wayland: Add setting/api to check the policy to set up the X11 display

This replaces meta_should_autostart_x11_display(). The "on-demand" policy
is not honored yet.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/709

data/org.gnome.mutter.gschema.xml.in

@@ -124,6 +124,8 @@
                                         real-time scheduling. The executable
                                         or user must have CAP_SYS_NICE.
                                         Requires a restart.
+        • “autostart-xwayland”        — initializes Xwayland lazily if there are
+                                        X11 clients. Requires restart.
       </description>
     </key>
 

src/backends/meta-settings-private.h

@@ -34,6 +34,7 @@ typedef enum _MetaExperimentalFeature
   META_EXPERIMENTAL_FEATURE_SCALE_MONITOR_FRAMEBUFFER = (1 << 0),
   META_EXPERIMENTAL_FEATURE_KMS_MODIFIERS  = (1 << 1),
   META_EXPERIMENTAL_FEATURE_RT_SCHEDULER = (1 << 2),
+  META_EXPERIMENTAL_FEATURE_AUTOSTART_XWAYLAND  = (1 << 3),
 } MetaExperimentalFeature;
 
 #define META_TYPE_SETTINGS (meta_settings_get_type ())

src/backends/meta-settings.c

@@ -266,6 +266,8 @@ experimental_features_handler (GVariant *features_variant,
         features |= META_EXPERIMENTAL_FEATURE_KMS_MODIFIERS;
       else if (g_str_equal (feature, "rt-scheduler"))
         features |= META_EXPERIMENTAL_FEATURE_RT_SCHEDULER;
+      else if (g_str_equal (feature, "autostart-xwayland"))
+        features |= META_EXPERIMENTAL_FEATURE_AUTOSTART_XWAYLAND;
       else
         g_info ("Unknown experimental feature '%s'\n", feature);
     }

src/core/display.c

@@ -760,7 +760,7 @@ meta_display_open (void)
   display->selection = meta_selection_new (display);
   meta_clipboard_manager_init (display);
 
-  if (meta_should_autostart_x11_display ())
+  if (meta_get_x11_display_policy () == META_DISPLAY_POLICY_MANDATORY)
     {
       if (!meta_display_init_x11 (display, &error))
         g_error ("Failed to start Xwayland: %s", error->message);

src/core/main-private.h

@@ -30,10 +30,17 @@ typedef enum _MetaCompositorType
   META_COMPOSITOR_TYPE_X11,
 } MetaCompositorType;
 
+typedef enum _MetaDisplayPolicy
+{
+  META_DISPLAY_POLICY_MANDATORY,
+  META_DISPLAY_POLICY_ON_DEMAND,
+  META_DISPLAY_POLICY_DISABLED,
+} MetaDisplayPolicy;
+
 META_EXPORT_TEST
 void meta_override_compositor_configuration (MetaCompositorType compositor_type,
                                              GType              backend_gtype);
 
-gboolean meta_should_autostart_x11_display (void);
+MetaDisplayPolicy meta_get_x11_display_policy (void);
 
 #endif /* META_MAIN_PRIVATE_H */

src/core/main.c

@@ -717,15 +717,27 @@ prefs_changed_callback (MetaPreference pref,
     }
 }
 
-gboolean
-meta_should_autostart_x11_display (void)
+MetaDisplayPolicy
+meta_get_x11_display_policy (void)
 {
   MetaBackend *backend = meta_get_backend ();
-  gboolean wants_x11 = TRUE;
+
+  if (META_IS_BACKEND_X11_CM (backend))
+    return META_DISPLAY_POLICY_MANDATORY;
 
 #ifdef HAVE_WAYLAND
-  wants_x11 = !opt_no_x11;
+  if (meta_is_wayland_compositor ())
+    {
+      MetaSettings *settings = meta_backend_get_settings (backend);
+
+      if (opt_no_x11)
+        return META_DISPLAY_POLICY_DISABLED;
+
+      if (meta_settings_is_experimental_feature_enabled (settings,
+                                                         META_EXPERIMENTAL_FEATURE_AUTOSTART_XWAYLAND))
+        return META_DISPLAY_POLICY_ON_DEMAND;
+    }
 #endif
 
-  return META_IS_BACKEND_X11_CM (backend) || wants_x11;
+  return META_DISPLAY_POLICY_MANDATORY;
 }

src/wayland/meta-wayland.c

@@ -418,7 +418,7 @@ meta_wayland_init (void)
   meta_wayland_eglstream_controller_init (compositor);
 #endif
 
-  if (meta_should_autostart_x11_display ())
+  if (meta_get_x11_display_policy () != META_DISPLAY_POLICY_DISABLED)
     {
       if (!meta_xwayland_init (&compositor->xwayland_manager, compositor->wayland_display))
         g_error ("Failed to start X Wayland");
@@ -443,7 +443,7 @@ meta_wayland_init (void)
       compositor->display_name = g_strdup (display_name);
     }
 
-  if (meta_should_autostart_x11_display ())
+  if (meta_get_x11_display_policy () != META_DISPLAY_POLICY_DISABLED)
     {
       set_gnome_env ("DISPLAY", meta_wayland_get_xwayland_display_name (compositor));
       set_gnome_env ("XAUTHORITY", meta_wayland_get_xwayland_auth_file (compositor));