[mutter] workspace: Use existing focus_window when asked to focus default window

[Marge Bot <marge-bot src gnome org>]

commit d0de671c1d23a4869f35bd7b832871bacdfeb212
Author: Jonas Dreßler <verdre v0yd nl>
Date:   Mon Mar 7 16:33:16 2022 +0100

    workspace: Use existing focus_window when asked to focus default window
    
    We use meta_workpace_focus_default_window() to sync the input focus back
    to a window after it was on shell UI, this is not really necessary on
    Wayland, but it is on X11. What this function does internally is ask
    MetaWindowStack about the topmost window and focus+raise that window.
    
    In gnome-shell we set the input focus to the default window every time
    the key-focus changes to NULL (see shell-global.c ->
    sync_stage_window_focus()). Now when closing the alt-tab switcher and
    activating a window while there's an always-on-top window on the
    workspace, meta_workspace_focus_default_window() will focus that
    always-on-top window right after closing the alt-tab switcher, making it
    impossible to focus another window using alt-tab.
    
    To fix this, make meta_workspace_focus_default_window() check if there's
    an existing focus_window first, if there is, use that, and if there
    isn't, resort to just focusing the topmost one.
    
    Fixes: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/5162
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2328>

 src/core/workspace.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)
---
diff --git a/src/core/workspace.c b/src/core/workspace.c
index 3bd517fca6..357e37d894 100644
--- a/src/core/workspace.c
+++ b/src/core/workspace.c
@@ -1332,10 +1332,22 @@ meta_workspace_focus_default_window (MetaWorkspace *workspace,
                                      MetaWindow    *not_this_one,
                                      guint32        timestamp)
 {
+  MetaWindow *current_focus;
+
   if (timestamp == META_CURRENT_TIME)
     meta_warning ("META_CURRENT_TIME used to choose focus window; "
                   "focus window may not be correct.");
 
+  current_focus = workspace->display->focus_window;
+
+  if (current_focus &&
+      current_focus != not_this_one &&
+      meta_window_located_on_workspace (current_focus, workspace))
+    {
+      meta_window_focus (current_focus, timestamp);
+      return;
+    }
+
   if (meta_prefs_get_focus_mode () == G_DESKTOP_FOCUS_MODE_CLICK ||
       !workspace->display->mouse_mode)
     focus_ancestor_or_top_window (workspace, not_this_one, timestamp);