diff --git a/core/core.services.yml b/core/core.services.yml
index d9b1839..2ae0391 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -475,6 +475,14 @@ services:
       - { name: service_collector, tag: 'module_install.uninstall_validator', call: addUninstallValidator }
     arguments: ['@app.root', '@module_handler', '@kernel', '@router.builder']
     lazy: true
+  extension.list.module:
+    class: Drupal\Core\Extension\Hub\ExtensionHubInterface
+    factory: Drupal\Core\Extension\Hub\ExtensionHub::createForModules
+    arguments: ['@app.root', '@info_parser', '@module_handler', '@config.factory', '@extension.list.profile', '@cache.default']
+  extension.list.profile:
+    class: Drupal\Core\Extension\Hub\ExtensionHubInterface
+    factory: Drupal\Core\Extension\Hub\ExtensionHub::createForProfiles
+    arguments: ['@app.root', '@info_parser', '@module_handler', '@cache.default']
   content_uninstall_validator:
     class: Drupal\Core\Entity\ContentUninstallValidator
     tags:
diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 589d451..76c1be7 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -200,11 +200,26 @@ function drupal_get_filename($type, $name, $filename = NULL) {
     return 'core/core.info.yml';
   }
 
-  // Profiles are converted into modules in system_rebuild_module_data().
-  // @todo Remove false-exposure of profiles as modules.
-  if ($type == 'profile') {
-    $type = 'module';
+  if ($type === 'module' || $type === 'profile') {
+    $service_id = 'extension.list.' . $type;
+    /** @var \Drupal\Core\Extension\ExtensionList $extension_list */
+    $extension_list = \Drupal::service($service_id);
+    if (isset($filename)) {
+      // Manually add the info file path of an extension.
+      $extension_list->nameSetFilename($name, $filename);
+      return;
+    }
+    else {
+      try {
+        return $extension_list->nameGetFilename($name);
+      }
+      catch (\InvalidArgumentException $e) {
+        // Catch the exception and trigger error to maintain existing behavior.
+        trigger_error(SafeMarkup::format('The following @type is missing from the file system: @name', array('@type' => $type, '@name' => $name)), E_USER_WARNING);
+      }
+    }
   }
+
   if (!isset($files[$type])) {
     $files[$type] = array();
   }
@@ -213,15 +228,6 @@ function drupal_get_filename($type, $name, $filename = NULL) {
     $files[$type][$name] = $filename;
   }
   elseif (!isset($files[$type][$name])) {
-    // If the pathname of the requested extension is not known, try to retrieve
-    // the list of extension pathnames from various providers, checking faster
-    // providers first.
-    // Retrieve the current module list (derived from the service container).
-    if ($type == 'module' && \Drupal::hasService('module_handler')) {
-      foreach (\Drupal::moduleHandler()->getModuleList() as $module_name => $module) {
-        $files[$type][$module_name] = $module->getPathname();
-      }
-    }
     // If still unknown, retrieve the file list prepared in state by
     // system_rebuild_module_data() and
     // \Drupal\Core\Extension\ThemeHandlerInterface::rebuildThemeData().
diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index 7a9812f..9c6604c 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -301,12 +301,6 @@ function install_begin_request($class_loader, &$install_state) {
   // Allow command line scripts to override server variables used by Drupal.
   require_once __DIR__ . '/bootstrap.inc';
 
-  // Before having installed the system module and being able to do a module
-  // rebuild, prime the drupal_get_filename() static cache with the module's
-  // exact location.
-  // @todo Remove as part of https://www.drupal.org/node/2186491
-  drupal_get_filename('module', 'system', 'core/modules/system/system.info.yml');
-
   // If the hash salt leaks, it becomes possible to forge a valid testing user
   // agent, install a new copy of Drupal, and take over the original site.
   // The user agent header is used to pass a database prefix in the request when
diff --git a/core/includes/install.inc b/core/includes/install.inc
index 3120799..f35d0f2 100644
--- a/core/includes/install.inc
+++ b/core/includes/install.inc
@@ -615,6 +615,11 @@ function drupal_install_system($install_state) {
   $kernel->rebuildContainer(FALSE);
   $kernel->prepareLegacyRequest($request);
 
+  // Before having installed the system module and being able to do a module
+  // rebuild, prime the ModuleExtensionList static cache with the module's
+  // exact location.
+  \Drupal::service('extension.list.module')->nameSetFilename('system', 'core/modules/system/system.info.yml');
+
   // Install base system configuration.
   \Drupal::service('config.installer')->installDefaultConfig('core', 'core');
 
diff --git a/core/includes/module.inc b/core/includes/module.inc
index bc50d2c..3044815 100644
--- a/core/includes/module.inc
+++ b/core/includes/module.inc
@@ -57,7 +57,7 @@ function system_list($type) {
  */
 function system_list_reset() {
   drupal_static_reset('system_list');
-  drupal_static_reset('system_rebuild_module_data');
+  \Drupal::service('extension.list.module')->reset();
   \Drupal::cache('bootstrap')->delete('system_list');
 }
 
diff --git a/core/lib/Drupal/Core/DrupalKernel.php b/core/lib/Drupal/Core/DrupalKernel.php
index ef0489b..f83bc7c 100644
--- a/core/lib/Drupal/Core/DrupalKernel.php
+++ b/core/lib/Drupal/Core/DrupalKernel.php
@@ -780,7 +780,10 @@ protected function initializeContainer() {
     if (isset($this->container)) {
       // Save the id of the currently logged in user.
       if ($this->container->initialized('current_user')) {
-        $current_user_id = $this->container->get('current_user')->id();
+        /** @var \Drupal\Core\Session\AccountProxyInterface $current_user */
+        $current_user = $this->container->get('current_user');
+        // Ensure to not accidentally initialize the user.
+        $current_user_id = $current_user->hasAccount() ? $current_user->id() : 0;
       }
 
       // If there is a session, close and save it.
diff --git a/core/lib/Drupal/Core/Extension/Extension.php b/core/lib/Drupal/Core/Extension/Extension.php
index 0238714..2c3cf81 100644
--- a/core/lib/Drupal/Core/Extension/Extension.php
+++ b/core/lib/Drupal/Core/Extension/Extension.php
@@ -45,6 +45,13 @@ class Extension implements \Serializable {
   protected $root;
 
   /**
+   * Parsed contents of the *.info.yml file. Stays null until initialized.
+   *
+   * @var array|null
+   */
+  public $info;
+
+  /**
    * Constructs a new Extension object.
    *
    * @param string $root
diff --git a/core/lib/Drupal/Core/Extension/ExtensionDiscovery.php b/core/lib/Drupal/Core/Extension/ExtensionDiscovery.php
index cdee878..cdbd521 100644
--- a/core/lib/Drupal/Core/Extension/ExtensionDiscovery.php
+++ b/core/lib/Drupal/Core/Extension/ExtensionDiscovery.php
@@ -18,7 +18,7 @@
  * to your settings.php.
  *
  */
-class ExtensionDiscovery {
+class ExtensionDiscovery implements ExtensionDiscoveryInterface {
 
   /**
    * Origin directory weight: Core.
diff --git a/core/lib/Drupal/Core/Extension/ExtensionDiscoveryInterface.php b/core/lib/Drupal/Core/Extension/ExtensionDiscoveryInterface.php
new file mode 100644
index 0000000..24af3c8
--- /dev/null
+++ b/core/lib/Drupal/Core/Extension/ExtensionDiscoveryInterface.php
@@ -0,0 +1,58 @@
+<?php
+namespace Drupal\Core\Extension;
+
+/**
+ * Discovers available extensions in the filesystem.
+ *
+ * To also discover test modules, add
+ *
+ * @code
+ * $settings['extension_discovery_scan_tests'] = TRUE;
+ * @encode
+ * to your settings.php.
+ *
+ */
+interface ExtensionDiscoveryInterface {
+
+  /**
+   * Discovers available extensions of a given type.
+   *
+   * Finds all extensions (modules, themes, etc) that exist on the site. It
+   * searches in several locations. For instance, to discover all available
+   * modules:
+   *
+   * @code
+   * $listing = new ExtensionDiscovery(\Drupal::root());
+   * $modules = $listing->scan('module');
+   * @endcode
+   *
+   * The following directories will be searched (in the order stated):
+   * - the core directory; i.e., /core
+   * - the installation profile directory; e.g., /core/profiles/standard
+   * - the legacy site-wide directory; i.e., /sites/all
+   * - the site-wide directory; i.e., /
+   * - the site-specific directory; e.g., /sites/example.com
+   *
+   * To also find test modules, add
+   * @code
+   * $settings['extension_discovery_scan_tests'] = TRUE;
+   * @encode
+   * to your settings.php.
+   *
+   * The information is returned in an associative array, keyed by the extension
+   * name (without .info.yml extension). Extensions found later in the search
+   * will take precedence over extensions found earlier - unless they are not
+   * compatible with the current version of Drupal core.
+   *
+   * @param string $type
+   *   The extension type to search for. One of 'profile', 'module', 'theme', or
+   *   'theme_engine'.
+   * @param bool $include_tests
+   *   (optional) Whether to explicitly include or exclude test extensions. By
+   *   default, test extensions are only discovered when in a test environment.
+   *
+   * @return \Drupal\Core\Extension\Extension[]
+   *   An associative array of Extension objects, keyed by extension name.
+   */
+  public function scan($type, $include_tests = NULL);
+}
diff --git a/core/lib/Drupal/Core/Extension/FilenameList/ExtensionFilenameList.php b/core/lib/Drupal/Core/Extension/FilenameList/ExtensionFilenameList.php
new file mode 100644
index 0000000..1d537ca
--- /dev/null
+++ b/core/lib/Drupal/Core/Extension/FilenameList/ExtensionFilenameList.php
@@ -0,0 +1,40 @@
+<?php
+
+namespace Drupal\Core\Extension\FilenameList;
+
+use Drupal\Core\Extension\List_\ExtensionListInterface;
+
+class ExtensionFilenameList implements ExtensionFilenameListInterface {
+
+  /**
+   * @var \Drupal\Core\Extension\List_\ExtensionListInterface
+   */
+  private $extensionList;
+
+  /**
+   * @param \Drupal\Core\Extension\List_\ExtensionListInterface $extension_list
+   */
+  function __construct(ExtensionListInterface $extension_list) {
+    $this->extensionList = $extension_list;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function reset() {
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFilenames() {
+    $file_names = [];
+    $extensions = $this->extensionList->listExtensions();
+    ksort($extensions);
+    foreach ($extensions as $name => $extension) {
+      $file_names[$name] = $extension->getPathname();
+    }
+    return $file_names;
+  }
+}
diff --git a/core/lib/Drupal/Core/Extension/FilenameList/ExtensionFilenameListBuffer.php b/core/lib/Drupal/Core/Extension/FilenameList/ExtensionFilenameListBuffer.php
new file mode 100644
index 0000000..ab5887b
--- /dev/null
+++ b/core/lib/Drupal/Core/Extension/FilenameList/ExtensionFilenameListBuffer.php
@@ -0,0 +1,41 @@
+<?php
+
+namespace Drupal\Core\Extension\FilenameList;
+
+class ExtensionFilenameListBuffer implements ExtensionFilenameListInterface {
+
+  /**
+   * @var \Drupal\Core\Extension\FilenameList\ExtensionFilenameListInterface
+   */
+  private $decorated;
+
+  /**
+   * @var string[]|null
+   */
+  private $fileNames;
+
+  /**
+   * @param \Drupal\Core\Extension\FilenameList\ExtensionFilenameListInterface $decorated
+   */
+  function __construct(ExtensionFilenameListInterface $decorated) {
+    $this->decorated = $decorated;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function reset() {
+    $this->fileNames = NULL;
+    $this->decorated->reset();
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFilenames() {
+    return $this->fileNames !== NULL
+      ? $this->fileNames
+      : $this->fileNames = $this->decorated->getFilenames();
+  }
+}
diff --git a/core/lib/Drupal/Core/Extension/FilenameList/ExtensionFilenameListCache.php b/core/lib/Drupal/Core/Extension/FilenameList/ExtensionFilenameListCache.php
new file mode 100644
index 0000000..b1da4c3
--- /dev/null
+++ b/core/lib/Drupal/Core/Extension/FilenameList/ExtensionFilenameListCache.php
@@ -0,0 +1,59 @@
+<?php
+
+namespace Drupal\Core\Extension\FilenameList;
+
+use Drupal\Core\Cache\CacheBackendInterface;
+
+/**
+ * Cache decorator for extension file list.
+ */
+class ExtensionFilenameListCache implements ExtensionFilenameListInterface {
+
+  /**
+   * @var \Drupal\Core\Extension\FilenameList\ExtensionFilenameListInterface
+   */
+  private $decorated;
+
+  /**
+   * @var \Drupal\Core\Cache\CacheBackendInterface
+   */
+  private $cache;
+
+  /**
+   * @var string
+   */
+  private $cacheId;
+
+  /**
+   * @param \Drupal\Core\Extension\FilenameList\ExtensionFilenameListInterface $decorated
+   * @param \Drupal\Core\Cache\CacheBackendInterface $cache
+   * @param string $cache_id
+   */
+  function __construct(ExtensionFilenameListInterface $decorated, CacheBackendInterface $cache, $cache_id) {
+    $this->decorated = $decorated;
+    $this->cache = $cache;
+    $this->cacheId = $cache_id;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function reset() {
+    $this->cache->delete($this->cacheId);
+    $this->decorated->reset();
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFilenames() {
+    if ($cache = $this->cache->get($this->cacheId)) {
+      return $cache->data;
+    }
+    // Resolve cache miss.
+    $file_names = $this->decorated->getFilenames();
+    $this->cache->set($this->cacheId, $file_names);
+    return $file_names;
+  }
+}
diff --git a/core/lib/Drupal/Core/Extension/FilenameList/ExtensionFilenameListInterface.php b/core/lib/Drupal/Core/Extension/FilenameList/ExtensionFilenameListInterface.php
new file mode 100644
index 0000000..b2ac3a4
--- /dev/null
+++ b/core/lib/Drupal/Core/Extension/FilenameList/ExtensionFilenameListInterface.php
@@ -0,0 +1,21 @@
+<?php
+
+namespace Drupal\Core\Extension\FilenameList;
+
+interface ExtensionFilenameListInterface {
+
+  /**
+   * Resets cached or buffered extension file names.
+   *
+   * @return $this
+   */
+  public function reset();
+
+  /**
+   * Returns a list of extension folder names keyed by extension name.
+   *
+   * @return string[]
+   */
+  public function getFilenames();
+
+}
diff --git a/core/lib/Drupal/Core/Extension/Hub/ExtensionHub.php b/core/lib/Drupal/Core/Extension/Hub/ExtensionHub.php
new file mode 100644
index 0000000..2e5bd6e
--- /dev/null
+++ b/core/lib/Drupal/Core/Extension/Hub/ExtensionHub.php
@@ -0,0 +1,257 @@
+<?php
+
+namespace Drupal\Core\Extension\Hub;
+
+use Drupal\Core\Cache\CacheBackendInterface;
+use Drupal\Core\Config\ConfigFactoryInterface;
+use Drupal\Core\Extension\ExtensionDiscovery;
+use Drupal\Core\Extension\FilenameList\ExtensionFilenameList;
+use Drupal\Core\Extension\FilenameList\ExtensionFilenameListBuffer;
+use Drupal\Core\Extension\FilenameList\ExtensionFilenameListCache;
+use Drupal\Core\Extension\FilenameList\ExtensionFilenameListInterface;
+use Drupal\Core\Extension\InfoList\ExtensionInfoList;
+use Drupal\Core\Extension\InfoList\ExtensionInfoListBuffer;
+use Drupal\Core\Extension\InfoList\ExtensionInfoListCache;
+use Drupal\Core\Extension\InfoList\ExtensionInfoListInterface;
+use Drupal\Core\Extension\InfoParserInterface;
+use Drupal\Core\Extension\List_\ExtensionListBuffer;
+use Drupal\Core\Extension\List_\ExtensionListCache;
+use Drupal\Core\Extension\List_\ExtensionListInterface;
+use Drupal\Core\Extension\List_\ModuleDiscoveryExtensionList;
+use Drupal\Core\Extension\List_\ProfileDiscoveryExtensionList;
+use Drupal\Core\Extension\ModuleHandlerInterface;
+
+/**
+ * Default implementation for ExtensionHubInterface.
+ */
+class ExtensionHub implements ExtensionHubInterface {
+
+  /**
+   * The type of the extension, such as "module" or "theme".
+   *
+   * @var string
+   */
+  private $type;
+
+  /**
+   * @var \Drupal\Core\Extension\List_\ExtensionListInterface
+   */
+  private $source;
+
+  /**
+   * @var \Drupal\Core\Extension\InfoList\ExtensionInfoListInterface
+   */
+  private $infoList;
+
+  /**
+   * @var \Drupal\Core\Extension\FilenameList\ExtensionFilenameListInterface
+   */
+  private $fileList;
+
+  /**
+   * A list of extension file names directly added in code (not discovered).
+   *
+   * It is important to keep a separate list to ensure that it takes priority
+   * over the discovered extension folders.
+   *
+   * @var string[]
+   */
+  private $addedFileNames = [];
+
+  /**
+   * @param string $root
+   * @param \Drupal\Core\Extension\InfoParserInterface $info_parser
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+   * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
+   * @param \Drupal\Core\Extension\List_\ExtensionListInterface $profile_list
+   *
+   * @param \Drupal\Core\Cache\CacheBackendInterface $cache
+   *
+   * @return \Drupal\Core\Extension\Hub\ExtensionHubInterface
+   */
+  static function createForModules(
+    $root,
+    InfoParserInterface $info_parser,
+    ModuleHandlerInterface $module_handler,
+    ConfigFactoryInterface $config_factory,
+    ExtensionListInterface $profile_list,
+    CacheBackendInterface $cache
+  ) {
+    return self::create(
+      'module',
+      ModuleDiscoveryExtensionList::create(
+        $info_parser,
+        $module_handler,
+        new ExtensionDiscovery($root),
+        $config_factory,
+        $profile_list),
+      $cache);
+  }
+
+  /**
+   * @param $root
+   * @param \Drupal\Core\Extension\InfoParserInterface $info_parser
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+   * @param \Drupal\Core\Cache\CacheBackendInterface $cache
+   *
+   * @return \Drupal\Core\Extension\Hub\ExtensionHubInterface
+   */
+  static function createForProfiles(
+    $root,
+    InfoParserInterface $info_parser,
+    ModuleHandlerInterface $module_handler,
+    CacheBackendInterface $cache
+  ) {
+    return self::create(
+      'profile',
+      ProfileDiscoveryExtensionList::create(
+        $info_parser,
+        $module_handler,
+        new ExtensionDiscovery($root)),
+      $cache);
+  }
+
+  /**
+   * @param string $type
+   * @param \Drupal\Core\Extension\List_\ExtensionListInterface $extension_list
+   * @param \Drupal\Core\Cache\CacheBackendInterface $cache
+   *
+   * @return \Drupal\Core\Extension\Hub\ExtensionHubInterface
+   */
+  static function create(
+    $type,
+    ExtensionListInterface $extension_list,
+    CacheBackendInterface $cache
+  ) {
+
+    $extension_list = new ExtensionListCache($extension_list, $cache, 'core.extension.list.' . $type);
+    $extension_list = new ExtensionListBuffer($extension_list);
+
+    $info_list = new ExtensionInfoList($extension_list);
+    $info_list = new ExtensionInfoListCache($info_list, $cache, "system.$type.info");
+    $info_list = new ExtensionInfoListBuffer($info_list);
+
+    $file_list = new ExtensionFilenameList($extension_list);
+    $file_list = new ExtensionFilenameListCache($file_list, $cache, "system.$type.files");
+    $file_list = new ExtensionFilenameListBuffer($file_list);
+
+    return new self($type, $extension_list, $info_list, $file_list);
+  }
+
+  /**
+   * @param string $type
+   * @param \Drupal\Core\Extension\List_\ExtensionListInterface $source
+   * @param \Drupal\Core\Extension\InfoList\ExtensionInfoListInterface $info_list
+   * @param \Drupal\Core\Extension\FilenameList\ExtensionFilenameListInterface $file_list
+   */
+  function __construct(
+    $type,
+    ExtensionListInterface $source,
+    ExtensionInfoListInterface $info_list,
+    ExtensionFilenameListInterface $file_list
+  ) {
+    $this->type = $type;
+    $this->source = $source;
+    $this->infoList = $info_list;
+    $this->fileList = $file_list;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function reset() {
+    $this->source->reset();
+    $this->infoList->reset();
+    $this->fileList->reset();
+    $this->addedFileNames = NULL;
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function extensionExists($name) {
+    $extensions = $this->listExtensions();
+    return isset($extensions[$name]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function nameGetLabel($machine_name) {
+    return $this->nameGetExtension($machine_name)->info['name'];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function nameGetExtension($name) {
+    $extensions = $this->listExtensions();
+    if (isset($extensions[$name])) {
+      return $extensions[$name];
+    }
+
+    throw new \InvalidArgumentException("The {$this->type} $name does not exist.");
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function listExtensions() {
+    return $this->source->listExtensions();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function nameGetInfo($extension_name) {
+    // Ensure that $this->extensionInfo is primed.
+    $allInfo = $this->getAllInfo();
+    if (isset($allInfo[$extension_name])) {
+      return $allInfo[$extension_name];
+    }
+    throw new \InvalidArgumentException("The {$this->type} $extension_name does not exist.");
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getAllInfo() {
+    return $this->infoList->getAllInfo();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFilenames() {
+    return $this->fileList->getFilenames();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function nameSetFilename($extension_name, $filename) {
+    $this->addedFileNames[$extension_name] = $filename;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function nameGetFilename($extension_name) {
+    if (isset($this->addedFileNames[$extension_name])) {
+      return $this->addedFileNames[$extension_name];
+    }
+    $filenames = $this->getFilenames();
+    if (isset($filenames[$extension_name])) {
+      return $filenames[$extension_name];
+    }
+    throw new \InvalidArgumentException("The {$this->type} $extension_name does not exist.");
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function nameGetPath($extension_name) {
+    return dirname($this->nameGetFilename($extension_name));
+  }
+}
diff --git a/core/lib/Drupal/Core/Extension/Hub/ExtensionHubInterface.php b/core/lib/Drupal/Core/Extension/Hub/ExtensionHubInterface.php
new file mode 100644
index 0000000..5001aac
--- /dev/null
+++ b/core/lib/Drupal/Core/Extension/Hub/ExtensionHubInterface.php
@@ -0,0 +1,144 @@
+<?php
+namespace Drupal\Core\Extension\Hub;
+
+use Drupal\Core\Extension\FilenameList\ExtensionFilenameListInterface;
+use Drupal\Core\Extension\InfoList\ExtensionInfoListInterface;
+use Drupal\Core\Extension\List_\ExtensionListInterface;
+
+/**
+ * Provides various information about available extensions, for a specific
+ * extension type (e.g. 'module', 'theme' or 'profile').
+ */
+interface ExtensionHubInterface extends ExtensionListInterface, ExtensionFilenameListInterface, ExtensionInfoListInterface {
+
+  /**
+   * Resets any stored or buffered data.
+   *
+   * @return $this
+   */
+  public function reset();
+
+  /**
+   * Determines if an extension exists in the filesystem.
+   *
+   * @param string $name
+   *   The machine name of the extension.
+   *
+   * @return bool
+   *   True if the extension exists (whether installed or not) and false if not.
+   */
+  public function extensionExists($name);
+
+  /**
+   * Returns the human readable name of the extension.
+   *
+   * @param string $machine_name
+   *   The extension name.
+   *
+   * @return string
+   *   The human readable name of the extension.
+   *
+   * @throws \InvalidArgumentException
+   *   If there is no extension with the supplied machine name.
+   */
+  public function nameGetLabel($machine_name);
+
+  /**
+   * Returns a single extension.
+   *
+   * @param string $name
+   *   The extension machine name.
+   *
+   * @return \Drupal\Core\Extension\Extension
+   *
+   * @throws \InvalidArgumentException
+   *   If there is no extension with the supplied name.
+   */
+  public function nameGetExtension($name);
+
+  /**
+   * Returns information about a specified extension.
+   *
+   * This function returns the contents of the .info.yml file for the specified
+   * installed extension.
+   *
+   * @param string $extension_name
+   *   The name of an extension whose information shall be returned. If an
+   *   extension with this name does not exist, an exception is thrown.
+   *
+   * @return mixed[]
+   *   An associative array of extension information.
+   *
+   * @throws \InvalidArgumentException
+   *   If there is no extension with the supplied name.
+   */
+  public function nameGetInfo($extension_name);
+
+  /**
+   * Sets the filename for an extension.
+   *
+   * This method is used in the Drupal bootstrapping phase, when the extension
+   * system is not fully initialized, to manually set locations of modules and
+   * profiles needed to complete bootstrapping.
+   *
+   * It is not recommended to call this method except in those rare cases.
+   *
+   * @param string $extension_name
+   *   The name of the extension for which the filename is requested.
+   * @param string $filename
+   *   The filename of the extension which is to be set explicitly rather
+   *   than by consulting the dynamic extension listing.
+   */
+  public function nameSetFilename($extension_name, $filename);
+
+  /**
+   * Gets the filename for a system resource.
+   *
+   * The filename, whether provided, cached, or retrieved from the database, is
+   * only returned if the file exists.
+   *
+   * This function plays a key role in allowing Drupal's extensions (modules,
+   * themes, profiles, theme_engines, etc.) to be located in different places
+   * depending on a site's configuration. For example, a module 'foo' may
+   * legally be located in any of these three places:
+   *
+   * core/modules/foo/foo.info.yml
+   * modules/foo/foo.info.yml
+   * sites/all/modules/foo/foo.info.yml
+   * sites/example.com/modules/foo/foo.info.yml
+   *
+   * while a theme 'bar' may be located in any of similar places:
+   *
+   * core/themes/bar/bar.info.yml
+   * themes/bar/bar.info.yml
+   * sites/all/themes/bar/bar.info.yml
+   * sites/example.com/themes/bar/bar.info.yml
+   *
+   * Calling ExtensionList::getFilename('foo') will give you one of the above,
+   * depending on where the extension is located and what type it is.
+   *
+   * @param string $extension_name
+   *   The name of the extension for which the filename is requested.
+   *
+   * @return string
+   *   The filename of the requested extension's .info.yml file.
+   *
+   * @throws \InvalidArgumentException
+   *   If there is no extension with the supplied name.
+   */
+  public function nameGetFilename($extension_name);
+
+  /**
+   * Gets the path to an extension of a specific type (module, theme, etc.).
+   *
+   * @param string $extension_name
+   *   The name of the extension for which the path is requested.
+   *
+   * @return string
+   *   The drupal-root-relative path to the specified extension.
+   *
+   * @throws \InvalidArgumentException
+   *   If there is no extension with the supplied name.
+   */
+  public function nameGetPath($extension_name);
+}
diff --git a/core/lib/Drupal/Core/Extension/InfoList/ExtensionInfoList.php b/core/lib/Drupal/Core/Extension/InfoList/ExtensionInfoList.php
new file mode 100644
index 0000000..66693da
--- /dev/null
+++ b/core/lib/Drupal/Core/Extension/InfoList/ExtensionInfoList.php
@@ -0,0 +1,38 @@
+<?php
+
+namespace Drupal\Core\Extension\InfoList;
+
+use Drupal\Core\Extension\List_\ExtensionListInterface;
+
+class ExtensionInfoList implements ExtensionInfoListInterface {
+
+  /**
+   * @var \Drupal\Core\Extension\List_\ExtensionListInterface
+   */
+  private $extensionList;
+
+  /**
+   * @param \Drupal\Core\Extension\List_\ExtensionListInterface $extension_list
+   */
+  function __construct(ExtensionListInterface $extension_list) {
+    $this->extensionList = $extension_list;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function reset() {
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getAllInfo() {
+    $info = [];
+    foreach ($this->extensionList->listExtensions() as $name => $extension) {
+      $info[$name] = $extension->info;
+    }
+    return $info;
+  }
+}
diff --git a/core/lib/Drupal/Core/Extension/InfoList/ExtensionInfoListBuffer.php b/core/lib/Drupal/Core/Extension/InfoList/ExtensionInfoListBuffer.php
new file mode 100644
index 0000000..27245d3
--- /dev/null
+++ b/core/lib/Drupal/Core/Extension/InfoList/ExtensionInfoListBuffer.php
@@ -0,0 +1,41 @@
+<?php
+
+namespace Drupal\Core\Extension\InfoList;
+
+class ExtensionInfoListBuffer implements ExtensionInfoListInterface {
+
+  /**
+   * @var \Drupal\Core\Extension\InfoList\ExtensionInfoListInterface
+   */
+  private $decorated;
+
+  /**
+   * @var array[]|null
+   */
+  private $extensionInfo;
+
+  /**
+   * @param \Drupal\Core\Extension\InfoList\ExtensionInfoListInterface $decorated
+   */
+  function __construct(ExtensionInfoListInterface $decorated) {
+    $this->decorated = $decorated;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function reset() {
+    $this->extensionInfo = NULL;
+    $this->decorated->reset();
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getAllInfo() {
+    return $this->extensionInfo !== NULL
+      ? $this->extensionInfo
+      : $this->extensionInfo = $this->decorated->getAllInfo();
+  }
+}
diff --git a/core/lib/Drupal/Core/Extension/InfoList/ExtensionInfoListCache.php b/core/lib/Drupal/Core/Extension/InfoList/ExtensionInfoListCache.php
new file mode 100644
index 0000000..d8458c6
--- /dev/null
+++ b/core/lib/Drupal/Core/Extension/InfoList/ExtensionInfoListCache.php
@@ -0,0 +1,56 @@
+<?php
+
+namespace Drupal\Core\Extension\InfoList;
+
+use Drupal\Core\Cache\CacheBackendInterface;
+
+class ExtensionInfoListCache implements ExtensionInfoListInterface {
+
+  /**
+   * @var \Drupal\Core\Extension\InfoList\ExtensionInfoListInterface
+   */
+  private $decorated;
+
+  /**
+   * @var \Drupal\Core\Cache\CacheBackendInterface
+   */
+  private $cache;
+
+  /**
+   * @var string
+   */
+  private $cache_id;
+
+  /**
+   * @param \Drupal\Core\Extension\InfoList\ExtensionInfoListInterface $decorated
+   * @param \Drupal\Core\Cache\CacheBackendInterface $cache
+   * @param string $cache_id
+   */
+  function __construct(ExtensionInfoListInterface $decorated, CacheBackendInterface $cache, $cache_id) {
+    $this->decorated = $decorated;
+    $this->cache = $cache;
+    $this->cache_id = $cache_id;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function reset() {
+    $this->cache->delete($this->cache_id);
+    $this->decorated->reset();
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getAllInfo() {
+    if ($cache = $this->cache->get($this->cache_id)) {
+      return $cache->data;
+    }
+    // Resolve cache miss.
+    $info = $this->decorated->getAllInfo();
+    $this->cache->set($this->cache_id, $info);
+    return $info;
+  }
+}
diff --git a/core/lib/Drupal/Core/Extension/InfoList/ExtensionInfoListInterface.php b/core/lib/Drupal/Core/Extension/InfoList/ExtensionInfoListInterface.php
new file mode 100644
index 0000000..0c57d93
--- /dev/null
+++ b/core/lib/Drupal/Core/Extension/InfoList/ExtensionInfoListInterface.php
@@ -0,0 +1,26 @@
+<?php
+
+namespace Drupal\Core\Extension\InfoList;
+
+interface ExtensionInfoListInterface {
+
+  /**
+   * Resets cached or buffered extension info.
+   *
+   * @return $this
+   */
+  public function reset();
+
+  /**
+   * Returns an array of information about enabled modules or themes.
+   *
+   * This function returns the contents of the .info.yml file for each installed
+   * extension.
+   *
+   * @return array[]
+   *   An associative array of extension information keyed by name. If no
+   *   records are available, an empty array is returned.
+   */
+  public function getAllInfo();
+
+}
diff --git a/core/lib/Drupal/Core/Extension/List_/DiscoveryExtensionListBase.php b/core/lib/Drupal/Core/Extension/List_/DiscoveryExtensionListBase.php
new file mode 100644
index 0000000..1188ef3
--- /dev/null
+++ b/core/lib/Drupal/Core/Extension/List_/DiscoveryExtensionListBase.php
@@ -0,0 +1,127 @@
+<?php
+
+namespace Drupal\Core\Extension\List_;
+
+use Drupal\Core\Extension\ExtensionDiscovery;
+use Drupal\Core\Extension\InfoParserInterface;
+use Drupal\Core\Extension\ModuleHandlerInterface;
+
+abstract class DiscoveryExtensionListBase implements ExtensionListInterface {
+
+  /**
+   * The type of the extension, such as "module" or "theme".
+   *
+   * @var string
+   */
+  private $type;
+
+  /**
+   * The info parser.
+   *
+   * @var \Drupal\Core\Extension\InfoParserInterface
+   */
+  private $infoParser;
+
+  /**
+   * The module handler.
+   *
+   * @var \Drupal\Core\Extension\ModuleHandlerInterface
+   */
+  protected $moduleHandler;
+
+  /**
+   * The extension discovery service.
+   *
+   * @var \Drupal\Core\Extension\ExtensionDiscovery
+   */
+  protected $extensionDiscovery;
+
+  /**
+   * Default values to be merged into *.info.yml file arrays.
+   *
+   * @var mixed[]
+   */
+  private $defaults;
+
+  /**
+   * Constructs a new DiscoveryExtensionListSource instance.
+   *
+   * @param string $type
+   *   The extension type.
+   * @param \Drupal\Core\Extension\InfoParserInterface $info_parser
+   *   The info parser.
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+   *   The module handler.
+   * @param \Drupal\Core\Extension\ExtensionDiscovery $extension_discovery
+   *   The extension discovery object.
+   * @param array $info_defaults
+   *   Defaults to merge into $extension->info.
+   */
+  public function __construct(
+    $type,
+    InfoParserInterface $info_parser,
+    ModuleHandlerInterface $module_handler,
+    ExtensionDiscovery $extension_discovery,
+    array $info_defaults
+  ) {
+    $this->type = $type;
+    $this->infoParser = $info_parser;
+    $this->moduleHandler = $module_handler;
+    $this->extensionDiscovery = $extension_discovery;
+    $this->defaults = $info_defaults;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function reset() {
+    // Nothing to do.
+  }
+
+  /**
+   * Scans the available extensions.
+   *
+   * Overriding this method gives other code the chance to add additional
+   * extensions to this raw listing.
+   *
+   * @return \Drupal\Core\Extension\Extension[]
+   */
+  protected function doScanExtensions() {
+    return $this->extensionDiscovery->scan($this->type);
+  }
+
+  /**
+   * Returns all available extensions.
+   *
+   * @return \Drupal\Core\Extension\Extension[]
+   *
+   * @throws \Drupal\Core\Extension\InfoParserException
+   *   If one of the .info.yml is broken or incomplete.
+   */
+  public function listExtensions() {
+    // Find extensions.
+    $extensions = $this->doScanExtensions();
+
+    // Read info files for each extension.
+    foreach ($extensions as $name => $extension) {
+      // @todo Clone the extension object, to prevent side effects?
+      
+      // Look for the info file.
+      $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.
+      /** @noinspection PhpUndefinedMethodInspection */
+      $extension->info['mtime'] = $extension->getMTime();
+
+      // Merge in defaults and save.
+      $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.
+      $this->moduleHandler->alter('system_info', $extensions[$name]->info, $extensions[$name], $this->type);
+    }
+
+    return $extensions;
+  }
+}
diff --git a/core/lib/Drupal/Core/Extension/List_/ExtensionListBuffer.php b/core/lib/Drupal/Core/Extension/List_/ExtensionListBuffer.php
new file mode 100644
index 0000000..1132ee9
--- /dev/null
+++ b/core/lib/Drupal/Core/Extension/List_/ExtensionListBuffer.php
@@ -0,0 +1,43 @@
+<?php
+
+namespace Drupal\Core\Extension\List_;
+
+class ExtensionListBuffer implements ExtensionListInterface {
+
+  /**
+   * @var \Drupal\Core\Extension\List_\ExtensionListInterface
+   */
+  private $decorated;
+
+  /**
+   * @var \Drupal\Core\Extension\Extension[]|null
+   */
+  private $extensions;
+
+  /**
+   * @param \Drupal\Core\Extension\List_\ExtensionListInterface $decorated
+   */
+  function __construct(ExtensionListInterface $decorated) {
+    $this->decorated = $decorated;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function reset() {
+    $this->decorated->reset();
+    $this->extensions = NULL;
+    return $this;
+  }
+
+  /**
+   * Returns all available extensions, with $extension->info filled in.
+   *
+   * @return \Drupal\Core\Extension\Extension[]
+   */
+  public function listExtensions() {
+    return NULL !== $this->extensions
+      ? $this->extensions
+      : $this->extensions = $this->decorated->listExtensions();
+  }
+}
diff --git a/core/lib/Drupal/Core/Extension/List_/ExtensionListCache.php b/core/lib/Drupal/Core/Extension/List_/ExtensionListCache.php
new file mode 100644
index 0000000..7e10e9c
--- /dev/null
+++ b/core/lib/Drupal/Core/Extension/List_/ExtensionListCache.php
@@ -0,0 +1,58 @@
+<?php
+
+namespace Drupal\Core\Extension\List_;
+
+use Drupal\Core\Cache\CacheBackendInterface;
+
+class ExtensionListCache implements ExtensionListInterface {
+
+  /**
+   * @var \Drupal\Core\Extension\List_\ExtensionListInterface
+   */
+  private $decorated;
+
+  /**
+   * The cache.
+   *
+   * @var \Drupal\Core\Cache\CacheBackendInterface
+   */
+  private $cache;
+
+  /**
+   * @var string
+   */
+  private $cache_id;
+
+  /**
+   * Constructs a new ExtensionList instance.
+   *
+   * @param \Drupal\Core\Extension\List_\ExtensionListInterface $decorated
+   * @param \Drupal\Core\Cache\CacheBackendInterface $cache
+   * @param string $cache_id
+   */
+  public function __construct(ExtensionListInterface $decorated, CacheBackendInterface $cache, $cache_id) {
+    $this->cache = $cache;
+    $this->decorated = $decorated;
+    $this->cache_id = $cache_id;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function reset() {
+    $this->cache->delete($this->cache_id);
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function listExtensions() {
+    if ($cache = $this->cache->get($this->cache_id)) {
+      return $cache->data;
+    }
+    $extensions = $this->decorated->listExtensions();
+    $this->cache->set($this->cache_id, $extensions);
+    return $extensions;
+  }
+}
diff --git a/core/lib/Drupal/Core/Extension/List_/ExtensionListInterface.php b/core/lib/Drupal/Core/Extension/List_/ExtensionListInterface.php
new file mode 100644
index 0000000..df866c1
--- /dev/null
+++ b/core/lib/Drupal/Core/Extension/List_/ExtensionListInterface.php
@@ -0,0 +1,21 @@
+<?php
+
+namespace Drupal\Core\Extension\List_;
+
+interface ExtensionListInterface {
+
+  /**
+   * Resets any stored or cached extension list.
+   *
+   * @return $this
+   */
+  public function reset();
+
+  /**
+   * Returns all available extensions, with $extension->info filled in.
+   *
+   * @return \Drupal\Core\Extension\Extension[]
+   */
+  public function listExtensions();
+
+}
diff --git a/core/lib/Drupal/Core/Extension/List_/ModuleDiscoveryExtensionList.php b/core/lib/Drupal/Core/Extension/List_/ModuleDiscoveryExtensionList.php
new file mode 100644
index 0000000..b37ce36
--- /dev/null
+++ b/core/lib/Drupal/Core/Extension/List_/ModuleDiscoveryExtensionList.php
@@ -0,0 +1,184 @@
+<?php
+
+namespace Drupal\Core\Extension\List_;
+
+use Drupal\Core\Config\ConfigFactoryInterface;
+use Drupal\Core\Extension\Extension;
+use Drupal\Core\Extension\ExtensionDiscovery;
+use Drupal\Core\Extension\InfoParserInterface;
+use Drupal\Core\Extension\ModuleHandler;
+use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+
+class ModuleDiscoveryExtensionList extends DiscoveryExtensionListBase {
+
+  // @todo Use an injected (lazy/proxy) translation service.
+  use StringTranslationTrait;
+
+  /**
+   * @var \Drupal\Core\Config\ConfigFactoryInterface
+   */
+  private $configFactory;
+
+  /**
+   * @var \Drupal\Core\Extension\List_\ExtensionListInterface
+   */
+  private $profileList;
+
+  /**
+   * @param \Drupal\Core\Extension\InfoParserInterface $info_parser
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+   * @param \Drupal\Core\Extension\ExtensionDiscovery $extension_discovery
+   * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
+   * @param \Drupal\Core\Extension\List_\ExtensionListInterface $profile_list
+   *
+   * @return \Drupal\Core\Extension\List_\ModuleDiscoveryExtensionList
+   */
+  static function create(
+    InfoParserInterface $info_parser,
+    ModuleHandlerInterface $module_handler,
+    ExtensionDiscovery $extension_discovery,
+    ConfigFactoryInterface $config_factory,
+    ExtensionListInterface $profile_list
+  ) {
+    return new self(
+      'module',
+      $info_parser,
+      $module_handler,
+      $extension_discovery,
+      [
+        'dependencies' => [],
+        'description' => '',
+        'package' => 'Other',
+        'version' => NULL,
+        'php' => DRUPAL_MINIMUM_PHP,
+      ],
+      $config_factory,
+      $profile_list);
+  }
+
+  /**
+   * @param string $type
+   * @param \Drupal\Core\Extension\InfoParserInterface $info_parser
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+   * @param \Drupal\Core\Extension\ExtensionDiscovery $extension_discovery
+   * @param array $info_defaults
+   * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
+   * @param \Drupal\Core\Extension\List_\ExtensionListInterface $profile_list
+   */
+  function __construct(
+    $type,
+    InfoParserInterface $info_parser,
+    ModuleHandlerInterface $module_handler,
+    ExtensionDiscovery $extension_discovery,
+    array $info_defaults,
+    ConfigFactoryInterface $config_factory,
+    ExtensionListInterface $profile_list
+  ) {
+    parent::__construct($type, $info_parser, $module_handler, $extension_discovery, $info_defaults);
+
+    $this->configFactory = $config_factory;
+    $this->profileList = $profile_list;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function doScanExtensions() {
+    $extensions = parent::doScanExtensions();
+
+    // Find installation profiles.
+    $profiles = $this->profileList->listExtensions();
+
+    // Include the installation profile in modules that are loaded.
+    if ($profile = drupal_get_profile()) {
+      $extensions[$profile] = $profiles[$profile];
+      // Installation profile hooks are always executed last.
+      $extensions[$profile]->weight = 1000;
+    }
+
+    return $extensions;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function listExtensions() {
+    // Find installation profiles. This needs to happen before performing a
+    // module scan as the module scan needs to know what the active profile is.
+    $profiles = $this->profileList->listExtensions();
+    $profile = drupal_get_profile();
+    if ($profile && isset($profiles[$profile])) {
+      // Set the profile in the ExtensionDiscovery so we can scan from the right
+      // profile directory.
+      $this->extensionDiscovery->setProfileDirectories([
+        $profile => $profiles[$profile]->getPathname(),
+      ]);
+    }
+
+    // Find modules.
+    $extensions = parent::listExtensions();
+    // It is possible that a module was marked as required by
+    // hook_system_info_alter() and modules that it depends on are not required.
+    foreach ($extensions as $extension) {
+      $this->ensureRequiredDependencies($extension, $extensions);
+    }
+
+    if ($profile) {
+      // Installation profiles are hidden by default, unless explicitly
+      // specified otherwise in the .info.yml file.
+      if (!isset($extensions[$profile]->info['hidden'])) {
+        $extensions[$profile]->info['hidden'] = TRUE;
+      }
+
+      if (isset($extensions[$profile])) {
+        // The installation profile is required, if it's a valid module.
+        $extensions[$profile]->info['required'] = TRUE;
+        // Add a default distribution name if the profile did not provide one.
+        // @see install_profile_info()
+        // @see drupal_install_profile_distribution_name()
+        if (!isset($extensions[$profile]->info['distribution']['name'])) {
+          $extensions[$profile]->info['distribution']['name'] = 'Drupal';
+        }
+      }
+    }
+
+    // Add status, weight, and schema version.
+    $installed_modules = $this->configFactory->get('core.extension')->get('module') ?: [];
+    foreach ($extensions as $name => $module) {
+      /** @noinspection PhpUndefinedFieldInspection */
+      $module->weight = isset($installed_modules[$name]) ? $installed_modules[$name] : 0;
+      /** @noinspection PhpUndefinedFieldInspection */
+      $module->status = (int) isset($installed_modules[$name]);
+      /** @noinspection PhpUndefinedFieldInspection */
+      $module->schema_version = SCHEMA_UNINSTALLED;
+    }
+    $extensions = $this->moduleHandler->buildModuleDependencies($extensions);
+
+    return $extensions;
+  }
+
+  /**
+   * Ensures that dependencies of required modules are also required.
+   *
+   * @param \Drupal\Core\Extension\Extension $module
+   *   The module info.
+   * @param \Drupal\Core\Extension\Extension[] $modules
+   *   The array of all module info.
+   */
+  protected function ensureRequiredDependencies(Extension $module, array $modules = []) {
+    if (!empty($module->info['required'])) {
+      foreach ($module->info['dependencies'] as $dependency) {
+        $dependency_name = ModuleHandler::parseDependency($dependency)['name'];
+        if (!isset($modules[$dependency_name]->info['required'])) {
+          $modules[$dependency_name]->info['required'] = TRUE;
+          // @todo Use an injected (lazy/proxy) translation service.
+          $modules[$dependency_name]->info['explanation'] = $this->t('Dependency of required module @module', array('@module' => $module->info['name']));
+          // Ensure any dependencies it has are required.
+          $this->ensureRequiredDependencies($modules[$dependency_name], $modules);
+        }
+      }
+    }
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Extension/List_/ProfileDiscoveryExtensionList.php b/core/lib/Drupal/Core/Extension/List_/ProfileDiscoveryExtensionList.php
new file mode 100644
index 0000000..06d903d
--- /dev/null
+++ b/core/lib/Drupal/Core/Extension/List_/ProfileDiscoveryExtensionList.php
@@ -0,0 +1,37 @@
+<?php
+
+namespace Drupal\Core\Extension\List_;
+
+use Drupal\Core\Extension\ExtensionDiscovery;
+use Drupal\Core\Extension\InfoParserInterface;
+use Drupal\Core\Extension\ModuleHandlerInterface;
+
+class ProfileDiscoveryExtensionList extends DiscoveryExtensionListBase {
+
+  /**
+   * @param \Drupal\Core\Extension\InfoParserInterface $info_parser
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+   * @param \Drupal\Core\Extension\ExtensionDiscovery $extension_discovery
+   *
+   * @return \Drupal\Core\Extension\List_\ExtensionListInterface
+   */
+  static function create(
+    InfoParserInterface $info_parser,
+    ModuleHandlerInterface $module_handler,
+    ExtensionDiscovery $extension_discovery
+  ) {
+    return new self(
+      'profile',
+      $info_parser,
+      $module_handler,
+      $extension_discovery,
+      [
+        'dependencies' => [],
+        'description' => '',
+        'package' => 'Other',
+        'version' => NULL,
+        'php' => DRUPAL_MINIMUM_PHP,
+      ]);
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Extension/ModuleHandler.php b/core/lib/Drupal/Core/Extension/ModuleHandler.php
index 8ea10ad..5316166 100644
--- a/core/lib/Drupal/Core/Extension/ModuleHandler.php
+++ b/core/lib/Drupal/Core/Extension/ModuleHandler.php
@@ -717,8 +717,7 @@ public function getModuleDirectories() {
    * {@inheritdoc}
    */
   public function getName($module) {
-    $info = system_get_info('module', $module);
-    return isset($info['name']) ? $info['name'] : $module;
+    return \Drupal::service('extension.list.module')->nameGetLabel($module);
   }
 
 }
diff --git a/core/lib/Drupal/Core/Extension/ModuleHandlerInterface.php b/core/lib/Drupal/Core/Extension/ModuleHandlerInterface.php
index 124efa2..b04a22c 100644
--- a/core/lib/Drupal/Core/Extension/ModuleHandlerInterface.php
+++ b/core/lib/Drupal/Core/Extension/ModuleHandlerInterface.php
@@ -306,6 +306,9 @@ public function getModuleDirectories();
    * @return string
    *   Returns the human readable name of the module or the machine name passed
    *   in if no matching module is found.
+   *
+   * @deprecated in Drupal 8.2.0, will be removed before Drupal 9.0.0.
+   *   Use \Drupal::service('extension.list.module')->nameGetLabel() instead.
    */
   public function getName($module);
 
diff --git a/core/lib/Drupal/Core/Extension/ModuleInstaller.php b/core/lib/Drupal/Core/Extension/ModuleInstaller.php
index a903b8a..e2ba5ab 100644
--- a/core/lib/Drupal/Core/Extension/ModuleInstaller.php
+++ b/core/lib/Drupal/Core/Extension/ModuleInstaller.php
@@ -166,7 +166,7 @@ public function install(array $module_list, $enable_dependencies = TRUE) {
             $module_filenames[$name] = $current_module_filenames[$name];
           }
           else {
-            $module_path = drupal_get_path('module', $name);
+            $module_path = \Drupal::service('extension.list.module')->nameGetPath($name);
             $pathname = "$module_path/$name.info.yml";
             $filename = file_exists($module_path . "/$name.module") ? "$name.module" : NULL;
             $module_filenames[$name] = new Extension($this->root, 'module', $pathname, $filename);
@@ -182,10 +182,10 @@ public function install(array $module_list, $enable_dependencies = TRUE) {
         $this->moduleHandler->load($module);
         module_load_install($module);
 
-        // Clear the static cache of system_rebuild_module_data() to pick up the
-        // new module, since it merges the installation status of modules into
-        // its statically cached list.
-        drupal_static_reset('system_rebuild_module_data');
+        // Clear the static cache of the "extension.list.module" service to pick
+        // up the new module, since it merges the installation status of modules
+        // into its statically cached list.
+        \Drupal::service('extension.list.module')->reset();
 
         // Update the kernel to include it.
         $this->updateKernel($module_filenames);
@@ -437,10 +437,10 @@ public function uninstall(array $module_list, $uninstall_dependents = TRUE) {
       // Remove any potential cache bins provided by the module.
       $this->removeCacheBins($module);
 
-      // Clear the static cache of system_rebuild_module_data() to pick up the
-      // new module, since it merges the installation status of modules into
-      // its statically cached list.
-      drupal_static_reset('system_rebuild_module_data');
+      // Clear the static cache of the "extension.list.module" service to pick
+      // up the new module, since it merges the installation status of modules
+      // into its statically cached list.
+      \Drupal::service('extension.list.module')->reset();
 
       // Clear plugin manager caches.
       \Drupal::getContainer()->get('plugin.cache_clearer')->clearCachedDefinitions();
diff --git a/core/lib/Drupal/Core/Session/AccountProxy.php b/core/lib/Drupal/Core/Session/AccountProxy.php
index a50a289..7c48619 100644
--- a/core/lib/Drupal/Core/Session/AccountProxy.php
+++ b/core/lib/Drupal/Core/Session/AccountProxy.php
@@ -45,6 +45,13 @@ public function setAccount(AccountInterface $account) {
   /**
    * {@inheritdoc}
    */
+  public function hasAccount() {
+    return isset($this->account);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public function getAccount() {
     if (!isset($this->account)) {
       if ($this->initialAccountId) {
diff --git a/core/lib/Drupal/Core/Session/AccountProxyInterface.php b/core/lib/Drupal/Core/Session/AccountProxyInterface.php
index 378b89d..b7525aa 100644
--- a/core/lib/Drupal/Core/Session/AccountProxyInterface.php
+++ b/core/lib/Drupal/Core/Session/AccountProxyInterface.php
@@ -6,6 +6,7 @@
  * Defines an interface for a service which has the current account stored.
  *
  * @ingroup user_api
+ * @internal
  */
 interface AccountProxyInterface extends AccountInterface {
 
@@ -43,4 +44,12 @@ public function getAccount();
    */
   public function setInitialAccountId($account_id);
 
+  /**
+   * Checks whether an account is currently wrapped.
+   *
+   * @return bool
+   *   TRUE, if an account is currently wrapped. FALSE otherwise.
+   */
+  public function hasAccount();
+
 }
diff --git a/core/lib/Drupal/Core/Updater/Module.php b/core/lib/Drupal/Core/Updater/Module.php
index c7cbb7f..4258c90 100644
--- a/core/lib/Drupal/Core/Updater/Module.php
+++ b/core/lib/Drupal/Core/Updater/Module.php
@@ -49,8 +49,7 @@ public static function getRootDirectoryRelativePath() {
   public function isInstalled() {
     // Check if the module exists in the file system, regardless of whether it
     // is enabled or not.
-    $modules = \Drupal::state()->get('system.module.files', array());
-    return isset($modules[$this->name]);
+    return \Drupal::service('extension.list.module')->extensionExists($this->name);
   }
 
   /**
diff --git a/core/modules/book/tests/src/Kernel/BookUninstallTest.php b/core/modules/book/tests/src/Kernel/BookUninstallTest.php
index bcd0812..17f1803 100644
--- a/core/modules/book/tests/src/Kernel/BookUninstallTest.php
+++ b/core/modules/book/tests/src/Kernel/BookUninstallTest.php
@@ -76,7 +76,7 @@ public function testBookUninstall() {
 
     $book_node->delete();
     // No nodes exist therefore the book module is not required.
-    $module_data = _system_rebuild_module_data();
+    $module_data = \Drupal::service('extension.list.module')->reset()->listExtensions();
     $this->assertFalse(isset($module_data['book']->info['required']), 'The book module is not required.');
 
     $node = Node::create(array('title' => $this->randomString(), 'type' => $content_type->id()));
diff --git a/core/modules/config/src/Tests/ConfigImportAllTest.php b/core/modules/config/src/Tests/ConfigImportAllTest.php
index a7623a9..402133a 100644
--- a/core/modules/config/src/Tests/ConfigImportAllTest.php
+++ b/core/modules/config/src/Tests/ConfigImportAllTest.php
@@ -97,7 +97,7 @@ public function testInstallUninstall() {
 
     // Ensure that only core required modules and the install profile can not be uninstalled.
     $validation_reasons = \Drupal::service('module_installer')->validateUninstall(array_keys($all_modules));
-    $this->assertEqual(['standard', 'system', 'user'], array_keys($validation_reasons));
+    $this->assertEqual(['system', 'user', 'standard'], array_keys($validation_reasons));
 
     $modules_to_uninstall = array_filter($all_modules, function ($module) use ($validation_reasons) {
       // Filter required and not enabled modules.
diff --git a/core/modules/filter/tests/src/Kernel/FilterAPITest.php b/core/modules/filter/tests/src/Kernel/FilterAPITest.php
index 49dde8a..485fba7 100644
--- a/core/modules/filter/tests/src/Kernel/FilterAPITest.php
+++ b/core/modules/filter/tests/src/Kernel/FilterAPITest.php
@@ -485,7 +485,7 @@ public function testDependencyRemoval() {
 
     drupal_static_reset('filter_formats');
     \Drupal::entityManager()->getStorage('filter_format')->resetCache();
-    $module_data = _system_rebuild_module_data();
+    $module_data = \Drupal::service('extension.list.module')->reset()->listExtensions();
     $this->assertFalse(isset($module_data['filter_test']->info['required']), 'The filter_test module is required.');
 
     // Verify that a dependency exists on the module that provides the filter
diff --git a/core/modules/simpletest/src/KernelTestBase.php b/core/modules/simpletest/src/KernelTestBase.php
index 7714259..519d273 100644
--- a/core/modules/simpletest/src/KernelTestBase.php
+++ b/core/modules/simpletest/src/KernelTestBase.php
@@ -100,7 +100,7 @@ function __construct($test_id = NULL) {
   protected function beforePrepareEnvironment() {
     // Copy/prime extension file lists once to avoid filesystem scans.
     if (!isset($this->moduleFiles)) {
-      $this->moduleFiles = \Drupal::state()->get('system.module.files') ?: array();
+      $this->moduleFiles = \Drupal::cache('default')->get('system.module.files') ?: array();
       $this->themeFiles = \Drupal::state()->get('system.theme.files') ?: array();
     }
   }
@@ -222,7 +222,7 @@ protected function setUp() {
     // Re-inject extension file listings into state, unless the key/value
     // service was overridden (in which case its storage does not exist yet).
     if ($this->container->get('keyvalue') instanceof KeyValueMemoryFactory) {
-      $this->container->get('state')->set('system.module.files', $this->moduleFiles);
+      $this->container->get('cache.default')->set('system.module.files', $this->moduleFiles);
       $this->container->get('state')->set('system.theme.files', $this->themeFiles);
     }
 
diff --git a/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php b/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php
index 9d5ef09..2c92f74 100644
--- a/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php
+++ b/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php
@@ -21,8 +21,6 @@ function testDrupalGetFilename() {
     $install_state['parameters']['profile'] = 'testing';
 
     // Rebuild system.module.files state data.
-    // @todo Remove as part of https://www.drupal.org/node/2186491
-    drupal_static_reset('system_rebuild_module_data');
     system_rebuild_module_data();
 
     // Retrieving the location of a module.
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 3033a11..b286e37 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -915,27 +915,15 @@ function system_check_directory($form_element, FormStateInterface $form_state) {
  */
 function system_get_info($type, $name = NULL) {
   if ($type == 'module') {
-    $info = &drupal_static(__FUNCTION__);
-    if (!isset($info)) {
-      if ($cache = \Drupal::cache()->get('system.module.info')) {
-        $info = $cache->data;
-      }
-      else {
-        $data = system_rebuild_module_data();
-        foreach (\Drupal::moduleHandler()->getModuleList() as $module => $filename) {
-          if (isset($data[$module])) {
-            $info[$module] = $data[$module]->info;
-          }
-        }
-        // Store the module information in cache. This cache is cleared by
-        // calling system_rebuild_module_data(), for example, when listing
-        // modules, (un)installing modules, importing configuration, updating
-        // the site and when flushing all the caches.
-        \Drupal::cache()->set('system.module.info', $info);
-      }
+    if (isset($name)) {
+      return \Drupal::service('extension.list.module')->nameGetInfo($name);
+    }
+    else {
+      return \Drupal::service('extension.list.module')->getAllInfo();
     }
   }
   else {
+    // @todo move into ThemeExtensionList https://www.drupal.org/node/2659940
     $info = array();
     $list = system_list($type);
     foreach ($list as $shortname => $item) {
@@ -943,11 +931,11 @@ function system_get_info($type, $name = NULL) {
         $info[$shortname] = $item->info;
       }
     }
+    if (isset($name)) {
+      return isset($info[$name]) ? $info[$name] : array();
+    }
+    return $info;
   }
-  if (isset($name)) {
-    return isset($info[$name]) ? $info[$name] : array();
-  }
-  return $info;
 }
 
 /**
@@ -957,105 +945,7 @@ function system_get_info($type, $name = NULL) {
  *   An associative array of module information.
  */
 function _system_rebuild_module_data() {
-  $listing = new ExtensionDiscovery(\Drupal::root());
-
-  // Find installation profiles. This needs to happen before performing a
-  // module scan as the module scan requires knowing what the active profile is.
-  // @todo Remove as part of https://www.drupal.org/node/2186491.
-  $profiles = $listing->scan('profile');
-  $profile = drupal_get_profile();
-  if ($profile && isset($profiles[$profile])) {
-    // Prime the drupal_get_filename() static cache with the profile info file
-    // location so we can use drupal_get_path() on the active profile during
-    // the module scan.
-    // @todo Remove as part of https://www.drupal.org/node/2186491.
-    drupal_get_filename('profile', $profile, $profiles[$profile]->getPathname());
-  }
-
-  // Find modules.
-  $modules = $listing->scan('module');
-  // Include the installation profile in modules that are loaded.
-  if ($profile) {
-    $modules[$profile] = $profiles[$profile];
-    // Installation profile hooks are always executed last.
-    $modules[$profile]->weight = 1000;
-  }
-
-  // Set defaults for module info.
-  $defaults = array(
-    'dependencies' => array(),
-    'description' => '',
-    'package' => 'Other',
-    'version' => NULL,
-    'php' => DRUPAL_MINIMUM_PHP,
-  );
-
-  // Read info files for each module.
-  foreach ($modules as $key => $module) {
-    // Look for the info file.
-    $module->info = \Drupal::service('info_parser')->parse($module->getPathname());
-
-    // Add the info file modification time, so it becomes available for
-    // contributed modules to use for ordering module lists.
-    $module->info['mtime'] = $module->getMTime();
-
-    // Merge in defaults and save.
-    $modules[$key]->info = $module->info + $defaults;
-
-    // Installation profiles are hidden by default, unless explicitly specified
-    // otherwise in the .info.yml file.
-    if ($key == $profile && !isset($modules[$key]->info['hidden'])) {
-      $modules[$key]->info['hidden'] = TRUE;
-    }
-
-    // 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 $module->getType().
-    $type = 'module';
-    \Drupal::moduleHandler()->alter('system_info', $modules[$key]->info, $modules[$key], $type);
-  }
-
-  // It is possible that a module was marked as required by
-  // hook_system_info_alter() and modules that it depends on are not required.
-  foreach ($modules as $module) {
-    _system_rebuild_module_data_ensure_required($module, $modules);
-  }
-
-
-  if ($profile && isset($modules[$profile])) {
-    // The installation profile is required, if it's a valid module.
-    $modules[$profile]->info['required'] = TRUE;
-    // Add a default distribution name if the profile did not provide one.
-    // @see install_profile_info()
-    // @see drupal_install_profile_distribution_name()
-    if (!isset($modules[$profile]->info['distribution']['name'])) {
-      $modules[$profile]->info['distribution']['name'] = 'Drupal';
-    }
-  }
-
-  return $modules;
-}
-
-/**
- * Ensures that dependencies of required modules are also required.
- *
- * @param \Drupal\Core\Extension\Extension $module
- *   The module info.
- * @param \Drupal\Core\Extension\Extension[] $modules
- *   The array of all module info.
- */
-function _system_rebuild_module_data_ensure_required($module, &$modules) {
-  if (!empty($module->info['required'])) {
-    foreach ($module->info['dependencies'] as $dependency) {
-      $dependency_name = ModuleHandler::parseDependency($dependency)['name'];
-      if (!isset($modules[$dependency_name]->info['required'])) {
-        $modules[$dependency_name]->info['required'] = TRUE;
-        $modules[$dependency_name]->info['explanation'] = t('Dependency of required module @module', array('@module' => $module->info['name']));
-        // Ensure any dependencies it has are required.
-        _system_rebuild_module_data_ensure_required($modules[$dependency_name], $modules);
-      }
-    }
-  }
+  return \Drupal::service('extension.list.module')->reset()->listExtensions();
 }
 
 /**
@@ -1065,33 +955,7 @@ function _system_rebuild_module_data_ensure_required($module, &$modules) {
  *   Array of all available modules and their data.
  */
 function system_rebuild_module_data() {
-  $modules_cache = &drupal_static(__FUNCTION__);
-  // Only rebuild once per request. $modules and $modules_cache cannot be
-  // combined into one variable, because the $modules_cache variable is reset by
-  // reference from system_list_reset() during the rebuild.
-  if (!isset($modules_cache)) {
-    $modules = _system_rebuild_module_data();
-    $files = array();
-    ksort($modules);
-    // Add status, weight, and schema version.
-    $installed_modules = \Drupal::config('core.extension')->get('module') ?: array();
-    foreach ($modules as $name => $module) {
-      $module->weight = isset($installed_modules[$name]) ? $installed_modules[$name] : 0;
-      $module->status = (int) isset($installed_modules[$name]);
-      $module->schema_version = SCHEMA_UNINSTALLED;
-      $files[$name] = $module->getPathname();
-    }
-    $modules = \Drupal::moduleHandler()->buildModuleDependencies($modules);
-    $modules_cache = $modules;
-
-    // Store filenames to allow drupal_get_filename() to retrieve them without
-    // having to rebuild or scan the filesystem.
-    \Drupal::state()->set('system.module.files', $files);
-    // Clear the module info cache.
-    \Drupal::cache()->delete('system.module.info');
-    drupal_static_reset('system_get_info');
-  }
-  return $modules_cache;
+  return \Drupal::service('extension.list.module')->reset()->listExtensions();
 }
 
 /**
diff --git a/core/modules/system/tests/src/Kernel/Extension/ModuleHandlerTest.php b/core/modules/system/tests/src/Kernel/Extension/ModuleHandlerTest.php
index d691beb..b4154d0 100644
--- a/core/modules/system/tests/src/Kernel/Extension/ModuleHandlerTest.php
+++ b/core/modules/system/tests/src/Kernel/Extension/ModuleHandlerTest.php
@@ -115,7 +115,7 @@ function testDependencyResolution() {
     // Color will depend on Config, which depends on a non-existing module Foo.
     // Nothing should be installed.
     \Drupal::state()->set('module_test.dependency', 'missing dependency');
-    drupal_static_reset('system_rebuild_module_data');
+    \Drupal::service('extension.list.module')->reset();
 
     try {
       $result = $this->moduleInstaller()->install(array('color'));
@@ -130,7 +130,7 @@ function testDependencyResolution() {
     // Fix the missing dependency.
     // Color module depends on Config. Config depends on Help module.
     \Drupal::state()->set('module_test.dependency', 'dependency');
-    drupal_static_reset('system_rebuild_module_data');
+    \Drupal::service('extension.list.module')->reset();
 
     $result = $this->moduleInstaller()->install(array('color'));
     $this->assertTrue($result, 'ModuleHandler::install() returns the correct value.');
@@ -162,7 +162,7 @@ function testDependencyResolution() {
     // dependency on a specific version of Help module in its info file. Make
     // sure that Drupal\Core\Extension\ModuleHandler::install() still works.
     \Drupal::state()->set('module_test.dependency', 'version dependency');
-    drupal_static_reset('system_rebuild_module_data');
+    \Drupal::service('extension.list.module')->reset();
 
     $result = $this->moduleInstaller()->install(array('color'));
     $this->assertTrue($result, 'ModuleHandler::install() returns the correct value.');
@@ -192,8 +192,7 @@ function testUninstallProfileDependency() {
     drupal_get_filename('profile', $profile, 'core/profiles/' . $profile . '/' . $profile . '.info.yml');
     $this->enableModules(array('module_test', $profile));
 
-    drupal_static_reset('system_rebuild_module_data');
-    $data = system_rebuild_module_data();
+    $data = \Drupal::service('extension.list.module')->reset()->listExtensions();
     $this->assertTrue(isset($data[$profile]->requires[$dependency]));
 
     $this->moduleInstaller()->install(array($dependency));
@@ -231,7 +230,7 @@ function testUninstallContentDependency() {
     // entity_test will depend on help. This way help can not be uninstalled
     // when there is test content preventing entity_test from being uninstalled.
     \Drupal::state()->set('module_test.dependency', 'dependency');
-    drupal_static_reset('system_rebuild_module_data');
+    \Drupal::service('extension.list.module')->reset();
 
     // Create an entity so that the modules can not be disabled.
     $entity = EntityTest::create(array('name' => $this->randomString()));
diff --git a/core/tests/Drupal/Tests/Core/Extension/ExtensionHubTest.php b/core/tests/Drupal/Tests/Core/Extension/ExtensionHubTest.php
new file mode 100644
index 0000000..198996a
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Extension/ExtensionHubTest.php
@@ -0,0 +1,237 @@
+<?php
+
+namespace Drupal\Tests\Core\Extension;
+
+use Drupal\Component\Serialization\Yaml;
+use Drupal\Core\Cache\CacheBackendInterface;
+use Drupal\Core\Extension\Extension;
+use Drupal\Core\Extension\ExtensionDiscovery;
+use Drupal\Core\Extension\Hub\ExtensionHub;
+use Drupal\Core\Extension\InfoParserInterface;
+use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\Extension\List_\DiscoveryExtensionListBase;
+use Drupal\Tests\UnitTestCase;
+use org\bovigo\vfs\vfsStream;
+use Prophecy\Argument;
+
+/**
+ * @coversDefaultClass \Drupal\Core\Extension\Hub\ExtensionHub
+ * @group Extension
+ */
+class ExtensionHubTest extends UnitTestCase {
+
+  /**
+   * @covers ::nameGetLabel
+   * @expectedException \InvalidArgumentException
+   */
+  public function testGetNameWithNonExistingExtension() {
+    $test_extension_hub = $this->setupEmptyTestExtensionHub();
+
+    $test_extension_hub->nameGetLabel('test_name');
+  }
+
+  /**
+   * @covers ::nameGetLabel
+   */
+  public function testGetName() {
+    $test_extension_hub = $this->setupTestExtensionHub();
+
+    static::assertEquals('test name', $test_extension_hub->nameGetLabel('test_name'));
+  }
+
+  /**
+   * @covers ::nameGetExtension
+   * @expectedException \InvalidArgumentException
+   */
+  public function testGetExtensionWithNonExistingExtension() {
+    $test_extension_hub = $this->setupEmptyTestExtensionHub();
+
+    $test_extension_hub->nameGetExtension('test_name');
+  }
+
+  /**
+   * @covers ::nameGetExtension
+   */
+  public function testGetExtension() {
+    $test_extension_hub = $this->setupTestExtensionHub();
+
+    $extension = $test_extension_hub->nameGetExtension('test_name');
+    static::assertInstanceOf(Extension::class, $extension);
+    static::assertEquals('test_name', $extension->getName());
+  }
+
+  /**
+   * @covers ::listExtensions
+   */
+  public function testListExtensions() {
+    $test_extension_list = $this->setupTestExtensionHub();
+
+    $extensions = $test_extension_list->listExtensions();
+    static::assertCount(1, $extensions);
+    static::assertEquals('test_name', $extensions['test_name']->getName());
+  }
+
+  /**
+   * @covers ::nameGetInfo
+   * @covers ::getAllInfo
+   */
+  public function testGetInfo() {
+    $test_extension_list = $this->setupTestExtensionHub();
+
+    $info = $test_extension_list->nameGetInfo('test_name');
+    static::assertEquals([
+      'type' => 'test_extension',
+      'core' => '8.x',
+      'name' => 'test name',
+      'mtime' => 123456789,
+    ], $info);
+  }
+
+  /**
+   * @covers ::getAllInfo
+   */
+  public function testGetAllInfo() {
+    $test_extension_list = $this->setupTestExtensionHub();
+
+    $infos = $test_extension_list->getAllInfo();
+    static::assertEquals(['test_name' => [
+      'type' => 'test_extension',
+      'core' => '8.x',
+      'name' => 'test name',
+      'mtime' => 123456789,
+    ]], $infos);
+  }
+
+  /**
+   * @covers ::getFilenames
+   */
+  public function testGetFilenames() {
+    $test_extension_list = $this->setupTestExtensionHub();
+
+    $filenames = $test_extension_list->getFilenames();
+    static::assertEquals([
+      'test_name' => 'vfs://drupal_root/example/test_name/test_name.info.yml',
+    ], $filenames);
+  }
+
+  /**
+   * @covers ::nameGetFilename
+   */
+  public function testGetFilename() {
+    $test_extension_list = $this->setupTestExtensionHub();
+
+    $filename = $test_extension_list->nameGetFilename('test_name');
+    static::assertEquals('vfs://drupal_root/example/test_name/test_name.info.yml', $filename);
+  }
+
+
+  /**
+   * @covers ::nameSetFilename
+   * @covers ::nameGetFilename
+   */
+  public function testSetFilename() {
+    $test_extension_list = $this->setupTestExtensionHub();
+
+    $test_extension_list->nameSetFilename('test_name', 'vfs://drupal_root/example2/test_name/test_name.info.yml');
+    static::assertEquals('vfs://drupal_root/example2/test_name/test_name.info.yml', $test_extension_list->nameGetFilename('test_name'));
+  }
+
+  /**
+   * @covers ::nameGetPath
+   */
+  public function testGetPath() {
+    $test_extension_list = $this->setupTestExtensionHub();
+
+    $path = $test_extension_list->nameGetPath('test_name');
+    static::assertEquals('vfs://drupal_root/example/test_name', $path);
+  }
+
+  /**
+   * @return \Drupal\Core\Extension\Hub\ExtensionHubInterface
+   */
+  protected function setupEmptyTestExtensionHub() {
+    list($cache, $info_parser, $module_handler) = $this->getMocks();
+
+    $extension_discovery = $this->prophesize(ExtensionDiscovery::class);
+    $extension_discovery->scan('test_extension')->willReturn([]);
+
+    return ExtensionHub::create(
+      'test_extension',
+      TestExtensionList::create(
+        'test_extension',
+        $info_parser->reveal(),
+        $module_handler->reveal(),
+        $extension_discovery->reveal()),
+      $cache->reveal());
+  }
+
+  /**
+   * @return \Drupal\Core\Extension\Hub\ExtensionHubInterface
+   */
+  protected function setupTestExtensionHub() {
+    vfsStream::setup('drupal_root');
+    vfsStream::create([
+      'example' => [
+        'test_name' => [
+          'test_name.info.yml' => Yaml::encode([
+            'name' => 'test name',
+            'type' => 'test_extension',
+            'core' => '8.x',
+          ]),
+        ],
+      ],
+    ]);
+    touch('vfs://drupal_root/example/test_name/test_name.info.yml', 123456789);
+
+    list($cache, $info_parser, $module_handler) = $this->getMocks();
+    $info_parser->parse(Argument::any())->will(function($args) {
+      return Yaml::decode(file_get_contents($args[0]));
+    });
+
+    $extension_discovery = $this->prophesize(ExtensionDiscovery::class);
+    $extension_discovery->scan('test_extension')->willReturn(['test_name' => new Extension($this->root, 'test_extension', 'vfs://drupal_root/example/test_name/test_name.info.yml')]);
+
+    return ExtensionHub::create(
+      'test_extension',
+      TestExtensionList::create(
+        'test_extension',
+        $info_parser->reveal(),
+        $module_handler->reveal(),
+        $extension_discovery->reveal()),
+      $cache->reveal());
+  }
+
+  protected function getMocks() {
+    $cache = $this->prophesize(CacheBackendInterface::class);
+    $info_parser = $this->prophesize(InfoParserInterface::class);
+    $module_handler = $this->prophesize(ModuleHandlerInterface::class);
+    return [$cache, $info_parser, $module_handler];
+  }
+
+}
+
+class TestExtensionList extends DiscoveryExtensionListBase {
+
+  /**
+   * @param string $type
+   * @param \Drupal\Core\Extension\InfoParserInterface $info_parser
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+   * @param \Drupal\Core\Extension\ExtensionDiscovery $extension_discovery
+   *
+   * @return \Drupal\Core\Extension\List_\ExtensionListInterface
+   */
+  static function create(
+    $type,
+    InfoParserInterface $info_parser,
+    ModuleHandlerInterface $module_handler,
+    ExtensionDiscovery $extension_discovery
+  ) {
+    return new self(
+      $type,
+      $info_parser,
+      $module_handler,
+      $extension_discovery,
+      []);
+  }
+
+}