[mutter] x11: Set WM_S0 last

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

commit eb4307c3501f347a701d376a591adaab17ba3986
Author: Olivier Fourdan <ofourdan redhat com>
Date:   Wed Mar 9 14:41:13 2022 +0100

    x11: Set WM_S0 last
    
    With Xwayland on demand, a number of maintenance X11 applications need
    to be run first, before Xwayland starts accepting requests from the
    normal clients, as soon as the WM_S0 selection is acquired by mutter.
    
    On startup, mutter also sets a number of X11 properties that can be
    queried by X11 clients.
    
    Unfortunately, mutter acquires the WM_S0 selection before setting those
    properties, so mutter and the first regular X11 client will race on
    startup.
    
    As a result, the X11 properties set by mutter on startup may not be
    available to the very first X11 client when Xwayland starts.
    
    To avoid that issue, make sure to take the WM_S0 selection last when
    opening the display.
    
    Closes: https://gitlab.gnome.org/GNOME/mutter/-/issues/2176
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2336>

 src/x11/meta-x11-display.c | 42 +++++++++++++++++++++++-------------------
 1 file changed, 23 insertions(+), 19 deletions(-)
---
diff --git a/src/x11/meta-x11-display.c b/src/x11/meta-x11-display.c
index d4b5ff425e..5343633ce4 100644
--- a/src/x11/meta-x11-display.c
+++ b/src/x11/meta-x11-display.c
@@ -1303,25 +1303,6 @@ meta_x11_display_new (MetaDisplay *display, GError **error)
                                               xroot,
                                               PropertyChangeMask);
 
-  sprintf (buf, "WM_S%d", number);
-
-  wm_sn_atom = XInternAtom (xdisplay, buf, False);
-  new_wm_sn_owner = take_manager_selection (x11_display, xroot, wm_sn_atom, timestamp, replace_current_wm);
-  if (new_wm_sn_owner == None)
-    {
-      g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
-                   "Failed to acquire window manager ownership");
-
-      g_object_run_dispose (G_OBJECT (x11_display));
-      g_clear_object (&x11_display);
-
-      return NULL;
-    }
-
-  x11_display->wm_sn_selection_window = new_wm_sn_owner;
-  x11_display->wm_sn_atom = wm_sn_atom;
-  x11_display->wm_sn_timestamp = timestamp;
-
   init_event_masks (x11_display);
 
   /* Select for cursor changes so the cursor tracker is up to date. */
@@ -1418,6 +1399,29 @@ meta_x11_display_new (MetaDisplay *display, GError **error)
   if (!meta_is_wayland_compositor ())
     meta_dnd_init_xdnd (x11_display);
 
+  sprintf (buf, "WM_S%d", number);
+
+  wm_sn_atom = XInternAtom (xdisplay, buf, False);
+  new_wm_sn_owner = take_manager_selection (x11_display,
+                                            xroot,
+                                            wm_sn_atom,
+                                            timestamp,
+                                            replace_current_wm);
+  if (new_wm_sn_owner == None)
+    {
+      g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                   "Failed to acquire window manager ownership");
+
+      g_object_run_dispose (G_OBJECT (x11_display));
+      g_clear_object (&x11_display);
+
+      return NULL;
+    }
+
+  x11_display->wm_sn_selection_window = new_wm_sn_owner;
+  x11_display->wm_sn_atom = wm_sn_atom;
+  x11_display->wm_sn_timestamp = timestamp;
+
   return x11_display;
 }