the container has a size of 1 byte. Violating this
-    precondition yields undefined behavior. **This precondition is enforced
-    with a static assertion.**
-
-    @pre The container storage is contiguous. Violating this precondition
-    yields undefined behavior. **This precondition is enforced with an
-    assertion.**
-    @pre Each element of the container has a size of 1 byte. Violating this
-    precondition yields undefined behavior. **This precondition is enforced
-    with a static assertion.**
-
-    @warning There is no way to enforce all preconditions at compile-time. If
-             the function is called with a noncompliant container and with
-             assertions switched off, the behavior is undefined and will most
-             likely yield segmentation violation.
+    - an std::istream object
+    - a FILE pointer
+    - a C-style array of characters
+    - a pointer to a null-terminated string of single byte characters
+    - an object obj for which begin(obj) and end(obj) produces a valid pair of
+      iterators.
 
     @param[in] i  input to read from
     @param[in,out] sax  SAX event listener
     @param[in] format  the format to parse (JSON, CBOR, MessagePack, or UBJSON)
     @param[in] strict  whether the input has to be consumed completely
+    @param[in] ignore_comments  whether comments should be ignored and treated
+    like whitespace (true) or yield a parse error (true); (optional, false by
+    default); only applies to the JSON file format.
 
     @return return value of the last processed SAX event
 
@@ -18499,97 +23286,44 @@ class basic_json
 
     @since version 3.2.0
     */
-    template <typename SAX>
-    static bool sax_parse(detail::input_adapter&& i, SAX* sax,
+    template <typename InputType, typename SAX>
+    JSON_HEDLEY_NON_NULL(2)
+    static bool sax_parse(InputType&& i, SAX* sax,
                           input_format_t format = input_format_t::json,
-                          const bool strict = true)
-    {
-        assert(sax);
-        switch (format)
-        {
-            case input_format_t::json:
-                return parser(std::move(i)).sax_parse(sax, strict);
-            default:
-                return detail::binary_reader<basic_json, SAX>(std::move(i)).sax_parse(format, sax, strict);
-        }
-    }
-
-    /*!
-    @brief deserialize from an iterator range with contiguous storage
-
-    This function reads from an iterator range of a container with contiguous
-    storage of 1-byte values. Compatible container types include
-    `std::vector`, `std::string`, `std::array`, `std::valarray`, and
-    `std::initializer_list`. Furthermore, C-style arrays can be used with
-    `std::begin()`/`std::end()`. User-defined containers can be used as long
-    as they implement random-access iterators and a contiguous storage.
-
-    @pre The iterator range is contiguous. Violating this precondition yields
-    undefined behavior. **This precondition is enforced with an assertion.**
-    @pre Each element in the range has a size of 1 byte. Violating this
-    precondition yields undefined behavior. **This precondition is enforced
-    with a static assertion.**
-
-    @warning There is no way to enforce all preconditions at compile-time. If
-             the function is called with noncompliant iterators and with
-             assertions switched off, the behavior is undefined and will most
-             likely yield segmentation violation.
-
-    @tparam IteratorType iterator of container with contiguous storage
-    @param[in] first  begin of the range to parse (included)
-    @param[in] last  end of the range to parse (excluded)
-    @param[in] cb  a parser callback function of type @ref parser_callback_t
-    which is used to control the deserialization by filtering unwanted values
-    (optional)
-    @param[in] allow_exceptions  whether to throw exceptions in case of a
-    parse error (optional, true by default)
-
-    @return result of the deserialization
-
-    @throw parse_error.101 in case of an unexpected token
-    @throw parse_error.102 if to_unicode fails or surrogate error
-    @throw parse_error.103 if to_unicode fails
-
-    @complexity Linear in the length of the input. The parser is a predictive
-    LL(1) parser. The complexity can be higher if the parser callback function
-    @a cb has a super-linear complexity.
-
-    @note A UTF-8 byte order mark is silently ignored.
-
-    @liveexample{The example below demonstrates the `parse()` function reading
-    from an iterator range.,parse__iteratortype__parser_callback_t}
-
-    @since version 2.0.3
-    */
-    template<class IteratorType, typename std::enable_if<
-                 std::is_base_of<
-                     std::random_access_iterator_tag,
-                     typename std::iterator_traits<IteratorType>::iterator_category>::value, int>::type = 0>
-    static basic_json parse(IteratorType first, IteratorType last,
-                            const parser_callback_t cb = nullptr,
-                            const bool allow_exceptions = true)
+                          const bool strict = true,
+                          const bool ignore_comments = false)
     {
-        basic_json result;
-        parser(detail::input_adapter(first, last), cb, allow_exceptions).parse(true, result);
-        return result;
+        auto ia = detail::input_adapter(std::forward<InputType>(i));
+        return format == input_format_t::json
+               ? parser(std::move(ia), nullptr, true, ignore_comments).sax_parse(sax, strict)
+               : detail::binary_reader<basic_json, decltype(ia), SAX>(std::move(ia)).sax_parse(format, sax, strict);
     }
 
-    template<class IteratorType, typename std::enable_if<
-                 std::is_base_of<
-                     std::random_access_iterator_tag,
-                     typename std::iterator_traits<IteratorType>::iterator_category>::value, int>::type = 0>
-    static bool accept(IteratorType first, IteratorType last)
+    template<class IteratorType, class SAX>
+    JSON_HEDLEY_NON_NULL(3)
+    static bool sax_parse(IteratorType first, IteratorType last, SAX* sax,
+                          input_format_t format = input_format_t::json,
+                          const bool strict = true,
+                          const bool ignore_comments = false)
     {
-        return parser(detail::input_adapter(first, last)).accept(true);
+        auto ia = detail::input_adapter(std::move(first), std::move(last));
+        return format == input_format_t::json
+               ? parser(std::move(ia), nullptr, true, ignore_comments).sax_parse(sax, strict)
+               : detail::binary_reader<basic_json, decltype(ia), SAX>(std::move(ia)).sax_parse(format, sax, strict);
     }
 
-    template<class IteratorType, class SAX, typename std::enable_if<
-                 std::is_base_of<
-                     std::random_access_iterator_tag,
-                     typename std::iterator_traits<IteratorType>::iterator_category>::value, int>::type = 0>
-    static bool sax_parse(IteratorType first, IteratorType last, SAX* sax)
+    template <typename SAX>
+    JSON_HEDLEY_DEPRECATED_FOR(3.8.0, sax_parse(ptr, ptr + len, ...))
+    JSON_HEDLEY_NON_NULL(2)
+    static bool sax_parse(detail::span_input_adapter&& i, SAX* sax,
+                          input_format_t format = input_format_t::json,
+                          const bool strict = true,
+                          const bool ignore_comments = false)
     {
-        return parser(detail::input_adapter(first, last)).sax_parse(sax);
+        auto ia = i.get();
+        return format == input_format_t::json
+               ? parser(std::move(ia), nullptr, true, ignore_comments).sax_parse(sax, strict)
+               : detail::binary_reader<basic_json, decltype(ia), SAX>(std::move(ia)).sax_parse(format, sax, strict);
     }
 
     /*!
@@ -18600,7 +23334,7 @@ class basic_json
                 instead; that is, replace calls like `j << i;` with `i >> j;`.
     @since version 1.0.0; deprecated since version 3.0.0
     */
-    JSON_DEPRECATED
+    JSON_HEDLEY_DEPRECATED_FOR(3.0.0, operator>>(std::istream&, basic_json&))
     friend std::istream& operator<<(basic_json& j, std::istream& i)
     {
         return operator>>(i, j);
@@ -18658,6 +23392,7 @@ class basic_json
             number      | `"number"` (for all number types)
             object      | `"object"`
             array       | `"array"`
+            binary      | `"binary"`
             discarded   | `"discarded"`
 
     @exceptionsafety No-throw guarantee: this function never throws exceptions.
@@ -18673,6 +23408,7 @@ class basic_json
     @since version 1.0.0, public since 2.1.0, `const char*` and `noexcept`
     since 3.0.0
     */
+    JSON_HEDLEY_RETURNS_NON_NULL
     const char* type_name() const noexcept
     {
         {
@@ -18688,6 +23424,8 @@ class basic_json
                     return "string";
                 case value_t::boolean:
                     return "boolean";
+                case value_t::binary:
+                    return "binary";
                 case value_t::discarded:
                     return "discarded";
                 default:
@@ -18747,7 +23485,8 @@ class basic_json
     number_unsigned | 256..65535                                 | Unsigned integer (2 bytes follow)  | 0x19
     number_unsigned | 65536..4294967295                          | Unsigned integer (4 bytes follow)  | 0x1A
     number_unsigned | 4294967296..18446744073709551615           | Unsigned integer (8 bytes follow)  | 0x1B
-    number_float    | *any value*                                | Double-Precision Float             | 0xFB
+    number_float    | *any value representable by a float*       | Single-Precision Float             | 0xFA
+    number_float    | *any value NOT representable by a float*   | Double-Precision Float             | 0xFB
     string          | *length*: 0..23                            | UTF-8 string                       | 0x60..0x77
     string          | *length*: 23..255                          | UTF-8 string (1 byte follow)       | 0x78
     string          | *length*: 256..65535                       | UTF-8 string (2 bytes follow)      | 0x79
@@ -18763,6 +23502,11 @@ class basic_json
     object          | *size*: 256..65535                         | map (2 bytes follow)               | 0xB9
     object          | *size*: 65536..4294967295                  | map (4 bytes follow)               | 0xBA
     object          | *size*: 4294967296..18446744073709551615   | map (8 bytes follow)               | 0xBB
+    binary          | *size*: 0..23                              | byte string                        | 0x40..0x57
+    binary          | *size*: 23..255                            | byte string (1 byte follow)        | 0x58
+    binary          | *size*: 256..65535                         | byte string (2 bytes follow)       | 0x59
+    binary          | *size*: 65536..4294967295                  | byte string (4 bytes follow)       | 0x5A
+    binary          | *size*: 4294967296..18446744073709551615   | byte string (8 bytes follow)       | 0x5B
 
     @note The mapping is **complete** in the sense that any JSON value type
           can be converted to a CBOR value.
@@ -18772,23 +23516,22 @@ class basic_json
           function which serializes NaN or Infinity to `null`.
 
     @note The following CBOR types are not used in the conversion:
-          - byte strings (0x40..0x5F)
           - UTF-8 strings terminated by "break" (0x7F)
           - arrays terminated by "break" (0x9F)
           - maps terminated by "break" (0xBF)
+          - byte strings terminated by "break" (0x5F)
           - date/time (0xC0..0xC1)
           - bignum (0xC2..0xC3)
           - decimal fraction (0xC4)
           - bigfloat (0xC5)
-          - tagged items (0xC6..0xD4, 0xD8..0xDB)
           - expected conversions (0xD5..0xD7)
           - simple values (0xE0..0xF3, 0xF8)
           - undefined (0xF7)
-          - half and single-precision floats (0xF9-0xFA)
+          - half-precision floats (0xF9)
           - break (0xFF)
 
     @param[in] j  JSON value to serialize
-    @return MessagePack serialization as byte vector
+    @return CBOR serialization as byte vector
 
     @complexity Linear in the size of the JSON value @a j.
 
@@ -18796,13 +23539,14 @@ class basic_json
     vector in CBOR format.,to_cbor}
 
     @sa http://cbor.io
-    @sa @ref from_cbor(detail::input_adapter&&, const bool, const bool) for the
+    @sa @ref from_cbor(detail::input_adapter&&, const bool, const bool, const cbor_tag_handler_t) for the
         analogous deserialization
     @sa @ref to_msgpack(const basic_json&) for the related MessagePack format
     @sa @ref to_ubjson(const basic_json&, const bool, const bool) for the
              related UBJSON format
 
-    @since version 2.0.9
+    @since version 2.0.9; compact representation of floating-point numbers
+           since version 3.8.0
     */
     static std::vector<uint8_t> to_cbor(const basic_json& j)
     {
@@ -18851,7 +23595,8 @@ class basic_json
     number_unsigned | 256..65535                        | uint 16          | 0xCD
     number_unsigned | 65536..4294967295                 | uint 32          | 0xCE
     number_unsigned | 4294967296..18446744073709551615  | uint 64          | 0xCF
-    number_float    | *any value*                       | float 64         | 0xCB
+    number_float    | *any value representable by a float*     | float 32 | 0xCA
+    number_float    | *any value NOT representable by a float* | float 64 | 0xCB
     string          | *length*: 0..31                   | fixstr           | 0xA0..0xBF
     string          | *length*: 32..255                 | str 8            | 0xD9
     string          | *length*: 256..65535              | str 16           | 0xDA
@@ -18862,21 +23607,19 @@ class basic_json
     object          | *size*: 0..15                     | fix map          | 0x80..0x8F
     object          | *size*: 16..65535                 | map 16           | 0xDE
     object          | *size*: 65536..4294967295         | map 32           | 0xDF
+    binary          | *size*: 0..255                    | bin 8            | 0xC4
+    binary          | *size*: 256..65535                | bin 16           | 0xC5
+    binary          | *size*: 65536..4294967295         | bin 32           | 0xC6
 
     @note The mapping is **complete** in the sense that any JSON value type
           can be converted to a MessagePack value.
 
     @note The following values can **not** be converted to a MessagePack value:
           - strings with more than 4294967295 bytes
+          - byte strings with more than 4294967295 bytes
           - arrays with more than 4294967295 elements
           - objects with more than 4294967295 elements
 
-    @note The following MessagePack types are not used in the conversion:
-          - bin 8 - bin 32 (0xC4..0xC6)
-          - ext 8 - ext 32 (0xC7..0xC9)
-          - float 32 (0xCA)
-          - fixext 1 - fixext 16 (0xD4..0xD8)
-
     @note Any MessagePack output created @ref to_msgpack can be successfully
           parsed by @ref from_msgpack.
 
@@ -18945,6 +23688,7 @@ class basic_json
     number_unsigned | 256..32767                        | int16       | `I`
     number_unsigned | 32768..2147483647                 | int32       | `l`
     number_unsigned | 2147483648..9223372036854775807   | int64       | `L`
+    number_unsigned | 2147483649..18446744073709551615  | high-precision | `H`
     number_float    | *any value*                       | float64     | `D`
     string          | *with shortest length indicator*  | string      | `S`
     array           | *see notes on optimized format*   | array       | `[`
@@ -18955,7 +23699,6 @@ class basic_json
 
     @note The following values can **not** be converted to a UBJSON value:
           - strings with more than 9223372036854775807 bytes (theoretical)
-          - unsigned integer numbers above 9223372036854775807
 
     @note The following markers are not used in the conversion:
           - `Z`: no-op values are not created.
@@ -18978,6 +23721,12 @@ class basic_json
           the benefit of this parameter is that the receiving side is
           immediately informed on the number of elements of the container.
 
+    @note If the JSON data contains the binary type, the value stored is a list
+          of integers, as suggested by the UBJSON documentation.  In particular,
+          this means that serialization and the deserialization of a JSON
+          containing binary values into UBJSON and back will result in a
+          different JSON object.
+
     @param[in] j  JSON value to serialize
     @param[in] use_size  whether to add size annotations to container types
     @param[in] use_type  whether to add type annotations to container types
@@ -19042,6 +23791,7 @@ class basic_json
     string          | *any value*                       | string      | 0x02
     array           | *any value*                       | document    | 0x04
     object          | *any value*                       | document    | 0x03
+    binary          | *any value*                       | binary      | 0x05
 
     @warning The mapping is **incomplete**, since only JSON-objects (and things
     contained therein) can be serialized to BSON.
@@ -19123,7 +23873,11 @@ class basic_json
     Negative integer       | number_integer  | 0x39
     Negative integer       | number_integer  | 0x3A
     Negative integer       | number_integer  | 0x3B
-    Negative integer       | number_integer  | 0x40..0x57
+    Byte string            | binary          | 0x40..0x57
+    Byte string            | binary          | 0x58
+    Byte string            | binary          | 0x59
+    Byte string            | binary          | 0x5A
+    Byte string            | binary          | 0x5B
     UTF-8 string           | string          | 0x60..0x77
     UTF-8 string           | string          | 0x78
     UTF-8 string           | string          | 0x79
@@ -19152,12 +23906,10 @@ class basic_json
     @warning The mapping is **incomplete** in the sense that not all CBOR
              types can be converted to a JSON value. The following CBOR types
              are not supported and will yield parse errors (parse_error.112):
-             - byte strings (0x40..0x5F)
              - date/time (0xC0..0xC1)
              - bignum (0xC2..0xC3)
              - decimal fraction (0xC4)
              - bigfloat (0xC5)
-             - tagged items (0xC6..0xD4, 0xD8..0xDB)
              - expected conversions (0xD5..0xD7)
              - simple values (0xE0..0xF3, 0xF8)
              - undefined (0xF7)
@@ -19174,8 +23926,11 @@ class basic_json
                        (true by default)
     @param[in] allow_exceptions  whether to throw exceptions in case of a
     parse error (optional, true by default)
+    @param[in] tag_handler how to treat CBOR tags (optional, error by default)
 
-    @return deserialized JSON value
+    @return deserialized JSON value; in case of a parse error and
+            @a allow_exceptions set to `false`, the return value will be
+            value_t::discarded.
 
     @throw parse_error.110 if the given input ends prematurely or the end of
     file was not reached when @a strict was set to true
@@ -19198,30 +23953,62 @@ class basic_json
     @since version 2.0.9; parameter @a start_index since 2.1.1; changed to
            consume input adapters, removed start_index parameter, and added
            @a strict parameter since 3.0.0; added @a allow_exceptions parameter
-           since 3.2.0
+           since 3.2.0; added @a tag_handler parameter since 3.9.0.
     */
-    static basic_json from_cbor(detail::input_adapter&& i,
+    template<typename InputType>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    static basic_json from_cbor(InputType&& i,
                                 const bool strict = true,
-                                const bool allow_exceptions = true)
+                                const bool allow_exceptions = true,
+                                const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error)
     {
         basic_json result;
         detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
-        const bool res = binary_reader(detail::input_adapter(i)).sax_parse(input_format_t::cbor, &sdp, strict);
+        auto ia = detail::input_adapter(std::forward<InputType>(i));
+        const bool res = binary_reader<decltype(ia)>(std::move(ia)).sax_parse(input_format_t::cbor, &sdp, strict, tag_handler);
         return res ? result : basic_json(value_t::discarded);
     }
 
     /*!
-    @copydoc from_cbor(detail::input_adapter&&, const bool, const bool)
+    @copydoc from_cbor(detail::input_adapter&&, const bool, const bool, const cbor_tag_handler_t)
     */
-    template<typename A1, typename A2,
-             detail::enable_if_t<std::is_constructible<detail::input_adapter, A1, A2>::value, int> = 0>
-    static basic_json from_cbor(A1 && a1, A2 && a2,
+    template<typename IteratorType>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    static basic_json from_cbor(IteratorType first, IteratorType last,
                                 const bool strict = true,
-                                const bool allow_exceptions = true)
+                                const bool allow_exceptions = true,
+                                const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error)
     {
         basic_json result;
         detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
-        const bool res = binary_reader(detail::input_adapter(std::forward<A1>(a1), std::forward<A2>(a2))).sax_parse(input_format_t::cbor, &sdp, strict);
+        auto ia = detail::input_adapter(std::move(first), std::move(last));
+        const bool res = binary_reader<decltype(ia)>(std::move(ia)).sax_parse(input_format_t::cbor, &sdp, strict, tag_handler);
+        return res ? result : basic_json(value_t::discarded);
+    }
+
+    template<typename T>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_cbor(ptr, ptr + len))
+    static basic_json from_cbor(const T* ptr, std::size_t len,
+                                const bool strict = true,
+                                const bool allow_exceptions = true,
+                                const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error)
+    {
+        return from_cbor(ptr, ptr + len, strict, allow_exceptions, tag_handler);
+    }
+
+
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_cbor(ptr, ptr + len))
+    static basic_json from_cbor(detail::span_input_adapter&& i,
+                                const bool strict = true,
+                                const bool allow_exceptions = true,
+                                const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error)
+    {
+        basic_json result;
+        detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
+        auto ia = i.get();
+        const bool res = binary_reader<decltype(ia)>(std::move(ia)).sax_parse(input_format_t::cbor, &sdp, strict, tag_handler);
         return res ? result : basic_json(value_t::discarded);
     }
 
@@ -19259,15 +24046,19 @@ class basic_json
     array 32         | array           | 0xDD
     map 16           | object          | 0xDE
     map 32           | object          | 0xDF
+    bin 8            | binary          | 0xC4
+    bin 16           | binary          | 0xC5
+    bin 32           | binary          | 0xC6
+    ext 8            | binary          | 0xC7
+    ext 16           | binary          | 0xC8
+    ext 32           | binary          | 0xC9
+    fixext 1         | binary          | 0xD4
+    fixext 2         | binary          | 0xD5
+    fixext 4         | binary          | 0xD6
+    fixext 8         | binary          | 0xD7
+    fixext 16        | binary          | 0xD8
     negative fixint  | number_integer  | 0xE0-0xFF
 
-    @warning The mapping is **incomplete** in the sense that not all
-             MessagePack types can be converted to a JSON value. The following
-             MessagePack types are not supported and will yield parse errors:
-              - bin 8 - bin 32 (0xC4..0xC6)
-              - ext 8 - ext 32 (0xC7..0xC9)
-              - fixext 1 - fixext 16 (0xD4..0xD8)
-
     @note Any MessagePack output created @ref to_msgpack can be successfully
           parsed by @ref from_msgpack.
 
@@ -19278,7 +24069,9 @@ class basic_json
     @param[in] allow_exceptions  whether to throw exceptions in case of a
     parse error (optional, true by default)
 
-    @return deserialized JSON value
+    @return deserialized JSON value; in case of a parse error and
+            @a allow_exceptions set to `false`, the return value will be
+            value_t::discarded.
 
     @throw parse_error.110 if the given input ends prematurely or the end of
     file was not reached when @a strict was set to true
@@ -19293,7 +24086,7 @@ class basic_json
 
     @sa http://msgpack.org
     @sa @ref to_msgpack(const basic_json&) for the analogous serialization
-    @sa @ref from_cbor(detail::input_adapter&&, const bool, const bool) for the
+    @sa @ref from_cbor(detail::input_adapter&&, const bool, const bool, const cbor_tag_handler_t) for the
         related CBOR format
     @sa @ref from_ubjson(detail::input_adapter&&, const bool, const bool) for
         the related UBJSON format
@@ -19305,31 +24098,60 @@ class basic_json
            @a strict parameter since 3.0.0; added @a allow_exceptions parameter
            since 3.2.0
     */
-    static basic_json from_msgpack(detail::input_adapter&& i,
+    template<typename InputType>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    static basic_json from_msgpack(InputType&& i,
                                    const bool strict = true,
                                    const bool allow_exceptions = true)
     {
         basic_json result;
         detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
-        const bool res = binary_reader(detail::input_adapter(i)).sax_parse(input_format_t::msgpack, &sdp, strict);
+        auto ia = detail::input_adapter(std::forward<InputType>(i));
+        const bool res = binary_reader<decltype(ia)>(std::move(ia)).sax_parse(input_format_t::msgpack, &sdp, strict);
         return res ? result : basic_json(value_t::discarded);
     }
 
     /*!
     @copydoc from_msgpack(detail::input_adapter&&, const bool, const bool)
     */
-    template<typename A1, typename A2,
-             detail::enable_if_t<std::is_constructible<detail::input_adapter, A1, A2>::value, int> = 0>
-    static basic_json from_msgpack(A1 && a1, A2 && a2,
+    template<typename IteratorType>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    static basic_json from_msgpack(IteratorType first, IteratorType last,
                                    const bool strict = true,
                                    const bool allow_exceptions = true)
     {
         basic_json result;
         detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
-        const bool res = binary_reader(detail::input_adapter(std::forward<A1>(a1), std::forward<A2>(a2))).sax_parse(input_format_t::msgpack, &sdp, strict);
+        auto ia = detail::input_adapter(std::move(first), std::move(last));
+        const bool res = binary_reader<decltype(ia)>(std::move(ia)).sax_parse(input_format_t::msgpack, &sdp, strict);
         return res ? result : basic_json(value_t::discarded);
     }
 
+
+    template<typename T>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_msgpack(ptr, ptr + len))
+    static basic_json from_msgpack(const T* ptr, std::size_t len,
+                                   const bool strict = true,
+                                   const bool allow_exceptions = true)
+    {
+        return from_msgpack(ptr, ptr + len, strict, allow_exceptions);
+    }
+
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_msgpack(ptr, ptr + len))
+    static basic_json from_msgpack(detail::span_input_adapter&& i,
+                                   const bool strict = true,
+                                   const bool allow_exceptions = true)
+    {
+        basic_json result;
+        detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
+        auto ia = i.get();
+        const bool res = binary_reader<decltype(ia)>(std::move(ia)).sax_parse(input_format_t::msgpack, &sdp, strict);
+        return res ? result : basic_json(value_t::discarded);
+    }
+
+
     /*!
     @brief create a JSON value from an input in UBJSON format
 
@@ -19351,6 +24173,7 @@ class basic_json
     int16       | number_integer                          | `I`
     int32       | number_integer                          | `l`
     int64       | number_integer                          | `L`
+    high-precision number | number_integer, number_unsigned, or number_float - depends on number string | 'H'
     string      | string                                  | `S`
     char        | string                                  | `C`
     array       | array (optimized values are supported)  | `[`
@@ -19365,7 +24188,9 @@ class basic_json
     @param[in] allow_exceptions  whether to throw exceptions in case of a
     parse error (optional, true by default)
 
-    @return deserialized JSON value
+    @return deserialized JSON value; in case of a parse error and
+            @a allow_exceptions set to `false`, the return value will be
+            value_t::discarded.
 
     @throw parse_error.110 if the given input ends prematurely or the end of
     file was not reached when @a strict was set to true
@@ -19380,7 +24205,7 @@ class basic_json
     @sa http://ubjson.org
     @sa @ref to_ubjson(const basic_json&, const bool, const bool) for the
              analogous serialization
-    @sa @ref from_cbor(detail::input_adapter&&, const bool, const bool) for the
+    @sa @ref from_cbor(detail::input_adapter&&, const bool, const bool, const cbor_tag_handler_t) for the
         related CBOR format
     @sa @ref from_msgpack(detail::input_adapter&&, const bool, const bool) for
         the related MessagePack format
@@ -19389,31 +24214,59 @@ class basic_json
 
     @since version 3.1.0; added @a allow_exceptions parameter since 3.2.0
     */
-    static basic_json from_ubjson(detail::input_adapter&& i,
+    template<typename InputType>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    static basic_json from_ubjson(InputType&& i,
                                   const bool strict = true,
                                   const bool allow_exceptions = true)
     {
         basic_json result;
         detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
-        const bool res = binary_reader(detail::input_adapter(i)).sax_parse(input_format_t::ubjson, &sdp, strict);
+        auto ia = detail::input_adapter(std::forward<InputType>(i));
+        const bool res = binary_reader<decltype(ia)>(std::move(ia)).sax_parse(input_format_t::ubjson, &sdp, strict);
         return res ? result : basic_json(value_t::discarded);
     }
 
     /*!
     @copydoc from_ubjson(detail::input_adapter&&, const bool, const bool)
     */
-    template<typename A1, typename A2,
-             detail::enable_if_t<std::is_constructible<detail::input_adapter, A1, A2>::value, int> = 0>
-    static basic_json from_ubjson(A1 && a1, A2 && a2,
+    template<typename IteratorType>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    static basic_json from_ubjson(IteratorType first, IteratorType last,
                                   const bool strict = true,
                                   const bool allow_exceptions = true)
     {
         basic_json result;
         detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
-        const bool res = binary_reader(detail::input_adapter(std::forward<A1>(a1), std::forward<A2>(a2))).sax_parse(input_format_t::ubjson, &sdp, strict);
+        auto ia = detail::input_adapter(std::move(first), std::move(last));
+        const bool res = binary_reader<decltype(ia)>(std::move(ia)).sax_parse(input_format_t::ubjson, &sdp, strict);
         return res ? result : basic_json(value_t::discarded);
     }
 
+    template<typename T>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_ubjson(ptr, ptr + len))
+    static basic_json from_ubjson(const T* ptr, std::size_t len,
+                                  const bool strict = true,
+                                  const bool allow_exceptions = true)
+    {
+        return from_ubjson(ptr, ptr + len, strict, allow_exceptions);
+    }
+
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_ubjson(ptr, ptr + len))
+    static basic_json from_ubjson(detail::span_input_adapter&& i,
+                                  const bool strict = true,
+                                  const bool allow_exceptions = true)
+    {
+        basic_json result;
+        detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
+        auto ia = i.get();
+        const bool res = binary_reader<decltype(ia)>(std::move(ia)).sax_parse(input_format_t::ubjson, &sdp, strict);
+        return res ? result : basic_json(value_t::discarded);
+    }
+
+
     /*!
     @brief Create a JSON value from an input in BSON format
 
@@ -19454,7 +24307,9 @@ class basic_json
     @param[in] allow_exceptions  whether to throw exceptions in case of a
     parse error (optional, true by default)
 
-    @return deserialized JSON value
+    @return deserialized JSON value; in case of a parse error and
+            @a allow_exceptions set to `false`, the return value will be
+            value_t::discarded.
 
     @throw parse_error.114 if an unsupported BSON record type is encountered
 
@@ -19465,40 +24320,64 @@ class basic_json
 
     @sa http://bsonspec.org/spec.html
     @sa @ref to_bson(const basic_json&) for the analogous serialization
-    @sa @ref from_cbor(detail::input_adapter&&, const bool, const bool) for the
+    @sa @ref from_cbor(detail::input_adapter&&, const bool, const bool, const cbor_tag_handler_t) for the
         related CBOR format
     @sa @ref from_msgpack(detail::input_adapter&&, const bool, const bool) for
         the related MessagePack format
     @sa @ref from_ubjson(detail::input_adapter&&, const bool, const bool) for the
         related UBJSON format
     */
-    static basic_json from_bson(detail::input_adapter&& i,
+    template<typename InputType>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    static basic_json from_bson(InputType&& i,
                                 const bool strict = true,
                                 const bool allow_exceptions = true)
     {
         basic_json result;
         detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
-        const bool res = binary_reader(detail::input_adapter(i)).sax_parse(input_format_t::bson, &sdp, strict);
+        auto ia = detail::input_adapter(std::forward<InputType>(i));
+        const bool res = binary_reader<decltype(ia)>(std::move(ia)).sax_parse(input_format_t::bson, &sdp, strict);
         return res ? result : basic_json(value_t::discarded);
     }
 
     /*!
     @copydoc from_bson(detail::input_adapter&&, const bool, const bool)
     */
-    template<typename A1, typename A2,
-             detail::enable_if_t<std::is_constructible<detail::input_adapter, A1, A2>::value, int> = 0>
-    static basic_json from_bson(A1 && a1, A2 && a2,
+    template<typename IteratorType>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    static basic_json from_bson(IteratorType first, IteratorType last,
                                 const bool strict = true,
                                 const bool allow_exceptions = true)
     {
         basic_json result;
         detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
-        const bool res = binary_reader(detail::input_adapter(std::forward<A1>(a1), std::forward<A2>(a2))).sax_parse(input_format_t::bson, &sdp, strict);
+        auto ia = detail::input_adapter(std::move(first), std::move(last));
+        const bool res = binary_reader<decltype(ia)>(std::move(ia)).sax_parse(input_format_t::bson, &sdp, strict);
         return res ? result : basic_json(value_t::discarded);
     }
 
+    template<typename T>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_bson(ptr, ptr + len))
+    static basic_json from_bson(const T* ptr, std::size_t len,
+                                const bool strict = true,
+                                const bool allow_exceptions = true)
+    {
+        return from_bson(ptr, ptr + len, strict, allow_exceptions);
+    }
 
-
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_bson(ptr, ptr + len))
+    static basic_json from_bson(detail::span_input_adapter&& i,
+                                const bool strict = true,
+                                const bool allow_exceptions = true)
+    {
+        basic_json result;
+        detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
+        auto ia = i.get();
+        const bool res = binary_reader<decltype(ia)>(std::move(ia)).sax_parse(input_format_t::bson, &sdp, strict);
+        return res ? result : basic_json(value_t::discarded);
+    }
     /// @}
 
     //////////////////////////
@@ -19551,7 +24430,7 @@ class basic_json
 
     Uses a JSON pointer to retrieve a reference to the respective JSON value.
     No bound checking is performed. The function does not change the JSON
-    value; no `null` values are created. In particular, the the special value
+    value; no `null` values are created. In particular, the special value
     `-` yields an exception.
 
     @param[in] ptr  JSON pointer to the desired element
@@ -19822,63 +24701,59 @@ class basic_json
         const auto operation_add = [&result](json_pointer & ptr, basic_json val)
         {
             // adding to the root of the target document means replacing it
-            if (ptr.is_root())
+            if (ptr.empty())
             {
                 result = val;
+                return;
             }
-            else
+
+            // make sure the top element of the pointer exists
+            json_pointer top_pointer = ptr.top();
+            if (top_pointer != ptr)
+            {
+                result.at(top_pointer);
+            }
+
+            // get reference to parent of JSON pointer ptr
+            const auto last_path = ptr.back();
+            ptr.pop_back();
+            basic_json& parent = result[ptr];
+
+            switch (parent.m_type)
             {
-                // make sure the top element of the pointer exists
-                json_pointer top_pointer = ptr.top();
-                if (top_pointer != ptr)
+                case value_t::null:
+                case value_t::object:
                 {
-                    result.at(top_pointer);
+                    // use operator[] to add value
+                    parent[last_path] = val;
+                    break;
                 }
 
-                // get reference to parent of JSON pointer ptr
-                const auto last_path = ptr.pop_back();
-                basic_json& parent = result[ptr];
-
-                switch (parent.m_type)
+                case value_t::array:
                 {
-                    case value_t::null:
-                    case value_t::object:
+                    if (last_path == "-")
                     {
-                        // use operator[] to add value
-                        parent[last_path] = val;
-                        break;
+                        // special case: append to back
+                        parent.push_back(val);
                     }
-
-                    case value_t::array:
+                    else
                     {
-                        if (last_path == "-")
+                        const auto idx = json_pointer::array_index(last_path);
+                        if (JSON_HEDLEY_UNLIKELY(idx > parent.size()))
                         {
-                            // special case: append to back
-                            parent.push_back(val);
+                            // avoid undefined behavior
+                            JSON_THROW(out_of_range::create(401, "array index " + std::to_string(idx) + " is out of range"));
                         }
-                        else
-                        {
-                            const auto idx = json_pointer::array_index(last_path);
-                            if (JSON_UNLIKELY(static_cast<size_type>(idx) > parent.size()))
-                            {
-                                // avoid undefined behavior
-                                JSON_THROW(out_of_range::create(401, "array index " + std::to_string(idx) + " is out of range"));
-                            }
-
-                            // default case: insert add offset
-                            parent.insert(parent.begin() + static_cast<difference_type>(idx), val);
-                        }
-                        break;
-                    }
 
-                    // LCOV_EXCL_START
-                    default:
-                    {
-                        // if there exists a parent it cannot be primitive
-                        assert(false);
+                        // default case: insert add offset
+                        parent.insert(parent.begin() + static_cast<difference_type>(idx), val);
                     }
-                        // LCOV_EXCL_STOP
+                    break;
                 }
+
+                // if there exists a parent it cannot be primitive
+                default:            // LCOV_EXCL_LINE
+                    JSON_ASSERT(false);  // LCOV_EXCL_LINE
             }
         };
 
@@ -19886,7 +24761,8 @@ class basic_json
         const auto operation_remove = [&result](json_pointer & ptr)
         {
             // get reference to parent of JSON pointer ptr
-            const auto last_path = ptr.pop_back();
+            const auto last_path = ptr.back();
+            ptr.pop_back();
             basic_json& parent = result.at(ptr);
 
             // remove child
@@ -19894,7 +24770,7 @@ class basic_json
             {
                 // perform range check
                 auto it = parent.find(last_path);
-                if (JSON_LIKELY(it != parent.end()))
+                if (JSON_HEDLEY_LIKELY(it != parent.end()))
                 {
                     parent.erase(it);
                 }
@@ -19906,12 +24782,12 @@ class basic_json
             else if (parent.is_array())
             {
                 // note erase performs range check
-                parent.erase(static_cast<size_type>(json_pointer::array_index(last_path)));
+                parent.erase(json_pointer::array_index(last_path));
             }
         };
 
         // type check: top level value must be an array
-        if (JSON_UNLIKELY(not json_patch.is_array()))
+        if (JSON_HEDLEY_UNLIKELY(!json_patch.is_array()))
         {
             JSON_THROW(parse_error::create(104, 0, "JSON patch must be an array of objects"));
         }
@@ -19931,13 +24807,13 @@ class basic_json
                 const auto error_msg = (op == "op") ? "operation" : "operation '" + op + "'";
 
                 // check if desired value is present
-                if (JSON_UNLIKELY(it == val.m_value.object->end()))
+                if (JSON_HEDLEY_UNLIKELY(it == val.m_value.object->end()))
                 {
                     JSON_THROW(parse_error::create(105, 0, error_msg + " must have member '" + member + "'"));
                 }
 
                 // check if result is of type string
-                if (JSON_UNLIKELY(string_type and not it->second.is_string()))
+                if (JSON_HEDLEY_UNLIKELY(string_type && !it->second.is_string()))
                 {
                     JSON_THROW(parse_error::create(105, 0, error_msg + " must have string member '" + member + "'"));
                 }
@@ -19947,14 +24823,14 @@ class basic_json
             };
 
             // type check: every element of the array must be an object
-            if (JSON_UNLIKELY(not val.is_object()))
+            if (JSON_HEDLEY_UNLIKELY(!val.is_object()))
             {
                 JSON_THROW(parse_error::create(104, 0, "JSON patch must be an array of objects"));
             }
 
             // collect mandatory members
-            const std::string op = get_value("op", "op", true);
-            const std::string path = get_value(op, "path", true);
+            const auto op = get_value("op", "op", true).template get<std::string>();
+            const auto path = get_value(op, "path", true).template get<std::string>();
             json_pointer ptr(path);
 
             switch (get_op(op))
@@ -19980,7 +24856,7 @@ class basic_json
 
                 case patch_operations::move:
                 {
-                    const std::string from_path = get_value("move", "from", true);
+                    const auto from_path = get_value("move", "from", true).template get<std::string>();
                     json_pointer from_ptr(from_path);
 
                     // the "from" location must exist - use at()
@@ -19997,7 +24873,7 @@ class basic_json
 
                 case patch_operations::copy:
                 {
-                    const std::string from_path = get_value("copy", "from", true);
+                    const auto from_path = get_value("copy", "from", true).template get<std::string>();
                     const json_pointer from_ptr(from_path);
 
                     // the "from" location must exist - use at()
@@ -20025,7 +24901,7 @@ class basic_json
                     }
 
                     // throw an exception if test fails
-                    if (JSON_UNLIKELY(not success))
+                    if (JSON_HEDLEY_UNLIKELY(!success))
                     {
                         JSON_THROW(other_error::create(501, "unsuccessful: " + val.dump()));
                     }
@@ -20033,7 +24909,7 @@ class basic_json
                     break;
                 }
 
-                case patch_operations::invalid:
+                default:
                 {
                     // op must be "add", "remove", "replace", "move", "copy", or
                     // "test"
@@ -20078,6 +24954,7 @@ class basic_json
 
     @since version 2.0.0
     */
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json diff(const basic_json& source, const basic_json& target,
                            const std::string& path = "")
     {
@@ -20097,106 +24974,105 @@ class basic_json
             {
                 {"op", "replace"}, {"path", path}, {"value", target}
             });
+            return result;
         }
-        else
+
+        switch (source.type())
         {
-            switch (source.type())
+            case value_t::array:
             {
-                case value_t::array:
+                // first pass: traverse common elements
+                std::size_t i = 0;
+                while (i < source.size() && i < target.size())
                 {
-                    // first pass: traverse common elements
-                    std::size_t i = 0;
-                    while (i < source.size() and i < target.size())
-                    {
-                        // recursive call to compare array values at index i
-                        auto temp_diff = diff(source[i], target[i], path + "/" + std::to_string(i));
-                        result.insert(result.end(), temp_diff.begin(), temp_diff.end());
-                        ++i;
-                    }
+                    // recursive call to compare array values at index i
+                    auto temp_diff = diff(source[i], target[i], path + "/" + std::to_string(i));
+                    result.insert(result.end(), temp_diff.begin(), temp_diff.end());
+                    ++i;
+                }
 
-                    // i now reached the end of at least one array
-                    // in a second pass, traverse the remaining elements
+                // i now reached the end of at least one array
+                // in a second pass, traverse the remaining elements
 
-                    // remove my remaining elements
-                    const auto end_index = static_cast<difference_type>(result.size());
-                    while (i < source.size())
+                // remove my remaining elements
+                const auto end_index = static_cast<difference_type>(result.size());
+                while (i < source.size())
+                {
+                    // add operations in reverse order to avoid invalid
+                    // indices
+                    result.insert(result.begin() + end_index, object(
                     {
-                        // add operations in reverse order to avoid invalid
-                        // indices
-                        result.insert(result.begin() + end_index, object(
-                        {
-                            {"op", "remove"},
-                            {"path", path + "/" + std::to_string(i)}
-                        }));
-                        ++i;
-                    }
+                        {"op", "remove"},
+                        {"path", path + "/" + std::to_string(i)}
+                    }));
+                    ++i;
+                }
 
-                    // add other remaining elements
-                    while (i < target.size())
+                // add other remaining elements
+                while (i < target.size())
+                {
+                    result.push_back(
                     {
-                        result.push_back(
-                        {
-                            {"op", "add"},
-                            {"path", path + "/" + std::to_string(i)},
-                            {"value", target[i]}
-                        });
-                        ++i;
-                    }
-
-                    break;
+                        {"op", "add"},
+                        {"path", path + "/-"},
+                        {"value", target[i]}
+                    });
+                    ++i;
                 }
 
-                case value_t::object:
+                break;
+            }
+
+            case value_t::object:
+            {
+                // first pass: traverse this object's elements
+                for (auto it = source.cbegin(); it != source.cend(); ++it)
                 {
-                    // first pass: traverse this object's elements
-                    for (auto it = source.cbegin(); it != source.cend(); ++it)
-                    {
-                        // escape the key name to be used in a JSON patch
-                        const auto key = json_pointer::escape(it.key());
+                    // escape the key name to be used in a JSON patch
+                    const auto key = json_pointer::escape(it.key());
 
-                        if (target.find(it.key()) != target.end())
-                        {
-                            // recursive call to compare object values at key it
-                            auto temp_diff = diff(it.value(), target[it.key()], path + "/" + key);
-                            result.insert(result.end(), temp_diff.begin(), temp_diff.end());
-                        }
-                        else
-                        {
-                            // found a key that is not in o -> remove it
-                            result.push_back(object(
-                            {
-                                {"op", "remove"}, {"path", path + "/" + key}
-                            }));
-                        }
+                    if (target.find(it.key()) != target.end())
+                    {
+                        // recursive call to compare object values at key it
+                        auto temp_diff = diff(it.value(), target[it.key()], path + "/" + key);
+                        result.insert(result.end(), temp_diff.begin(), temp_diff.end());
                     }
-
-                    // second pass: traverse other object's elements
-                    for (auto it = target.cbegin(); it != target.cend(); ++it)
+                    else
                     {
-                        if (source.find(it.key()) == source.end())
+                        // found a key that is not in o -> remove it
+                        result.push_back(object(
                         {
-                            // found a key that is not in this -> add it
-                            const auto key = json_pointer::escape(it.key());
-                            result.push_back(
-                            {
-                                {"op", "add"}, {"path", path + "/" + key},
-                                {"value", it.value()}
-                            });
-                        }
+                            {"op", "remove"}, {"path", path + "/" + key}
+                        }));
                     }
-
-                    break;
                 }
 
-                default:
+                // second pass: traverse other object's elements
+                for (auto it = target.cbegin(); it != target.cend(); ++it)
                 {
-                    // both primitive type: replace value
-                    result.push_back(
+                    if (source.find(it.key()) == source.end())
                     {
-                        {"op", "replace"}, {"path", path}, {"value", target}
-                    });
-                    break;
+                        // found a key that is not in this -> add it
+                        const auto key = json_pointer::escape(it.key());
+                        result.push_back(
+                        {
+                            {"op", "add"}, {"path", path + "/" + key},
+                            {"value", it.value()}
+                        });
+                    }
                 }
+
+                break;
+            }
+
+            default:
+            {
+                // both primitive type: replace value
+                result.push_back(
+                {
+                    {"op", "replace"}, {"path", path}, {"value", target}
+                });
+                break;
             }
         }
 
@@ -20258,7 +25134,7 @@ class basic_json
     {
         if (apply_patch.is_object())
         {
-            if (not is_object())
+            if (!is_object())
             {
                 *this = object();
             }
@@ -20282,6 +25158,21 @@ class basic_json
 
     /// @}
 };
+
+/*!
+@brief user-defined to_string function for JSON values
+
+This function implements a user-defined to_string  for JSON objects.
+
+@param[in] j  a JSON object
+@return a std::string object
+*/
+
+NLOHMANN_BASIC_JSON_TPL_DECLARATION
+std::string to_string(const NLOHMANN_BASIC_JSON_TPL& j)
+{
+    return j.dump();
+}
 } // namespace nlohmann
 
 ///////////////////////
@@ -20303,9 +25194,7 @@ struct hash<nlohmann::json>
     */
     std::size_t operator()(const nlohmann::json& j) const
     {
-        // a naive hashing via the string representation
-        const auto& h = hash<nlohmann::json::string_t>();
-        return h(j.dump());
+        return nlohmann::detail::hash(j);
     }
 };
 
@@ -20313,7 +25202,7 @@ struct hash<nlohmann::json>
 /// @note: do not remove the space after '<',
 ///        see https://github.com/nlohmann/json/pull/679
 template<>
-struct less< ::nlohmann::detail::value_t>
+struct less<::nlohmann::detail::value_t>
 {
     /*!
     @brief compare two value_t enum values
@@ -20326,6 +25215,9 @@ struct less< ::nlohmann::detail::value_t>
     }
 };
 
+// C++20 prohibit function specialization in the std namespace.
+#ifndef JSON_HAS_CPP_20
+
 /*!
 @brief exchanges the values of two JSON objects
 
@@ -20333,13 +25225,15 @@ struct less< ::nlohmann::detail::value_t>
 */
 template<>
 inline void swap<nlohmann::json>(nlohmann::json& j1, nlohmann::json& j2) noexcept(
-    is_nothrow_move_constructible<nlohmann::json>::value and
+    is_nothrow_move_constructible<nlohmann::json>::value&&
     is_nothrow_move_assignable<nlohmann::json>::value
-)
+                              )
 {
     j1.swap(j2);
 }
 
+#endif
+
 } // namespace std
 
 /*!
@@ -20355,6 +25249,7 @@ if no parse error occurred.
 
 @since version 1.0.0
 */
+JSON_HEDLEY_NON_NULL(1)
 inline nlohmann::json operator "" _json(const char* s, std::size_t n)
 {
     return nlohmann::json::parse(s, s + n);
@@ -20373,6 +25268,7 @@ object if no parse error occurred.
 
 @since version 2.0.0
 */
+JSON_HEDLEY_NON_NULL(1)
 inline nlohmann::json::json_pointer operator "" _json_pointer(const char* s, std::size_t n)
 {
     return nlohmann::json::json_pointer(std::string(s, n));
@@ -20390,17 +25286,162 @@ inline nlohmann::json::json_pointer operator "" _json_pointer(const char* s, std
 #endif
 
 // clean up
+#undef JSON_ASSERT
 #undef JSON_INTERNAL_CATCH
 #undef JSON_CATCH
 #undef JSON_THROW
 #undef JSON_TRY
-#undef JSON_LIKELY
-#undef JSON_UNLIKELY
-#undef JSON_DEPRECATED
 #undef JSON_HAS_CPP_14
 #undef JSON_HAS_CPP_17
 #undef NLOHMANN_BASIC_JSON_TPL_DECLARATION
 #undef NLOHMANN_BASIC_JSON_TPL
-
-
-#endif
+#undef JSON_EXPLICIT
+
+// #include <nlohmann/thirdparty/hedley/hedley_undef.hpp>
+#undef JSON_HEDLEY_ALWAYS_INLINE
+#undef JSON_HEDLEY_ARM_VERSION
+#undef JSON_HEDLEY_ARM_VERSION_CHECK
+#undef JSON_HEDLEY_ARRAY_PARAM
+#undef JSON_HEDLEY_ASSUME
+#undef JSON_HEDLEY_BEGIN_C_DECLS
+#undef JSON_HEDLEY_CLANG_HAS_ATTRIBUTE
+#undef JSON_HEDLEY_CLANG_HAS_BUILTIN
+#undef JSON_HEDLEY_CLANG_HAS_CPP_ATTRIBUTE
+#undef JSON_HEDLEY_CLANG_HAS_DECLSPEC_DECLSPEC_ATTRIBUTE
+#undef JSON_HEDLEY_CLANG_HAS_EXTENSION
+#undef JSON_HEDLEY_CLANG_HAS_FEATURE
+#undef JSON_HEDLEY_CLANG_HAS_WARNING
+#undef JSON_HEDLEY_COMPCERT_VERSION
+#undef JSON_HEDLEY_COMPCERT_VERSION_CHECK
+#undef JSON_HEDLEY_CONCAT
+#undef JSON_HEDLEY_CONCAT3
+#undef JSON_HEDLEY_CONCAT3_EX
+#undef JSON_HEDLEY_CONCAT_EX
+#undef JSON_HEDLEY_CONST
+#undef JSON_HEDLEY_CONSTEXPR
+#undef JSON_HEDLEY_CONST_CAST
+#undef JSON_HEDLEY_CPP_CAST
+#undef JSON_HEDLEY_CRAY_VERSION
+#undef JSON_HEDLEY_CRAY_VERSION_CHECK
+#undef JSON_HEDLEY_C_DECL
+#undef JSON_HEDLEY_DEPRECATED
+#undef JSON_HEDLEY_DEPRECATED_FOR
+#undef JSON_HEDLEY_DIAGNOSTIC_DISABLE_CAST_QUAL
+#undef JSON_HEDLEY_DIAGNOSTIC_DISABLE_CPP98_COMPAT_WRAP_
+#undef JSON_HEDLEY_DIAGNOSTIC_DISABLE_DEPRECATED
+#undef JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_CPP_ATTRIBUTES
+#undef JSON_HEDLEY_DIAGNOSTIC_DISABLE_UNKNOWN_PRAGMAS
+#undef JSON_HEDLEY_DIAGNOSTIC_POP
+#undef JSON_HEDLEY_DIAGNOSTIC_PUSH
+#undef JSON_HEDLEY_DMC_VERSION
+#undef JSON_HEDLEY_DMC_VERSION_CHECK
+#undef JSON_HEDLEY_EMPTY_BASES
+#undef JSON_HEDLEY_EMSCRIPTEN_VERSION
+#undef JSON_HEDLEY_EMSCRIPTEN_VERSION_CHECK
+#undef JSON_HEDLEY_END_C_DECLS
+#undef JSON_HEDLEY_FLAGS
+#undef JSON_HEDLEY_FLAGS_CAST
+#undef JSON_HEDLEY_GCC_HAS_ATTRIBUTE
+#undef JSON_HEDLEY_GCC_HAS_BUILTIN
+#undef JSON_HEDLEY_GCC_HAS_CPP_ATTRIBUTE
+#undef JSON_HEDLEY_GCC_HAS_DECLSPEC_ATTRIBUTE
+#undef JSON_HEDLEY_GCC_HAS_EXTENSION
+#undef JSON_HEDLEY_GCC_HAS_FEATURE
+#undef JSON_HEDLEY_GCC_HAS_WARNING
+#undef JSON_HEDLEY_GCC_NOT_CLANG_VERSION_CHECK
+#undef JSON_HEDLEY_GCC_VERSION
+#undef JSON_HEDLEY_GCC_VERSION_CHECK
+#undef JSON_HEDLEY_GNUC_HAS_ATTRIBUTE
+#undef JSON_HEDLEY_GNUC_HAS_BUILTIN
+#undef JSON_HEDLEY_GNUC_HAS_CPP_ATTRIBUTE
+#undef JSON_HEDLEY_GNUC_HAS_DECLSPEC_ATTRIBUTE
+#undef JSON_HEDLEY_GNUC_HAS_EXTENSION
+#undef JSON_HEDLEY_GNUC_HAS_FEATURE
+#undef JSON_HEDLEY_GNUC_HAS_WARNING
+#undef JSON_HEDLEY_GNUC_VERSION
+#undef JSON_HEDLEY_GNUC_VERSION_CHECK
+#undef JSON_HEDLEY_HAS_ATTRIBUTE
+#undef JSON_HEDLEY_HAS_BUILTIN
+#undef JSON_HEDLEY_HAS_CPP_ATTRIBUTE
+#undef JSON_HEDLEY_HAS_CPP_ATTRIBUTE_NS
+#undef JSON_HEDLEY_HAS_DECLSPEC_ATTRIBUTE
+#undef JSON_HEDLEY_HAS_EXTENSION
+#undef JSON_HEDLEY_HAS_FEATURE
+#undef JSON_HEDLEY_HAS_WARNING
+#undef JSON_HEDLEY_IAR_VERSION
+#undef JSON_HEDLEY_IAR_VERSION_CHECK
+#undef JSON_HEDLEY_IBM_VERSION
+#undef JSON_HEDLEY_IBM_VERSION_CHECK
+#undef JSON_HEDLEY_IMPORT
+#undef JSON_HEDLEY_INLINE
+#undef JSON_HEDLEY_INTEL_VERSION
+#undef JSON_HEDLEY_INTEL_VERSION_CHECK
+#undef JSON_HEDLEY_IS_CONSTANT
+#undef JSON_HEDLEY_IS_CONSTEXPR_
+#undef JSON_HEDLEY_LIKELY
+#undef JSON_HEDLEY_MALLOC
+#undef JSON_HEDLEY_MESSAGE
+#undef JSON_HEDLEY_MSVC_VERSION
+#undef JSON_HEDLEY_MSVC_VERSION_CHECK
+#undef JSON_HEDLEY_NEVER_INLINE
+#undef JSON_HEDLEY_NON_NULL
+#undef JSON_HEDLEY_NO_ESCAPE
+#undef JSON_HEDLEY_NO_RETURN
+#undef JSON_HEDLEY_NO_THROW
+#undef JSON_HEDLEY_NULL
+#undef JSON_HEDLEY_PELLES_VERSION
+#undef JSON_HEDLEY_PELLES_VERSION_CHECK
+#undef JSON_HEDLEY_PGI_VERSION
+#undef JSON_HEDLEY_PGI_VERSION_CHECK
+#undef JSON_HEDLEY_PREDICT
+#undef JSON_HEDLEY_PRINTF_FORMAT
+#undef JSON_HEDLEY_PRIVATE
+#undef JSON_HEDLEY_PUBLIC
+#undef JSON_HEDLEY_PURE
+#undef JSON_HEDLEY_REINTERPRET_CAST
+#undef JSON_HEDLEY_REQUIRE
+#undef JSON_HEDLEY_REQUIRE_CONSTEXPR
+#undef JSON_HEDLEY_REQUIRE_MSG
+#undef JSON_HEDLEY_RESTRICT
+#undef JSON_HEDLEY_RETURNS_NON_NULL
+#undef JSON_HEDLEY_SENTINEL
+#undef JSON_HEDLEY_STATIC_ASSERT
+#undef JSON_HEDLEY_STATIC_CAST
+#undef JSON_HEDLEY_STRINGIFY
+#undef JSON_HEDLEY_STRINGIFY_EX
+#undef JSON_HEDLEY_SUNPRO_VERSION
+#undef JSON_HEDLEY_SUNPRO_VERSION_CHECK
+#undef JSON_HEDLEY_TINYC_VERSION
+#undef JSON_HEDLEY_TINYC_VERSION_CHECK
+#undef JSON_HEDLEY_TI_ARMCL_VERSION
+#undef JSON_HEDLEY_TI_ARMCL_VERSION_CHECK
+#undef JSON_HEDLEY_TI_CL2000_VERSION
+#undef JSON_HEDLEY_TI_CL2000_VERSION_CHECK
+#undef JSON_HEDLEY_TI_CL430_VERSION
+#undef JSON_HEDLEY_TI_CL430_VERSION_CHECK
+#undef JSON_HEDLEY_TI_CL6X_VERSION
+#undef JSON_HEDLEY_TI_CL6X_VERSION_CHECK
+#undef JSON_HEDLEY_TI_CL7X_VERSION
+#undef JSON_HEDLEY_TI_CL7X_VERSION_CHECK
+#undef JSON_HEDLEY_TI_CLPRU_VERSION
+#undef JSON_HEDLEY_TI_CLPRU_VERSION_CHECK
+#undef JSON_HEDLEY_TI_VERSION
+#undef JSON_HEDLEY_TI_VERSION_CHECK
+#undef JSON_HEDLEY_UNAVAILABLE
+#undef JSON_HEDLEY_UNLIKELY
+#undef JSON_HEDLEY_UNPREDICTABLE
+#undef JSON_HEDLEY_UNREACHABLE
+#undef JSON_HEDLEY_UNREACHABLE_RETURN
+#undef JSON_HEDLEY_VERSION
+#undef JSON_HEDLEY_VERSION_DECODE_MAJOR
+#undef JSON_HEDLEY_VERSION_DECODE_MINOR
+#undef JSON_HEDLEY_VERSION_DECODE_REVISION
+#undef JSON_HEDLEY_VERSION_ENCODE
+#undef JSON_HEDLEY_WARNING
+#undef JSON_HEDLEY_WARN_UNUSED_RESULT
+#undef JSON_HEDLEY_WARN_UNUSED_RESULT_MSG
+#undef JSON_HEDLEY_FALL_THROUGH
+
+
+
+#endif  // INCLUDE_NLOHMANN_JSON_HPP_
diff --git a/src/nlohmann/json_fwd.hpp b/src/nlohmann/json_fwd.hpp
new file mode 100644
index 000000000..332227c1b
--- /dev/null
+++ b/src/nlohmann/json_fwd.hpp
@@ -0,0 +1,78 @@
+#ifndef INCLUDE_NLOHMANN_JSON_FWD_HPP_
+#define INCLUDE_NLOHMANN_JSON_FWD_HPP_
+
+#include <cstdint> // int64_t, uint64_t
+#include <map> // map
+#include <memory> // allocator
+#include <string> // string
+#include <vector> // vector
+
+/*!
+@brief namespace for Niels Lohmann
+@see https://github.com/nlohmann
+@since version 1.0.0
+*/
+namespace nlohmann
+{
+/*!
+@brief default JSONSerializer template argument
+
+This serializer ignores the template arguments and uses ADL
+([argument-dependent lookup](https://en.cppreference.com/w/cpp/language/adl))
+for serialization.
+*/
+template<typename T = void, typename SFINAE = void>
+struct adl_serializer;
+
+template<template<typename U, typename V, typename... Args> class ObjectType =
+         std::map,
+         template<typename U, typename... Args> class ArrayType = std::vector,
+         class StringType = std::string, class BooleanType = bool,
+         class NumberIntegerType = std::int64_t,
+         class NumberUnsignedType = std::uint64_t,
+         class NumberFloatType = double,
+         template<typename U> class AllocatorType = std::allocator,
+         template<typename T, typename SFINAE = void> class JSONSerializer =
+         adl_serializer,
+         class BinaryType = std::vector<std::uint8_t>>
+class basic_json;
+
+/*!
+@brief JSON Pointer
+
+A JSON pointer defines a string syntax for identifying a specific value
+within a JSON document. It can be used with functions `at` and
+`operator[]`. Furthermore, JSON pointers are the base for JSON patches.
+
+@sa [RFC 6901](https://tools.ietf.org/html/rfc6901)
+
+@since version 2.0.0
+*/
+template<typename BasicJsonType>
+class json_pointer;
+
+/*!
+@brief default JSON class
+
+This type is the default specialization of the @ref basic_json class which
+uses the standard template types.
+
+@since version 1.0.0
+*/
+using json = basic_json<>;
+
+template<class Key, class T, class IgnoredLess, class Allocator>
+struct ordered_map;
+
+/*!
+@brief ordered JSON class
+
+This type preserves the insertion order of object keys.
+
+@since version 3.9.0
+*/
+using ordered_json = basic_json<nlohmann::ordered_map>;
+
+}  // namespace nlohmann
+
+#endif  // INCLUDE_NLOHMANN_JSON_FWD_HPP_
diff --git a/src/resolve-system-dependencies/local.mk b/src/resolve-system-dependencies/local.mk
index 054ae01cb..fc48a8417 100644
--- a/src/resolve-system-dependencies/local.mk
+++ b/src/resolve-system-dependencies/local.mk
@@ -1,4 +1,4 @@
-ifeq ($(OS), Darwin)
+ifdef HOST_DARWIN
   programs += resolve-system-dependencies
 endif