x11/x11-display: Set compositor selection earlier on XWayland

When the X11 display is actually XWayland there's no point to delay the
compositor selection, given that mutter itself is the compositor and
doing this may cause the first X11 client that starts not to receive the
right information (and in some cases misbehave).

Since some toolkits are not handling the compositor selection changes
properly at later times, let's make their life easier by just
initializing the selection as early as the other X11 properties, given
that in this case there's nothing to replace.

Fixes: https://gitlab.gnome.org/GNOME/mutter/-/issues/2472
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2970>

src/compositor/meta-compositor-x11.c

@@ -171,7 +171,7 @@ meta_compositor_x11_manage (MetaCompositor  *compositor,
 
   determine_server_clock_source (compositor_x11);
 
-  meta_x11_display_set_cm_selection (display->x11_display);
+  meta_x11_display_set_cm_selection (display->x11_display, CurrentTime);
 
   compositor_x11->output = display->x11_display->composite_overlay_window;
 

src/core/display.c

@@ -762,7 +762,6 @@ meta_display_init_x11_finish (MetaDisplay   *display,
   if (!display->display_opening)
     {
       g_signal_emit (display, display_signals[X11_DISPLAY_OPENED], 0);
-      meta_x11_display_set_cm_selection (x11_display);
       meta_display_manage_all_xwindows (display);
       meta_compositor_redirect_x11_windows (display->compositor);
     }

src/x11/meta-x11-display-private.h

@@ -292,7 +292,8 @@ int meta_x11_display_get_screen_number (MetaX11Display *x11_display);
 
 int meta_x11_display_get_damage_event_base (MetaX11Display *x11_display);
 
-void meta_x11_display_set_cm_selection (MetaX11Display *x11_display);
+void meta_x11_display_set_cm_selection (MetaX11Display *x11_display,
+                                        uint32_t        timestamp);
 
 gboolean meta_x11_display_xwindow_is_a_no_focus_window (MetaX11Display *x11_display,
                                                         Window xwindow);

src/x11/meta-x11-display.c

@@ -736,6 +736,10 @@ take_manager_selection (MetaX11Display *x11_display,
     {
       XEvent event;
 
+#ifdef HAVE_XWAYLAND
+      g_return_val_if_fail (!meta_is_wayland_compositor (), new_owner);
+#endif
+
       /* We sort of block infinitely here which is probably lame. */
 
       meta_verbose ("Waiting for old window manager to exit");
@@ -1430,6 +1434,22 @@ meta_x11_display_new (MetaDisplay  *display,
   x11_display->wm_sn_atom = wm_sn_atom;
   x11_display->wm_sn_timestamp = timestamp;
 
+#ifdef HAVE_XWAYLAND
+  if (meta_is_wayland_compositor ())
+    {
+      meta_x11_display_set_cm_selection (x11_display, timestamp);
+
+      if (x11_display->wm_cm_selection_window == None)
+        {
+          g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                       "Failed to acquire compositor ownership");
+
+          g_object_run_dispose (G_OBJECT (x11_display));
+          return NULL;
+        }
+    }
+#endif
+
   init_event_masks (x11_display);
 
   meta_x11_display_init_frames_client (x11_display);
@@ -1854,13 +1874,15 @@ on_monitors_changed_internal (MetaMonitorManager *monitor_manager,
 }
 
 void
-meta_x11_display_set_cm_selection (MetaX11Display *x11_display)
+meta_x11_display_set_cm_selection (MetaX11Display *x11_display,
+                                   uint32_t        timestamp)
 {
   char selection[32];
   Atom a;
-  guint32 timestamp;
 
+  if (timestamp == CurrentTime)
     timestamp = meta_x11_display_get_current_time_roundtrip (x11_display);
+
   g_snprintf (selection, sizeof (selection), "_NET_WM_CM_S%d",
               DefaultScreen (x11_display->xdisplay));
   a = XInternAtom (x11_display->xdisplay, selection, False);