[mutter] main: Add --x11 command line argument

[Jonas Ådahl <jadahl src gnome org>]

commit 70fcf745b8386dc86debacbea153d0d60bfd8154
Author: Jonas Ådahl <jadahl gmail com>
Date:   Mon Feb 5 15:39:21 2018 +0800

    main: Add --x11 command line argument
    
    This is in order to force running as a X11 window manager/compositing
    manager. Useful for debugging and other cases where the automatic
    detection does not work as expected.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/15

 src/core/main.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)
---
diff --git a/src/core/main.c b/src/core/main.c
index dc1f1c4f6..079f6a9ef 100644
--- a/src/core/main.c
+++ b/src/core/main.c
@@ -181,6 +181,7 @@ static gboolean  opt_nested;
 #ifdef HAVE_NATIVE_BACKEND
 static gboolean  opt_display_server;
 #endif
+static gboolean  opt_x11;
 
 static GOptionEntry meta_options[] = {
   {
@@ -239,6 +240,11 @@ static GOptionEntry meta_options[] = {
     N_("Run as a full display server, rather than nested")
   },
 #endif
+  {
+    "x11", 0, 0, G_OPTION_ARG_NONE,
+    &opt_x11,
+    N_("Run with X11 backend")
+  },
   {NULL}
 };
 
@@ -424,7 +430,13 @@ calculate_compositor_configuration (MetaCompositorType *compositor_type,
                                     GType              *backend_gtype)
 {
 #ifdef HAVE_WAYLAND
-  gboolean run_as_wayland_compositor = opt_wayland;
+  gboolean run_as_wayland_compositor = opt_wayland && !opt_x11;
+
+  if ((opt_wayland || opt_nested || opt_display_server) && opt_x11)
+    {
+      meta_warning ("Can't run both as Wayland compositor and X11 compositing manager\n");
+      meta_exit (META_EXIT_ERROR);
+    }
 
 #ifdef HAVE_NATIVE_BACKEND
   if (opt_nested && opt_display_server)
@@ -433,7 +445,7 @@ calculate_compositor_configuration (MetaCompositorType *compositor_type,
       meta_exit (META_EXIT_ERROR);
     }
 
-  if (!run_as_wayland_compositor)
+  if (!run_as_wayland_compositor && !opt_x11)
     run_as_wayland_compositor = check_for_wayland_session_type ();
 #endif /* HAVE_NATIVE_BACKEND */