swww: add extraArgs for swww-daemon

modules/services/swww.nix

@@ -13,6 +13,20 @@ in
   options.services.swww = {
     enable = lib.mkEnableOption "swww, a Solution to your Wayland Wallpaper Woes";
     package = lib.mkPackageOption pkgs "swww" { };
+    extraArgs = lib.mkOption {
+      type = lib.types.listOf lib.types.str;
+      default = [ ];
+      example = [
+        "--no-cache"
+        "--layer"
+        "bottom"
+      ];
+      description = ''
+        Options given to swww-daemon when the service is run.
+
+        See `swww-daemon --help` for more information.
+      '';
+    };
   };
 
   config = lib.mkIf cfg.enable {
@@ -35,7 +49,7 @@ in
       };
 
       Service = {
-        ExecStart = "${lib.getExe' cfg.package "swww-daemon"}";
+        ExecStart = "${lib.getExe' cfg.package "swww-daemon"} ${lib.escapeShellArgs cfg.extraArgs}";
         Restart = "always";
         RestartSec = 10;
       };

tests/modules/services/swww/swww-graphical-session-target.nix

@@ -3,6 +3,11 @@
   services.swww = {
     enable = true;
     package = config.lib.test.mkStubPackage { outPath = "@swww@"; };
+    extraArgs = [
+      "--no-cache"
+      "--layer"
+      "bottom"
+    ];
   };
 
   nmt.script = ''

tests/modules/services/swww/swww-graphical-session-target.service

@@ -2,7 +2,7 @@
 WantedBy=graphical-session.target
 
 [Service]
-ExecStart=@swww@/bin/swww-daemon
+ExecStart=@swww@/bin/swww-daemon --no-cache --layer bottom
 Restart=always
 RestartSec=10