widget: add helpers to resolve GActionGroups available to GtkWidget

These functions, while added for use by the GTK inspector, are generally
useful to applications that need to resolve what action groups are
available to a particular GtkWidget.

https://bugzilla.gnome.org/show_bug.cgi?id=741386

docs/reference/gtk/gtk3-sections.txt

@@ -5543,6 +5543,8 @@ gtk_widget_get_modifier_mask
 gtk_widget_insert_action_group
 gtk_widget_get_opacity
 gtk_widget_set_opacity
+gtk_widget_list_action_prefixes
+gtk_widget_get_action_group
 
 <SUBSECTION>
 gtk_widget_get_path

gtk/gtkactionmuxer.c

@@ -732,10 +732,10 @@ gtk_action_muxer_remove (GtkActionMuxer *muxer,
     }
 }
 
-gchar **
+const gchar **
 gtk_action_muxer_list_prefixes (GtkActionMuxer *muxer)
 {
-  return (gchar **) g_hash_table_get_keys_as_array (muxer->groups, NULL);
+  return (const gchar **) g_hash_table_get_keys_as_array (muxer->groups, NULL);
 }
 
 GActionGroup *

gtk/gtkactionmuxer.h

@@ -41,7 +41,7 @@ void                    gtk_action_muxer_insert                         (GtkActi
 
 void                    gtk_action_muxer_remove                         (GtkActionMuxer *muxer,
                                                                          const gchar    *prefix);
-gchar **                gtk_action_muxer_list_prefixes                  (GtkActionMuxer *muxer);
+const gchar **          gtk_action_muxer_list_prefixes                  (GtkActionMuxer *muxer);
 GActionGroup *          gtk_action_muxer_lookup                         (GtkActionMuxer *muxer,
                                                                          const gchar    *prefix);
 GtkActionMuxer *        gtk_action_muxer_get_parent                     (GtkActionMuxer *muxer);

gtk/gtkwidget.c

@@ -17037,18 +17037,49 @@ gtk_widget_get_template_child (GtkWidget   *widget,
   return ret;
 }
 
-gchar **
-_gtk_widget_list_action_prefixes (GtkWidget *widget)
+/**
+ * gtk_widget_list_action_prefixes:
+ * @widget: A #GtkWidget
+ *
+ * Retrieves a %NULL-terminated array of strings containing the prefixes of
+ * #GActionGroup's available to @widget.
+ *
+ * Returns: (transfer container): a %NULL-terminated array of strings.
+ *
+ * Since: 3.16
+ */
+const gchar **
+gtk_widget_list_action_prefixes (GtkWidget *widget)
 {
+  g_return_val_if_fail (GTK_IS_WIDGET (widget), NULL);
+
   if (widget->priv->muxer)
-    return gtk_action_muxer_list_prefixes (widget->priv->muxer);
-  return NULL;
+      return gtk_action_muxer_list_prefixes (widget->priv->muxer);
+  return g_new0 (const gchar *, 0 + 1);
 }
 
+/**
+ * gtk_widget_get_action_group:
+ * @widget: A #GtkWidget
+ * @prefix: The “prefix” of the action group.
+ *
+ * Retrieves the #GActionGroup that was registered using @prefix. The resulting
+ * #GActionGroup may have been registered to @widget or any #GtkWidget in its
+ * ancestry.
+ *
+ * If no action group was found matching @prefix, then %NULL is returned.
+ *
+ * Returns: (transfer none) (nullable): A #GActionGroup or %NULL.
+ *
+ * Since: 3.16
+ */
 GActionGroup *
-_gtk_widget_get_action_group (GtkWidget   *widget,
-                              const gchar *prefix)
+gtk_widget_get_action_group (GtkWidget   *widget,
+                             const gchar *prefix)
 {
+  g_return_val_if_fail (GTK_IS_WIDGET (widget), NULL);
+  g_return_val_if_fail (prefix, NULL);
+
   if (widget->priv->muxer)
     return gtk_action_muxer_lookup (widget->priv->muxer, prefix);
   return NULL;

gtk/gtkwidget.h

@@ -1475,6 +1475,13 @@ void    gtk_widget_class_bind_template_child_full       (GtkWidgetClass        *
 						         gboolean               internal_child,
 						         gssize                 struct_offset);
 
+GDK_AVAILABLE_IN_3_16
+GActionGroup           *gtk_widget_get_action_group                     (GtkWidget    *widget,
+                                                                         const gchar  *prefix);
+
+GDK_AVAILABLE_IN_3_16
+const gchar **          gtk_widget_list_action_prefixes                 (GtkWidget    *widget);
+
 G_END_DECLS
 
 #endif /* __GTK_WIDGET_H__ */

gtk/gtkwidgetprivate.h

@@ -153,9 +153,6 @@ void              _gtk_widget_style_context_invalidated    (GtkWidget    *widget
 void              _gtk_widget_update_parent_muxer          (GtkWidget    *widget);
 GtkActionMuxer *  _gtk_widget_get_action_muxer             (GtkWidget    *widget,
                                                             gboolean      create);
-gchar **          _gtk_widget_list_action_prefixes         (GtkWidget    *widget);
-GActionGroup *    _gtk_widget_get_action_group             (GtkWidget    *widget,
-                                                            const gchar  *prefix);
 
 void              _gtk_widget_add_controller               (GtkWidget           *widget,
                                                             GtkEventController  *controller);

gtk/inspector/actions.c

@@ -220,12 +220,12 @@ gtk_inspector_actions_set_object (GtkInspectorActions *sl,
       GActionGroup *group;
       gint i;
 
-      prefixes = _gtk_widget_list_action_prefixes (GTK_WIDGET (object));
+      prefixes = gtk_widget_list_action_prefixes (GTK_WIDGET (object));
       if (prefixes)
         {
           for (i = 0; prefixes[i]; i++)
             {
-              group = _gtk_widget_get_action_group (GTK_WIDGET (object), prefixes[i]);
+              group = gtk_widget_get_action_group (GTK_WIDGET (object), prefixes[i]);
               add_group (sl, group, prefixes[i]);
             }
           g_free (prefixes);

gtk/inspector/prop-editor.c

@@ -1262,7 +1262,7 @@ find_action_owner (GtkActionable *actionable)
 
   while (widget != NULL)
     {
-      group = _gtk_widget_get_action_group (widget, prefix);
+      group = gtk_widget_get_action_group (widget, prefix);
       if (group && g_action_group_has_action (group, name))
         return (GObject *)widget;
       widget = action_ancestor (widget);