syncthingtray: add extraOptions

The test currently fails, because the nix path in the generated unit
does not get rewritten to `@syncthingtray@`. Pointers would be
appreciated.

modules/services/syncthing.nix

@@ -49,6 +49,15 @@ in {
                 description = "Syncthing tray command to use.";
               };
 
+              extraOptions = mkOption {
+                type = types.listOf types.str;
+                default = [ ];
+                example = [ "--wait" ];
+                description = ''
+                  Extra command-line arguments to pass to {command}`syncthingtray`.
+                '';
+              };
+
               package = mkOption {
                 type = types.package;
                 default = pkgs.syncthingtray-minimal;
@@ -126,7 +135,9 @@ in {
           };
 
           Service = {
-            ExecStart = "${cfg.tray.package}/bin/${cfg.tray.command}";
+            ExecStart = escapeShellArgs
+              ([ "${cfg.tray.package}/bin/${cfg.tray.command}" ]
+                ++ cfg.tray.extraOptions);
           };
 
           Install = { WantedBy = [ "graphical-session.target" ]; };

tests/modules/services/syncthing/linux/tray.nix

@@ -4,7 +4,12 @@ with lib;
 
 {
   config = {
-    services.syncthing.tray.enable = true;
+    services.syncthing.tray = {
+      enable = true;
+      extraOptions = [ "--wait" ];
+    };
+
+    test.stubs.syncthingtray = { };
 
     nixpkgs.overlays = [
       (self: super: {
@@ -16,6 +21,7 @@ with lib;
 
     nmt.script = ''
       assertFileExists home-files/.config/systemd/user/syncthingtray.service
+      assertFileContains home-files/.config/systemd/user/syncthingtray.service "ExecStart='@syncthingtray@/bin/syncthingtray' '--wait'"
     '';
   };
 }