xwayland: Make setup/teardown a bit more symmetrical

We setup Xwayland in an early phase of the X11 display, before we had a
MetaX11Display, and teared down in a couple of places happening when
tearing down the Xwayland integration if the X server died or
terminated. It was a bit hard to follow what happened and when it
happened. Attempt to clean this up a bit, with things being structured
as follows:

 * Early during X11 display connection setup, only setup the rudimentary
   X11 hooks, being the libX11 error callbacks, and adding the local
   user to XHost.

 * Move "initialize Xwayland component" code to a new
   'x11-display-setup' signal handler. Things setup here are cleaned up
   in the 'x11-display-closing' handler.

 * Connect to 'x11-display-setup' and 'x11-display-closing' up front,
   and stay connected to these two.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1796>

src/core/display.c

@@ -889,8 +889,12 @@ meta_display_new (MetaContext  *context,
 #ifdef HAVE_WAYLAND
   if (meta_is_wayland_compositor ())
     {
+      MetaWaylandCompositor *wayland_compositor =
+        meta_wayland_compositor_get_default ();
       MetaX11DisplayPolicy x11_display_policy;
 
+      meta_wayland_compositor_init_display (wayland_compositor, display);
+
       x11_display_policy = meta_context_get_x11_display_policy (context);
       if (x11_display_policy == META_X11_DISPLAY_POLICY_MANDATORY)
         {

src/wayland/meta-wayland.c

@@ -400,6 +400,13 @@ set_gnome_env (const char *name,
     }
 }
 
+void
+meta_wayland_compositor_init_display (MetaWaylandCompositor *compositor,
+                                      MetaDisplay           *display)
+{
+  meta_xwayland_init_display (&compositor->xwayland_manager, display);
+}
+
 static void meta_wayland_log_func (const char *, va_list) G_GNUC_PRINTF (1, 0);
 
 static void

src/wayland/meta-wayland.h

@@ -36,6 +36,9 @@ MetaWaylandCompositor * meta_wayland_compositor_new             (MetaContext *co
 
 void                    meta_wayland_compositor_prepare_shutdown (MetaWaylandCompositor *compositor);
 
+void                    meta_wayland_compositor_init_display    (MetaWaylandCompositor *compositor,
+                                                                 MetaDisplay           *display);
+
 META_EXPORT_TEST
 MetaWaylandCompositor  *meta_wayland_compositor_get_default     (void);
 

src/wayland/meta-xwayland-private.h

@@ -31,8 +31,12 @@ meta_xwayland_init (MetaXWaylandManager    *manager,
                     GError                **error);
 
 void
-meta_xwayland_complete_init (MetaDisplay *display,
+meta_xwayland_init_display (MetaXWaylandManager  *manager,
-                             Display     *xdisplay);
+                            MetaDisplay          *display);
+
+void
+meta_xwayland_setup_xdisplay (MetaXWaylandManager *manager,
+                              Display             *xdisplay);
 
 void
 meta_xwayland_shutdown (MetaXWaylandManager *manager);

src/wayland/meta-xwayland.c

@@ -1137,9 +1137,6 @@ meta_xwayland_stop_xserver (MetaXWaylandManager *manager)
 {
   if (manager->proc)
     g_subprocess_send_signal (manager->proc, SIGTERM);
-  g_signal_handlers_disconnect_by_func (meta_get_display (),
-                                        window_created_cb,
-                                        manager);
   g_clear_object (&manager->xserver_died_cancellable);
   g_clear_object (&manager->proc);
 }
@@ -1230,6 +1227,9 @@ on_x11_display_closing (MetaDisplay         *display,
   g_signal_handlers_disconnect_by_func (display,
                                         on_x11_display_closing,
                                         manager);
+  g_signal_handlers_disconnect_by_func (display,
+                                        window_created_cb,
+                                        manager);
 }
 
 static void
@@ -1254,15 +1254,41 @@ meta_xwayland_init_xrandr (MetaXWaylandManager *manager,
   meta_xwayland_set_primary_output (xdisplay);
 }
 
-/* To be called right after connecting */
+static void
-void
+on_x11_display_setup (MetaDisplay         *display,
-meta_xwayland_complete_init (MetaDisplay *display,
+                      MetaXWaylandManager *manager)
-                             Display     *xdisplay)
 {
-  MetaWaylandCompositor *compositor = meta_wayland_compositor_get_default ();
+  MetaX11Display *x11_display = meta_display_get_x11_display (display);
-  MetaXWaylandManager *manager = &compositor->xwayland_manager;
+  MetaContext *context = meta_display_get_context (display);
+  Display *xdisplay = meta_x11_display_get_xdisplay (x11_display);
   MetaX11DisplayPolicy x11_display_policy;
 
+  meta_xwayland_init_dnd (xdisplay);
+  meta_xwayland_init_xrandr (manager, xdisplay);
+  meta_xwayland_stop_xserver_timeout (manager);
+
+  x11_display_policy = meta_context_get_x11_display_policy (context);
+  if (x11_display_policy == META_X11_DISPLAY_POLICY_ON_DEMAND)
+    {
+      g_signal_connect (display, "window-created",
+                        G_CALLBACK (window_created_cb), manager);
+    }
+}
+
+void
+meta_xwayland_init_display (MetaXWaylandManager *manager,
+                            MetaDisplay         *display)
+{
+  g_signal_connect (display, "x11-display-setup",
+                    G_CALLBACK (on_x11_display_setup), manager);
+  g_signal_connect (display, "x11-display-closing",
+                    G_CALLBACK (on_x11_display_closing), manager);
+}
+
+void
+meta_xwayland_setup_xdisplay (MetaXWaylandManager *manager,
+                              Display             *xdisplay)
+{
   /* We install an X IO error handler in addition to the child watch,
      because after Xlib connects our child watch may not be called soon
      enough, and therefore we won't crash when X exits (and most important
@@ -1273,20 +1299,7 @@ meta_xwayland_complete_init (MetaDisplay *display,
   XSetIOErrorExitHandler (xdisplay, x_io_error_exit, manager);
 #endif
 
-  g_signal_connect (display, "x11-display-closing",
-                    G_CALLBACK (on_x11_display_closing), manager);
-  meta_xwayland_init_dnd (xdisplay);
   add_local_user_to_xhost (xdisplay);
-  meta_xwayland_init_xrandr (manager, xdisplay);
-
-  x11_display_policy =
-    meta_context_get_x11_display_policy (compositor->context);
-  if (x11_display_policy == META_X11_DISPLAY_POLICY_ON_DEMAND)
-    {
-      meta_xwayland_stop_xserver_timeout (manager);
-      g_signal_connect (meta_get_display (), "window-created",
-                        G_CALLBACK (window_created_cb), manager);
-    }
 }
 
 static void

src/x11/meta-x11-display.c

@@ -1151,7 +1151,13 @@ meta_x11_display_new (MetaDisplay *display, GError **error)
 
 #ifdef HAVE_WAYLAND
   if (meta_is_wayland_compositor ())
-    meta_xwayland_complete_init (display, xdisplay);
+    {
+      MetaContext *context = meta_display_get_context (display);
+      MetaWaylandCompositor *compositor =
+        meta_context_get_wayland_compositor (context);
+
+      meta_xwayland_setup_xdisplay (&compositor->xwayland_manager, xdisplay);
+    }
 #endif
 
   if (meta_is_syncing ())