[mutter] clutter/actor-meta: Warn if an actor modifier is altered mid paint

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

commit 50e0ae3cf3a28f3c4f28dd38b9aa28ed2bdaea21
Author: Jonas Ådahl <jadahl gmail com>
Date:   Tue Mar 31 19:41:33 2020 +0200

    clutter/actor-meta: Warn if an actor modifier is altered mid paint
    
    Nothing should ever disable an actor modifier (e.g. effect) during the
    paint sequence, nor should any actor be set or unset on it. If this
    would happen, log warnings so that it can be tracked down.
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1166

 clutter/clutter/clutter-actor-meta.c | 7 +++++++
 1 file changed, 7 insertions(+)
---
diff --git a/clutter/clutter/clutter-actor-meta.c b/clutter/clutter/clutter-actor-meta.c
index eba098584..f90c44e9d 100644
--- a/clutter/clutter/clutter-actor-meta.c
+++ b/clutter/clutter/clutter-actor-meta.c
@@ -88,6 +88,10 @@ static void
 clutter_actor_meta_real_set_actor (ClutterActorMeta *meta,
                                    ClutterActor     *actor)
 {
+  g_warn_if_fail (!meta->priv->actor ||
+                  !CLUTTER_ACTOR_IN_PAINT (meta->priv->actor));
+  g_warn_if_fail (!actor || !CLUTTER_ACTOR_IN_PAINT (actor));
+
   if (meta->priv->actor == actor)
     return;
 
@@ -293,6 +297,9 @@ clutter_actor_meta_set_enabled (ClutterActorMeta *meta,
 {
   g_return_if_fail (CLUTTER_IS_ACTOR_META (meta));
 
+  g_warn_if_fail (!meta->priv->actor ||
+                  !CLUTTER_ACTOR_IN_PAINT (meta->priv->actor));
+
   is_enabled = !!is_enabled;
 
   if (meta->priv->is_enabled == is_enabled)