[mutter] clutter/actor: Remove actors from shallow relayout list when unrealizing

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit ae83a61e670cd2f25bd3ee6d757cdb64eaba1710
Author: Jonas Dreßler <verdre v0yd nl>
Date:   Mon Jul 6 15:35:14 2020 +0200

    clutter/actor: Remove actors from shallow relayout list when unrealizing
    
    With the introduction of the shallow relayout mechanism another small
    but severe regression sneaked into our layout machinery: We might
    allocate an actor twice during the same allocation cycle, with one
    allocation happening using the wrong parent.
    
    This issue happens when reparenting an actor from a NO_LAYOUT parent to
    a non-NO_LAYOUT parent, in particular it triggered a bug in gnome-shell
    when DND reparents a child from the NO_LAYOUT uiGroup to the overviews
    Workspace actor after a drag ended. The reason the issue happens is the
    following chain of events:
    
    1. child of a NO_LAYOUT parent queues a relayout, this child is added to
    the priv->pending_relayouts list maintained by ClutterStage
    
    2. child is reparented to a different parent which doesn't have the
    NO_LAYOUT flag set, another relayout is queued, this time a different
    actor is added to the priv->pending_relayouts list
    
    3. the relayout happens and we go through the pending_relayouts list
    backwards, that means the correct relayout queued during 2. happens
    first, then the old one happens and we simply call
    clutter_actor_allocate_preferred_size() on the actor, that allocation
    overrides the other, correct one.
    
    So fix that issue by adding a method to ClutterStage which removes
    actors from the pending_relayouts list again and call this method as
    soon as an actor with a NO_LAYOUT parent is detached from the stage.
    
    With that in place, we can also remove the check whether an actor is
    still on stage while looping through pending_relayouts. In case
    something else is going wrong and the actor is not on stage,
    clutter_actor_allocate() will warn anyway.
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1356

 clutter/clutter/clutter-actor.c         |  8 ++++++++
 clutter/clutter/clutter-stage-private.h |  3 +++
 clutter/clutter/clutter-stage.c         | 26 ++++++++++++++++++++++----
 3 files changed, 33 insertions(+), 4 deletions(-)
---
diff --git a/clutter/clutter/clutter-actor.c b/clutter/clutter/clutter-actor.c
index 1bd88bcd35..d3ca1b22d7 100644
--- a/clutter/clutter/clutter-actor.c
+++ b/clutter/clutter/clutter-actor.c
@@ -2201,11 +2201,19 @@ unrealize_actor_after_children_cb (ClutterActor *self,
                                    int depth,
                                    void *user_data)
 {
+  ClutterActor *stage = _clutter_actor_get_stage_internal (self);
+
   /* We want to unset the realized flag only _after_
    * child actors are unrealized, to maintain invariants.
    */
   CLUTTER_ACTOR_UNSET_FLAGS (self, CLUTTER_ACTOR_REALIZED);
   g_object_notify_by_pspec (G_OBJECT (self), obj_props[PROP_REALIZED]);
+
+  if (stage != NULL &&
+      self->priv->parent != NULL &&
+      self->priv->parent->flags & CLUTTER_ACTOR_NO_LAYOUT)
+    clutter_stage_dequeue_actor_relayout (CLUTTER_STAGE (stage), self);
+
   return CLUTTER_ACTOR_TRAVERSE_VISIT_CONTINUE;
 }
 
diff --git a/clutter/clutter/clutter-stage-private.h b/clutter/clutter/clutter-stage-private.h
index 7297d56a6d..f2a371c5ef 100644
--- a/clutter/clutter/clutter-stage-private.h
+++ b/clutter/clutter/clutter-stage-private.h
@@ -141,6 +141,9 @@ void            clutter_stage_presented                 (ClutterStage      *stag
 void            clutter_stage_queue_actor_relayout      (ClutterStage *stage,
                                                          ClutterActor *actor);
 
+void clutter_stage_dequeue_actor_relayout (ClutterStage *stage,
+                                           ClutterActor *actor);
+
 GList * clutter_stage_get_views_for_rect (ClutterStage          *stage,
                                           const graphene_rect_t *rect);
 
diff --git a/clutter/clutter/clutter-stage.c b/clutter/clutter/clutter-stage.c
index e9368fe444..51f7382175 100644
--- a/clutter/clutter/clutter-stage.c
+++ b/clutter/clutter/clutter-stage.c
@@ -1202,6 +1202,28 @@ clutter_stage_queue_actor_relayout (ClutterStage *stage,
                                              g_object_ref (actor));
 }
 
+void
+clutter_stage_dequeue_actor_relayout (ClutterStage *stage,
+                                      ClutterActor *actor)
+{
+  ClutterStagePrivate *priv = stage->priv;
+  GSList *l;
+
+  for (l = priv->pending_relayouts; l; l = l->next)
+    {
+      ClutterActor *relayout_actor = l->data;
+
+      if (relayout_actor == actor)
+        {
+          g_object_unref (relayout_actor);
+          priv->pending_relayouts =
+            g_slist_delete_link (priv->pending_relayouts, l);
+
+          return;
+        }
+    }
+}
+
 void
 clutter_stage_maybe_relayout (ClutterActor *actor)
 {
@@ -1227,10 +1249,6 @@ clutter_stage_maybe_relayout (ClutterActor *actor)
       if (CLUTTER_ACTOR_IN_RELAYOUT (queued_actor))  /* avoid reentrancy */
         continue;
 
-      /* An actor may have been destroyed or hidden between queuing and now */
-      if (clutter_actor_get_stage (queued_actor) != actor)
-        continue;
-
       if (queued_actor == actor)
         CLUTTER_NOTE (ACTOR, "    Deep relayout of stage %s",
                       _clutter_actor_get_debug_name (queued_actor));