Merge commit 'aa99005004bccc9be506a2a2f162f78bad4bcb41' into ca-drv-exotic

55 files changed, 542 insertions, 381 deletions

diff --git a/src/nix/app.cc b/src/nix/app.cc
index 5cd65136f..fd4569bb4 100644
--- a/src/nix/app.cc
+++ b/src/nix/app.cc
@@ -1,5 +1,6 @@
 #include "installables.hh"
 #include "installable-derived-path.hh"
+#include "installable-value.hh"
 #include "store-api.hh"
 #include "eval-inline.hh"
 #include "eval-cache.hh"
@@ -40,7 +41,7 @@ std::string resolveString(
     return rewriteStrings(toResolve, rewrites);
 }
 
-UnresolvedApp Installable::toApp(EvalState & state)
+UnresolvedApp InstallableValue::toApp(EvalState & state)
 {
     auto cursor = getCursor(state);
     auto attrPath = cursor->getAttrPath();
@@ -119,11 +120,11 @@ App UnresolvedApp::resolve(ref<Store> evalStore, ref<Store> store)
 {
     auto res = unresolved;
 
-    std::vector<std::shared_ptr<Installable>> installableContext;
+    Installables installableContext;
 
     for (auto & ctxElt : unresolved.context)
         installableContext.push_back(
-            std::make_shared<InstallableDerivedPath>(store, DerivedPath { ctxElt }));
+            make_ref<InstallableDerivedPath>(store, DerivedPath { ctxElt }));
 
     auto builtContext = Installable::build(evalStore, store, Realise::Outputs, installableContext);
     res.program = resolveString(*store, unresolved.program, builtContext);
diff --git a/src/nix/build.cc b/src/nix/build.cc
index 12b22d999..4e133e288 100644
--- a/src/nix/build.cc
+++ b/src/nix/build.cc
@@ -1,4 +1,3 @@
-#include "eval.hh"
 #include "command.hh"
 #include "common-args.hh"
 #include "shared.hh"
@@ -41,6 +40,29 @@ nlohmann::json builtPathsWithResultToJSON(const std::vector<BuiltPathWithResult>
     return res;
 }
 
+// TODO deduplicate with other code also setting such out links.
+static void createOutLinks(const Path& outLink, const std::vector<BuiltPathWithResult>& buildables, LocalFSStore& store2)
+{
+    for (const auto & [_i, buildable] : enumerate(buildables)) {
+        auto i = _i;
+        std::visit(overloaded {
+            [&](const BuiltPath::Opaque & bo) {
+                std::string symlink = outLink;
+                if (i) symlink += fmt("-%d", i);
+                store2.addPermRoot(bo.path, absPath(symlink));
+            },
+            [&](const BuiltPath::Built & bfd) {
+                for (auto & output : bfd.outputs) {
+                    std::string symlink = outLink;
+                    if (i) symlink += fmt("-%d", i);
+                    if (output.first != "out") symlink += fmt("-%s", output.first);
+                    store2.addPermRoot(output.second, absPath(symlink));
+                }
+            },
+        }, buildable.path.raw());
+    }
+}
+
 struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
 {
     Path outLink = "result";
@@ -89,7 +111,7 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
           ;
     }
 
-    void run(ref<Store> store) override
+    void run(ref<Store> store, Installables && installables) override
     {
         if (dryRun) {
             std::vector<DerivedPath> pathsToBuild;
@@ -115,35 +137,18 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
 
         if (outLink != "")
             if (auto store2 = store.dynamic_pointer_cast<LocalFSStore>())
-                for (const auto & [_i, buildable] : enumerate(buildables)) {
-                    auto i = _i;
-                    std::visit(overloaded {
-                        [&](const BuiltPath::Opaque & bo) {
-                            std::string symlink = outLink;
-                            if (i) symlink += fmt("-%d", i);
-                            store2->addPermRoot(bo.path, absPath(symlink));
-                        },
-                        [&](const BuiltPath::Built & bfd) {
-                            for (auto & output : bfd.outputs) {
-                                std::string symlink = outLink;
-                                if (i) symlink += fmt("-%d", i);
-                                if (output.first != "out") symlink += fmt("-%s", output.first);
-                                store2->addPermRoot(output.second, absPath(symlink));
-                            }
-                        },
-                    }, buildable.path.raw());
-                }
+                createOutLinks(outLink, buildables, *store2);
 
         if (printOutputPaths) {
             stopProgressBar();
             for (auto & buildable : buildables) {
                 std::visit(overloaded {
                     [&](const BuiltPath::Opaque & bo) {
-                        std::cout << store->printStorePath(bo.path) << std::endl;
+                        logger->cout(store->printStorePath(bo.path));
                     },
                     [&](const BuiltPath::Built & bfd) {
                         for (auto & output : bfd.outputs) {
-                            std::cout << store->printStorePath(output.second) << std::endl;
+                            logger->cout(store->printStorePath(output.second));
                         }
                     },
                 }, buildable.path.raw());
diff --git a/src/nix/build.md b/src/nix/build.md
index 6a79f308c..ee414dc86 100644
--- a/src/nix/build.md
+++ b/src/nix/build.md
@@ -82,7 +82,7 @@ R""(
 
 # Description
 
-`nix build` builds the specified *installables*. Installables that
+`nix build` builds the specified *installables*. [Installables](./nix.md#installables) that
 resolve to derivations are built (or substituted if possible). Store
 path installables are substituted.
 
diff --git a/src/nix/bundle.cc b/src/nix/bundle.cc
index dcf9a6f2d..57c355f0c 100644
--- a/src/nix/bundle.cc
+++ b/src/nix/bundle.cc
@@ -1,14 +1,15 @@
-#include "command.hh"
 #include "installable-flake.hh"
+#include "command-installable-value.hh"
 #include "common-args.hh"
 #include "shared.hh"
 #include "store-api.hh"
 #include "local-fs-store.hh"
 #include "fs-accessor.hh"
+#include "eval-inline.hh"
 
 using namespace nix;
 
-struct CmdBundle : InstallableCommand
+struct CmdBundle : InstallableValueCommand
 {
     std::string bundler = "github:NixOS/bundlers";
     std::optional<Path> outLink;
@@ -70,7 +71,7 @@ struct CmdBundle : InstallableCommand
         return res;
     }
 
-    void run(ref<Store> store) override
+    void run(ref<Store> store, ref<InstallableValue> installable) override
     {
         auto evalState = getEvalState();
 
diff --git a/src/nix/bundle.md b/src/nix/bundle.md
index a18161a3c..89458aaaa 100644
--- a/src/nix/bundle.md
+++ b/src/nix/bundle.md
@@ -29,7 +29,7 @@ R""(
 
 # Description
 
-`nix bundle`, by default, packs the closure of the *installable* into a single
+`nix bundle`, by default, packs the closure of the [*installable*](./nix.md#installables) into a single
 self-extracting executable. See the [`bundlers`
 homepage](https://github.com/NixOS/bundlers) for more details.
 
diff --git a/src/nix/cat.cc b/src/nix/cat.cc
index 6420a0f79..60aa66ce0 100644
--- a/src/nix/cat.cc
+++ b/src/nix/cat.cc
@@ -17,7 +17,7 @@ struct MixCat : virtual Args
         if (st.type != FSAccessor::Type::tRegular)
             throw Error("path '%1%' is not a regular file", path);
 
-        std::cout << accessor->readFile(path);
+        writeFull(STDOUT_FILENO, accessor->readFile(path));
     }
 };
 
diff --git a/src/nix/copy.cc b/src/nix/copy.cc
index 8730a9a5c..151d28277 100644
--- a/src/nix/copy.cc
+++ b/src/nix/copy.cc
@@ -10,8 +10,6 @@ struct CmdCopy : virtual CopyCommand, virtual BuiltPathsCommand
 
     SubstituteFlag substitute = NoSubstitute;
 
-    using BuiltPathsCommand::run;
-
     CmdCopy()
         : BuiltPathsCommand(true)
     {
diff --git a/src/nix/daemon.cc b/src/nix/daemon.cc
index a22bccba1..7e4a7ba86 100644
--- a/src/nix/daemon.cc
+++ b/src/nix/daemon.cc
@@ -249,9 +249,9 @@ static void daemonLoop()
             if ((!trusted && !matchUser(user, group, allowedUsers)) || group == settings.buildUsersGroup)
                 throw Error("user '%1%' is not allowed to connect to the Nix daemon", user);
 
-            printInfo(format((std::string) "accepted connection from pid %1%, user %2%" + (trusted ? " (trusted)" : ""))
-                % (peer.pidKnown ? std::to_string(peer.pid) : "<unknown>")
-                % (peer.uidKnown ? user : "<unknown>"));
+            printInfo((std::string) "accepted connection from pid %1%, user %2%" + (trusted ? " (trusted)" : ""),
+                peer.pidKnown ? std::to_string(peer.pid) : "<unknown>",
+                peer.uidKnown ? user : "<unknown>");
 
             //  Fork a child to handle the connection.
             ProcessOptions options;
diff --git a/src/nix/describe-stores.cc b/src/nix/describe-stores.cc
deleted file mode 100644
index 1dd384c0e..000000000
--- a/src/nix/describe-stores.cc
+++ /dev/null
@@ -1,44 +0,0 @@
-#include "command.hh"
-#include "common-args.hh"
-#include "shared.hh"
-#include "store-api.hh"
-
-#include <nlohmann/json.hpp>
-
-using namespace nix;
-
-struct CmdDescribeStores : Command, MixJSON
-{
-    std::string description() override
-    {
-        return "show registered store types and their available options";
-    }
-
-    Category category() override { return catUtility; }
-
-    void run() override
-    {
-        auto res = nlohmann::json::object();
-        for (auto & implem : *Implementations::registered) {
-            auto storeConfig = implem.getConfig();
-            auto storeName = storeConfig->name();
-            res[storeName] = storeConfig->toJSON();
-        }
-        if (json) {
-            std::cout << res;
-        } else {
-            for (auto & [storeName, storeConfig] : res.items()) {
-                std::cout << "## " << storeName << std::endl << std::endl;
-                for (auto & [optionName, optionDesc] : storeConfig.items()) {
-                    std::cout << "### " << optionName << std::endl << std::endl;
-                    std::cout << optionDesc["description"].get<std::string>() << std::endl;
-                    std::cout << "default: " << optionDesc["defaultValue"] << std::endl <<std::endl;
-                    if (!optionDesc["aliases"].empty())
-                        std::cout << "aliases: " << optionDesc["aliases"] << std::endl << std::endl;
-                }
-            }
-        }
-    }
-};
-
-static auto rDescribeStore = registerCommand<CmdDescribeStores>("describe-stores");
diff --git a/src/nix/develop.cc b/src/nix/develop.cc
index 9d07a7a85..9e2dcff61 100644
--- a/src/nix/develop.cc
+++ b/src/nix/develop.cc
@@ -1,6 +1,6 @@
 #include "eval.hh"
-#include "command.hh"
 #include "installable-flake.hh"
+#include "command-installable-value.hh"
 #include "common-args.hh"
 #include "shared.hh"
 #include "store-api.hh"
@@ -208,7 +208,7 @@ static StorePath getDerivationEnvironment(ref<Store> store, ref<Store> evalStore
     drv.name += "-env";
     drv.env.emplace("name", drv.name);
     drv.inputSrcs.insert(std::move(getEnvShPath));
-    if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations)) {
+    if (experimentalFeatureSettings.isEnabled(Xp::CaDerivations)) {
         for (auto & output : drv.outputs) {
             output.second = DerivationOutput::Deferred {},
             drv.env[output.first] = hashPlaceholder(output.first);
@@ -252,7 +252,7 @@ static StorePath getDerivationEnvironment(ref<Store> store, ref<Store> evalStore
     throw Error("get-env.sh failed to produce an environment");
 }
 
-struct Common : InstallableCommand, MixProfile
+struct Common : InstallableValueCommand, MixProfile
 {
     std::set<std::string> ignoreVars{
         "BASHOPTS",
@@ -313,7 +313,7 @@ struct Common : InstallableCommand, MixProfile
         buildEnvironment.toBash(out, ignoreVars);
 
         for (auto & var : savedVars)
-            out << fmt("%s=\"$%s:$nix_saved_%s\"\n", var, var, var);
+            out << fmt("%s=\"$%s${nix_saved_%s:+:$nix_saved_%s}\"\n", var, var, var, var);
 
         out << "export NIX_BUILD_TOP=\"$(mktemp -d -t nix-shell.XXXXXX)\"\n";
         for (auto & i : {"TMP", "TMPDIR", "TEMP", "TEMPDIR"})
@@ -374,7 +374,7 @@ struct Common : InstallableCommand, MixProfile
         return res;
     }
 
-    StorePath getShellOutPath(ref<Store> store)
+    StorePath getShellOutPath(ref<Store> store, ref<InstallableValue> installable)
     {
         auto path = installable->getStorePath();
         if (path && hasSuffix(path->to_string(), "-env"))
@@ -392,9 +392,10 @@ struct Common : InstallableCommand, MixProfile
         }
     }
 
-    std::pair<BuildEnvironment, std::string> getBuildEnvironment(ref<Store> store)
+    std::pair<BuildEnvironment, std::string>
+    getBuildEnvironment(ref<Store> store, ref<InstallableValue> installable)
     {
-        auto shellOutPath = getShellOutPath(store);
+        auto shellOutPath = getShellOutPath(store, installable);
 
         auto strPath = store->printStorePath(shellOutPath);
 
@@ -480,9 +481,9 @@ struct CmdDevelop : Common, MixEnvironment
           ;
     }
 
-    void run(ref<Store> store) override
+    void run(ref<Store> store, ref<InstallableValue> installable) override
     {
-        auto [buildEnvironment, gcroot] = getBuildEnvironment(store);
+        auto [buildEnvironment, gcroot] = getBuildEnvironment(store, installable);
 
         auto [rcFileFd, rcFilePath] = createTempFile("nix-shell");
 
@@ -537,7 +538,7 @@ struct CmdDevelop : Common, MixEnvironment
             nixpkgsLockFlags.inputOverrides = {};
             nixpkgsLockFlags.inputUpdates = {};
 
-            auto bashInstallable = std::make_shared<InstallableFlake>(
+            auto bashInstallable = make_ref<InstallableFlake>(
                 this,
                 state,
                 installable->nixpkgsFlakeRef(),
@@ -573,7 +574,7 @@ struct CmdDevelop : Common, MixEnvironment
         // Need to chdir since phases assume in flake directory
         if (phase) {
             // chdir if installable is a flake of type git+file or path
-            auto installableFlake = std::dynamic_pointer_cast<InstallableFlake>(installable);
+            auto installableFlake = installable.dynamic_pointer_cast<InstallableFlake>();
             if (installableFlake) {
                 auto sourcePath = installableFlake->getLockedFlake()->flake.resolvedRef.input.getSourcePath();
                 if (sourcePath) {
@@ -604,9 +605,9 @@ struct CmdPrintDevEnv : Common, MixJSON
 
     Category category() override { return catUtility; }
 
-    void run(ref<Store> store) override
+    void run(ref<Store> store, ref<InstallableValue> installable) override
     {
-        auto buildEnvironment = getBuildEnvironment(store).first;
+        auto buildEnvironment = getBuildEnvironment(store, installable).first;
 
         stopProgressBar();
 
diff --git a/src/nix/develop.md b/src/nix/develop.md
index 4e8542d1b..c49b39669 100644
--- a/src/nix/develop.md
+++ b/src/nix/develop.md
@@ -76,7 +76,7 @@ R""(
 
 `nix develop` starts a `bash` shell that provides an interactive build
 environment nearly identical to what Nix would use to build
-*installable*. Inside this shell, environment variables and shell
+[*installable*](./nix.md#installables). Inside this shell, environment variables and shell
 functions are set up so that you can interactively and incrementally
 build your package.
 
diff --git a/src/nix/diff-closures.cc b/src/nix/diff-closures.cc
index 3489cc132..c7c37b66f 100644
--- a/src/nix/diff-closures.cc
+++ b/src/nix/diff-closures.cc
@@ -97,7 +97,7 @@ void printClosureDiff(
                 items.push_back(fmt("%s → %s", showVersions(removed), showVersions(added)));
             if (showDelta)
                 items.push_back(fmt("%s%+.1f KiB" ANSI_NORMAL, sizeDelta > 0 ? ANSI_RED : ANSI_GREEN, sizeDelta / 1024.0));
-            std::cout << fmt("%s%s: %s\n", indent, name, concatStringsSep(", ", items));
+            logger->cout("%s%s: %s", indent, name, concatStringsSep(", ", items));
         }
     }
 }
diff --git a/src/nix/doctor.cc b/src/nix/doctor.cc
index ea87e3d87..7da4549a1 100644
--- a/src/nix/doctor.cc
+++ b/src/nix/doctor.cc
@@ -18,7 +18,7 @@ std::string formatProtocol(unsigned int proto)
     if (proto) {
         auto major = GET_PROTOCOL_MAJOR(proto) >> 8;
         auto minor = GET_PROTOCOL_MINOR(proto);
-        return (format("%1%.%2%") % major % minor).str();
+        return fmt("%1%.%2%", major, minor);
     }
     return "unknown";
 }
diff --git a/src/nix/edit.cc b/src/nix/edit.cc
index dfe75fbdf..66629fab0 100644
--- a/src/nix/edit.cc
+++ b/src/nix/edit.cc
@@ -1,4 +1,4 @@
-#include "command.hh"
+#include "command-installable-value.hh"
 #include "shared.hh"
 #include "eval.hh"
 #include "attr-path.hh"
@@ -9,7 +9,7 @@
 
 using namespace nix;
 
-struct CmdEdit : InstallableCommand
+struct CmdEdit : InstallableValueCommand
 {
     std::string description() override
     {
@@ -25,7 +25,7 @@ struct CmdEdit : InstallableCommand
 
     Category category() override { return catSecondary; }
 
-    void run(ref<Store> store) override
+    void run(ref<Store> store, ref<InstallableValue> installable) override
     {
         auto state = getEvalState();
 
diff --git a/src/nix/eval.cc b/src/nix/eval.cc
index a579213fd..43db5150c 100644
--- a/src/nix/eval.cc
+++ b/src/nix/eval.cc
@@ -1,4 +1,4 @@
-#include "command.hh"
+#include "command-installable-value.hh"
 #include "common-args.hh"
 #include "shared.hh"
 #include "store-api.hh"
@@ -11,13 +11,13 @@
 
 using namespace nix;
 
-struct CmdEval : MixJSON, InstallableCommand, MixReadOnlyOption
+struct CmdEval : MixJSON, InstallableValueCommand, MixReadOnlyOption
 {
     bool raw = false;
     std::optional<std::string> apply;
     std::optional<Path> writeTo;
 
-    CmdEval() : InstallableCommand()
+    CmdEval() : InstallableValueCommand()
     {
         addFlag({
             .longName = "raw",
@@ -54,7 +54,7 @@ struct CmdEval : MixJSON, InstallableCommand, MixReadOnlyOption
 
     Category category() override { return catSecondary; }
 
-    void run(ref<Store> store) override
+    void run(ref<Store> store, ref<InstallableValue> installable) override
     {
         if (raw && json)
             throw UsageError("--raw and --json are mutually exclusive");
@@ -112,11 +112,11 @@ struct CmdEval : MixJSON, InstallableCommand, MixReadOnlyOption
 
         else if (raw) {
             stopProgressBar();
-            std::cout << *state->coerceToString(noPos, *v, context, "while generating the eval command output");
+            writeFull(STDOUT_FILENO, *state->coerceToString(noPos, *v, context, "while generating the eval command output"));
         }
 
         else if (json) {
-            std::cout << printValueAsJSON(*state, true, *v, pos, context, false).dump() << std::endl;
+            logger->cout("%s", printValueAsJSON(*state, true, *v, pos, context, false));
         }
 
         else {
diff --git a/src/nix/eval.md b/src/nix/eval.md
index 61334cde1..3b510737a 100644
--- a/src/nix/eval.md
+++ b/src/nix/eval.md
@@ -50,7 +50,7 @@ R""(
 
 # Description
 
-This command evaluates the Nix expression *installable* and prints the
+This command evaluates the given Nix expression and prints the
 result on standard output.
 
 # Output format
diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index 053a9c9e1..cd4ee5921 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -952,7 +952,7 @@ struct CmdFlakeArchive : FlakeCommand, MixJSON, MixDryRun
                 {"path", store->printStorePath(flake.flake.sourceInfo->storePath)},
                 {"inputs", traverse(*flake.lockFile.root)},
             };
-            std::cout << jsonRoot.dump() << std::endl;
+            logger->cout("%s", jsonRoot);
         } else {
             traverse(*flake.lockFile.root);
         }
@@ -1026,36 +1026,43 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
 
             auto visitor2 = visitor.getAttr(attrName);
 
-            if ((attrPathS[0] == "apps"
-                    || attrPathS[0] == "checks"
-                    || attrPathS[0] == "devShells"
-                    || attrPathS[0] == "legacyPackages"
-                    || attrPathS[0] == "packages")
-                && (attrPathS.size() == 1 || attrPathS.size() == 2)) {
-                for (const auto &subAttr : visitor2->getAttrs()) {
-                    if (hasContent(*visitor2, attrPath2, subAttr)) {
-                        return true;
+            try {
+                if ((attrPathS[0] == "apps"
+                        || attrPathS[0] == "checks"
+                        || attrPathS[0] == "devShells"
+                        || attrPathS[0] == "legacyPackages"
+                        || attrPathS[0] == "packages")
+                    && (attrPathS.size() == 1 || attrPathS.size() == 2)) {
+                    for (const auto &subAttr : visitor2->getAttrs()) {
+                        if (hasContent(*visitor2, attrPath2, subAttr)) {
+                            return true;
+                        }
                     }
+                    return false;
                 }
-                return false;
-            }
 
-            if ((attrPathS.size() == 1)
-                && (attrPathS[0] == "formatter"
-                    || attrPathS[0] == "nixosConfigurations"
-                    || attrPathS[0] == "nixosModules"
-                    || attrPathS[0] == "overlays"
-                    )) {
-                for (const auto &subAttr : visitor2->getAttrs()) {
-                    if (hasContent(*visitor2, attrPath2, subAttr)) {
-                        return true;
+                if ((attrPathS.size() == 1)
+                    && (attrPathS[0] == "formatter"
+                        || attrPathS[0] == "nixosConfigurations"
+                        || attrPathS[0] == "nixosModules"
+                        || attrPathS[0] == "overlays"
+                        )) {
+                    for (const auto &subAttr : visitor2->getAttrs()) {
+                        if (hasContent(*visitor2, attrPath2, subAttr)) {
+                            return true;
+                        }
                     }
+                    return false;
                 }
-                return false;
-            }
 
-            // If we don't recognize it, it's probably content
-            return true;
+                // If we don't recognize it, it's probably content
+                return true;
+            } catch (EvalError & e) {
+                // Some attrs may contain errors, eg. legacyPackages of
+                // nixpkgs. We still want to recurse into it, instead of
+                // skipping it at all.
+                return true;
+            }
         };
 
         std::function<nlohmann::json(
@@ -1328,8 +1335,7 @@ struct CmdFlake : NixMultiCommand
     {
         if (!command)
             throw UsageError("'nix flake' requires a sub-command.");
-        settings.requireExperimentalFeature(Xp::Flakes);
-        command->second->prepare();
+        experimentalFeatureSettings.require(Xp::Flakes);
         command->second->run();
     }
 };
diff --git a/src/nix/flake.md b/src/nix/flake.md
index 810e9ebea..cd9f656e3 100644
--- a/src/nix/flake.md
+++ b/src/nix/flake.md
@@ -54,7 +54,7 @@ output attribute). They are also allowed in the `inputs` attribute
 of a flake, e.g.
 
 ```nix
-inputs.nixpkgs.url = github:NixOS/nixpkgs;
+inputs.nixpkgs.url = "github:NixOS/nixpkgs";
 ```
 
 is equivalent to
@@ -275,14 +275,14 @@ Currently the `type` attribute can be one of the following:
 # Flake format
 
 As an example, here is a simple `flake.nix` that depends on the
-Nixpkgs flake and provides a single package (i.e. an installable
-derivation):
+Nixpkgs flake and provides a single package (i.e. an
+[installable](./nix.md#installables) derivation):
 
 ```nix
 {
   description = "A flake for building Hello World";
 
-  inputs.nixpkgs.url = github:NixOS/nixpkgs/nixos-20.03;
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-20.03";
 
   outputs = { self, nixpkgs }: {
 
@@ -317,6 +317,8 @@ The following attributes are supported in `flake.nix`:
   also contains some metadata about the inputs. These are:
 
   * `outPath`: The path in the Nix store of the flake's source tree.
+     This way, the attribute set can be passed to `import` as if it was a path,
+     as in the example above (`import nixpkgs`).
 
   * `rev`: The commit hash of the flake's repository, if applicable.
 
@@ -374,7 +376,7 @@ inputs.nixpkgs = {
 Alternatively, you can use the URL-like syntax:
 
 ```nix
-inputs.import-cargo.url = github:edolstra/import-cargo;
+inputs.import-cargo.url = "github:edolstra/import-cargo";
 inputs.nixpkgs.url = "nixpkgs";
 ```
 
diff --git a/src/nix/fmt.cc b/src/nix/fmt.cc
index 6f6a4a632..c85eacded 100644
--- a/src/nix/fmt.cc
+++ b/src/nix/fmt.cc
@@ -1,4 +1,5 @@
 #include "command.hh"
+#include "installable-value.hh"
 #include "run.hh"
 
 using namespace nix;
@@ -31,8 +32,9 @@ struct CmdFmt : SourceExprCommand {
         auto evalState = getEvalState();
         auto evalStore = getEvalStore();
 
-        auto installable = parseInstallable(store, ".");
-        auto app = installable->toApp(*evalState).resolve(evalStore, store);
+        auto installable_ = parseInstallable(store, ".");
+        auto & installable = InstallableValue::require(*installable_);
+        auto app = installable.toApp(*evalState).resolve(evalStore, store);
 
         Strings programArgs{app.program};
 
diff --git a/src/nix/hash.cc b/src/nix/hash.cc
index 60d9593a7..9feca9345 100644
--- a/src/nix/hash.cc
+++ b/src/nix/hash.cc
@@ -151,7 +151,6 @@ struct CmdHash : NixMultiCommand
     {
         if (!command)
             throw UsageError("'nix hash' requires a sub-command.");
-        command->second->prepare();
         command->second->run();
     }
 };
@@ -161,11 +160,11 @@ static auto rCmdHash = registerCommand<CmdHash>("hash");
 /* Legacy nix-hash command. */
 static int compatNixHash(int argc, char * * argv)
 {
-    HashType ht = htMD5;
+    std::optional<HashType> ht;
     bool flat = false;
-    bool base32 = false;
+    Base base = Base16;
     bool truncate = false;
-    enum { opHash, opTo32, opTo16 } op = opHash;
+    enum { opHash, opTo } op = opHash;
     std::vector<std::string> ss;
 
     parseCmdLine(argc, argv, [&](Strings::iterator & arg, const Strings::iterator & end) {
@@ -174,14 +173,31 @@ static int compatNixHash(int argc, char * * argv)
         else if (*arg == "--version")
             printVersion("nix-hash");
         else if (*arg == "--flat") flat = true;
-        else if (*arg == "--base32") base32 = true;
+        else if (*arg == "--base16") base = Base16;
+        else if (*arg == "--base32") base = Base32;
+        else if (*arg == "--base64") base = Base64;
+        else if (*arg == "--sri") base = SRI;
         else if (*arg == "--truncate") truncate = true;
         else if (*arg == "--type") {
             std::string s = getArg(*arg, arg, end);
             ht = parseHashType(s);
         }
-        else if (*arg == "--to-base16") op = opTo16;
-        else if (*arg == "--to-base32") op = opTo32;
+        else if (*arg == "--to-base16") {
+            op = opTo;
+            base = Base16;
+        }
+        else if (*arg == "--to-base32") {
+            op = opTo;
+            base = Base32;
+        }
+        else if (*arg == "--to-base64") {
+            op = opTo;
+            base = Base64;
+        }
+        else if (*arg == "--to-sri") {
+            op = opTo;
+            base = SRI;
+        }
         else if (*arg != "" && arg->at(0) == '-')
             return false;
         else
@@ -191,17 +207,18 @@ static int compatNixHash(int argc, char * * argv)
 
     if (op == opHash) {
         CmdHashBase cmd(flat ? FileIngestionMethod::Flat : FileIngestionMethod::Recursive);
-        cmd.ht = ht;
-        cmd.base = base32 ? Base32 : Base16;
+        if (!ht.has_value()) ht = htMD5;
+        cmd.ht = ht.value();
+        cmd.base = base;
         cmd.truncate = truncate;
         cmd.paths = ss;
         cmd.run();
     }
 
     else {
-        CmdToBase cmd(op == opTo32 ? Base32 : Base16);
+        CmdToBase cmd(base);
         cmd.args = ss;
-        cmd.ht = ht;
+        if (ht.has_value()) cmd.ht = ht;
         cmd.run();
     }
 
diff --git a/src/nix/help-stores.md b/src/nix/help-stores.md
new file mode 100644
index 000000000..47ba9b94d
--- /dev/null
+++ b/src/nix/help-stores.md
@@ -0,0 +1,46 @@
+R"(
+
+Nix supports different types of stores. These are described below.
+
+## Store URL format
+
+Stores are specified using a URL-like syntax. For example, the command
+
+```console
+# nix path-info --store https://cache.nixos.org/ --json \
+  /nix/store/a7gvj343m05j2s32xcnwr35v31ynlypr-coreutils-9.1
+```
+
+fetches information about a store path in the HTTP binary cache
+located at https://cache.nixos.org/, which is a type of store.
+
+Store URLs can specify **store settings** using URL query strings,
+i.e. by appending `?name1=value1&name2=value2&...` to the URL. For
+instance,
+
+```
+--store ssh://machine.example.org?ssh-key=/path/to/my/key
+```
+
+tells Nix to access the store on a remote machine via the SSH
+protocol, using `/path/to/my/key` as the SSH private key. The
+supported settings for each store type are documented below.
+
+The special store URL `auto` causes Nix to automatically select a
+store as follows:
+
+* Use the [local store](#local-store) `/nix/store` if `/nix/var/nix`
+  is writable by the current user.
+
+* Otherwise, if `/nix/var/nix/daemon-socket/socket` exists, [connect
+  to the Nix daemon listening on that socket](#local-daemon-store).
+
+* Otherwise, on Linux only, use the [local chroot store](#local-store)
+  `~/.local/share/nix/root`, which will be created automatically if it
+  does not exist.
+
+* Otherwise, use the [local store](#local-store) `/nix/store`.
+
+@stores@
+
+)"
diff --git a/src/nix/log.cc b/src/nix/log.cc
index a0598ca13..aaf829764 100644
--- a/src/nix/log.cc
+++ b/src/nix/log.cc
@@ -23,7 +23,7 @@ struct CmdLog : InstallableCommand
 
     Category category() override { return catSecondary; }
 
-    void run(ref<Store> store) override
+    void run(ref<Store> store, ref<Installable> installable) override
     {
         settings.readOnlyMode = true;
 
@@ -53,7 +53,7 @@ struct CmdLog : InstallableCommand
             if (!log) continue;
             stopProgressBar();
             printInfo("got build log for '%s' from '%s'", installable->what(), logSub.getUri());
-            std::cout << *log;
+            writeFull(STDOUT_FILENO, *log);
             return;
         }
 
diff --git a/src/nix/log.md b/src/nix/log.md
index 1c76226a3..01e9801df 100644
--- a/src/nix/log.md
+++ b/src/nix/log.md
@@ -22,8 +22,7 @@ R""(
 
 # Description
 
-This command prints the log of a previous build of the derivation
-*installable* on standard output.
+This command prints the log of a previous build of the [*installable*](./nix.md#installables) on standard output.
 
 Nix looks for build logs in two places:
 
diff --git a/src/nix/ls.cc b/src/nix/ls.cc
index e964b01b3..c990a303c 100644
--- a/src/nix/ls.cc
+++ b/src/nix/ls.cc
@@ -93,7 +93,7 @@ struct MixLs : virtual Args, MixJSON
         if (json) {
             if (showDirectory)
                 throw UsageError("'--directory' is useless with '--json'");
-            std::cout << listNar(accessor, path, recursive);
+            logger->cout("%s", listNar(accessor, path, recursive));
         } else
             listText(accessor);
     }
diff --git a/src/nix/main.cc b/src/nix/main.cc
index d3d2f5b16..54c920b4e 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -54,17 +54,17 @@ static bool haveInternet()
 
 std::string programPath;
 
-struct HelpRequested { };
-
 struct NixArgs : virtual MultiCommand, virtual MixCommonArgs
 {
     bool useNet = true;
     bool refresh = false;
+    bool helpRequested = false;
     bool showVersion = false;
 
     NixArgs() : MultiCommand(RegisterCommand::getCommandsFor({})), MixCommonArgs("nix")
     {
         categories.clear();
+        categories[catHelp] = "Help commands";
         categories[Command::catDefault] = "Main commands";
         categories[catSecondary] = "Infrequently used commands";
         categories[catUtility] = "Utility/scripting commands";
@@ -74,7 +74,7 @@ struct NixArgs : virtual MultiCommand, virtual MixCommonArgs
             .longName = "help",
             .description = "Show usage information.",
             .category = miscCategory,
-            .handler = {[&]() { throw HelpRequested(); }},
+            .handler = {[this]() { this->helpRequested = true; }},
         });
 
         addFlag({
@@ -164,11 +164,29 @@ struct NixArgs : virtual MultiCommand, virtual MixCommonArgs
     {
         commands = RegisterCommand::getCommandsFor({});
     }
+
+    std::string dumpCli()
+    {
+        auto res = nlohmann::json::object();
+
+        res["args"] = toJSON();
+
+        auto stores = nlohmann::json::object();
+        for (auto & implem : *Implementations::registered) {
+            auto storeConfig = implem.getConfig();
+            auto storeName = storeConfig->name();
+            stores[storeName]["doc"] = storeConfig->doc();
+            stores[storeName]["settings"] = storeConfig->toJSON();
+        }
+        res["stores"] = std::move(stores);
+
+        return res.dump();
+    }
 };
 
 /* Render the help for the specified subcommand to stdout using
    lowdown. */
-static void showHelp(std::vector<std::string> subcommand, MultiCommand & toplevel)
+static void showHelp(std::vector<std::string> subcommand, NixArgs & toplevel)
 {
     auto mdName = subcommand.empty() ? "nix" : fmt("nix3-%s", concatStringsSep("-", subcommand));
 
@@ -189,11 +207,11 @@ static void showHelp(std::vector<std::string> subcommand, MultiCommand & topleve
             , "/"),
         *vUtils);
 
-    auto attrs = state.buildBindings(16);
-    attrs.alloc("toplevel").mkString(toplevel.toJSON().dump());
+    auto vDump = state.allocValue();
+    vDump->mkString(toplevel.dumpCli());
 
     auto vRes = state.allocValue();
-    state.callFunction(*vGenerateManpage, state.allocValue()->mkAttrs(attrs), *vRes, noPos);
+    state.callFunction(*vGenerateManpage, *vDump, *vRes, noPos);
 
     auto attr = vRes->attrs->get(state.symbols.create(mdName + ".md"));
     if (!attr)
@@ -205,6 +223,14 @@ static void showHelp(std::vector<std::string> subcommand, MultiCommand & topleve
     std::cout << renderMarkdownToTerminal(markdown) << "\n";
 }
 
+static NixArgs & getNixArgs(Command & cmd)
+{
+    assert(cmd.parent);
+    MultiCommand * toplevel = cmd.parent;
+    while (toplevel->parent) toplevel = toplevel->parent;
+    return dynamic_cast<NixArgs &>(*toplevel);
+}
+
 struct CmdHelp : Command
 {
     std::vector<std::string> subcommand;
@@ -229,17 +255,43 @@ struct CmdHelp : Command
           ;
     }
 
+    Category category() override { return catHelp; }
+
     void run() override
     {
         assert(parent);
         MultiCommand * toplevel = parent;
         while (toplevel->parent) toplevel = toplevel->parent;
-        showHelp(subcommand, *toplevel);
+        showHelp(subcommand, getNixArgs(*this));
     }
 };
 
 static auto rCmdHelp = registerCommand<CmdHelp>("help");
 
+struct CmdHelpStores : Command
+{
+    std::string description() override
+    {
+        return "show help about store types and their settings";
+    }
+
+    std::string doc() override
+    {
+        return
+          #include "help-stores.md"
+          ;
+    }
+
+    Category category() override { return catHelp; }
+
+    void run() override
+    {
+        showHelp({"help-stores"}, getNixArgs(*this));
+    }
+};
+
+static auto rCmdHelpStores = registerCommand<CmdHelpStores>("help-stores");
+
 void mainWrapped(int argc, char * * argv)
 {
     savedArgv = argv;
@@ -291,13 +343,16 @@ void mainWrapped(int argc, char * * argv)
 
     NixArgs args;
 
-    if (argc == 2 && std::string(argv[1]) == "__dump-args") {
-        std::cout << args.toJSON().dump() << "\n";
+    if (argc == 2 && std::string(argv[1]) == "__dump-cli") {
+        logger->cout(args.dumpCli());
         return;
     }
 
     if (argc == 2 && std::string(argv[1]) == "__dump-builtins") {
-        settings.experimentalFeatures = {Xp::Flakes, Xp::FetchClosure};
+        experimentalFeatureSettings.experimentalFeatures = {
+            Xp::Flakes,
+            Xp::FetchClosure,
+        };
         evalSettings.pureEval = false;
         EvalState state({}, openStore("dummy://"));
         auto res = nlohmann::json::object();
@@ -312,7 +367,7 @@ void mainWrapped(int argc, char * * argv)
             b["doc"] = trim(stripIndentation(primOp->doc));
             res[state.symbols[builtin.name]] = std::move(b);
         }
-        std::cout << res.dump() << "\n";
+        logger->cout("%s", res);
         return;
     }
 
@@ -321,20 +376,24 @@ void mainWrapped(int argc, char * * argv)
         if (completions) {
             switch (completionType) {
             case ctNormal:
-                std::cout << "normal\n"; break;
+                logger->cout("normal"); break;
             case ctFilenames:
-                std::cout << "filenames\n"; break;
+                logger->cout("filenames"); break;
             case ctAttrs:
-                std::cout << "attrs\n"; break;
+                logger->cout("attrs"); break;
             }
             for (auto & s : *completions)
-                std::cout << s.completion << "\t" << trim(s.description) << "\n";
+                logger->cout(s.completion + "\t" + trim(s.description));
         }
     });
 
     try {
         args.parseCmdline(argvToStrings(argc, argv));
-    } catch (HelpRequested &) {
+    } catch (UsageError &) {
+        if (!args.helpRequested && !completions) throw;
+    }
+
+    if (args.helpRequested) {
         std::vector<std::string> subcommand;
         MultiCommand * command = &args;
         while (command) {
@@ -346,8 +405,6 @@ void mainWrapped(int argc, char * * argv)
         }
         showHelp(subcommand, args);
         return;
-    } catch (UsageError &) {
-        if (!completions) throw;
     }
 
     if (completions) {
@@ -366,7 +423,7 @@ void mainWrapped(int argc, char * * argv)
     if (args.command->first != "repl"
         && args.command->first != "doctor"
         && args.command->first != "upgrade-nix")
-        settings.requireExperimentalFeature(Xp::NixCommand);
+        experimentalFeatureSettings.require(Xp::NixCommand);
 
     if (args.useNet && !haveInternet()) {
         warn("you don't have Internet access; disabling some network-dependent features");
@@ -394,7 +451,6 @@ void mainWrapped(int argc, char * * argv)
     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 d86b90fc7..d9c988a9f 100644
--- a/src/nix/make-content-addressed.cc
+++ b/src/nix/make-content-addressed.cc
@@ -28,7 +28,6 @@ struct CmdMakeContentAddressed : virtual CopyCommand, virtual StorePathsCommand,
           ;
     }
 
-    using StorePathsCommand::run;
     void run(ref<Store> srcStore, StorePaths && storePaths) override
     {
         auto dstStore = dstUri.empty() ? openStore() : openStore(dstUri);
@@ -45,7 +44,7 @@ struct CmdMakeContentAddressed : virtual CopyCommand, virtual StorePathsCommand,
             }
             auto json = json::object();
             json["rewrites"] = jsonRewrites;
-            std::cout << json.dump();
+            logger->cout("%s", json);
         } 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 32eecc880..b1f7da525 100644
--- a/src/nix/make-content-addressed.md
+++ b/src/nix/make-content-addressed.md
@@ -35,7 +35,9 @@ R""(
 # Description
 
 This command converts the closure of the store paths specified by
-*installables* to content-addressed form. Nix store paths are usually
+[*installables*](./nix.md#installables) to content-addressed form.
+
+Nix store paths are usually
 *input-addressed*, meaning that the hash part of the store path is
 computed from the contents of the derivation (i.e., the build-time
 dependency graph). Input-addressed paths need to be signed by a
diff --git a/src/nix/nar.cc b/src/nix/nar.cc
index dbb043d9b..9815410cf 100644
--- a/src/nix/nar.cc
+++ b/src/nix/nar.cc
@@ -25,7 +25,6 @@ struct CmdNar : NixMultiCommand
     {
         if (!command)
             throw UsageError("'nix nar' requires a sub-command.");
-        command->second->prepare();
         command->second->run();
     }
 };
diff --git a/src/nix/nix.md b/src/nix/nix.md
index db60c59ff..e1865b31c 100644
--- a/src/nix/nix.md
+++ b/src/nix/nix.md
@@ -48,102 +48,112 @@ manual](https://nixos.org/manual/nix/stable/).
 
 # Installables
 
-Many `nix` subcommands operate on one or more *installables*. These are
-command line arguments that represent something that can be built in
-the Nix store. Here are the recognised types of installables:
-
-* **Flake output attributes**: `nixpkgs#hello`
-
-  These have the form *flakeref*[`#`*attrpath*], where *flakeref* is a
-  flake reference and *attrpath* is an optional attribute path. For
-  more information on flakes, see [the `nix flake` manual
-  page](./nix3-flake.md).  Flake references are most commonly a flake
-  identifier in the flake registry (e.g. `nixpkgs`), or a raw path
-  (e.g. `/path/to/my-flake` or `.` or `../foo`), or a full URL
-  (e.g. `github:nixos/nixpkgs` or `path:.`)
-
-  When the flake reference is a raw path (a path without any URL
-  scheme), it is interpreted as a `path:` or `git+file:` url in the following
-  way:
-  
-  - If the path is within a Git repository, then the url will be of the form
-    `git+file://[GIT_REPO_ROOT]?dir=[RELATIVE_FLAKE_DIR_PATH]`
-    where `GIT_REPO_ROOT` is the path to the root of the git repository,
-    and `RELATIVE_FLAKE_DIR_PATH` is the path (relative to the directory
-    root) of the closest parent of the given path that contains a `flake.nix` within
-    the git repository.
-    If no such directory exists, then Nix will error-out.
-    
-    Note that the search will only include files indexed by git. In particular, files
-    which are matched by `.gitignore` or have never been `git add`-ed will not be
-    available in the flake. If this is undesirable, specify `path:<directory>` explicitly;
-    
-    For example, if `/foo/bar` is a git repository with the following structure:
-    ```
-    .
-    └── baz
-        ├── blah
-        │   └── file.txt
-        └── flake.nix
-    ```
+Many `nix` subcommands operate on one or more *installables*.
+These are command line arguments that represent something that can be realised in the Nix store.
 
-  Then `/foo/bar/baz/blah` will resolve to `git+file:///foo/bar?dir=baz`
+The following types of installable are supported by most commands:
 
-  - If the supplied path is not a git repository, then the url will have the form
-    `path:FLAKE_DIR_PATH` where `FLAKE_DIR_PATH` is the closest parent
-    of the supplied path that contains a `flake.nix` file (within the same file-system).
-    If no such directory exists, then Nix will error-out.
-    
-    For example, if `/foo/bar/flake.nix` exists, then `/foo/bar/baz/` will resolve to
-   `path:/foo/bar`
+- [Flake output attribute](#flake-output-attribute)
+- [Store path](#store-path)
+- [Nix file](#nix-file), optionally qualified by an attribute path
+- [Nix expression](#nix-expression), optionally qualified by an attribute path
 
-  If *attrpath* is omitted, Nix tries some default values; for most
-  subcommands, the default is `packages.`*system*`.default`
-  (e.g. `packages.x86_64-linux.default`), but some subcommands have
-  other defaults. If *attrpath* *is* specified, *attrpath* is
-  interpreted as relative to one or more prefixes; for most
-  subcommands, these are `packages.`*system*,
-  `legacyPackages.*system*` and the empty prefix. Thus, on
-  `x86_64-linux` `nix build nixpkgs#hello` will try to build the
-  attributes `packages.x86_64-linux.hello`,
-  `legacyPackages.x86_64-linux.hello` and `hello`.
+For most commands, if no installable is specified, `.` as assumed.
+That is, Nix will operate on the default flake output attribute of the flake in the current directory.
 
-* **Store paths**: `/nix/store/v5sv61sszx301i0x6xysaqzla09nksnd-hello-2.10`
+### Flake output attribute
 
-  These are paths inside the Nix store, or symlinks that resolve to a
-  path in the Nix store.
+Example: `nixpkgs#hello`
 
-* **Store derivations**: `/nix/store/p7gp6lxdg32h4ka1q398wd9r2zkbbz2v-hello-2.10.drv`
+These have the form *flakeref*[`#`*attrpath*], where *flakeref* is a
+[flake reference](./nix3-flake.md#flake-references) and *attrpath* is an optional attribute path. For
+more information on flakes, see [the `nix flake` manual
+page](./nix3-flake.md).  Flake references are most commonly a flake
+identifier in the flake registry (e.g. `nixpkgs`), or a raw path
+(e.g. `/path/to/my-flake` or `.` or `../foo`), or a full URL
+(e.g. `github:nixos/nixpkgs` or `path:.`)
 
-  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.
+When the flake reference is a raw path (a path without any URL
+scheme), it is interpreted as a `path:` or `git+file:` url in the following
+way:
 
-  [output path]: ../../glossary.md#gloss-output-path
+- If the path is within a Git repository, then the url will be of the form
+  `git+file://[GIT_REPO_ROOT]?dir=[RELATIVE_FLAKE_DIR_PATH]`
+  where `GIT_REPO_ROOT` is the path to the root of the git repository,
+  and `RELATIVE_FLAKE_DIR_PATH` is the path (relative to the directory
+  root) of the closest parent of the given path that contains a `flake.nix` within
+  the git repository.
+  If no such directory exists, then Nix will error-out.
 
-  For example, `nix path-info` prints information about the output paths:
+  Note that the search will only include files indexed by git. In particular, files
+  which are matched by `.gitignore` or have never been `git add`-ed will not be
+  available in the flake. If this is undesirable, specify `path:<directory>` explicitly;
 
-  ```console
-  # nix path-info --json /nix/store/p7gp6lxdg32h4ka1q398wd9r2zkbbz2v-hello-2.10.drv
-  [{"path":"/nix/store/v5sv61sszx301i0x6xysaqzla09nksnd-hello-2.10",…}]
+  For example, if `/foo/bar` is a git repository with the following structure:
+  ```
+  .
+  └── baz
+      ├── blah
+      │   └── file.txt
+      └── flake.nix
   ```
 
-  If you want to operate on the store derivation itself, pass the
-  `--derivation` flag.
+  Then `/foo/bar/baz/blah` will resolve to `git+file:///foo/bar?dir=baz`
+
+- If the supplied path is not a git repository, then the url will have the form
+  `path:FLAKE_DIR_PATH` where `FLAKE_DIR_PATH` is the closest parent
+  of the supplied path that contains a `flake.nix` file (within the same file-system).
+  If no such directory exists, then Nix will error-out.
+
+  For example, if `/foo/bar/flake.nix` exists, then `/foo/bar/baz/` will resolve to
+ `path:/foo/bar`
+
+If *attrpath* is omitted, Nix tries some default values; for most
+subcommands, the default is `packages.`*system*`.default`
+(e.g. `packages.x86_64-linux.default`), but some subcommands have
+other defaults. If *attrpath* *is* specified, *attrpath* is
+interpreted as relative to one or more prefixes; for most
+subcommands, these are `packages.`*system*,
+`legacyPackages.*system*` and the empty prefix. Thus, on
+`x86_64-linux` `nix build nixpkgs#hello` will try to build the
+attributes `packages.x86_64-linux.hello`,
+`legacyPackages.x86_64-linux.hello` and `hello`.
+
+### Store path
+
+Example: `/nix/store/v5sv61sszx301i0x6xysaqzla09nksnd-hello-2.10`
+
+These are paths inside the Nix store, or symlinks that resolve to a path in the Nix store.
 
-* **Nix attributes**: `--file /path/to/nixpkgs hello`
+A [store derivation] is also addressed by store path.
 
-  When the `-f` / `--file` *path* option is given, installables are
-  interpreted as attribute paths referencing a value returned by
-  evaluating the Nix file *path*.
+Example: `/nix/store/p7gp6lxdg32h4ka1q398wd9r2zkbbz2v-hello-2.10.drv`
 
-* **Nix expressions**: `--expr '(import <nixpkgs> {}).hello.overrideDerivation (prev: { name = "my-hello"; })'`.
+If you want to refer to an output path of that store derivation, add the output name preceded by a caret (`^`).
 
-  When the `--expr` option is given, all installables are interpreted
-  as Nix expressions. You may need to specify `--impure` if the
-  expression references impure inputs (such as `<nixpkgs>`).
+Example: `/nix/store/p7gp6lxdg32h4ka1q398wd9r2zkbbz2v-hello-2.10.drv^out`
 
-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.
+All outputs can be referred to at once with the special syntax `^*`.
+
+Example: `/nix/store/p7gp6lxdg32h4ka1q398wd9r2zkbbz2v-hello-2.10.drv^*`
+
+### Nix file
+
+Example: `--file /path/to/nixpkgs hello`
+
+When the option `-f` / `--file` *path* \[*attrpath*...\] is given, installables are interpreted as the value of the expression in the Nix file at *path*.
+If attribute paths are provided, commands will operate on the corresponding values accessible at these paths.
+The Nix expression in that file, or any selected attribute, must evaluate to a derivation.
+
+### Nix expression
+
+Example: `--expr 'import <nixpkgs> {}' hello`
+
+When the option `--expr` *expression* \[*attrpath*...\] is given, installables are interpreted as the value of the of the Nix expression.
+If attribute paths are provided, commands will operate on the corresponding values accessible at these paths.
+The Nix expression, or any selected attribute, must evaluate to a derivation.
+
+You may need to specify `--impure` if the expression references impure inputs (such as `<nixpkgs>`).
 
 ## Derivation output selection
 
@@ -210,8 +220,7 @@ operate are determined as follows:
 
 # Nix stores
 
-Most `nix` subcommands operate on a *Nix store*.
-
-TODO: list store types, options
+Most `nix` subcommands operate on a *Nix store*. These are documented
+in [`nix help-stores`](./nix3-help-stores.md).
 
 )""
diff --git a/src/nix/path-info.md b/src/nix/path-info.md
index b30898ac0..6ad23a02e 100644
--- a/src/nix/path-info.md
+++ b/src/nix/path-info.md
@@ -80,7 +80,7 @@ R""(
 # Description
 
 This command shows information about the store paths produced by
-*installables*, or about all paths in the store if you pass `--all`.
+[*installables*](./nix.md#installables), or about all paths in the store if you pass `--all`.
 
 By default, this command only prints the store paths. You can get
 additional information by passing flags such as `--closure-size`,
diff --git a/src/nix/prefetch.cc b/src/nix/prefetch.cc
index 209517b21..b06b8a320 100644
--- a/src/nix/prefetch.cc
+++ b/src/nix/prefetch.cc
@@ -240,9 +240,9 @@ static int main_nix_prefetch_url(int argc, char * * argv)
         if (!printPath)
             printInfo("path is '%s'", store->printStorePath(storePath));
 
-        std::cout << printHash16or32(hash) << std::endl;
+        logger->cout(printHash16or32(hash));
         if (printPath)
-            std::cout << store->printStorePath(storePath) << std::endl;
+            logger->cout(store->printStorePath(storePath));
 
         return 0;
     }
diff --git a/src/nix/print-dev-env.md b/src/nix/print-dev-env.md
index 2aad491de..a8ce9d36a 100644
--- a/src/nix/print-dev-env.md
+++ b/src/nix/print-dev-env.md
@@ -40,7 +40,7 @@ R""(
 
 This command prints a shell script that can be sourced by `bash` and
 that sets the variables and shell functions defined by the build
-process of *installable*. This allows you to get a similar build
+process of [*installable*](./nix.md#installables). This allows you to get a similar build
 environment in your current shell rather than in a subshell (as with
 `nix develop`).
 
diff --git a/src/nix/profile-install.md b/src/nix/profile-install.md
index aed414963..4c0f82c09 100644
--- a/src/nix/profile-install.md
+++ b/src/nix/profile-install.md
@@ -29,6 +29,6 @@ R""(
 
 # Description
 
-This command adds *installables* to a Nix profile.
+This command adds [*installables*](./nix.md#installables) to a Nix profile.
 
 )""
diff --git a/src/nix/profile.cc b/src/nix/profile.cc
index 04ac48f00..5aa87a313 100644
--- a/src/nix/profile.cc
+++ b/src/nix/profile.cc
@@ -237,12 +237,12 @@ struct ProfileManifest
 
         while (i != prevElems.end() || j != curElems.end()) {
             if (j != curElems.end() && (i == prevElems.end() || i->describe() > j->describe())) {
-                std::cout << fmt("%s%s: ∅ -> %s\n", indent, j->describe(), j->versions());
+                logger->cout("%s%s: ∅ -> %s", indent, j->describe(), j->versions());
                 changes = true;
                 ++j;
             }
             else if (i != prevElems.end() && (j == curElems.end() || i->describe() < j->describe())) {
-                std::cout << fmt("%s%s: %s -> ∅\n", indent, i->describe(), i->versions());
+                logger->cout("%s%s: %s -> ∅", indent, i->describe(), i->versions());
                 changes = true;
                 ++i;
             }
@@ -250,7 +250,7 @@ struct ProfileManifest
                 auto v1 = i->versions();
                 auto v2 = j->versions();
                 if (v1 != v2) {
-                    std::cout << fmt("%s%s: %s -> %s\n", indent, i->describe(), v1, v2);
+                    logger->cout("%s%s: %s -> %s", indent, i->describe(), v1, v2);
                     changes = true;
                 }
                 ++i;
@@ -259,17 +259,23 @@ struct ProfileManifest
         }
 
         if (!changes)
-            std::cout << fmt("%sNo changes.\n", indent);
+            logger->cout("%sNo changes.", indent);
     }
 };
 
-static std::map<Installable *, std::pair<BuiltPaths, ExtraPathInfo>>
+static std::map<Installable *, std::pair<BuiltPaths, ref<ExtraPathInfo>>>
 builtPathsPerInstallable(
-    const std::vector<std::pair<std::shared_ptr<Installable>, BuiltPathWithResult>> & builtPaths)
+    const std::vector<std::pair<ref<Installable>, BuiltPathWithResult>> & builtPaths)
 {
-    std::map<Installable *, std::pair<BuiltPaths, ExtraPathInfo>> res;
+    std::map<Installable *, std::pair<BuiltPaths, ref<ExtraPathInfo>>> res;
     for (auto & [installable, builtPath] : builtPaths) {
-        auto & r = res[installable.get()];
+        auto & r = res.insert({
+            &*installable,
+            {
+                {},
+                make_ref<ExtraPathInfo>(),
+            }
+        }).first->second;
         /* Note that there could be conflicting info
            (e.g. meta.priority fields) if the installable returned
            multiple derivations. So pick one arbitrarily. FIXME:
@@ -305,7 +311,7 @@ struct CmdProfileInstall : InstallablesCommand, MixDefaultProfile
           ;
     }
 
-    void run(ref<Store> store) override
+    void run(ref<Store> store, Installables && installables) override
     {
         ProfileManifest manifest(*getEvalState(), *profile);
 
@@ -316,14 +322,16 @@ struct CmdProfileInstall : InstallablesCommand, MixDefaultProfile
         for (auto & installable : installables) {
             ProfileElement element;
 
-            auto & [res, info] = builtPaths[installable.get()];
+            auto iter = builtPaths.find(&*installable);
+            if (iter == builtPaths.end()) continue;
+            auto & [res, info] = iter->second;
 
-            if (info.originalRef && info.resolvedRef && info.attrPath && info.extendedOutputsSpec) {
+            if (auto * info2 = dynamic_cast<ExtraPathInfoFlake *>(&*info)) {
                 element.source = ProfileElementSource {
-                    .originalRef = *info.originalRef,
-                    .resolvedRef = *info.resolvedRef,
-                    .attrPath = *info.attrPath,
-                    .outputs = *info.extendedOutputsSpec,
+                    .originalRef = info2->flake.originalRef,
+                    .resolvedRef = info2->flake.resolvedRef,
+                    .attrPath = info2->value.attrPath,
+                    .outputs = info2->value.extendedOutputsSpec,
                 };
             }
 
@@ -332,14 +340,75 @@ struct CmdProfileInstall : InstallablesCommand, MixDefaultProfile
             element.priority =
                 priority
                 ? *priority
-                : info.priority.value_or(defaultPriority);
+                : ({
+                    auto * info2 = dynamic_cast<ExtraPathInfoValue *>(&*info);
+                    info2
+                        ? info2->value.priority.value_or(defaultPriority)
+                        : defaultPriority;
+                });
 
             element.updateStorePaths(getEvalStore(), store, res);
 
             manifest.elements.push_back(std::move(element));
         }
 
-        updateProfile(manifest.build(store));
+        try {
+            updateProfile(manifest.build(store));
+        } catch (BuildEnvFileConflictError & conflictError) {
+            // FIXME use C++20 std::ranges once macOS has it
+            //       See https://github.com/NixOS/nix/compare/3efa476c5439f8f6c1968a6ba20a31d1239c2f04..1fe5d172ece51a619e879c4b86f603d9495cc102
+            auto findRefByFilePath = [&]<typename Iterator>(Iterator begin, Iterator end) {
+                for (auto it = begin; it != end; it++) {
+                    auto profileElement = *it;
+                    for (auto & storePath : profileElement.storePaths) {
+                        if (conflictError.fileA.starts_with(store->printStorePath(storePath))) {
+                            return std::pair(conflictError.fileA, profileElement.source->originalRef);
+                        }
+                        if (conflictError.fileB.starts_with(store->printStorePath(storePath))) {
+                            return std::pair(conflictError.fileB, profileElement.source->originalRef);
+                        }
+                    }
+                }
+                throw conflictError;
+            };
+            // There are 2 conflicting files. We need to find out which one is from the already installed package and
+            // which one is the package that is the new package that is being installed.
+            // The first matching package is the one that was already installed (original).
+            auto [originalConflictingFilePath, originalConflictingRef] = findRefByFilePath(manifest.elements.begin(), manifest.elements.end());
+            // The last matching package is the one that was going to be installed (new).
+            auto [newConflictingFilePath, newConflictingRef] = findRefByFilePath(manifest.elements.rbegin(), manifest.elements.rend());
+
+            throw Error(
+                "An existing package already provides the following file:\n"
+                "\n"
+                "  %1%\n"
+                "\n"
+                "This is the conflicting file from the new package:\n"
+                "\n"
+                "  %2%\n"
+                "\n"
+                "To remove the existing package:\n"
+                "\n"
+                "  nix profile remove %3%\n"
+                "\n"
+                "The new package can also be installed next to the existing one by assigning a different priority.\n"
+                "The conflicting packages have a priority of %5%.\n"
+                "To prioritise the new package:\n"
+                "\n"
+                "  nix profile install %4% --priority %6%\n"
+                "\n"
+                "To prioritise the existing package:\n"
+                "\n"
+                "  nix profile install %4% --priority %7%\n",
+                originalConflictingFilePath,
+                newConflictingFilePath,
+                originalConflictingRef.to_string(),
+                newConflictingRef.to_string(),
+                conflictError.priority,
+                conflictError.priority - 1,
+                conflictError.priority + 1
+            );
+        }
     }
 };
 
@@ -466,7 +535,7 @@ struct CmdProfileUpgrade : virtual SourceExprCommand, MixDefaultProfile, MixProf
 
         auto matchers = getMatchers(store);
 
-        std::vector<std::shared_ptr<Installable>> installables;
+        Installables installables;
         std::vector<size_t> indices;
 
         auto upgradedCount = 0;
@@ -482,7 +551,7 @@ struct CmdProfileUpgrade : virtual SourceExprCommand, MixDefaultProfile, MixProf
                 Activity act(*logger, lvlChatty, actUnknown,
                     fmt("checking '%s' for updates", element.source->attrPath));
 
-                auto installable = std::make_shared<InstallableFlake>(
+                auto installable = make_ref<InstallableFlake>(
                     this,
                     getEvalState(),
                     FlakeRef(element.source->originalRef),
@@ -494,19 +563,20 @@ struct CmdProfileUpgrade : virtual SourceExprCommand, MixDefaultProfile, MixProf
 
                 auto derivedPaths = installable->toDerivedPaths();
                 if (derivedPaths.empty()) continue;
-                auto & info = derivedPaths[0].info;
-
-                assert(info.resolvedRef && info.attrPath);
+                auto * infop = dynamic_cast<ExtraPathInfoFlake *>(&*derivedPaths[0].info);
+                // `InstallableFlake` should use `ExtraPathInfoFlake`.
+                assert(infop);
+                auto & info = *infop;
 
-                if (element.source->resolvedRef == info.resolvedRef) continue;
+                if (element.source->resolvedRef == info.flake.resolvedRef) continue;
 
                 printInfo("upgrading '%s' from flake '%s' to '%s'",
-                    element.source->attrPath, element.source->resolvedRef, *info.resolvedRef);
+                    element.source->attrPath, element.source->resolvedRef, info.flake.resolvedRef);
 
                 element.source = ProfileElementSource {
                     .originalRef = installable->flakeRef,
-                    .resolvedRef = *info.resolvedRef,
-                    .attrPath = *info.attrPath,
+                    .resolvedRef = info.flake.resolvedRef,
+                    .attrPath = info.value.attrPath,
                     .outputs = installable->extendedOutputsSpec,
                 };
 
@@ -535,7 +605,10 @@ struct CmdProfileUpgrade : virtual SourceExprCommand, MixDefaultProfile, MixProf
         for (size_t i = 0; i < installables.size(); ++i) {
             auto & installable = installables.at(i);
             auto & element = manifest.elements[indices.at(i)];
-            element.updateStorePaths(getEvalStore(), store, builtPaths[installable.get()].first);
+            element.updateStorePaths(
+                getEvalStore(),
+                store,
+                builtPaths.find(&*installable)->second.first);
         }
 
         updateProfile(manifest.build(store));
@@ -593,9 +666,9 @@ struct CmdProfileDiffClosures : virtual StoreCommand, MixDefaultProfile
 
         for (auto & gen : gens) {
             if (prevGen) {
-                if (!first) std::cout << "\n";
+                if (!first) logger->cout("");
                 first = false;
-                std::cout << fmt("Version %d -> %d:\n", prevGen->number, gen.number);
+                logger->cout("Version %d -> %d:", prevGen->number, gen.number);
                 printClosureDiff(store,
                     store->followLinksToStorePath(prevGen->path),
                     store->followLinksToStorePath(gen.path),
@@ -631,10 +704,10 @@ struct CmdProfileHistory : virtual StoreCommand, EvalCommand, MixDefaultProfile
         for (auto & gen : gens) {
             ProfileManifest manifest(*getEvalState(), gen.path);
 
-            if (!first) std::cout << "\n";
+            if (!first) logger->cout("");
             first = false;
 
-            std::cout << fmt("Version %s%d" ANSI_NORMAL " (%s)%s:\n",
+            logger->cout("Version %s%d" ANSI_NORMAL " (%s)%s:",
                 gen.number == curGen ? ANSI_GREEN : ANSI_BOLD,
                 gen.number,
                 std::put_time(std::gmtime(&gen.creationTime), "%Y-%m-%d"),
@@ -751,7 +824,6 @@ struct CmdProfile : NixMultiCommand
     {
         if (!command)
             throw UsageError("'nix profile' requires a sub-command.");
-        command->second->prepare();
         command->second->run();
     }
 };
diff --git a/src/nix/profile.md b/src/nix/profile.md
index 273e02280..bf61ef4b9 100644
--- a/src/nix/profile.md
+++ b/src/nix/profile.md
@@ -12,7 +12,7 @@ them to be rolled back easily.
 The default profile used by `nix profile` is `$HOME/.nix-profile`,
 which, if it does not exist, is created as a symlink to
 `/nix/var/nix/profiles/default` if Nix is invoked by the
-`root` user, or `/nix/var/nix/profiles/per-user/`*username* otherwise.
+`root` user, or `${XDG_STATE_HOME-$HOME/.local/state}/nix/profiles/profile` otherwise.
 
 You can specify another profile location using `--profile` *path*.
 
@@ -24,11 +24,11 @@ the profile. In turn, *path*`-`*N* is a symlink to a path in the Nix
 store. For example:
 
 ```console
-$ ls -l /nix/var/nix/profiles/per-user/alice/profile*
-lrwxrwxrwx 1 alice users 14 Nov 25 14:35 /nix/var/nix/profiles/per-user/alice/profile -> profile-7-link
-lrwxrwxrwx 1 alice users 51 Oct 28 16:18 /nix/var/nix/profiles/per-user/alice/profile-5-link -> /nix/store/q69xad13ghpf7ir87h0b2gd28lafjj1j-profile
-lrwxrwxrwx 1 alice users 51 Oct 29 13:20 /nix/var/nix/profiles/per-user/alice/profile-6-link -> /nix/store/6bvhpysd7vwz7k3b0pndn7ifi5xr32dg-profile
-lrwxrwxrwx 1 alice users 51 Nov 25 14:35 /nix/var/nix/profiles/per-user/alice/profile-7-link -> /nix/store/mp0x6xnsg0b8qhswy6riqvimai4gm677-profile
+$ ls -l ~alice/.local/state/nix/profiles/profile*
+lrwxrwxrwx 1 alice users 14 Nov 25 14:35 /home/alice/.local/state/nix/profiles/profile -> profile-7-link
+lrwxrwxrwx 1 alice users 51 Oct 28 16:18 /home/alice/.local/state/nix/profiles/profile-5-link -> /nix/store/q69xad13ghpf7ir87h0b2gd28lafjj1j-profile
+lrwxrwxrwx 1 alice users 51 Oct 29 13:20 /home/alice/.local/state/nix/profiles/profile-6-link -> /nix/store/6bvhpysd7vwz7k3b0pndn7ifi5xr32dg-profile
+lrwxrwxrwx 1 alice users 51 Nov 25 14:35 /home/alice/.local/state/nix/profiles/profile-7-link -> /nix/store/mp0x6xnsg0b8qhswy6riqvimai4gm677-profile
 ```
 
 Each of these symlinks is a root for the Nix garbage collector.
@@ -38,20 +38,20 @@ profile is a tree of symlinks to the files of the installed packages,
 e.g.
 
 ```console
-$ ll -R /nix/var/nix/profiles/per-user/eelco/profile-7-link/
-/nix/var/nix/profiles/per-user/eelco/profile-7-link/:
+$ ll -R ~eelco/.local/state/nix/profiles/profile-7-link/
+/home/eelco/.local/state/nix/profiles/profile-7-link/:
 total 20
 dr-xr-xr-x 2 root root 4096 Jan  1  1970 bin
 -r--r--r-- 2 root root 1402 Jan  1  1970 manifest.json
 dr-xr-xr-x 4 root root 4096 Jan  1  1970 share
 
-/nix/var/nix/profiles/per-user/eelco/profile-7-link/bin:
+/home/eelco/.local/state/nix/profiles/profile-7-link/bin:
 total 20
 lrwxrwxrwx 5 root root 79 Jan  1  1970 chromium -> /nix/store/ijm5k0zqisvkdwjkc77mb9qzb35xfi4m-chromium-86.0.4240.111/bin/chromium
 lrwxrwxrwx 7 root root 87 Jan  1  1970 spotify -> /nix/store/w9182874m1bl56smps3m5zjj36jhp3rn-spotify-1.1.26.501.gbe11e53b-15/bin/spotify
 lrwxrwxrwx 3 root root 79 Jan  1  1970 zoom-us -> /nix/store/wbhg2ga8f3h87s9h5k0slxk0m81m4cxl-zoom-us-5.3.469451.0927/bin/zoom-us
 
-/nix/var/nix/profiles/per-user/eelco/profile-7-link/share/applications:
+/home/eelco/.local/state/nix/profiles/profile-7-link/share/applications:
 total 12
 lrwxrwxrwx 4 root root 120 Jan  1  1970 chromium-browser.desktop -> /nix/store/4cf803y4vzfm3gyk3vzhzb2327v0kl8a-chromium-unwrapped-86.0.4240.111/share/applications/chromium-browser.desktop
 lrwxrwxrwx 7 root root 110 Jan  1  1970 spotify.desktop -> /nix/store/w9182874m1bl56smps3m5zjj36jhp3rn-spotify-1.1.26.501.gbe11e53b-15/share/applications/spotify.desktop
diff --git a/src/nix/realisation.cc b/src/nix/realisation.cc
index c9a7157cd..e19e93219 100644
--- a/src/nix/realisation.cc
+++ b/src/nix/realisation.cc
@@ -21,7 +21,6 @@ struct CmdRealisation : virtual NixMultiCommand
     {
         if (!command)
             throw UsageError("'nix realisation' requires a sub-command.");
-        command->second->prepare();
         command->second->run();
     }
 };
@@ -46,7 +45,7 @@ struct CmdRealisationInfo : BuiltPathsCommand, MixJSON
 
     void run(ref<Store> store, BuiltPaths && paths) override
     {
-        settings.requireExperimentalFeature(Xp::CaDerivations);
+        experimentalFeatureSettings.require(Xp::CaDerivations);
         RealisedPath::Set realisations;
 
         for (auto & builtPath : paths) {
@@ -65,18 +64,16 @@ struct CmdRealisationInfo : BuiltPathsCommand, MixJSON
 
                 res.push_back(currentPath);
             }
-            std::cout << res.dump();
+            logger->cout("%s", res);
         }
         else {
             for (auto & path : realisations) {
                 if (auto realisation = std::get_if<Realisation>(&path.raw)) {
-                    std::cout <<
-                        realisation->id.to_string() << " " <<
-                        store->printStorePath(realisation->outPath);
+                    logger->cout("%s %s",
+                        realisation->id.to_string(),
+                        store->printStorePath(realisation->outPath));
                 } else
-                    std::cout << store->printStorePath(path.path());
-
-                std::cout << std::endl;
+                    logger->cout("%s", store->printStorePath(path.path()));
             }
         }
     }
diff --git a/src/nix/registry.cc b/src/nix/registry.cc
index b5bdfba95..cb94bbd31 100644
--- a/src/nix/registry.cc
+++ b/src/nix/registry.cc
@@ -224,10 +224,9 @@ struct CmdRegistry : virtual NixMultiCommand
 
     void run() override
     {
-        settings.requireExperimentalFeature(Xp::Flakes);
+        experimentalFeatureSettings.require(Xp::Flakes);
         if (!command)
             throw UsageError("'nix registry' requires a sub-command.");
-        command->second->prepare();
         command->second->run();
     }
 };
diff --git a/src/nix/repl.cc b/src/nix/repl.cc
index 679bdea77..7aa8774e9 100644
--- a/src/nix/repl.cc
+++ b/src/nix/repl.cc
@@ -1,30 +1,17 @@
 #include "eval.hh"
 #include "globals.hh"
 #include "command.hh"
+#include "installable-value.hh"
 #include "repl.hh"
 
 namespace nix {
 
-struct CmdRepl : InstallablesCommand
+struct CmdRepl : RawInstallablesCommand
 {
     CmdRepl() {
         evalSettings.pureEval = false;
     }
 
-    void prepare() override
-    {
-        if (!settings.isExperimentalFeatureEnabled(Xp::ReplFlake) && !(file) && this->_installables.size() >= 1) {
-            warn("future versions of Nix will require using `--file` to load a file");
-            if (this->_installables.size() > 1)
-                warn("more than one input file is not currently supported");
-            auto filePath = this->_installables[0].data();
-            file = std::optional(filePath);
-            _installables.front() = _installables.back();
-            _installables.pop_back();
-        }
-        installables = InstallablesCommand::load();
-    }
-
     std::vector<std::string> files;
 
     Strings getDefaultFlakeAttrPaths() override
@@ -32,11 +19,6 @@ struct CmdRepl : InstallablesCommand
         return {""};
     }
 
-    bool useDefaultInstallables() override
-    {
-        return file.has_value() or expr.has_value();
-    }
-
     bool forceImpureByDefault() override
     {
         return true;
@@ -54,17 +36,34 @@ struct CmdRepl : InstallablesCommand
           ;
     }
 
-    void run(ref<Store> store) override
+    void applyDefaultInstallables(std::vector<std::string> & rawInstallables) override
+    {
+        if (!experimentalFeatureSettings.isEnabled(Xp::ReplFlake) && !(file) && rawInstallables.size() >= 1) {
+            warn("future versions of Nix will require using `--file` to load a file");
+            if (rawInstallables.size() > 1)
+                warn("more than one input file is not currently supported");
+            auto filePath = rawInstallables[0].data();
+            file = std::optional(filePath);
+            rawInstallables.front() = rawInstallables.back();
+            rawInstallables.pop_back();
+        }
+        if (rawInstallables.empty() && (file.has_value() || expr.has_value())) {
+            rawInstallables.push_back(".");
+        }
+    }
+
+    void run(ref<Store> store, std::vector<std::string> && rawInstallables) override
     {
         auto state = getEvalState();
         auto getValues = [&]()->AbstractNixRepl::AnnotatedValues{
-            auto installables = load();
+            auto installables = parseInstallables(store, rawInstallables);
             AbstractNixRepl::AnnotatedValues values;
-            for (auto & installable: installables){
-                auto what = installable->what();
+            for (auto & installable_: installables){
+                auto & installable = InstallableValue::require(*installable_);
+                auto what = installable.what();
                 if (file){
-                    auto [val, pos] = installable->toValue(*state);
-                    auto what = installable->what();
+                    auto [val, pos] = installable.toValue(*state);
+                    auto what = installable.what();
                     state->forceValue(*val, pos);
                     auto autoArgs = getAutoArgs(*state);
                     auto valPost = state->allocValue();
@@ -72,7 +71,7 @@ struct CmdRepl : InstallablesCommand
                     state->forceValue(*valPost, pos);
                     values.push_back( {valPost, what });
                 } else {
-                    auto [val, pos] = installable->toValue(*state);
+                    auto [val, pos] = installable.toValue(*state);
                     values.push_back( {val, what} );
                 }
             }
diff --git a/src/nix/run.cc b/src/nix/run.cc
index 6fca68047..1baf299ab 100644
--- a/src/nix/run.cc
+++ b/src/nix/run.cc
@@ -1,5 +1,5 @@
 #include "run.hh"
-#include "command.hh"
+#include "command-installable-value.hh"
 #include "common-args.hh"
 #include "shared.hh"
 #include "store-api.hh"
@@ -97,7 +97,7 @@ struct CmdShell : InstallablesCommand, MixEnvironment
           ;
     }
 
-    void run(ref<Store> store) override
+    void run(ref<Store> store, Installables && installables) override
     {
         auto outPaths = Installable::toStorePaths(getEvalStore(), store, Realise::Outputs, OperateOn::Output, installables);
 
@@ -137,7 +137,7 @@ struct CmdShell : InstallablesCommand, MixEnvironment
 
 static auto rCmdShell = registerCommand<CmdShell>("shell");
 
-struct CmdRun : InstallableCommand
+struct CmdRun : InstallableValueCommand
 {
     using InstallableCommand::run;
 
@@ -183,7 +183,7 @@ struct CmdRun : InstallableCommand
         return res;
     }
 
-    void run(ref<Store> store) override
+    void run(ref<Store> store, ref<InstallableValue> installable) override
     {
         auto state = getEvalState();
 
diff --git a/src/nix/run.md b/src/nix/run.md
index a0f362076..250ea65aa 100644
--- a/src/nix/run.md
+++ b/src/nix/run.md
@@ -35,7 +35,7 @@ R""(
 
 # Description
 
-`nix run` builds and runs *installable*, which must evaluate to an
+`nix run` builds and runs [*installable*](./nix.md#installables), which must evaluate to an
 *app* or a regular Nix derivation.
 
 If *installable* evaluates to an *app* (see below), it executes the
diff --git a/src/nix/search.cc b/src/nix/search.cc
index 4fa1e7837..c92ed1663 100644
--- a/src/nix/search.cc
+++ b/src/nix/search.cc
@@ -1,4 +1,4 @@
-#include "command.hh"
+#include "command-installable-value.hh"
 #include "globals.hh"
 #include "eval.hh"
 #include "eval-inline.hh"
@@ -22,7 +22,7 @@ std::string wrap(std::string prefix, std::string s)
     return concatStrings(prefix, s, ANSI_NORMAL);
 }
 
-struct CmdSearch : InstallableCommand, MixJSON
+struct CmdSearch : InstallableValueCommand, MixJSON
 {
     std::vector<std::string> res;
     std::vector<std::string> excludeRes;
@@ -61,7 +61,7 @@ struct CmdSearch : InstallableCommand, MixJSON
         };
     }
 
-    void run(ref<Store> store) override
+    void run(ref<Store> store, ref<InstallableValue> installable) override
     {
         settings.readOnlyMode = true;
         evalSettings.enableImportFromDerivation.setDefault(false);
@@ -196,9 +196,8 @@ 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)
+            logger->cout("%s", *jsonOut);
 
         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 5a5b5ae05..4caa90654 100644
--- a/src/nix/search.md
+++ b/src/nix/search.md
@@ -62,10 +62,10 @@ R""(
 
 # Description
 
-`nix search` searches *installable* (which must be evaluatable, e.g. a
-flake) for packages whose name or description matches all of the
+`nix search` searches [*installable*](./nix.md#installables) (which can be evaluated, that is, a
+flake or Nix expression, but not a store path or store derivation path) for packages whose name or description matches all of the
 regular expressions *regex*.  For each matching package, It prints the
-full attribute name (from the root of the installable), the version
+full attribute name (from the root of the [installable](./nix.md#installables)), the version
 and the `meta.description` field, highlighting the substrings that
 were matched by the regular expressions. If no regular expressions are
 specified, all packages are shown.
diff --git a/src/nix/shell.md b/src/nix/shell.md
index 9fa1031f5..13a389103 100644
--- a/src/nix/shell.md
+++ b/src/nix/shell.md
@@ -48,7 +48,7 @@ R""(
 # Description
 
 `nix shell` runs a command in an environment in which the `$PATH` variable
-provides the specified *installables*. If no command is specified, it starts the
+provides the specified [*installables*](./nix.md#installable). If no command is specified, it starts the
 default shell of your user account specified by `$SHELL`.
 
 )""
diff --git a/src/nix/show-derivation.cc b/src/nix/show-derivation.cc
index d1a516cad..4a406ae08 100644
--- a/src/nix/show-derivation.cc
+++ b/src/nix/show-derivation.cc
@@ -39,7 +39,7 @@ struct CmdShowDerivation : InstallablesCommand
 
     Category category() override { return catUtility; }
 
-    void run(ref<Store> store) override
+    void run(ref<Store> store, Installables && installables) override
     {
         auto drvPaths = Installable::toDerivations(store, installables, true);
 
@@ -57,7 +57,7 @@ struct CmdShowDerivation : InstallablesCommand
             jsonRoot[store->printStorePath(drvPath)] =
                 store->readDerivation(drvPath).toJSON(*store);
         }
-        std::cout << jsonRoot.dump(2) << std::endl;
+        logger->cout(jsonRoot.dump(2));
     }
 };
 
diff --git a/src/nix/show-derivation.md b/src/nix/show-derivation.md
index 2cd93aa62..1d37c6f5a 100644
--- a/src/nix/show-derivation.md
+++ b/src/nix/show-derivation.md
@@ -39,7 +39,7 @@ R""(
 # Description
 
 This command prints on standard output a JSON representation of the
-[store derivation]s to which *installables* evaluate. Store derivations
+[store derivation]s to which [*installables*](./nix.md#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/sigs.cc b/src/nix/sigs.cc
index 3d659d6d2..45cd2e1a6 100644
--- a/src/nix/sigs.cc
+++ b/src/nix/sigs.cc
@@ -45,7 +45,7 @@ struct CmdCopySigs : StorePathsCommand
         //logger->setExpected(doneLabel, storePaths.size());
 
         auto doPath = [&](const Path & storePathS) {
-            //Activity act(*logger, lvlInfo, format("getting signatures for '%s'") % storePath);
+            //Activity act(*logger, lvlInfo, "getting signatures for '%s'", storePath);
 
             checkInterrupt();
 
@@ -173,7 +173,7 @@ struct CmdKeyGenerateSecret : Command
         if (!keyName)
             throw UsageError("required argument '--key-name' is missing");
 
-        std::cout << SecretKey::generate(*keyName).to_string();
+        writeFull(STDOUT_FILENO, SecretKey::generate(*keyName).to_string());
     }
 };
 
@@ -194,7 +194,7 @@ struct CmdKeyConvertSecretToPublic : Command
     void run() override
     {
         SecretKey secretKey(drainFD(STDIN_FILENO));
-        std::cout << secretKey.toPublicKey().to_string();
+        writeFull(STDOUT_FILENO, secretKey.toPublicKey().to_string());
     }
 };
 
@@ -219,7 +219,6 @@ struct CmdKey : NixMultiCommand
     {
         if (!command)
             throw UsageError("'nix key' requires a sub-command.");
-        command->second->prepare();
         command->second->run();
     }
 };
diff --git a/src/nix/store-copy-log.cc b/src/nix/store-copy-log.cc
index d5fab5f2f..a6e8aeff7 100644
--- a/src/nix/store-copy-log.cc
+++ b/src/nix/store-copy-log.cc
@@ -24,9 +24,7 @@ struct CmdCopyLog : virtual CopyCommand, virtual InstallablesCommand
           ;
     }
 
-    Category category() override { return catUtility; }
-
-    void run(ref<Store> srcStore) override
+    void run(ref<Store> srcStore, Installables && installables) override
     {
         auto & srcLogStore = require<LogStore>(*srcStore);
 
diff --git a/src/nix/store-delete.cc b/src/nix/store-delete.cc
index ca43f1530..6719227df 100644
--- a/src/nix/store-delete.cc
+++ b/src/nix/store-delete.cc
@@ -32,7 +32,7 @@ struct CmdStoreDelete : StorePathsCommand
           ;
     }
 
-    void run(ref<Store> store, std::vector<StorePath> && storePaths) override
+    void run(ref<Store> store, StorePaths && storePaths) override
     {
         auto & gcStore = require<GcStore>(*store);
 
diff --git a/src/nix/store-delete.md b/src/nix/store-delete.md
index db535f87c..431bc5f5e 100644
--- a/src/nix/store-delete.md
+++ b/src/nix/store-delete.md
@@ -10,7 +10,7 @@ R""(
 
 # Description
 
-This command deletes the store paths specified by *installables*. ,
+This command deletes the store paths specified by [*installables*](./nix.md#installables),
 but only if it is safe to do so; that is, when the path is not
 reachable from a root of the garbage collector. This means that you
 can only delete paths that would also be deleted by `nix store
diff --git a/src/nix/store-dump-path.md b/src/nix/store-dump-path.md
index 4ef563526..56e2174b6 100644
--- a/src/nix/store-dump-path.md
+++ b/src/nix/store-dump-path.md
@@ -18,6 +18,6 @@ R""(
 # Description
 
 This command generates a NAR file containing the serialisation of the
-store path *installable*. The NAR is written to standard output.
+store path [*installable*](./nix.md#installables). The NAR is written to standard output.
 
 )""
diff --git a/src/nix/store-repair.cc b/src/nix/store-repair.cc
index 8fcb3639a..895e39685 100644
--- a/src/nix/store-repair.cc
+++ b/src/nix/store-repair.cc
@@ -17,7 +17,7 @@ struct CmdStoreRepair : StorePathsCommand
           ;
     }
 
-    void run(ref<Store> store, std::vector<StorePath> && storePaths) override
+    void run(ref<Store> store, StorePaths && storePaths) override
     {
         for (auto & path : storePaths)
             store->repairPath(path);
diff --git a/src/nix/store-repair.md b/src/nix/store-repair.md
index 92d2205a9..180c577ac 100644
--- a/src/nix/store-repair.md
+++ b/src/nix/store-repair.md
@@ -17,7 +17,7 @@ R""(
 # Description
 
 This command attempts to "repair" the store paths specified by
-*installables* by redownloading them using the available
+[*installables*](./nix.md#installables) by redownloading them using the available
 substituters. If no substitutes are available, then repair is not
 possible.
 
diff --git a/src/nix/store.cc b/src/nix/store.cc
index 44e53c7c7..2879e03b3 100644
--- a/src/nix/store.cc
+++ b/src/nix/store.cc
@@ -18,7 +18,6 @@ struct CmdStore : virtual NixMultiCommand
     {
         if (!command)
             throw UsageError("'nix store' requires a sub-command.");
-        command->second->prepare();
         command->second->run();
     }
 };
diff --git a/src/nix/upgrade-nix.md b/src/nix/upgrade-nix.md
index 084c80ba2..08757aebd 100644
--- a/src/nix/upgrade-nix.md
+++ b/src/nix/upgrade-nix.md
@@ -11,7 +11,7 @@ R""(
 * Upgrade Nix in a specific profile:
 
   ```console
-  # nix upgrade-nix -p /nix/var/nix/profiles/per-user/alice/profile
+  # nix upgrade-nix -p ~alice/.local/state/nix/profiles/profile
   ```
 
 # Description
diff --git a/src/nix/verify.md b/src/nix/verify.md
index 1c43792e7..cc1122c02 100644
--- a/src/nix/verify.md
+++ b/src/nix/verify.md
@@ -24,7 +24,7 @@ R""(
 
 # Description
 
-This command verifies the integrity of the store paths *installables*,
+This command verifies the integrity of the store paths [*installables*](./nix.md#installables),
 or, if `--all` is given, the entire Nix store. For each path, it
 checks that