monitor-config-manager: Prefer to use stored config

If not explicitly set by the backend, prefer to use the stored config
instead of creating a new one, if available.

https://bugzilla.gnome.org/show_bug.cgi?id=777732

src/backends/meta-monitor-config-manager.c

@@ -299,6 +299,58 @@ meta_monitor_config_manager_assign (MetaMonitorManager *manager,
   return TRUE;
 }
 
+static MetaMonitorsConfigKey *
+create_key_for_current_state (MetaMonitorManager *monitor_manager)
+{
+  MetaMonitorsConfigKey *config_key;
+  GList *l;
+  GList *monitor_specs;
+
+  monitor_specs = NULL;
+  for (l = monitor_manager->monitors; l; l = l->next)
+    {
+      MetaMonitor *monitor = l->data;
+      MetaMonitorSpec *monitor_spec;
+
+      if (meta_monitor_is_laptop_panel (monitor) &&
+          meta_monitor_manager_is_lid_closed (monitor_manager))
+        continue;
+
+      monitor_spec = meta_monitor_spec_clone (meta_monitor_get_spec (monitor));
+      monitor_specs = g_list_prepend (monitor_specs, monitor_spec);
+    }
+
+  if (!monitor_specs)
+    return NULL;
+
+  monitor_specs = g_list_sort (monitor_specs,
+                               (GCompareFunc) meta_monitor_spec_compare);
+
+  config_key = g_new0 (MetaMonitorsConfigKey, 1);
+  *config_key = (MetaMonitorsConfigKey) {
+    .monitor_specs = monitor_specs
+  };
+
+  return config_key;
+}
+
+MetaMonitorsConfig *
+meta_monitor_config_manager_get_stored (MetaMonitorConfigManager *config_manager)
+{
+  MetaMonitorsConfigKey *config_key;
+  MetaMonitorsConfig *config;
+
+  config_key = create_key_for_current_state (config_manager->monitor_manager);
+  if (!config_key)
+    return NULL;
+
+  config = meta_monitor_config_store_lookup (config_manager->config_store,
+                                             config_key);
+  meta_monitors_config_key_free (config_key);
+
+  return config;
+}
+
 typedef enum _MonitorMatchRule
 {
   MONITOR_MATCH_ALL = 0,

src/backends/meta-monitor-config-manager.h

@@ -70,6 +70,8 @@ gboolean meta_monitor_config_manager_assign (MetaMonitorManager *manager,
                                              GPtrArray         **output_infos,
                                              GError            **error);
 
+MetaMonitorsConfig * meta_monitor_config_manager_get_stored (MetaMonitorConfigManager *config_manager);
+
 MetaMonitorsConfig * meta_monitor_config_manager_create_linear (MetaMonitorConfigManager *config_manager);
 
 MetaMonitorsConfig * meta_monitor_config_manager_create_fallback (MetaMonitorConfigManager *config_manager);

src/backends/meta-monitor-manager.c

@@ -353,6 +353,12 @@ meta_monitor_manager_has_hotplug_mode_update (MetaMonitorManager *manager)
   return FALSE;
 }
 
+static gboolean
+should_use_stored_config (MetaMonitorManager *manager)
+{
+  return !meta_monitor_manager_has_hotplug_mode_update (manager);
+}
+
 static void
 legacy_ensure_configured (MetaMonitorManager *manager)
 {
@@ -372,6 +378,27 @@ meta_monitor_manager_ensure_configured (MetaMonitorManager *manager)
       return NULL;
     }
 
+  if (should_use_stored_config (manager))
+    {
+      config = meta_monitor_config_manager_get_stored (manager->config_manager);
+      if (config)
+        {
+          if (!meta_monitor_manager_apply_monitors_config (manager, config,
+                                                           &error))
+            {
+              config = NULL;
+              g_warning ("Failed to use stored monitor configuration: %s",
+                         error->message);
+              g_clear_error (&error);
+            }
+          else
+            {
+              g_object_ref (config);
+              goto done;
+            }
+        }
+    }
+
   config = meta_monitor_config_manager_create_suggested (manager->config_manager);
   if (config)
     {