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: #4436
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2065>

diff --git a/src/shell-app.c b/src/shell-app.c
index 3e4d4a5e8188a80539514734dc92a6e09131937f..28e819a05ae029abb2352039e7ee1f8d89f26b2c 100644 (file)
--- 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--;