xdg: fix typo and add test

modules/misc/xdg.nix

@@ -108,7 +108,7 @@ in {
       xdg.cacheHome = mkDefault defaultCacheHome;
       xdg.configHome = mkDefault defaultConfigHome;
       xdg.dataHome = mkDefault defaultDataHome;
-      xdg.stateHome = mkDefault stateHome;
+      xdg.stateHome = mkDefault defaultStateHome;
     })
 
     {

tests/modules/misc/xdg/default-locations.nix

@@ -0,0 +1,35 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+  config = {
+    # Test fallback behavior for stateVersion >= 20.09, which is pure.
+    xdg.enable = lib.mkForce false;
+    home.stateVersion = "20.09";
+
+    xdg.configFile.test.text = "config";
+    xdg.dataFile.test.text = "data";
+    home.file."${config.xdg.cacheHome}/test".text = "cache";
+    home.file."${config.xdg.stateHome}/test".text = "state";
+
+    nmt.script = ''
+      assertFileExists home-files/.config/test
+      assertFileExists home-files/.local/share/test
+      assertFileExists home-files/.cache/test
+      assertFileExists home-files/.local/state/test
+      assertFileContent \
+        home-files/.config/test \
+        ${builtins.toFile "test" "config"}
+      assertFileContent \
+        home-files/.local/share/test \
+        ${builtins.toFile "test" "data"}
+      assertFileContent \
+        home-files/.cache/test \
+        ${builtins.toFile "test" "cache"}
+      assertFileContent \
+        home-files/.local/state/test \
+        ${builtins.toFile "test" "state"}
+    '';
+  };
+}

tests/modules/misc/xdg/default.nix

@@ -3,4 +3,5 @@
   xdg-system-dirs = ./system-dirs.nix;
   xdg-desktop-entries = ./desktop-entries.nix;
   xdg-file-gen = ./file-gen.nix;
+  xdg-default-locations = ./default-locations.nix;
 }