[gnome-shell/gnome-40] shell/app: Correctly track the window used for the fallback icon

[Robert Mader <rmader src gnome org>]

commit 5a7243ae268eb31c5ffb22f88632f306d2bb15ca
Author: Benjamin Berg <bberg redhat com>
Date:   Wed Dec 15 16:03:52 2021 +0100

    shell/app: Correctly track the window used for the fallback icon
    
    We were not properly tracking the window used for the fallback icon.
    This could trigger a crash, as disconnection of the signal handler might
    happen on the wrong window, which in turn could cause the icon change
    notification to happen on a destroyed ShellApp instance.
    
    Fix this by tracking the window used for the fallback icon. Disconnect
    the icon notify callback explicitly for this window only when it is
    removed.
    
    Also, just to be extra safe, make sure that the icon is never NULL even
    if x11_window_create_fallback_gicon should return NULL for some reason.
    
    Closes: https://gitlab.gnome.org/GNOME/gnome-shell/issues/4436
    Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2065>
    (cherry picked from commit 1807be1277f0895898c5e26ec72a75f4a4cafce4)

 src/shell-app.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)
---
diff --git a/src/shell-app.c b/src/shell-app.c
index 3e4d4a5e81..28e819a05a 100644
--- a/src/shell-app.c
+++ b/src/shell-app.c
@@ -38,8 +38,6 @@ typedef struct {
   /* Signal connection to dirty window sort list on workspace changes */
   gulong workspace_switch_id;
 
-  gulong icon_changed_id;
-
   GSList *windows;
 
   guint interesting_windows;
@@ -81,6 +79,7 @@ struct _ShellApp
                           * the way shell-window-tracker.c works).
                           */
   GIcon *fallback_icon;
+  MetaWindow *fallback_icon_window;
 
   ShellAppRunningState *running_state;
 
@@ -210,6 +209,9 @@ on_window_icon_changed (GObject          *object,
   g_clear_object (&app->fallback_icon);
   app->fallback_icon = x11_window_create_fallback_gicon (window);
 
+  if (!app->fallback_icon)
+    app->fallback_icon = g_themed_icon_new ("application-x-executable");
+
   g_object_notify (G_OBJECT (app), "icon");
 }
 
@@ -243,10 +245,10 @@ shell_app_get_icon (ShellApp *app)
   if (window &&
       meta_window_get_client_type (window) == META_WINDOW_CLIENT_TYPE_X11)
     {
+      app->fallback_icon_window = window;
       app->fallback_icon = x11_window_create_fallback_gicon (window);
-      app->running_state->icon_changed_id =
-        g_signal_connect (G_OBJECT (window),
-                         "notify::icon", G_CALLBACK (on_window_icon_changed), app);
+      g_signal_connect (G_OBJECT (window),
+                        "notify::icon", G_CALLBACK (on_window_icon_changed), app);
     }
   else
     {
@@ -1136,11 +1138,19 @@ _shell_app_remove_window (ShellApp   *app,
   if (!g_slist_find (app->running_state->windows, window))
     return;
 
+  app->running_state->windows = g_slist_remove (app->running_state->windows, window);
+
   g_signal_handlers_disconnect_by_func (window, G_CALLBACK(shell_app_on_user_time_changed), app);
   g_signal_handlers_disconnect_by_func (window, G_CALLBACK(shell_app_on_skip_taskbar_changed), app);
-  app->running_state->windows = g_slist_remove (app->running_state->windows, window);
+  if (window == app->fallback_icon_window)
+    {
+      g_signal_handlers_disconnect_by_func (window, G_CALLBACK(on_window_icon_changed), app);
+      app->fallback_icon_window = NULL;
 
-  g_clear_signal_handler (&app->running_state->icon_changed_id, window);
+      /* Select a new icon from a different window. */
+      g_clear_object (&app->fallback_icon);
+      g_object_notify (G_OBJECT (app), "icon");
+    }
 
   if (!meta_window_is_skip_taskbar (window))
     app->running_state->interesting_windows--;