wayland: create tray.target if xsession is not enabled

Create a internal/read-only trayTarget option for the xsession, which is
also used in wayland's config, if the former is not enabled.

Remove all other definitions of `systemd.user.targets.tray`, i. e, the
ones from the following modules: hyprland, sway, river and wayfire.

modules/services/window-managers/hyprland.nix

@@ -277,12 +277,5 @@ in {
           [ "xdg-desktop-autostart.target" ];
       };
     };
-
-    systemd.user.targets.tray = {
-      Unit = {
-        Description = "Home Manager System Tray";
-        Requires = [ "graphical-session-pre.target" ];
-      };
-    };
   };
 }

modules/services/window-managers/i3-sway/sway.nix

@@ -553,13 +553,6 @@ in {
             optional cfg.systemd.xdgAutostart "xdg-desktop-autostart.target";
         };
       };
-
-      systemd.user.targets.tray = {
-        Unit = {
-          Description = "Home Manager System Tray";
-          Requires = [ "graphical-session-pre.target" ];
-        };
-      };
     }
   ]);
 }

modules/services/window-managers/river.nix

@@ -201,12 +201,5 @@ in {
         After = [ "graphical-session-pre.target" ];
       };
     };
-
-    systemd.user.targets.tray = {
-      Unit = {
-        Description = "Home Manager System Tray";
-        Requires = [ "graphical-session-pre.target" ];
-      };
-    };
   };
 }

modules/services/window-managers/wayfire.nix

@@ -189,12 +189,5 @@
         After = [ "graphical-session-pre.target" ];
       };
     };
-
-    systemd.user.targets.tray = {
-      Unit = {
-        Description = "Home Manager System Tray";
-        Requires = [ "graphical-session-pre.target" ];
-      };
-    };
   };
 }

modules/wayland.nix

@@ -1,4 +1,4 @@
-{ lib, ... }:
+{ config, lib, ... }:
 
 {
   meta.maintainers = [ lib.maintainers.thiagokokada ];
@@ -21,4 +21,8 @@
       };
     };
   };
+
+  config = lib.mkIf (!config.xsession.enable) {
+    systemd.user.targets.tray = config.xsession.trayTarget;
+  };
 }

modules/xsession.nix

@@ -13,6 +13,20 @@ in {
     xsession = {
       enable = mkEnableOption "X Session";
 
+      trayTarget = mkOption {
+        readOnly = true;
+        internal = true;
+        visible = false;
+        description = "Common tray.target for both xsession and wayland";
+        type = types.attrs;
+        default = {
+          Unit = {
+            Description = "Home Manager System Tray";
+            Requires = [ "graphical-session-pre.target" ];
+          };
+        };
+      };
+
       scriptPath = mkOption {
         type = types.str;
         default = ".xsession";
@@ -163,12 +177,7 @@ in {
           };
         };
 
-        tray = {
+        tray = cfg.trayTarget;
-          Unit = {
-            Description = "Home Manager System Tray";
-            Requires = [ "graphical-session-pre.target" ];
-          };
-        };
       };
     };