[gnome-shell/wip/chergert/has-accessible] st: implement ClutterActorClass.has_accessible()

[Christian Hergert <chergert src gnome org>]

commit 40c9185467857a2d6316ee558d43c7bb54d78ca7
Author: Christian Hergert <chergert redhat com>
Date:   Sun Feb 23 14:08:41 2020 -0800

    st: implement ClutterActorClass.has_accessible()
    
    Implement ClutterActorClass.has_accessible() to ensure that CallyActor does not
    recreate accessibles during the removal/destruction of an actor.  This relies
    on GNOME/mutter!1083 for the ClutterActorClass.has_accessible virtual function.
    
    Running GNOME Shell for about 30 seconds results in a difference between
    the two runs.
    
    Before:
    
        ALLOCATED      TOTAL    FUNCTION
    [   52.2 KiB] [   0.05%]    cally_actor_real_remove_actor
    [   36.3 KiB] [   0.04%]      st_widget_get_accessible
    [    9.8 KiB] [   0.01%]      atk_gobject_accessible_for_object
    [    3.2 KiB] [   0.00%]      g_signal_emit_by_name
    [    2.9 KiB] [   0.00%]      clutter_actor_get_children
    
    After:
    
        ALLOCATED      TOTAL    FUNCTION
    [    1.8 KiB] [   0.00%]    cally_actor_real_remove_actor
    [    1.1 KiB] [   0.00%]      clutter_actor_get_children
    [  659 bytes] [   0.00%]      g_signal_emit_by_name
    
    Obviously 50KiB isn't a huge savings.
    
    Although fixing things to avoid re-entrancy on destruction can be very useful
    from a correctness standpoint.
    
    Fixes https://gitlab.gnome.org/GNOME/gnome-shell/issues/2263

 src/st/st-widget.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)
---
diff --git a/src/st/st-widget.c b/src/st/st-widget.c
index b402593687..7314a6ca5f 100644
--- a/src/st/st-widget.c
+++ b/src/st/st-widget.c
@@ -141,6 +141,7 @@ static gboolean st_widget_real_navigate_focus (StWidget         *widget,
                                                StDirectionType   direction);
 
 static AtkObject * st_widget_get_accessible (ClutterActor *actor);
+static gboolean    st_widget_has_accessible (ClutterActor *actor);
 
 static void
 st_widget_set_property (GObject      *gobject,
@@ -846,6 +847,7 @@ st_widget_class_init (StWidgetClass *klass)
   actor_class->key_press_event = st_widget_key_press_event;
 
   actor_class->get_accessible = st_widget_get_accessible;
+  actor_class->has_accessible = st_widget_has_accessible;
 
   klass->style_changed = st_widget_real_style_changed;
   klass->navigate_focus = st_widget_real_navigate_focus;
@@ -2650,6 +2652,20 @@ struct _StWidgetAccessiblePrivate
 
 G_DEFINE_TYPE_WITH_PRIVATE (StWidgetAccessible, st_widget_accessible, CALLY_TYPE_ACTOR)
 
+static gboolean
+st_widget_has_accessible (ClutterActor *actor)
+{
+  StWidget *widget;
+  StWidgetPrivate *priv;
+
+  g_return_val_if_fail (ST_IS_WIDGET (actor), FALSE);
+
+  widget = ST_WIDGET (actor);
+  priv = st_widget_get_instance_private (widget);
+
+  return priv->accessible != NULL;
+}
+
 static AtkObject *
 st_widget_get_accessible (ClutterActor *actor)
 {