[gnome-shell] st/theme-context: Also invalidate root node on stylesheet changes

[Carlos Garnacho <carlosg src gnome org>]

commit bc973b80d77ba36e29fbeba27a2bed9e2ea6cf09
Author: Jonas Dreßler <verdre v0yd nl>
Date:   Mon Apr 6 02:11:27 2020 +0200

    st/theme-context: Also invalidate root node on stylesheet changes
    
    Since commit 6a42d7726119c538d260e54cdbe2f31e5fbeb03c we invalidate the
    cached properties for each theme node on stylesheet changes by iterating
    over the hashtable of the theme context instead of listening to the
    signal in each individual theme node.
    
    That commit forgot one particular node though that's not stored in the
    hashtable, but using the `priv->root_node` property instead: The theme
    node that belongs to the stage.
    
    So make sure we also invalidate the cached properties of the stage theme
    node on stylesheet changes. This fixes various crashes that happened
    with extensions providing custom stylesheets (emitting the
    "custom-stylesheets-changed" signal on every extension enable/disable),
    trying to access an already freed CSS property of the stage.
    
    Fixes: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/2584

 src/st/st-theme-context.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/src/st/st-theme-context.c b/src/st/st-theme-context.c
index de112aa499..bc0f89a4e2 100644
--- a/src/st/st-theme-context.c
+++ b/src/st/st-theme-context.c
@@ -297,6 +297,9 @@ on_custom_stylesheets_changed (StTheme        *theme,
   GHashTableIter iter;
   StThemeNode *node;
 
+  if (context->root_node)
+    _st_theme_node_reset_for_stylesheet_change (context->root_node);
+
   g_hash_table_iter_init (&iter, context->nodes);
 
   while (g_hash_table_iter_next (&iter, (gpointer *) &node, NULL))