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>

tests/common.sh.in

@@ -27,6 +27,8 @@ export NIX_REMOTE=$NIX_REMOTE_
 unset NIX_PATH
 export TEST_HOME=$TEST_ROOT/test-home
 export HOME=$TEST_HOME
+unset XDG_STATE_HOME
+unset XDG_DATA_HOME
 unset XDG_CONFIG_HOME
 unset XDG_CONFIG_DIRS
 unset XDG_CACHE_HOME
@@ -62,8 +64,8 @@ readLink() {
 }
 
 clearProfiles() {
-    profiles="$HOME"/.local/share/nix/profiles
-    rm -rf $profiles
+    profiles="$HOME"/.local/state/nix/profiles
+    rm -rf "$profiles"
 }
 
 clearStore() {

tests/nix-channel.sh

@@ -12,6 +12,19 @@ nix-channel --remove xyzzy
 [ -e $TEST_HOME/.nix-channels ]
 [ "$(cat $TEST_HOME/.nix-channels)" = '' ]
 
+# Test the XDG Base Directories support
+
+export NIX_CONFIG="use-xdg-base-directories = true"
+
+nix-channel --add http://foo/bar xyzzy
+nix-channel --list | grep -q http://foo/bar
+nix-channel --remove xyzzy
+
+unset NIX_CONFIG
+
+[ -e $TEST_HOME/.local/state/nix/channels ]
+[ "$(cat $TEST_HOME/.local/state/nix/channels)" = '' ]
+
 # Create a channel.
 rm -rf $TEST_ROOT/foo
 mkdir -p $TEST_ROOT/foo

tests/nix-profile.sh

@@ -56,6 +56,14 @@ nix profile history
 nix profile history | grep "packages.$system.default: ∅ -> 1.0"
 nix profile diff-closures | grep 'env-manifest.nix: ε → ∅'
 
+# Test XDG Base Directories support
+
+export NIX_CONFIG="use-xdg-base-directories = true"
+nix profile remove 1
+nix profile install $flake1Dir
+[[ $($TEST_HOME/.local/state/nix/profile/bin/hello) = "Hello World" ]]
+unset NIX_CONFIG
+
 # Test upgrading a package.
 printf NixOS > $flake1Dir/who
 printf 2.0 > $flake1Dir/version