Use envvars NIX_CACHE_HOME, NIX_CONFIG_HOME, NIX_DATA_HOME, NIX_STATE_HOME if defined

doc/manual/rl-next/add-nix-state-home.md

@@ -0,0 +1,18 @@
+---
+synopsis: Use envvars NIX_CACHE_HOME, NIX_CONFIG_HOME, NIX_DATA_HOME, NIX_STATE_HOME if defined
+prs: [11351]
+---
+
+Look for 4 new environment variables: NIX_CACHE_HOME, NIX_CONFIG_HOME, NIX_DATA_HOME, NIX_STATE_HOME.
+If one of them is defined, it takes precedence over its respective XDG envvar.
+
+This provides more fine-grained control over where Nix looks for files, and allows to have a stand-alone Nix
+environment, which only uses files in a specific directory, and doesn't touch any global user configuration.
+
+For example, when [`use-xdg-base-directories`] is enabled, the configuration directory is:
+
+1. `$NIX_CONFIG_HOME`, if it is defined
+2. Otherwise, `$XDG_CONFIG_HOME/nix`, if `XDG_CONFIG_HOME` is defined
+3. Otherwise, `~/.config/nix`.
+
+Likewise for the state and cache directories.

doc/manual/src/command-ref/env-common.md

@@ -138,6 +138,19 @@ The following environment variables are used to determine locations of various s
 - [`XDG_STATE_HOME`]{#env-XDG_STATE_HOME} (default `~/.local/state`)
 - [`XDG_CACHE_HOME`]{#env-XDG_CACHE_HOME} (default `~/.cache`)
 
-
 [XDG Base Directory Specification]: https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html
 [`use-xdg-base-directories`]: @docroot@/command-ref/conf-file.md#conf-use-xdg-base-directories
+
+In addition, setting the following environment variables overrides the XDG base directories:
+
+- [`NIX_CONFIG_HOME`]{#env-NIX_CONFIG_HOME} (default `$XDG_CONFIG_HOME/nix`)
+- [`NIX_STATE_HOME`]{#env-NIX_STATE_HOME} (default `$XDG_STATE_HOME/nix`)
+- [`NIX_CACHE_HOME`]{#env-NIX_CACHE_HOME} (default `$XDG_CACHE_HOME/nix`)
+
+For example, when [`use-xdg-base-directories`] is enabled, the configuration directory is:
+
+1. `$NIX_CONFIG_HOME`, if it is defined
+2. Otherwise, `$XDG_CONFIG_HOME/nix`, if `XDG_CONFIG_HOME` is defined
+3. Otherwise, `~/.config/nix`.
+
+Likewise for the state and cache directories.

scripts/nix-profile.sh.in

@@ -3,29 +3,33 @@ if [ -n "$HOME" ] && [ -n "$USER" ]; then
 
     # Set up the per-user profile.
 
-    NIX_LINK="$HOME/.nix-profile"
-    if [ -n "${XDG_STATE_HOME-}" ]; then
-        NIX_LINK_NEW="$XDG_STATE_HOME/nix/profile"
+    if [ -n "$NIX_STATE_HOME" ]; then
+        NIX_LINK="$NIX_STATE_HOME/profile"
     else
-        NIX_LINK_NEW="$HOME/.local/state/nix/profile"
-    fi
-    if [ -e "$NIX_LINK_NEW" ]; then
-        if [ -t 2 ] && [ -e "$NIX_LINK" ]; then
-            warning="\033[1;35mwarning:\033[0m"
-            printf "$warning Both %s and legacy %s exist; using the former.\n" "$NIX_LINK_NEW" "$NIX_LINK" 1>&2
-            if [ "$(realpath "$NIX_LINK")" = "$(realpath "$NIX_LINK_NEW")" ]; then
-                printf "         Since the profiles match, you can safely delete either of them.\n" 1>&2
-            else
-                # This should be an exceptionally rare occasion: the only way to get it would be to
-                # 1. Update to newer Nix;
-                # 2. Remove .nix-profile;
-                # 3. Set the $NIX_LINK_NEW to something other than the default user profile;
-                # 4. Roll back to older Nix.
-                # If someone did all that, they can probably figure out how to migrate the profile.
-                printf "$warning Profiles do not match. You should manually migrate from %s to %s.\n" "$NIX_LINK" "$NIX_LINK_NEW" 1>&2
+        NIX_LINK="$HOME/.nix-profile"
+        if [ -n "${XDG_STATE_HOME-}" ]; then
+            NIX_LINK_NEW="$XDG_STATE_HOME/nix/profile"
+        else
+            NIX_LINK_NEW="$HOME/.local/state/nix/profile"
+        fi
+        if [ -e "$NIX_LINK_NEW" ]; then
+            if [ -t 2 ] && [ -e "$NIX_LINK" ]; then
+                warning="\033[1;35mwarning:\033[0m"
+                printf "$warning Both %s and legacy %s exist; using the former.\n" "$NIX_LINK_NEW" "$NIX_LINK" 1>&2
+                if [ "$(realpath "$NIX_LINK")" = "$(realpath "$NIX_LINK_NEW")" ]; then
+                    printf "         Since the profiles match, you can safely delete either of them.\n" 1>&2
+                else
+                    # This should be an exceptionally rare occasion: the only way to get it would be to
+                    # 1. Update to newer Nix;
+                    # 2. Remove .nix-profile;
+                    # 3. Set the $NIX_LINK_NEW to something other than the default user profile;
+                    # 4. Roll back to older Nix.
+                    # If someone did all that, they can probably figure out how to migrate the profile.
+                    printf "$warning Profiles do not match. You should manually migrate from %s to %s.\n" "$NIX_LINK" "$NIX_LINK_NEW" 1>&2
+                fi
             fi
+            NIX_LINK="$NIX_LINK_NEW"
         fi
-        NIX_LINK="$NIX_LINK_NEW"
     fi
 
     # Set up environment.

src/libcmd/repl.cc

@@ -134,7 +134,7 @@ NixRepl::NixRepl(const LookupPath & lookupPath, nix::ref<Store> store, ref<EvalS
     , getValues(getValues)
     , staticEnv(new StaticEnv(nullptr, state->staticBaseEnv.get()))
     , runNixPtr{runNix}
-    , interacter(make_unique<ReadlineLikeInteracter>(getDataDir() + "/nix/repl-history"))
+    , interacter(make_unique<ReadlineLikeInteracter>(getDataDir() + "/repl-history"))
 {
 }
 

src/libexpr/eval-cache.cc

@@ -69,7 +69,7 @@ struct AttrDb
     {
         auto state(_state->lock());
 
-        Path cacheDir = getCacheDir() + "/nix/eval-cache-v5";
+        Path cacheDir = getCacheDir() + "/eval-cache-v5";
         createDirs(cacheDir);
 
         Path dbPath = cacheDir + "/" + fingerprint.to_string(HashFormat::Base16, false) + ".sqlite";

src/libexpr/eval-settings.cc

@@ -99,7 +99,7 @@ const std::string & EvalSettings::getCurrentSystem() const
 Path getNixDefExpr()
 {
     return settings.useXDGBaseDirectories
-        ? getStateDir() + "/nix/defexpr"
+        ? getStateDir() + "/defexpr"
         : getHome() + "/.nix-defexpr";
 }
 

src/libfetchers/cache.cc

@@ -36,7 +36,7 @@ struct CacheImpl : Cache
     {
         auto state(_state.lock());
 
-        auto dbPath = getCacheDir() + "/nix/fetcher-cache-v2.sqlite";
+        auto dbPath = getCacheDir() + "/fetcher-cache-v2.sqlite";
         createDirs(dirOf(dbPath));
 
         state->db = SQLite(dbPath);

src/libfetchers/git-utils.cc

@@ -1083,7 +1083,7 @@ std::vector<std::tuple<GitRepoImpl::Submodule, Hash>> GitRepoImpl::getSubmodules
 
 ref<GitRepo> getTarballCache()
 {
-    static auto repoDir = std::filesystem::path(getCacheDir()) / "nix" / "tarball-cache";
+    static auto repoDir = std::filesystem::path(getCacheDir()) / "tarball-cache";
 
     return GitRepo::openRepo(repoDir, true, true);
 }

src/libfetchers/git.cc

@@ -44,7 +44,7 @@ bool isCacheFileWithinTtl(time_t now, const struct stat & st)
 Path getCachePath(std::string_view key, bool shallow)
 {
     return getCacheDir()
-    + "/nix/gitv3/"
+    + "/gitv3/"
     + hashString(HashAlgorithm::SHA256, key).to_string(HashFormat::Nix32, false)
     + (shallow ? "-shallow" : "");
 }

src/libfetchers/mercurial.cc

@@ -263,7 +263,7 @@ struct MercurialInputScheme : InputScheme
                 return makeResult(res->value, res->storePath);
         }
 
-        Path cacheDir = fmt("%s/nix/hg/%s", getCacheDir(), hashString(HashAlgorithm::SHA256, actualUrl).to_string(HashFormat::Nix32, false));
+        Path cacheDir = fmt("%s/hg/%s", getCacheDir(), hashString(HashAlgorithm::SHA256, actualUrl).to_string(HashFormat::Nix32, false));
 
         /* If this is a commit hash that we already have, we don't
            have to pull again. */

src/libfetchers/registry.cc

@@ -116,7 +116,7 @@ static std::shared_ptr<Registry> getSystemRegistry(const Settings & settings)
 
 Path getUserRegistryPath()
 {
-    return getConfigDir() + "/nix/registry.json";
+    return getConfigDir() + "/registry.json";
 }
 
 std::shared_ptr<Registry> getUserRegistry(const Settings & settings)
@@ -159,7 +159,7 @@ static std::shared_ptr<Registry> getGlobalRegistry(const Settings & settings, re
         if (!hasPrefix(path, "/")) {
             auto storePath = downloadFile(store, path, "flake-registry.json").storePath;
             if (auto store2 = store.dynamic_pointer_cast<LocalFSStore>())
-                store2->addPermRoot(storePath, getCacheDir() + "/nix/flake-registry.json");
+                store2->addPermRoot(storePath, getCacheDir() + "/flake-registry.json");
             path = store->toRealPath(storePath);
         }
 

src/libflake/flake/config.cc

@@ -12,7 +12,7 @@ typedef std::map<std::string, std::map<std::string, bool>> TrustedList;
 
 Path trustedListPath()
 {
-    return getDataDir() + "/nix/trusted-settings.json";
+    return getDataDir() + "/trusted-settings.json";
 }
 
 static TrustedList readTrustedList()

src/libstore/globals.cc

@@ -135,7 +135,7 @@ std::vector<Path> getUserConfigFiles()
     std::vector<Path> files;
     auto dirs = getConfigDirs();
     for (auto & dir : dirs) {
-        files.insert(files.end(), dir + "/nix/nix.conf");
+        files.insert(files.end(), dir + "/nix.conf");
     }
     return files;
 }

src/libstore/nar-info-disk-cache.cc

@@ -87,7 +87,7 @@ class NarInfoDiskCacheImpl : public NarInfoDiskCache
 
     Sync<State> _state;
 
-    NarInfoDiskCacheImpl(Path dbPath = getCacheDir() + "/nix/binary-cache-v6.sqlite")
+    NarInfoDiskCacheImpl(Path dbPath = getCacheDir() + "/binary-cache-v6.sqlite")
     {
         auto state(_state.lock());
 

src/libstore/store-api.cc

@@ -1315,7 +1315,7 @@ ref<Store> openStore(StoreReference && storeURI)
                 /* If /nix doesn't exist, there is no daemon socket, and
                    we're not root, then automatically set up a chroot
                    store in ~/.local/share/nix/root. */
-                auto chrootStore = getDataDir() + "/nix/root";
+                auto chrootStore = getDataDir() + "/root";
                 if (!pathExists(chrootStore)) {
                     try {
                         createDirs(chrootStore);

src/libutil/users.cc

@@ -7,42 +7,81 @@ namespace nix {
 
 Path getCacheDir()
 {
-    auto cacheDir = getEnv("XDG_CACHE_HOME");
-    return cacheDir ? *cacheDir : getHome() + "/.cache";
+    auto dir = getEnv("NIX_CACHE_HOME");
+    if (dir) {
+        return *dir;
+    } else {
+        auto xdgDir = getEnv("XDG_CACHE_HOME");
+        if (xdgDir) {
+            return *xdgDir + "/nix";
+        } else {
+            return getHome() + "/.cache/nix";
+        }
+    }
 }
 
 
 Path getConfigDir()
 {
-    auto configDir = getEnv("XDG_CONFIG_HOME");
-    return configDir ? *configDir : getHome() + "/.config";
+    auto dir = getEnv("NIX_CONFIG_HOME");
+    if (dir) {
+        return *dir;
+    } else {
+        auto xdgDir = getEnv("XDG_CONFIG_HOME");
+        if (xdgDir) {
+            return *xdgDir + "/nix";
+        } else {
+            return getHome() + "/.config/nix";
+        }
+    }
 }
 
 std::vector<Path> getConfigDirs()
 {
     Path configHome = getConfigDir();
     auto configDirs = getEnv("XDG_CONFIG_DIRS").value_or("/etc/xdg");
     std::vector<Path> result = tokenizeString<std::vector<std::string>>(configDirs, ":");
+    for (auto& p : result) {
+        p += "/nix";
+    }
     result.insert(result.begin(), configHome);
     return result;
 }
 
 
 Path getDataDir()
 {
-    auto dataDir = getEnv("XDG_DATA_HOME");
-    return dataDir ? *dataDir : getHome() + "/.local/share";
+    auto dir = getEnv("NIX_DATA_HOME");
+    if (dir) {
+        return *dir;
+    } else {
+        auto xdgDir = getEnv("XDG_DATA_HOME");
+        if (xdgDir) {
+            return *xdgDir + "/nix";
+        } else {
+            return getHome() + "/.local/share/nix";
+        }
+    }
 }
 
 Path getStateDir()
 {
-    auto stateDir = getEnv("XDG_STATE_HOME");
-    return stateDir ? *stateDir : getHome() + "/.local/state";
+    auto dir = getEnv("NIX_STATE_HOME");
+    if (dir) {
+        return *dir;
+    } else {
+        auto xdgDir = getEnv("XDG_STATE_HOME");
+        if (xdgDir) {
+            return *xdgDir + "/nix";
+        } else {
+            return getHome() + "/.local/state/nix";
+        }
+    }
 }
 
 Path createNixStateDir()
 {
-    Path dir = getStateDir() + "/nix";
+    Path dir = getStateDir();
     createDirs(dir);
     return dir;
 }

src/libutil/users.hh

@@ -24,12 +24,12 @@ Path getHomeOf(uid_t userId);
 Path getHome();
 
 /**
- * @return $XDG_CACHE_HOME or $HOME/.cache.
+ * @return $NIX_CACHE_HOME or $XDG_CACHE_HOME/nix or $HOME/.cache/nix.
  */
 Path getCacheDir();
 
 /**
- * @return $XDG_CONFIG_HOME or $HOME/.config.
+ * @return $NIX_CONFIG_HOME or $XDG_CONFIG_HOME/nix or $HOME/.config/nix.
  */
 Path getConfigDir();
 
@@ -39,12 +39,12 @@ Path getConfigDir();
 std::vector<Path> getConfigDirs();
 
 /**
- * @return $XDG_DATA_HOME or $HOME/.local/share.
+ * @return $NIX_DATA_HOME or $XDG_DATA_HOME/nix or $HOME/.local/share/nix.
  */
 Path getDataDir();
 
 /**
- * @return $XDG_STATE_HOME or $HOME/.local/state.
+ * @return $NIX_STATE_HOME or $XDG_STATE_HOME/nix or $HOME/.local/state/nix.
  */
 Path getStateDir();