application: Bring back app menus

Being able to override the app menu is relevant on macOS, so
bring back the api needed to do that. All the machinery was
still around from when we stripped it before 4.0.

gtk/gtkapplication.c

@@ -74,6 +74,10 @@
  * It is also possible to provide the menubar manually using
  * [method@Gtk.Application.set_menubar].
  *
+ * A custom 'Application' menu can be set using [method@Gtk.Application.set_app_menu].
+ * This is mainly relevant on macOS, where GTK will otherwise provide a standard
+ * app menu.
+ *
  * `GtkApplication` will also automatically setup an icon search path for
  * the default icon theme by appending "icons" to the resource base
  * path. This allows your application to easily store its icons as
@@ -125,6 +129,7 @@ enum {
   PROP_ZERO,
   PROP_REGISTER_SESSION,
   PROP_SCREENSAVER_ACTIVE,
+  PROP_APP_MENU,
   PROP_MENUBAR,
   PROP_ACTIVE_WINDOW,
   NUM_PROPERTIES
@@ -139,6 +144,7 @@ typedef struct
 
   GList *windows;
 
+  GMenuModel      *app_menu;
   GMenuModel      *menubar;
   guint            last_window_id;
 
@@ -215,6 +221,9 @@ gtk_application_load_resources (GtkApplication *application)
       {
         GObject *menu;
 
+        menu = gtk_builder_get_object (priv->menus_builder, "app-menu");
+        if (menu != NULL && G_IS_MENU_MODEL (menu))
+          gtk_application_set_app_menu (application, G_MENU_MODEL (menu));
         menu = gtk_builder_get_object (priv->menus_builder, "menubar");
         if (menu != NULL && G_IS_MENU_MODEL (menu))
           gtk_application_set_menubar (application, G_MENU_MODEL (menu));
@@ -438,6 +447,10 @@ gtk_application_get_property (GObject    *object,
       g_value_set_boolean (value, priv->screensaver_active);
       break;
 
+    case PROP_APP_MENU:
+      g_value_set_object (value, gtk_application_get_app_menu (application));
+      break;
+
     case PROP_MENUBAR:
       g_value_set_object (value, gtk_application_get_menubar (application));
       break;
@@ -467,6 +480,10 @@ gtk_application_set_property (GObject      *object,
       priv->register_session = g_value_get_boolean (value);
       break;
 
+    case PROP_APP_MENU:
+      gtk_application_set_app_menu (application, g_value_get_object (value));
+      break;
+
     case PROP_MENUBAR:
       gtk_application_set_menubar (application, g_value_get_object (value));
       break;
@@ -484,6 +501,7 @@ gtk_application_finalize (GObject *object)
   GtkApplicationPrivate *priv = gtk_application_get_instance_private (application);
 
   g_clear_object (&priv->menus_builder);
+  g_clear_object (&priv->app_menu);
   g_clear_object (&priv->menubar);
   g_clear_object (&priv->muxer);
   g_clear_object (&priv->accels);
@@ -611,6 +629,21 @@ gtk_application_class_init (GtkApplicationClass *class)
                           FALSE,
                           G_PARAM_READABLE|G_PARAM_STATIC_STRINGS);
 
+  /**
+   * GtkApplication:app-menu: (attributes org.gtk.Property.get=gtk_application_get_app_menu org.gtk.Property.set=gtk_application_set_app_menu)
+   *
+   * The `GMenuModel` to be used for the application's app menu.
+   *
+   * This is mainly relevant on macOS, where GTK will provide a
+   * standard app menu, unless it is overwritten by setting this property.
+   *
+   * Since: 4.16
+   */
+  gtk_application_props[PROP_APP_MENU] =
+    g_param_spec_object ("app-menu", NULL, NULL,
+                         G_TYPE_MENU_MODEL,
+                         G_PARAM_READWRITE|G_PARAM_STATIC_STRINGS);
+
   /**
    * GtkApplication:menubar: (attributes org.gtk.Property.get=gtk_application_get_menubar org.gtk.Property.set=gtk_application_set_menubar)
    *
@@ -833,6 +866,75 @@ gtk_application_update_accels (GtkApplication *application)
     _gtk_window_notify_keys_changed (l->data);
 }
 
+/**
+ * gtk_application_set_app_menu:
+ * @application: a #GtkApplication
+ * @app_menu: (allow-none): a #GMenuModel, or %NULL
+ *
+ * Sets or unsets the application menu for @application.
+ *
+ * This can only be done in the primary instance of the application,
+ * after it has been registered.  #GApplication::startup is a good place
+ * to call this.
+ *
+ * The application menu is a single menu containing items that typically
+ * impact the application as a whole, rather than acting on a specific
+ * window or document.  For example, you would expect to see
+ * “Preferences” or “Quit” in an application menu, but not “Save” or
+ * “Print”.
+ *
+ * If supported, the application menu will be rendered by the desktop
+ * environment.
+ *
+ * Use the base #GActionMap interface to add actions, to respond to the user
+ * selecting these menu items.
+ *
+ * Note that setting an app menu is mainly relevant on macOS, where GTK
+ * provides a standard app menu unless overwritten by this function.
+ *
+ * Since: 4.16
+ */
+void
+gtk_application_set_app_menu (GtkApplication *application,
+                              GMenuModel     *app_menu)
+{
+  GtkApplicationPrivate *priv = gtk_application_get_instance_private (application);
+
+  g_return_if_fail (GTK_IS_APPLICATION (application));
+  g_return_if_fail (g_application_get_is_registered (G_APPLICATION (application)));
+  g_return_if_fail (!g_application_get_is_remote (G_APPLICATION (application)));
+  g_return_if_fail (app_menu == NULL || G_IS_MENU_MODEL (app_menu));
+
+  if (g_set_object (&priv->app_menu, app_menu))
+    {
+      gtk_application_impl_set_app_menu (priv->impl, app_menu);
+
+      g_object_notify_by_pspec (G_OBJECT (application), gtk_application_props[PROP_APP_MENU]
+);
+    }
+}
+
+/**
+ * gtk_application_get_app_menu:
+ * @application: a #GtkApplication
+ *
+ * Returns the menu model that has been set with gtk_application_set_app_menu().
+ *
+ * Returns: (transfer none) (nullable): the application menu of @application
+ *   or %NULL if no application menu has been set.
+ *
+ * Since: 4.16
+ */
+GMenuModel *
+gtk_application_get_app_menu (GtkApplication *application)
+{
+  GtkApplicationPrivate *priv = gtk_application_get_instance_private (application);
+
+  g_return_val_if_fail (GTK_IS_APPLICATION (application), NULL);
+
+  return priv->app_menu;
+}
+
 /**
  * gtk_application_set_menubar: (attributes org.gtk.Method.set_property=menubar)
  * @application: a `GtkApplication`

gtk/gtkapplication.h

@@ -84,6 +84,12 @@ void             gtk_application_remove_window (GtkApplication    *application,
 GDK_AVAILABLE_IN_ALL
 GList *          gtk_application_get_windows   (GtkApplication    *application);
 
+GDK_AVAILABLE_IN_4_16
+GMenuModel *     gtk_application_get_app_menu  (GtkApplication    *application);
+GDK_AVAILABLE_IN_4_16
+void             gtk_application_set_app_menu  (GtkApplication    *application,
+                                                GMenuModel        *app_menu);
+
 GDK_AVAILABLE_IN_ALL
 GMenuModel *     gtk_application_get_menubar   (GtkApplication    *application);
 GDK_AVAILABLE_IN_ALL