dunst: add option to read alternative configuration file (#2113)

modules/services/dunst.nix

@@ -64,6 +64,21 @@ in {
         description = "Package providing <command>dunst</command>.";
       };
 
+      configFile = mkOption {
+        type = with types; either str path;
+        default = "${config.xdg.configHome}/dunst/dunstrc";
+        defaultText = "$XDG_CONFIG_HOME/dunst/dunstrc";
+        description = ''
+          Path to the configuration file read by dunst.
+          </para><para>
+          Note that the configuration generated by Home Manager will be
+          written to <filename>$XDG_CONFIG_HOME/dunst/dunstrc</filename>
+          regardless. This allows using a mutable configuration file generated
+          from the immutable one, useful in scenarios where live reloading is
+          desired.
+        '';
+      };
+
       iconTheme = mkOption {
         type = themeType;
         default = hicolorTheme;
@@ -88,7 +103,8 @@ in {
           };
         };
         default = { };
-        description = "Configuration written to ~/.config/dunst/dunstrc";
+        description =
+          "Configuration written to <filename>$XDG_CONFIG_HOME/dunst/dunstrc</filename>.";
         example = literalExample ''
           {
             global = {
@@ -165,7 +181,7 @@ in {
         Service = {
           Type = "dbus";
           BusName = "org.freedesktop.Notifications";
-          ExecStart = "${cfg.package}/bin/dunst";
+          ExecStart = "${cfg.package}/bin/dunst -config ${cfg.configFile}";
           Environment = optionalString (cfg.waylandDisplay != "")
             "WAYLAND_DISPLAY=${cfg.waylandDisplay}";
         };