[gnome-shell] st/theme: Remove entry from files_by_stylesheet after emitting signal

[Florian Müllner <fmuellner src gnome org>]

commit 0f947d4ff99e220fbc91e64a10511f5ebc69d06e
Author: Jonas Dreßler <verdre v0yd nl>
Date:   Mon May 11 20:41:37 2020 +0200

    st/theme: Remove entry from files_by_stylesheet after emitting signal
    
    Since e06109c23ce2a6dd53d32c26a89ab46a952d7373 we keep old theme nodes
    valid during the emission of the "custom-stylesheets-changed" signal.
    
    It turns out that we might still look up the file of a stylesheet using
    the files_by_stylesheet hashtable during the emission of that signal,
    causing a crash because the assertion in _st_theme_resolve_url() fails.
    
    So fix that and remove the stylesheet entry from the files_by_stylesheet
    hashtable after emitting the "custom-stylesheets-changed" signal. And to
    be consistent, also remove the entry from the stylesheets_by_file
    hashtable after emitting the signal.
    
    Fixes: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/2757

 src/st/st-theme.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
---
diff --git a/src/st/st-theme.c b/src/st/st-theme.c
index 7ccf7b5bad..3f08833a8a 100644
--- a/src/st/st-theme.c
+++ b/src/st/st-theme.c
@@ -285,11 +285,15 @@ st_theme_unload_stylesheet (StTheme    *theme,
     return;
 
   theme->custom_stylesheets = g_slist_remove (theme->custom_stylesheets, stylesheet);
-  g_hash_table_remove (theme->stylesheets_by_file, file);
-  g_hash_table_remove (theme->files_by_stylesheet, stylesheet);
 
   g_signal_emit (theme, signals[STYLESHEETS_CHANGED], 0);
 
+  /* We need to remove the entry from the hashtable after emitting the signal
+   * since we might still access the files_by_stylesheet hashtable in
+   * _st_theme_resolve_url() during the signal emission.
+   */
+  g_hash_table_remove (theme->stylesheets_by_file, file);
+  g_hash_table_remove (theme->files_by_stylesheet, stylesheet);
   cr_stylesheet_unref (stylesheet);
 }