starship: set STARSHIP_CONFIG var and add option to set config path (#7435)

modules/programs/starship.nix

@@ -82,14 +82,27 @@ in
         https://starship.rs/advanced-config/#transientprompt-and-transientrightprompt-in-cmd
       '';
     };
+
+    configPath = mkOption {
+      type = lib.types.str;
+      default = "${config.xdg.configHome}/starship.toml";
+      defaultText = lib.literalExpression "\${config.xdg.configHome}/starship.toml";
+      description = ''
+        Relative path to the user's home directory where the Starship config should be stored.
+      '';
+    };
   };
 
   config = mkIf cfg.enable {
-    home.packages = [ cfg.package ];
+    home = {
+      packages = [ cfg.package ];
 
-    xdg.configFile."starship.toml" = mkIf (cfg.settings != { }) {
+      sessionVariables.STARSHIP_CONFIG = cfg.configPath;
+
+      file.${cfg.configPath} = mkIf (cfg.settings != { }) {
         source = tomlFormat.generate "starship-config" cfg.settings;
       };
+    };
 
     programs.bash.initExtra = mkIf cfg.enableBashIntegration ''
       if [[ $TERM != "dumb" ]]; then

tests/modules/programs/starship/settings.nix

@@ -46,6 +46,11 @@
   };
 
   nmt.script = ''
+    sessionVarsFile=home-path/etc/profile.d/hm-session-vars.sh
+    assertFileExists $sessionVarsFile
+    assertFileContains $sessionVarsFile \
+        'export STARSHIP_CONFIG="/home/hm-user/.config/starship.toml"'
+
     assertFileContent \
       home-files/.config/starship.toml \
       ${./settings-expected.toml}