[gnome-shell/wip/carlosg/invalidate-styles] st: Ensure to reset all widget theme nodes

[Carlos Garnacho <carlosg src gnome org>]

commit 13b461cbc9649a62e8f20cfcce8f99a4de3b1e29
Author: Carlos Garnacho <carlosg gnome org>
Date:   Sat Apr 25 18:31:11 2020 +0200

    st: Ensure to reset all widget theme nodes
    
    Theme node invalidation stops at unmapped widgets, and widgets
    that forget to chain up to the default ::style-changed implementation.
    This may leave stale nodes that were invalidated on
    StThemeContext::changed, but are still set on widgets, and maybe
    used for CSS property lookups.
    
    Make sure that theme node invalidation happens always by moving
    propagation outside the vfunc, and ensure the theme nodes are reset
    across the full actor tree. Emission of ::style-changed, and obtaining
    a new theme node may be delayed till when the actor is mapped.
    
    The theme node is also cleared after unparenting an actor to avoid
    stale references.
    
    This ensures that all widgets get their theme node cleared after
    stylesheet changes, instead of maybe being left with a theme node
    that's been cleared of all its properties.
    
    Fixes: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/2541
    
    https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1223

 src/st/st-widget.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)
---
diff --git a/src/st/st-widget.c b/src/st/st-widget.c
index 7314a6ca5f..e48f826412 100644
--- a/src/st/st-widget.c
+++ b/src/st/st-widget.c
@@ -455,17 +455,12 @@ st_widget_parent_set (ClutterActor *widget,
 {
   StWidget *self = ST_WIDGET (widget);
   ClutterActorClass *parent_class;
-  ClutterActor *new_parent;
 
   parent_class = CLUTTER_ACTOR_CLASS (st_widget_parent_class);
   if (parent_class->parent_set)
     parent_class->parent_set (widget, old_parent);
 
-  new_parent = clutter_actor_get_parent (widget);
-
-  /* don't send the style changed signal if we no longer have a parent actor */
-  if (new_parent)
-    st_widget_style_changed (self);
+  st_widget_style_changed (self);
 }
 
 static void
@@ -510,7 +505,6 @@ static void
 st_widget_real_style_changed (StWidget *self)
 {
   clutter_actor_queue_redraw ((ClutterActor *) self);
-  notify_children_of_style_change ((ClutterActor *) self);
 }
 
 void
@@ -530,6 +524,11 @@ st_widget_style_changed (StWidget *widget)
   if (clutter_actor_is_mapped (CLUTTER_ACTOR (widget)))
     st_widget_recompute_style (widget, old_theme_node);
 
+  /* Descend through all children. If the actor is not mapped,
+   * children will clear their theme node without recomputing style.
+   */
+  notify_children_of_style_change (CLUTTER_ACTOR (widget));
+
   if (old_theme_node)
     g_object_unref (old_theme_node);
 }
@@ -1772,8 +1771,6 @@ st_widget_recompute_style (StWidget    *widget,
 
   if (!paint_equal || !geometry_equal)
     g_signal_emit (widget, signals[STYLE_CHANGED], 0);
-  else
-    notify_children_of_style_change ((ClutterActor *) widget);
 
   priv->is_style_dirty = FALSE;
 }
@@ -1795,7 +1792,10 @@ st_widget_ensure_style (StWidget *widget)
   priv = st_widget_get_instance_private (widget);
 
   if (priv->is_style_dirty)
-    st_widget_recompute_style (widget, NULL);
+    {
+      st_widget_recompute_style (widget, NULL);
+      notify_children_of_style_change (CLUTTER_ACTOR (widget));
+    }
 }
 
 /**