Merge branch 'master' of github.com:NixOS/nix into path-in-exec

src/libcmd/common-eval-args.cc

@@ -171,7 +171,9 @@ SourcePath lookupFileArg(EvalState & state, std::string_view s, const Path * bas
 {
     if (EvalSettings::isPseudoUrl(s)) {
         auto accessor = fetchers::downloadTarball(
-            EvalSettings::resolvePseudoUrl(s)).accessor;
+            state.store,
+            state.fetchSettings,
+            EvalSettings::resolvePseudoUrl(s));
         auto storePath = fetchToStore(*state.store, SourcePath(accessor), FetchMode::Copy);
         return state.rootPath(CanonPath(state.store->toRealPath(storePath)));
     }

src/libcmd/repl.cc

@@ -7,7 +7,6 @@
 
 #include "ansicolor.hh"
 #include "shared.hh"
-#include "config-global.hh"
 #include "eval.hh"
 #include "eval-settings.hh"
 #include "attr-path.hh"
@@ -77,10 +76,14 @@ struct NixRepl
     int displ;
     StringSet varNames;
 
+    RunNix * runNixPtr;
+
+    void runNix(Path program, const Strings & args, const std::optional<std::string> & input = {});
+
     std::unique_ptr<ReplInteracter> interacter;
 
     NixRepl(const LookupPath & lookupPath, nix::ref<Store> store,ref<EvalState> state,
-            std::function<AnnotatedValues()> getValues);
+            std::function<AnnotatedValues()> getValues, RunNix * runNix);
     virtual ~NixRepl() = default;
 
     ReplExitStatus mainLoop() override;
@@ -125,32 +128,16 @@ std::string removeWhitespace(std::string s)
 
 
 NixRepl::NixRepl(const LookupPath & lookupPath, nix::ref<Store> store, ref<EvalState> state,
-            std::function<NixRepl::AnnotatedValues()> getValues)
+            std::function<NixRepl::AnnotatedValues()> getValues, RunNix * runNix = nullptr)
     : AbstractNixRepl(state)
     , debugTraceIndex(0)
     , getValues(getValues)
     , staticEnv(new StaticEnv(nullptr, state->staticBaseEnv.get()))
+    , runNixPtr{runNix}
     , interacter(make_unique<ReadlineLikeInteracter>(getDataDir() + "/nix/repl-history"))
 {
 }
 
-void runNix(Path program, const Strings & args,
-    const std::optional<std::string> & input = {})
-{
-    auto subprocessEnv = getEnv();
-    subprocessEnv["NIX_CONFIG"] = globalConfig.toKeyValue();
-    //isInteractive avoid grabling interactive commands
-    runProgram2(RunOptions {
-        .program = settings.nixBinDir+ "/" + program,
-        .args = args,
-        .environment = subprocessEnv,
-        .input = input,
-        .isInteractive = true,
-    });
-
-    return;
-}
-
 static std::ostream & showDebugTrace(std::ostream & out, const PosTable & positions, const DebugTrace & dt)
 {
     if (dt.isError)
@@ -833,9 +820,18 @@ void NixRepl::evalString(std::string s, Value & v)
 }
 
 
+void NixRepl::runNix(Path program, const Strings & args, const std::optional<std::string> & input)
+{
+    if (runNixPtr)
+        (*runNixPtr)(program, args, input);
+    else
+        throw Error("Cannot run '%s', no method of calling the Nix CLI provided", program);
+}
+
+
 std::unique_ptr<AbstractNixRepl> AbstractNixRepl::create(
    const LookupPath & lookupPath, nix::ref<Store> store, ref<EvalState> state,
-   std::function<AnnotatedValues()> getValues)
+   std::function<AnnotatedValues()> getValues, RunNix * runNix)
 {
     return std::make_unique<NixRepl>(
         lookupPath,

src/libcmd/repl.hh

@@ -19,9 +19,19 @@ struct AbstractNixRepl
 
     typedef std::vector<std::pair<Value*,std::string>> AnnotatedValues;
 
+    using RunNix = void(Path program, const Strings & args, const std::optional<std::string> & input);
+
+    /**
+     * @param runNix Function to run the nix CLI to support various
+     * `:<something>` commands. Optional; if not provided,
+     * everything else will still work fine, but those commands won't.
+     */
     static std::unique_ptr<AbstractNixRepl> create(
-        const LookupPath & lookupPath, nix::ref<Store> store, ref<EvalState> state,
-        std::function<AnnotatedValues()> getValues);
+        const LookupPath & lookupPath,
+        nix::ref<Store> store,
+        ref<EvalState> state,
+        std::function<AnnotatedValues()> getValues,
+        RunNix * runNix = nullptr);
 
     static ReplExitStatus runSimple(
         ref<EvalState> evalState,

src/libexpr/eval.cc

@@ -3088,7 +3088,9 @@ std::optional<std::string> EvalState::resolveLookupPathPath(const LookupPath::Pa
     if (EvalSettings::isPseudoUrl(value)) {
         try {
             auto accessor = fetchers::downloadTarball(
-                EvalSettings::resolvePseudoUrl(value)).accessor;
+                store,
+                fetchSettings,
+                EvalSettings::resolvePseudoUrl(value));
             auto storePath = fetchToStore(*store, SourcePath(accessor), FetchMode::Copy);
             return finish(store->toRealPath(storePath));
         } catch (Error & e) {

src/libexpr/primops.cc

@@ -4857,7 +4857,10 @@ void EvalState::createBaseEnv()
     addConstant("__nixPath", v, {
         .type = nList,
         .doc = R"(
-          The value of the [`nix-path` configuration setting](@docroot@/command-ref/conf-file.md#conf-nix-path): a list of search path entries used to resolve [lookup paths](@docroot@/language/constructs/lookup-path.md).
+          A list of search path entries used to resolve [lookup paths](@docroot@/language/constructs/lookup-path.md).
+          Its value is primarily determined by the [`nix-path` configuration setting](@docroot@/command-ref/conf-file.md#conf-nix-path), which are
+          - Overridden by the [`NIX_PATH`](@docroot@/command-ref/env-common.md#env-NIX_PATH) environment variable or the `--nix-path` option
+          - Extended by the [`-I` option](@docroot@/command-ref/opt-common.md#opt-I) or `--extra-nix-path`
 
           > **Example**
           >

src/libexpr/primops/fetchTree.cc

@@ -507,7 +507,11 @@ static void fetch(EvalState & state, const PosIdx pos, Value * * args, Value & v
     //       https://github.com/NixOS/nix/issues/4313
     auto storePath =
         unpack
-        ? fetchToStore(*state.store, fetchers::downloadTarball(*url).accessor, FetchMode::Copy, name)
+        ? fetchToStore(
+            *state.store,
+            fetchers::downloadTarball(state.store, state.fetchSettings, *url),
+            FetchMode::Copy,
+            name)
         : fetchers::downloadFile(state.store, *url, name).storePath;
 
     if (expectedHash) {

src/libexpr/value.hh

@@ -331,9 +331,9 @@ public:
 
     void mkStringMove(const char * s, const NixStringContext & context);
 
-    inline void mkString(const Symbol & s)
+    inline void mkString(const SymbolStr & s)
     {
-        mkString(((const std::string &) s).c_str());
+        mkString(s.c_str());
     }
 
     void mkPath(const SourcePath & path);

src/libfetchers/tarball.cc

@@ -102,7 +102,7 @@ DownloadFileResult downloadFile(
     };
 }
 
-DownloadTarballResult downloadTarball(
+static DownloadTarballResult downloadTarball_(
     const std::string & url,
     const Headers & headers)
 {
@@ -202,6 +202,22 @@ DownloadTarballResult downloadTarball(
     return attrsToResult(infoAttrs);
 }
 
+ref<SourceAccessor> downloadTarball(
+    ref<Store> store,
+    const Settings & settings,
+    const std::string & url)
+{
+    /* Go through Input::getAccessor() to ensure that the resulting
+       accessor has a fingerprint. */
+    fetchers::Attrs attrs;
+    attrs.insert_or_assign("type", "tarball");
+    attrs.insert_or_assign("url", url);
+
+    auto input = Input::fromAttrs(settings, std::move(attrs));
+
+    return input.getAccessor(store).first;
+}
+
 // An input scheme corresponding to a curl-downloadable resource.
 struct CurlInputScheme : InputScheme
 {
@@ -353,7 +369,7 @@ struct TarballInputScheme : CurlInputScheme
     {
         auto input(_input);
 
-        auto result = downloadTarball(getStrAttr(input.attrs, "url"), {});
+        auto result = downloadTarball_(getStrAttr(input.attrs, "url"), {});
 
         result.accessor->setPathDisplay("«" + input.to_string() + "»");
 

src/libfetchers/tarball.hh

@@ -14,6 +14,8 @@ struct SourceAccessor;
 
 namespace nix::fetchers {
 
+struct Settings;
+
 struct DownloadFileResult
 {
     StorePath storePath;
@@ -40,8 +42,9 @@ struct DownloadTarballResult
  * Download and import a tarball into the Git cache. The result is the
  * Git tree hash of the root directory.
  */
-DownloadTarballResult downloadTarball(
-    const std::string & url,
-    const Headers & headers = {});
+ref<SourceAccessor> downloadTarball(
+    ref<Store> store,
+    const Settings & settings,
+    const std::string & url);
 
 }

src/libstore/globals.cc

@@ -64,7 +64,6 @@ Settings::Settings()
     , nixStateDir(canonPath(getEnvNonEmpty("NIX_STATE_DIR").value_or(NIX_STATE_DIR)))
     , nixConfDir(canonPath(getEnvNonEmpty("NIX_CONF_DIR").value_or(NIX_CONF_DIR)))
     , nixUserConfFiles(getUserConfigFiles())
-    , nixBinDir(canonPath(getEnvNonEmpty("NIX_BIN_DIR").value_or(NIX_BIN_DIR)))
     , nixManDir(canonPath(NIX_MAN_DIR))
     , nixDaemonSocketFile(canonPath(getEnvNonEmpty("NIX_DAEMON_SOCKET_PATH").value_or(nixStateDir + DEFAULT_SOCKET_PATH)))
 {
@@ -95,34 +94,6 @@ Settings::Settings()
     sandboxPaths = tokenizeString<StringSet>("/System/Library/Frameworks /System/Library/PrivateFrameworks /bin/sh /bin/bash /private/tmp /private/var/tmp /usr/lib");
     allowedImpureHostPrefixes = tokenizeString<StringSet>("/System/Library /usr/lib /dev /bin/sh");
 #endif
-
-    /* Set the build hook location
-
-       For builds we perform a self-invocation, so Nix has to be self-aware.
-       That is, it has to know where it is installed. We don't think it's sentient.
-
-       Normally, nix is installed according to `nixBinDir`, which is set at compile time,
-       but can be overridden. This makes for a great default that works even if this
-       code is linked as a library into some other program whose main is not aware
-       that it might need to be a build remote hook.
-
-       However, it may not have been installed at all. For example, if it's a static build,
-       there's a good chance that it has been moved out of its installation directory.
-       That makes `nixBinDir` useless. Instead, we'll query the OS for the path to the
-       current executable, using `getSelfExe()`.
-
-       As a last resort, we resort to `PATH`. Hopefully we find a `nix` there that's compatible.
-       If you're porting Nix to a new platform, that might be good enough for a while, but
-       you'll want to improve `getSelfExe()` to work on your platform.
-     */
-    std::string nixExePath = nixBinDir + "/nix";
-    if (!pathExists(nixExePath)) {
-        nixExePath = getSelfExe().value_or("nix");
-    }
-    buildHook = {
-        nixExePath,
-        "__build-remote",
-    };
 }
 
 void loadConfFile(AbstractConfig & config)

src/libstore/globals.hh

@@ -84,11 +84,6 @@ public:
      */
     std::vector<Path> nixUserConfFiles;
 
-    /**
-     * The directory where the main programs are stored.
-     */
-    Path nixBinDir;
-
     /**
      * The directory where the man pages are stored.
      */
@@ -246,7 +241,7 @@ public:
         )",
         {"build-timeout"}};
 
-    Setting<Strings> buildHook{this, {}, "build-hook",
+    Setting<Strings> buildHook{this, {"nix", "__build-remote"}, "build-hook",
         R"(
           The path to the helper program that executes remote builds.
 

src/libstore/local.mk

@@ -71,7 +71,6 @@ libstore_CXXFLAGS += \
  -DNIX_STATE_DIR=\"$(NIX_ROOT)$(localstatedir)/nix\" \
  -DNIX_LOG_DIR=\"$(NIX_ROOT)$(localstatedir)/log/nix\" \
  -DNIX_CONF_DIR=\"$(NIX_ROOT)$(sysconfdir)/nix\" \
- -DNIX_BIN_DIR=\"$(NIX_ROOT)$(bindir)\" \
  -DNIX_MAN_DIR=\"$(NIX_ROOT)$(mandir)\" \
  -DLSOF=\"$(NIX_ROOT)$(lsof)\"
 

src/libstore/meson.build

@@ -21,7 +21,7 @@ configdata = configuration_data()
 # TODO rename, because it will conflict with downstream projects
 configdata.set_quoted('PACKAGE_VERSION', meson.project_version())
 
-configdata.set_quoted('SYSTEM', host_machine.system())
+configdata.set_quoted('SYSTEM', host_machine.cpu_family() + '-' + host_machine.system())
 
 deps_private_maybe_subproject = [
 ]
@@ -328,7 +328,6 @@ prefix = get_option('prefix')
 path_opts = [
   # Meson built-ins.
   'datadir',
-  'bindir',
   'mandir',
   'libdir',
   'includedir',
@@ -373,7 +372,6 @@ cpp_str_defines = {
   'NIX_STATE_DIR': state_dir / 'nix',
   'NIX_LOG_DIR':   log_dir,
   'NIX_CONF_DIR':  sysconfdir / 'nix',
-  'NIX_BIN_DIR':   bindir,
   'NIX_MAN_DIR':   mandir,
 }
 

src/libstore/unix/build/hook-instance.cc

@@ -4,6 +4,7 @@
 #include "file-system.hh"
 #include "child.hh"
 #include "strings.hh"
+#include "executable-path.hh"
 
 namespace nix {
 
@@ -16,11 +17,18 @@ HookInstance::HookInstance()
     if (buildHookArgs.empty())
         throw Error("'build-hook' setting is empty");
 
-    auto buildHook = canonPath(buildHookArgs.front());
+    std::filesystem::path buildHook = buildHookArgs.front();
     buildHookArgs.pop_front();
 
+    try {
+        buildHook = ExecutablePath::load().findPath(buildHook);
+    } catch (ExecutableLookupError & e) {
+        e.addTrace(nullptr, "while resolving the 'build-hook' setting'");
+        throw;
+    }
+
     Strings args;
-    args.push_back(std::string(baseNameOf(buildHook)));
+    args.push_back(buildHook.filename().string());
 
     for (auto & arg : buildHookArgs)
         args.push_back(arg);
@@ -59,7 +67,7 @@ HookInstance::HookInstance()
         if (dup2(builderOut.readSide.get(), 5) == -1)
             throw SysError("dupping builder's stdout/stderr");
 
-        execv(buildHook.c_str(), stringsToCharPtrs(args).data());
+        execv(buildHook.native().c_str(), stringsToCharPtrs(args).data());
 
         throw SysError("executing '%s'", buildHook);
     });

src/libstore/unix/build/sandbox-defaults.sb

@@ -49,6 +49,7 @@ R""(
 (if (param "_ALLOW_LOCAL_NETWORKING")
     (begin
       (allow network* (remote ip "localhost:*"))
+      (allow network-inbound (local ip "*:*")) ; required to bind and listen
 
       ; Allow access to /etc/resolv.conf (which is a symlink to
       ; /private/var/run/resolv.conf).

src/libutil/executable-path.cc

@@ -60,7 +60,7 @@ OsString ExecutablePath::render() const
 }
 
 std::optional<fs::path>
-ExecutablePath::find(const OsString & exe, std::function<bool(const fs::path &)> isExecutable) const
+ExecutablePath::findName(const OsString & exe, std::function<bool(const fs::path &)> isExecutable) const
 {
     // "If the pathname being sought contains a <slash>, the search
     // through the path prefixes shall not be performed."
@@ -76,4 +76,20 @@ ExecutablePath::find(const OsString & exe, std::function<bool(const fs::path &)>
     return std::nullopt;
 }
 
+fs::path ExecutablePath::findPath(const fs::path & exe, std::function<bool(const fs::path &)> isExecutable) const
+{
+    // "If the pathname being sought contains a <slash>, the search
+    // through the path prefixes shall not be performed."
+    // https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08_03
+    if (exe.filename() == exe) {
+        auto resOpt = findName(exe, isExecutable);
+        if (resOpt)
+            return *resOpt;
+        else
+            throw ExecutableLookupError("Could not find executable '%s'", exe.native());
+    } else {
+        return exe;
+    }
+}
+
 } // namespace nix

src/libutil/executable-path.hh

@@ -5,6 +5,8 @@
 
 namespace nix {
 
+MakeError(ExecutableLookupError, Error);
+
 struct ExecutablePath
 {
     std::vector<std::filesystem::path> directories;
@@ -54,10 +56,21 @@ struct ExecutablePath
      *
      * @return path to a resolved executable
      */
-    std::optional<std::filesystem::path> find(
+    std::optional<std::filesystem::path> findName(
         const OsString & exe,
         std::function<bool(const std::filesystem::path &)> isExecutableFile = isExecutableFileAmbient) const;
 
+    /**
+     * Like the `findName` but also allows a file path as input.
+     *
+     * This implements the full POSIX spec: if the path is just a name,
+     * it searches like the above. Otherwise, it returns the path as is.
+     * If (in the name case) the search fails, an exception is thrown.
+     */
+    std::filesystem::path findPath(
+        const std::filesystem::path & exe,
+        std::function<bool(const std::filesystem::path &)> isExecutable = isExecutableFileAmbient) const;
+
     bool operator==(const ExecutablePath &) const = default;
 };
 

src/nix-channel/nix-channel.cc

@@ -7,6 +7,7 @@
 #include "eval-settings.hh" // for defexpr
 #include "users.hh"
 #include "tarball.hh"
+#include "self-exe.hh"
 
 #include <fcntl.h>
 #include <regex>
@@ -67,7 +68,7 @@ static void removeChannel(const std::string & name)
     channels.erase(name);
     writeChannels();
 
-    runProgram(settings.nixBinDir + "/nix-env", true, { "--profile", profile, "--uninstall", name });
+    runProgram(getNixBin("nix-env").string(), true, { "--profile", profile, "--uninstall", name });
 }
 
 static Path nixDefExpr;
@@ -118,7 +119,7 @@ static void update(const StringSet & channelNames)
 
             bool unpacked = false;
             if (std::regex_search(filename, std::regex("\\.tar\\.(gz|bz2|xz)$"))) {
-                runProgram(settings.nixBinDir + "/nix-build", false, { "--no-out-link", "--expr", "import " + unpackChannelPath +
+                runProgram(getNixBin("nix-build").string(), false, { "--no-out-link", "--expr", "import " + unpackChannelPath +
                             "{ name = \"" + cname + "\"; channelName = \"" + name + "\"; src = builtins.storePath \"" + filename + "\"; }" });
                 unpacked = true;
             }
@@ -143,7 +144,7 @@ static void update(const StringSet & channelNames)
     for (auto & expr : exprs)
         envArgs.push_back(std::move(expr));
     envArgs.push_back("--quiet");
-    runProgram(settings.nixBinDir + "/nix-env", false, envArgs);
+    runProgram(getNixBin("nix-env").string(), false, envArgs);
 
     // Make the channels appear in nix-env.
     struct stat st;
@@ -244,7 +245,7 @@ static int main_nix_channel(int argc, char ** argv)
             case cListGenerations:
                 if (!args.empty())
                     throw UsageError("'--list-generations' expects no arguments");
-                std::cout << runProgram(settings.nixBinDir + "/nix-env", false, {"--profile", profile, "--list-generations"}) << std::flush;
+                std::cout << runProgram(getNixBin("nix-env").string(), false, {"--profile", profile, "--list-generations"}) << std::flush;
                 break;
             case cRollback:
                 if (args.size() > 1)
@@ -256,7 +257,7 @@ static int main_nix_channel(int argc, char ** argv)
                 } else {
                     envArgs.push_back("--rollback");
                 }
-                runProgram(settings.nixBinDir + "/nix-env", false, envArgs);
+                runProgram(getNixBin("nix-env").string(), false, envArgs);
                 break;
         }
 

src/nix-functional-tests

@@ -0,0 +1 @@
+../tests/functional

src/nix/flake.cc

@@ -438,14 +438,39 @@ struct CmdFlakeCheck : FlakeCommand
 
         auto checkApp = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
             try {
-                #if 0
-                // FIXME
-                auto app = App(*state, v);
-                for (auto & i : app.context) {
-                    auto [drvPathS, outputName] = NixStringContextElem::parse(i);
-                    store->parseStorePath(drvPathS);
+                Activity act(*logger, lvlInfo, actUnknown, fmt("checking app '%s'", attrPath));
+                state->forceAttrs(v, pos, "");
+                if (auto attr = v.attrs()->get(state->symbols.create("type")))
+                    state->forceStringNoCtx(*attr->value, attr->pos, "");
+                else
+                    throw Error("app '%s' lacks attribute 'type'", attrPath);
+
+                if (auto attr = v.attrs()->get(state->symbols.create("program"))) {
+                    if (attr->name == state->symbols.create("program")) {
+                        NixStringContext context;
+                        state->forceString(*attr->value, context, attr->pos, "");
+                    }
+                } else
+                    throw Error("app '%s' lacks attribute 'program'", attrPath);
+
+                if (auto attr = v.attrs()->get(state->symbols.create("meta"))) {
+                    state->forceAttrs(*attr->value, attr->pos, "");
+                    if (auto dAttr = attr->value->attrs()->get(state->symbols.create("description")))
+                        state->forceStringNoCtx(*dAttr->value, dAttr->pos, "");
+                    else
+                        logWarning({
+                            .msg = HintFmt("app '%s' lacks attribute 'meta.description'", attrPath),
+                        });
+                } else
+                    logWarning({
+                        .msg = HintFmt("app '%s' lacks attribute 'meta'", attrPath),
+                    });
+
+                for (auto & attr : *v.attrs()) {
+                    std::string_view name(state->symbols[attr.name]);
+                    if (name != "type" && name != "program" && name != "meta")
+                        throw Error("app '%s' has unsupported attribute '%s'", attrPath, name);
                 }
-                #endif
             } catch (Error & e) {
                 e.addTrace(resolve(pos), HintFmt("while checking the app definition '%s'", attrPath));
                 reportError(e);
@@ -630,7 +655,7 @@ struct CmdFlakeCheck : FlakeCommand
                                 const auto & attr_name = state->symbols[attr.name];
                                 checkSystemName(attr_name, attr.pos);
                                 if (checkSystemType(attr_name, attr.pos)) {
-                                    checkApp(
+                                    checkDerivation(
                                         fmt("%s.%s", name, attr_name),
                                         *attr.value, attr.pos);
                                 };
@@ -1252,8 +1277,7 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
                         }
                         j.emplace("type", "derivation");
                         j.emplace("name", name);
-                        if (description)
-                            j.emplace("description", *description);
+                        j.emplace("description", description ? *description : "");
                     } else {
                         logger->cout("%s: %s '%s'",
                             headerPrefix,
@@ -1341,12 +1365,19 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
                     (attrPath.size() == 3 && attrPathS[0] == "apps"))
                 {
                     auto aType = visitor.maybeGetAttr("type");
+                    std::optional<std::string> description;
+                    if (auto aMeta = visitor.maybeGetAttr(state->sMeta)) {
+                        if (auto aDescription = aMeta->maybeGetAttr(state->sDescription))
+                            description = aDescription->getString();
+                    }
                     if (!aType || aType->getString() != "app")
                         state->error<EvalError>("not an app definition").debugThrow();
                     if (json) {
                         j.emplace("type", "app");
+                        if (description)
+                            j.emplace("description", *description);
                     } else {
-                        logger->cout("%s: app", headerPrefix);
+                        logger->cout("%s: app: " ANSI_BOLD "%s" ANSI_NORMAL, headerPrefix, description ? *description : "no description");
                     }
                 }
 

src/nix/local.mk

@@ -26,6 +26,8 @@ endif
 
 nix_CXXFLAGS += $(INCLUDE_libutil) $(INCLUDE_libstore) $(INCLUDE_libfetchers) $(INCLUDE_libexpr) $(INCLUDE_libflake) $(INCLUDE_libmain) -I src/libcmd -I doc/manual $(INCLUDE_nix)
 
+nix_CXXFLAGS += -DNIX_BIN_DIR=\"$(NIX_ROOT)$(bindir)\"
+
 nix_LIBS = libexpr libmain libfetchers libflake libstore libutil libcmd
 
 nix_LDFLAGS = $(THREAD_LDFLAGS) $(SODIUM_LIBS) $(EDITLINE_LIBS) $(BOOST_LDFLAGS) $(LOWDOWN_LIBS)

src/nix/main.cc

@@ -19,6 +19,7 @@
 #include "network-proxy.hh"
 #include "eval-cache.hh"
 #include "flake/flake.hh"
+#include "self-exe.hh"
 
 #include <sys/types.h>
 #include <regex>
@@ -366,6 +367,17 @@ void mainWrapped(int argc, char * * argv)
     initGC();
     flake::initLib(flakeSettings);
 
+    /* Set the build hook location
+
+       For builds we perform a self-invocation, so Nix has to be
+       self-aware. That is, it has to know where it is installed. We
+       don't think it's sentient.
+     */
+    settings.buildHook.setDefault(Strings {
+        getNixBin({}).string(),
+        "__build-remote",
+    });
+
     #if __linux__
     if (isRootUser()) {
         try {

src/nix/meson.build

@@ -33,6 +33,21 @@ subdir('build-utils-meson/threads')
 
 subdir('build-utils-meson/export-all-symbols')
 
+configdata = configuration_data()
+
+fs = import('fs')
+
+bindir = get_option('bindir')
+if not fs.is_absolute(bindir)
+  bindir = get_option('prefix') / bindir
+endif
+configdata.set_quoted('NIX_BIN_DIR', bindir)
+
+config_h = configure_file(
+  configuration : configdata,
+  output : 'config-nix-cli.hh',
+)
+
 add_project_arguments(
   # TODO(Qyriad): Yes this is how the autoconf+Make system did it.
   # It would be nice for our headers to be idempotent instead.
@@ -42,15 +57,17 @@ add_project_arguments(
   #'-include', 'config-fetchers.hh',
   '-include', 'config-main.hh',
   '-include', 'config-cmd.hh',
+  '-include', 'config-nix-cli.hh',
   language : 'cpp',
 )
 
 subdir('build-utils-meson/diagnostics')
 subdir('build-utils-meson/generate-header')
 
-nix_sources = files(
+nix_sources = [config_h] + files(
   'add-to-store.cc',
   'app.cc',
+  'self-exe.cc',
   'build.cc',
   'bundle.cc',
   'cat.cc',
@@ -175,3 +192,55 @@ this_exe = executable(
   link_args: linker_export_flags,
   install : true,
 )
+
+meson.override_find_program('nix', this_exe)
+
+nix_symlinks = [
+  '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',
+]
+
+foreach linkname : nix_symlinks
+  install_symlink(
+    linkname,
+    # TODO(Qyriad): should these continue to be relative symlinks?
+    pointing_to : 'nix',
+    install_dir : get_option('bindir'),
+    # The 'runtime' tag is what executables default to, which we want to emulate here.
+    install_tag : 'runtime'
+  )
+  t = custom_target(
+    command: ['ln', '-sf', fs.name(this_exe), '@OUTPUT@'],
+    output: linkname,
+    # TODO(Ericson2314): Don't do this once we have the `meson.override_find_program` working)
+    build_by_default: true
+  )
+  # TODO(Ericson3214): Dosen't yet work
+  #meson.override_find_program(linkname, t)
+endforeach
+
+install_symlink(
+  'build-remote',
+  pointing_to : '..' / '..'/ get_option('bindir') / 'nix',
+  install_dir : get_option('libexecdir') / 'nix',
+  # The 'runtime' tag is what executables default to, which we want to emulate here.
+  install_tag : 'runtime'
+)
+
+custom_target(
+  command: ['ln', '-sf', fs.name(this_exe), '@OUTPUT@'],
+  output: 'build-remote',
+  # TODO(Ericson2314): Don't do this once we have the `meson.override_find_program` working)
+  build_by_default: true
+)
+# TODO(Ericson3214): Dosen't yet work
+#meson.override_find_program(linkname, t)

src/nix/repl.cc

@@ -1,12 +1,32 @@
 #include "eval.hh"
 #include "eval-settings.hh"
+#include "config-global.hh"
 #include "globals.hh"
 #include "command.hh"
 #include "installable-value.hh"
 #include "repl.hh"
+#include "processes.hh"
+#include "self-exe.hh"
 
 namespace nix {
 
+void runNix(Path program, const Strings & args,
+    const std::optional<std::string> & input = {})
+{
+    auto subprocessEnv = getEnv();
+    subprocessEnv["NIX_CONFIG"] = globalConfig.toKeyValue();
+    //isInteractive avoid grabling interactive commands
+    runProgram2(RunOptions {
+        .program = getNixBin(program).string(),
+        .args = args,
+        .environment = subprocessEnv,
+        .input = input,
+        .isInteractive = true,
+    });
+
+    return;
+}
+
 struct CmdRepl : RawInstallablesCommand
 {
     CmdRepl() {
@@ -81,7 +101,8 @@ struct CmdRepl : RawInstallablesCommand
             lookupPath,
             openStore(),
             state,
-            getValues
+            getValues,
+            runNix
         );
         repl->autoArgs = getAutoArgs(*repl->state);
         repl->initEnv();

src/nix/run.md

@@ -80,6 +80,7 @@ An app is specified by a flake output attribute named
 apps.x86_64-linux.blender_2_79 = {
   type = "app";
   program = "${self.packages.x86_64-linux.blender_2_79}/bin/blender";
+  meta.description = "Run Blender, a free and open-source 3D creation suite.";
 };
 ```
 
@@ -90,4 +91,6 @@ The only supported attributes are:
 * `program` (required): The full path of the executable to run. It
   must reside in the Nix store.
 
+* `meta.description` (optional): A description of the app.
+
 )""

src/nix/self-exe.cc

@@ -0,0 +1,38 @@
+#include "current-process.hh"
+#include "file-system.hh"
+#include "globals.hh"
+#include "self-exe.hh"
+
+namespace nix {
+
+namespace fs = std::filesystem;
+
+fs::path getNixBin(std::optional<std::string_view> binaryNameOpt)
+{
+    auto getBinaryName = [&] { return binaryNameOpt ? *binaryNameOpt : "nix"; };
+
+    // If the environment variable is set, use it unconditionally
+    if (auto envOpt = getEnvNonEmpty("NIX_BIN_DIR"))
+        return fs::path{*envOpt} / std::string{getBinaryName()};
+
+    // Use some-times avaiable OS tricks to get to the path of this Nix, and try that
+    if (auto selfOpt = getSelfExe()) {
+        fs::path path{*selfOpt};
+        if (binaryNameOpt)
+            path = path.parent_path() / std::string{*binaryNameOpt};
+        if (fs::exists(path))
+            return path;
+    }
+
+    // If `nix` exists at the hardcoded fallback path, use it.
+    {
+        auto path = fs::path{NIX_BIN_DIR} / std::string{getBinaryName()};
+        if (fs::exists(path))
+            return path;
+    }
+
+    // return just the name, hoping the exe is on the `PATH`
+    return getBinaryName();
+}
+
+}

src/nix/self-exe.hh

@@ -0,0 +1,31 @@
+#pragma once
+///@file
+
+#include <filesystem>
+
+namespace nix {
+
+/**
+ * Get a path to the given Nix binary.
+ *
+ * Normally, nix is installed according to `NIX_BIN_DIR`, which is set
+ * at compile time, but can be overridden.
+ *
+ * However, it may not have been installed at all. For example, if it's
+ * a static build, there's a good chance that it has been moved out of
+ * its installation directory. That makes `NIX_BIN_DIR` useless.
+ * Instead, we'll query the OS for the path to the current executable,
+ * using `getSelfExe()`.
+ *
+ * As a last resort, we resort to `PATH`. Hopefully we find a `nix`
+ * there that's compatible. If you're porting Nix to a new platform,
+ * that might be good enough for a while, but you'll want to improve
+ * `getSelfExe()` to work on your platform.
+ *
+ * @param binary_name the exact binary name we're looking up. Might be
+ * `nix-*` instead of `nix` for the legacy CLI commands. Optional to use
+ * current binary name.
+ */
+std::filesystem::path getNixBin(std::optional<std::string_view> binary_name = {});
+
+}

src/nix/upgrade-nix.cc

@@ -9,6 +9,7 @@
 #include "names.hh"
 #include "progress-bar.hh"
 #include "executable-path.hh"
+#include "self-exe.hh"
 
 using namespace nix;
 
@@ -93,7 +94,7 @@ struct CmdUpgradeNix : MixDryRun, StoreCommand
         {
             Activity act(*logger, lvlInfo, actUnknown,
                 fmt("installing '%s' into profile '%s'...", store->printStorePath(storePath), profileDir));
-            runProgram(settings.nixBinDir + "/nix-env", false,
+            runProgram(getNixBin("nix-env").string(), false,
                 {"--profile", profileDir, "-i", store->printStorePath(storePath), "--no-sandbox"});
         }
 
@@ -103,7 +104,7 @@ struct CmdUpgradeNix : MixDryRun, StoreCommand
     /* Return the profile in which Nix is installed. */
     Path getProfileDir(ref<Store> store)
     {
-        auto whereOpt = ExecutablePath::load().find(OS_STR("nix-env"));
+        auto whereOpt = ExecutablePath::load().findName(OS_STR("nix-env"));
         if (!whereOpt)
             throw Error("couldn't figure out how Nix is installed, so I can't upgrade it");
         auto & where = *whereOpt;

src/perl/lib/Nix/Config.pm.in

@@ -5,7 +5,6 @@ use Nix::Store;
 
 $version = "@PACKAGE_VERSION@";
 
-$binDir = Nix::Store::getBinDir;
 $storeDir = Nix::Store::getStoreDir;
 
 %config = ();

src/perl/lib/Nix/Store.pm

@@ -24,7 +24,7 @@ our @EXPORT = qw(
 
     hashPath hashFile hashString convertHash
     signString checkSignature
-    getBinDir getStoreDir
+    getStoreDir
     setVerbosity
 );
 

src/perl/lib/Nix/Store.xs

@@ -424,11 +424,6 @@ StoreWrapper::addTempRoot(char * storePath)
         }
 
 
-SV * getBinDir()
-    PPCODE:
-        XPUSHs(sv_2mortal(newSVpv(settings.nixBinDir.c_str(), 0)));
-
-
 SV * getStoreDir()
     PPCODE:
         XPUSHs(sv_2mortal(newSVpv(settings.nixStore.c_str(), 0)));