Issue #2659940 by almaudoh, alexpott, phenaproxima, Jo Fitzgerald, markcarver, oriol_e9g, dawehner, dsnopek, jibran, larowlan: Extension System, Part III: ThemeExtensionList and ThemeEngineExtensionList

core/core.services.yml

@@ -517,6 +517,12 @@ services:
   extension.list.profile:
     class: Drupal\Core\Extension\ProfileExtensionList
     arguments: ['@app.root', 'profile', '@cache.default', '@info_parser', '@module_handler', '@state', '%install_profile%']
+  extension.list.theme:
+    class: Drupal\Core\Extension\ThemeExtensionList
+    arguments: ['@app.root', 'theme', '@cache.default', '@info_parser', '@module_handler', '@state', '@config.factory', '@extension.list.theme_engine', '%install_profile%']
+  extension.list.theme_engine:
+    class: Drupal\Core\Extension\ThemeEngineExtensionList
+    arguments: ['@app.root', 'theme_engine', '@cache.default', '@info_parser', '@module_handler', '@state', '%install_profile%']
   content_uninstall_validator:
     class: Drupal\Core\Entity\ContentUninstallValidator
     tags:
@@ -531,7 +537,7 @@ services:
     lazy: true
   theme_handler:
     class: Drupal\Core\Extension\ThemeHandler
-    arguments: ['@app.root', '@config.factory', '@module_handler', '@state', '@info_parser']
+    arguments: ['@app.root', '@config.factory', '@extension.list.theme']
   theme_installer:
     class: Drupal\Core\Extension\ThemeInstaller
     arguments: ['@theme_handler', '@config.factory', '@config.installer', '@module_handler', '@config.manager', '@asset.css.collection_optimizer', '@router.builder', '@logger.channel.default', '@state']

core/includes/bootstrap.inc

@@ -10,12 +10,12 @@ use Drupal\Component\Utility\Html;
 use Drupal\Component\Render\FormattableMarkup;
 use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Config\BootstrapConfigStorageFactory;
-use Drupal\Core\Extension\Exception\UnknownExtensionException;
 use Drupal\Core\Logger\RfcLogLevel;
 use Drupal\Core\Test\TestDatabase;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Core\Utility\Error;
 use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Symfony\Component\DependencyInjection\Exception\ServiceNotFoundException;
 
 /**
  * Minimum supported version of PHP.
@@ -223,10 +223,6 @@ function config_get_config_directory($type) {
  *   The filename of the requested item or NULL if the item is not found.
  */
 function drupal_get_filename($type, $name, $filename = NULL) {
-  // The location of files will not change during the request, so do not use
-  // drupal_static().
-  static $files = [];
-
   // Type 'core' only exists to simplify application-level logic; it always maps
   // to the /core directory, whereas $name is ignored. It is only requested via
   // drupal_get_path(). /core/core.info.yml does not exist, but is required
@@ -235,45 +231,31 @@ function drupal_get_filename($type, $name, $filename = NULL) {
     return 'core/core.info.yml';
   }
 
-  if ($type === 'module' || $type === 'profile') {
+  try {
-    $service_id = 'extension.list.' . $type;
     /** @var \Drupal\Core\Extension\ExtensionList $extension_list */
-    $extension_list = \Drupal::service($service_id);
+    $extension_list = \Drupal::service("extension.list.$type");
     if (isset($filename)) {
       // Manually add the info file path of an extension.
       $extension_list->setPathname($name, $filename);
     }
-    try {
+    return $extension_list->getPathname($name);
-      return $extension_list->getPathname($name);
-    }
-    catch (UnknownExtensionException $e) {
-      // Catch the exception. This will result in triggering an error.
-    }
   }
-  else {
+  catch (ServiceNotFoundException $e) {
-
+    // Catch the exception. This will result in triggering an error.
-    if (!isset($files[$type])) {
+    // If the service is unknown, create a user-level error message.
-      $files[$type] = [];
+    trigger_error(
-    }
+      sprintf('Unknown type specified: "%s". Must be one of: "core", "profile", "module", "theme", or "theme_engine".', $type),
-
+      E_USER_WARNING
-    if (isset($filename)) {
+    );
-      $files[$type][$name] = $filename;
+  }
-    }
+  catch (\InvalidArgumentException $e) {
-    elseif (!isset($files[$type][$name])) {
+    // Catch the exception. This will result in triggering an error.
-      // If still unknown, retrieve the file list prepared in state by
+    // If the filename is still unknown, create a user-level error message.
-      // \Drupal\Core\Extension\ExtensionList() and
+    trigger_error(
-      // \Drupal\Core\Extension\ThemeHandlerInterface::rebuildThemeData().
+      sprintf('The following %s is missing from the file system: %s', $type, $name),
-      if (!isset($files[$type][$name]) && \Drupal::hasService('state')) {
+      E_USER_WARNING
-        $files[$type] += \Drupal::state()->get('system.' . $type . '.files', []);
+    );
-      }
-    }
-
-    if (isset($files[$type][$name])) {
-      return $files[$type][$name];
-    }
   }
-  // If the filename is still unknown, create a user-level error message.
-  trigger_error(new FormattableMarkup('The following @type is missing from the file system: @name', ['@type' => $type, '@name' => $name]), E_USER_WARNING);
 }
 
 /**

core/includes/module.inc

@@ -14,41 +14,31 @@ use Drupal\Core\Extension\ExtensionDiscovery;
  *   The type of list to return:
  *   - theme: All installed themes.
  *
- * @return
+ * @return array
  *   An associative array of themes, keyed by name.
  *   For $type 'theme', the array values are objects representing the
  *   respective database row, with the 'info' property already unserialized.
  *
+ * @deprecated in Drupal 8.7.0 and will be removed before Drupal 9.0.0. Use
+ *   \Drupal::service('theme_handler')->listInfo() instead.
+ *
+ * @see https://www.drupal.org/node/2709919
  * @see \Drupal\Core\Extension\ThemeHandler::listInfo()
  */
 function system_list($type) {
-  $lists = &drupal_static(__FUNCTION__);
+  @trigger_error('system_list() is deprecated in Drupal 8.7.0 and will be removed before Drupal 9.0.0. Use \Drupal::service(\'theme_handler\')->listInfo() instead. See https://www.drupal.org/node/2709919', E_USER_DEPRECATED);
-  if ($cached = \Drupal::cache('bootstrap')->get('system_list')) {
-    $lists = $cached->data;
-  }
-  else {
-    $lists = [
-      'theme' => [],
-      'filepaths' => [],
-    ];
-    // ThemeHandler maintains the 'system.theme.data' state record.
-    $theme_data = \Drupal::state()->get('system.theme.data', []);
-    foreach ($theme_data as $name => $theme) {
-      $lists['theme'][$name] = $theme;
-      $lists['filepaths'][] = [
-        'type' => 'theme',
-        'name' => $name,
-        'filepath' => $theme->getPathname(),
-      ];
-    }
-    \Drupal::cache('bootstrap')->set('system_list', $lists);
-  }
-  // To avoid a separate database lookup for the filepath, prime the
-  // drupal_get_filename() static cache with all enabled themes.
-  foreach ($lists['filepaths'] as $item) {
-    system_register($item['type'], $item['name'], $item['filepath']);
-  }
 
+  $lists = [
+    'theme' => \Drupal::service('theme_handler')->listInfo(),
+    'filepaths' => [],
+  ];
+  foreach ($lists['theme'] as $name => $theme) {
+    $lists['filepaths'][] = [
+      'type' => 'theme',
+      'name' => $name,
+      'filepath' => $theme->getPathname(),
+    ];
+  }
   return $lists[$type];
 }
 
@@ -56,9 +46,10 @@ function system_list($type) {
  * Resets all system_list() caches.
  */
 function system_list_reset() {
-  drupal_static_reset('system_list');
+  \Drupal::service('extension.list.profile')->reset();
   \Drupal::service('extension.list.module')->reset();
-  \Drupal::cache('bootstrap')->delete('system_list');
+  \Drupal::service('extension.list.theme_engine')->reset();
+  \Drupal::service('extension.list.theme')->reset();
 }
 
 /**

core/includes/theme.inc

@@ -99,7 +99,7 @@ function theme_get_registry($complete = TRUE) {
 /**
  * Returns an array of default theme features.
  *
- * @see \Drupal\Core\Extension\ThemeHandler::$defaultFeatures
+ * @see \Drupal\Core\Extension\ThemeExtensionList::$defaults
  */
 function _system_default_theme_features() {
   return [

core/includes/theme.maintenance.inc

@@ -68,7 +68,7 @@ function _drupal_maintenance_theme() {
   $theme_init = \Drupal::service('theme.initialization');
   $theme_handler = \Drupal::service('theme_handler');
   if (empty($themes) || !isset($themes[$custom_theme])) {
-    $themes = $theme_handler->rebuildThemeData();
+    $themes = \Drupal::service('extension.list.theme')->getList();
     $theme_handler->addTheme($themes[$custom_theme]);
   }
 

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

@@ -169,8 +169,8 @@ class Extension implements \Serializable {
       'filename' => $this->filename,
     ];
 
-    // @todo ThemeHandler::listInfo(), ThemeHandler::rebuildThemeData(), and
+    // @todo \Drupal\Core\Extension\ThemeExtensionList is adding custom
-    //   system_list() are adding custom properties to the Extension object.
+    //   properties to the Extension object.
     $info = new \ReflectionObject($this);
     foreach ($info->getProperties(\ReflectionProperty::IS_PUBLIC) as $property) {
       $data[$property->getName()] = $property->getValue($this);

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

@@ -11,6 +11,12 @@ use Drupal\Core\State\StateInterface;
  * Provides available extensions.
  *
  * The extension list is per extension type, like module, theme and profile.
+ *
+ * @internal
+ *   This class is not yet stable and therefore there are no guarantees that the
+ *   internal implementations including constructor signature and protected
+ *   properties / methods will not change over time. This will be reviewed after
+ *   https://www.drupal.org/project/drupal/issues/2940481
  */
 abstract class ExtensionList {
 
@@ -305,15 +311,7 @@ abstract class ExtensionList {
 
     // Read info files for each extension.
     foreach ($extensions as $extension_name => $extension) {
-      // Look for the info file.
+      $extension->info = $this->createExtensionInfo($extension);
-      $extension->info = $this->infoParser->parse($extension->getPathname());
-
-      // Add the info file modification time, so it becomes available for
-      // contributed extensions to use for ordering extension lists.
-      $extension->info['mtime'] = $extension->getMTime();
-
-      // Merge extension type-specific defaults.
-      $extension->info += $this->defaults;
 
       // Invoke hook_system_info_alter() to give installed modules a chance to
       // modify the data in the .info.yml files if necessary.
@@ -541,4 +539,26 @@ abstract class ExtensionList {
     return dirname($this->getPathname($extension_name));
   }
 
+  /**
+   * Creates the info value for an extension object.
+   *
+   * @param \Drupal\Core\Extension\Extension $extension
+   *   The extension whose info is to be altered.
+   *
+   * @return array
+   *   The extension info array.
+   */
+  protected function createExtensionInfo(Extension $extension) {
+    $info = $this->infoParser->parse($extension->getPathname());
+
+    // Add the info file modification time, so it becomes available for
+    // contributed extensions to use for ordering extension lists.
+    $info['mtime'] = $extension->getMTime();
+
+    // Merge extension type-specific defaults.
+    $info += $this->defaults;
+
+    return $info;
+  }
+
 }

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

@@ -9,6 +9,12 @@ use Drupal\Core\StringTranslation\StringTranslationTrait;
 
 /**
  * Provides a list of available modules.
+ *
+ * @internal
+ *   This class is not yet stable and therefore there are no guarantees that the
+ *   internal implementations including constructor signature and protected
+ *   properties / methods will not change over time. This will be reviewed after
+ *   https://www.drupal.org/project/drupal/issues/2940481
  */
 class ModuleExtensionList extends ExtensionList {
 

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

@@ -4,6 +4,12 @@ namespace Drupal\Core\Extension;
 
 /**
  * Provides a list of installation profiles.
+ *
+ * @internal
+ *   This class is not yet stable and therefore there are no guarantees that the
+ *   internal implementations including constructor signature and protected
+ *   properties / methods will not change over time. This will be reviewed after
+ *   https://www.drupal.org/project/drupal/issues/2940481
  */
 class ProfileExtensionList extends ExtensionList {
 

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

@@ -0,0 +1,36 @@
+<?php
+
+namespace Drupal\Core\Extension;
+
+/**
+ * Provides a list of available theme engines.
+ *
+ * @internal
+ *   This class is not yet stable and therefore there are no guarantees that the
+ *   internal implementations including constructor signature and protected
+ *   properties / methods will not change over time. This will be reviewed after
+ *   https://www.drupal.org/project/drupal/issues/2940481
+ */
+class ThemeEngineExtensionList extends ExtensionList {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaults = [
+    'dependencies' => [],
+    'description' => '',
+    'package' => 'Other',
+    'version' => NULL,
+    'php' => DRUPAL_MINIMUM_PHP,
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getInstalledExtensionNames() {
+    // Theme engines do not have an 'install' state, so return names of all
+    // discovered theme engines.
+    return array_keys($this->extensions);
+  }
+
+}

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

@@ -0,0 +1,289 @@
+<?php
+
+namespace Drupal\Core\Extension;
+
+use Drupal\Core\Cache\CacheBackendInterface;
+use Drupal\Core\Config\ConfigFactoryInterface;
+use Drupal\Core\State\StateInterface;
+
+/**
+ * Provides a list of available themes.
+ *
+ * @internal
+ *   This class is not yet stable and therefore there are no guarantees that the
+ *   internal implementations including constructor signature and protected
+ *   properties / methods will not change over time. This will be reviewed after
+ *   https://www.drupal.org/project/drupal/issues/2940481
+ */
+class ThemeExtensionList extends ExtensionList {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaults = [
+    'engine' => 'twig',
+    'base theme' => 'stable',
+    'regions' => [
+      'sidebar_first' => 'Left sidebar',
+      'sidebar_second' => 'Right sidebar',
+      'content' => 'Content',
+      'header' => 'Header',
+      'primary_menu' => 'Primary menu',
+      'secondary_menu' => 'Secondary menu',
+      'footer' => 'Footer',
+      'highlighted' => 'Highlighted',
+      'help' => 'Help',
+      'page_top' => 'Page top',
+      'page_bottom' => 'Page bottom',
+      'breadcrumb' => 'Breadcrumb',
+    ],
+    'description' => '',
+    // The following array should be kept inline with
+    // _system_default_theme_features().
+    'features' => [
+      'favicon',
+      'logo',
+      'node_user_picture',
+      'comment_user_picture',
+      'comment_user_verification',
+    ],
+    'screenshot' => 'screenshot.png',
+    'php' => DRUPAL_MINIMUM_PHP,
+    'libraries' => [],
+    'libraries_extend' => [],
+    'libraries_override' => [],
+  ];
+
+  /**
+   * The config factory.
+   *
+   * @var \Drupal\Core\Config\ConfigFactoryInterface
+   */
+  protected $configFactory;
+
+  /**
+   * The theme engine list needed by this theme list.
+   *
+   * @var \Drupal\Core\Extension\ThemeEngineExtensionList
+   */
+  protected $engineList;
+
+  /**
+   * The list of installed themes.
+   *
+   * @var string[]
+   */
+  protected $installedThemes;
+
+  /**
+   * Constructs a new ThemeExtensionList instance.
+   *
+   * @param string $root
+   *   The app root.
+   * @param string $type
+   *   The extension type.
+   * @param \Drupal\Core\Cache\CacheBackendInterface $cache
+   *   The cache.
+   * @param \Drupal\Core\Extension\InfoParserInterface $info_parser
+   *   The info parser.
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+   *   The module handler.
+   * @param \Drupal\Core\State\StateInterface $state
+   *   The state service.
+   * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
+   *   The config factory.
+   * @param \Drupal\Core\Extension\ThemeEngineExtensionList $engine_list
+   *   The theme engine extension listing.
+   * @param string $install_profile
+   *   The install profile used by the site.
+   */
+  public function __construct($root, $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, $install_profile);
+
+    $this->configFactory = $config_factory;
+    $this->engineList = $engine_list;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function doList() {
+    // Find themes.
+    $themes = parent::doList();
+
+    $engines = $this->engineList->getList();
+    // Always get the freshest list of themes (rather than the already cached
+    // list in $this->installedThemes) when building the theme listing because a
+    // theme could have just been installed or uninstalled.
+    $this->installedThemes = $this->configFactory->get('core.extension')->get('theme') ?: [];
+
+    $sub_themes = [];
+    // Read info files for each theme.
+    foreach ($themes as $name => $theme) {
+      // Defaults to 'twig' (see self::defaults above).
+      $engine = $theme->info['engine'];
+      if (isset($engines[$engine])) {
+        $theme->owner = $engines[$engine]->getExtensionPathname();
+        $theme->prefix = $engines[$engine]->getName();
+      }
+      // Add this theme as a sub-theme if it has a base theme.
+      if (!empty($theme->info['base theme'])) {
+        $sub_themes[] = $name;
+      }
+      // Add weight and status.
+      $theme->status = (int) isset($this->installedThemes[$name]);
+      $theme->weight = isset($this->installedThemes[$name]) ? $this->installedThemes[$name] : 0;
+    }
+
+    // Build dependencies.
+    $themes = $this->moduleHandler->buildModuleDependencies($themes);
+
+    // After establishing the full list of available themes, fill in data for
+    // sub-themes.
+    $this->fillInSubThemeData($themes, $sub_themes);
+
+    return $themes;
+  }
+
+  /**
+   * Fills in data for themes that are also sub-themes.
+   *
+   * @param array $themes
+   *   The array of partly processed theme information.
+   * @param array $sub_themes
+   *   A list of themes from the $theme array that are also sub-themes.
+   */
+  protected function fillInSubThemeData(array &$themes, array $sub_themes) {
+    foreach ($sub_themes as $name) {
+      $sub_theme = $themes[$name];
+      // The $base_themes property is optional; only set for sub themes.
+      // @see ThemeHandlerInterface::listInfo()
+      $sub_theme->base_themes = $this->doGetBaseThemes($themes, $name);
+      // empty() cannot be used here, since static::doGetBaseThemes() adds
+      // the key of a base theme with a value of NULL in case it is not found,
+      // in order to prevent needless iterations.
+      if (!current($sub_theme->base_themes)) {
+        continue;
+      }
+      // Determine the root base theme.
+      $root_key = key($sub_theme->base_themes);
+      // Build the list of sub-themes for each of the theme's base themes.
+      foreach (array_keys($sub_theme->base_themes) as $base_theme) {
+        $themes[$base_theme]->sub_themes[$name] = $sub_theme->info['name'];
+      }
+      // Add the theme engine info from the root base theme.
+      if (isset($themes[$root_key]->owner)) {
+        $sub_theme->info['engine'] = $themes[$root_key]->info['engine'];
+        $sub_theme->owner = $themes[$root_key]->owner;
+        $sub_theme->prefix = $themes[$root_key]->prefix;
+      }
+    }
+  }
+
+  /**
+   * Finds all the base themes for the specified theme.
+   *
+   * Themes can inherit templates and function implementations from earlier
+   * themes.
+   *
+   * @param \Drupal\Core\Extension\Extension[] $themes
+   *   An array of available themes.
+   * @param string $theme
+   *   The name of the theme whose base we are looking for.
+   *
+   * @return array
+   *   Returns an array of all of the theme's ancestors; the first element's
+   *   value will be NULL if an error occurred.
+   */
+  public function getBaseThemes(array $themes, $theme) {
+    return $this->doGetBaseThemes($themes, $theme);
+  }
+
+  /**
+   * Finds the base themes for the specific theme.
+   *
+   * @param array $themes
+   *   An array of available themes.
+   * @param string $theme
+   *   The name of the theme whose base we are looking for.
+   * @param array $used_themes
+   *   (optional) A recursion parameter preventing endless loops. Defaults to
+   *   an empty array.
+   *
+   * @return array
+   *   An array of base themes.
+   */
+  protected function doGetBaseThemes(array $themes, $theme, array $used_themes = []) {
+    if (!isset($themes[$theme]->info['base theme'])) {
+      return [];
+    }
+
+    $base_key = $themes[$theme]->info['base theme'];
+    // Does the base theme exist?
+    if (!isset($themes[$base_key])) {
+      return [$base_key => NULL];
+    }
+
+    $current_base_theme = [$base_key => $themes[$base_key]->info['name']];
+
+    // Is the base theme itself a child of another theme?
+    if (isset($themes[$base_key]->info['base theme'])) {
+      // Do we already know the base themes of this theme?
+      if (isset($themes[$base_key]->base_themes)) {
+        return $themes[$base_key]->base_themes + $current_base_theme;
+      }
+      // Prevent loops.
+      if (!empty($used_themes[$base_key])) {
+        return [$base_key => NULL];
+      }
+      $used_themes[$base_key] = TRUE;
+      return $this->doGetBaseThemes($themes, $base_key, $used_themes) + $current_base_theme;
+    }
+    // If we get here, then this is our parent theme.
+    return $current_base_theme;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function createExtensionInfo(Extension $extension) {
+    $info = parent::createExtensionInfo($extension);
+    // Remove the default Stable base theme when 'base theme: false' is set in
+    // a theme .info.yml file.
+    if ($info['base theme'] === FALSE) {
+      unset($info['base theme']);
+    }
+
+    if (!empty($info['base theme'])) {
+      // Add the base theme as a proper dependency.
+      $info['dependencies'][] = $info['base theme'];
+    }
+
+    // Prefix screenshot with theme path.
+    if (!empty($info['screenshot'])) {
+      $info['screenshot'] = $extension->getPath() . '/' . $info['screenshot'];
+    }
+    return $info;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getInstalledExtensionNames() {
+    // Cache the installed themes to avoid multiple calls to the config system.
+    if (!isset($this->installedThemes)) {
+      $this->installedThemes = $this->configFactory->get('core.extension')->get('theme') ?: [];
+    }
+    return array_keys($this->installedThemes);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function reset() {
+    parent::reset();
+    $this->installedThemes = NULL;
+    return $this;
+  }
+
+}

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

@@ -5,28 +5,12 @@ namespace Drupal\Core\Extension;
 use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\Extension\Exception\UninstalledExtensionException;
 use Drupal\Core\Extension\Exception\UnknownExtensionException;
-use Drupal\Core\State\StateInterface;
 
 /**
  * Default theme handler using the config system to store installation statuses.
  */
 class ThemeHandler implements ThemeHandlerInterface {
 
-  /**
-   * Contains the features enabled for themes by default.
-   *
-   * @var array
-   *
-   * @see _system_default_theme_features()
-   */
-  protected $defaultFeatures = [
-    'favicon',
-    'logo',
-    'node_user_picture',
-    'comment_user_picture',
-    'comment_user_verification',
-  ];
-
   /**
    * A list of all currently available themes.
    *
@@ -41,68 +25,12 @@ class ThemeHandler implements ThemeHandlerInterface {
    */
   protected $configFactory;
 
-  /**
-   * The module handler to fire themes_installed/themes_uninstalled hooks.
-   *
-   * @var \Drupal\Core\Extension\ModuleHandlerInterface
-   */
-  protected $moduleHandler;
-
-  /**
-   * The state backend.
-   *
-   * @var \Drupal\Core\State\StateInterface
-   */
-  protected $state;
-
-  /**
-   * The config installer to install configuration.
-   *
-   * @var \Drupal\Core\Config\ConfigInstallerInterface
-   */
-  protected $configInstaller;
-
-  /**
-   * The info parser to parse the theme.info.yml files.
-   *
-   * @var \Drupal\Core\Extension\InfoParserInterface
-   */
-  protected $infoParser;
-
-  /**
-   * A logger instance.
-   *
-   * @var \Psr\Log\LoggerInterface
-   */
-  protected $logger;
-
-  /**
-   * The route builder to rebuild the routes if a theme is installed.
-   *
-   * @var \Drupal\Core\Routing\RouteBuilderInterface
-   */
-  protected $routeBuilder;
-
   /**
    * An extension discovery instance.
    *
-   * @var \Drupal\Core\Extension\ExtensionDiscovery
+   * @var \Drupal\Core\Extension\ThemeExtensionList
    */
-  protected $extensionDiscovery;
+  protected $themeList;
-
-  /**
-   * The CSS asset collection optimizer service.
-   *
-   * @var \Drupal\Core\Asset\AssetCollectionOptimizerInterface
-   */
-  protected $cssCollectionOptimizer;
-
-  /**
-   * The config manager used to uninstall a theme.
-   *
-   * @var \Drupal\Core\Config\ConfigManagerInterface
-   */
-  protected $configManager;
 
   /**
    * The app root.
@@ -118,22 +46,13 @@ class ThemeHandler implements ThemeHandlerInterface {
    *   The app root.
    * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
    *   The config factory to get the installed themes.
-   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+   * @param \Drupal\Core\Extension\ThemeExtensionList $theme_list
-   *   The module handler to fire themes_installed/themes_uninstalled hooks.
+   *   A extension discovery instance.
-   * @param \Drupal\Core\State\StateInterface $state
-   *   The state store.
-   * @param \Drupal\Core\Extension\InfoParserInterface $info_parser
-   *   The info parser to parse the theme.info.yml files.
-   * @param \Drupal\Core\Extension\ExtensionDiscovery $extension_discovery
-   *   (optional) A extension discovery instance (for unit tests).
    */
-  public function __construct($root, ConfigFactoryInterface $config_factory, ModuleHandlerInterface $module_handler, StateInterface $state, InfoParserInterface $info_parser, ExtensionDiscovery $extension_discovery = NULL) {
+  public function __construct($root, ConfigFactoryInterface $config_factory, ThemeExtensionList $theme_list) {
     $this->root = $root;
     $this->configFactory = $config_factory;
-    $this->moduleHandler = $module_handler;
+    $this->themeList = $theme_list;
-    $this->state = $state;
-    $this->infoParser = $info_parser;
-    $this->extensionDiscovery = $extension_discovery;
   }
 
   /**
@@ -181,16 +100,10 @@ class ThemeHandler implements ThemeHandlerInterface {
   public function listInfo() {
     if (!isset($this->list)) {
       $this->list = [];
-      $themes = $this->systemThemeList();
+      $installed_themes = $this->configFactory->get('core.extension')->get('theme');
-      // @todo Ensure that systemThemeList() does not contain an empty list
+      if (!empty($installed_themes)) {
-      //   during the batch installer, see https://www.drupal.org/node/2322619.
+        $installed_themes = array_intersect_key($this->themeList->getList(), $installed_themes);
-      if (empty($themes)) {
+        array_map([$this, 'addTheme'], $installed_themes);
-        $this->refreshInfo();
-        $this->list = $this->list ?: [];
-        $themes = \Drupal::state()->get('system.theme.data', []);
-      }
-      foreach ($themes as $theme) {
-        $this->addTheme($theme);
       }
     }
     return $this->list;
@@ -200,6 +113,11 @@ class ThemeHandler implements ThemeHandlerInterface {
    * {@inheritdoc}
    */
   public function addTheme(Extension $theme) {
+    // Register the namespaces of installed themes.
+    // @todo Implement proper theme registration
+    // https://www.drupal.org/project/drupal/issues/2941757
+    \Drupal::service('class_loader')->addPsr4('Drupal\\' . $theme->getName() . '\\', $this->root . '/' . $theme->getPath() . '/src');
+
     if (!empty($theme->info['libraries'])) {
       foreach ($theme->info['libraries'] as $library => $name) {
         $theme->libraries[$library] = $name;
@@ -218,32 +136,21 @@ class ThemeHandler implements ThemeHandlerInterface {
    * {@inheritdoc}
    */
   public function refreshInfo() {
-    $extension_config = $this->configFactory->get('core.extension');
+    $installed = $this->configFactory->get('core.extension')->get('theme');
-    $installed = $extension_config->get('theme');
     // Only refresh the info if a theme has been installed. Modules are
     // installed before themes by the installer and this method is called during
     // module installation.
     if (empty($installed) && empty($this->list)) {
       return;
     }
-
     $this->reset();
-    // @todo Avoid re-scanning all themes by retaining the original (unaltered)
-    //   theme info somewhere.
-    $list = $this->rebuildThemeData();
-    foreach ($list as $name => $theme) {
-      if (isset($installed[$name])) {
-        $this->addTheme($theme);
-      }
-    }
-    $this->state->set('system.theme.data', $this->list);
   }
 
   /**
    * {@inheritdoc}
    */
   public function reset() {
-    $this->systemListReset();
+    $this->themeList->reset();
     $this->list = NULL;
   }
 
@@ -251,214 +158,21 @@ class ThemeHandler implements ThemeHandlerInterface {
    * {@inheritdoc}
    */
   public function rebuildThemeData() {
-    $listing = $this->getExtensionDiscovery();
+    return $this->themeList->reset()->getList();
-    $themes = $listing->scan('theme');
-    $engines = $listing->scan('theme_engine');
-    $extension_config = $this->configFactory->get('core.extension');
-    $installed = $extension_config->get('theme') ?: [];
-
-    // Set defaults for theme info.
-    $defaults = [
-      'engine' => 'twig',
-      'base theme' => 'stable',
-      'regions' => [
-        'sidebar_first' => 'Left sidebar',
-        'sidebar_second' => 'Right sidebar',
-        'content' => 'Content',
-        'header' => 'Header',
-        'primary_menu' => 'Primary menu',
-        'secondary_menu' => 'Secondary menu',
-        'footer' => 'Footer',
-        'highlighted' => 'Highlighted',
-        'help' => 'Help',
-        'page_top' => 'Page top',
-        'page_bottom' => 'Page bottom',
-        'breadcrumb' => 'Breadcrumb',
-      ],
-      'description' => '',
-      'features' => $this->defaultFeatures,
-      'screenshot' => 'screenshot.png',
-      'php' => DRUPAL_MINIMUM_PHP,
-      'libraries' => [],
-    ];
-
-    $sub_themes = [];
-    $files_theme = [];
-    $files_theme_engine = [];
-    // Read info files for each theme.
-    foreach ($themes as $key => $theme) {
-      // @todo Remove all code that relies on the $status property.
-      $theme->status = (int) isset($installed[$key]);
-
-      $theme->info = $this->infoParser->parse($theme->getPathname()) + $defaults;
-      // Remove the default Stable base theme when 'base theme: false' is set in
-      // a theme .info.yml file.
-      if ($theme->info['base theme'] === FALSE) {
-        unset($theme->info['base theme']);
-      }
-
-      // Add the info file modification time, so it becomes available for
-      // contributed modules to use for ordering theme lists.
-      $theme->info['mtime'] = $theme->getMTime();
-
-      // Invoke hook_system_info_alter() to give installed modules a chance to
-      // modify the data in the .info.yml files if necessary.
-      // @todo Remove $type argument, obsolete with $theme->getType().
-      $type = 'theme';
-      $this->moduleHandler->alter('system_info', $theme->info, $theme, $type);
-
-      if (!empty($theme->info['base theme'])) {
-        $sub_themes[] = $key;
-        // Add the base theme as a proper dependency.
-        $themes[$key]->info['dependencies'][] = $themes[$key]->info['base theme'];
-      }
-
-      // Defaults to 'twig' (see $defaults above).
-      $engine = $theme->info['engine'];
-      if (isset($engines[$engine])) {
-        $theme->owner = $engines[$engine]->getExtensionPathname();
-        $theme->prefix = $engines[$engine]->getName();
-        $files_theme_engine[$engine] = $engines[$engine]->getPathname();
-      }
-
-      // Prefix screenshot with theme path.
-      if (!empty($theme->info['screenshot'])) {
-        $theme->info['screenshot'] = $theme->getPath() . '/' . $theme->info['screenshot'];
-      }
-
-      $files_theme[$key] = $theme->getPathname();
-    }
-    // Build dependencies.
-    // @todo Move into a generic ExtensionHandler base class.
-    // @see https://www.drupal.org/node/2208429
-    $themes = $this->moduleHandler->buildModuleDependencies($themes);
-
-    // Store filenames to allow system_list() and drupal_get_filename() to
-    // retrieve them for themes and theme engines without having to scan the
-    // filesystem.
-    $this->state->set('system.theme.files', $files_theme);
-    $this->state->set('system.theme_engine.files', $files_theme_engine);
-
-    // After establishing the full list of available themes, fill in data for
-    // sub-themes.
-    foreach ($sub_themes as $key) {
-      $sub_theme = $themes[$key];
-      // The $base_themes property is optional; only set for sub themes.
-      // @see ThemeHandlerInterface::listInfo()
-      $sub_theme->base_themes = $this->getBaseThemes($themes, $key);
-      // empty() cannot be used here, since ThemeHandler::doGetBaseThemes() adds
-      // the key of a base theme with a value of NULL in case it is not found,
-      // in order to prevent needless iterations.
-      if (!current($sub_theme->base_themes)) {
-        continue;
-      }
-      // Determine the root base theme.
-      $root_key = key($sub_theme->base_themes);
-      // Build the list of sub-themes for each of the theme's base themes.
-      foreach (array_keys($sub_theme->base_themes) as $base_theme) {
-        $themes[$base_theme]->sub_themes[$key] = $sub_theme->info['name'];
-      }
-      // Add the theme engine info from the root base theme.
-      if (isset($themes[$root_key]->owner)) {
-        $sub_theme->info['engine'] = $themes[$root_key]->info['engine'];
-        $sub_theme->owner = $themes[$root_key]->owner;
-        $sub_theme->prefix = $themes[$root_key]->prefix;
-      }
-    }
-
-    return $themes;
   }
 
   /**
    * {@inheritdoc}
    */
   public function getBaseThemes(array $themes, $theme) {
-    return $this->doGetBaseThemes($themes, $theme);
+    return $this->themeList->getBaseThemes($themes, $theme);
-  }
-
-  /**
-   * Finds the base themes for the specific theme.
-   *
-   * @param array $themes
-   *   An array of available themes.
-   * @param string $theme
-   *   The name of the theme whose base we are looking for.
-   * @param array $used_themes
-   *   (optional) A recursion parameter preventing endless loops. Defaults to
-   *   an empty array.
-   *
-   * @return array
-   *   An array of base themes.
-   */
-  protected function doGetBaseThemes(array $themes, $theme, $used_themes = []) {
-    if (!isset($themes[$theme]->info['base theme'])) {
-      return [];
-    }
-
-    $base_key = $themes[$theme]->info['base theme'];
-    // Does the base theme exist?
-    if (!isset($themes[$base_key])) {
-      return [$base_key => NULL];
-    }
-
-    $current_base_theme = [$base_key => $themes[$base_key]->info['name']];
-
-    // Is the base theme itself a child of another theme?
-    if (isset($themes[$base_key]->info['base theme'])) {
-      // Do we already know the base themes of this theme?
-      if (isset($themes[$base_key]->base_themes)) {
-        return $themes[$base_key]->base_themes + $current_base_theme;
-      }
-      // Prevent loops.
-      if (!empty($used_themes[$base_key])) {
-        return [$base_key => NULL];
-      }
-      $used_themes[$base_key] = TRUE;
-      return $this->doGetBaseThemes($themes, $base_key, $used_themes) + $current_base_theme;
-    }
-    // If we get here, then this is our parent theme.
-    return $current_base_theme;
-  }
-
-  /**
-   * Returns an extension discovery object.
-   *
-   * @return \Drupal\Core\Extension\ExtensionDiscovery
-   *   The extension discovery object.
-   */
-  protected function getExtensionDiscovery() {
-    if (!isset($this->extensionDiscovery)) {
-      $this->extensionDiscovery = new ExtensionDiscovery($this->root);
-    }
-    return $this->extensionDiscovery;
   }
 
   /**
    * {@inheritdoc}
    */
   public function getName($theme) {
-    $themes = $this->listInfo();
+    return $this->themeList->getName($theme);
-    if (!isset($themes[$theme])) {
-      throw new UnknownExtensionException("Requested the name of a non-existing theme $theme");
-    }
-    return $themes[$theme]->info['name'];
-  }
-
-  /**
-   * Wraps system_list_reset().
-   */
-  protected function systemListReset() {
-    system_list_reset();
-  }
-
-  /**
-   * Wraps system_list().
-   *
-   * @return array
-   *   A list of themes keyed by name.
-   */
-  protected function systemThemeList() {
-    return system_list('theme');
   }
 
   /**

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

@@ -56,8 +56,8 @@ interface ThemeHandlerInterface {
    *
    * @return \Drupal\Core\Extension\Extension[]
    *   An associative array of the currently installed themes. The keys are the
-   *   themes' machine names and the values are objects having the following
+   *   themes' machine names and the values are Extension objects having the
-   *   properties:
+   *   following properties:
    *   - filename: The filepath and name of the .info.yml file.
    *   - name: The machine name of the theme.
    *   - status: 1 for installed, 0 for uninstalled themes.

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

@@ -174,22 +174,12 @@ class ThemeInstaller implements ThemeInstallerInterface {
         ->set("theme.$key", 0)
         ->save(TRUE);
 
-      // Add the theme to the current list.
-      // @todo Remove all code that relies on $status property.
-      $theme_data[$key]->status = 1;
-      $this->themeHandler->addTheme($theme_data[$key]);
-
-      // Update the current theme data accordingly.
-      $current_theme_data = $this->state->get('system.theme.data', []);
-      $current_theme_data[$key] = $theme_data[$key];
-      $this->state->set('system.theme.data', $current_theme_data);
-
       // Reset theme settings.
       $theme_settings = &drupal_static('theme_get_setting');
       unset($theme_settings[$key]);
 
-      // @todo Remove system_list().
+      // Reset theme listing.
-      $this->systemListReset();
+      $this->themeHandler->reset();
 
       // Only install default configuration if this theme has not been installed
       // already.
@@ -245,14 +235,10 @@ class ThemeInstaller implements ThemeInstallerInterface {
     }
 
     $this->cssCollectionOptimizer->deleteAll();
-    $current_theme_data = $this->state->get('system.theme.data', []);
     foreach ($theme_list as $key) {
       // The value is not used; the weight is ignored for themes currently.
       $extension_config->clear("theme.$key");
 
-      // Update the current theme data accordingly.
-      unset($current_theme_data[$key]);
-
       // Reset theme settings.
       $theme_settings = &drupal_static('theme_get_setting');
       unset($theme_settings[$key]);
@@ -264,11 +250,10 @@ class ThemeInstaller implements ThemeInstallerInterface {
     // Don't check schema when uninstalling a theme since we are only clearing
     // keys.
     $extension_config->save(TRUE);
-    $this->state->set('system.theme.data', $current_theme_data);
 
-    // @todo Remove system_list().
+    // Refresh theme info.
-    $this->themeHandler->refreshInfo();
     $this->resetSystem();
+    $this->themeHandler->reset();
 
     $this->moduleHandler->invokeAll('themes_uninstalled', [$theme_list]);
   }
@@ -280,7 +265,6 @@ class ThemeInstaller implements ThemeInstallerInterface {
     if ($this->routeBuilder) {
       $this->routeBuilder->setRebuildNeeded();
     }
-    $this->systemListReset();
 
     // @todo It feels wrong to have the requirement to clear the local tasks
     //   cache here.
@@ -295,11 +279,4 @@ class ThemeInstaller implements ThemeInstallerInterface {
     drupal_theme_rebuild();
   }
 
-  /**
-   * Wraps system_list_reset().
-   */
-  protected function systemListReset() {
-    system_list_reset();
-  }
-
 }

core/lib/Drupal/Core/Extension/module.api.php

@@ -129,10 +129,9 @@ function hook_module_implements_alter(&$implementations, $hook) {
 /**
  * Alter the information parsed from module and theme .info.yml files.
  *
- * This hook is invoked in _system_rebuild_module_data() and in
+ * This hook is invoked in \Drupal\Core\Extension\ExtensionList::doList(). A
- * \Drupal\Core\Extension\ThemeHandlerInterface::rebuildThemeData(). A module
+ * module may implement this hook in order to add to or alter the data generated
- * may implement this hook in order to add to or alter the data generated by
+ * by reading the .info.yml file with \Drupal\Core\Extension\InfoParser.
- * reading the .info.yml file with \Drupal\Core\Extension\InfoParser.
  *
  * Using implementations of this hook to make modules required by setting the
  * $info['required'] key is discouraged. Doing so will slow down the module

core/lib/Drupal/Core/Installer/ExtensionListTrait.php

@@ -0,0 +1,56 @@
+<?php
+
+namespace Drupal\Core\Installer;
+
+/**
+ * Provides common functionality for the extension list classes.
+ */
+trait ExtensionListTrait {
+
+  /**
+   * Static version of the added file names during the installer.
+   *
+   * @var string[]
+   *
+   * @internal
+   */
+  protected static $staticAddedPathNames;
+
+  /**
+   * @see \Drupal\Core\Extension\ExtensionList::setPathname()
+   */
+  public function setPathname($extension_name, $pathname) {
+    parent::setPathname($extension_name, $pathname);
+
+    // In the early installer the container is rebuilt multiple times. Therefore
+    // we have to keep the added filenames across those rebuilds. This is not a
+    // final design, but rather just a workaround resolved at some point,
+    // hopefully.
+    // @todo Remove as part of https://drupal.org/project/drupal/issues/2934063
+    static::$staticAddedPathNames[$extension_name] = $pathname;
+  }
+
+  /**
+   * @see \Drupal\Core\Extension\ExtensionList::getPathname()
+   */
+  public function getPathname($extension_name) {
+    if (isset($this->addedPathNames[$extension_name])) {
+      return $this->addedPathNames[$extension_name];
+    }
+    elseif (isset($this->pathNames[$extension_name])) {
+      return $this->pathNames[$extension_name];
+    }
+    elseif (isset(static::$staticAddedPathNames[$extension_name])) {
+      return static::$staticAddedPathNames[$extension_name];
+    }
+    elseif (($path_names = $this->getPathnames()) && isset($path_names[$extension_name])) {
+      // Ensure we don't have to do path scanning more than really needed.
+      foreach ($path_names as $extension => $path_name) {
+        static::$staticAddedPathNames[$extension] = $path_name;
+      }
+      return $path_names[$extension_name];
+    }
+    throw new \InvalidArgumentException("The {$this->type} $extension_name does not exist.");
+  }
+
+}

core/lib/Drupal/Core/Installer/InstallerModuleExtensionList.php

@@ -8,51 +8,6 @@ use Drupal\Core\Extension\ModuleExtensionList;
  * Overrides the module extension list to have a static cache.
  */
 class InstallerModuleExtensionList extends ModuleExtensionList {
-
+  use ExtensionListTrait;
-  /**
-   * Static version of the added file names during the installer.
-   *
-   * @var string[]
-   *
-   * @internal
-   */
-  protected static $staticAddedPathNames;
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setPathname($extension_name, $pathname) {
-    parent::setPathname($extension_name, $pathname);
-
-    // In the early installer the container is rebuilt multiple times. Therefore
-    // we have to keep the added filenames across those rebuilds. This is not a
-    // final design, but rather just a workaround resolved at some point,
-    // hopefully.
-    // @todo Remove as part of https://drupal.org/project/drupal/issues/2934063
-    static::$staticAddedPathNames[$extension_name] = $pathname;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getPathname($extension_name) {
-    if (isset($this->addedPathNames[$extension_name])) {
-      return $this->addedPathNames[$extension_name];
-    }
-    elseif (isset($this->pathNames[$extension_name])) {
-      return $this->pathNames[$extension_name];
-    }
-    elseif (isset(static::$staticAddedPathNames[$extension_name])) {
-      return static::$staticAddedPathNames[$extension_name];
-    }
-    elseif (($path_names = $this->getPathnames()) && isset($path_names[$extension_name])) {
-      // Ensure we don't have to do path scanning more than really needed.
-      foreach ($path_names as $extension => $path_name) {
-        static::$staticAddedPathNames[$extension] = $path_name;
-      }
-      return $path_names[$extension_name];
-    }
-    throw new \InvalidArgumentException("The {$this->type} $extension_name does not exist.");
-  }
 
 }

core/lib/Drupal/Core/Installer/InstallerThemeEngineExtensionList.php

@@ -0,0 +1,13 @@
+<?php
+
+namespace Drupal\Core\Installer;
+
+use Drupal\Core\Extension\ThemeEngineExtensionList;
+
+/**
+ * Overrides the theme engine extension list to have a static cache.
+ */
+class InstallerThemeEngineExtensionList extends ThemeEngineExtensionList {
+  use ExtensionListTrait;
+
+}

core/lib/Drupal/Core/Installer/InstallerThemeExtensionList.php

@@ -0,0 +1,13 @@
+<?php
+
+namespace Drupal\Core\Installer;
+
+use Drupal\Core\Extension\ThemeExtensionList;
+
+/**
+ * Overrides the theme extension list to have a static cache.
+ */
+class InstallerThemeExtensionList extends ThemeExtensionList {
+  use ExtensionListTrait;
+
+}

core/lib/Drupal/Core/Installer/NormalInstallerServiceProvider.php

@@ -16,6 +16,8 @@ class NormalInstallerServiceProvider implements ServiceProviderInterface {
   public function register(ContainerBuilder $container) {
     // Use a performance optimised module extension list.
     $container->getDefinition('extension.list.module')->setClass('Drupal\Core\Installer\InstallerModuleExtensionList');
+    $container->getDefinition('extension.list.theme')->setClass('Drupal\Core\Installer\InstallerThemeExtensionList');
+    $container->getDefinition('extension.list.theme_engine')->setClass('Drupal\Core\Installer\InstallerThemeEngineExtensionList');
   }
 
 }

core/lib/Drupal/Core/Theme/ActiveTheme.php

@@ -161,7 +161,7 @@ class ActiveTheme {
   /**
    * Returns the path to the theme engine for root themes.
    *
-   * @see \Drupal\Core\Extension\ThemeHandler::rebuildThemeData
+   * @see \Drupal\Core\Extension\ThemeExtensionList::doList()
    *
    * @return mixed
    */

core/modules/system/system.install

@@ -1829,7 +1829,8 @@ function system_update_8014() {
   $theme_handler->refreshInfo();
   foreach ($theme_handler->listInfo() as $theme) {
     // We first check that a base theme is set because if it's set to false then
-    // it's unset in \Drupal\Core\Extension\ThemeHandler::rebuildThemeData().
+    // it's unset in
+    // \Drupal\Core\Extension\ThemeExtensionList::createExtensionInfo().
     if (isset($theme->info['base theme']) && $theme->info['base theme'] == 'stable') {
       $theme_handler->install(['stable']);
       return;

core/modules/system/system.module

@@ -11,7 +11,6 @@ use Drupal\Component\Render\PlainTextOutput;
 use Drupal\Component\Utility\UrlHelper;
 use Drupal\Core\Asset\AttachedAssetsInterface;
 use Drupal\Core\Cache\Cache;
-use Drupal\Core\Extension\Exception\UnknownExtensionException;
 use Drupal\Core\Queue\QueueGarbageCollectionInterface;
 use Drupal\Core\Database\Query\AlterableInterface;
 use Drupal\Core\Extension\Extension;
@@ -963,38 +962,20 @@ function system_check_directory($form_element, FormStateInterface $form_state) {
  *   array is returned.
  *
  * @see system_rebuild_module_data()
- * @see \Drupal\Core\Extension\ThemeHandlerInterface::rebuildThemeData()
+ * @see \Drupal\Core\Extension\ThemeExtensionList
  */
 function system_get_info($type, $name = NULL) {
-  if ($type == 'module') {
+  /** @var \Drupal\Core\Extension\ExtensionList $extension_list */
-    /** @var \Drupal\Core\Extension\ModuleExtensionList $module_list */
+  $extension_list = \Drupal::service('extension.list.' . $type);
-    $module_list = \Drupal::service('extension.list.module');
+  if (isset($name)) {
-    if (isset($name)) {
+    try {
-      try {
+      return $extension_list->getExtensionInfo($name);
-        return $module_list->getExtensionInfo($name);
-      }
-      catch (UnknownExtensionException $e) {
-        return [];
-      }
     }
-    else {
+    catch (\InvalidArgumentException $e) {
-      return $module_list->getAllInstalledInfo();
+      return [];
     }
   }
-  else {
+  return $extension_list->getAllInstalledInfo();
-    // @todo move into ThemeExtensionList https://www.drupal.org/node/2659940
-    $info = [];
-    $list = system_list($type);
-    foreach ($list as $shortname => $item) {
-      if (!empty($item->status)) {
-        $info[$shortname] = $item->info;
-      }
-    }
-    if (isset($name)) {
-      return isset($info[$name]) ? $info[$name] : [];
-    }
-    return $info;
-  }
 }
 
 /**

core/modules/system/tests/modules/theme_test/src/ThemeTestController.php

@@ -158,4 +158,14 @@ class ThemeTestController extends ControllerBase {
     ];
   }
 
+  /**
+   * Controller for testing a namespaced class in a theme.
+   */
+  public function testThemeClass() {
+    return [
+      '#theme' => 'theme_test_theme_class',
+      '#title' => 'Testing loading a class from a .theme file',
+    ];
+  }
+
 }

core/modules/system/tests/modules/theme_test/templates/theme-test-theme-class.html.twig

@@ -0,0 +1 @@
+<p>{{ message }}</p>

core/modules/system/tests/modules/theme_test/theme_test.module

@@ -70,6 +70,11 @@ function theme_test_theme($existing, $type, $theme, $path) {
     'render element' => 'content',
     'base hook' => 'container',
   ];
+  $items['theme_test_theme_class'] = [
+    'variables' => [
+      'message' => '',
+    ],
+  ];
   return $items;
 }
 

core/modules/system/tests/modules/theme_test/theme_test.routing.yml

@@ -110,3 +110,10 @@ theme_test.preprocess_suggestions:
     _controller: '\Drupal\theme_test\ThemeTestController::preprocessSuggestions'
   requirements:
     _access: 'TRUE'
+
+theme_test.test_theme_class:
+  path: '/theme-test/test-theme-class'
+  defaults:
+    _controller: '\Drupal\theme_test\ThemeTestController::testThemeClass'
+  requirements:
+    _access: 'TRUE'

core/modules/system/tests/src/Functional/Theme/ThemeTest.php

@@ -80,6 +80,20 @@ class ThemeTest extends BrowserTestBase {
     $this->assertTrue(in_array('page__front', $suggestions), 'Front page template was suggested.');
   }
 
+  /**
+   * Tests theme can provide classes.
+   */
+  public function testClassLoading() {
+    // Install test theme and set it as default.
+    $this->config('system.theme')
+      ->set('default', 'test_theme')
+      ->save();
+    $this->resetAll();
+    // Visit page controller and confirm that the theme class is loaded.
+    $this->drupalGet('/theme-test/test-theme-class');
+    $this->assertText('Loading ThemeClass was successful.');
+  }
+
   /**
    * Ensures a theme's .info.yml file is able to override a module CSS file from being added to the page.
    *

core/modules/system/tests/src/Kernel/Theme/ThemeTest.php

@@ -4,7 +4,6 @@ namespace Drupal\Tests\system\Kernel\Theme;
 
 use Drupal\KernelTests\KernelTestBase;
 use Drupal\Component\Render\MarkupInterface;
-use Drupal\test_theme\ThemeClass;
 
 /**
  * Tests low-level theme functions.
@@ -146,13 +145,6 @@ class ThemeTest extends KernelTestBase {
     $this->assertThemeOutput('theme_test_render_element_children', $element, 'Foo', 'drupal_render() avoids #theme_wrappers recursion loop when rendering a render element.');
   }
 
-  /**
-   * Tests theme can provide classes.
-   */
-  public function testClassLoading() {
-    new ThemeClass();
-  }
-
   /**
    * Tests drupal_find_theme_templates().
    */

core/modules/system/tests/themes/test_theme/test_theme.theme

@@ -154,3 +154,15 @@ function test_theme_preprocess_theme_test_preprocess_suggestions__kitten__flamin
 function test_theme_preprocess_theme_test_preprocess_suggestions__kitten__meerkat__tarsier__moose(&$variables) {
   $variables['bar'] = 'Moose';
 }
+
+/**
+ * Tests that a class can be loaded within a .theme file.
+ */
+function test_theme_preprocess_theme_test_theme_class(&$variables) {
+  if (class_exists('\Drupal\test_theme\ThemeClass')) {
+    $variables['message'] = 'Loading ThemeClass was successful.';
+  }
+  else {
+    $variables['message'] = 'Loading ThemeClass failed.';
+  }
+}

core/tests/Drupal/KernelTests/Core/Extension/ThemeEngineExtensionListTest.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace Drupal\KernelTests\Core\Extension;
+
+use Drupal\Core\Site\Settings;
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * @coversDefaultClass \Drupal\Core\Extension\ThemeEngineExtensionList
+ * @group Extension
+ */
+class ThemeEngineExtensionListTest extends KernelTestBase {
+
+  /**
+   * @covers ::getList
+   */
+  public function testGetlist() {
+    $settings = Settings::getAll();
+    $settings['install_profile'] = 'testing';
+    new Settings($settings);
+
+    // Confirm that all theme engines are available.
+    $theme_engines = \Drupal::service('extension.list.theme_engine')->getList();
+    $this->assertArrayHasKey('twig', $theme_engines);
+    $this->assertArrayHasKey('nyan_cat', $theme_engines);
+    $this->assertCount(2, $theme_engines);
+  }
+
+}

core/tests/Drupal/KernelTests/Core/Extension/ThemeExtensionListTest.php

@@ -0,0 +1,39 @@
+<?php
+
+namespace Drupal\KernelTests\Core\Extension;
+
+use Drupal\Core\Site\Settings;
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * @coversDefaultClass \Drupal\Core\Extension\ThemeExtensionList
+ * @group Extension
+ */
+class ThemeExtensionListTest extends KernelTestBase {
+
+  /**
+   * @covers ::getList
+   */
+  public function testGetlist() {
+    $settings = Settings::getAll();
+    $settings['install_profile'] = 'testing';
+    new Settings($settings);
+
+    \Drupal::configFactory()->getEditable('core.extension')
+      ->set('module.testing', 1000)
+      ->set('theme.test_theme', 0)
+      ->save();
+
+    // The installation profile is provided by a container parameter.
+    // Saving the configuration doesn't automatically trigger invalidation
+    $this->container->get('kernel')->rebuildContainer();
+
+    /** @var \Drupal\Core\Extension\ThemeExtensionList $theme_extension_list */
+    $theme_extension_list = \Drupal::service('extension.list.theme');
+    $extensions = $theme_extension_list->getList();
+
+    $this->assertArrayHasKey('test_theme', $extensions);
+    $this->assertEquals(0, $extensions['test_theme']->weight);
+  }
+
+}

core/tests/Drupal/KernelTests/Core/Theme/SystemListTest.php

@@ -0,0 +1,68 @@
+<?php
+
+namespace Drupal\KernelTests\Core\Theme;
+
+use Drupal\Core\DependencyInjection\ContainerBuilder;
+use Drupal\Core\Routing\NullMatcherDumper;
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * Tests system_list() function.
+ *
+ * In Drupal 8 the system_list() function only lists themes.
+ *
+ * @group Extension
+ * @group legacy
+ */
+class SystemListTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['system'];
+
+  /**
+   * {@inheritdoc}
+   */
+  public function register(ContainerBuilder $container) {
+    parent::register($container);
+    // Some test methods involve ModuleHandler operations, which attempt to
+    // rebuild and dump routes.
+    $container->register('router.dumper', NullMatcherDumper::class);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+    $this->installConfig(['system']);
+  }
+
+  /**
+   * Tests installing a theme.
+   *
+   * @expectedDeprecation system_list() is deprecated in Drupal 8.7.0 and will be removed before Drupal 9.0.0. Use \Drupal::service('theme_handler')->listInfo() instead. See https://www.drupal.org/node/2709919
+   */
+  public function testSystemList() {
+    // Verifies that no themes are listed by default.
+    $this->assertEmpty(system_list('theme'));
+    $this->assertEmpty(system_list('filepaths'));
+
+    $this->container->get('theme_installer')->install(['test_basetheme']);
+
+    $themes = system_list('theme');
+    $this->assertTrue(isset($themes['test_basetheme']));
+    $this->assertEqual($themes['test_basetheme']->getName(), 'test_basetheme');
+    $filepaths = system_list('filepaths');
+    $this->assertEquals('test_basetheme', $filepaths[0]['name']);
+    $this->assertEquals('core/modules/system/tests/themes/test_basetheme/test_basetheme.info.yml', $filepaths[0]['filepath']);
+    $this->assertCount(1, $filepaths);
+
+    $this->container->get('theme_installer')->uninstall(['test_basetheme']);
+
+    $this->assertEmpty(system_list('theme'));
+    $this->assertEmpty(system_list('filepaths'));
+  }
+
+}

core/tests/Drupal/KernelTests/Core/Theme/ThemeInstallerTest.php

@@ -44,7 +44,7 @@ class ThemeInstallerTest extends KernelTestBase {
     $this->assertFalse($this->extensionConfig()->get('theme'));
 
     $this->assertFalse(array_keys($this->themeHandler()->listInfo()));
-    $this->assertFalse(array_keys(system_list('theme')));
+    $this->assertFalse(array_keys(\Drupal::service('theme_handler')->listInfo()));
 
     // Rebuilding available themes should always yield results though.
     $this->assertTrue($this->themeHandler()->rebuildThemeData()['stark'], 'ThemeHandler::rebuildThemeData() yields all available themes.');
@@ -70,8 +70,6 @@ class ThemeInstallerTest extends KernelTestBase {
     $this->assertTrue(isset($themes[$name]));
     $this->assertEqual($themes[$name]->getName(), $name);
 
-    $this->assertEqual(array_keys(system_list('theme')), array_keys($themes));
-
     // Verify that test_basetheme.settings is active.
     $this->assertIdentical(theme_get_setting('features.favicon', $name), FALSE);
     $this->assertEqual(theme_get_setting('base', $name), 'only');
@@ -272,7 +270,6 @@ class ThemeInstallerTest extends KernelTestBase {
     $this->themeInstaller()->uninstall([$name]);
 
     $this->assertFalse(array_keys($this->themeHandler()->listInfo()));
-    $this->assertFalse(array_keys(system_list('theme')));
 
     $this->assertFalse($this->config("$name.settings")->get());
 
@@ -281,7 +278,6 @@ class ThemeInstallerTest extends KernelTestBase {
     $themes = $this->themeHandler()->listInfo();
     $this->assertTrue(isset($themes[$name]));
     $this->assertEqual($themes[$name]->getName(), $name);
-    $this->assertEqual(array_keys(system_list('theme')), array_keys($themes));
     $this->assertTrue($this->config("$name.settings")->get());
   }
 
@@ -331,8 +327,8 @@ class ThemeInstallerTest extends KernelTestBase {
     $this->assertTrue(isset($info['regions']['test_region']));
     $regions = system_region_list($name);
     $this->assertTrue(isset($regions['test_region']));
-    $system_list = system_list('theme');
+    $theme_list = \Drupal::service('theme_handler')->listInfo();
-    $this->assertTrue(isset($system_list[$name]->info['regions']['test_region']));
+    $this->assertTrue(isset($theme_list[$name]->info['regions']['test_region']));
 
     $this->moduleInstaller()->uninstall(['module_test']);
     $this->assertFalse($this->moduleHandler()->moduleExists('module_test'));
@@ -347,8 +343,8 @@ class ThemeInstallerTest extends KernelTestBase {
     $this->assertFalse(isset($info['regions']['test_region']));
     $regions = system_region_list($name);
     $this->assertFalse(isset($regions['test_region']));
-    $system_list = system_list('theme');
+    $theme_list = \Drupal::service('theme_handler')->listInfo();
-    $this->assertFalse(isset($system_list[$name]->info['regions']['test_region']));
+    $this->assertFalse(isset($theme_list[$name]->info['regions']['test_region']));
   }
 
   /**

core/tests/Drupal/Tests/Core/Extension/ThemeExtensionListTest.php

@@ -0,0 +1,264 @@
+<?php
+
+namespace Drupal\Tests\Core\Extension;
+
+use Drupal\Core\Cache\MemoryBackend;
+use Drupal\Core\Cache\NullBackend;
+use Drupal\Core\Extension\Extension;
+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\KeyValueStore\KeyValueMemoryFactory;
+use Drupal\Core\Lock\NullLockBackend;
+use Drupal\Core\State\State;
+use Drupal\Tests\UnitTestCase;
+use Prophecy\Argument;
+
+/**
+ * @coversDefaultClass \Drupal\Core\Extension\ThemeExtensionList
+ * @group Extension
+ */
+class ThemeExtensionListTest extends UnitTestCase {
+
+  /**
+   * Tests rebuild the theme data with theme parents.
+   */
+  public function testRebuildThemeDataWithThemeParents() {
+    $extension_discovery = $this->prophesize(ExtensionDiscovery::class);
+    $extension_discovery
+      ->scan('theme')
+      ->willReturn([
+        'test_subtheme'  => new Extension($this->root, 'theme', $this->root . '/core/modules/system/tests/themes/test_subtheme/test_subtheme.info.yml', 'test_subtheme.info.yml'),
+        'test_basetheme' => new Extension($this->root, 'theme', $this->root . '/core/modules/system/tests/themes/test_basetheme/test_basetheme.info.yml', 'test_basetheme.info.yml'),
+      ]);
+    $extension_discovery
+      ->scan('theme_engine')
+      ->willReturn([
+        'twig' => new Extension($this->root, 'theme_engine', $this->root . '/core/themes/engines/twig/twig.info.yml', 'twig.engine'),
+      ]);
+
+    // Verify that info parser is called with the specified paths.
+    $argument_condition = function ($path) {
+      return in_array($path, [
+        $this->root . '/core/modules/system/tests/themes/test_subtheme/test_subtheme.info.yml',
+        $this->root . '/core/modules/system/tests/themes/test_basetheme/test_basetheme.info.yml',
+        $this->root . '/core/themes/engines/twig/twig.info.yml',
+      ], TRUE);
+    };
+    $info_parser = $this->prophesize(InfoParserInterface::class);
+    $info_parser->parse(Argument::that($argument_condition))
+      ->shouldBeCalled()
+      ->will(function ($file) {
+        $info_parser = new InfoParser();
+        return $info_parser->parse($file[0]);
+      });
+
+    $module_handler = $this->prophesize(ModuleHandlerInterface::class);
+    $module_handler
+      ->buildModuleDependencies(Argument::type('array'))
+      ->willReturnArgument(0);
+    $module_handler
+      ->alter('system_info', Argument::type('array'), Argument::type(Extension::class), Argument::any())
+      ->shouldBeCalled();
+
+    $state = new State(new KeyValueMemoryFactory(), new MemoryBackend(), new NullLockBackend());
+
+    $config_factory = $this->getConfigFactoryStub([
+      'core.extension' => [
+        'module' => [],
+        'theme' => [],
+        'disabled' => [
+          'theme' => [],
+        ],
+        'theme_engine' => '',
+      ],
+    ]);
+
+    $theme_engine_list = new TestThemeEngineExtensionList($this->root, 'theme_engine', new NullBackend('test'), $info_parser->reveal(), $module_handler->reveal(), $state, $config_factory, 'testing');
+    $theme_engine_list->setExtensionDiscovery($extension_discovery->reveal());
+
+    $theme_list = new TestThemeExtensionList($this->root, 'theme', new NullBackend('test'), $info_parser->reveal(), $module_handler->reveal(), $state, $config_factory, $theme_engine_list, 'testing');
+    $theme_list->setExtensionDiscovery($extension_discovery->reveal());
+
+    $theme_data = $theme_list->reset()->getList();
+    $this->assertCount(2, $theme_data);
+
+    $info_basetheme = $theme_data['test_basetheme'];
+    $info_subtheme = $theme_data['test_subtheme'];
+
+    // Ensure some basic properties.
+    $this->assertInstanceOf('Drupal\Core\Extension\Extension', $info_basetheme);
+    $this->assertEquals('test_basetheme', $info_basetheme->getName());
+    $this->assertInstanceOf('Drupal\Core\Extension\Extension', $info_subtheme);
+    $this->assertEquals('test_subtheme', $info_subtheme->getName());
+
+    // Test the parent/child-theme properties.
+    $info_subtheme->info['base theme'] = 'test_basetheme';
+    $info_basetheme->sub_themes = ['test_subtheme'];
+
+    $this->assertEquals($this->root . '/core/themes/engines/twig/twig.engine', $info_basetheme->owner);
+    $this->assertEquals('twig', $info_basetheme->prefix);
+    $this->assertEquals($this->root . '/core/themes/engines/twig/twig.engine', $info_subtheme->owner);
+    $this->assertEquals('twig', $info_subtheme->prefix);
+  }
+
+  /**
+   * Tests getting the base themes for a set a defines themes.
+   *
+   * @param array $themes
+   *   An array of available themes, keyed by the theme name.
+   * @param string $theme
+   *   The theme name to find all its base themes.
+   * @param array $expected
+   *   The expected base themes.
+   *
+   * @dataProvider providerTestGetBaseThemes
+   */
+  public function testGetBaseThemes(array $themes, $theme, array $expected) {
+    // Mocks and stubs.
+    $module_handler = $this->prophesize(ModuleHandlerInterface::class);
+    $state = new State(new KeyValueMemoryFactory(), new MemoryBackend(), new NullLockBackend());
+    $config_factory = $this->getConfigFactoryStub([]);
+    $theme_engine_list = $this->prophesize(ThemeEngineExtensionList::class);
+    $theme_listing = new ThemeExtensionList($this->root, 'theme', new NullBackend('test'), new InfoParser(), $module_handler->reveal(), $state, $config_factory, $theme_engine_list->reveal(), 'test');
+
+    $base_themes = $theme_listing->getBaseThemes($themes, $theme);
+
+    $this->assertEquals($expected, $base_themes);
+  }
+
+  /**
+   * Provides test data for testGetBaseThemes.
+   *
+   * @return array
+   *   An array of theme test data.
+   */
+  public function providerTestGetBaseThemes() {
+    $data = [];
+
+    // Tests a theme without any base theme.
+    $themes = [];
+    $themes['test_1'] = (object) [
+      'name' => 'test_1',
+      'info' => [
+        'name' => 'test_1',
+      ],
+    ];
+    $data[] = [$themes, 'test_1', []];
+
+    // Tests a theme with a non existing base theme.
+    $themes = [];
+    $themes['test_1'] = (object) [
+      'name' => 'test_1',
+      'info' => [
+        'name'       => 'test_1',
+        'base theme' => 'test_2',
+      ],
+    ];
+    $data[] = [$themes, 'test_1', ['test_2' => NULL]];
+
+    // Tests a theme with a single existing base theme.
+    $themes = [];
+    $themes['test_1'] = (object) [
+      'name' => 'test_1',
+      'info' => [
+        'name'       => 'test_1',
+        'base theme' => 'test_2',
+      ],
+    ];
+    $themes['test_2'] = (object) [
+      'name' => 'test_2',
+      'info' => [
+        'name' => 'test_2',
+      ],
+    ];
+    $data[] = [$themes, 'test_1', ['test_2' => 'test_2']];
+
+    // Tests a theme with multiple base themes.
+    $themes = [];
+    $themes['test_1'] = (object) [
+      'name' => 'test_1',
+      'info' => [
+        'name'       => 'test_1',
+        'base theme' => 'test_2',
+      ],
+    ];
+    $themes['test_2'] = (object) [
+      'name' => 'test_2',
+      'info' => [
+        'name'       => 'test_2',
+        'base theme' => 'test_3',
+      ],
+    ];
+    $themes['test_3'] = (object) [
+      'name' => 'test_3',
+      'info' => [
+        'name' => 'test_3',
+      ],
+    ];
+    $data[] = [
+      $themes,
+      'test_1',
+      ['test_2' => 'test_2', 'test_3' => 'test_3'],
+    ];
+
+    return $data;
+  }
+
+}
+
+/**
+ * Trait that allows extension discovery to be set.
+ */
+trait SettableDiscoveryExtensionListTrait {
+
+  /**
+   * The extension discovery for this extension list.
+   *
+   * @var \Drupal\Core\Extension\ExtensionDiscovery
+   */
+  protected $extensionDiscovery;
+
+  /**
+   * Sets the extension discovery.
+   *
+   * @param \Drupal\Core\Extension\ExtensionDiscovery $discovery
+   *   The extension discovery.
+   */
+  public function setExtensionDiscovery(ExtensionDiscovery $discovery) {
+    $this->extensionDiscovery = $discovery;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getExtensionDiscovery() {
+    return $this->extensionDiscovery;
+  }
+
+}
+
+/**
+ * Test theme extension list class.
+ */
+class TestThemeExtensionList extends ThemeExtensionList {
+
+  use SettableDiscoveryExtensionListTrait;
+
+}
+
+/**
+ * Test theme engine extension list class.
+ */
+class TestThemeEngineExtensionList extends ThemeEngineExtensionList {
+
+  use SettableDiscoveryExtensionListTrait;
+
+}
+
+if (!defined('DRUPAL_MINIMUM_PHP')) {
+  define('DRUPAL_MINIMUM_PHP', '5.5.9');
+}

core/tests/Drupal/Tests/Core/Extension/ThemeHandlerTest.php

@@ -7,11 +7,10 @@
 
 namespace Drupal\Tests\Core\Extension;
 
+use Composer\Autoload\ClassLoader;
 use Drupal\Core\Extension\Extension;
-use Drupal\Core\Extension\InfoParser;
+use Drupal\Core\Extension\ThemeExtensionList;
 use Drupal\Core\Extension\ThemeHandler;
-use Drupal\Core\KeyValueStore\KeyValueMemoryFactory;
-use Drupal\Core\State\State;
 use Drupal\Tests\UnitTestCase;
 
 /**
@@ -20,20 +19,6 @@ use Drupal\Tests\UnitTestCase;
  */
 class ThemeHandlerTest extends UnitTestCase {
 
-  /**
-   * The mocked info parser.
-   *
-   * @var \Drupal\Core\Extension\InfoParserInterface|\PHPUnit_Framework_MockObject_MockObject
-   */
-  protected $infoParser;
-
-  /**
-   * The mocked state backend.
-   *
-   * @var \Drupal\Core\State\StateInterface|\PHPUnit_Framework_MockObject_MockObject
-   */
-  protected $state;
-
   /**
    * The mocked config factory.
    *
@@ -42,18 +27,11 @@ class ThemeHandlerTest extends UnitTestCase {
   protected $configFactory;
 
   /**
-   * The mocked module handler.
+   * The theme listing service.
    *
-   * @var \Drupal\Core\Extension\ModuleHandlerInterface|\PHPUnit_Framework_MockObject_MockObject
+   * @var \Drupal\Core\Extension\ThemeExtensionList|\PHPUnit_Framework_MockObject_MockObject
    */
-  protected $moduleHandler;
+  protected $themeList;
-
-  /**
-   * The extension discovery.
-   *
-   * @var \Drupal\Core\Extension\ExtensionDiscovery|\PHPUnit_Framework_MockObject_MockObject
-   */
-  protected $extensionDiscovery;
 
   /**
    * The tested theme handler.
@@ -77,16 +55,17 @@ class ThemeHandlerTest extends UnitTestCase {
         ],
       ],
     ]);
-    $this->moduleHandler = $this->getMock('Drupal\Core\Extension\ModuleHandlerInterface');
+    $this->themeList = $this->getMockBuilder(ThemeExtensionList::class)
-    $this->state = new State(new KeyValueMemoryFactory());
-    $this->infoParser = $this->getMock('Drupal\Core\Extension\InfoParserInterface');
-    $this->extensionDiscovery = $this->getMockBuilder('Drupal\Core\Extension\ExtensionDiscovery')
       ->disableOriginalConstructor()
       ->getMock();
-    $this->themeHandler = new StubThemeHandler($this->root, $this->configFactory, $this->moduleHandler, $this->state, $this->infoParser, $this->extensionDiscovery);
+    $this->themeHandler = new StubThemeHandler($this->root, $this->configFactory, $this->themeList);
 
-    $cache_tags_invalidator = $this->getMock('Drupal\Core\Cache\CacheTagsInvalidatorInterface');
+    $container = $this->createMock('Symfony\Component\DependencyInjection\ContainerInterface');
-    $this->getContainerWithCacheTagsInvalidator($cache_tags_invalidator);
+    $container->expects($this->any())
+      ->method('get')
+      ->with('class_loader')
+      ->will($this->returnValue($this->createMock(ClassLoader::class)));
+    \Drupal::setContainer($container);
   }
 
   /**
@@ -95,31 +74,14 @@ class ThemeHandlerTest extends UnitTestCase {
    * @see \Drupal\Core\Extension\ThemeHandler::rebuildThemeData()
    */
   public function testRebuildThemeData() {
-    $this->extensionDiscovery->expects($this->at(0))
+    $this->themeList->expects($this->at(0))
-      ->method('scan')
+      ->method('reset')
-      ->with('theme')
+      ->willReturnSelf();
+    $this->themeList->expects($this->at(1))
+      ->method('getList')
       ->will($this->returnValue([
         'seven' => new Extension($this->root, 'theme', $this->root . '/core/themes/seven/seven.info.yml', 'seven.theme'),
       ]));
-    $this->extensionDiscovery->expects($this->at(1))
-      ->method('scan')
-      ->with('theme_engine')
-      ->will($this->returnValue([
-        'twig' => new Extension($this->root, 'theme_engine', $this->root . '/core/themes/engines/twig/twig.info.yml', 'twig.engine'),
-      ]));
-    $this->infoParser->expects($this->once())
-      ->method('parse')
-      ->with($this->root . '/core/themes/seven/seven.info.yml')
-      ->will($this->returnCallback(function ($file) {
-        $info_parser = new InfoParser();
-        return $info_parser->parse($file);
-      }));
-    $this->moduleHandler->expects($this->once())
-      ->method('buildModuleDependencies')
-      ->will($this->returnArgument(0));
-
-    $this->moduleHandler->expects($this->once())
-      ->method('alter');
 
     $theme_data = $this->themeHandler->rebuildThemeData();
     $this->assertCount(1, $theme_data);
@@ -130,11 +92,7 @@ class ThemeHandlerTest extends UnitTestCase {
     $this->assertEquals('seven', $info->getName());
     $this->assertEquals($this->root . '/core/themes/seven/seven.info.yml', $info->getPathname());
     $this->assertEquals($this->root . '/core/themes/seven/seven.theme', $info->getExtensionPathname());
-    $this->assertEquals($this->root . '/core/themes/engines/twig/twig.engine', $info->owner);
-    $this->assertEquals('twig', $info->prefix);
 
-    $this->assertEquals('twig', $info->info['engine']);
-    $this->assertEquals(['seven/global-styling'], $info->info['libraries']);
   }
 
   /**
@@ -151,158 +109,6 @@ class ThemeHandlerTest extends UnitTestCase {
     }
   }
 
-  /**
-   * Tests rebuild the theme data with theme parents.
-   */
-  public function testRebuildThemeDataWithThemeParents() {
-    $this->extensionDiscovery->expects($this->at(0))
-      ->method('scan')
-      ->with('theme')
-      ->will($this->returnValue([
-        'test_subtheme' => new Extension($this->root, 'theme', $this->root . '/core/modules/system/tests/themes/test_subtheme/test_subtheme.info.yml', 'test_subtheme.info.yml'),
-        'test_basetheme' => new Extension($this->root, 'theme', $this->root . '/core/modules/system/tests/themes/test_basetheme/test_basetheme.info.yml', 'test_basetheme.info.yml'),
-      ]));
-    $this->extensionDiscovery->expects($this->at(1))
-      ->method('scan')
-      ->with('theme_engine')
-      ->will($this->returnValue([
-        'twig' => new Extension($this->root, 'theme_engine', $this->root . '/core/themes/engines/twig/twig.info.yml', 'twig.engine'),
-      ]));
-    $this->infoParser->expects($this->at(0))
-      ->method('parse')
-      ->with($this->root . '/core/modules/system/tests/themes/test_subtheme/test_subtheme.info.yml')
-      ->will($this->returnCallback(function ($file) {
-        $info_parser = new InfoParser();
-        return $info_parser->parse($file);
-      }));
-    $this->infoParser->expects($this->at(1))
-      ->method('parse')
-      ->with($this->root . '/core/modules/system/tests/themes/test_basetheme/test_basetheme.info.yml')
-      ->will($this->returnCallback(function ($file) {
-        $info_parser = new InfoParser();
-        return $info_parser->parse($file);
-      }));
-    $this->moduleHandler->expects($this->once())
-      ->method('buildModuleDependencies')
-      ->will($this->returnArgument(0));
-
-    $theme_data = $this->themeHandler->rebuildThemeData();
-    $this->assertCount(2, $theme_data);
-
-    $info_basetheme = $theme_data['test_basetheme'];
-    $info_subtheme = $theme_data['test_subtheme'];
-
-    // Ensure some basic properties.
-    $this->assertInstanceOf('Drupal\Core\Extension\Extension', $info_basetheme);
-    $this->assertEquals('test_basetheme', $info_basetheme->getName());
-    $this->assertInstanceOf('Drupal\Core\Extension\Extension', $info_subtheme);
-    $this->assertEquals('test_subtheme', $info_subtheme->getName());
-
-    // Test the parent/child-theme properties.
-    $info_subtheme->info['base theme'] = 'test_basetheme';
-    $info_basetheme->sub_themes = ['test_subtheme'];
-
-    $this->assertEquals($this->root . '/core/themes/engines/twig/twig.engine', $info_basetheme->owner);
-    $this->assertEquals('twig', $info_basetheme->prefix);
-    $this->assertEquals($this->root . '/core/themes/engines/twig/twig.engine', $info_subtheme->owner);
-    $this->assertEquals('twig', $info_subtheme->prefix);
-  }
-
-  /**
-   * Tests getting the base themes for a set a defines themes.
-   *
-   * @param array $themes
-   *   An array of available themes, keyed by the theme name.
-   * @param string $theme
-   *   The theme name to find all its base themes.
-   * @param array $expected
-   *   The expected base themes.
-   *
-   * @dataProvider providerTestGetBaseThemes
-   */
-  public function testGetBaseThemes(array $themes, $theme, array $expected) {
-    $base_themes = $this->themeHandler->getBaseThemes($themes, $theme);
-    $this->assertEquals($expected, $base_themes);
-  }
-
-  /**
-   * Provides test data for testGetBaseThemes.
-   *
-   * @return array
-   *   An array of theme test data.
-   */
-  public function providerTestGetBaseThemes() {
-    $data = [];
-
-    // Tests a theme without any base theme.
-    $themes = [];
-    $themes['test_1'] = (object) [
-      'name' => 'test_1',
-      'info' => [
-        'name' => 'test_1',
-      ],
-    ];
-    $data[] = [$themes, 'test_1', []];
-
-    // Tests a theme with a non existing base theme.
-    $themes = [];
-    $themes['test_1'] = (object) [
-      'name' => 'test_1',
-      'info' => [
-        'name' => 'test_1',
-        'base theme' => 'test_2',
-      ],
-    ];
-    $data[] = [$themes, 'test_1', ['test_2' => NULL]];
-
-    // Tests a theme with a single existing base theme.
-    $themes = [];
-    $themes['test_1'] = (object) [
-      'name' => 'test_1',
-      'info' => [
-        'name' => 'test_1',
-        'base theme' => 'test_2',
-      ],
-    ];
-    $themes['test_2'] = (object) [
-      'name' => 'test_2',
-      'info' => [
-        'name' => 'test_2',
-      ],
-    ];
-    $data[] = [$themes, 'test_1', ['test_2' => 'test_2']];
-
-    // Tests a theme with multiple base themes.
-    $themes = [];
-    $themes['test_1'] = (object) [
-      'name' => 'test_1',
-      'info' => [
-        'name' => 'test_1',
-        'base theme' => 'test_2',
-      ],
-    ];
-    $themes['test_2'] = (object) [
-      'name' => 'test_2',
-      'info' => [
-        'name' => 'test_2',
-        'base theme' => 'test_3',
-      ],
-    ];
-    $themes['test_3'] = (object) [
-      'name' => 'test_3',
-      'info' => [
-        'name' => 'test_3',
-      ],
-    ];
-    $data[] = [
-      $themes,
-      'test_1',
-      ['test_2' => 'test_2', 'test_3' => 'test_3'],
-    ];
-
-    return $data;
-  }
-
 }
 
 /**
@@ -324,13 +130,6 @@ class StubThemeHandler extends ThemeHandler {
    */
   protected $registryRebuild;
 
-  /**
-   * A list of themes keyed by name.
-   *
-   * @var array
-   */
-  protected $systemList;
-
   /**
    * {@inheritdoc}
    */
@@ -345,27 +144,8 @@ class StubThemeHandler extends ThemeHandler {
     $this->registryRebuild = TRUE;
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  protected function systemThemeList() {
-    return $this->systemList;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function systemListReset() {
-  }
-
 }
 
-if (!defined('DRUPAL_EXTENSION_NAME_MAX_LENGTH')) {
-  define('DRUPAL_EXTENSION_NAME_MAX_LENGTH', 50);
-}
-if (!defined('DRUPAL_PHP_FUNCTION_PATTERN')) {
-  define('DRUPAL_PHP_FUNCTION_PATTERN', '[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*');
-}
 if (!defined('DRUPAL_MINIMUM_PHP')) {
-  define('DRUPAL_MINIMUM_PHP', '5.3.10');
+  define('DRUPAL_MINIMUM_PHP', '5.5.9');
 }