monitor-manager: Try to restore previous config before regenerating

When opening a laptop lid, one will likely want to restore the
configuration one had prior to closing it, so when ensuring monitor
configuration, first try to see if the previously set configuration is
both complete (all connected monitors are configured) and applicable
(it is a valid configuration) and only try to generate a new from
scratch if that failed.

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

src/backends/meta-monitor-manager.c

@@ -71,6 +71,10 @@ G_DEFINE_ABSTRACT_TYPE_WITH_CODE (MetaMonitorManager, meta_monitor_manager, META
 
 static void initialize_dbus_interface (MetaMonitorManager *manager);
 
+static gboolean
+meta_monitor_manager_is_config_complete (MetaMonitorManager *manager,
+                                         MetaMonitorsConfig *config);
+
 static void
 meta_monitor_manager_init (MetaMonitorManager *manager)
 {
@@ -529,6 +533,31 @@ meta_monitor_manager_ensure_configured (MetaMonitorManager *manager)
         }
     }
 
+  config = meta_monitor_config_manager_get_previous (manager->config_manager);
+  if (config)
+    {
+      config = g_object_ref (config);
+
+      if (meta_monitor_manager_is_config_complete (manager, config))
+        {
+          if (!meta_monitor_manager_apply_monitors_config (manager,
+                                                           config,
+                                                           method,
+                                                           &error))
+            {
+              g_warning ("Failed to use suggested monitor configuration: %s",
+                         error->message);
+              g_clear_error (&error);
+            }
+          else
+            {
+              goto done;
+            }
+        }
+
+      g_clear_object (&config);
+    }
+
   config = meta_monitor_config_manager_create_linear (manager->config_manager);
   if (config)
     {
@@ -1494,6 +1523,44 @@ meta_monitor_manager_is_config_applicable (MetaMonitorManager *manager,
   return TRUE;
 }
 
+static gboolean
+meta_monitor_manager_is_config_complete (MetaMonitorManager *manager,
+                                         MetaMonitorsConfig *config)
+{
+  GList *l;
+  unsigned int configured_monitor_count = 0;
+  unsigned int expected_monitor_count = 0;
+
+  for (l = config->logical_monitor_configs; l; l = l->next)
+    {
+      MetaLogicalMonitorConfig *logical_monitor_config = l->data;
+      GList *k;
+
+      for (k = logical_monitor_config->monitor_configs; k; k = k->next)
+        configured_monitor_count++;
+    }
+
+  for (l = manager->monitors; l; l = l->next)
+    {
+      MetaMonitor *monitor = l->data;
+
+      if (meta_monitor_is_laptop_panel (monitor))
+        {
+          if (!meta_monitor_manager_is_lid_closed (manager))
+            expected_monitor_count++;
+        }
+      else
+        {
+          expected_monitor_count++;
+        }
+    }
+
+  if (configured_monitor_count != expected_monitor_count)
+    return FALSE;
+
+  return meta_monitor_manager_is_config_applicable (manager, config, NULL);
+}
+
 static MetaMonitor *
 find_monitor_from_connector (MetaMonitorManager *manager,
                              char               *connector)

src/tests/monitor-unit-tests.c

@@ -2281,33 +2281,20 @@ meta_test_monitor_lid_switch_config (void)
   meta_monitor_manager_test_set_is_lid_closed (monitor_manager_test, FALSE);
   meta_monitor_manager_lid_is_closed_changed (monitor_manager);
 
-  test_case.expect.n_logical_monitors = 2;
-  test_case.expect.screen_width = 1024 * 2;
-  test_case.expect.monitors[0].current_mode = 0;
-
-  test_case.expect.crtcs[0].current_mode = 0;
-  test_case.expect.crtcs[1].current_mode = 0;
-
-  /*
-   * FIXME: The above expectation is correct, but MetaMonitorConfigManager
-   * doesn't support restoring previous configurations yet, so it'll
-   * pick keep the external monitor as primary and put it first.
-   */
   test_case.expect.logical_monitors[0] = (MonitorTestCaseLogicalMonitor) {
-    .monitors = { 1 },
+    .monitors = { 0 },
     .n_monitors = 1,
     .layout = {.x = 0, .y = 0, .width = 1024, .height = 768 },
     .scale = 1
   };
-  test_case.expect.logical_monitors[1] = (MonitorTestCaseLogicalMonitor) {
-    .monitors = { 0 },
-    .n_monitors = 1,
-    .layout = {.x = 1024, .y = 0, .width = 1024, .height = 768 },
-    .scale = 1
-  };
   test_case.expect.n_logical_monitors = 2;
+  test_case.expect.screen_width = 1024 * 2;
+  test_case.expect.monitors[0].current_mode = 0;
   test_case.expect.primary_logical_monitor = 0;
 
+  test_case.expect.crtcs[0].current_mode = 0;
+  test_case.expect.crtcs[1].current_mode = 0;
+
   check_monitor_configuration (&test_case);
 }