waybar: configurable systemd WantedBy target (#2524)

Before this commit, a user needed to override the systemd target that
would start Waybar with `mkForce`, this is no longer necessary.

modules/programs/waybar.nix

@@ -197,6 +197,20 @@ in {
 
     systemd.enable = mkEnableOption "Waybar systemd integration";
 
+    systemd.target = mkOption {
+      type = str;
+      default = "graphical-session.target";
+      example = "sway-session.target";
+      description = ''
+        The systemd target that will automatically start the Waybar service.
+        </para>
+        <para>
+        When setting this value to <literal>"sway-session.target"</literal>,
+        make sure to also enable <option>wayland.windowManager.sway.systemdIntegration</option>,
+        otherwise the service may never be started.
+      '';
+    };
+
     style = mkOption {
       type = nullOr (either path str);
       default = null;
@@ -309,7 +323,7 @@ in {
           KillMode = "mixed";
         };
 
-        Install = { WantedBy = [ "graphical-session.target" ]; };
+        Install = { WantedBy = [ cfg.systemd.target ]; };
       };
     })
   ]);

tests/modules/programs/waybar/systemd-with-graphical-session-target.nix

@@ -10,6 +10,7 @@ with lib;
       package = config.lib.test.mkStubPackage { outPath = "@waybar@"; };
       enable = true;
       systemd.enable = true;
+      systemd.target = "sway-session.target";
     };
 
     nmt.script = ''

tests/modules/programs/waybar/systemd-with-graphical-session-target.service

@@ -1,5 +1,5 @@
 [Install]
-WantedBy=graphical-session.target
+WantedBy=sway-session.target
 
 [Service]
 ExecReload=kill -SIGUSR2 $MAINPID