[mutter] tests: Override X11 display number

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit bd624e4dfb4de728b5cd8ed9e5fd2d6d6104b84f
Author: Jonas Ådahl <jadahl gmail com>
Date:   Mon Nov 12 11:29:44 2018 +0100

    tests: Override X11 display number
    
    As with the Wayland display name, to avoid clashes with already an
    running Xwayland or Xorg instance, override the X11 display name to
    something less likely to cause a clash.
    
    https://gitlab.gnome.org/GNOME/mutter/issues/193

 src/tests/test-utils.c      |  2 ++
 src/wayland/meta-xwayland.c | 16 +++++++++++-----
 src/wayland/meta-xwayland.h |  3 +++
 3 files changed, 16 insertions(+), 5 deletions(-)
---
diff --git a/src/tests/test-utils.c b/src/tests/test-utils.c
index 8ffaff14f..b752bf94c 100644
--- a/src/tests/test-utils.c
+++ b/src/tests/test-utils.c
@@ -27,6 +27,7 @@
 #include "core/display-private.h"
 #include "core/window-private.h"
 #include "wayland/meta-wayland.h"
+#include "wayland/meta-xwayland.h"
 #include "x11/meta-x11-display-private.h"
 
 struct _TestClient {
@@ -94,6 +95,7 @@ test_init (int    *argc,
   ensure_test_client_path (*argc, *argv);
 
   meta_wayland_override_display_name ("mutter-test-display");
+  meta_xwayland_override_display_number (512);
 }
 
 AsyncWaiter *
diff --git a/src/wayland/meta-xwayland.c b/src/wayland/meta-xwayland.c
index 7cd99a072..be29033cf 100644
--- a/src/wayland/meta-xwayland.c
+++ b/src/wayland/meta-xwayland.c
@@ -59,6 +59,8 @@ G_DEFINE_TYPE (MetaWaylandSurfaceRoleXWayland,
                meta_wayland_surface_role_xwayland,
                META_TYPE_WAYLAND_ACTOR_SURFACE)
 
+static int display_number_override = -1;
+
 void
 meta_xwayland_associate_window_with_surface (MetaWindow          *window,
                                              MetaWaylandSurface  *surface)
@@ -371,6 +373,12 @@ x_io_error (Display *display)
   return 0;
 }
 
+void
+meta_xwayland_override_display_number (int number)
+{
+  display_number_override = number;
+}
+
 static gboolean
 choose_xdisplay (MetaXWaylandManager *manager)
 {
@@ -378,11 +386,9 @@ choose_xdisplay (MetaXWaylandManager *manager)
   char *lock_file = NULL;
   gboolean fatal = FALSE;
 
-  /* Hack to keep the unused Xwayland instance on
-   * the login screen from taking the prime :0 display
-   * number.
-   */
-  if (g_getenv ("RUNNING_UNDER_GDM") != NULL)
+  if (display_number_override != -1)
+    display = display_number_override;
+  else if (!g_getenv ("RUNNING_UNDER_GDM"))
     display = 1024;
 
   do
diff --git a/src/wayland/meta-xwayland.h b/src/wayland/meta-xwayland.h
index 9cb4c0b1d..0d120fee0 100644
--- a/src/wayland/meta-xwayland.h
+++ b/src/wayland/meta-xwayland.h
@@ -30,6 +30,9 @@
 #include "meta/types.h"
 #include "wayland/meta-wayland-types.h"
 
+void
+meta_xwayland_override_display_number (int number);
+
 void
 meta_xwayland_handle_wl_surface_id (MetaWindow *window,
                                     guint32     surface_id);