A setting to follow XDG Base Directory standard

XDG Base Directory is a standard for locations for storing various
files. Nix has a few files which seem to fit in the standard, but
currently use a custom location directly in the user's ~, polluting
it:

- ~/.nix-profile
- ~/.nix-defexpr
- ~/.nix-channels

This commit adds a config option (use-xdg-base-directories) to follow
the XDG spec and instead use the following locations:

- $XDG_STATE_HOME/nix/profile
- $XDG_STATE_HOME/nix/defexpr
- $XDG_STATE_HOME/nix/channels

If $XDG_STATE_HOME is not set, it is assumed to be ~/.local/state.

Co-authored-by: Théophane Hufschmitt <7226587+thufschmitt@users.noreply.github.com>
Co-authored-by: Tim Fenney <kodekata@gmail.com>
Co-authored-by: pasqui23 <pasqui23@users.noreply.github.com>
Co-authored-by: Artturin <Artturin@artturin.com>
Co-authored-by: John Ericson <Ericson2314@Yahoo.com>

2 files changed, 19 insertions, 0 deletions

diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 40faa4bf2..40a54b010 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -608,6 +608,19 @@ Path getDataDir()
     return dataDir ? *dataDir : getHome() + "/.local/share";
 }
 
+Path getStateDir()
+{
+    auto stateDir = getEnv("XDG_STATE_HOME");
+    return stateDir ? *stateDir : getHome() + "/.local/state";
+}
+
+Path createNixStateDir()
+{
+    Path dir = getStateDir() + "/nix";
+    createDirs(dir);
+    return dir;
+}
+
 
 std::optional<Path> getSelfExe()
 {
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index 266da0ae3..4fadafaf2 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -158,6 +158,12 @@ Path getDataDir();
 /* Return the path of the current executable. */
 std::optional<Path> getSelfExe();
 
+/* Return $XDG_STATE_HOME or $HOME/.local/state. */
+Path getStateDir();
+
+/* Create the Nix state directory and return the path to it. */
+Path createNixStateDir();
+
 /* Create a directory and all its parents, if necessary.  Returns the
    list of created directories, in order of creation. */
 Paths createDirs(const Path & path);