Merge remote-tracking branch 'upstream/master' into path-info

49 files changed, 874 insertions, 1339 deletions

diff --git a/src/nix/app.cc b/src/nix/app.cc
index df7303e15..5658f2a52 100644
--- a/src/nix/app.cc
+++ b/src/nix/app.cc
@@ -37,11 +37,13 @@ struct InstallableDerivedPath : Installable
  * Return the rewrites that are needed to resolve a string whose context is
  * included in `dependencies`.
  */
-StringPairs resolveRewrites(Store & store, const BuiltPaths dependencies)
+StringPairs resolveRewrites(
+    Store & store,
+    const std::vector<BuiltPathWithResult> & dependencies)
 {
     StringPairs res;
     for (auto & dep : dependencies)
-        if (auto drvDep = std::get_if<BuiltPathBuilt>(&dep))
+        if (auto drvDep = std::get_if<BuiltPathBuilt>(&dep.path))
             for (auto & [ outputName, outputPath ] : drvDep->outputs)
                 res.emplace(
                     downstreamPlaceholder(store, drvDep->drvPath, outputName),
@@ -53,7 +55,10 @@ StringPairs resolveRewrites(Store & store, const BuiltPaths dependencies)
 /**
  * Resolve the given string assuming the given context.
  */
-std::string resolveString(Store & store, const std::string & toResolve, const BuiltPaths dependencies)
+std::string resolveString(
+    Store & store,
+    const std::string & toResolve,
+    const std::vector<BuiltPathWithResult> & dependencies)
 {
     auto rewrites = resolveRewrites(store, dependencies);
     return rewriteStrings(toResolve, rewrites);
@@ -66,7 +71,9 @@ UnresolvedApp Installable::toApp(EvalState & state)
 
     auto type = cursor->getAttr("type")->getString();
 
-    std::string expected = !attrPath.empty() && attrPath[0] == "apps" ? "app" : "derivation";
+    std::string expected = !attrPath.empty() &&
+        (state.symbols[attrPath[0]] == "apps" || state.symbols[attrPath[0]] == "defaultApp")
+        ? "app" : "derivation";
     if (type != expected)
         throw Error("attribute '%s' should have type '%s'", cursor->getAttrPathStr(), expected);
 
@@ -89,7 +96,7 @@ UnresolvedApp Installable::toApp(EvalState & state)
         auto outputName = cursor->getAttr(state.sOutputName)->getString();
         auto name = cursor->getAttr(state.sName)->getString();
         auto aPname = cursor->maybeGetAttr("pname");
-        auto aMeta = cursor->maybeGetAttr("meta");
+        auto aMeta = cursor->maybeGetAttr(state.sMeta);
         auto aMainProgram = aMeta ? aMeta->maybeGetAttr("mainProgram") : nullptr;
         auto mainProgram =
             aMainProgram
diff --git a/src/nix/build.cc b/src/nix/build.cc
index 840c7ca38..94b169167 100644
--- a/src/nix/build.cc
+++ b/src/nix/build.cc
@@ -4,14 +4,47 @@
 #include "shared.hh"
 #include "store-api.hh"
 #include "local-fs-store.hh"
+#include "progress-bar.hh"
 
 #include <nlohmann/json.hpp>
 
 using namespace nix;
 
+nlohmann::json derivedPathsToJSON(const DerivedPaths & paths, ref<Store> store)
+{
+    auto res = nlohmann::json::array();
+    for (auto & t : paths) {
+        std::visit([&res, store](const auto & t) {
+            res.push_back(t.toJSON(store));
+        }, t.raw());
+    }
+    return res;
+}
+
+nlohmann::json builtPathsWithResultToJSON(const std::vector<BuiltPathWithResult> & buildables, ref<Store> store)
+{
+    auto res = nlohmann::json::array();
+    for (auto & b : buildables) {
+        std::visit([&](const auto & t) {
+            auto j = t.toJSON(store);
+            if (b.result) {
+                j["startTime"] = b.result->startTime;
+                j["stopTime"] = b.result->stopTime;
+                if (b.result->cpuUser)
+                    j["cpuUser"] = ((double) b.result->cpuUser->count()) / 1000000;
+                if (b.result->cpuSystem)
+                    j["cpuSystem"] = ((double) b.result->cpuSystem->count()) / 1000000;
+            }
+            res.push_back(j);
+        }, b.path.raw());
+    }
+    return res;
+}
+
 struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
 {
     Path outLink = "result";
+    bool printOutputPaths = false;
     BuildMode buildMode = bmNormal;
 
     CmdBuild()
@@ -32,6 +65,12 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
         });
 
         addFlag({
+            .longName = "print-out-paths",
+            .description = "Print the resulting output paths",
+            .handler = {&printOutputPaths, true},
+        });
+
+        addFlag({
             .longName = "rebuild",
             .description = "Rebuild an already built package and compare the result to the existing store paths.",
             .handler = {&buildMode, bmCheck},
@@ -70,7 +109,7 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
             Realise::Outputs,
             installables, buildMode);
 
-        if (json) logger->cout("%s", derivedPathsWithHintsToJSON(buildables, store).dump());
+        if (json) logger->cout("%s", builtPathsWithResultToJSON(buildables, store).dump());
 
         if (outLink != "")
             if (auto store2 = store.dynamic_pointer_cast<LocalFSStore>())
@@ -90,10 +129,29 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
                                 store2->addPermRoot(output.second, absPath(symlink));
                             }
                         },
-                    }, buildable.raw());
+                    }, buildable.path.raw());
                 }
 
-        updateProfile(buildables);
+        if (printOutputPaths) {
+            stopProgressBar();
+            for (auto & buildable : buildables) {
+                std::visit(overloaded {
+                    [&](const BuiltPath::Opaque & bo) {
+                        std::cout << store->printStorePath(bo.path) << std::endl;
+                    },
+                    [&](const BuiltPath::Built & bfd) {
+                        for (auto & output : bfd.outputs) {
+                            std::cout << store->printStorePath(output.second) << std::endl;
+                        }
+                    },
+                }, buildable.path.raw());
+            }
+        }
+
+        BuiltPaths buildables2;
+        for (auto & b : buildables)
+            buildables2.push_back(b.path);
+        updateProfile(buildables2);
     }
 };
 
diff --git a/src/nix/build.md b/src/nix/build.md
index 20138b7e0..6a79f308c 100644
--- a/src/nix/build.md
+++ b/src/nix/build.md
@@ -25,6 +25,13 @@ R""(
   lrwxrwxrwx 1 … result-1 -> /nix/store/rkfrm0z6x6jmi7d3gsmma4j53h15mg33-cowsay-3.03+dfsg2
   ```
 
+* Build GNU Hello and print the resulting store path.
+
+  ```console
+  # nix build nixpkgs#hello --print-out-paths
+  /nix/store/v5sv61sszx301i0x6xysaqzla09nksnd-hello-2.10
+  ```
+
 * Build a specific output:
 
   ```console
diff --git a/src/nix/bundle.cc b/src/nix/bundle.cc
index 81fb8464a..74a7973b0 100644
--- a/src/nix/bundle.cc
+++ b/src/nix/bundle.cc
@@ -75,10 +75,10 @@ struct CmdBundle : InstallableCommand
 
         auto val = installable->toValue(*evalState).first;
 
-        auto [bundlerFlakeRef, bundlerName] = parseFlakeRefWithFragment(bundler, absPath("."));
+        auto [bundlerFlakeRef, bundlerName, outputsSpec] = parseFlakeRefWithFragmentAndOutputsSpec(bundler, absPath("."));
         const flake::LockFlags lockFlags{ .writeLockFile = false };
         InstallableFlake bundler{this,
-            evalState, std::move(bundlerFlakeRef), bundlerName,
+            evalState, std::move(bundlerFlakeRef), bundlerName, outputsSpec,
             {"bundlers." + settings.thisSystem.get() + ".default",
              "defaultBundler." + settings.thisSystem.get()
             },
@@ -97,21 +97,23 @@ struct CmdBundle : InstallableCommand
             throw Error("the bundler '%s' does not produce a derivation", bundler.what());
 
         PathSet context2;
-        auto drvPath = evalState->coerceToStorePath(*attr1->pos, *attr1->value, context2);
+        auto drvPath = evalState->coerceToStorePath(attr1->pos, *attr1->value, context2, "");
 
         auto attr2 = vRes->attrs->get(evalState->sOutPath);
         if (!attr2)
             throw Error("the bundler '%s' does not produce a derivation", bundler.what());
 
-        auto outPath = evalState->coerceToStorePath(*attr2->pos, *attr2->value, context2);
+        auto outPath = evalState->coerceToStorePath(attr2->pos, *attr2->value, context2, "");
 
         store->buildPaths({ DerivedPath::Built { drvPath } });
 
         auto outPathS = store->printStorePath(outPath);
 
         if (!outLink) {
-            auto &attr = vRes->attrs->need(evalState->sName);
-            outLink = evalState->forceStringNoCtx(*attr.value,*attr.pos);
+            auto * attr = vRes->attrs->get(evalState->sName);
+            if (!attr)
+                throw Error("attribute 'name' missing");
+            outLink = evalState->forceStringNoCtx(*attr->value, attr->pos, "");
         }
 
         // TODO: will crash if not a localFSStore?
diff --git a/src/nix/bundle.md b/src/nix/bundle.md
index 2bb70711f..a18161a3c 100644
--- a/src/nix/bundle.md
+++ b/src/nix/bundle.md
@@ -44,7 +44,7 @@ flake output attributes:
 
 * `bundlers.<system>.default`
 
-If an attribute *name* is given, `nix run` tries the following flake
+If an attribute *name* is given, `nix bundle` tries the following flake
 output attributes:
 
 * `bundlers.<system>.<name>`
diff --git a/src/nix/daemon.cc b/src/nix/daemon.cc
index 940923d3b..c527fdb0a 100644
--- a/src/nix/daemon.cc
+++ b/src/nix/daemon.cc
@@ -257,7 +257,7 @@ static void daemonLoop()
         } catch (Interrupted & e) {
             return;
         } catch (Error & error) {
-            ErrorInfo ei = error.info();
+            auto ei = error.info();
             // FIXME: add to trace?
             ei.msg = hintfmt("error processing connection: %1%", ei.msg.str());
             logError(ei);
diff --git a/src/nix/daemon.md b/src/nix/daemon.md
index e97016a94..d5cdadf08 100644
--- a/src/nix/daemon.md
+++ b/src/nix/daemon.md
@@ -11,7 +11,7 @@ R""(
 # Description
 
 This command runs the Nix daemon, which is a required component in
-multi-user Nix installations. It performs build actions and other
+multi-user Nix installations. It runs build tasks and other
 operations on the Nix store on behalf of non-root users. Usually you
 don't run the daemon directly; instead it's managed by a service
 management framework such as `systemd`.
diff --git a/src/nix/develop.cc b/src/nix/develop.cc
index 7fc74d34e..1d90d1dac 100644
--- a/src/nix/develop.cc
+++ b/src/nix/develop.cc
@@ -18,6 +18,9 @@ struct DevelopSettings : Config
     Setting<std::string> bashPrompt{this, "", "bash-prompt",
         "The bash prompt (`PS1`) in `nix develop` shells."};
 
+    Setting<std::string> bashPromptPrefix{this, "", "bash-prompt-prefix",
+        "Prefix prepended to the `PS1` environment variable in `nix develop` shells."};
+
     Setting<std::string> bashPromptSuffix{this, "", "bash-prompt-suffix",
         "Suffix appended to the `PS1` environment variable in `nix develop` shells."};
 };
@@ -161,6 +164,14 @@ struct BuildEnvironment
     {
         return vars == other.vars && bashFunctions == other.bashFunctions;
     }
+
+    std::string getSystem() const
+    {
+        if (auto v = get(vars, "system"))
+            return getString(*v);
+        else
+            return settings.thisSystem;
+    }
 };
 
 const static std::string getEnvSh =
@@ -189,10 +200,12 @@ static StorePath getDerivationEnvironment(ref<Store> store, ref<Store> evalStore
     drv.env.erase("allowedRequisites");
     drv.env.erase("disallowedReferences");
     drv.env.erase("disallowedRequisites");
+    drv.env.erase("name");
 
     /* Rehash and write the derivation. FIXME: would be nice to use
        'buildDerivation', but that's privileged. */
     drv.name += "-env";
+    drv.env.emplace("name", drv.name);
     drv.inputSrcs.insert(std::move(getEnvShPath));
     if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations)) {
         for (auto & output : drv.outputs) {
@@ -243,6 +256,7 @@ struct Common : InstallableCommand, MixProfile
         "NIX_LOG_FD",
         "NIX_REMOTE",
         "PPID",
+        "SHELL",
         "SHELLOPTS",
         "SSL_CERT_FILE", // FIXME: only want to ignore /no-cert-file.crt
         "TEMP",
@@ -273,15 +287,27 @@ struct Common : InstallableCommand, MixProfile
         const BuildEnvironment & buildEnvironment,
         const Path & outputsDir = absPath(".") + "/outputs")
     {
+        // A list of colon-separated environment variables that should be
+        // prepended to, rather than overwritten, in order to keep the shell usable.
+        // Please keep this list minimal in order to avoid impurities.
+        static const char * const savedVars[] = {
+            "PATH",          // for commands
+            "XDG_DATA_DIRS", // for loadable completion
+        };
+
         std::ostringstream out;
 
         out << "unset shellHook\n";
 
-        out << "nix_saved_PATH=\"$PATH\"\n";
+        for (auto & var : savedVars) {
+            out << fmt("%s=${%s:-}\n", var, var);
+            out << fmt("nix_saved_%s=\"$%s\"\n", var, var);
+        }
 
         buildEnvironment.toBash(out, ignoreVars);
 
-        out << "PATH=\"$PATH:$nix_saved_PATH\"\n";
+        for (auto & var : savedVars)
+            out << fmt("%s=\"$%s:$nix_saved_%s\"\n", var, var, var);
 
         out << "export NIX_BUILD_TOP=\"$(mktemp -d -t nix-shell.XXXXXX)\"\n";
         for (auto & i : {"TMP", "TMPDIR", "TEMP", "TEMPDIR"})
@@ -482,6 +508,9 @@ struct CmdDevelop : Common, MixEnvironment
             if (developSettings.bashPrompt != "")
                 script += fmt("[ -n \"$PS1\" ] && PS1=%s;\n",
                     shellEscape(developSettings.bashPrompt.get()));
+            if (developSettings.bashPromptPrefix != "")
+                script += fmt("[ -n \"$PS1\" ] && PS1=%s\"$PS1\";\n",
+                    shellEscape(developSettings.bashPromptPrefix.get()));
             if (developSettings.bashPromptSuffix != "")
                 script += fmt("[ -n \"$PS1\" ] && PS1+=%s;\n",
                     shellEscape(developSettings.bashPromptSuffix.get()));
@@ -507,13 +536,25 @@ struct CmdDevelop : Common, MixEnvironment
                 state,
                 installable->nixpkgsFlakeRef(),
                 "bashInteractive",
+                DefaultOutputs(),
                 Strings{},
                 Strings{"legacyPackages." + settings.thisSystem.get() + "."},
                 nixpkgsLockFlags);
 
-            shell = store->printStorePath(
-                Installable::toStorePath(getEvalStore(), store, Realise::Outputs, OperateOn::Output, bashInstallable))
-                + "/bin/bash";
+            bool found = false;
+
+            for (auto & path : Installable::toStorePaths(getEvalStore(), store, Realise::Outputs, OperateOn::Output, {bashInstallable})) {
+                auto s = store->printStorePath(path) + "/bin/bash";
+                if (pathExists(s)) {
+                    shell = s;
+                    found = true;
+                    break;
+                }
+            }
+
+            if (!found)
+                throw Error("package 'nixpkgs#bashInteractive' does not provide a 'bin/bash'");
+
         } catch (Error &) {
             ignoreException();
         }
@@ -537,7 +578,7 @@ struct CmdDevelop : Common, MixEnvironment
             }
         }
 
-        runProgramInStore(store, shell, args);
+        runProgramInStore(store, shell, args, buildEnvironment.getSystem());
     }
 };
 
diff --git a/src/nix/develop.md b/src/nix/develop.md
index 8bcff66c9..4e8542d1b 100644
--- a/src/nix/develop.md
+++ b/src/nix/develop.md
@@ -66,6 +66,12 @@ R""(
   `nixpkgs#glibc` in `~/my-glibc` and want to compile another package
   against it.
 
+* Run a series of script commands:
+
+  ```console
+  # nix develop --command bash -c "mkdir build && cmake .. && make"
+  ```
+
 # Description
 
 `nix develop` starts a `bash` shell that provides an interactive build
@@ -80,8 +86,8 @@ initialised by `stdenv` and exits. This build environment can be
 recorded into a profile using `--profile`.
 
 The prompt used by the `bash` shell can be customised by setting the
-`bash-prompt` and `bash-prompt-suffix` settings in `nix.conf` or in
-the flake's `nixConfig` attribute.
+`bash-prompt`, `bash-prompt-prefix`, and `bash-prompt-suffix` settings in
+`nix.conf` or in the flake's `nixConfig` attribute.
 
 # Flake output attributes
 
diff --git a/src/nix/edit.cc b/src/nix/edit.cc
index fc48db0d7..76a134b1f 100644
--- a/src/nix/edit.cc
+++ b/src/nix/edit.cc
@@ -28,19 +28,19 @@ struct CmdEdit : InstallableCommand
     {
         auto state = getEvalState();
 
-        auto [v, pos] = installable->toValue(*state);
+        const auto [file, line] = [&] {
+            auto [v, pos] = installable->toValue(*state);
 
-        try {
-            pos = findPackageFilename(*state, *v, installable->what());
-        } catch (NoPositionInfo &) {
-        }
-
-        if (pos == noPos)
-            throw Error("cannot find position information for '%s", installable->what());
+            try {
+                return findPackageFilename(*state, *v, installable->what());
+            } catch (NoPositionInfo &) {
+                throw Error("cannot find position information for '%s", installable->what());
+            }
+        }();
 
         stopProgressBar();
 
-        auto args = editorFor(pos);
+        auto args = editorFor(file, line);
 
         restoreProcessContext();
 
diff --git a/src/nix/eval.cc b/src/nix/eval.cc
index 733b93661..ccee074e9 100644
--- a/src/nix/eval.cc
+++ b/src/nix/eval.cc
@@ -4,10 +4,11 @@
 #include "store-api.hh"
 #include "eval.hh"
 #include "eval-inline.hh"
-#include "json.hh"
 #include "value-to-json.hh"
 #include "progress-bar.hh"
 
+#include <nlohmann/json.hpp>
+
 using namespace nix;
 
 struct CmdEval : MixJSON, InstallableCommand
@@ -77,9 +78,9 @@ struct CmdEval : MixJSON, InstallableCommand
             if (pathExists(*writeTo))
                 throw Error("path '%s' already exists", *writeTo);
 
-            std::function<void(Value & v, const Pos & pos, const Path & path)> recurse;
+            std::function<void(Value & v, const PosIdx pos, const Path & path)> recurse;
 
-            recurse = [&](Value & v, const Pos & pos, const Path & path)
+            recurse = [&](Value & v, const PosIdx pos, const Path & path)
             {
                 state->forceValue(v, pos);
                 if (v.type() == nString)
@@ -88,18 +89,22 @@ struct CmdEval : MixJSON, InstallableCommand
                 else if (v.type() == nAttrs) {
                     if (mkdir(path.c_str(), 0777) == -1)
                         throw SysError("creating directory '%s'", path);
-                    for (auto & attr : *v.attrs)
+                    for (auto & attr : *v.attrs) {
+                        std::string_view name = state->symbols[attr.name];
                         try {
-                            if (attr.name == "." || attr.name == "..")
-                                throw Error("invalid file name '%s'", attr.name);
-                            recurse(*attr.value, *attr.pos, path + "/" + std::string(attr.name));
+                            if (name == "." || name == "..")
+                                throw Error("invalid file name '%s'", name);
+                            recurse(*attr.value, attr.pos, concatStrings(path, "/", name));
                         } catch (Error & e) {
-                            e.addTrace(*attr.pos, hintfmt("while evaluating the attribute '%s'", attr.name));
+                            e.addTrace(
+                                state->positions[attr.pos],
+                                hintfmt("while evaluating the attribute '%s'", name));
                             throw;
                         }
+                    }
                 }
                 else
-                    throw TypeError("value at '%s' is not a string or an attribute set", pos);
+                    throw TypeError("value at '%s' is not a string or an attribute set", state->positions[pos]);
             };
 
             recurse(*v, pos, *writeTo);
@@ -107,17 +112,16 @@ struct CmdEval : MixJSON, InstallableCommand
 
         else if (raw) {
             stopProgressBar();
-            std::cout << *state->coerceToString(noPos, *v, context);
+            std::cout << *state->coerceToString(noPos, *v, context, "while generating the eval command output");
         }
 
         else if (json) {
-            JSONPlaceholder jsonOut(std::cout);
-            printValueAsJSON(*state, true, *v, pos, jsonOut, context);
+            std::cout << printValueAsJSON(*state, true, *v, pos, context, false).dump() << std::endl;
         }
 
         else {
             state->forceValueDeep(*v);
-            logger->cout("%s", *v);
+            logger->cout("%s", printValue(*state, *v));
         }
     }
 };
diff --git a/src/nix/flake-update.md b/src/nix/flake-update.md
index 03b50e38e..8c6042d94 100644
--- a/src/nix/flake-update.md
+++ b/src/nix/flake-update.md
@@ -6,7 +6,7 @@ R""(
   lock file:
 
   ```console
-  # nix flake update
+  # nix flake update --commit-lock-file
   * Updated 'nix': 'github:NixOS/nix/9fab14adbc3810d5cc1f88672fde1eee4358405c' -> 'github:NixOS/nix/8927cba62f5afb33b01016d5c4f7f8b7d0adde3c'
   * Updated 'nixpkgs': 'github:NixOS/nixpkgs/3d2d8f281a27d466fa54b469b5993f7dde198375' -> 'github:NixOS/nixpkgs/a3a3dda3bacf61e8a39258a0ed9c924eeca8e293'
   …
@@ -16,7 +16,7 @@ R""(
 # Description
 
 This command recreates the lock file of a flake (`flake.lock`), thus
-updating the lock for every mutable input (like `nixpkgs`) to its
+updating the lock for every unlocked input (like `nixpkgs`) to its
 current version. This is equivalent to passing `--recreate-lock-file`
 to any command that operates on a flake. That is,
 
diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index 04b23ed0f..9b4cdf35a 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -11,7 +11,6 @@
 #include "attr-path.hh"
 #include "fetchers.hh"
 #include "registry.hh"
-#include "json.hh"
 #include "eval-cache.hh"
 #include "markdown.hh"
 
@@ -21,6 +20,7 @@
 
 using namespace nix;
 using namespace nix::flake;
+using json = nlohmann::json;
 
 class FlakeCommand : virtual Args, public MixFlakeOptions
 {
@@ -50,9 +50,9 @@ public:
         return flake::lockFlake(*getEvalState(), getFlakeRef(), lockFlags);
     }
 
-    std::optional<FlakeRef> getFlakeRefForCompletion() override
+    std::vector<std::string> getFlakesForCompletion() override
     {
-        return getFlakeRef();
+        return {flakeUrl};
     }
 };
 
@@ -123,15 +123,15 @@ struct CmdFlakeLock : FlakeCommand
 };
 
 static void enumerateOutputs(EvalState & state, Value & vFlake,
-    std::function<void(const std::string & name, Value & vProvide, const Pos & pos)> callback)
+    std::function<void(const std::string & name, Value & vProvide, const PosIdx pos)> callback)
 {
     auto pos = vFlake.determinePos(noPos);
-    state.forceAttrs(vFlake, pos);
+    state.forceAttrs(vFlake, pos, "while evaluating a flake to get its outputs");
 
     auto aOutputs = vFlake.attrs->get(state.symbols.create("outputs"));
     assert(aOutputs);
 
-    state.forceAttrs(*aOutputs->value, pos);
+    state.forceAttrs(*aOutputs->value, pos, "while evaluating the outputs of a flake");
 
     auto sHydraJobs = state.symbols.create("hydraJobs");
 
@@ -139,11 +139,11 @@ static void enumerateOutputs(EvalState & state, Value & vFlake,
        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);
+        callback(state.symbols[attr->name], *attr->value, attr->pos);
 
     for (auto & attr : *aOutputs->value->attrs) {
         if (attr.name != sHydraJobs)
-            callback(attr.name, *attr.value, *attr.pos);
+            callback(state.symbols[attr.name], *attr.value, attr.pos);
     }
 }
 
@@ -212,9 +212,10 @@ struct CmdFlakeMetadata : FlakeCommand, MixJSON
                     ANSI_BOLD "Last modified:" ANSI_NORMAL " %s",
                     std::put_time(std::localtime(&*lastModified), "%F %T"));
 
-            logger->cout(ANSI_BOLD "Inputs:" ANSI_NORMAL);
+            if (!lockedFlake.lockFile.root->inputs.empty())
+                logger->cout(ANSI_BOLD "Inputs:" ANSI_NORMAL);
 
-            std::unordered_set<std::shared_ptr<Node>> visited;
+            std::set<ref<Node>> visited;
 
             std::function<void(const Node & node, const std::string & prefix)> recurse;
 
@@ -226,7 +227,7 @@ struct CmdFlakeMetadata : FlakeCommand, MixJSON
                     if (auto lockedNode = std::get_if<0>(&input.second)) {
                         logger->cout("%s" ANSI_BOLD "%s" ANSI_NORMAL ": %s",
                             prefix + (last ? treeLast : treeConn), input.first,
-                            *lockedNode ? (*lockedNode)->lockedRef : flake.lockedRef);
+                            (*lockedNode)->lockedRef);
 
                         bool firstVisit = visited.insert(*lockedNode).second;
 
@@ -254,14 +255,6 @@ 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;
@@ -315,13 +308,25 @@ struct CmdFlakeCheck : FlakeCommand
 
         // FIXME: rewrite to use EvalCache.
 
-        auto checkSystemName = [&](const std::string & system, const Pos & pos) {
+        auto resolve = [&] (PosIdx p) {
+            return state->positions[p];
+        };
+
+        auto argHasName = [&] (Symbol arg, std::string_view expected) {
+            std::string_view name = state->symbols[arg];
+            return
+                name == expected
+                || name == "_"
+                || (hasPrefix(name, "_") && name.substr(1) == expected);
+        };
+
+        auto checkSystemName = [&](const std::string & system, const PosIdx pos) {
             // FIXME: what's the format of "system"?
             if (system.find('-') == std::string::npos)
-                reportError(Error("'%s' is not a valid system type, at %s", system, pos));
+                reportError(Error("'%s' is not a valid system type, at %s", system, resolve(pos)));
         };
 
-        auto checkDerivation = [&](const std::string & attrPath, Value & v, const Pos & pos) -> std::optional<StorePath> {
+        auto checkDerivation = [&](const std::string & attrPath, Value & v, const PosIdx pos) -> std::optional<StorePath> {
             try {
                 auto drvInfo = getDerivation(*state, v, false);
                 if (!drvInfo)
@@ -329,7 +334,7 @@ struct CmdFlakeCheck : FlakeCommand
                 // FIXME: check meta attributes
                 return drvInfo->queryDrvPath();
             } catch (Error & e) {
-                e.addTrace(pos, hintfmt("while checking the derivation '%s'", attrPath));
+                e.addTrace(resolve(pos), hintfmt("while checking the derivation '%s'", attrPath));
                 reportError(e);
             }
             return std::nullopt;
@@ -337,7 +342,7 @@ struct CmdFlakeCheck : FlakeCommand
 
         std::vector<DerivedPath> drvPaths;
 
-        auto checkApp = [&](const std::string & attrPath, Value & v, const Pos & pos) {
+        auto checkApp = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
             try {
                 #if 0
                 // FIXME
@@ -348,12 +353,12 @@ struct CmdFlakeCheck : FlakeCommand
                 }
                 #endif
             } catch (Error & e) {
-                e.addTrace(pos, hintfmt("while checking the app definition '%s'", attrPath));
+                e.addTrace(resolve(pos), hintfmt("while checking the app definition '%s'", attrPath));
                 reportError(e);
             }
         };
 
-        auto checkOverlay = [&](const std::string & attrPath, Value & v, const Pos & pos) {
+        auto checkOverlay = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
             try {
                 state->forceValue(v, pos);
                 if (!v.isLambda()
@@ -368,87 +373,72 @@ struct CmdFlakeCheck : FlakeCommand
                 // 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));
+                e.addTrace(resolve(pos), hintfmt("while checking the overlay '%s'", attrPath));
                 reportError(e);
             }
         };
 
-        auto checkModule = [&](const std::string & attrPath, Value & v, const Pos & pos) {
+        auto checkModule = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
             try {
                 state->forceValue(v, pos);
-                if (v.isLambda()) {
-                    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)
-                        try {
-                            state->forceValue(*attr.value, *attr.pos);
-                        } catch (Error & e) {
-                            e.addTrace(*attr.pos, hintfmt("while evaluating the option '%s'", attr.name));
-                            throw;
-                        }
-                } else
-                    throw Error("module must be a function or an attribute set");
-                // FIXME: if we have a 'nixpkgs' input, use it to
-                // check the module.
             } catch (Error & e) {
-                e.addTrace(pos, hintfmt("while checking the NixOS module '%s'", attrPath));
+                e.addTrace(resolve(pos), hintfmt("while checking the NixOS module '%s'", attrPath));
                 reportError(e);
             }
         };
 
-        std::function<void(const std::string & attrPath, Value & v, const Pos & pos)> checkHydraJobs;
+        std::function<void(const std::string & attrPath, Value & v, const PosIdx pos)> checkHydraJobs;
 
-        checkHydraJobs = [&](const std::string & attrPath, Value & v, const Pos & pos) {
+        checkHydraJobs = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
             try {
-                state->forceAttrs(v, pos);
+                state->forceAttrs(v, pos, "");
 
                 if (state->isDerivation(v))
                     throw Error("jobset should not be a derivation at top-level");
 
                 for (auto & attr : *v.attrs) {
-                    state->forceAttrs(*attr.value, *attr.pos);
-                    auto attrPath2 = attrPath + "." + (std::string) attr.name;
+                    state->forceAttrs(*attr.value, attr.pos, "");
+                    auto attrPath2 = concatStrings(attrPath, ".", state->symbols[attr.name]);
                     if (state->isDerivation(*attr.value)) {
                         Activity act(*logger, lvlChatty, actUnknown,
                             fmt("checking Hydra job '%s'", attrPath2));
-                        checkDerivation(attrPath2, *attr.value, *attr.pos);
+                        checkDerivation(attrPath2, *attr.value, attr.pos);
                     } else
-                        checkHydraJobs(attrPath2, *attr.value, *attr.pos);
+                        checkHydraJobs(attrPath2, *attr.value, attr.pos);
                 }
 
             } catch (Error & e) {
-                e.addTrace(pos, hintfmt("while checking the Hydra jobset '%s'", attrPath));
+                e.addTrace(resolve(pos), hintfmt("while checking the Hydra jobset '%s'", attrPath));
                 reportError(e);
             }
         };
 
-        auto checkNixOSConfiguration = [&](const std::string & attrPath, Value & v, const Pos & pos) {
+        auto checkNixOSConfiguration = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
             try {
                 Activity act(*logger, lvlChatty, actUnknown,
                     fmt("checking NixOS configuration '%s'", attrPath));
                 Bindings & bindings(*state->allocBindings(0));
                 auto vToplevel = findAlongAttrPath(*state, "config.system.build.toplevel", bindings, v).first;
-                state->forceAttrs(*vToplevel, pos);
+                state->forceValue(*vToplevel, pos);
                 if (!state->isDerivation(*vToplevel))
                     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));
+                e.addTrace(resolve(pos), hintfmt("while checking the NixOS configuration '%s'", attrPath));
                 reportError(e);
             }
         };
 
-        auto checkTemplate = [&](const std::string & attrPath, Value & v, const Pos & pos) {
+        auto checkTemplate = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
             try {
                 Activity act(*logger, lvlChatty, actUnknown,
                     fmt("checking template '%s'", attrPath));
 
-                state->forceAttrs(v, pos);
+                state->forceAttrs(v, pos, "");
 
                 if (auto attr = v.attrs->get(state->symbols.create("path"))) {
                     if (attr->name == state->symbols.create("path")) {
                         PathSet context;
-                        auto path = state->coerceToPath(*attr->pos, *attr->value, context);
+                        auto path = state->coerceToPath(attr->pos, *attr->value, context, "");
                         if (!store->isInStore(path))
                             throw Error("template '%s' has a bad 'path' attribute");
                         // TODO: recursively check the flake in 'path'.
@@ -457,29 +447,29 @@ struct CmdFlakeCheck : FlakeCommand
                     throw Error("template '%s' lacks attribute 'path'", attrPath);
 
                 if (auto attr = v.attrs->get(state->symbols.create("description")))
-                    state->forceStringNoCtx(*attr->value, *attr->pos);
+                    state->forceStringNoCtx(*attr->value, attr->pos, "");
                 else
                     throw Error("template '%s' lacks attribute 'description'", attrPath);
 
                 for (auto & attr : *v.attrs) {
-                    std::string name(attr.name);
+                    std::string_view name(state->symbols[attr.name]);
                     if (name != "path" && name != "description" && name != "welcomeText")
                         throw Error("template '%s' has unsupported attribute '%s'", attrPath, name);
                 }
             } catch (Error & e) {
-                e.addTrace(pos, hintfmt("while checking the template '%s'", attrPath));
+                e.addTrace(resolve(pos), hintfmt("while checking the template '%s'", attrPath));
                 reportError(e);
             }
         };
 
-        auto checkBundler = [&](const std::string & attrPath, Value & v, const Pos & pos) {
+        auto checkBundler = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
             try {
                 state->forceValue(v, pos);
                 if (!v.isLambda())
                     throw Error("bundler must be a function");
                 // TODO: check types of inputs/outputs?
             } catch (Error & e) {
-                e.addTrace(pos, hintfmt("while checking the template '%s'", attrPath));
+                e.addTrace(resolve(pos), hintfmt("while checking the template '%s'", attrPath));
                 reportError(e);
             }
         };
@@ -492,7 +482,7 @@ struct CmdFlakeCheck : FlakeCommand
 
             enumerateOutputs(*state,
                 *vFlake,
-                [&](const std::string & name, Value & vOutput, const Pos & pos) {
+                [&](const std::string & name, Value & vOutput, const PosIdx pos) {
                     Activity act(*logger, lvlChatty, actUnknown,
                         fmt("checking flake output '%s'", name));
 
@@ -503,7 +493,7 @@ struct CmdFlakeCheck : FlakeCommand
 
                         std::string_view replacement =
                             name == "defaultPackage" ? "packages.<system>.default" :
-                            name == "defaultApps" ? "apps.<system>.default" :
+                            name == "defaultApp" ? "apps.<system>.default" :
                             name == "defaultTemplate" ? "templates.default" :
                             name == "defaultBundler" ? "bundlers.<system>.default" :
                             name == "overlay" ? "overlays.default" :
@@ -514,78 +504,84 @@ struct CmdFlakeCheck : FlakeCommand
                             warn("flake output attribute '%s' is deprecated; use '%s' instead", name, replacement);
 
                         if (name == "checks") {
-                            state->forceAttrs(vOutput, pos);
+                            state->forceAttrs(vOutput, pos, "");
                             for (auto & attr : *vOutput.attrs) {
-                                checkSystemName(attr.name, *attr.pos);
-                                state->forceAttrs(*attr.value, *attr.pos);
+                                const auto & attr_name = state->symbols[attr.name];
+                                checkSystemName(attr_name, attr.pos);
+                                state->forceAttrs(*attr.value, attr.pos, "");
                                 for (auto & attr2 : *attr.value->attrs) {
                                     auto drvPath = checkDerivation(
-                                        fmt("%s.%s.%s", name, attr.name, attr2.name),
-                                        *attr2.value, *attr2.pos);
-                                    if (drvPath && (std::string) attr.name == settings.thisSystem.get())
+                                        fmt("%s.%s.%s", name, attr_name, state->symbols[attr2.name]),
+                                        *attr2.value, attr2.pos);
+                                    if (drvPath && attr_name == settings.thisSystem.get())
                                         drvPaths.push_back(DerivedPath::Built{*drvPath});
                                 }
                             }
                         }
 
                         else if (name == "formatter") {
-                            state->forceAttrs(vOutput, pos);
+                            state->forceAttrs(vOutput, pos, "");
                             for (auto & attr : *vOutput.attrs) {
-                                checkSystemName(attr.name, *attr.pos);
+                                const auto & attr_name = state->symbols[attr.name];
+                                checkSystemName(attr_name, attr.pos);
                                 checkApp(
-                                    fmt("%s.%s", name, attr.name),
-                                    *attr.value, *attr.pos);
+                                    fmt("%s.%s", name, attr_name),
+                                    *attr.value, attr.pos);
                             }
                         }
 
                         else if (name == "packages" || name == "devShells") {
-                            state->forceAttrs(vOutput, pos);
+                            state->forceAttrs(vOutput, pos, "");
                             for (auto & attr : *vOutput.attrs) {
-                                checkSystemName(attr.name, *attr.pos);
-                                state->forceAttrs(*attr.value, *attr.pos);
+                                const auto & attr_name = state->symbols[attr.name];
+                                checkSystemName(attr_name, attr.pos);
+                                state->forceAttrs(*attr.value, attr.pos, "");
                                 for (auto & attr2 : *attr.value->attrs)
                                     checkDerivation(
-                                        fmt("%s.%s.%s", name, attr.name, attr2.name),
-                                        *attr2.value, *attr2.pos);
+                                        fmt("%s.%s.%s", name, attr_name, state->symbols[attr2.name]),
+                                        *attr2.value, attr2.pos);
                             }
                         }
 
                         else if (name == "apps") {
-                            state->forceAttrs(vOutput, pos);
+                            state->forceAttrs(vOutput, pos, "");
                             for (auto & attr : *vOutput.attrs) {
-                                checkSystemName(attr.name, *attr.pos);
-                                state->forceAttrs(*attr.value, *attr.pos);
+                                const auto & attr_name = state->symbols[attr.name];
+                                checkSystemName(attr_name, attr.pos);
+                                state->forceAttrs(*attr.value, attr.pos, "");
                                 for (auto & attr2 : *attr.value->attrs)
                                     checkApp(
-                                        fmt("%s.%s.%s", name, attr.name, attr2.name),
-                                        *attr2.value, *attr2.pos);
+                                        fmt("%s.%s.%s", name, attr_name, state->symbols[attr2.name]),
+                                        *attr2.value, attr2.pos);
                             }
                         }
 
                         else if (name == "defaultPackage" || name == "devShell") {
-                            state->forceAttrs(vOutput, pos);
+                            state->forceAttrs(vOutput, pos, "");
                             for (auto & attr : *vOutput.attrs) {
-                                checkSystemName(attr.name, *attr.pos);
+                                const auto & attr_name = state->symbols[attr.name];
+                                checkSystemName(attr_name, attr.pos);
                                 checkDerivation(
-                                    fmt("%s.%s", name, attr.name),
-                                    *attr.value, *attr.pos);
+                                    fmt("%s.%s", name, attr_name),
+                                    *attr.value, attr.pos);
                             }
                         }
 
                         else if (name == "defaultApp") {
-                            state->forceAttrs(vOutput, pos);
+                            state->forceAttrs(vOutput, pos, "");
                             for (auto & attr : *vOutput.attrs) {
-                                checkSystemName(attr.name, *attr.pos);
+                                const auto & attr_name = state->symbols[attr.name];
+                                checkSystemName(attr_name, attr.pos);
                                 checkApp(
-                                    fmt("%s.%s", name, attr.name),
-                                    *attr.value, *attr.pos);
+                                    fmt("%s.%s", name, attr_name),
+                                    *attr.value, attr.pos);
                             }
                         }
 
                         else if (name == "legacyPackages") {
-                            state->forceAttrs(vOutput, pos);
+                            state->forceAttrs(vOutput, pos, "");
                             for (auto & attr : *vOutput.attrs) {
-                                checkSystemName(attr.name, *attr.pos);
+                                checkSystemName(state->symbols[attr.name], attr.pos);
                                 // FIXME: do getDerivations?
                             }
                         }
@@ -594,27 +590,27 @@ struct CmdFlakeCheck : FlakeCommand
                             checkOverlay(name, vOutput, pos);
 
                         else if (name == "overlays") {
-                            state->forceAttrs(vOutput, pos);
+                            state->forceAttrs(vOutput, pos, "");
                             for (auto & attr : *vOutput.attrs)
-                                checkOverlay(fmt("%s.%s", name, attr.name),
-                                    *attr.value, *attr.pos);
+                                checkOverlay(fmt("%s.%s", name, state->symbols[attr.name]),
+                                    *attr.value, attr.pos);
                         }
 
                         else if (name == "nixosModule")
                             checkModule(name, vOutput, pos);
 
                         else if (name == "nixosModules") {
-                            state->forceAttrs(vOutput, pos);
+                            state->forceAttrs(vOutput, pos, "");
                             for (auto & attr : *vOutput.attrs)
-                                checkModule(fmt("%s.%s", name, attr.name),
-                                    *attr.value, *attr.pos);
+                                checkModule(fmt("%s.%s", name, state->symbols[attr.name]),
+                                    *attr.value, attr.pos);
                         }
 
                         else if (name == "nixosConfigurations") {
-                            state->forceAttrs(vOutput, pos);
+                            state->forceAttrs(vOutput, pos, "");
                             for (auto & attr : *vOutput.attrs)
-                                checkNixOSConfiguration(fmt("%s.%s", name, attr.name),
-                                    *attr.value, *attr.pos);
+                                checkNixOSConfiguration(fmt("%s.%s", name, state->symbols[attr.name]),
+                                    *attr.value, attr.pos);
                         }
 
                         else if (name == "hydraJobs")
@@ -624,31 +620,33 @@ struct CmdFlakeCheck : FlakeCommand
                             checkTemplate(name, vOutput, pos);
 
                         else if (name == "templates") {
-                            state->forceAttrs(vOutput, pos);
+                            state->forceAttrs(vOutput, pos, "");
                             for (auto & attr : *vOutput.attrs)
-                                checkTemplate(fmt("%s.%s", name, attr.name),
-                                    *attr.value, *attr.pos);
+                                checkTemplate(fmt("%s.%s", name, state->symbols[attr.name]),
+                                    *attr.value, attr.pos);
                         }
 
                         else if (name == "defaultBundler") {
-                            state->forceAttrs(vOutput, pos);
+                            state->forceAttrs(vOutput, pos, "");
                             for (auto & attr : *vOutput.attrs) {
-                                checkSystemName(attr.name, *attr.pos);
+                                const auto & attr_name = state->symbols[attr.name];
+                                checkSystemName(attr_name, attr.pos);
                                 checkBundler(
-                                    fmt("%s.%s", name, attr.name),
-                                    *attr.value, *attr.pos);
+                                    fmt("%s.%s", name, attr_name),
+                                    *attr.value, attr.pos);
                             }
                         }
 
                         else if (name == "bundlers") {
-                            state->forceAttrs(vOutput, pos);
+                            state->forceAttrs(vOutput, pos, "");
                             for (auto & attr : *vOutput.attrs) {
-                                checkSystemName(attr.name, *attr.pos);
-                                state->forceAttrs(*attr.value, *attr.pos);
+                                const auto & attr_name = state->symbols[attr.name];
+                                checkSystemName(attr_name, attr.pos);
+                                state->forceAttrs(*attr.value, attr.pos, "");
                                 for (auto & attr2 : *attr.value->attrs) {
                                     checkBundler(
-                                        fmt("%s.%s.%s", name, attr.name, attr2.name),
-                                        *attr2.value, *attr2.pos);
+                                        fmt("%s.%s.%s", name, attr_name, state->symbols[attr2.name]),
+                                        *attr2.value, attr2.pos);
                                 }
                             }
                         }
@@ -657,7 +655,7 @@ struct CmdFlakeCheck : FlakeCommand
                             warn("unknown flake output '%s'", name);
 
                     } catch (Error & e) {
-                        e.addTrace(pos, hintfmt("while checking flake output '%s'", name));
+                        e.addTrace(resolve(pos), hintfmt("while checking flake output '%s'", name));
                         reportError(e);
                     }
                 });
@@ -710,7 +708,7 @@ struct CmdFlakeInitCommon : virtual Args, EvalCommand
         auto [templateFlakeRef, templateName] = parseFlakeRefWithFragment(templateUrl, absPath("."));
 
         auto installable = InstallableFlake(nullptr,
-            evalState, std::move(templateFlakeRef), templateName,
+            evalState, std::move(templateFlakeRef), templateName, DefaultOutputs(),
             defaultTemplateAttrPaths,
             defaultTemplateAttrPathsPrefixes,
             lockFlags);
@@ -726,7 +724,8 @@ struct CmdFlakeInitCommon : virtual Args, EvalCommand
                 "If you've set '%s' to a string, try using a path instead.",
                 templateDir, templateDirAttr->getAttrPathStr());
 
-        std::vector<Path> files;
+        std::vector<Path> changedFiles;
+        std::vector<Path> conflictedFiles;
 
         std::function<void(const Path & from, const Path & to)> copyDir;
         copyDir = [&](const Path & from, const Path & to)
@@ -743,31 +742,41 @@ struct CmdFlakeInitCommon : virtual Args, EvalCommand
                     auto contents = readFile(from2);
                     if (pathExists(to2)) {
                         auto contents2 = readFile(to2);
-                        if (contents != contents2)
-                            throw Error("refusing to overwrite existing file '%s'", to2);
+                        if (contents != contents2) {
+                            printError("refusing to overwrite existing file '%s'\n please merge it manually with '%s'", to2, from2);
+                            conflictedFiles.push_back(to2);
+                        } else {
+                            notice("skipping identical file: %s", from2);
+                        }
+                        continue;
                     } else
                         writeFile(to2, contents);
                 }
                 else if (S_ISLNK(st.st_mode)) {
                     auto target = readLink(from2);
                     if (pathExists(to2)) {
-                        if (readLink(to2) != target)
-                            throw Error("refusing to overwrite existing symlink '%s'", to2);
+                        if (readLink(to2) != target) {
+                            printError("refusing to overwrite existing file '%s'\n please merge it manually with '%s'", to2, from2);
+                            conflictedFiles.push_back(to2);
+                        } else {
+                            notice("skipping identical file: %s", from2);
+                        }
+                        continue;
                     } else
                           createSymlink(target, to2);
                 }
                 else
                     throw Error("file '%s' has unsupported type", from2);
-                files.push_back(to2);
+                changedFiles.push_back(to2);
                 notice("wrote: %s", to2);
             }
         };
 
         copyDir(templateDir, flakeDir);
 
-        if (pathExists(flakeDir + "/.git")) {
+        if (!changedFiles.empty() && pathExists(flakeDir + "/.git")) {
             Strings args = { "-C", flakeDir, "add", "--intent-to-add", "--force", "--" };
-            for (auto & s : files) args.push_back(s);
+            for (auto & s : changedFiles) args.push_back(s);
             runProgram("git", true, args);
         }
         auto welcomeText = cursor->maybeGetAttr("welcomeText");
@@ -775,6 +784,9 @@ struct CmdFlakeInitCommon : virtual Args, EvalCommand
             notice("\n");
             notice(renderMarkdownToTerminal(welcomeText->getString()));
         }
+
+        if (!conflictedFiles.empty())
+            throw Error("Encountered %d conflicts - see above", conflictedFiles.size());
     }
 };
 
@@ -888,35 +900,44 @@ struct CmdFlakeArchive : FlakeCommand, MixJSON, MixDryRun
     {
         auto flake = lockFlake();
 
-        auto jsonRoot = json ? std::optional<JSONObject>(std::cout) : std::nullopt;
-
         StorePathSet sources;
 
         sources.insert(flake.flake.sourceInfo->storePath);
-        if (jsonRoot)
-            jsonRoot->attr("path", store->printStorePath(flake.flake.sourceInfo->storePath));
 
         // FIXME: use graph output, handle cycles.
-        std::function<void(const Node & node, std::optional<JSONObject> & jsonObj)> traverse;
-        traverse = [&](const Node & node, std::optional<JSONObject> & jsonObj)
+        std::function<nlohmann::json(const Node & node)> traverse;
+        traverse = [&](const Node & node)
         {
-            auto jsonObj2 = jsonObj ? jsonObj->object("inputs") : std::optional<JSONObject>();
+            nlohmann::json jsonObj2 = json ? json::object() : nlohmann::json(nullptr);
             for (auto & [inputName, input] : node.inputs) {
                 if (auto inputNode = std::get_if<0>(&input)) {
-                    auto jsonObj3 = jsonObj2 ? jsonObj2->object(inputName) : std::optional<JSONObject>();
                     auto storePath =
                         dryRun
                         ? (*inputNode)->lockedRef.input.computeStorePath(*store)
                         : (*inputNode)->lockedRef.input.fetch(store).first.storePath;
-                    if (jsonObj3)
-                        jsonObj3->attr("path", store->printStorePath(storePath));
-                    sources.insert(std::move(storePath));
-                    traverse(**inputNode, jsonObj3);
+                    if (json) {
+                        auto& jsonObj3 = jsonObj2[inputName];
+                        jsonObj3["path"] = store->printStorePath(storePath);
+                        sources.insert(std::move(storePath));
+                        jsonObj3["inputs"] = traverse(**inputNode);
+                    } else {
+                        sources.insert(std::move(storePath));
+                        traverse(**inputNode);
+                    }
                 }
             }
+            return jsonObj2;
         };
 
-        traverse(*flake.lockFile.root, jsonRoot);
+        if (json) {
+            nlohmann::json jsonRoot = {
+                {"path", store->printStorePath(flake.flake.sourceInfo->storePath)},
+                {"inputs", traverse(*flake.lockFile.root)},
+            };
+            std::cout << jsonRoot.dump() << std::endl;
+        } else {
+            traverse(*flake.lockFile.root);
+        }
 
         if (!dryRun && !dstUri.empty()) {
             ref<Store> dstStore = dstUri.empty() ? openStore() : openStore(dstUri);
@@ -972,8 +993,11 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
         {
             auto j = nlohmann::json::object();
 
+            auto attrPathS = state->symbols.resolve(attrPath);
+
             Activity act(*logger, lvlInfo, actUnknown,
-                fmt("evaluating '%s'", concatStringsSep(".", attrPath)));
+                fmt("evaluating '%s'", concatStringsSep(".", attrPathS)));
+
             try {
                 auto recurse = [&]()
                 {
@@ -981,14 +1005,15 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
                         logger->cout("%s", headerPrefix);
                     auto attrs = visitor.getAttrs();
                     for (const auto & [i, attr] : enumerate(attrs)) {
+                        const auto & attrName = state->symbols[attr];
                         bool last = i + 1 == attrs.size();
-                        auto visitor2 = visitor.getAttr(attr);
+                        auto visitor2 = visitor.getAttr(attrName);
                         auto attrPath2(attrPath);
                         attrPath2.push_back(attr);
                         auto j2 = visit(*visitor2, attrPath2,
-                            fmt(ANSI_GREEN "%s%s" ANSI_NORMAL ANSI_BOLD "%s" ANSI_NORMAL, nextPrefix, last ? treeLast : treeConn, attr),
+                            fmt(ANSI_GREEN "%s%s" ANSI_NORMAL ANSI_BOLD "%s" ANSI_NORMAL, nextPrefix, last ? treeLast : treeConn, attrName),
                             nextPrefix + (last ? treeNull : treeLine));
-                        if (json) j.emplace(attr, std::move(j2));
+                        if (json) j.emplace(attrName, std::move(j2));
                     }
                 };
 
@@ -997,8 +1022,8 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
                     auto name = visitor.getAttr(state->sName)->getString();
                     if (json) {
                         std::optional<std::string> description;
-                        if (auto aMeta = visitor.maybeGetAttr("meta")) {
-                            if (auto aDescription = aMeta->maybeGetAttr("description"))
+                        if (auto aMeta = visitor.maybeGetAttr(state->sMeta)) {
+                            if (auto aDescription = aMeta->maybeGetAttr(state->sDescription))
                                 description = aDescription->getString();
                         }
                         j.emplace("type", "derivation");
@@ -1008,10 +1033,10 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
                     } 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" :
+                            attrPath.size() == 2 && attrPathS[0] == "devShell" ? "development environment" :
+                            attrPath.size() >= 2 && attrPathS[0] == "devShells" ? "development environment" :
+                            attrPath.size() == 3 && attrPathS[0] == "checks" ? "derivation" :
+                            attrPath.size() >= 1 && attrPathS[0] == "hydraJobs" ? "derivation" :
                             "package",
                             name);
                     }
@@ -1019,27 +1044,27 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
 
                 if (attrPath.size() == 0
                     || (attrPath.size() == 1 && (
-                            attrPath[0] == "defaultPackage"
-                            || attrPath[0] == "devShell"
-                            || attrPath[0] == "formatter"
-                            || attrPath[0] == "nixosConfigurations"
-                            || attrPath[0] == "nixosModules"
-                            || attrPath[0] == "defaultApp"
-                            || attrPath[0] == "templates"
-                            || attrPath[0] == "overlays"))
+                            attrPathS[0] == "defaultPackage"
+                            || attrPathS[0] == "devShell"
+                            || attrPathS[0] == "formatter"
+                            || attrPathS[0] == "nixosConfigurations"
+                            || attrPathS[0] == "nixosModules"
+                            || attrPathS[0] == "defaultApp"
+                            || attrPathS[0] == "templates"
+                            || attrPathS[0] == "overlays"))
                     || ((attrPath.size() == 1 || attrPath.size() == 2)
-                        && (attrPath[0] == "checks"
-                            || attrPath[0] == "packages"
-                            || attrPath[0] == "devShells"
-                            || attrPath[0] == "apps"))
+                        && (attrPathS[0] == "checks"
+                            || attrPathS[0] == "packages"
+                            || attrPathS[0] == "devShells"
+                            || attrPathS[0] == "apps"))
                     )
                 {
                     recurse();
                 }
 
                 else if (
-                    (attrPath.size() == 2 && (attrPath[0] == "defaultPackage" || attrPath[0] == "devShell" || attrPath[0] == "formatter"))
-                    || (attrPath.size() == 3 && (attrPath[0] == "checks" || attrPath[0] == "packages" || attrPath[0] == "devShells"))
+                    (attrPath.size() == 2 && (attrPathS[0] == "defaultPackage" || attrPathS[0] == "devShell" || attrPathS[0] == "formatter"))
+                    || (attrPath.size() == 3 && (attrPathS[0] == "checks" || attrPathS[0] == "packages" || attrPathS[0] == "devShells"))
                     )
                 {
                     if (visitor.isDerivation())
@@ -1048,19 +1073,23 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
                         throw Error("expected a derivation");
                 }
 
-                else if (attrPath.size() > 0 && attrPath[0] == "hydraJobs") {
+                else if (attrPath.size() > 0 && attrPathS[0] == "hydraJobs") {
                     if (visitor.isDerivation())
                         showDerivation();
                     else
                         recurse();
                 }
 
-                else if (attrPath.size() > 0 && attrPath[0] == "legacyPackages") {
+                else if (attrPath.size() > 0 && attrPathS[0] == "legacyPackages") {
                     if (attrPath.size() == 1)
                         recurse();
-                    else if (!showLegacy)
-                        logger->warn(fmt("%s: " ANSI_WARNING "omitted" ANSI_NORMAL " (use '--legacy' to show)", headerPrefix));
-                    else {
+                    else if (!showLegacy){
+                        if (!json)
+                            logger->cout(fmt("%s " ANSI_WARNING "omitted" ANSI_NORMAL " (use '--legacy' to show)", headerPrefix));
+                        else {
+                            logger->warn(fmt("%s omitted (use '--legacy' to show)", concatStringsSep(".", attrPathS)));
+                        }
+                    } else {
                         if (visitor.isDerivation())
                             showDerivation();
                         else if (attrPath.size() <= 2)
@@ -1070,8 +1099,8 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
                 }
 
                 else if (
-                    (attrPath.size() == 2 && attrPath[0] == "defaultApp") ||
-                    (attrPath.size() == 3 && attrPath[0] == "apps"))
+                    (attrPath.size() == 2 && attrPathS[0] == "defaultApp") ||
+                    (attrPath.size() == 3 && attrPathS[0] == "apps"))
                 {
                     auto aType = visitor.maybeGetAttr("type");
                     if (!aType || aType->getString() != "app")
@@ -1084,8 +1113,8 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
                 }
 
                 else if (
-                    (attrPath.size() == 1 && attrPath[0] == "defaultTemplate") ||
-                    (attrPath.size() == 2 && attrPath[0] == "templates"))
+                    (attrPath.size() == 1 && attrPathS[0] == "defaultTemplate") ||
+                    (attrPath.size() == 2 && attrPathS[0] == "templates"))
                 {
                     auto description = visitor.getAttr("description")->getString();
                     if (json) {
@@ -1098,11 +1127,11 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
 
                 else {
                     auto [type, description] =
-                        (attrPath.size() == 1 && attrPath[0] == "overlay")
-                        || (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") :
+                        (attrPath.size() == 1 && attrPathS[0] == "overlay")
+                        || (attrPath.size() == 2 && attrPathS[0] == "overlays") ? std::make_pair("nixpkgs-overlay", "Nixpkgs overlay") :
+                        attrPath.size() == 2 && attrPathS[0] == "nixosConfigurations" ? std::make_pair("nixos-configuration", "NixOS configuration") :
+                        (attrPath.size() == 1 && attrPathS[0] == "nixosModule")
+                        || (attrPath.size() == 2 && attrPathS[0] == "nixosModules") ? std::make_pair("nixos-module", "NixOS module") :
                         std::make_pair("unknown", "unknown");
                     if (json) {
                         j.emplace("type", type);
@@ -1111,7 +1140,7 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
                     }
                 }
             } catch (EvalError & e) {
-                if (!(attrPath.size() > 0 && attrPath[0] == "legacyPackages"))
+                if (!(attrPath.size() > 0 && attrPathS[0] == "legacyPackages"))
                     throw;
             }
 
diff --git a/src/nix/flake.md b/src/nix/flake.md
index 7d179a6c4..810e9ebea 100644
--- a/src/nix/flake.md
+++ b/src/nix/flake.md
@@ -18,51 +18,56 @@ values such as packages or NixOS modules provided by the flake).
 Flake references (*flakerefs*) are a way to specify the location of a
 flake. These have two different forms:
 
-* An attribute set representation, e.g.
 
-  ```nix
-  {
-    type = "github";
-    owner = "NixOS";
-    repo = "nixpkgs";
-  }
-  ```
+## Attribute set representation
 
-  The only required attribute is `type`. The supported types are
-  listed below.
+Example:
 
-* A URL-like syntax, e.g.
+```nix
+{
+  type = "github";
+  owner = "NixOS";
+  repo = "nixpkgs";
+}
+```
 
-  ```
-  github:NixOS/nixpkgs
-  ```
+The only required attribute is `type`. The supported types are
+listed below.
 
-  These are used on the command line as a more convenient alternative
-  to the attribute set representation. For instance, in the command
+## URL-like syntax
 
-  ```console
-  # nix build github:NixOS/nixpkgs#hello
-  ```
+Example:
 
-  `github:NixOS/nixpkgs` is a flake reference (while `hello` is an
-  output attribute). They are also allowed in the `inputs` attribute
-  of a flake, e.g.
+```
+github:NixOS/nixpkgs
+```
 
-  ```nix
-  inputs.nixpkgs.url = github:NixOS/nixpkgs;
-  ```
+These are used on the command line as a more convenient alternative
+to the attribute set representation. For instance, in the command
 
-  is equivalent to
+```console
+# nix build github:NixOS/nixpkgs#hello
+```
 
-  ```nix
-  inputs.nixpkgs = {
-    type = "github";
-    owner = "NixOS";
-    repo = "nixpkgs";
-  };
-  ```
+`github:NixOS/nixpkgs` is a flake reference (while `hello` is an
+output attribute). They are also allowed in the `inputs` attribute
+of a flake, e.g.
+
+```nix
+inputs.nixpkgs.url = github:NixOS/nixpkgs;
+```
 
-## Examples
+is equivalent to
+
+```nix
+inputs.nixpkgs = {
+  type = "github";
+  owner = "NixOS";
+  repo = "nixpkgs";
+};
+```
+
+### Examples
 
 Here are some examples of flake references in their URL-like representation:
 
@@ -153,7 +158,7 @@ Currently the `type` attribute can be one of the following:
   git(+http|+https|+ssh|+git|+file|):(//<server>)?<path>(\?<params>)?
   ```
 
-  The `ref` attribute defaults to `master`.
+  The `ref` attribute defaults to resolving the `HEAD` reference.
 
   The `rev` attribute must denote a commit that exists in the branch
   or tag specified by the `ref` attribute, since Nix doesn't do a full
@@ -161,6 +166,11 @@ Currently the `type` attribute can be one of the following:
   doesn't allow fetching a `rev` without a known `ref`). The default
   is the commit currently pointed to by `ref`.
 
+  When `git+file` is used without specifying `ref` or `rev`, files are
+  fetched directly from the local `path` as long as they have been added
+  to the Git repository. If there are uncommitted changes, the reference
+  is treated as dirty and a warning is printed.
+
   For example, the following are valid Git flake references:
 
   * `git+https://example.org/my/repo`
@@ -176,9 +186,17 @@ Currently the `type` attribute can be one of the following:
 * `tarball`: Tarballs. The location of the tarball is specified by the
   attribute `url`.
 
-  In URL form, the schema must be `http://`, `https://` or `file://`
-  URLs and the extension must be `.zip`, `.tar`, `.tgz`, `.tar.gz`,
-  `.tar.xz`, `.tar.bz2` or `.tar.zst`.
+  In URL form, the schema must be `tarball+http://`, `tarball+https://` or `tarball+file://`.
+  If the extension corresponds to a known archive format (`.zip`, `.tar`,
+  `.tgz`, `.tar.gz`, `.tar.xz`, `.tar.bz2` or `.tar.zst`), then the `tarball+`
+  can be dropped.
+
+* `file`: Plain files or directory tarballs, either over http(s) or from the local
+  disk.
+
+  In URL form, the schema must be `file+http://`, `file+https://` or `file+file://`.
+  If the extension doesn’t correspond to a known archive format (as defined by the
+  `tarball` fetcher), then the `file+` prefix can be dropped.
 
 * `github`: A more efficient way to fetch repositories from
   GitHub. The following attributes are required:
@@ -326,9 +344,10 @@ The following attributes are supported in `flake.nix`:
 
 * `nixConfig`: a set of `nix.conf` options to be set when evaluating any
   part of a flake. In the interests of security, only a small set of
-  whitelisted options (currently `bash-prompt`, `bash-prompt-suffix`,
-  and `flake-registry`) are allowed to be set without confirmation so long as
-  `accept-flake-config` is not set in the global configuration.
+  whitelisted options (currently `bash-prompt`, `bash-prompt-prefix`,
+  `bash-prompt-suffix`, and `flake-registry`) are allowed to be set without
+  confirmation so long as `accept-flake-config` is not set in the global
+  configuration.
 
 ## Flake inputs
 
diff --git a/src/nix/fmt.cc b/src/nix/fmt.cc
index e5d44bd38..6f6a4a632 100644
--- a/src/nix/fmt.cc
+++ b/src/nix/fmt.cc
@@ -26,7 +26,8 @@ struct CmdFmt : SourceExprCommand {
 
     Strings getDefaultFlakeAttrPathPrefixes() override { return Strings{}; }
 
-    void run(ref<Store> store) {
+    void run(ref<Store> store) override
+    {
         auto evalState = getEvalState();
         auto evalStore = getEvalStore();
 
diff --git a/src/nix/get-env.sh b/src/nix/get-env.sh
index 42c806450..a7a8a01b9 100644
--- a/src/nix/get-env.sh
+++ b/src/nix/get-env.sh
@@ -43,6 +43,7 @@ __dumpEnv() {
         local __var_name="${BASH_REMATCH[2]}"
 
         if [[ $__var_name =~ ^BASH_ || \
+              $__var_name =~ ^COMP_ || \
               $__var_name = _ || \
               $__var_name = DIRSTACK || \
               $__var_name = EUID || \
@@ -54,7 +55,9 @@ __dumpEnv() {
               $__var_name = PWD || \
               $__var_name = RANDOM || \
               $__var_name = SHLVL || \
-              $__var_name = SECONDS \
+              $__var_name = SECONDS || \
+              $__var_name = EPOCHREALTIME || \
+              $__var_name = EPOCHSECONDS \
             ]]; then continue; fi
 
         if [[ -z $__first ]]; then printf ',\n'; else __first=; fi
diff --git a/src/nix/key-generate-secret.md b/src/nix/key-generate-secret.md
index 4938f637c..609b1abcc 100644
--- a/src/nix/key-generate-secret.md
+++ b/src/nix/key-generate-secret.md
@@ -30,7 +30,7 @@ convert-secret-to-public` to get the corresponding public key for
 verifying signed store paths.
 
 The mandatory argument `--key-name` specifies a key name (such as
-`cache.example.org-1). It is used to look up keys on the client when
+`cache.example.org-1`). It is used to look up keys on the client when
 it verifies signatures. It can be anything, but it’s suggested to use
 the host name of your cache (e.g.  `cache.example.org`) with a suffix
 denoting the number of the key (to be incremented every time you need
diff --git a/src/nix/local.mk b/src/nix/local.mk
index e4ec7634d..0f2f016ec 100644
--- a/src/nix/local.mk
+++ b/src/nix/local.mk
@@ -18,7 +18,7 @@ nix_CXXFLAGS += -I src/libutil -I src/libstore -I src/libfetchers -I src/libexpr
 
 nix_LIBS = libexpr libmain libfetchers libstore libutil libcmd
 
-nix_LDFLAGS = -pthread $(SODIUM_LIBS) $(EDITLINE_LIBS) $(BOOST_LDFLAGS) -llowdown
+nix_LDFLAGS = -pthread $(SODIUM_LIBS) $(EDITLINE_LIBS) $(BOOST_LDFLAGS) $(LOWDOWN_LIBS)
 
 $(foreach name, \
   nix-build nix-channel nix-collect-garbage nix-copy-closure nix-daemon nix-env nix-hash nix-instantiate nix-prefetch-url nix-shell nix-store, \
diff --git a/src/nix/ls.cc b/src/nix/ls.cc
index 07554994b..e964b01b3 100644
--- a/src/nix/ls.cc
+++ b/src/nix/ls.cc
@@ -3,7 +3,7 @@
 #include "fs-accessor.hh"
 #include "nar-accessor.hh"
 #include "common-args.hh"
-#include "json.hh"
+#include <nlohmann/json.hpp>
 
 using namespace nix;
 
@@ -91,10 +91,9 @@ struct MixLs : virtual Args, MixJSON
         if (path == "/") path = "";
 
         if (json) {
-            JSONPlaceholder jsonRoot(std::cout);
             if (showDirectory)
                 throw UsageError("'--directory' is useless with '--json'");
-            listNar(jsonRoot, accessor, path, recursive);
+            std::cout << listNar(accessor, path, recursive);
         } else
             listText(accessor);
     }
diff --git a/src/nix/main.cc b/src/nix/main.cc
index 6198681e7..d3d2f5b16 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -53,7 +53,6 @@ static bool haveInternet()
 }
 
 std::string programPath;
-char * * savedArgv;
 
 struct HelpRequested { };
 
@@ -74,6 +73,7 @@ struct NixArgs : virtual MultiCommand, virtual MixCommonArgs
         addFlag({
             .longName = "help",
             .description = "Show usage information.",
+            .category = miscCategory,
             .handler = {[&]() { throw HelpRequested(); }},
         });
 
@@ -82,12 +82,13 @@ struct NixArgs : virtual MultiCommand, virtual MixCommonArgs
             .shortName = 'L',
             .description = "Print full build logs on standard error.",
             .category = loggingCategory,
-            .handler = {[&]() {setLogFormat(LogFormat::barWithLogs); }},
+            .handler = {[&]() { logger->setPrintBuildLogs(true); }},
         });
 
         addFlag({
             .longName = "version",
             .description = "Show version information.",
+            .category = miscCategory,
             .handler = {[&]() { showVersion = true; }},
         });
 
@@ -95,12 +96,14 @@ struct NixArgs : virtual MultiCommand, virtual MixCommonArgs
             .longName = "offline",
             .aliases = {"no-net"}, // FIXME: remove
             .description = "Disable substituters and consider all previously downloaded files up-to-date.",
+            .category = miscCategory,
             .handler = {[&]() { useNet = false; }},
         });
 
         addFlag({
             .longName = "refresh",
             .description = "Consider all previously downloaded files out-of-date.",
+            .category = miscCategory,
             .handler = {[&]() { refresh = true; }},
         });
     }
@@ -187,7 +190,7 @@ static void showHelp(std::vector<std::string> subcommand, MultiCommand & topleve
         *vUtils);
 
     auto attrs = state.buildBindings(16);
-    attrs.alloc("command").mkString(toplevel.toJSON().dump());
+    attrs.alloc("toplevel").mkString(toplevel.toJSON().dump());
 
     auto vRes = state.allocValue();
     state.callFunction(*vGenerateManpage, state.allocValue()->mkAttrs(attrs), *vRes, noPos);
@@ -196,7 +199,7 @@ static void showHelp(std::vector<std::string> subcommand, MultiCommand & topleve
     if (!attr)
         throw UsageError("Nix has no subcommand '%s'", concatStringsSep("", subcommand));
 
-    auto markdown = state.forceString(*attr->value);
+    auto markdown = state.forceString(*attr->value, noPos, "while evaluating the lowdown help text");
 
     RunPager pager;
     std::cout << renderMarkdownToTerminal(markdown) << "\n";
@@ -261,9 +264,16 @@ void mainWrapped(int argc, char * * argv)
     }
     #endif
 
+    Finally f([] { logger->stop(); });
+
     programPath = argv[0];
     auto programName = std::string(baseNameOf(programPath));
 
+    if (argc > 1 && std::string_view(argv[1]) == "__build-remote") {
+        programName = "build-remote";
+        argv++; argc--;
+    }
+
     {
         auto legacy = (*RegisterLegacyCommand::commands)[programName];
         if (legacy) return legacy(argc, argv);
@@ -279,8 +289,6 @@ void mainWrapped(int argc, char * * argv)
         verbosity = lvlInfo;
     }
 
-    Finally f([] { logger->stop(); });
-
     NixArgs args;
 
     if (argc == 2 && std::string(argv[1]) == "__dump-args") {
@@ -302,7 +310,7 @@ void mainWrapped(int argc, char * * argv)
             b["arity"] = primOp->arity;
             b["args"] = primOp->args;
             b["doc"] = trim(stripIndentation(primOp->doc));
-            res[(std::string) builtin.name] = std::move(b);
+            res[state.symbols[builtin.name]] = std::move(b);
         }
         std::cout << res.dump() << "\n";
         return;
@@ -320,7 +328,7 @@ void mainWrapped(int argc, char * * argv)
                 std::cout << "attrs\n"; break;
             }
             for (auto & s : *completions)
-                std::cout << s.completion << "\t" << s.description << "\n";
+                std::cout << s.completion << "\t" << trim(s.description) << "\n";
         }
     });
 
@@ -342,7 +350,10 @@ void mainWrapped(int argc, char * * argv)
         if (!completions) throw;
     }
 
-    if (completions) return;
+    if (completions) {
+        args.completionHook();
+        return;
+    }
 
     if (args.showVersion) {
         printVersion(programName);
@@ -380,6 +391,9 @@ void mainWrapped(int argc, char * * argv)
         settings.ttlPositiveNarInfoCache = 0;
     }
 
+    if (args.command->second->forceImpureByDefault() && !evalSettings.pureEval.overridden) {
+        evalSettings.pureEval = false;
+    }
     args.command->second->prepare();
     args.command->second->run();
 }
diff --git a/src/nix/make-content-addressed.cc b/src/nix/make-content-addressed.cc
index 34860c38f..d86b90fc7 100644
--- a/src/nix/make-content-addressed.cc
+++ b/src/nix/make-content-addressed.cc
@@ -2,10 +2,13 @@
 #include "store-api.hh"
 #include "make-content-addressed.hh"
 #include "common-args.hh"
-#include "json.hh"
+
+#include <nlohmann/json.hpp>
 
 using namespace nix;
 
+using nlohmann::json;
+
 struct CmdMakeContentAddressed : virtual CopyCommand, virtual StorePathsCommand, MixJSON
 {
     CmdMakeContentAddressed()
@@ -25,6 +28,7 @@ struct CmdMakeContentAddressed : virtual CopyCommand, virtual StorePathsCommand,
           ;
     }
 
+    using StorePathsCommand::run;
     void run(ref<Store> srcStore, StorePaths && storePaths) override
     {
         auto dstStore = dstUri.empty() ? openStore() : openStore(dstUri);
@@ -33,13 +37,15 @@ struct CmdMakeContentAddressed : virtual CopyCommand, virtual StorePathsCommand,
             StorePathSet(storePaths.begin(), storePaths.end()));
 
         if (json) {
-            JSONObject jsonRoot(std::cout);
-            JSONObject jsonRewrites(jsonRoot.object("rewrites"));
+            auto jsonRewrites = json::object();
             for (auto & path : storePaths) {
                 auto i = remappings.find(path);
                 assert(i != remappings.end());
-                jsonRewrites.attr(srcStore->printStorePath(path), srcStore->printStorePath(i->second));
+                jsonRewrites[srcStore->printStorePath(path)] = srcStore->printStorePath(i->second);
             }
+            auto json = json::object();
+            json["rewrites"] = jsonRewrites;
+            std::cout << json.dump();
         } else {
             for (auto & path : storePaths) {
                 auto i = remappings.find(path);
diff --git a/src/nix/make-content-addressed.md b/src/nix/make-content-addressed.md
index 215683e6d..32eecc880 100644
--- a/src/nix/make-content-addressed.md
+++ b/src/nix/make-content-addressed.md
@@ -22,7 +22,7 @@ R""(
 
   ```console
   # nix copy --to /tmp/nix --trusted-public-keys '' nixpkgs#hello
-  cannot add path '/nix/store/zy9wbxwcygrwnh8n2w9qbbcr6zk87m26-libunistring-0.9.10' because it lacks a valid signature
+  cannot add path '/nix/store/zy9wbxwcygrwnh8n2w9qbbcr6zk87m26-libunistring-0.9.10' because it lacks a signature by a trusted key
   ```
 
 * Create a content-addressed representation of the current NixOS
diff --git a/src/nix/nix.md b/src/nix/nix.md
index 0dacadee6..db60c59ff 100644
--- a/src/nix/nix.md
+++ b/src/nix/nix.md
@@ -115,12 +115,11 @@ the Nix store. Here are the recognised types of installables:
 
 * **Store derivations**: `/nix/store/p7gp6lxdg32h4ka1q398wd9r2zkbbz2v-hello-2.10.drv`
 
-  Store derivations are store paths with extension `.drv` and are a
-  low-level representation of a build-time dependency graph used
-  internally by Nix. By default, if you pass a store derivation to a
-  `nix` subcommand, it will operate on the *output paths* of the
-  derivation. For example, `nix path-info` prints information about
-  the output paths:
+  By default, if you pass a [store derivation] path to a `nix` subcommand, the command will operate on the [output path]s of the derivation.
+
+  [output path]: ../../glossary.md#gloss-output-path
+
+  For example, `nix path-info` prints information about the output paths:
 
   ```console
   # nix path-info --json /nix/store/p7gp6lxdg32h4ka1q398wd9r2zkbbz2v-hello-2.10.drv
@@ -146,6 +145,69 @@ For most commands, if no installable is specified, the default is `.`,
 i.e. Nix will operate on the default flake output attribute of the
 flake in the current directory.
 
+## Derivation output selection
+
+Derivations can have multiple outputs, each corresponding to a
+different store path. For instance, a package can have a `bin` output
+that contains programs, and a `dev` output that provides development
+artifacts like C/C++ header files. The outputs on which `nix` commands
+operate are determined as follows:
+
+* You can explicitly specify the desired outputs using the syntax
+  *installable*`^`*output1*`,`*...*`,`*outputN*. For example, you can
+  obtain the `dev` and `static` outputs of the `glibc` package:
+
+  ```console
+  # nix build 'nixpkgs#glibc^dev,static'
+  # ls ./result-dev/include/ ./result-static/lib/
+  …
+  ```
+
+  and likewise, using a store path to a "drv" file to specify the derivation:
+
+  ```console
+  # nix build '/nix/store/gzaflydcr6sb3567hap9q6srzx8ggdgg-glibc-2.33-78.drv^dev,static'
+  …
+  ```
+
+* You can also specify that *all* outputs should be used using the
+  syntax *installable*`^*`. For example, the following shows the size
+  of all outputs of the `glibc` package in the binary cache:
+
+  ```console
+  # nix path-info -S --eval-store auto --store https://cache.nixos.org 'nixpkgs#glibc^*'
+  /nix/store/g02b1lpbddhymmcjb923kf0l7s9nww58-glibc-2.33-123                 33208200
+  /nix/store/851dp95qqiisjifi639r0zzg5l465ny4-glibc-2.33-123-bin             36142896
+  /nix/store/kdgs3q6r7xdff1p7a9hnjr43xw2404z7-glibc-2.33-123-debug          155787312
+  /nix/store/n4xa8h6pbmqmwnq0mmsz08l38abb06zc-glibc-2.33-123-static          42488328
+  /nix/store/q6580lr01jpcsqs4r5arlh4ki2c1m9rv-glibc-2.33-123-dev             44200560
+  ```
+
+  and likewise, using a store path to a "drv" file to specify the derivation:
+
+  ```console
+  # nix path-info -S '/nix/store/gzaflydcr6sb3567hap9q6srzx8ggdgg-glibc-2.33-78.drv^*'
+  …
+  ```
+* If you didn't specify the desired outputs, but the derivation has an
+  attribute `meta.outputsToInstall`, Nix will use those outputs. For
+  example, since the package `nixpkgs#libxml2` has this attribute:
+
+  ```console
+  # nix eval 'nixpkgs#libxml2.meta.outputsToInstall'
+  [ "bin" "man" ]
+  ```
+
+  a command like `nix shell nixpkgs#libxml2` will provide only those
+  two outputs by default.
+
+  Note that a [store derivation] (given by its `.drv` file store path) doesn't have
+  any attributes like `meta`, and thus this case doesn't apply to it.
+
+  [store derivation]: ../../glossary.md#gloss-store-derivation
+
+* Otherwise, Nix will use all outputs of the derivation.
+
 # Nix stores
 
 Most `nix` subcommands operate on a *Nix store*.
diff --git a/src/nix/path-from-hash-part.cc b/src/nix/path-from-hash-part.cc
new file mode 100644
index 000000000..7f7cda8d3
--- /dev/null
+++ b/src/nix/path-from-hash-part.cc
@@ -0,0 +1,39 @@
+#include "command.hh"
+#include "store-api.hh"
+
+using namespace nix;
+
+struct CmdPathFromHashPart : StoreCommand
+{
+    std::string hashPart;
+
+    CmdPathFromHashPart()
+    {
+        expectArgs({
+            .label = "hash-part",
+            .handler = {&hashPart},
+        });
+    }
+
+    std::string description() override
+    {
+        return "get a store path from its hash part";
+    }
+
+    std::string doc() override
+    {
+        return
+          #include "path-from-hash-part.md"
+          ;
+    }
+
+    void run(ref<Store> store) override
+    {
+        if (auto storePath = store->queryPathFromHashPart(hashPart))
+            logger->cout(store->printStorePath(*storePath));
+        else
+            throw Error("there is no store path corresponding to '%s'", hashPart);
+    }
+};
+
+static auto rCmdPathFromHashPart = registerCommand2<CmdPathFromHashPart>({"store", "path-from-hash-part"});
diff --git a/src/nix/path-from-hash-part.md b/src/nix/path-from-hash-part.md
new file mode 100644
index 000000000..788e13ab6
--- /dev/null
+++ b/src/nix/path-from-hash-part.md
@@ -0,0 +1,20 @@
+R""(
+
+# Examples
+
+* Return the full store path with the given hash part:
+
+  ```console
+  # nix store path-from-hash-part --store https://cache.nixos.org/ 0i2jd68mp5g6h2sa5k9c85rb80sn8hi9
+  /nix/store/0i2jd68mp5g6h2sa5k9c85rb80sn8hi9-hello-2.10
+  ```
+
+# Description
+
+Given the hash part of a store path (that is, the 32 characters
+following `/nix/store/`), return the full store path. This is
+primarily useful in the implementation of binary caches, where a
+request for a `.narinfo` file only supplies the hash part
+(e.g. `https://cache.nixos.org/0i2jd68mp5g6h2sa5k9c85rb80sn8hi9.narinfo`).
+
+)""
diff --git a/src/nix/path-info.cc b/src/nix/path-info.cc
index d690fe594..613c5b191 100644
--- a/src/nix/path-info.cc
+++ b/src/nix/path-info.cc
@@ -1,12 +1,13 @@
 #include "command.hh"
 #include "shared.hh"
 #include "store-api.hh"
-#include "json.hh"
 #include "common-args.hh"
 
 #include <algorithm>
 #include <array>
 
+#include <nlohmann/json.hpp>
+
 using namespace nix;
 
 struct CmdPathInfo : StorePathsCommand, MixJSON
@@ -86,11 +87,10 @@ struct CmdPathInfo : StorePathsCommand, MixJSON
             pathLen = std::max(pathLen, store->printStorePath(storePath).size());
 
         if (json) {
-            JSONPlaceholder jsonRoot(std::cout);
-            store->pathInfoToJSON(jsonRoot,
+            std::cout << store->pathInfoToJSON(
                 // FIXME: preserve order?
                 StorePathSet(storePaths.begin(), storePaths.end()),
-                true, showClosureSize, SRI, AllowInvalid);
+                true, showClosureSize, SRI, AllowInvalid).dump();
         }
 
         else {
diff --git a/src/nix/path-info.md b/src/nix/path-info.md
index 7a1714ba4..b30898ac0 100644
--- a/src/nix/path-info.md
+++ b/src/nix/path-info.md
@@ -68,7 +68,9 @@ R""(
   ]
   ```
 
-* Print the path of the store derivation produced by `nixpkgs#hello`:
+* Print the path of the [store derivation] produced by `nixpkgs#hello`:
+
+  [store derivation]: ../../glossary.md#gloss-store-derivation
 
   ```console
   # nix path-info --derivation nixpkgs#hello
diff --git a/src/nix/prefetch.cc b/src/nix/prefetch.cc
index 35faa7a88..aa302efc1 100644
--- a/src/nix/prefetch.cc
+++ b/src/nix/prefetch.cc
@@ -28,17 +28,17 @@ std::string resolveMirrorUrl(EvalState & state, const std::string & url)
     Value vMirrors;
     // FIXME: use nixpkgs flake
     state.eval(state.parseExprFromString("import <nixpkgs/pkgs/build-support/fetchurl/mirrors.nix>", "."), vMirrors);
-    state.forceAttrs(vMirrors, noPos);
+    state.forceAttrs(vMirrors, noPos, "while evaluating the set of all mirrors");
 
     auto mirrorList = vMirrors.attrs->find(state.symbols.create(mirrorName));
     if (mirrorList == vMirrors.attrs->end())
         throw Error("unknown mirror name '%s'", mirrorName);
-    state.forceList(*mirrorList->value, noPos);
+    state.forceList(*mirrorList->value, noPos, "while evaluating one mirror configuration");
 
     if (mirrorList->value->listSize() < 1)
         throw Error("mirror URL '%s' did not expand to anything", url);
 
-    std::string mirror(state.forceString(*mirrorList->value->listElems()[0]));
+    std::string mirror(state.forceString(*mirrorList->value->listElems()[0], noPos, "while evaluating the first available mirror"));
     return mirror + (hasSuffix(mirror, "/") ? "" : "/") + s.substr(p + 1);
 }
 
@@ -202,27 +202,29 @@ static int main_nix_prefetch_url(int argc, char * * argv)
             Value vRoot;
             state->evalFile(path, vRoot);
             Value & v(*findAlongAttrPath(*state, attrPath, autoArgs, vRoot).first);
-            state->forceAttrs(v, noPos);
+            state->forceAttrs(v, noPos, "while evaluating the source attribute to prefetch");
 
             /* Extract the URL. */
-            auto & attr = v.attrs->need(state->symbols.create("urls"));
-            state->forceList(*attr.value, noPos);
-            if (attr.value->listSize() < 1)
+            auto * attr = v.attrs->get(state->symbols.create("urls"));
+            if (!attr)
+                throw Error("attribute 'urls' missing");
+            state->forceList(*attr->value, noPos, "while evaluating the urls to prefetch");
+            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], noPos, "while evaluating the first url from the urls list");
 
             /* Extract the hash mode. */
             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(*attr2->value) == "recursive";
+                unpack = state->forceString(*attr2->value, noPos, "while evaluating the outputHashMode of the source to prefetch") == "recursive";
 
             /* Extract the name. */
             if (!name) {
                 auto attr3 = v.attrs->get(state->symbols.create("name"));
                 if (!attr3)
-                    name = state->forceString(*attr3->value);
+                    name = state->forceString(*attr3->value, noPos, "while evaluating the name of the source to prefetch");
             }
         }
 
diff --git a/src/nix/profile-install.md b/src/nix/profile-install.md
index e3009491e..aed414963 100644
--- a/src/nix/profile-install.md
+++ b/src/nix/profile-install.md
@@ -20,6 +20,13 @@ R""(
   # nix profile install nixpkgs/d73407e8e6002646acfdef0e39ace088bacc83da#hello
   ```
 
+* Install a specific output of a package:
+
+  ```console
+  # nix profile install nixpkgs#bash^man
+  ```
+
+
 # Description
 
 This command adds *installables* to a Nix profile.
diff --git a/src/nix/profile-list.md b/src/nix/profile-list.md
index bdab9a208..fa786162f 100644
--- a/src/nix/profile-list.md
+++ b/src/nix/profile-list.md
@@ -20,11 +20,11 @@ following fields:
 * An integer that can be used to unambiguously identify the package in
   invocations of `nix profile remove` and `nix profile upgrade`.
 
-* The original ("mutable") flake reference and output attribute path
+* The original ("unlocked") flake reference and output attribute path
   used at installation time.
 
-* The immutable flake reference to which the mutable flake reference
-  was resolved.
+* The locked flake reference to which the unlocked flake reference was
+  resolved.
 
 * The store path(s) of the package.
 
diff --git a/src/nix/profile-upgrade.md b/src/nix/profile-upgrade.md
index e06e74abe..39cca428b 100644
--- a/src/nix/profile-upgrade.md
+++ b/src/nix/profile-upgrade.md
@@ -2,7 +2,7 @@ R""(
 
 # Examples
 
-* Upgrade all packages that were installed using a mutable flake
+* Upgrade all packages that were installed using an unlocked flake
   reference:
 
   ```console
@@ -32,9 +32,9 @@ the package was installed.
 
 > **Warning**
 >
-> This only works if you used a *mutable* flake reference at
+> This only works if you used an *unlocked* flake reference at
 > installation time, e.g. `nixpkgs#hello`. It does not work if you
-> used an *immutable* flake reference
+> used a *locked* flake reference
 > (e.g. `github:NixOS/nixpkgs/13d0c311e3ae923a00f734b43fd1d35b47d8943a#hello`),
 > since in that case the "latest version" is always the same.
 
diff --git a/src/nix/profile.cc b/src/nix/profile.cc
index 3a32a7b55..024849e3b 100644
--- a/src/nix/profile.cc
+++ b/src/nix/profile.cc
@@ -22,13 +22,13 @@ struct ProfileElementSource
     // FIXME: record original attrpath.
     FlakeRef resolvedRef;
     std::string attrPath;
-    // FIXME: output names
+    OutputsSpec outputs;
 
     bool operator < (const ProfileElementSource & other) const
     {
         return
-            std::pair(originalRef.to_string(), attrPath) <
-            std::pair(other.originalRef.to_string(), other.attrPath);
+            std::tuple(originalRef.to_string(), attrPath, outputs) <
+            std::tuple(other.originalRef.to_string(), other.attrPath, other.outputs);
     }
 };
 
@@ -37,12 +37,12 @@ struct ProfileElement
     StorePathSet storePaths;
     std::optional<ProfileElementSource> source;
     bool active = true;
-    // FIXME: priority
+    int priority = 5;
 
     std::string describe() const
     {
         if (source)
-            return fmt("%s#%s", source->originalRef, source->attrPath);
+            return fmt("%s#%s%s", source->originalRef, source->attrPath, printOutputsSpec(source->outputs));
         StringSet names;
         for (auto & path : storePaths)
             names.insert(DrvName(path.name()).name);
@@ -67,7 +67,6 @@ struct ProfileElement
         ref<Store> store,
         const BuiltPaths & builtPaths)
     {
-        // FIXME: respect meta.outputsToInstall
         storePaths.clear();
         for (auto & buildable : builtPaths) {
             std::visit(overloaded {
@@ -99,7 +98,7 @@ struct ProfileManifest
             auto version = json.value("version", 0);
             std::string sUrl;
             std::string sOriginalUrl;
-            switch(version){
+            switch (version) {
                 case 1:
                     sUrl = "uri";
                     sOriginalUrl = "originalUri";
@@ -117,11 +116,15 @@ struct ProfileManifest
                 for (auto & p : e["storePaths"])
                     element.storePaths.insert(state.store->parseStorePath((std::string) p));
                 element.active = e["active"];
-                if (e.value(sUrl,"") != "") {
-                    element.source = ProfileElementSource{
+                if(e.contains("priority")) {
+                    element.priority = e["priority"];
+                }
+                if (e.value(sUrl, "") != "") {
+                    element.source = ProfileElementSource {
                         parseFlakeRef(e[sOriginalUrl]),
                         parseFlakeRef(e[sUrl]),
-                        e["attrPath"]
+                        e["attrPath"],
+                        e["outputs"].get<OutputsSpec>()
                     };
                 }
                 elements.emplace_back(std::move(element));
@@ -153,10 +156,12 @@ struct ProfileManifest
             nlohmann::json obj;
             obj["storePaths"] = paths;
             obj["active"] = element.active;
+            obj["priority"] = element.priority;
             if (element.source) {
                 obj["originalUrl"] = element.source->originalRef.to_string();
                 obj["url"] = element.source->resolvedRef.to_string();
                 obj["attrPath"] = element.source->attrPath;
+                obj["outputs"] = element.source->outputs;
             }
             array.push_back(obj);
         }
@@ -176,7 +181,7 @@ struct ProfileManifest
         for (auto & element : elements) {
             for (auto & path : element.storePaths) {
                 if (element.active)
-                    pkgs.emplace_back(store->printStorePath(path), true, 5);
+                    pkgs.emplace_back(store->printStorePath(path), true, element.priority);
                 references.insert(path);
             }
         }
@@ -257,16 +262,27 @@ struct ProfileManifest
 
 static std::map<Installable *, BuiltPaths>
 builtPathsPerInstallable(
-    const std::vector<std::pair<std::shared_ptr<Installable>, BuiltPath>> & builtPaths)
+    const std::vector<std::pair<std::shared_ptr<Installable>, BuiltPathWithResult>> & builtPaths)
 {
     std::map<Installable *, BuiltPaths> res;
     for (auto & [installable, builtPath] : builtPaths)
-        res[installable.get()].push_back(builtPath);
+        res[installable.get()].push_back(builtPath.path);
     return res;
 }
 
 struct CmdProfileInstall : InstallablesCommand, MixDefaultProfile
 {
+    std::optional<int64_t> priority;
+
+    CmdProfileInstall() {
+        addFlag({
+            .longName = "priority",
+            .description = "The priority of the package to install.",
+            .labels = {"priority"},
+            .handler = {&priority},
+        });
+    };
+
     std::string description() override
     {
         return "install a package into a profile";
@@ -290,16 +306,27 @@ struct CmdProfileInstall : InstallablesCommand, MixDefaultProfile
         for (auto & installable : installables) {
             ProfileElement element;
 
+
+
             if (auto installable2 = std::dynamic_pointer_cast<InstallableFlake>(installable)) {
                 // FIXME: make build() return this?
                 auto [attrPath, resolvedRef, drv] = installable2->toDerivation();
-                element.source = ProfileElementSource{
+                element.source = ProfileElementSource {
                     installable2->flakeRef,
                     resolvedRef,
                     attrPath,
+                    installable2->outputsSpec
                 };
+
+                if(drv.priority) {
+                    element.priority = *drv.priority;
+                }
             }
 
+            if(priority) { // if --priority was specified we want to override the priority of the installable
+                element.priority = *priority;
+            };
+
             element.updateStorePaths(getEvalStore(), store, builtPaths[installable.get()]);
 
             manifest.elements.push_back(std::move(element));
@@ -453,6 +480,7 @@ struct CmdProfileUpgrade : virtual SourceExprCommand, MixDefaultProfile, MixProf
                     getEvalState(),
                     FlakeRef(element.source->originalRef),
                     "",
+                    element.source->outputs,
                     Strings{element.source->attrPath},
                     Strings{},
                     lockFlags);
@@ -464,10 +492,11 @@ struct CmdProfileUpgrade : virtual SourceExprCommand, MixDefaultProfile, MixProf
                 printInfo("upgrading '%s' from flake '%s' to '%s'",
                     element.source->attrPath, element.source->resolvedRef, resolvedRef);
 
-                element.source = ProfileElementSource{
+                element.source = ProfileElementSource {
                     installable->flakeRef,
                     resolvedRef,
                     attrPath,
+                    installable->outputsSpec
                 };
 
                 installables.push_back(installable);
@@ -523,8 +552,8 @@ struct CmdProfileList : virtual EvalCommand, virtual StoreCommand, MixDefaultPro
         for (size_t i = 0; i < manifest.elements.size(); ++i) {
             auto & element(manifest.elements[i]);
             logger->cout("%d %s %s %s", i,
-                element.source ? element.source->originalRef.to_string() + "#" + element.source->attrPath : "-",
-                element.source ? element.source->resolvedRef.to_string() + "#" + element.source->attrPath : "-",
+                element.source ? element.source->originalRef.to_string() + "#" + element.source->attrPath + printOutputsSpec(element.source->outputs) : "-",
+                element.source ? element.source->resolvedRef.to_string() + "#" + element.source->attrPath + printOutputsSpec(element.source->outputs) : "-",
                 concatStringsSep(" ", store->printStorePathSet(element.storePaths)));
         }
     }
diff --git a/src/nix/profile.md b/src/nix/profile.md
index 8dade051d..273e02280 100644
--- a/src/nix/profile.md
+++ b/src/nix/profile.md
@@ -11,7 +11,7 @@ them to be rolled back easily.
 
 The default profile used by `nix profile` is `$HOME/.nix-profile`,
 which, if it does not exist, is created as a symlink to
-`/nix/var/nix/profiles/per-user/default` if Nix is invoked by the
+`/nix/var/nix/profiles/default` if Nix is invoked by the
 `root` user, or `/nix/var/nix/profiles/per-user/`*username* otherwise.
 
 You can specify another profile location using `--profile` *path*.
@@ -88,8 +88,7 @@ has the following fields:
   the user at the time of installation (e.g. `nixpkgs`). This is also
   the flake reference that will be used by `nix profile upgrade`.
 
-* `uri`: The immutable flake reference to which `originalUrl`
-  resolved.
+* `uri`: The locked flake reference to which `originalUrl` resolved.
 
 * `attrPath`: The flake output attribute that provided this
   package. Note that this is not necessarily the attribute that the
diff --git a/src/nix/registry.cc b/src/nix/registry.cc
index c496f94f8..b5bdfba95 100644
--- a/src/nix/registry.cc
+++ b/src/nix/registry.cc
@@ -183,14 +183,12 @@ struct CmdRegistryPin : RegistryCommand, EvalCommand
 
     void run(nix::ref<nix::Store> store) override
     {
-        if (locked.empty()) {
-            locked = url;
-        }
+        if (locked.empty()) locked = url;
         auto registry = getRegistry();
         auto ref = parseFlakeRef(url);
-        auto locked_ref = parseFlakeRef(locked);
+        auto lockedRef = parseFlakeRef(locked);
         registry->remove(ref.input);
-        auto [tree, resolved] = locked_ref.resolve(store).input.fetch(store);
+        auto [tree, resolved] = lockedRef.resolve(store).input.fetch(store);
         fetchers::Attrs extraAttrs;
         if (ref.subdir != "") extraAttrs["dir"] = ref.subdir;
         registry->add(ref.input, resolved, extraAttrs);
diff --git a/src/nix/registry.md b/src/nix/registry.md
index d5c9ef442..bd3575d1b 100644
--- a/src/nix/registry.md
+++ b/src/nix/registry.md
@@ -29,7 +29,7 @@ highest precedence:
   can be specified using the NixOS option `nix.registry`.
 
 * The user registry `~/.config/nix/registry.json`. This registry can
-  be modified by commands such as `nix flake pin`.
+  be modified by commands such as `nix registry pin`.
 
 * Overrides specified on the command line using the option
   `--override-flake`.
diff --git a/src/nix/repl.cc b/src/nix/repl.cc
deleted file mode 100644
index 1f9d4fb4e..000000000
--- a/src/nix/repl.cc
+++ /dev/null
@@ -1,913 +0,0 @@
-#include <iostream>
-#include <cstdlib>
-#include <cstring>
-#include <climits>
-
-#include <setjmp.h>
-
-#ifdef READLINE
-#include <readline/history.h>
-#include <readline/readline.h>
-#else
-// editline < 1.15.2 don't wrap their API for C++ usage
-// (added in https://github.com/troglobit/editline/commit/91398ceb3427b730995357e9d120539fb9bb7461).
-// This results in linker errors due to to name-mangling of editline C symbols.
-// For compatibility with these versions, we wrap the API here
-// (wrapping multiple times on newer versions is no problem).
-extern "C" {
-#include <editline.h>
-}
-#endif
-
-#include "ansicolor.hh"
-#include "shared.hh"
-#include "eval.hh"
-#include "eval-inline.hh"
-#include "attr-path.hh"
-#include "store-api.hh"
-#include "log-store.hh"
-#include "common-eval-args.hh"
-#include "get-drvs.hh"
-#include "derivations.hh"
-#include "globals.hh"
-#include "command.hh"
-#include "finally.hh"
-#include "markdown.hh"
-
-#if HAVE_BOEHMGC
-#define GC_INCLUDE_NEW
-#include <gc/gc_cpp.h>
-#endif
-
-namespace nix {
-
-struct NixRepl
-    #if HAVE_BOEHMGC
-    : gc
-    #endif
-{
-    std::string curDir;
-    std::unique_ptr<EvalState> state;
-    Bindings * autoArgs;
-
-    Strings loadedFiles;
-
-    const static int envSize = 32768;
-    StaticEnv staticEnv;
-    Env * env;
-    int displ;
-    StringSet varNames;
-
-    const Path historyFile;
-
-    NixRepl(const Strings & searchPath, nix::ref<Store> store);
-    ~NixRepl();
-    void mainLoop(const std::vector<std::string> & files);
-    StringSet completePrefix(const std::string & prefix);
-    bool getLine(std::string & input, const std::string &prompt);
-    StorePath getDerivationPath(Value & v);
-    bool processLine(std::string line);
-    void loadFile(const Path & path);
-    void loadFlake(const std::string & flakeRef);
-    void initEnv();
-    void reloadFiles();
-    void addAttrsToScope(Value & attrs);
-    void addVarToScope(const Symbol & name, Value & v);
-    Expr * parseString(std::string s);
-    void evalString(std::string s, Value & v);
-
-    typedef std::set<Value *> ValuesSeen;
-    std::ostream &  printValue(std::ostream & str, Value & v, unsigned int maxDepth);
-    std::ostream &  printValue(std::ostream & str, Value & v, unsigned int maxDepth, ValuesSeen & seen);
-};
-
-
-std::string removeWhitespace(std::string s)
-{
-    s = chomp(s);
-    size_t n = s.find_first_not_of(" \n\r\t");
-    if (n != std::string::npos) s = std::string(s, n);
-    return s;
-}
-
-
-NixRepl::NixRepl(const Strings & searchPath, nix::ref<Store> store)
-    : state(std::make_unique<EvalState>(searchPath, store))
-    , staticEnv(false, &state->staticBaseEnv)
-    , historyFile(getDataDir() + "/nix/repl-history")
-{
-    curDir = absPath(".");
-}
-
-
-NixRepl::~NixRepl()
-{
-    write_history(historyFile.c_str());
-}
-
-std::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) {
-  auto possible = curRepl->completePrefix(s);
-  if (possible.size() == 1) {
-    *match = 1;
-    auto *res = strdup(possible.begin()->c_str() + strlen(s));
-    if (!res) throw Error("allocation failure");
-    return res;
-  } else if (possible.size() > 1) {
-    auto checkAllHaveSameAt = [&](size_t pos) {
-      auto &first = *possible.begin();
-      for (auto &p : possible) {
-        if (p.size() <= pos || p[pos] != first[pos])
-          return false;
-      }
-      return true;
-    };
-    size_t start = strlen(s);
-    size_t len = 0;
-    while (checkAllHaveSameAt(start + len)) ++len;
-    if (len > 0) {
-      *match = 1;
-      auto *res = strdup(std::string(*possible.begin(), start, len).c_str());
-      if (!res) throw Error("allocation failure");
-      return res;
-    }
-  }
-
-  *match = 0;
-  return nullptr;
-}
-
-static int listPossibleCallback(char *s, char ***avp) {
-  auto possible = curRepl->completePrefix(s);
-
-  if (possible.size() > (INT_MAX / sizeof(char*)))
-    throw Error("too many completions");
-
-  int ac = 0;
-  char **vp = nullptr;
-
-  auto check = [&](auto *p) {
-    if (!p) {
-      if (vp) {
-        while (--ac >= 0)
-          free(vp[ac]);
-        free(vp);
-      }
-      throw Error("allocation failure");
-    }
-    return p;
-  };
-
-  vp = check((char **)malloc(possible.size() * sizeof(char*)));
-
-  for (auto & p : possible)
-    vp[ac++] = check(strdup(p.c_str()));
-
-  *avp = vp;
-
-  return ac;
-}
-
-namespace {
-    // Used to communicate to NixRepl::getLine whether a signal occurred in ::readline.
-    volatile sig_atomic_t g_signal_received = 0;
-
-    void sigintHandler(int signo) {
-        g_signal_received = signo;
-    }
-}
-
-void NixRepl::mainLoop(const std::vector<std::string> & files)
-{
-    std::string error = ANSI_RED "error:" ANSI_NORMAL " ";
-    notice("Welcome to Nix " + nixVersion + ". Type :? for help.\n");
-
-    for (auto & i : files)
-        loadedFiles.push_back(i);
-
-    reloadFiles();
-    if (!loadedFiles.empty()) notice("");
-
-    // Allow nix-repl specific settings in .inputrc
-    rl_readline_name = "nix-repl";
-    createDirs(dirOf(historyFile));
-#ifndef READLINE
-    el_hist_size = 1000;
-#endif
-    read_history(historyFile.c_str());
-    curRepl = this;
-#ifndef READLINE
-    rl_set_complete_func(completionCallback);
-    rl_set_list_possib_func(listPossibleCallback);
-#endif
-
-    std::string input;
-
-    while (true) {
-        // When continuing input from previous lines, don't print a prompt, just align to the same
-        // number of chars as the prompt.
-        if (!getLine(input, input.empty() ? "nix-repl> " : "          "))
-            break;
-
-        try {
-            if (!removeWhitespace(input).empty() && !processLine(input)) return;
-        } catch (ParseError & e) {
-            if (e.msg().find("unexpected end of file") != std::string::npos) {
-                // For parse errors on incomplete input, we continue waiting for the next line of
-                // input without clearing the input so far.
-                continue;
-            } else {
-              printMsg(lvlError, e.msg());
-            }
-        } catch (Error & e) {
-            printMsg(lvlError, e.msg());
-        } catch (Interrupted & e) {
-            printMsg(lvlError, e.msg());
-        }
-
-        // We handled the current input fully, so we should clear it
-        // and read brand new input.
-        input.clear();
-        std::cout << std::endl;
-    }
-}
-
-
-bool NixRepl::getLine(std::string & input, const std::string & prompt)
-{
-    struct sigaction act, old;
-    sigset_t savedSignalMask, set;
-
-    auto setupSignals = [&]() {
-        act.sa_handler = sigintHandler;
-        sigfillset(&act.sa_mask);
-        act.sa_flags = 0;
-        if (sigaction(SIGINT, &act, &old))
-            throw SysError("installing handler for SIGINT");
-
-        sigemptyset(&set);
-        sigaddset(&set, SIGINT);
-        if (sigprocmask(SIG_UNBLOCK, &set, &savedSignalMask))
-            throw SysError("unblocking SIGINT");
-    };
-    auto restoreSignals = [&]() {
-        if (sigprocmask(SIG_SETMASK, &savedSignalMask, nullptr))
-            throw SysError("restoring signals");
-
-        if (sigaction(SIGINT, &old, 0))
-            throw SysError("restoring handler for SIGINT");
-    };
-
-    setupSignals();
-    Finally resetTerminal([&]() { rl_deprep_terminal(); });
-    char * s = readline(prompt.c_str());
-    Finally doFree([&]() { free(s); });
-    restoreSignals();
-
-    if (g_signal_received) {
-        g_signal_received = 0;
-        input.clear();
-        return true;
-    }
-
-    if (!s)
-      return false;
-    input += s;
-    input += '\n';
-    return true;
-}
-
-
-StringSet NixRepl::completePrefix(const std::string & prefix)
-{
-    StringSet completions;
-
-    size_t start = prefix.find_last_of(" \n\r\t(){}[]");
-    std::string prev, cur;
-    if (start == std::string::npos) {
-        prev = "";
-        cur = prefix;
-    } else {
-        prev = std::string(prefix, 0, start + 1);
-        cur = std::string(prefix, start + 1);
-    }
-
-    size_t slash, dot;
-
-    if ((slash = cur.rfind('/')) != std::string::npos) {
-        try {
-            auto dir = std::string(cur, 0, slash);
-            auto prefix2 = std::string(cur, slash + 1);
-            for (auto & entry : readDirectory(dir == "" ? "/" : dir)) {
-                if (entry.name[0] != '.' && hasPrefix(entry.name, prefix2))
-                    completions.insert(prev + dir + "/" + entry.name);
-            }
-        } catch (Error &) {
-        }
-    } else if ((dot = cur.rfind('.')) == std::string::npos) {
-        /* This is a variable name; look it up in the current scope. */
-        StringSet::iterator i = varNames.lower_bound(cur);
-        while (i != varNames.end()) {
-            if (i->substr(0, cur.size()) != cur) break;
-            completions.insert(prev + *i);
-            i++;
-        }
-    } else {
-        try {
-            /* This is an expression that should evaluate to an
-               attribute set.  Evaluate it to get the names of the
-               attributes. */
-            auto expr = cur.substr(0, dot);
-            auto cur2 = cur.substr(dot + 1);
-
-            Expr * e = parseString(expr);
-            Value v;
-            e->eval(*state, *env, v);
-            state->forceAttrs(v, noPos);
-
-            for (auto & i : *v.attrs) {
-                std::string name = i.name;
-                if (name.substr(0, cur2.size()) != cur2) continue;
-                completions.insert(prev + expr + "." + name);
-            }
-
-        } catch (ParseError & e) {
-            // Quietly ignore parse errors.
-        } catch (EvalError & e) {
-            // Quietly ignore evaluation errors.
-        } catch (UndefinedVarError & e) {
-            // Quietly ignore undefined variable errors.
-        } catch (BadURL & e) {
-            // Quietly ignore BadURL flake-related errors.
-        }
-    }
-
-    return completions;
-}
-
-
-static bool isVarName(std::string_view s)
-{
-    if (s.size() == 0) return false;
-    char c = s[0];
-    if ((c >= '0' && c <= '9') || c == '-' || c == '\'') return false;
-    for (auto & i : s)
-        if (!((i >= 'a' && i <= 'z') ||
-              (i >= 'A' && i <= 'Z') ||
-              (i >= '0' && i <= '9') ||
-              i == '_' || i == '-' || i == '\''))
-            return false;
-    return true;
-}
-
-
-StorePath NixRepl::getDerivationPath(Value & v) {
-    auto drvInfo = getDerivation(*state, v, false);
-    if (!drvInfo)
-        throw Error("expression does not evaluate to a derivation, so I can't build it");
-    auto drvPath = drvInfo->queryDrvPath();
-    if (!drvPath)
-        throw Error("expression did not evaluate to a valid derivation (no 'drvPath' attribute)");
-    if (!state->store->isValidPath(*drvPath))
-        throw Error("expression evaluated to invalid derivation '%s'", state->store->printStorePath(*drvPath));
-    return *drvPath;
-}
-
-
-bool NixRepl::processLine(std::string line)
-{
-    line = trim(line);
-    if (line == "") return true;
-
-    _isInterrupted = false;
-
-    std::string command, arg;
-
-    if (line[0] == ':') {
-        size_t p = line.find_first_of(" \n\r\t");
-        command = line.substr(0, p);
-        if (p != std::string::npos) arg = removeWhitespace(line.substr(p));
-    } else {
-        arg = line;
-    }
-
-    if (command == ":?" || command == ":help") {
-        // FIXME: convert to Markdown, include in the 'nix repl' manpage.
-        std::cout
-             << "The following commands are available:\n"
-             << "\n"
-             << "  <expr>        Evaluate and print expression\n"
-             << "  <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 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"
-             << "  :s <expr>     Build dependencies of derivation, then start nix-shell\n"
-             << "  :t <expr>     Describe result of evaluation\n"
-             << "  :u <expr>     Build derivation, then start nix-shell\n"
-             << "  :doc <expr>   Show documentation of a builtin function\n"
-             << "  :log <expr>   Show logs for a derivation\n"
-             << "  :st [bool]    Enable, disable or toggle showing traces for errors\n";
-    }
-
-    else if (command == ":a" || command == ":add") {
-        Value v;
-        evalString(arg, v);
-        addAttrsToScope(v);
-    }
-
-    else if (command == ":l" || command == ":load") {
-        state->resetFileCache();
-        loadFile(arg);
-    }
-
-    else if (command == ":lf" || command == ":load-flake") {
-        loadFlake(arg);
-    }
-
-    else if (command == ":r" || command == ":reload") {
-        state->resetFileCache();
-        reloadFiles();
-    }
-
-    else if (command == ":e" || command == ":edit") {
-        Value v;
-        evalString(arg, v);
-
-        Pos pos;
-
-        if (v.type() == nPath || v.type() == nString) {
-            PathSet context;
-            auto filename = state->coerceToString(noPos, v, context);
-            pos.file = state->symbols.create(*filename);
-        } else if (v.isLambda()) {
-            pos = v.lambda.fun->pos;
-        } else {
-            // assume it's a derivation
-            pos = findPackageFilename(*state, v, arg);
-        }
-
-        // Open in EDITOR
-        auto args = editorFor(pos);
-        auto editor = args.front();
-        args.pop_front();
-
-        // 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();
-        reloadFiles();
-    }
-
-    else if (command == ":t") {
-        Value v;
-        evalString(arg, v);
-        logger->cout(showType(v));
-    }
-
-    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);
-        runNix("nix-shell", {state->store->printStorePath(drvPath)});
-    }
-
-    else if (command == ":b" || command == ":i" || command == ":s" || command == ":log") {
-        Value v;
-        evalString(arg, v);
-        StorePath drvPath = getDerivationPath(v);
-        Path drvPathRaw = state->store->printStorePath(drvPath);
-
-        if (command == ":b") {
-            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") {
-            runNix("nix-env", {"-i", drvPathRaw});
-        } else if (command == ":log") {
-            settings.readOnlyMode = true;
-            Finally roModeReset([&]() {
-                settings.readOnlyMode = false;
-            });
-            auto subs = getDefaultSubstituters();
-
-            subs.push_front(state->store);
-
-            bool foundLog = false;
-            RunPager pager;
-            for (auto & sub : subs) {
-                auto * logSubP = dynamic_cast<LogStore *>(&*sub);
-                if (!logSubP) {
-                    printInfo("Skipped '%s' which does not support retrieving build logs", sub->getUri());
-                    continue;
-                }
-                auto & logSub = *logSubP;
-
-                auto log = logSub.getBuildLog(drvPath);
-                if (log) {
-                    printInfo("got build log for '%s' from '%s'", drvPathRaw, logSub.getUri());
-                    logger->writeToStdout(*log);
-                    foundLog = true;
-                    break;
-                }
-            }
-            if (!foundLog) throw Error("build log of '%s' is not available", drvPathRaw);
-        } else {
-            runNix("nix-shell", {drvPathRaw});
-        }
-    }
-
-    else if (command == ":p" || command == ":print") {
-        Value v;
-        evalString(arg, v);
-        printValue(std::cout, v, 1000000000) << std::endl;
-    }
-
-    else if (command == ":q" || command == ":quit")
-        return false;
-
-    else if (command == ":doc") {
-        Value v;
-        evalString(arg, v);
-        if (auto doc = state->getDoc(v)) {
-            std::string markdown;
-
-            if (!doc->args.empty() && doc->name) {
-                auto args = doc->args;
-                for (auto & arg : args)
-                    arg = "*" + arg + "*";
-
-                markdown +=
-                    "**Synopsis:** `builtins." + (std::string) (*doc->name) + "` "
-                    + concatStringsSep(" ", args) + "\n\n";
-            }
-
-            markdown += stripIndentation(doc->doc);
-
-            logger->cout(trim(renderMarkdownToTerminal(markdown)));
-        } else
-            throw Error("value does not have documentation");
-    }
-
-    else if (command == ":st" || command == ":show-trace") {
-        if (arg == "false" || (arg == "" && loggerSettings.showTrace)) {
-            std::cout << "not showing error traces\n";
-            loggerSettings.showTrace = false;
-        } else if (arg == "true" || (arg == "" && !loggerSettings.showTrace)) {
-            std::cout << "showing error traces\n";
-            loggerSettings.showTrace = true;
-        } else {
-            throw Error("unexpected argument '%s' to %s", arg, command);
-        };
-    }
-
-    else if (command != "")
-        throw Error("unknown command '%1%'", command);
-
-    else {
-        size_t p = line.find('=');
-        std::string name;
-        if (p != std::string::npos &&
-            p < line.size() &&
-            line[p + 1] != '=' &&
-            isVarName(name = removeWhitespace(line.substr(0, p))))
-        {
-            Expr * e = parseString(line.substr(p + 1));
-            Value & v(*state->allocValue());
-            v.mkThunk(env, e);
-            addVarToScope(state->symbols.create(name), v);
-        } else {
-            Value v;
-            evalString(line, v);
-            printValue(std::cout, v, 1) << std::endl;
-        }
-    }
-
-    return true;
-}
-
-
-void NixRepl::loadFile(const Path & path)
-{
-    loadedFiles.remove(path);
-    loadedFiles.push_back(path);
-    Value v, v2;
-    state->evalFile(lookupFileArg(*state, path), v);
-    state->autoCallFunction(*autoArgs, v, v2);
-    addAttrsToScope(v2);
-}
-
-void NixRepl::loadFlake(const std::string & flakeRefS)
-{
-    if (flakeRefS.empty())
-        throw Error("cannot use ':load-flake' without a path specified. (Use '.' for the current working directory.)");
-
-    auto flakeRef = parseFlakeRef(flakeRefS, absPath("."), true);
-    if (evalSettings.pureEval && !flakeRef.input.isLocked())
-        throw Error("cannot use ':load-flake' on locked 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()
-{
-    env = &state->allocEnv(envSize);
-    env->up = &state->baseEnv;
-    displ = 0;
-    staticEnv.vars.clear();
-
-    varNames.clear();
-    for (auto & i : state->staticBaseEnv.vars)
-        varNames.insert(i.first);
-}
-
-
-void NixRepl::reloadFiles()
-{
-    initEnv();
-
-    Strings old = loadedFiles;
-    loadedFiles.clear();
-
-    bool first = true;
-    for (auto & i : old) {
-        if (!first) notice("");
-        first = false;
-        notice("Loading '%1%'...", i);
-        loadFile(i);
-    }
-}
-
-
-void NixRepl::addAttrsToScope(Value & attrs)
-{
-    state->forceAttrs(attrs, [&]() { return attrs.determinePos(noPos); });
-    if (displ + attrs.attrs->size() >= envSize)
-        throw Error("environment full; cannot add more variables");
-
-    for (auto & i : *attrs.attrs) {
-        staticEnv.vars.emplace_back(i.name, displ);
-        env->values[displ++] = i.value;
-        varNames.insert((std::string) i.name);
-    }
-    staticEnv.sort();
-    staticEnv.deduplicate();
-    notice("Added %1% variables.", attrs.attrs->size());
-}
-
-
-void NixRepl::addVarToScope(const Symbol & name, Value & v)
-{
-    if (displ >= envSize)
-        throw Error("environment full; cannot add more variables");
-    if (auto oldVar = staticEnv.find(name); oldVar != staticEnv.vars.end())
-        staticEnv.vars.erase(oldVar);
-    staticEnv.vars.emplace_back(name, displ);
-    staticEnv.sort();
-    env->values[displ++] = &v;
-    varNames.insert((std::string) name);
-}
-
-
-Expr * NixRepl::parseString(std::string s)
-{
-    Expr * e = state->parseExprFromString(std::move(s), curDir, staticEnv);
-    return e;
-}
-
-
-void NixRepl::evalString(std::string s, Value & v)
-{
-    Expr * e = parseString(s);
-    e->eval(*state, *env, v);
-    state->forceValue(v, [&]() { return v.determinePos(noPos); });
-}
-
-
-std::ostream & NixRepl::printValue(std::ostream & str, Value & v, unsigned int maxDepth)
-{
-    ValuesSeen seen;
-    return printValue(str, v, maxDepth, seen);
-}
-
-
-std::ostream & printStringValue(std::ostream & str, const char * string) {
-    str << "\"";
-    for (const char * i = string; *i; i++)
-        if (*i == '\"' || *i == '\\') str << "\\" << *i;
-        else if (*i == '\n') str << "\\n";
-        else if (*i == '\r') str << "\\r";
-        else if (*i == '\t') str << "\\t";
-        else str << *i;
-    str << "\"";
-    return str;
-}
-
-
-// FIXME: lot of cut&paste from Nix's eval.cc.
-std::ostream & NixRepl::printValue(std::ostream & str, Value & v, unsigned int maxDepth, ValuesSeen & seen)
-{
-    str.flush();
-    checkInterrupt();
-
-    state->forceValue(v, [&]() { return v.determinePos(noPos); });
-
-    switch (v.type()) {
-
-    case nInt:
-        str << ANSI_CYAN << v.integer << ANSI_NORMAL;
-        break;
-
-    case nBool:
-        str << ANSI_CYAN << (v.boolean ? "true" : "false") << ANSI_NORMAL;
-        break;
-
-    case nString:
-        str << ANSI_WARNING;
-        printStringValue(str, v.string.s);
-        str << ANSI_NORMAL;
-        break;
-
-    case nPath:
-        str << ANSI_GREEN << v.path << ANSI_NORMAL; // !!! escaping?
-        break;
-
-    case nNull:
-        str << ANSI_CYAN "null" ANSI_NORMAL;
-        break;
-
-    case nAttrs: {
-        seen.insert(&v);
-
-        bool isDrv = state->isDerivation(v);
-
-        if (isDrv) {
-            str << "«derivation ";
-            Bindings::iterator i = v.attrs->find(state->sDrvPath);
-            PathSet context;
-            if (i != v.attrs->end())
-                str << state->store->printStorePath(state->coerceToStorePath(*i->pos, *i->value, context));
-            else
-                str << "???";
-            str << "»";
-        }
-
-        else if (maxDepth > 0) {
-            str << "{ ";
-
-            typedef std::map<std::string, Value *> Sorted;
-            Sorted sorted;
-            for (auto & i : *v.attrs)
-                sorted[i.name] = i.value;
-
-            for (auto & i : sorted) {
-                if (isVarName(i.first))
-                    str << i.first;
-                else
-                    printStringValue(str, i.first.c_str());
-                str << " = ";
-                if (seen.count(i.second))
-                    str << "«repeated»";
-                else
-                    try {
-                        printValue(str, *i.second, maxDepth - 1, seen);
-                    } catch (AssertionError & e) {
-                        str << ANSI_RED "«error: " << e.msg() << "»" ANSI_NORMAL;
-                    }
-                str << "; ";
-            }
-
-            str << "}";
-        } else
-            str << "{ ... }";
-
-        break;
-    }
-
-    case nList:
-        seen.insert(&v);
-
-        str << "[ ";
-        if (maxDepth > 0)
-            for (auto elem : v.listItems()) {
-                if (seen.count(elem))
-                    str << "«repeated»";
-                else
-                    try {
-                        printValue(str, *elem, maxDepth - 1, seen);
-                    } catch (AssertionError & e) {
-                        str << ANSI_RED "«error: " << e.msg() << "»" ANSI_NORMAL;
-                    }
-                str << " ";
-            }
-        else
-            str << "... ";
-        str << "]";
-        break;
-
-    case nFunction:
-        if (v.isLambda()) {
-            std::ostringstream s;
-            s << v.lambda.fun->pos;
-            str << ANSI_BLUE "«lambda @ " << filterANSIEscapes(s.str()) << "»" ANSI_NORMAL;
-        } else if (v.isPrimOp()) {
-            str << ANSI_MAGENTA "«primop»" ANSI_NORMAL;
-        } else if (v.isPrimOpApp()) {
-            str << ANSI_BLUE "«primop-app»" ANSI_NORMAL;
-        } else {
-            abort();
-        }
-        break;
-
-    case nFloat:
-        str << v.fpoint;
-        break;
-
-    default:
-        str << ANSI_RED "«unknown»" ANSI_NORMAL;
-        break;
-    }
-
-    return str;
-}
-
-struct CmdRepl : StoreCommand, MixEvalArgs
-{
-    std::vector<std::string> files;
-
-    CmdRepl()
-    {
-        expectArgs({
-            .label = "files",
-            .handler = {&files},
-            .completer = completePath
-        });
-    }
-
-    std::string description() override
-    {
-        return "start an interactive environment for evaluating Nix expressions";
-    }
-
-    std::string doc() override
-    {
-        return
-          #include "repl.md"
-          ;
-    }
-
-    void run(ref<Store> store) override
-    {
-        evalSettings.pureEval = false;
-        auto repl = std::make_unique<NixRepl>(searchPath, openStore());
-        repl->autoArgs = getAutoArgs(*repl->state);
-        repl->mainLoop(files);
-    }
-};
-
-static auto rCmdRepl = registerCommand<CmdRepl>("repl");
-
-}
diff --git a/src/nix/repl.md b/src/nix/repl.md
index 9b6f2bee3..c5113be61 100644
--- a/src/nix/repl.md
+++ b/src/nix/repl.md
@@ -24,10 +24,34 @@ R""(
 * Interact with Nixpkgs in the REPL:
 
   ```console
-  # nix repl '<nixpkgs>'
+  # nix repl --file example.nix
+  Loading Installable ''...
+  Added 3 variables.
 
-  Loading '<nixpkgs>'...
-  Added 12428 variables.
+  # nix repl --expr '{a={b=3;c=4;};}'
+  Loading Installable ''...
+  Added 1 variables.
+
+  # nix repl --expr '{a={b=3;c=4;};}' a
+  Loading Installable ''...
+  Added 1 variables.
+
+  # nix repl --extra-experimental-features 'flakes repl-flake' nixpkgs
+  Loading Installable 'flake:nixpkgs#'...
+  Added 5 variables.
+
+  nix-repl> legacyPackages.x86_64-linux.emacs.name
+  "emacs-27.1"
+
+  nix-repl> legacyPackages.x86_64-linux.emacs.name
+  "emacs-27.1"
+
+  nix-repl> :q
+
+  # nix repl --expr 'import <nixpkgs>{}'
+
+  Loading Installable ''...
+  Added 12439 variables.
 
   nix-repl> emacs.name
   "emacs-27.1"
diff --git a/src/nix/run.cc b/src/nix/run.cc
index 25a8fa8d3..6fca68047 100644
--- a/src/nix/run.cc
+++ b/src/nix/run.cc
@@ -9,6 +9,7 @@
 #include "fs-accessor.hh"
 #include "progress-bar.hh"
 #include "eval.hh"
+#include "build/personality.hh"
 
 #if __linux__
 #include <sys/mount.h>
@@ -24,7 +25,8 @@ namespace nix {
 
 void runProgramInStore(ref<Store> store,
     const std::string & program,
-    const Strings & args)
+    const Strings & args,
+    std::optional<std::string_view> system)
 {
     stopProgressBar();
 
@@ -44,14 +46,17 @@ void runProgramInStore(ref<Store> store,
         throw Error("store '%s' is not a local store so it does not support command execution", store->getUri());
 
     if (store->storeDir != store2->getRealStoreDir()) {
-        Strings helperArgs = { chrootHelperName, store->storeDir, store2->getRealStoreDir(), program };
+        Strings helperArgs = { chrootHelperName, store->storeDir, store2->getRealStoreDir(), std::string(system.value_or("")), program };
         for (auto & arg : args) helperArgs.push_back(arg);
 
-        execv(readLink("/proc/self/exe").c_str(), stringsToCharPtrs(helperArgs).data());
+        execv(getSelfExe().value_or("nix").c_str(), stringsToCharPtrs(helperArgs).data());
 
         throw SysError("could not execute chroot helper");
     }
 
+    if (system)
+        setPersonality(*system);
+
     execvp(program.c_str(), stringsToCharPtrs(args).data());
 
     throw SysError("unable to execute '%s'", program);
@@ -199,6 +204,7 @@ void chrootHelper(int argc, char * * argv)
     int p = 1;
     std::string storeDir = argv[p++];
     std::string realStoreDir = argv[p++];
+    std::string system = argv[p++];
     std::string cmd = argv[p++];
     Strings args;
     while (p < argc)
@@ -262,6 +268,9 @@ void chrootHelper(int argc, char * * argv)
     writeFile("/proc/self/uid_map", fmt("%d %d %d", uid, uid, 1));
     writeFile("/proc/self/gid_map", fmt("%d %d %d", gid, gid, 1));
 
+    if (system != "")
+        setPersonality(system);
+
     execvp(cmd.c_str(), stringsToCharPtrs(args).data());
 
     throw SysError("unable to exec '%s'", cmd);
diff --git a/src/nix/run.hh b/src/nix/run.hh
index 6180a87dd..fed360158 100644
--- a/src/nix/run.hh
+++ b/src/nix/run.hh
@@ -6,6 +6,7 @@ namespace nix {
 
 void runProgramInStore(ref<Store> store,
     const std::string & program,
-    const Strings & args);
+    const Strings & args,
+    std::optional<std::string_view> system = std::nullopt);
 
 }
diff --git a/src/nix/search.cc b/src/nix/search.cc
index e96a85ea2..d2a31607d 100644
--- a/src/nix/search.cc
+++ b/src/nix/search.cc
@@ -5,29 +5,40 @@
 #include "names.hh"
 #include "get-drvs.hh"
 #include "common-args.hh"
-#include "json.hh"
 #include "shared.hh"
 #include "eval-cache.hh"
 #include "attr-path.hh"
-#include "fmt.hh"
+#include "hilite.hh"
 
 #include <regex>
 #include <fstream>
+#include <nlohmann/json.hpp>
 
 using namespace nix;
+using json = nlohmann::json;
 
 std::string wrap(std::string prefix, std::string s)
 {
-    return prefix + s + ANSI_NORMAL;
+    return concatStrings(prefix, s, ANSI_NORMAL);
 }
 
 struct CmdSearch : InstallableCommand, MixJSON
 {
     std::vector<std::string> res;
+    std::vector<std::string> excludeRes;
 
     CmdSearch()
     {
         expectArgs("regex", &res);
+        addFlag(Flag {
+            .longName = "exclude",
+            .shortName = 'e',
+            .description = "Hide packages whose attribute path, name or description contain *regex*.",
+            .labels = {"regex"},
+            .handler = {[this](std::string s) {
+                excludeRes.push_back(s);
+            }},
+        });
     }
 
     std::string description() override
@@ -62,14 +73,20 @@ struct CmdSearch : InstallableCommand, MixJSON
             res.push_back("^");
 
         std::vector<std::regex> regexes;
+        std::vector<std::regex> excludeRegexes;
         regexes.reserve(res.size());
+        excludeRegexes.reserve(excludeRes.size());
 
         for (auto & re : res)
             regexes.push_back(std::regex(re, std::regex::extended | std::regex::icase));
 
+        for (auto & re : excludeRes)
+            excludeRegexes.emplace_back(re, std::regex::extended | std::regex::icase);
+
         auto state = getEvalState();
 
-        auto jsonOut = json ? std::make_unique<JSONObject>(std::cout) : nullptr;
+        std::optional<nlohmann::json> jsonOut;
+        if (json) jsonOut = json::object();
 
         uint64_t results = 0;
 
@@ -77,13 +94,15 @@ struct CmdSearch : InstallableCommand, MixJSON
 
         visit = [&](eval_cache::AttrCursor & cursor, const std::vector<Symbol> & attrPath, bool initialRecurse)
         {
+            auto attrPathS = state->symbols.resolve(attrPath);
+
             Activity act(*logger, lvlInfo, actUnknown,
-                fmt("evaluating '%s'", concatStringsSep(".", attrPath)));
+                fmt("evaluating '%s'", concatStringsSep(".", attrPathS)));
             try {
                 auto recurse = [&]()
                 {
                     for (const auto & attr : cursor.getAttrs()) {
-                        auto cursor2 = cursor.getAttr(attr);
+                        auto cursor2 = cursor.getAttr(state->symbols[attr]);
                         auto attrPath2(attrPath);
                         attrPath2.push_back(attr);
                         visit(*cursor2, attrPath2, false);
@@ -91,19 +110,27 @@ struct CmdSearch : InstallableCommand, MixJSON
                 };
 
                 if (cursor.isDerivation()) {
-                    DrvName name(cursor.getAttr("name")->getString());
+                    DrvName name(cursor.getAttr(state->sName)->getString());
 
-                    auto aMeta = cursor.maybeGetAttr("meta");
-                    auto aDescription = aMeta ? aMeta->maybeGetAttr("description") : nullptr;
+                    auto aMeta = cursor.maybeGetAttr(state->sMeta);
+                    auto aDescription = aMeta ? aMeta->maybeGetAttr(state->sDescription) : nullptr;
                     auto description = aDescription ? aDescription->getString() : "";
                     std::replace(description.begin(), description.end(), '\n', ' ');
-                    auto attrPath2 = concatStringsSep(".", attrPath);
+                    auto attrPath2 = concatStringsSep(".", attrPathS);
 
                     std::vector<std::smatch> attrPathMatches;
                     std::vector<std::smatch> descriptionMatches;
                     std::vector<std::smatch> nameMatches;
                     bool found = false;
 
+                    for (auto & regex : excludeRegexes) {
+                        if (
+                            std::regex_search(attrPath2, regex)
+                            || std::regex_search(name.name, regex)
+                            || std::regex_search(description, regex))
+                            return;
+                    }
+
                     for (auto & regex : regexes) {
                         found = false;
                         auto addAll = [&found](std::sregex_iterator it, std::vector<std::smatch> & vec) {
@@ -126,41 +153,42 @@ struct CmdSearch : InstallableCommand, MixJSON
                     {
                         results++;
                         if (json) {
-                            auto jsonElem = jsonOut->object(attrPath2);
-                            jsonElem.attr("pname", name.name);
-                            jsonElem.attr("version", name.version);
-                            jsonElem.attr("description", description);
+                            (*jsonOut)[attrPath2] = {
+                                {"pname", name.name},
+                                {"version", name.version},
+                                {"description", description},
+                            };
                         } else {
-                            auto name2 = hiliteMatches(name.name, std::move(nameMatches), ANSI_GREEN, "\e[0;2m");
+                            auto name2 = hiliteMatches(name.name, nameMatches, ANSI_GREEN, "\e[0;2m");
                             if (results > 1) logger->cout("");
                             logger->cout(
                                 "* %s%s",
-                                wrap("\e[0;1m", hiliteMatches(attrPath2, std::move(attrPathMatches), ANSI_GREEN, "\e[0;1m")),
+                                wrap("\e[0;1m", hiliteMatches(attrPath2, attrPathMatches, ANSI_GREEN, "\e[0;1m")),
                                 name.version != "" ? " (" + name.version + ")" : "");
                             if (description != "")
                                 logger->cout(
-                                    "  %s", hiliteMatches(description, std::move(descriptionMatches), ANSI_GREEN, ANSI_NORMAL));
+                                    "  %s", hiliteMatches(description, descriptionMatches, ANSI_GREEN, ANSI_NORMAL));
                         }
                     }
                 }
 
                 else if (
                     attrPath.size() == 0
-                    || (attrPath[0] == "legacyPackages" && attrPath.size() <= 2)
-                    || (attrPath[0] == "packages" && attrPath.size() <= 2))
+                    || (attrPathS[0] == "legacyPackages" && attrPath.size() <= 2)
+                    || (attrPathS[0] == "packages" && attrPath.size() <= 2))
                     recurse();
 
                 else if (initialRecurse)
                     recurse();
 
-                else if (attrPath[0] == "legacyPackages" && attrPath.size() > 2) {
+                else if (attrPathS[0] == "legacyPackages" && attrPath.size() > 2) {
                     auto attr = cursor.maybeGetAttr(state->sRecurseForDerivations);
                     if (attr && attr->getBool())
                         recurse();
                 }
 
             } catch (EvalError & e) {
-                if (!(attrPath.size() > 0 && attrPath[0] == "legacyPackages"))
+                if (!(attrPath.size() > 0 && attrPathS[0] == "legacyPackages"))
                     throw;
             }
         };
@@ -168,6 +196,10 @@ struct CmdSearch : InstallableCommand, MixJSON
         for (auto & cursor : installable->getCursors(*state))
             visit(*cursor, cursor->getAttrPath(), true);
 
+        if (json) {
+            std::cout << jsonOut->dump() << std::endl;
+        }
+
         if (!json && !results)
             throw Error("no results for the given search term(s)!");
     }
diff --git a/src/nix/search.md b/src/nix/search.md
index d182788a6..5a5b5ae05 100644
--- a/src/nix/search.md
+++ b/src/nix/search.md
@@ -43,12 +43,23 @@ R""(
   # nix search nixpkgs 'firefox|chromium'
   ```
 
-* Search for packages containing `git'`and either `frontend` or `gui`:
+* Search for packages containing `git` and either `frontend` or `gui`:
 
   ```console
   # nix search nixpkgs git 'frontend|gui'
   ```
 
+* Search for packages containing `neovim` but hide ones containing either `gui` or `python`:
+
+  ```console
+  # nix search nixpkgs neovim -e 'python|gui'
+  ```
+  or
+
+  ```console
+  # nix search nixpkgs neovim -e 'python' -e 'gui'
+  ```
+
 # Description
 
 `nix search` searches *installable* (which must be evaluatable, e.g. a
diff --git a/src/nix/shell.md b/src/nix/shell.md
index 90b81fb2f..9fa1031f5 100644
--- a/src/nix/shell.md
+++ b/src/nix/shell.md
@@ -23,6 +23,12 @@ R""(
   Hi everybody!
   ```
 
+* Run multiple commands in a shell environment:
+
+  ```console
+  # nix shell nixpkgs#gnumake -c sh -c "cd src && make"
+  ```
+
 * Run GNU Hello in a chroot store:
 
   ```console
diff --git a/src/nix/show-derivation.cc b/src/nix/show-derivation.cc
index fb46b4dbf..af2e676a4 100644
--- a/src/nix/show-derivation.cc
+++ b/src/nix/show-derivation.cc
@@ -5,10 +5,11 @@
 #include "common-args.hh"
 #include "store-api.hh"
 #include "archive.hh"
-#include "json.hh"
 #include "derivations.hh"
+#include <nlohmann/json.hpp>
 
 using namespace nix;
+using json = nlohmann::json;
 
 struct CmdShowDerivation : InstallablesCommand
 {
@@ -48,77 +49,63 @@ struct CmdShowDerivation : InstallablesCommand
             drvPaths = std::move(closure);
         }
 
-        {
-
-        JSONObject jsonRoot(std::cout, true);
+        json jsonRoot = json::object();
 
         for (auto & drvPath : drvPaths) {
             if (!drvPath.isDerivation()) continue;
 
-            auto drvObj(jsonRoot.object(store->printStorePath(drvPath)));
+            json& drvObj = jsonRoot[store->printStorePath(drvPath)];
 
             auto drv = store->readDerivation(drvPath);
 
             {
-                auto outputsObj(drvObj.object("outputs"));
+                json& outputsObj = drvObj["outputs"];
+                outputsObj = json::object();
                 for (auto & [_outputName, output] : drv.outputs) {
                     auto & outputName = _outputName; // work around clang bug
-                    auto outputObj { outputsObj.object(outputName) };
+                    auto& outputObj = outputsObj[outputName];
+                    outputObj = json::object();
                     std::visit(overloaded {
                         [&](const DerivationOutput::InputAddressed & doi) {
-                            outputObj.attr("path", store->printStorePath(doi.path));
+                            outputObj["path"] = store->printStorePath(doi.path);
                         },
                         [&](const DerivationOutput::CAFixed & 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));
+                            outputObj["path"] = store->printStorePath(dof.path(*store, drv.name, outputName));
+                            outputObj["hashAlgo"] = dof.hash.printMethodAlgo();
+                            outputObj["hash"] = dof.hash.hash.to_string(Base16, false);
                         },
                         [&](const DerivationOutput::CAFloating & dof) {
-                            outputObj.attr("hashAlgo", makeFileIngestionPrefix(dof.method) + printHashType(dof.hashType));
+                            outputObj["hashAlgo"] = makeFileIngestionPrefix(dof.method) + printHashType(dof.hashType);
                         },
                         [&](const DerivationOutput::Deferred &) {},
                         [&](const DerivationOutput::Impure & doi) {
-                            outputObj.attr("hashAlgo", makeFileIngestionPrefix(doi.method) + printHashType(doi.hashType));
-                            outputObj.attr("impure", true);
+                            outputObj["hashAlgo"] = makeFileIngestionPrefix(doi.method) + printHashType(doi.hashType);
+                            outputObj["impure"] = true;
                         },
                     }, output.raw());
                 }
             }
 
             {
-                auto inputsList(drvObj.list("inputSrcs"));
+                auto& inputsList = drvObj["inputSrcs"];
+                inputsList = json::array();
                 for (auto & input : drv.inputSrcs)
-                    inputsList.elem(store->printStorePath(input));
-            }
-
-            {
-                auto inputDrvsObj(drvObj.object("inputDrvs"));
-                for (auto & input : drv.inputDrvs) {
-                    auto inputList(inputDrvsObj.list(store->printStorePath(input.first)));
-                    for (auto & outputId : input.second)
-                        inputList.elem(outputId);
-                }
+                    inputsList.emplace_back(store->printStorePath(input));
             }
 
-            drvObj.attr("system", drv.platform);
-            drvObj.attr("builder", drv.builder);
-
             {
-                auto argsList(drvObj.list("args"));
-                for (auto & arg : drv.args)
-                    argsList.elem(arg);
+                auto& inputDrvsObj = drvObj["inputDrvs"];
+                inputDrvsObj = json::object();
+                for (auto & input : drv.inputDrvs)
+                    inputDrvsObj[store->printStorePath(input.first)] = input.second;
             }
 
-            {
-                auto envObj(drvObj.object("env"));
-                for (auto & var : drv.env)
-                    envObj.attr(var.first, var.second);
-            }
+            drvObj["system"] = drv.platform;
+            drvObj["builder"] = drv.builder;
+            drvObj["args"] = drv.args;
+            drvObj["env"] = drv.env;
         }
-
-        }
-
-        std::cout << "\n";
+        std::cout << jsonRoot.dump(2) << std::endl;
     }
 };
 
diff --git a/src/nix/show-derivation.md b/src/nix/show-derivation.md
index aa863899c..2cd93aa62 100644
--- a/src/nix/show-derivation.md
+++ b/src/nix/show-derivation.md
@@ -2,9 +2,11 @@ R""(
 
 # Examples
 
-* Show the store derivation that results from evaluating the Hello
+* Show the [store derivation] that results from evaluating the Hello
   package:
 
+  [store derivation]: ../../glossary.md#gloss-store-derivation
+
   ```console
   # nix show-derivation nixpkgs#hello
   {
@@ -37,7 +39,7 @@ R""(
 # Description
 
 This command prints on standard output a JSON representation of the
-store derivations to which *installables* evaluate. Store derivations
+[store derivation]s to which *installables* evaluate. Store derivations
 are used internally by Nix. They are store paths with extension `.drv`
 that represent the build-time dependency graph to which a Nix
 expression evaluates.
diff --git a/src/nix/store-copy-log.md b/src/nix/store-copy-log.md
index 19ae57079..0937250f2 100644
--- a/src/nix/store-copy-log.md
+++ b/src/nix/store-copy-log.md
@@ -18,7 +18,9 @@ R""(
   (The flag `--substituters ''` avoids querying
   `https://cache.nixos.org` for the log.)
 
-* To copy the log for a specific store derivation via SSH:
+* To copy the log for a specific [store derivation] via SSH:
+
+  [store derivation]: ../../glossary.md#gloss-store-derivation
 
   ```console
   # nix store copy-log --to ssh-ng://machine /nix/store/ilgm50plpmcgjhcp33z6n4qbnpqfhxym-glibc-2.33-59.drv
diff --git a/src/nix/upgrade-nix.cc b/src/nix/upgrade-nix.cc
index 17a5a77ee..17796d6b8 100644
--- a/src/nix/upgrade-nix.cc
+++ b/src/nix/upgrade-nix.cc
@@ -34,7 +34,7 @@ struct CmdUpgradeNix : MixDryRun, StoreCommand
 
     std::string description() override
     {
-        return "upgrade Nix to the latest stable version";
+        return "upgrade Nix to the stable version declared in Nixpkgs";
     }
 
     std::string doc() override
@@ -144,7 +144,7 @@ struct CmdUpgradeNix : MixDryRun, StoreCommand
         Bindings & bindings(*state->allocBindings(0));
         auto v2 = findAlongAttrPath(*state, settings.thisSystem, bindings, *v).first;
 
-        return store->parseStorePath(state->forceString(*v2));
+        return store->parseStorePath(state->forceString(*v2, noPos, "while evaluating the path tho latest nix version"));
     }
 };
 
diff --git a/src/nix/upgrade-nix.md b/src/nix/upgrade-nix.md
index 4d27daad9..084c80ba2 100644
--- a/src/nix/upgrade-nix.md
+++ b/src/nix/upgrade-nix.md
@@ -2,7 +2,7 @@ R""(
 
 # Examples
 
-* Upgrade Nix to the latest stable version:
+* Upgrade Nix to the stable version declared in Nixpkgs:
 
   ```console
   # nix upgrade-nix
@@ -16,8 +16,11 @@ R""(
 
 # Description
 
-This command upgrades Nix to the latest version. By default, it
-locates the directory containing the `nix` binary in the `$PATH`
+This command upgrades Nix to the stable version declared in Nixpkgs.
+This stable version is defined in [nix-fallback-paths.nix](https://github.com/NixOS/nixpkgs/raw/master/nixos/modules/installer/tools/nix-fallback-paths.nix)
+and updated manually. It may not always be the latest tagged release.
+
+By default, it locates the directory containing the `nix` binary in the `$PATH`
 environment variable. If that directory is a Nix profile, it will
 upgrade the `nix` package in that profile to the latest stable binary
 release.
diff --git a/src/nix/verify.cc b/src/nix/verify.cc
index d132768ec..0b306cc11 100644
--- a/src/nix/verify.cc
+++ b/src/nix/verify.cc
@@ -41,7 +41,7 @@ struct CmdVerify : StorePathsCommand
         addFlag({
             .longName = "sigs-needed",
             .shortName = 'n',
-            .description = "Require that each path has at least *n* valid signatures.",
+            .description = "Require that each path is signed by at least *n* different keys.",
             .labels = {"n"},
             .handler = {&sigsNeeded}
         });
diff --git a/src/nix/why-depends.cc b/src/nix/why-depends.cc
index 1d9ab28ba..76125e5e4 100644
--- a/src/nix/why-depends.cc
+++ b/src/nix/why-depends.cc
@@ -83,20 +83,37 @@ struct CmdWhyDepends : SourceExprCommand
     {
         auto package = parseInstallable(store, _package);
         auto packagePath = Installable::toStorePath(getEvalStore(), store, Realise::Outputs, operateOn, package);
+
+        /* We don't need to build `dependency`. We try to get the store
+         * path if it's already known, and if not, then it's not a dependency.
+         *
+         * Why? If `package` does depends on `dependency`, then getting the
+         * store path of `package` above necessitated having the store path
+         * of `dependency`. The contrapositive is, if the store path of
+         * `dependency` is not already known at this point (i.e. it's a CA
+         * derivation which hasn't been built), then `package` did not need it
+         * to build.
+         */
         auto dependency = parseInstallable(store, _dependency);
-        auto dependencyPath = Installable::toStorePath(getEvalStore(), store, Realise::Derivation, operateOn, dependency);
-        auto dependencyPathHash = dependencyPath.hashPart();
+        auto optDependencyPath = [&]() -> std::optional<StorePath> {
+            try {
+                return {Installable::toStorePath(getEvalStore(), store, Realise::Derivation, operateOn, dependency)};
+            } catch (MissingRealisation &) {
+                return std::nullopt;
+            }
+        }();
 
         StorePathSet closure;
         store->computeFSClosure({packagePath}, closure, false, false);
 
-        if (!closure.count(dependencyPath)) {
-            printError("'%s' does not depend on '%s'",
-                store->printStorePath(packagePath),
-                store->printStorePath(dependencyPath));
+        if (!optDependencyPath.has_value() || !closure.count(*optDependencyPath)) {
+            printError("'%s' does not depend on '%s'", package->what(), dependency->what());
             return;
         }
 
+        auto dependencyPath = *optDependencyPath;
+        auto dependencyPathHash = dependencyPath.hashPart();
+
         stopProgressBar(); // FIXME
 
         auto accessor = store->getFSAccessor();