Issue #3065545 by Wim Leers, lauriii, alexpott, xjm: Deprecate base theme fallback to Stable

core/lib/Drupal/Core/Extension/ThemeExtensionList.php

@@ -22,7 +22,6 @@ class ThemeExtensionList extends ExtensionList {
    */
   protected $defaults = [
     'engine' => 'twig',
-    'base theme' => 'stable',
     'regions' => [
       'sidebar_first' => 'Left sidebar',
       'sidebar_second' => 'Right sidebar',
@@ -247,6 +246,23 @@ protected function doGetBaseThemes(array $themes, $theme, array $used_themes = [
    */
   protected function createExtensionInfo(Extension $extension) {
     $info = parent::createExtensionInfo($extension);
+
+    // In the past, Drupal used to default to the `stable` theme as the base
+    // theme. Explicitly opting out by specifying `base theme: false` was (and
+    // still is) possible. However, defaulting to `base theme: stable` prevents
+    // automatic updates to the next major version of Drupal, since each major
+    // version may have a different version of "the stable theme", for example:
+    // - for Drupal 8: `stable`
+    // - for Drupal 9: `stable9`
+    // - for Drupal 10: `stable10`
+    // - et cetera
+    // It is impossible to reliably determine which should be used by default,
+    // hence we now require the base theme to be explicitly specified.
+    if (!isset($info['base theme'])) {
+      @trigger_error(sprintf('There is no `base theme` property specified in the %s.info.yml file. The optionality of the `base theme` property is deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. All Drupal 8 themes must add `base theme: stable` to their *.info.yml file for them to continue to work as-is in future versions of Drupal. Drupal 9 requires the `base theme` property to be specified. See https://www.drupal.org/node/3066038', $extension->getName()), E_USER_DEPRECATED);
+      $info['base theme'] = 'stable';
+    }
+
     // Remove the default Stable base theme when 'base theme: false' is set in
     // a theme .info.yml file.
     if ($info['base theme'] === FALSE) {

core/modules/big_pipe/tests/themes/big_pipe_test_theme/big_pipe_test_theme.info.yml

 name: 'BigPipe test theme'
 type: theme
+base theme: stable
 description: 'Theme for testing BigPipe edge cases.'
 version: VERSION
 core: 8.x

core/modules/block/tests/modules/block_test/themes/block_test_specialchars_theme/block_test_specialchars_theme.info.yml

 name: '<"Cat" & ''Mouse''>'
 type: theme
+base theme: stable
 description: 'Theme for testing special characters in block admin.'
 core: 8.x
 regions:

core/modules/block/tests/modules/block_test/themes/block_test_theme/block_test_theme.info.yml

 name: 'Block test theme'
 type: theme
+base theme: stable
 description: 'Theme for testing the block system'
 version: VERSION
 core: 8.x

core/modules/color/tests/modules/color_test/themes/color_test_theme/color_test_theme.info.yml

 name: 'Color test theme'
 type: theme
+base theme: stable
 description: 'Theme for testing the color module'
 version: VERSION
 core: 8.x

core/modules/config_translation/tests/themes/config_translation_test_theme/config_translation_test_theme.info.yml

 name: 'Configuration Translation Test Theme'
 type: theme
+base theme: stable
 description: 'Theme for testing the configuration translation mapper system'
 version: VERSION
 core: 8.x

core/modules/help_topics/tests/themes/help_topics_test_theme/help_topics_test_theme.info.yml

 name: Test Help Topics
 type: theme
+base theme: stable
 description: A theme to test help topics.
 version: VERSION
 core: 8.x

core/modules/statistics/tests/themes/statistics_test_attached/statistics_test_attached.info.yml

 name: 'Statistics test attached theme'
 type: theme
+base theme: stable
 description: 'Theme for testing attached library'
 version: VERSION
 core: 8.x

core/modules/system/tests/src/Functional/Update/StableBaseThemeUpdateTest.php

@@ -2,7 +2,19 @@
 
 namespace Drupal\Tests\system\Functional\Update;
 
+use Drupal\Core\Cache\CacheBackendInterface;
+use Drupal\Core\Config\ConfigFactoryInterface;
+use Drupal\Core\DependencyInjection\ContainerBuilder;
+use Drupal\Core\DependencyInjection\ServiceProviderInterface;
+use Drupal\Core\Extension\ExtensionDiscovery;
+use Drupal\Core\Extension\InfoParser;
+use Drupal\Core\Extension\InfoParserInterface;
+use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\Extension\ThemeEngineExtensionList;
+use Drupal\Core\Extension\ThemeExtensionList;
+use Drupal\Core\State\StateInterface;
 use Drupal\FunctionalTests\Update\UpdatePathTestBase;
+use org\bovigo\vfs\vfsStream;
 
 /**
  * Tests the upgrade path for introducing the Stable base theme.
@@ -12,7 +24,7 @@
  * @group system
  * @group legacy
  */
-class StableBaseThemeUpdateTest extends UpdatePathTestBase {
+class StableBaseThemeUpdateTest extends UpdatePathTestBase implements ServiceProviderInterface {
 
   /**
    * The theme handler.
@@ -31,6 +43,22 @@ protected function setDatabaseDumpFiles() {
     ];
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function register(ContainerBuilder $container) {
+    $container->getDefinition('extension.list.theme')
+      ->setClass(VfsThemeExtensionList::class);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function prepareEnvironment() {
+    parent::prepareEnvironment();
+    $GLOBALS['conf']['container_service_providers']['test'] = $this;
+  }
+
   /**
    * {@inheritdoc}
    */
@@ -38,10 +66,28 @@ protected function setUp() {
     parent::setUp();
     $this->themeHandler = $this->container->get('theme_handler');
     $this->themeHandler->refreshInfo();
+
+    $vfs_root = vfsStream::setup('root');
+    $vfs_root->addChild(vfsStream::newDirectory($this->siteDirectory));
+    $site_dir = $vfs_root->getChild($this->siteDirectory);
+    vfsStream::create([
+      'themes' => [
+        'test_stable' => [
+          'test_stable.info.yml' => file_get_contents(DRUPAL_ROOT . '/core/tests/fixtures/test_stable/test_stable.info.yml'),
+          'test_stable.theme' => file_get_contents(DRUPAL_ROOT . '/core/tests/fixtures/test_stable/test_stable.theme'),
+        ],
+        'stable' => [
+          'stable.info.yml' => file_get_contents(DRUPAL_ROOT . '/core/themes/stable/stable.info.yml'),
+          'stable.theme' => file_get_contents(DRUPAL_ROOT . '/core/themes/stable/stable.theme'),
+        ],
+      ],
+    ], $site_dir);
   }
 
   /**
    * Tests that the Stable base theme is installed if necessary.
+   *
+   * @expectedDeprecation There is no `base theme` property specified in the test_stable.info.yml file. The optionality of the `base theme` property is deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. All Drupal 8 themes must add `base theme: stable` to their *.info.yml file for them to continue to work as-is in future versions of Drupal. Drupal 9 requires the `base theme` property to be specified. See https://www.drupal.org/node/3066038
    */
   public function testUpdateHookN() {
     $this->assertTrue($this->themeHandler->themeExists('test_stable'));
@@ -55,3 +101,41 @@ public function testUpdateHookN() {
   }
 
 }
+
+class VfsThemeExtensionList extends ThemeExtensionList {
+
+  /**
+   * The extension discovery for this extension list.
+   *
+   * @var \Drupal\Core\Extension\ExtensionDiscovery
+   */
+  protected $extensionDiscovery;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function __construct(string $root, string $type, CacheBackendInterface $cache, InfoParserInterface $info_parser, ModuleHandlerInterface $module_handler, StateInterface $state, ConfigFactoryInterface $config_factory, ThemeEngineExtensionList $engine_list, $install_profile) {
+    parent::__construct($root, $type, $cache, $info_parser, $module_handler, $state, $config_factory, $engine_list, $install_profile);
+    $this->extensionDiscovery = new ExtensionDiscovery('vfs://root');
+    $this->infoParser = new VfsInfoParser();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getExtensionDiscovery() {
+    return $this->extensionDiscovery;
+  }
+
+}
+
+class VfsInfoParser extends InfoParser {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function parse($filename) {
+    return parent::parse("vfs://root/$filename");
+  }
+
+}

core/modules/system/tests/themes/test_core_semver/test_core_semver.info.yml

 name: 'Theme test with semver core version'
 type: theme
+base theme: stable
 description: 'Test theme which has semver core version.'
 version: VERSION
 core_version_requirement: ^8 || ^9

core/modules/system/tests/themes/test_invalid_core/test_invalid_core.info.yml

 name: 'Theme test with invalid core version'
 type: theme
+base theme: stable
 description: 'Test theme which has an invalid core version.'
 version: VERSION
 core: 7.x

core/modules/system/tests/themes/test_invalid_core_semver/test_invalid_core_semver.info.yml

 name: 'Theme test with invalid semver core version'
 type: theme
+base theme: stable
 description: 'Test theme which has an invalid semver core version.'
 version: VERSION
 core_version_requirement: ^7

core/modules/system/tests/themes/test_invalid_region/test_invalid_region.info.yml

 name: 'Theme test with missing content region'
 type: theme
+base theme: stable
 description: 'Test theme which has a non-existent content region.'
 version: VERSION
 core: 8.x

core/modules/system/tests/themes/test_theme_having_veery_long_name_which_is_too_long/test_theme_having_veery_long_name_which_is_too_long.info.yml

 type: theme
+base theme: stable
 core: 8.x
 name: 'Test theme with a too long name'
 version: VERSION

core/modules/system/tests/themes/test_theme_settings_features/test_theme_settings_features.info.yml

 name: Test features
 type: theme
+base theme: stable
 core: 8.x
 description: 'Test theme to test theme settings with limited features.'
 features:

core/modules/system/tests/themes/test_theme_twig_registry_loader/test_theme_twig_registry_loader.info.yml

 name: 'Twig registry loader test'
 type: theme
+base theme: stable
 description: 'Support module for Twig registry loader testing.'
 version: VERSION
 core: 8.x

core/modules/update/tests/themes/update_test_basetheme/update_test_basetheme.info.yml

 name: 'Update test base theme'
 type: theme
+base theme: stable
 description: 'Test theme which acts as a base theme for other test subthemes.'
 version: VERSION
 core: 8.x

core/modules/user/tests/themes/user_test_theme/user_test_theme.info.yml

 name: 'User Test theme'
 type: theme
+base theme: stable
 description: 'Theme for testing the available fields in user twig template'
 version: VERSION
 core: 8.x

core/modules/views/tests/themes/views_test_checkboxes_theme/views_test_checkboxes_theme.info.yml

 name: Views test checkboxes theme
 type: theme
+base theme: stable
 description: Theme for testing Views rendering of checkboxes.
 version: VERSION
 core: 8.x

core/modules/views/tests/themes/views_test_theme/views_test_theme.info.yml

 name: Views test theme
 type: theme
+base theme: stable
 description: Theme for testing Views functionality.
 version: VERSION
 core: 8.x