[mutter] wayland/gtk-shell: Fix MetaWaylandGtkSurface leak on surface destroy

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

commit b41c4aec2677a48e30a54f731b3d7ef9924b48ea
Author: Sebastian Keller <skeller gnome org>
Date:   Tue Jun 9 04:07:52 2020 +0200

    wayland/gtk-shell: Fix MetaWaylandGtkSurface leak on surface destroy
    
    The MetaWaylandSurface corresponding to a MetaWaylandGtkSurface can be
    destroyed before the MetaWaylandGtkSurface is destroyed. In its destroy
    function MetaWaylandSurface however was unsetting the destructor of the
    correspnding resource along with the gtk_surface1 interface
    implementation. This was done to prevent further gtk_surface1 requests
    on a NULLed MetaWaylandSurface, if it has been destroyed before the
    MetaWaylandGtkSurface.
    
    It would be enough to just unset the resource implementation, while
    keeping the destructor to fix this leak. However the following commit
    will rely on the implementation being available after the
    MetaWaylandSurface has been destroyed. So instead introduce NULL checks
    for all functions that can be called on the gtk_surface1 interface and
    do not unset the implementation.
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1307>

 src/wayland/meta-wayland-gtk-shell.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)
---
diff --git a/src/wayland/meta-wayland-gtk-shell.c b/src/wayland/meta-wayland-gtk-shell.c
index 9c5357b914..1fc74787b9 100644
--- a/src/wayland/meta-wayland-gtk-shell.c
+++ b/src/wayland/meta-wayland-gtk-shell.c
@@ -83,6 +83,9 @@ gtk_surface_set_dbus_properties (struct wl_client   *client,
   MetaWaylandSurface *surface = gtk_surface->surface;
   MetaWindow *window;
 
+  if (!surface)
+    return;
+
   window = meta_wayland_surface_get_window (surface);
   if (!window)
     return;
@@ -104,6 +107,9 @@ gtk_surface_set_modal (struct wl_client   *client,
   MetaWaylandSurface *surface = gtk_surface->surface;
   MetaWindow *window;
 
+  if (!surface)
+    return;
+
   window = meta_wayland_surface_get_window (surface);
   if (!window)
     return;
@@ -123,6 +129,9 @@ gtk_surface_unset_modal (struct wl_client   *client,
   MetaWaylandSurface *surface = gtk_surface->surface;
   MetaWindow *window;
 
+  if (!surface)
+    return;
+
   window = meta_wayland_surface_get_window (surface);
   if (!window)
     return;
@@ -143,6 +152,9 @@ gtk_surface_present (struct wl_client   *client,
   MetaWaylandSurface *surface = gtk_surface->surface;
   MetaWindow *window;
 
+  if (!surface)
+    return;
+
   window = meta_wayland_surface_get_window (surface);
   if (!window)
     return;
@@ -162,6 +174,9 @@ gtk_surface_request_focus (struct wl_client   *client,
   MetaStartupSequence *sequence = NULL;
   MetaWindow *window;
 
+  if (!surface)
+    return;
+
   window = meta_wayland_surface_get_window (surface);
   if (!window)
     return;
@@ -204,8 +219,6 @@ static const struct gtk_surface1_interface meta_wayland_gtk_surface_interface =
 static void
 gtk_surface_surface_destroyed (MetaWaylandGtkSurface *gtk_surface)
 {
-  wl_resource_set_implementation (gtk_surface->resource,
-                                  NULL, NULL, NULL);
   gtk_surface->surface = NULL;
 }