diff --git a/core/includes/common.inc b/core/includes/common.inc
index 03af03bbb5dc923dc8f8f77f31923eaedf847143..feceb5bbe6be6bd71f760a6d761032717fdec749 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -14,6 +14,7 @@
 use Drupal\Component\Utility\SortArray;
 use Drupal\Component\Utility\UrlHelper;
 use Drupal\Core\Cache\Cache;
+use Drupal\Core\Render\Element\Link;
 use Drupal\Core\Render\Markup;
 use Drupal\Core\StringTranslation\TranslatableMarkup;
 use Drupal\Core\PhpStorage\PhpStorageFactory;
@@ -748,7 +749,7 @@ function drupal_clear_js_cache() {
  *   Use \Drupal\Core\Render\Element\Link::preRenderLink().
  */
 function drupal_pre_render_link($element) {
-  return Element\Link::preRenderLink($element);
+  return Link::preRenderLink($element);
 }
 
 /**
diff --git a/core/includes/form.inc b/core/includes/form.inc
index c110c5b316a9060862e45eebd0862900f6a55bcf..06a806be9e621dba0d15a33b1b9312966295836a 100644
--- a/core/includes/form.inc
+++ b/core/includes/form.inc
@@ -7,6 +7,7 @@
 
 use Drupal\Component\Utility\UrlHelper;
 use Drupal\Core\Render\Element;
+use Drupal\Core\Render\Element\RenderElement;
 use Drupal\Core\Template\Attribute;
 use Drupal\Core\Url;
 use Symfony\Component\HttpFoundation\RedirectResponse;
@@ -29,7 +30,7 @@
 function template_preprocess_select(&$variables) {
   $element = $variables['element'];
   Element::setAttributes($element, array('id', 'name', 'size'));
-  Element\RenderElement::setAttributes($element, array('form-select'));
+  RenderElement::setAttributes($element, array('form-select'));
 
   $variables['attributes'] = $element['#attributes'];
   $variables['options'] = form_select_options($element);
@@ -191,7 +192,7 @@ function form_get_options($element, $key) {
 function template_preprocess_fieldset(&$variables) {
   $element = $variables['element'];
   Element::setAttributes($element, array('id'));
-  Element\RenderElement::setAttributes($element);
+  RenderElement::setAttributes($element);
   $variables['attributes'] = isset($element['#attributes']) ? $element['#attributes'] : array();
   $variables['prefix'] = isset($element['#field_prefix']) ? $element['#field_prefix'] : NULL;
   $variables['suffix'] = isset($element['#field_suffix']) ? $element['#field_suffix'] : NULL;
@@ -376,7 +377,7 @@ function template_preprocess_form(&$variables) {
 function template_preprocess_textarea(&$variables) {
   $element = $variables['element'];
   Element::setAttributes($element, array('id', 'name', 'rows', 'cols', 'placeholder'));
-  Element\RenderElement::setAttributes($element, array('form-textarea'));
+  RenderElement::setAttributes($element, array('form-textarea'));
   $variables['wrapper_attributes'] = new Attribute();
   $variables['attributes'] = new Attribute($element['#attributes']);
   $variables['value'] = $element['#value'];
diff --git a/core/lib/Drupal/Core/DrupalKernel.php b/core/lib/Drupal/Core/DrupalKernel.php
index bc693cde7761c0d9ae50fc0cc4ac9f2f2e4fece9..2df00f114e7725a6f9277960a68e536eac5fb4a2 100644
--- a/core/lib/Drupal/Core/DrupalKernel.php
+++ b/core/lib/Drupal/Core/DrupalKernel.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\Core;
 
+use Drupal\Component\Assertion\Handle;
 use Drupal\Component\FileCache\FileCacheFactory;
 use Drupal\Component\Utility\Unicode;
 use Drupal\Component\Utility\UrlHelper;
@@ -18,6 +19,7 @@
 use Drupal\Core\Language\Language;
 use Drupal\Core\Site\Settings;
 use Symfony\Cmf\Component\Routing\RouteObjectInterface;
+use Symfony\Component\ClassLoader\ApcClassLoader;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\DependencyInjection\ParameterBag\ParameterBag;
 use Symfony\Component\HttpFoundation\RedirectResponse;
@@ -923,7 +925,7 @@ public static function bootEnvironment() {
         assert_options(ASSERT_ACTIVE, TRUE);
         // Now synchronize PHP 5 and 7's handling of assertions as much as
         // possible.
-        \Drupal\Component\Assertion\Handle::register();
+        Handle::register();
 
         // Log fatal errors to the test site directory.
         ini_set('log_errors', 1);
@@ -978,7 +980,7 @@ protected function initializeSettings(Request $request) {
         && Settings::get('class_loader_auto_detect', TRUE)
         && extension_loaded('apc')) {
       $prefix = Settings::getApcuPrefix('class_loader', $this->root);
-      $apc_loader = new \Symfony\Component\ClassLoader\ApcClassLoader($prefix, $this->classLoader);
+      $apc_loader = new ApcClassLoader($prefix, $this->classLoader);
       $this->classLoader->unregister();
       $apc_loader->register();
       $this->classLoader = $apc_loader;
diff --git a/core/lib/Drupal/Core/PageCache/DefaultRequestPolicy.php b/core/lib/Drupal/Core/PageCache/DefaultRequestPolicy.php
index 731f22ff251209fde5dfe96590cf69399b09cce8..4616d989b1f11a573f12a59e1d33c3cbb8778e16 100644
--- a/core/lib/Drupal/Core/PageCache/DefaultRequestPolicy.php
+++ b/core/lib/Drupal/Core/PageCache/DefaultRequestPolicy.php
@@ -2,6 +2,8 @@
 
 namespace Drupal\Core\PageCache;
 
+use Drupal\Core\PageCache\RequestPolicy\CommandLineOrUnsafeMethod;
+use Drupal\Core\PageCache\RequestPolicy\NoSessionOpen;
 use Drupal\Core\Session\SessionConfigurationInterface;
 
 /**
@@ -20,8 +22,8 @@ class DefaultRequestPolicy extends ChainRequestPolicy {
    *   The session configuration.
    */
   public function __construct(SessionConfigurationInterface $session_configuration) {
-    $this->addPolicy(new RequestPolicy\CommandLineOrUnsafeMethod());
-    $this->addPolicy(new RequestPolicy\NoSessionOpen($session_configuration));
+    $this->addPolicy(new CommandLineOrUnsafeMethod());
+    $this->addPolicy(new NoSessionOpen($session_configuration));
   }
 
 }
diff --git a/core/modules/aggregator/src/Tests/ItemCacheTagsTest.php b/core/modules/aggregator/src/Tests/ItemCacheTagsTest.php
index 46a5df7ad05c28d5238b0d22885d7298d1a49e5d..1986ceaf5867f1c1e9c31fe5dcae21a16d8d42fa 100644
--- a/core/modules/aggregator/src/Tests/ItemCacheTagsTest.php
+++ b/core/modules/aggregator/src/Tests/ItemCacheTagsTest.php
@@ -4,6 +4,7 @@
 
 use Drupal\aggregator\Entity\Feed;
 use Drupal\aggregator\Entity\Item;
+use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\system\Tests\Entity\EntityCacheTagsTestBase;
 use Drupal\user\Entity\Role;
 use Drupal\user\RoleInterface;
@@ -63,7 +64,7 @@ protected function createEntity() {
    */
   public function testEntityCreation() {
     // Create a cache entry that is tagged with a feed cache tag.
-    \Drupal::cache('render')->set('foo', 'bar', \Drupal\Core\Cache\CacheBackendInterface::CACHE_PERMANENT, $this->entity->getCacheTags());
+    \Drupal::cache('render')->set('foo', 'bar', CacheBackendInterface::CACHE_PERMANENT, $this->entity->getCacheTags());
 
     // Verify a cache hit.
     $this->verifyRenderCache('foo', array('aggregator_feed:1'));
diff --git a/core/modules/big_pipe/src/Tests/BigPipePlaceholderTestCases.php b/core/modules/big_pipe/src/Tests/BigPipePlaceholderTestCases.php
index 45958444b3f42681799a0f52fd0399ea88fef842..1cf10d4dc14257c221918b347c913d50891e05b0 100644
--- a/core/modules/big_pipe/src/Tests/BigPipePlaceholderTestCases.php
+++ b/core/modules/big_pipe/src/Tests/BigPipePlaceholderTestCases.php
@@ -9,6 +9,7 @@
 
 use Drupal\big_pipe\Render\BigPipeMarkup;
 use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\StringTranslation\PluralTranslatableMarkup;
 use Drupal\Core\Url;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
@@ -93,7 +94,7 @@ public static function cases(ContainerInterface $container = NULL, AccountInterf
               'theme' => 'classy',
               'libraries' => 'big_pipe/big_pipe,classy/base,classy/messages,core/drupal.active-link,core/html5shiv,core/normalize,system/base',
             ],
-            'pluralDelimiter' => \Drupal\Core\StringTranslation\PluralTranslatableMarkup::DELIMITER,
+            'pluralDelimiter' => PluralTranslatableMarkup::DELIMITER,
             'user' => [
               'uid' => '1',
               'permissionsHash' => $container->get('user_permissions_hash_generator')->generate($user),
diff --git a/core/modules/big_pipe/src/Tests/BigPipeTest.php b/core/modules/big_pipe/src/Tests/BigPipeTest.php
index 9ae960b636510c6c346b1884a1919fc8196e4fea..f947c46bdcf9cc99bea371e34d53ce3c0ca36dad 100644
--- a/core/modules/big_pipe/src/Tests/BigPipeTest.php
+++ b/core/modules/big_pipe/src/Tests/BigPipeTest.php
@@ -361,7 +361,7 @@ protected function getTestCases() {
     $csrf_token_seed = unserialize(explode('_sf2_meta|', $session_data)[1])['s'];
     $this->container->get('session_manager.metadata_bag')->setCsrfTokenSeed($csrf_token_seed);
 
-    return \Drupal\big_pipe\Tests\BigPipePlaceholderTestCases::cases($this->container, $this->rootUser);
+    return BigPipePlaceholderTestCases::cases($this->container, $this->rootUser);
   }
 
   /**
diff --git a/core/modules/big_pipe/tests/modules/big_pipe_test/src/BigPipeTestController.php b/core/modules/big_pipe/tests/modules/big_pipe_test/src/BigPipeTestController.php
index 2ac5a99372ae59474ede7288a35d51479495eda9..450a464bd467eaea40db3657e74535e68a9ed5db 100644
--- a/core/modules/big_pipe/tests/modules/big_pipe_test/src/BigPipeTestController.php
+++ b/core/modules/big_pipe/tests/modules/big_pipe_test/src/BigPipeTestController.php
@@ -3,6 +3,7 @@
 namespace Drupal\big_pipe_test;
 
 use Drupal\big_pipe\Render\BigPipeMarkup;
+use Drupal\big_pipe\Tests\BigPipePlaceholderTestCases;
 use Drupal\big_pipe_test\EventSubscriber\BigPipeTestSubscriber;
 
 class BigPipeTestController {
@@ -15,7 +16,7 @@ class BigPipeTestController {
   public function test() {
     $build = [];
 
-    $cases = \Drupal\big_pipe\Tests\BigPipePlaceholderTestCases::cases(\Drupal::getContainer());
+    $cases = BigPipePlaceholderTestCases::cases(\Drupal::getContainer());
 
     // 1. HTML placeholder: status messages. Drupal renders those automatically,
     // so all that we need to do in this controller is set a message.
diff --git a/core/modules/big_pipe/tests/src/Unit/Render/Placeholder/BigPipeStrategyTest.php b/core/modules/big_pipe/tests/src/Unit/Render/Placeholder/BigPipeStrategyTest.php
index 9806fbf6454d0582d71f01e92dc0a2879553b850..f0f40ba29d771e91082bbca127bf9e89e3c40b3c 100644
--- a/core/modules/big_pipe/tests/src/Unit/Render/Placeholder/BigPipeStrategyTest.php
+++ b/core/modules/big_pipe/tests/src/Unit/Render/Placeholder/BigPipeStrategyTest.php
@@ -3,6 +3,7 @@
 namespace Drupal\Tests\big_pipe\Unit\Render\Placeholder;
 
 use Drupal\big_pipe\Render\Placeholder\BigPipeStrategy;
+use Drupal\big_pipe\Tests\BigPipePlaceholderTestCases;
 use Drupal\Core\Routing\RouteMatchInterface;
 use Drupal\Core\Session\SessionConfigurationInterface;
 use Drupal\Tests\UnitTestCase;
@@ -61,7 +62,7 @@ public function testProcessPlaceholders(array $placeholders, $method, $route_mat
    * @see \Drupal\big_pipe\Tests\BigPipePlaceholderTestCases
    */
   public function placeholdersProvider() {
-    $cases = \Drupal\big_pipe\Tests\BigPipePlaceholderTestCases::cases();
+    $cases = BigPipePlaceholderTestCases::cases();
 
     // Generate $placeholders variable as expected by
     // \Drupal\Core\Render\Placeholder\PlaceholderStrategyInterface::processPlaceholders().
diff --git a/core/modules/comment/src/Tests/CommentCacheTagsTest.php b/core/modules/comment/src/Tests/CommentCacheTagsTest.php
index e0e84c85810e2f6d303d1a3c374adee6308dad9f..3c7ab009638b192430ac68d94b03f3d22c1733fd 100644
--- a/core/modules/comment/src/Tests/CommentCacheTagsTest.php
+++ b/core/modules/comment/src/Tests/CommentCacheTagsTest.php
@@ -82,7 +82,7 @@ protected function createEntity() {
       'entity_id' => $this->entityTestCamelid->id(),
       'entity_type' => 'entity_test',
       'field_name' => 'comment',
-      'status' => \Drupal\comment\CommentInterface::PUBLISHED,
+      'status' => CommentInterface::PUBLISHED,
     ));
     $comment->save();
 
diff --git a/core/modules/config/tests/config_install_dependency_test/config_install_dependency_test.module b/core/modules/config/tests/config_install_dependency_test/config_install_dependency_test.module
index 08a169762a7f10cba637098b344d552e260dabf6..fbf11e5dabf6ad732da0dc2d2569c9cb6d63d0a6 100644
--- a/core/modules/config/tests/config_install_dependency_test/config_install_dependency_test.module
+++ b/core/modules/config/tests/config_install_dependency_test/config_install_dependency_test.module
@@ -5,10 +5,12 @@
  * Provides hook implementations for testing purposes.
  */
 
+use Drupal\Core\Entity\EntityInterface;
+
 /**
  * Implements hook_ENTITY_TYPE_create.
  */
-function config_install_dependency_test_config_test_create(\Drupal\Core\Entity\EntityInterface $entity) {
+function config_install_dependency_test_config_test_create(EntityInterface $entity) {
   // Add an enforced dependency on this module so that we can test if this is
   // possible during module installation.
   $entity->setEnforcedDependencies(['module' => ['config_install_dependency_test']]);
diff --git a/core/modules/contact/tests/modules/contact_storage_test/contact_storage_test.module b/core/modules/contact/tests/modules/contact_storage_test/contact_storage_test.module
index 0ecfee574a2107ee803694a27150d458b2f469e6..e20dc436fccd9d0a2255dad365f6fb2cd5b71baf 100644
--- a/core/modules/contact/tests/modules/contact_storage_test/contact_storage_test.module
+++ b/core/modules/contact/tests/modules/contact_storage_test/contact_storage_test.module
@@ -6,13 +6,14 @@
  */
 
 use Drupal\contact\ContactFormInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
 use Drupal\Core\Field\BaseFieldDefinition;
 use Drupal\Core\Form\FormStateInterface;
 
 /**
  * Implements hook_entity_base_field_info().
  */
-function contact_storage_test_entity_base_field_info(\Drupal\Core\Entity\EntityTypeInterface $entity_type) {
+function contact_storage_test_entity_base_field_info(EntityTypeInterface $entity_type) {
   if ($entity_type->id() == 'contact_message') {
     $fields = array();
 
diff --git a/core/modules/field/field.module b/core/modules/field/field.module
index 3f507747138b723ec6861d517ed90cf528d29c12..5fb3ae37f554d9a74c51ca9c31cceedc25373f2a 100644
--- a/core/modules/field/field.module
+++ b/core/modules/field/field.module
@@ -7,6 +7,7 @@
 use Drupal\Core\Config\ConfigImporter;
 use Drupal\Core\Entity\EntityTypeInterface;
 use Drupal\Core\Entity\DynamicallyFieldableEntityStorageInterface;
+use Drupal\field\ConfigImporterFieldPurger;
 use Drupal\field\Entity\FieldConfig;
 use Drupal\field\Entity\FieldStorageConfig;
 use Drupal\field\FieldConfigInterface;
@@ -168,7 +169,7 @@ function field_cron() {
 /**
  * Implements hook_entity_field_storage_info().
  */
-function field_entity_field_storage_info(\Drupal\Core\Entity\EntityTypeInterface $entity_type) {
+function field_entity_field_storage_info(EntityTypeInterface $entity_type) {
   if (\Drupal::entityManager()->getStorage($entity_type->id()) instanceof DynamicallyFieldableEntityStorageInterface) {
     // Query by filtering on the ID as this is more efficient than filtering
     // on the entity_type property directly.
@@ -301,7 +302,7 @@ function _field_create_entity_from_ids($ids) {
  * Implements hook_config_import_steps_alter().
  */
 function field_config_import_steps_alter(&$sync_steps, ConfigImporter $config_importer) {
-  $field_storages = \Drupal\field\ConfigImporterFieldPurger::getFieldStoragesToPurge(
+  $field_storages = ConfigImporterFieldPurger::getFieldStoragesToPurge(
     $config_importer->getStorageComparer()->getSourceStorage()->read('core.extension'),
     $config_importer->getStorageComparer()->getChangelist('delete')
   );
@@ -327,7 +328,7 @@ function field_form_config_admin_import_form_alter(&$form, FormStateInterface $f
   $user_input = $form_state->getUserInput();
   $storage_comparer = $form_state->get('storage_comparer');
   if ($storage_comparer && empty($user_input)) {
-    $field_storages = \Drupal\field\ConfigImporterFieldPurger::getFieldStoragesToPurge(
+    $field_storages = ConfigImporterFieldPurger::getFieldStoragesToPurge(
       $storage_comparer->getSourceStorage()->read('core.extension'),
       $storage_comparer->getChangelist('delete')
     );
diff --git a/core/modules/field/tests/fixtures/update/drupal-8.views_entity_reference_plugins-2429191.php b/core/modules/field/tests/fixtures/update/drupal-8.views_entity_reference_plugins-2429191.php
index ca7c51a1db7443bc1c744490ed46c0268b5e4a5d..4ad0a7779646d85d3184319f973e18395c2da95c 100644
--- a/core/modules/field/tests/fixtures/update/drupal-8.views_entity_reference_plugins-2429191.php
+++ b/core/modules/field/tests/fixtures/update/drupal-8.views_entity_reference_plugins-2429191.php
@@ -8,6 +8,7 @@
 
 use Drupal\Core\Database\Database;
 use Drupal\Component\Serialization\Yaml;
+use Drupal\field\Entity\FieldStorageConfig;
 
 $connection = Database::getConnection();
 
@@ -59,8 +60,8 @@
   ->execute()
   ->fetchField();
 $installed = unserialize($installed);
-$installed['field_ref_views_select_2429191'] = new \Drupal\field\Entity\FieldStorageConfig($field_ref_views_select_2429191);
-$installed['field_ref_autocreate_2412569'] = new \Drupal\field\Entity\FieldStorageConfig($field_ref_autocreate_2412569);
+$installed['field_ref_views_select_2429191'] = new FieldStorageConfig($field_ref_views_select_2429191);
+$installed['field_ref_autocreate_2412569'] = new FieldStorageConfig($field_ref_autocreate_2412569);
 $connection->update('key_value')
   ->condition('collection', 'entity.definitions.installed')
   ->condition('name', 'node.field_storage_definitions')
diff --git a/core/modules/field/tests/modules/field_test/field_test.module b/core/modules/field/tests/modules/field_test/field_test.module
index 9c994d6f758d45aac0e266ef52a33017281de50a..7eda28852726b3dee56e5a51d727c47cf88bdef3 100644
--- a/core/modules/field/tests/modules/field_test/field_test.module
+++ b/core/modules/field/tests/modules/field_test/field_test.module
@@ -13,8 +13,9 @@
  * test helper functions
  */
 
-use Drupal\field\FieldStorageConfigInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
 use Drupal\Core\Form\FormStateInterface;
+use Drupal\field\FieldStorageConfigInterface;
 
 require_once __DIR__ . '/field_test.entity.inc';
 require_once __DIR__ . '/field_test.field.inc';
@@ -149,7 +150,7 @@ function field_test_entity_extra_field_info_alter(&$info) {
 /**
  * Implements hook_entity_bundle_field_info_alter().
  */
-function field_test_entity_bundle_field_info_alter(&$fields, \Drupal\Core\Entity\EntityTypeInterface $entity_type, $bundle) {
+function field_test_entity_bundle_field_info_alter(&$fields, EntityTypeInterface $entity_type, $bundle) {
   if (($field_name = \Drupal::state()->get('field_test_set_constraint', FALSE)) && $entity_type->id() == 'entity_test' && $bundle == 'entity_test' && !empty($fields[$field_name])) {
     $fields[$field_name]->setPropertyConstraints('value', [
       'Range' => [
diff --git a/core/modules/field/tests/modules/field_third_party_test/field_third_party_test.module b/core/modules/field/tests/modules/field_third_party_test/field_third_party_test.module
index ac0ce1cbfc9583294d1ea877a9cf92c0169698c4..9dc2b1936304fea6d02701c5d5956cad4eb23d55 100644
--- a/core/modules/field/tests/modules/field_third_party_test/field_third_party_test.module
+++ b/core/modules/field/tests/modules/field_third_party_test/field_third_party_test.module
@@ -5,12 +5,15 @@
  * Test module.
  */
 
+use Drupal\Core\Field\FieldDefinitionInterface;
+use Drupal\Core\Field\FormatterInterface;
+use Drupal\Core\Field\WidgetInterface;
 use Drupal\Core\Form\FormStateInterface;
 
 /**
  * Implements hook_field_widget_third_party_settings_form().
  */
-function field_third_party_test_field_widget_third_party_settings_form(\Drupal\Core\Field\WidgetInterface $plugin, \Drupal\Core\Field\FieldDefinitionInterface $field_definition, $form_mode, $form, FormStateInterface $form_state) {
+function field_third_party_test_field_widget_third_party_settings_form(WidgetInterface $plugin, FieldDefinitionInterface $field_definition, $form_mode, $form, FormStateInterface $form_state) {
   $element['field_test_widget_third_party_settings_form'] = array(
     '#type' => 'textfield',
     '#title' => t('3rd party widget settings form'),
@@ -30,7 +33,7 @@ function field_third_party_test_field_widget_settings_summary_alter(&$summary, $
 /**
  * Implements hook_field_formatter_third_party_settings_form().
  */
-function field_third_party_test_field_formatter_third_party_settings_form(\Drupal\Core\Field\FormatterInterface $plugin, \Drupal\Core\Field\FieldDefinitionInterface $field_definition, $view_mode, $form, FormStateInterface $form_state) {
+function field_third_party_test_field_formatter_third_party_settings_form(FormatterInterface $plugin, FieldDefinitionInterface $field_definition, $view_mode, $form, FormStateInterface $form_state) {
   $element['field_test_field_formatter_third_party_settings_form'] = array(
     '#type' => 'textfield',
     '#title' => t('3rd party formatter settings form'),
diff --git a/core/modules/filter/tests/src/Kernel/FilterAPITest.php b/core/modules/filter/tests/src/Kernel/FilterAPITest.php
index 49dde8ae17b55296b18b2dc57896c83bb07bf652..0f9feff4f570348144f1c7b5c2a793eb41258018 100644
--- a/core/modules/filter/tests/src/Kernel/FilterAPITest.php
+++ b/core/modules/filter/tests/src/Kernel/FilterAPITest.php
@@ -207,7 +207,7 @@ function testFilterFormatAPI() {
     // Test on nonsensical_restricted_html, where the allowed attribute values
     // contain asterisks, which do not have any meaning, but which we also
     // cannot prevent because configuration can be modified outside of forms.
-    $nonsensical_restricted_html = \Drupal\filter\Entity\FilterFormat::create(array(
+    $nonsensical_restricted_html = FilterFormat::create(array(
       'format' => 'nonsensical_restricted_html',
       'name' => 'Nonsensical Restricted HTML',
       'filters' => array(
@@ -468,7 +468,7 @@ public function assertFilterFormatViolation(ConstraintViolationListInterface $vi
    */
   public function testDependencyRemoval() {
     $this->installSchema('user', array('users_data'));
-    $filter_format = \Drupal\filter\Entity\FilterFormat::load('filtered_html');
+    $filter_format = FilterFormat::load('filtered_html');
 
     // Disable the filter_test_restrict_tags_and_attributes filter plugin but
     // have custom configuration so that the filter plugin is still configured
@@ -498,7 +498,7 @@ public function testDependencyRemoval() {
     // Verify the filter format still exists but the dependency and filter is
     // gone.
     \Drupal::entityManager()->getStorage('filter_format')->resetCache();
-    $filter_format = \Drupal\filter\Entity\FilterFormat::load('filtered_html');
+    $filter_format = FilterFormat::load('filtered_html');
     $this->assertEqual([], $filter_format->getDependencies());
     // Use the get method since the FilterFormat::filters() method only returns
     // existing plugins.
diff --git a/core/modules/forum/forum.module b/core/modules/forum/forum.module
index 3722c45414cd2124ecaca1043acbc61c261ef4bc..42d5349f353f3905aff5c7bb439d57704e865fa3 100644
--- a/core/modules/forum/forum.module
+++ b/core/modules/forum/forum.module
@@ -8,6 +8,7 @@
 use Drupal\comment\CommentInterface;
 use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
 use Drupal\Core\Url;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Routing\RouteMatchInterface;
@@ -134,7 +135,7 @@ function forum_uri($forum) {
 /**
  * Implements hook_entity_bundle_field_info_alter().
  */
-function forum_entity_bundle_field_info_alter(&$fields, \Drupal\Core\Entity\EntityTypeInterface $entity_type, $bundle) {
+function forum_entity_bundle_field_info_alter(&$fields, EntityTypeInterface $entity_type, $bundle) {
   if ($entity_type->id() == 'node'  && !empty($fields['taxonomy_forums'])) {
     $fields['taxonomy_forums']->addConstraint('ForumLeaf', []);
   }
diff --git a/core/modules/locale/locale.bulk.inc b/core/modules/locale/locale.bulk.inc
index 72e8cfe47713d8c5118cfe029a592eba40ca58f6..1181b50f270a3010d7398da16c6c28921a3eaf0d 100644
--- a/core/modules/locale/locale.bulk.inc
+++ b/core/modules/locale/locale.bulk.inc
@@ -340,7 +340,7 @@ function locale_translate_batch_refresh(&$context) {
     // Clear cache and force refresh of JavaScript translations.
     _locale_refresh_translations($context['sandbox']['refresh']['languages'], $next);
     // Check whether we need to refresh configuration objects.
-    if ($names = \Drupal\locale\Locale::config()->getStringNames($next)) {
+    if ($names = Locale::config()->getStringNames($next)) {
       $context['sandbox']['refresh']['names_finished'] = $context['finished'];
       $context['sandbox']['refresh']['names'] = $names;
     }
@@ -533,7 +533,7 @@ function locale_translate_delete_translation_files(array $projects = array(), ar
  */
 function locale_config_batch_update_components(array $options, array $langcodes = array(), array $components = array()) {
   $langcodes = $langcodes ? $langcodes : array_keys(\Drupal::languageManager()->getLanguages());
-  if ($langcodes && $names = \Drupal\locale\Locale::config()->getComponentNames($components)) {
+  if ($langcodes && $names = Locale::config()->getComponentNames($components)) {
     return locale_config_batch_build($names, $langcodes, $options);
   }
 }
diff --git a/core/modules/locale/tests/src/Kernel/LocaleConfigSubscriberTest.php b/core/modules/locale/tests/src/Kernel/LocaleConfigSubscriberTest.php
index ee756584eaef60e4261f6f9e12e4516c06bc09e3..013a9ea21742a323c2ebbfc9e5ae2a7881c0e742 100644
--- a/core/modules/locale/tests/src/Kernel/LocaleConfigSubscriberTest.php
+++ b/core/modules/locale/tests/src/Kernel/LocaleConfigSubscriberTest.php
@@ -67,7 +67,7 @@ protected function setUp() {
     // @see locale_system_update()
     locale_system_set_config_langcodes();
     $langcodes = array_keys(\Drupal::languageManager()->getLanguages());
-    $names = \Drupal\locale\Locale::config()->getComponentNames();
+    $names = Locale::config()->getComponentNames();
     Locale::config()->updateConfigTranslations($names, $langcodes);
 
     $this->configFactory = $this->container->get('config.factory');
diff --git a/core/modules/node/tests/modules/node_access_test/node_access_test.module b/core/modules/node/tests/modules/node_access_test/node_access_test.module
index e195ea8993cd2888e4a26dd49858786002e76baa..56b53a92bd3c7149c879e59a0645ac80599e16bd 100644
--- a/core/modules/node/tests/modules/node_access_test/node_access_test.module
+++ b/core/modules/node/tests/modules/node_access_test/node_access_test.module
@@ -19,6 +19,7 @@
  * @see \Drupal\node\Tests\NodeAccessBaseTableTest
  */
 
+use Drupal\Core\Session\AccountInterface;
 use Drupal\Core\Access\AccessResult;
 use Drupal\field\Entity\FieldStorageConfig;
 use Drupal\field\Entity\FieldConfig;
@@ -144,7 +145,7 @@ function node_access_test_add_field(NodeTypeInterface $type) {
 /**
  * Implements hook_node_access().
  */
-function node_access_test_node_access(\Drupal\node\NodeInterface $node, $op, \Drupal\Core\Session\AccountInterface $account) {
+function node_access_test_node_access(NodeInterface $node, $op, AccountInterface $account) {
   $secret_catalan = \Drupal::state()
     ->get('node_access_test_secret_catalan') ?: 0;
   if ($secret_catalan && $node->language()->getId() == 'ca') {
diff --git a/core/modules/node/tests/modules/node_test/node_test.module b/core/modules/node/tests/modules/node_test/node_test.module
index aa7d4dd694635fd5e648c5539c6eba475c21e8aa..ab1777ea1d8804118c23f20c6a63a3f210613ea7 100644
--- a/core/modules/node/tests/modules/node_test/node_test.module
+++ b/core/modules/node/tests/modules/node_test/node_test.module
@@ -8,6 +8,7 @@
  * interaction with the Node module.
  */
 
+use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\Display\EntityViewDisplayInterface;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\node\NodeInterface;
@@ -151,7 +152,7 @@ function node_test_node_update(NodeInterface $node) {
 /**
  * Implements hook_entity_view_mode_alter().
  */
-function node_test_entity_view_mode_alter(&$view_mode, Drupal\Core\Entity\EntityInterface $entity, $context) {
+function node_test_entity_view_mode_alter(&$view_mode, EntityInterface $entity, $context) {
   // Only alter the view mode if we are on the test callback.
   $change_view_mode = \Drupal::state()->get( 'node_test_change_view_mode') ?: '';
   if ($change_view_mode) {
diff --git a/core/modules/node/tests/src/Kernel/NodeFieldOverridesTest.php b/core/modules/node/tests/src/Kernel/NodeFieldOverridesTest.php
index 2160621d52f4ba217ddbafe7e8e2e8b30483fc86..aee02728ec884da87c831c1904b1789e4352ed6c 100644
--- a/core/modules/node/tests/src/Kernel/NodeFieldOverridesTest.php
+++ b/core/modules/node/tests/src/Kernel/NodeFieldOverridesTest.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\Tests\node\Kernel;
 
+use Drupal\user\UserInterface;
 use Drupal\Core\Field\Entity\BaseFieldOverride;
 use Drupal\KernelTests\Core\Entity\EntityKernelTestBase;
 use Drupal\node\Entity\Node;
@@ -56,7 +57,7 @@ public function testFieldOverrides() {
     /** @var \Drupal\node\NodeInterface $node */
     $node = Node::create(['type' => 'ponies']);
     $owner = $node->getOwner();
-    $this->assertTrue($owner instanceof \Drupal\user\UserInterface);
+    $this->assertTrue($owner instanceof UserInterface);
     $this->assertEqual($owner->id(), $this->user->id());
   }
 
diff --git a/core/modules/responsive_image/responsive_image.module b/core/modules/responsive_image/responsive_image.module
index 7df1da81a9f63cd8ff637108fa664cfb607eee8a..89ac37f4903e6ed6f395313abb6645f3b746616b 100644
--- a/core/modules/responsive_image/responsive_image.module
+++ b/core/modules/responsive_image/responsive_image.module
@@ -5,6 +5,8 @@
  * Responsive image display formatter for image fields.
  */
 
+use Drupal\Core\Template\Attribute;
+use Drupal\Core\Logger\RfcLogLevel;
 use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Routing\RouteMatchInterface;
 use Drupal\image\Entity\ImageStyle;
@@ -162,7 +164,7 @@ function template_preprocess_responsive_image(&$variables) {
   // execution.
   if (!$responsive_image_style) {
     $variables['img_element'] = [];
-    \Drupal::logger('responsive_image')->log(\Drupal\Core\Logger\RfcLogLevel::ERROR, 'Failed to load responsive image style: “@style“ while displaying responsive image.', ['@style' => $variables['responsive_image_style_id']]);
+    \Drupal::logger('responsive_image')->log(RfcLogLevel::ERROR, 'Failed to load responsive image style: “@style“ while displaying responsive image.', ['@style' => $variables['responsive_image_style_id']]);
     return;
   }
   // Retrieve all breakpoints and multipliers and reverse order of breakpoints.
@@ -411,7 +413,7 @@ function responsive_image_build_source_attributes(ImageInterface $image, array $
   }
   // Sort the srcset from small to large image width or multiplier.
   ksort($srcset);
-  $source_attributes = new \Drupal\Core\Template\Attribute(array(
+  $source_attributes = new Attribute(array(
     'srcset' => implode(', ', array_unique($srcset)),
   ));
   $media_query = trim($breakpoint->getMediaQuery());
@@ -494,7 +496,7 @@ function _responsive_image_image_style_url($style_name, $path) {
     return 'data:image/gif;base64,R0lGODlhAQABAIABAP///wAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==';
   }
   $entity = ImageStyle::load($style_name);
-  if ($entity instanceof Drupal\image\Entity\ImageStyle) {
+  if ($entity instanceof ImageStyle) {
     return file_url_transform_relative($entity->buildUrl($path));
   }
   return file_url_transform_relative(file_create_url($path));
diff --git a/core/modules/shortcut/src/Tests/ShortcutCacheTagsTest.php b/core/modules/shortcut/src/Tests/ShortcutCacheTagsTest.php
index 8fdd86cb7173007c658a5c94663fe33bc26d4d83..a437ffb0102641b1de0cac24fcbb799743d0a1ec 100644
--- a/core/modules/shortcut/src/Tests/ShortcutCacheTagsTest.php
+++ b/core/modules/shortcut/src/Tests/ShortcutCacheTagsTest.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\shortcut\Tests;
 
+use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\shortcut\Entity\Shortcut;
 use Drupal\system\Tests\Entity\EntityCacheTagsTestBase;
 use Drupal\user\Entity\Role;
@@ -55,7 +56,7 @@ protected function createEntity() {
   public function testEntityCreation() {
     // Create a cache entry that is tagged with a shortcut set cache tag.
     $cache_tags = ['config:shortcut.set.default'];
-    \Drupal::cache('render')->set('foo', 'bar', \Drupal\Core\Cache\CacheBackendInterface::CACHE_PERMANENT, $cache_tags);
+    \Drupal::cache('render')->set('foo', 'bar', CacheBackendInterface::CACHE_PERMANENT, $cache_tags);
 
     // Verify a cache hit.
     $this->verifyRenderCache('foo', $cache_tags);
diff --git a/core/modules/simpletest/src/TestBase.php b/core/modules/simpletest/src/TestBase.php
index b6c086812cc436f27395a8aee28d5a7a9e904607..9bc2c5bed771da5bf1618eb427decccc5b4a30a4 100644
--- a/core/modules/simpletest/src/TestBase.php
+++ b/core/modules/simpletest/src/TestBase.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\simpletest;
 
+use Drupal\Component\Assertion\Handle;
 use Drupal\Component\Render\MarkupInterface;
 use Drupal\Component\Utility\Crypt;
 use Drupal\Component\Utility\SafeMarkup;
@@ -1019,7 +1020,7 @@ public function run(array $methods = array()) {
 
     // Force assertion failures to be thrown as AssertionError for PHP 5 & 7
     // compatibility.
-    \Drupal\Component\Assertion\Handle::register();
+    Handle::register();
 
     set_error_handler(array($this, 'errorHandler'));
     // Iterate through all the methods in this class, unless a specific list of
diff --git a/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
index 71ca68ef2d751fd36a44676e90f50c89a8a16ce0..627df293156677fd026d455fa663e1d06e3ffac4 100644
--- a/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -27,6 +27,7 @@
 use Drupal\Core\Url;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\Yaml\Yaml as SymfonyYaml;
 use Zend\Diactoros\Uri;
 
 /**
@@ -635,7 +636,7 @@ protected function prepareSettings() {
     copy($settings_services_file, $directory . '/services.yml');
     if ($this->strictConfigSchema) {
       // Add a listener to validate configuration schema on save.
-      $yaml = new \Symfony\Component\Yaml\Yaml();
+      $yaml = new SymfonyYaml();
       $content = file_get_contents($directory . '/services.yml');
       $services = $yaml->parse($content);
       $services['services']['simpletest.config_schema_checker'] = [
diff --git a/core/modules/simpletest/tests/src/Unit/TestInfoParsingTest.php b/core/modules/simpletest/tests/src/Unit/TestInfoParsingTest.php
index b96ea797c3e1c8073ff91bf9136d110e78937663..9a69d78af0bfb6b7866e4d4f2186d2ef0a77a744 100644
--- a/core/modules/simpletest/tests/src/Unit/TestInfoParsingTest.php
+++ b/core/modules/simpletest/tests/src/Unit/TestInfoParsingTest.php
@@ -25,7 +25,7 @@ class TestInfoParsingTest extends UnitTestCase {
    * @dataProvider infoParserProvider
    */
   public function testTestInfoParser($expected, $classname, $doc_comment = NULL) {
-    $info = \Drupal\simpletest\TestDiscovery::getTestInfo($classname, $doc_comment);
+    $info = TestDiscovery::getTestInfo($classname, $doc_comment);
     $this->assertEquals($expected, $info);
   }
 
@@ -245,7 +245,7 @@ public function testTestInfoParserMissingGroup() {
  * Bulk delete storages and fields, and clean up afterwards.
  */
 EOT;
-    \Drupal\simpletest\TestDiscovery::getTestInfo($classname, $doc_comment);
+    TestDiscovery::getTestInfo($classname, $doc_comment);
   }
 
   /**
@@ -258,7 +258,7 @@ public function testTestInfoParserMissingSummary() {
  * @group field
  */
 EOT;
-    $info = \Drupal\simpletest\TestDiscovery::getTestInfo($classname, $doc_comment);
+    $info = TestDiscovery::getTestInfo($classname, $doc_comment);
     $this->assertEmpty($info['description']);
   }
 
diff --git a/core/modules/system/src/Tests/Ajax/DialogTest.php b/core/modules/system/src/Tests/Ajax/DialogTest.php
index fdde6d0c822ba7326fbe5f517637f7e2c104f8b5..80b46506726586920879ca4ecbc02aa89c5b9609 100644
--- a/core/modules/system/src/Tests/Ajax/DialogTest.php
+++ b/core/modules/system/src/Tests/Ajax/DialogTest.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\system\Tests\Ajax;
 
+use Drupal\ajax_test\Controller\AjaxTestController;
 use Drupal\Core\EventSubscriber\MainContentViewSubscriber;
 use Drupal\Core\Form\FormBuilderInterface;
 use Drupal\Core\Url;
@@ -29,7 +30,7 @@ public function testDialog() {
     $this->drupalGet('ajax-test/dialog');
 
     // Set up variables for this test.
-    $dialog_renderable = \Drupal\ajax_test\Controller\AjaxTestController::dialogContents();
+    $dialog_renderable = AjaxTestController::dialogContents();
     $dialog_contents = \Drupal::service('renderer')->renderRoot($dialog_renderable);
     $modal_expected_response = array(
       'command' => 'openDialog',
diff --git a/core/modules/system/src/Tests/System/FloodTest.php b/core/modules/system/src/Tests/System/FloodTest.php
index 59f4852efd2c35439fc9c21ee9cae60bb54b6f27..a3a336831484124816ff677d17bc953bc266e67a 100644
--- a/core/modules/system/src/Tests/System/FloodTest.php
+++ b/core/modules/system/src/Tests/System/FloodTest.php
@@ -2,6 +2,8 @@
 
 namespace Drupal\system\Tests\System;
 
+use Drupal\Core\Flood\DatabaseBackend;
+use Drupal\Core\Flood\MemoryBackend;
 use Drupal\simpletest\WebTestBase;
 use Symfony\Component\HttpFoundation\Request;
 
@@ -59,7 +61,7 @@ public function testMemoryBackend() {
     $name = 'flood_test_cleanup';
 
     $request_stack = \Drupal::service('request_stack');
-    $flood = new \Drupal\Core\Flood\MemoryBackend($request_stack);
+    $flood = new MemoryBackend($request_stack);
     // Register expired event.
     $flood->register($name, $window_expired);
     // Verify event is not allowed.
@@ -87,7 +89,7 @@ public function testDatabaseBackend() {
 
     $connection = \Drupal::service('database');
     $request_stack = \Drupal::service('request_stack');
-    $flood = new \Drupal\Core\Flood\DatabaseBackend($connection, $request_stack);
+    $flood = new DatabaseBackend($connection, $request_stack);
     // Register expired event.
     $flood->register($name, $window_expired);
     // Verify event is not allowed.
diff --git a/core/modules/system/src/Tests/TypedData/TypedDataTest.php b/core/modules/system/src/Tests/TypedData/TypedDataTest.php
index 2f225338f0581fc3523a7d84884024aa894b9297..9903240b0564d213068e55b4f5cde89e2a19c71e 100644
--- a/core/modules/system/src/Tests/TypedData/TypedDataTest.php
+++ b/core/modules/system/src/Tests/TypedData/TypedDataTest.php
@@ -2,14 +2,22 @@
 
 namespace Drupal\system\Tests\TypedData;
 
+use Drupal\Core\Datetime\DrupalDateTime;
 use Drupal\Core\Field\BaseFieldDefinition;
 use Drupal\Core\TypedData\DataDefinition;
 use Drupal\Core\TypedData\ListDataDefinition;
 use Drupal\Core\TypedData\MapDataDefinition;
+use Drupal\Core\TypedData\Type\BinaryInterface;
+use Drupal\Core\TypedData\Type\BooleanInterface;
+use Drupal\Core\TypedData\Type\DateTimeInterface;
+use Drupal\Core\TypedData\Type\DurationInterface;
+use Drupal\Core\TypedData\Type\FloatInterface;
+use Drupal\Core\TypedData\Type\IntegerInterface;
+use Drupal\Core\TypedData\Type\StringInterface;
+use Drupal\Core\TypedData\Type\UriInterface;
 use Drupal\Core\TypedData\TypedDataInterface;
 use Drupal\file\Entity\File;
 use Drupal\simpletest\KernelTestBase;
-use Drupal\Core\Datetime\DrupalDateTime;
 
 /**
  * Tests the functionality of all core data types.
@@ -49,7 +57,7 @@ protected function createTypedData($definition, $value = NULL, $name = NULL) {
       $definition = DataDefinition::create($definition['type']);
     }
     $data = $this->typedDataManager->create($definition, $value, $name);
-    $this->assertTrue($data instanceof \Drupal\Core\TypedData\TypedDataInterface, 'Typed data object is an instance of the typed data interface.');
+    $this->assertTrue($data instanceof TypedDataInterface, 'Typed data object is an instance of the typed data interface.');
     return $data;
   }
 
@@ -59,7 +67,7 @@ protected function createTypedData($definition, $value = NULL, $name = NULL) {
   public function testGetAndSet() {
     // Boolean type.
     $typed_data = $this->createTypedData(array('type' => 'boolean'), TRUE);
-    $this->assertTrue($typed_data instanceof \Drupal\Core\TypedData\Type\BooleanInterface, 'Typed data object is an instance of BooleanInterface.');
+    $this->assertTrue($typed_data instanceof BooleanInterface, 'Typed data object is an instance of BooleanInterface.');
     $this->assertTrue($typed_data->getValue() === TRUE, 'Boolean value was fetched.');
     $this->assertEqual($typed_data->validate()->count(), 0);
     $typed_data->setValue(FALSE);
@@ -75,7 +83,7 @@ public function testGetAndSet() {
     // String type.
     $value = $this->randomString();
     $typed_data = $this->createTypedData(array('type' => 'string'), $value);
-    $this->assertTrue($typed_data instanceof \Drupal\Core\TypedData\Type\StringInterface, 'Typed data object is an instance of StringInterface.');
+    $this->assertTrue($typed_data instanceof StringInterface, 'Typed data object is an instance of StringInterface.');
     $this->assertTrue($typed_data->getValue() === $value, 'String value was fetched.');
     $this->assertEqual($typed_data->validate()->count(), 0);
     $new_value = $this->randomString();
@@ -93,7 +101,7 @@ public function testGetAndSet() {
     // Integer type.
     $value = rand();
     $typed_data = $this->createTypedData(array('type' => 'integer'), $value);
-    $this->assertTrue($typed_data instanceof \Drupal\Core\TypedData\Type\IntegerInterface, 'Typed data object is an instance of IntegerInterface.');
+    $this->assertTrue($typed_data instanceof IntegerInterface, 'Typed data object is an instance of IntegerInterface.');
     $this->assertTrue($typed_data->getValue() === $value, 'Integer value was fetched.');
     $this->assertEqual($typed_data->validate()->count(), 0);
     $new_value = rand();
@@ -110,7 +118,7 @@ public function testGetAndSet() {
     // Float type.
     $value = 123.45;
     $typed_data = $this->createTypedData(array('type' => 'float'), $value);
-    $this->assertTrue($typed_data instanceof \Drupal\Core\TypedData\Type\FloatInterface, 'Typed data object is an instance of FloatInterface.');
+    $this->assertTrue($typed_data instanceof FloatInterface, 'Typed data object is an instance of FloatInterface.');
     $this->assertTrue($typed_data->getValue() === $value, 'Float value was fetched.');
     $this->assertEqual($typed_data->validate()->count(), 0);
     $new_value = 678.90;
@@ -127,7 +135,7 @@ public function testGetAndSet() {
     // Date Time type.
     $value = '2014-01-01T20:00:00+00:00';
     $typed_data = $this->createTypedData(array('type' => 'datetime_iso8601'), $value);
-    $this->assertTrue($typed_data instanceof \Drupal\Core\TypedData\Type\DateTimeInterface, 'Typed data object is an instance of DateTimeInterface.');
+    $this->assertTrue($typed_data instanceof DateTimeInterface, 'Typed data object is an instance of DateTimeInterface.');
     $this->assertTrue($typed_data->getValue() == $value, 'Date value was fetched.');
     $this->assertEqual($typed_data->getValue(), $typed_data->getDateTime()->format('c'), 'Value representation of a date is ISO 8601');
     $this->assertEqual($typed_data->validate()->count(), 0);
@@ -153,7 +161,7 @@ public function testGetAndSet() {
     // Timestamp type.
     $value = REQUEST_TIME;
     $typed_data = $this->createTypedData(array('type' => 'timestamp'), $value);
-    $this->assertTrue($typed_data instanceof \Drupal\Core\TypedData\Type\DateTimeInterface, 'Typed data object is an instance of DateTimeInterface.');
+    $this->assertTrue($typed_data instanceof DateTimeInterface, 'Typed data object is an instance of DateTimeInterface.');
     $this->assertTrue($typed_data->getValue() == $value, 'Timestamp value was fetched.');
     $this->assertEqual($typed_data->validate()->count(), 0);
     $new_value = REQUEST_TIME + 1;
@@ -176,7 +184,7 @@ public function testGetAndSet() {
     // DurationIso8601 type.
     $value = 'PT20S';
     $typed_data = $this->createTypedData(array('type' => 'duration_iso8601'), $value);
-    $this->assertTrue($typed_data instanceof \Drupal\Core\TypedData\Type\DurationInterface, 'Typed data object is an instance of DurationInterface.');
+    $this->assertTrue($typed_data instanceof DurationInterface, 'Typed data object is an instance of DurationInterface.');
     $this->assertIdentical($typed_data->getValue(), $value, 'DurationIso8601 value was fetched.');
     $this->assertEqual($typed_data->validate()->count(), 0);
     $typed_data->setValue('P40D');
@@ -200,7 +208,7 @@ public function testGetAndSet() {
     // Time span type.
     $value = 20;
     $typed_data = $this->createTypedData(array('type' => 'timespan'), $value);
-    $this->assertTrue($typed_data instanceof \Drupal\Core\TypedData\Type\DurationInterface, 'Typed data object is an instance of DurationInterface.');
+    $this->assertTrue($typed_data instanceof DurationInterface, 'Typed data object is an instance of DurationInterface.');
     $this->assertIdentical($typed_data->getValue(), $value, 'Time span value was fetched.');
     $this->assertEqual($typed_data->validate()->count(), 0);
     $typed_data->setValue(60 * 60 * 4);
@@ -223,7 +231,7 @@ public function testGetAndSet() {
     // URI type.
     $uri = 'http://example.com/foo/';
     $typed_data = $this->createTypedData(array('type' => 'uri'), $uri);
-    $this->assertTrue($typed_data instanceof \Drupal\Core\TypedData\Type\UriInterface, 'Typed data object is an instance of UriInterface.');
+    $this->assertTrue($typed_data instanceof UriInterface, 'Typed data object is an instance of UriInterface.');
     $this->assertTrue($typed_data->getValue() === $uri, 'URI value was fetched.');
     $this->assertEqual($typed_data->validate()->count(), 0);
     $typed_data->setValue($uri . 'bar.txt');
@@ -251,7 +259,7 @@ public function testGetAndSet() {
     // Email type.
     $value = $this->randomString();
     $typed_data = $this->createTypedData(array('type' => 'email'), $value);
-    $this->assertTrue($typed_data instanceof \Drupal\Core\TypedData\Type\StringInterface, 'Typed data object is an instance of StringInterface.');
+    $this->assertTrue($typed_data instanceof StringInterface, 'Typed data object is an instance of StringInterface.');
     $this->assertIdentical($typed_data->getValue(), $value, 'Email value was fetched.');
     $new_value = 'test@example.com';
     $typed_data->setValue($new_value);
@@ -266,7 +274,7 @@ public function testGetAndSet() {
 
     // Binary type.
     $typed_data = $this->createTypedData(array('type' => 'binary'), $files[0]->getFileUri());
-    $this->assertTrue($typed_data instanceof \Drupal\Core\TypedData\Type\BinaryInterface, 'Typed data object is an instance of BinaryInterface.');
+    $this->assertTrue($typed_data instanceof BinaryInterface, 'Typed data object is an instance of BinaryInterface.');
     $this->assertTrue(is_resource($typed_data->getValue()), 'Binary value was fetched.');
     $this->assertEqual($typed_data->validate()->count(), 0);
     // Try setting by URI.
@@ -441,7 +449,7 @@ public function testTypedDataMaps() {
     // Test iterating.
     $count = 0;
     foreach ($typed_data as $item) {
-      $this->assertTrue($item instanceof \Drupal\Core\TypedData\TypedDataInterface);
+      $this->assertTrue($item instanceof TypedDataInterface);
       $count++;
     }
     $this->assertEqual($count, 3);
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 3033a110e58339c5ae4593026be4713eeac218a3..787225220c3c664a0b1695208c6bb9d3d7dba544 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -1254,7 +1254,7 @@ function system_get_module_admin_tasks($module, array $info) {
     $access_manager = \Drupal::service('access_manager');
     if ($access_manager->checkNamedRoute('user.admin_permissions', array(), \Drupal::currentUser())) {
       /** @var \Drupal\Core\Url $url */
-      $url = new \Drupal\Core\Url('user.admin_permissions');
+      $url = new Url('user.admin_permissions');
       $url->setOption('fragment', 'module-' . $module);
       $admin_tasks["user.admin_permissions.$module"] = array(
         'title' => t('Configure @module permissions', array('@module' => $info['name'])),
diff --git a/core/modules/system/tests/fixtures/update/drupal-8.block-context-manager-2354889.php b/core/modules/system/tests/fixtures/update/drupal-8.block-context-manager-2354889.php
index 23b67e55a4c57d2cbcac0a17980dbca5686d871d..34474bf625b46ed6b7525a078d6f6a3c178b9674 100644
--- a/core/modules/system/tests/fixtures/update/drupal-8.block-context-manager-2354889.php
+++ b/core/modules/system/tests/fixtures/update/drupal-8.block-context-manager-2354889.php
@@ -6,19 +6,20 @@
  * upgrade path of https://www.drupal.org/node/2354889.
  */
 
+use Drupal\Component\Serialization\Yaml;
 use Drupal\Core\Database\Database;
 
 $connection = Database::getConnection();
 
 // A custom block with visibility settings.
-$block_configs[] = \Drupal\Component\Serialization\Yaml::decode(file_get_contents(__DIR__ . '/block.block.testfor2354889.yml'));
+$block_configs[] = Yaml::decode(file_get_contents(__DIR__ . '/block.block.testfor2354889.yml'));
 
 // A custom block without any visibility settings.
-$block_configs[] = \Drupal\Component\Serialization\Yaml::decode(file_get_contents(__DIR__ . '/block.block.secondtestfor2354889.yml'));
+$block_configs[] = Yaml::decode(file_get_contents(__DIR__ . '/block.block.secondtestfor2354889.yml'));
 
 // A custom block with visibility settings that contain a non-existing context
 // mapping.
-$block_configs[] = \Drupal\Component\Serialization\Yaml::decode(file_get_contents(__DIR__ . '/block.block.thirdtestfor2354889.yml'));
+$block_configs[] = Yaml::decode(file_get_contents(__DIR__ . '/block.block.thirdtestfor2354889.yml'));
 
 foreach ($block_configs as $block_config) {
   $connection->insert('config')
diff --git a/core/modules/system/tests/fixtures/update/drupal-8.local-actions-tasks-into-blocks-507488.php b/core/modules/system/tests/fixtures/update/drupal-8.local-actions-tasks-into-blocks-507488.php
index 986362f26ffdada51825939bdc6770f6d4f0e033..33861a0f991768e3a854fb7978eabc486b3417fc 100644
--- a/core/modules/system/tests/fixtures/update/drupal-8.local-actions-tasks-into-blocks-507488.php
+++ b/core/modules/system/tests/fixtures/update/drupal-8.local-actions-tasks-into-blocks-507488.php
@@ -6,12 +6,13 @@
  * upgrade path of https://www.drupal.org/node/507488.
  */
 
+use Drupal\Component\Serialization\Yaml;
 use Drupal\Core\Database\Database;
 
 $connection = Database::getConnection();
 
 // Structure of a custom block with visibility settings.
-$block_configs[] = \Drupal\Component\Serialization\Yaml::decode(file_get_contents(__DIR__ . '/block.block.testfor507488.yml'));
+$block_configs[] = Yaml::decode(file_get_contents(__DIR__ . '/block.block.testfor507488.yml'));
 
 foreach ($block_configs as $block_config) {
   $connection->insert('config')
diff --git a/core/modules/system/tests/fixtures/update/drupal-8.page-title-into-block-2476947.php b/core/modules/system/tests/fixtures/update/drupal-8.page-title-into-block-2476947.php
index ae3e77720b808cbfa97705f1fcb92511a70fb90e..b259ccc9b6eb7a6899f750d1f2c927f7abd4e49b 100644
--- a/core/modules/system/tests/fixtures/update/drupal-8.page-title-into-block-2476947.php
+++ b/core/modules/system/tests/fixtures/update/drupal-8.page-title-into-block-2476947.php
@@ -6,12 +6,13 @@
  * upgrade path of https://www.drupal.org/node/2476947.
  */
 
+use Drupal\Component\Serialization\Yaml;
 use Drupal\Core\Database\Database;
 
 $connection = Database::getConnection();
 
 // Structure of a custom block with visibility settings.
-$block_configs[] = \Drupal\Component\Serialization\Yaml::decode(file_get_contents(__DIR__ . '/block.block.testfor2476947.yml'));
+$block_configs[] = Yaml::decode(file_get_contents(__DIR__ . '/block.block.testfor2476947.yml'));
 
 foreach ($block_configs as $block_config) {
   $connection->insert('config')
diff --git a/core/modules/system/tests/fixtures/update/drupal-8.seven-secondary-local-tasks-block-2569529.php b/core/modules/system/tests/fixtures/update/drupal-8.seven-secondary-local-tasks-block-2569529.php
index 474a085260893dffee48080048543d7899f9513c..f19c07c7de6ff27427650a5e9c8b73e9a822864c 100644
--- a/core/modules/system/tests/fixtures/update/drupal-8.seven-secondary-local-tasks-block-2569529.php
+++ b/core/modules/system/tests/fixtures/update/drupal-8.seven-secondary-local-tasks-block-2569529.php
@@ -6,12 +6,13 @@
  * upgrade path of https://www.drupal.org/node/507488.
  */
 
+use Drupal\Component\Serialization\Yaml;
 use Drupal\Core\Database\Database;
 
 $connection = Database::getConnection();
 
 // Structure of a custom block with visibility settings.
-$block_configs[] = \Drupal\Component\Serialization\Yaml::decode(file_get_contents(__DIR__ . '/block.block.testfor2569529.yml'));
+$block_configs[] = Yaml::decode(file_get_contents(__DIR__ . '/block.block.testfor2569529.yml'));
 
 foreach ($block_configs as $block_config) {
   $connection->insert('config')
diff --git a/core/modules/system/tests/fixtures/update/drupal-8.site-branding-into-block-2005546.php b/core/modules/system/tests/fixtures/update/drupal-8.site-branding-into-block-2005546.php
index 576762d088874ec17c75aa9e8ef6ed6515bbcad6..c632060afe793263af67698317d810f2b0ef2fb9 100644
--- a/core/modules/system/tests/fixtures/update/drupal-8.site-branding-into-block-2005546.php
+++ b/core/modules/system/tests/fixtures/update/drupal-8.site-branding-into-block-2005546.php
@@ -6,12 +6,13 @@
  * upgrade path of https://www.drupal.org/node/2005546.
  */
 
+use Drupal\Component\Serialization\Yaml;
 use Drupal\Core\Database\Database;
 
 $connection = Database::getConnection();
 
 // Structure of a custom block with visibility settings.
-$block_configs[] = \Drupal\Component\Serialization\Yaml::decode(file_get_contents(__DIR__ . '/block.block.testfor2005546.yml'));
+$block_configs[] = Yaml::decode(file_get_contents(__DIR__ . '/block.block.testfor2005546.yml'));
 
 foreach ($block_configs as $block_config) {
   $connection->insert('config')
diff --git a/core/modules/system/tests/fixtures/update/drupal-8.views-entity-views-data-2455125.php b/core/modules/system/tests/fixtures/update/drupal-8.views-entity-views-data-2455125.php
index 2d8da457fb82a6d0a36785283a58858c28e99936..fe72370b393f53007e751235df36fb52a8f77909 100644
--- a/core/modules/system/tests/fixtures/update/drupal-8.views-entity-views-data-2455125.php
+++ b/core/modules/system/tests/fixtures/update/drupal-8.views-entity-views-data-2455125.php
@@ -6,6 +6,7 @@
  * upgrade path of https://www.drupal.org/node/2455125.
  */
 
+use Drupal\Component\Serialization\Yaml;
 use Drupal\Core\Database\Database;
 
 $connection = Database::getConnection();
@@ -13,7 +14,7 @@
 // Structure of a view with timestamp fields.
 $views_configs = [];
 
-$views_configs[] = \Drupal\Component\Serialization\Yaml::decode(file_get_contents(__DIR__ . '/drupal-8.views-entity-views-data-2455125.yml'));
+$views_configs[] = Yaml::decode(file_get_contents(__DIR__ . '/drupal-8.views-entity-views-data-2455125.yml'));
 
 foreach ($views_configs as $views_config) {
 $connection->insert('config')
diff --git a/core/modules/system/tests/fixtures/update/drupal-8.without_automated_cron.php b/core/modules/system/tests/fixtures/update/drupal-8.without_automated_cron.php
index 87b635502da7495b7f9d465a0def92d6183cd190..b245f74e8136d0bb6c3d89a2a10423f06d0df408 100644
--- a/core/modules/system/tests/fixtures/update/drupal-8.without_automated_cron.php
+++ b/core/modules/system/tests/fixtures/update/drupal-8.without_automated_cron.php
@@ -5,7 +5,9 @@
  * Test fixture.
  */
 
-$connection = Drupal\Core\Database\Database::getConnection();
+use Drupal\Core\Database\Database;
+
+$connection = Database::getConnection();
 $config = $connection;
 
 $connection->merge('config')
diff --git a/core/modules/system/tests/modules/ajax_forms_test/ajax_forms_test.module b/core/modules/system/tests/modules/ajax_forms_test/ajax_forms_test.module
index 3e470884db0975ccb9c8edc4303449a3a5954b2e..ecde048bc51be0607bbc788856f3a30d605aa4be 100644
--- a/core/modules/system/tests/modules/ajax_forms_test/ajax_forms_test.module
+++ b/core/modules/system/tests/modules/ajax_forms_test/ajax_forms_test.module
@@ -5,8 +5,22 @@
  * Simpletest mock module for Ajax forms testing.
  */
 
-use Drupal\Core\Ajax;
+use Drupal\Core\Ajax\AddCssCommand;
+use Drupal\Core\Ajax\AfterCommand;
 use Drupal\Core\Ajax\AjaxResponse;
+use Drupal\Core\Ajax\AlertCommand;
+use Drupal\Core\Ajax\AppendCommand;
+use Drupal\Core\Ajax\BeforeCommand;
+use Drupal\Core\Ajax\ChangedCommand;
+use Drupal\Core\Ajax\CssCommand;
+use Drupal\Core\Ajax\DataCommand;
+use Drupal\Core\Ajax\HtmlCommand;
+use Drupal\Core\Ajax\InsertCommand;
+use Drupal\Core\Ajax\InvokeCommand;
+use Drupal\Core\Ajax\PrependCommand;
+use Drupal\Core\Ajax\RemoveCommand;
+use Drupal\Core\Ajax\RestripeCommand;
+use Drupal\Core\Ajax\SettingsCommand;
 use Drupal\Core\Form\FormStateInterface;
 
 /**
@@ -16,7 +30,7 @@ function ajax_forms_test_advanced_commands_after_callback($form, FormStateInterf
   $selector = '#after_div';
 
   $response = new AjaxResponse();
-  $response->addCommand(new Ajax\AfterCommand($selector, "This will be placed after"));
+  $response->addCommand(new AfterCommand($selector, "This will be placed after"));
   return $response;
 }
 
@@ -25,7 +39,7 @@ function ajax_forms_test_advanced_commands_after_callback($form, FormStateInterf
  */
 function ajax_forms_test_advanced_commands_alert_callback($form, FormStateInterface $form_state) {
   $response = new AjaxResponse();
-  $response->addCommand(new Ajax\AlertCommand('Alert'));
+  $response->addCommand(new AlertCommand('Alert'));
   return $response;
 }
 
@@ -35,7 +49,7 @@ function ajax_forms_test_advanced_commands_alert_callback($form, FormStateInterf
 function ajax_forms_test_advanced_commands_append_callback($form, FormStateInterface $form_state) {
   $selector = '#append_div';
   $response = new AjaxResponse();
-  $response->addCommand(new Ajax\AppendCommand($selector, "Appended text"));
+  $response->addCommand(new AppendCommand($selector, "Appended text"));
   return $response;
 }
 
@@ -45,7 +59,7 @@ function ajax_forms_test_advanced_commands_append_callback($form, FormStateInter
 function ajax_forms_test_advanced_commands_before_callback($form, FormStateInterface $form_state) {
   $selector = '#before_div';
   $response = new AjaxResponse();
-  $response->addCommand(new Ajax\BeforeCommand($selector, "Before text"));
+  $response->addCommand(new BeforeCommand($selector, "Before text"));
   return $response;
 }
 
@@ -54,7 +68,7 @@ function ajax_forms_test_advanced_commands_before_callback($form, FormStateInter
  */
 function ajax_forms_test_advanced_commands_changed_callback($form, FormStateInterface $form_state) {
   $response = new AjaxResponse();
-  $response->addCommand(new Ajax\ChangedCommand('#changed_div'));
+  $response->addCommand(new ChangedCommand('#changed_div'));
   return $response;
 }
 
@@ -63,7 +77,7 @@ function ajax_forms_test_advanced_commands_changed_callback($form, FormStateInte
  */
 function ajax_forms_test_advanced_commands_changed_asterisk_callback($form, FormStateInterface $form_state) {
   $response = new AjaxResponse();
-  $response->addCommand(new Ajax\ChangedCommand('#changed_div', '#changed_div_mark_this'));
+  $response->addCommand(new ChangedCommand('#changed_div', '#changed_div_mark_this'));
   return $response;
 }
 
@@ -75,7 +89,7 @@ function ajax_forms_test_advanced_commands_css_callback($form, FormStateInterfac
   $color = 'blue';
 
   $response = new AjaxResponse();
-  $response->addCommand(new Ajax\CssCommand($selector, array('background-color' => $color)));
+  $response->addCommand(new CssCommand($selector, array('background-color' => $color)));
   return $response;
 }
 
@@ -85,7 +99,7 @@ function ajax_forms_test_advanced_commands_css_callback($form, FormStateInterfac
 function ajax_forms_test_advanced_commands_data_callback($form, FormStateInterface $form_state) {
   $selector = '#data_div';
   $response = new AjaxResponse();
-  $response->addCommand(new Ajax\DataCommand($selector, 'testkey', 'testvalue'));
+  $response->addCommand(new DataCommand($selector, 'testkey', 'testvalue'));
   return $response;
 }
 
@@ -94,7 +108,7 @@ function ajax_forms_test_advanced_commands_data_callback($form, FormStateInterfa
  */
 function ajax_forms_test_advanced_commands_invoke_callback($form, FormStateInterface $form_state) {
   $response = new AjaxResponse();
-  $response->addCommand(new Ajax\InvokeCommand('#invoke_div', 'addClass', array('error')));
+  $response->addCommand(new InvokeCommand('#invoke_div', 'addClass', array('error')));
   return $response;
 }
 
@@ -103,7 +117,7 @@ function ajax_forms_test_advanced_commands_invoke_callback($form, FormStateInter
  */
 function ajax_forms_test_advanced_commands_html_callback($form, FormStateInterface $form_state) {
   $response = new AjaxResponse();
-  $response->addCommand(new Ajax\HtmlCommand('#html_div', 'replacement text'));
+  $response->addCommand(new HtmlCommand('#html_div', 'replacement text'));
   return $response;
 }
 
@@ -112,7 +126,7 @@ function ajax_forms_test_advanced_commands_html_callback($form, FormStateInterfa
  */
 function ajax_forms_test_advanced_commands_insert_callback($form, FormStateInterface $form_state) {
   $response = new AjaxResponse();
-  $response->addCommand(new Ajax\InsertCommand('#insert_div', 'insert replacement text'));
+  $response->addCommand(new InsertCommand('#insert_div', 'insert replacement text'));
   return $response;
 }
 
@@ -121,7 +135,7 @@ function ajax_forms_test_advanced_commands_insert_callback($form, FormStateInter
  */
 function ajax_forms_test_advanced_commands_prepend_callback($form, FormStateInterface $form_state) {
   $response = new AjaxResponse();
-  $response->addCommand(new Ajax\PrependCommand('#prepend_div', "prepended text"));
+  $response->addCommand(new PrependCommand('#prepend_div', "prepended text"));
   return $response;
 }
 
@@ -130,7 +144,7 @@ function ajax_forms_test_advanced_commands_prepend_callback($form, FormStateInte
  */
 function ajax_forms_test_advanced_commands_remove_callback($form, FormStateInterface $form_state) {
   $response = new AjaxResponse();
-  $response->addCommand(new Ajax\RemoveCommand('#remove_text'));
+  $response->addCommand(new RemoveCommand('#remove_text'));
   return $response;
 }
 
@@ -139,7 +153,7 @@ function ajax_forms_test_advanced_commands_remove_callback($form, FormStateInter
  */
 function ajax_forms_test_advanced_commands_restripe_callback($form, FormStateInterface $form_state) {
   $response = new AjaxResponse();
-  $response->addCommand(new Ajax\RestripeCommand('#restripe_table'));
+  $response->addCommand(new RestripeCommand('#restripe_table'));
   return $response;
 }
 
@@ -149,7 +163,7 @@ function ajax_forms_test_advanced_commands_restripe_callback($form, FormStateInt
 function ajax_forms_test_advanced_commands_settings_callback($form, FormStateInterface $form_state) {
   $setting['ajax_forms_test']['foo'] = 42;
   $response = new AjaxResponse();
-  $response->addCommand(new Ajax\SettingsCommand($setting));
+  $response->addCommand(new SettingsCommand($setting));
   return $response;
 }
 
@@ -158,7 +172,7 @@ function ajax_forms_test_advanced_commands_settings_callback($form, FormStateInt
  */
 function ajax_forms_test_advanced_commands_add_css_callback($form, FormStateInterface $form_state) {
   $response = new AjaxResponse();
-  $response->addCommand(new Ajax\AddCssCommand('my/file.css'));
+  $response->addCommand(new AddCssCommand('my/file.css'));
   return $response;
 }
 
diff --git a/core/modules/system/tests/modules/entity_test_operation/entity_test_operation.module b/core/modules/system/tests/modules/entity_test_operation/entity_test_operation.module
index bdea7ba2a029dd9acfa559324aeb00e1c3be8031..2b050ea93617bf7856a7b9b731d02d7d6e4e44b1 100644
--- a/core/modules/system/tests/modules/entity_test_operation/entity_test_operation.module
+++ b/core/modules/system/tests/modules/entity_test_operation/entity_test_operation.module
@@ -5,12 +5,13 @@
  * Contains hook implementations for Entity Operation Test Module.
  */
 
+use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Url;
 
 /**
  * Implements hook_entity_operation().
  */
-function entity_test_operation_entity_operation(\Drupal\Core\Entity\EntityInterface $entity) {
+function entity_test_operation_entity_operation(EntityInterface $entity) {
   return [
     'test' => [
       'title' => t('Front page'),
diff --git a/core/modules/system/tests/modules/module_test/src/Controller/ModuleTestController.php b/core/modules/system/tests/modules/module_test/src/Controller/ModuleTestController.php
index 040674fe1c890667f321f4c1a37772f24d067824..5bdb22a35f69158b73405c830d4e35952bb774a3 100644
--- a/core/modules/system/tests/modules/module_test/src/Controller/ModuleTestController.php
+++ b/core/modules/system/tests/modules/module_test/src/Controller/ModuleTestController.php
@@ -2,6 +2,8 @@
 
 namespace Drupal\module_test\Controller;
 
+use Drupal\module_autoload_test\SomeClass;
+
 /**
  * Controller routines for module_test routes.
  */
@@ -38,7 +40,7 @@ public function hookDynamicLoadingInvokeAll() {
   public function testClassLoading() {
     $markup = NULL;
     if (class_exists('Drupal\module_autoload_test\SomeClass')) {
-      $obj = new \Drupal\module_autoload_test\SomeClass();
+      $obj = new SomeClass();
       $markup = $obj->testMethod();
     }
     return ['#markup' => $markup];
diff --git a/core/modules/system/tests/src/Kernel/Extension/ModuleHandlerTest.php b/core/modules/system/tests/src/Kernel/Extension/ModuleHandlerTest.php
index d691beb776cf404757bca51230335b98f2326d55..9beac7a86371e07b2e31e9a2dfcd96bb34e4640b 100644
--- a/core/modules/system/tests/src/Kernel/Extension/ModuleHandlerTest.php
+++ b/core/modules/system/tests/src/Kernel/Extension/ModuleHandlerTest.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\Tests\system\Kernel\Extension;
 
+use Drupal\Core\Extension\MissingDependencyException;
 use Drupal\Core\DependencyInjection\ContainerBuilder;
 use \Drupal\Core\Extension\ModuleUninstallValidatorException;
 use Drupal\entity_test\Entity\EntityTest;
@@ -121,7 +122,7 @@ function testDependencyResolution() {
       $result = $this->moduleInstaller()->install(array('color'));
       $this->fail(t('ModuleInstaller::install() throws an exception if dependencies are missing.'));
     }
-    catch (\Drupal\Core\Extension\MissingDependencyException $e) {
+    catch (MissingDependencyException $e) {
       $this->pass(t('ModuleInstaller::install() throws an exception if dependencies are missing.'));
     }
 
diff --git a/core/modules/taxonomy/tests/modules/taxonomy_crud/taxonomy_crud.module b/core/modules/taxonomy/tests/modules/taxonomy_crud/taxonomy_crud.module
index 442ca090dba5f387bf2a4296a77e6431d79fc3cc..dbe8781cea25c5df6a1971ef53f8ff36585e99e5 100644
--- a/core/modules/taxonomy/tests/modules/taxonomy_crud/taxonomy_crud.module
+++ b/core/modules/taxonomy/tests/modules/taxonomy_crud/taxonomy_crud.module
@@ -5,9 +5,11 @@
  * Provides hook implementations for testing purposes.
  */
 
+use Drupal\taxonomy\VocabularyInterface;
+
 /**
  * Implements hook_ENTITY_TYPE_presave() for taxonomy_vocabulary entities.
  */
-function taxonomy_crud_taxonomy_vocabulary_presave(\Drupal\taxonomy\VocabularyInterface $vocabulary) {
+function taxonomy_crud_taxonomy_vocabulary_presave(VocabularyInterface $vocabulary) {
   $vocabulary->setThirdPartySetting('taxonomy_crud', 'foo', 'bar');
 }
diff --git a/core/modules/views/src/Tests/Plugin/DisplayExtenderTest.php b/core/modules/views/src/Tests/Plugin/DisplayExtenderTest.php
index 844143acc1a008346f6581ee727280955c7be06a..33c3713c1e1c3b31524a627666e51d3c1a110959 100644
--- a/core/modules/views/src/Tests/Plugin/DisplayExtenderTest.php
+++ b/core/modules/views/src/Tests/Plugin/DisplayExtenderTest.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\views\Tests\Plugin;
 
+use Drupal\views_test_data\Plugin\views\display_extender\DisplayExtenderTest as DisplayExtenderTestData;
 use Drupal\views\Views;
 
 /**
@@ -38,7 +39,7 @@ public function testDisplayExtenders() {
     $this->assertEqual(count($view->display_handler->getExtenders()), 1, 'Make sure that only one extender is initialized.');
 
     $display_extender = $view->display_handler->getExtenders()['display_extender_test'];
-    $this->assertTrue($display_extender instanceof \Drupal\views_test_data\Plugin\views\display_extender\DisplayExtenderTest, 'Make sure the right class got initialized.');
+    $this->assertTrue($display_extender instanceof DisplayExtenderTestData, 'Make sure the right class got initialized.');
 
     $view->preExecute();
     $this->assertTrue($display_extender->testState['preExecute'], 'Make sure the display extender was able to react on preExecute.');
diff --git a/core/modules/views/tests/fixtures/update/argument-placeholder.php b/core/modules/views/tests/fixtures/update/argument-placeholder.php
index 525299cdcd2cb4bc24ee5ea31d7dd78eb74d16fd..03181bbe5989f3c01ea70babb48bc3044013aae1 100644
--- a/core/modules/views/tests/fixtures/update/argument-placeholder.php
+++ b/core/modules/views/tests/fixtures/update/argument-placeholder.php
@@ -5,12 +5,15 @@
  * Text fixture.
  */
 
-$connection = Drupal\Core\Database\Database::getConnection();
+use Drupal\Component\Serialization\Yaml;
+use Drupal\Core\Database\Database;
+
+$connection = Database::getConnection();
 
 $connection->insert('config')
   ->fields(array(
     'collection' => '',
     'name' => 'views.view.test_token_view',
-    'data' => serialize(\Drupal\Component\Serialization\Yaml::decode(file_get_contents('core/modules/views/tests/modules/views_test_config/test_views/views.view.test_token_view.yml'))),
+    'data' => serialize(Yaml::decode(file_get_contents('core/modules/views/tests/modules/views_test_config/test_views/views.view.test_token_view.yml'))),
   ))
   ->execute();
diff --git a/core/modules/views/tests/fixtures/update/duplicate-field-handler.php b/core/modules/views/tests/fixtures/update/duplicate-field-handler.php
index 69aa8e8e3d153f40bcf184959287710d0f0d5c1c..32e74fb7cb290c4dcd7c9cb87559f093a0e7949e 100644
--- a/core/modules/views/tests/fixtures/update/duplicate-field-handler.php
+++ b/core/modules/views/tests/fixtures/update/duplicate-field-handler.php
@@ -5,12 +5,15 @@
  * Test fixture.
  */
 
-$connection = Drupal\Core\Database\Database::getConnection();
+use Drupal\Component\Serialization\Yaml;
+use Drupal\Core\Database\Database;
+
+$connection = Database::getConnection();
 
 $connection->insert('config')
   ->fields(array(
     'collection' => '',
     'name' => 'views.view.test_duplicate_field_handlers',
-    'data' => serialize(\Drupal\Component\Serialization\Yaml::decode(file_get_contents('core/modules/views/tests/modules/views_test_config/test_views/views.view.test_duplicate_field_handlers.yml'))),
+    'data' => serialize(Yaml::decode(file_get_contents('core/modules/views/tests/modules/views_test_config/test_views/views.view.test_duplicate_field_handlers.yml'))),
   ))
   ->execute();
diff --git a/core/modules/views/tests/modules/views_test_data/views_test_data.module b/core/modules/views/tests/modules/views_test_data/views_test_data.module
index f041651dc797269d26cf3d901ebcd27e9fedea45..bd917c7eee7e1c6bae8f1c28f2883eea3b71ea11 100644
--- a/core/modules/views/tests/modules/views_test_data/views_test_data.module
+++ b/core/modules/views/tests/modules/views_test_data/views_test_data.module
@@ -5,6 +5,8 @@
  * Helper module for Views tests.
  */
 
+use Drupal\Core\Form\FormStateInterface;
+
 /**
  * Access callback for the generic handler test.
  *
@@ -126,6 +128,6 @@ function views_test_data_test_pre_render_function($element) {
 /**
  * Implements hook_form_BASE_FORM_ID_alter().
  */
-function views_test_data_form_views_form_test_form_multiple_default_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
+function views_test_data_form_views_form_test_form_multiple_default_alter(&$form, FormStateInterface $form_state, $form_id) {
   drupal_set_message(t('Test base form ID with Views forms and arguments.'));
 }
diff --git a/core/modules/views_ui/src/Form/Ajax/ViewsFormBase.php b/core/modules/views_ui/src/Form/Ajax/ViewsFormBase.php
index 58344bf7133aacad1963546bb6bed77e84b75880..93bd049808062fd141032f10b42d49f8c338ee80 100644
--- a/core/modules/views_ui/src/Form/Ajax/ViewsFormBase.php
+++ b/core/modules/views_ui/src/Form/Ajax/ViewsFormBase.php
@@ -3,17 +3,20 @@
 namespace Drupal\views_ui\Form\Ajax;
 
 use Drupal\Component\Utility\Html;
+use Drupal\Core\Ajax\AjaxResponse;
+use Drupal\Core\Ajax\CloseModalDialogCommand;
 use Drupal\Core\Ajax\OpenModalDialogCommand;
 use Drupal\Core\Form\FormBase;
 use Drupal\Core\Form\FormState;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Render\BubbleableMetadata;
 use Drupal\Core\Render\RenderContext;
+use Drupal\views\Ajax\HighlightCommand;
+use Drupal\views\Ajax\ReplaceTitleCommand;
+use Drupal\views\Ajax\ShowButtonsCommand;
+use Drupal\views\Ajax\TriggerPreviewCommand;
 use Drupal\views\ViewEntityInterface;
-use Drupal\views\Ajax;
-use Drupal\views_ui\Ajax as AjaxUI;
-use Drupal\Core\Ajax\AjaxResponse;
-use Drupal\Core\Ajax\CloseModalDialogCommand;
+use Drupal\views_ui\Ajax\SetFormCommand;
 use Symfony\Component\HttpFoundation\RedirectResponse;
 
 /**
@@ -151,10 +154,10 @@ public function getForm(ViewEntityInterface $view, $display_id, $js) {
     else {
       $response = new AjaxResponse();
       $response->addCommand(new CloseModalDialogCommand());
-      $response->addCommand(new Ajax\ShowButtonsCommand(!empty($view->changed)));
-      $response->addCommand(new Ajax\TriggerPreviewCommand());
+      $response->addCommand(new ShowButtonsCommand(!empty($view->changed)));
+      $response->addCommand(new TriggerPreviewCommand());
       if ($page_title = $form_state->get('page_title')) {
-        $response->addCommand(new Ajax\ReplaceTitleCommand($page_title));
+        $response->addCommand(new ReplaceTitleCommand($page_title));
       }
     }
     // If this form was for view-wide changes, there's no need to regenerate
@@ -248,10 +251,10 @@ protected function ajaxFormWrapper($form_class, FormStateInterface &$form_state)
       // Usually this happens at the same path, but custom paths may be
       // specified in $form_state.
       $form_url = $form_state->has('url') ? $form_state->get('url')->toString() : $this->url('<current>');
-      $response->addCommand(new AjaxUI\SetFormCommand($form_url));
+      $response->addCommand(new SetFormCommand($form_url));
 
       if ($section = $form_state->get('#section')) {
-        $response->addCommand(new Ajax\HighlightCommand('.' . Html::cleanCssIdentifier($section)));
+        $response->addCommand(new HighlightCommand('.' . Html::cleanCssIdentifier($section)));
       }
 
       return $response;
diff --git a/core/modules/views_ui/views_ui.theme.inc b/core/modules/views_ui/views_ui.theme.inc
index f9b165a112ade844397dc653ecb36d2c0734da99..3b5867894d39721e4e8386d868aee6e7ad9bc01c 100644
--- a/core/modules/views_ui/views_ui.theme.inc
+++ b/core/modules/views_ui/views_ui.theme.inc
@@ -8,6 +8,8 @@
 use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Core\Form\FormState;
 use Drupal\Core\Render\Element;
+use Drupal\Core\Render\Element\Checkboxes;
+use Drupal\Core\Render\Element\Radios;
 use Drupal\Core\Url;
 
 /**
@@ -88,8 +90,8 @@ function template_preprocess_views_ui_build_group_filter_form(&$variables) {
 
   // Prepare default selectors.
   $form_state = new FormState();
-  $form['default_group'] = Element\Radios::processRadios($form['default_group'], $form_state, $form);
-  $form['default_group_multiple'] = Element\Checkboxes::processCheckboxes($form['default_group_multiple'], $form_state, $form);
+  $form['default_group'] = Radios::processRadios($form['default_group'], $form_state, $form);
+  $form['default_group_multiple'] = Checkboxes::processCheckboxes($form['default_group_multiple'], $form_state, $form);
   $form['default_group']['All']['#title'] = '';
 
   $rows[] = array(
diff --git a/core/phpcs.xml.dist b/core/phpcs.xml.dist
index 9a5581c1bded3315da28565202e805469c61177d..975c31f056adeced1cbe3214a09dbb37210e061f 100644
--- a/core/phpcs.xml.dist
+++ b/core/phpcs.xml.dist
@@ -13,6 +13,7 @@
   <!-- Only include specific sniffs that pass. This ensures that, if new sniffs are added, HEAD does not fail.-->
   <!-- Drupal sniffs -->
   <rule ref="Drupal.Classes.ClassCreateInstance"/>
+  <rule ref="Drupal.Classes.FullyQualifiedNamespace"/>
   <rule ref="Drupal.Classes.UnusedUseStatement"/>
   <rule ref="Drupal.CSS.ClassDefinitionNameSpacing"/>
   <rule ref="Drupal.CSS.ColourDefinition"/>
diff --git a/core/tests/Drupal/KernelTests/Core/Entity/EntityFieldTest.php b/core/tests/Drupal/KernelTests/Core/Entity/EntityFieldTest.php
index ec3f87a577e9d56a68569eb66f219c16475d2db8..85320141ae6ec9a452922502886ec99cc110ca75 100644
--- a/core/tests/Drupal/KernelTests/Core/Entity/EntityFieldTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Entity/EntityFieldTest.php
@@ -3,12 +3,16 @@
 namespace Drupal\KernelTests\Core\Entity;
 
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\TypedData\EntityDataDefinition;
+use Drupal\Core\Entity\TypedData\EntityDataDefinitionInterface;
 use Drupal\Core\Field\BaseFieldDefinition;
 use Drupal\Core\Field\FieldDefinitionInterface;
-use Drupal\Core\Field\FieldItemListInterface;
 use Drupal\Core\Field\FieldItemInterface;
+use Drupal\Core\Field\FieldItemListInterface;
 use Drupal\Core\TypedData\ComplexDataDefinitionInterface;
+use Drupal\Core\TypedData\ComplexDataInterface;
 use Drupal\Core\TypedData\DataDefinitionInterface;
+use Drupal\Core\TypedData\ListInterface;
 use Drupal\Core\TypedData\Type\StringInterface;
 use Drupal\Core\TypedData\TypedDataInterface;
 use Drupal\node\Entity\Node;
@@ -420,7 +424,7 @@ protected function doTestIntrospection($entity_type) {
     $this->assertEqual($value_definition->getDataType(), 'string');
 
     // Test deriving metadata from references.
-    $entity_definition = \Drupal\Core\Entity\TypedData\EntityDataDefinition::create($entity_type);
+    $entity_definition = EntityDataDefinition::create($entity_type);
     $langcode_key = $this->entityManager->getDefinition($entity_type)->getKey('langcode');
     $reference_definition = $entity_definition->getPropertyDefinition($langcode_key)
       ->getPropertyDefinition('language')
@@ -431,7 +435,7 @@ protected function doTestIntrospection($entity_type) {
       ->getPropertyDefinition('entity')
       ->getTargetDefinition();
 
-    $this->assertTrue($reference_definition instanceof \Drupal\Core\Entity\TypedData\EntityDataDefinitionInterface, 'Definition of the referenced user retrieved.');
+    $this->assertTrue($reference_definition instanceof EntityDataDefinitionInterface, 'Definition of the referenced user retrieved.');
     $this->assertEqual($reference_definition->getEntityTypeId(), 'user', 'Referenced entity is of type "user".');
 
     // Test propagating down.
@@ -583,12 +587,12 @@ public function getContainedStrings(TypedDataInterface $wrapper, $depth, array &
 
     // Recurse until a certain depth is reached if possible.
     if ($depth < 7) {
-      if ($wrapper instanceof \Drupal\Core\TypedData\ListInterface) {
+      if ($wrapper instanceof ListInterface) {
         foreach ($wrapper as $item) {
           $this->getContainedStrings($item, $depth + 1, $strings);
         }
       }
-      elseif ($wrapper instanceof \Drupal\Core\TypedData\ComplexDataInterface) {
+      elseif ($wrapper instanceof ComplexDataInterface) {
         foreach ($wrapper as $property) {
           $this->getContainedStrings($property, $depth + 1, $strings);
         }
diff --git a/core/tests/Drupal/Tests/Core/DrupalKernel/DiscoverServiceProvidersTest.php b/core/tests/Drupal/Tests/Core/DrupalKernel/DiscoverServiceProvidersTest.php
index be04507e6943d0db4f07badc21d410521f39f265..164da9d954c3ae6ab6e8e3520c2286eeb0a20066 100644
--- a/core/tests/Drupal/Tests/Core/DrupalKernel/DiscoverServiceProvidersTest.php
+++ b/core/tests/Drupal/Tests/Core/DrupalKernel/DiscoverServiceProvidersTest.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\Tests\Core\DrupalKernel;
 
+use Composer\Autoload\ClassLoader;
 use Drupal\Core\DrupalKernel;
 use Drupal\Core\Site\Settings;
 use Drupal\Tests\UnitTestCase;
@@ -24,7 +25,7 @@ public function testDiscoverServiceCustom() {
       ),
     ));
 
-    $kernel = new DrupalKernel('prod', new \Composer\Autoload\ClassLoader());
+    $kernel = new DrupalKernel('prod', new ClassLoader());
     $kernel->discoverServiceProviders();
 
     $expect = array(
@@ -44,7 +45,7 @@ public function testDiscoverServiceCustom() {
    */
   public function testDiscoverServiceNoContainerYamls() {
     new Settings([]);
-    $kernel = new DrupalKernel('prod', new \Composer\Autoload\ClassLoader());
+    $kernel = new DrupalKernel('prod', new ClassLoader());
     $kernel->discoverServiceProviders();
 
     $expect = [
diff --git a/core/tests/Drupal/Tests/Core/PageCache/NoSessionOpenTest.php b/core/tests/Drupal/Tests/Core/PageCache/NoSessionOpenTest.php
index 1af6afb9f4431d16c6da93bd9abaeb1ea76b977b..aa1f5d7d931401eec4fb07155152688417a9b711 100644
--- a/core/tests/Drupal/Tests/Core/PageCache/NoSessionOpenTest.php
+++ b/core/tests/Drupal/Tests/Core/PageCache/NoSessionOpenTest.php
@@ -2,8 +2,8 @@
 
 namespace Drupal\Tests\Core\PageCache;
 
+use Drupal\Core\PageCache\RequestPolicy\NoSessionOpen;
 use Drupal\Core\PageCache\RequestPolicyInterface;
-use Drupal\Core\PageCache\RequestPolicy;
 use Drupal\Tests\UnitTestCase;
 use Symfony\Component\HttpFoundation\Request;
 
@@ -29,7 +29,7 @@ class NoSessionOpenTest extends UnitTestCase {
 
   protected function setUp() {
     $this->sessionConfiguration = $this->getMock('Drupal\Core\Session\SessionConfigurationInterface');
-    $this->policy = new RequestPolicy\NoSessionOpen($this->sessionConfiguration);
+    $this->policy = new NoSessionOpen($this->sessionConfiguration);
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/Core/ParamConverter/EntityConverterTest.php b/core/tests/Drupal/Tests/Core/ParamConverter/EntityConverterTest.php
index ded278e9642190a5e1372d03e7789fca76968117..ebafab0c96a10b88cbd470ce64a74cf53e531a2a 100644
--- a/core/tests/Drupal/Tests/Core/ParamConverter/EntityConverterTest.php
+++ b/core/tests/Drupal/Tests/Core/ParamConverter/EntityConverterTest.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\Tests\Core\ParamConverter;
 
+use Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException;
 use Drupal\Core\ParamConverter\EntityConverter;
 use Drupal\Tests\UnitTestCase;
 use Symfony\Component\Routing\Route;
@@ -116,7 +117,7 @@ public function testConvertWithInvalidEntityType() {
     $this->entityManager->expects($this->once())
       ->method('getStorage')
       ->with('invalid_id')
-      ->willThrowException(new \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException('invalid_id'));
+      ->willThrowException(new InvalidPluginDefinitionException('invalid_id'));
 
     $this->entityConverter->convert('id', ['type' => 'entity:invalid_id'], 'foo', ['foo' => 'id']);
   }
diff --git a/core/tests/bootstrap.php b/core/tests/bootstrap.php
index ad02e5f3ecbfc2bb4adf187947c7ba2575bda5f2..49e350aca75908b6fdfc9b004f065758af950e76 100644
--- a/core/tests/bootstrap.php
+++ b/core/tests/bootstrap.php
@@ -7,6 +7,8 @@
  * @see phpunit.xml.dist
  */
 
+use Drupal\Component\Assertion\Handle;
+
 /**
  * Finds all valid extension directories recursively within a given directory.
  *
@@ -141,4 +143,4 @@ function drupal_phpunit_populate_class_loader() {
 // runtime assertions. By default this setting is on. Here we make a call to
 // make PHP 5 and 7 handle assertion failures the same way, but this call does
 // not turn runtime assertions on if they weren't on already.
-\Drupal\Component\Assertion\Handle::register();
+Handle::register();
diff --git a/core/themes/bartik/bartik.theme b/core/themes/bartik/bartik.theme
index 3d3ca1297aaaab912cc3f6a31fa4cc1b9b0361d9..b1b3308260a86f42d862d5ceca2fbbfc8c6d12f6 100644
--- a/core/themes/bartik/bartik.theme
+++ b/core/themes/bartik/bartik.theme
@@ -5,6 +5,7 @@
  * Functions to support theming in the Bartik theme.
  */
 
+use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Template\Attribute;
 
 /**
@@ -113,7 +114,7 @@ function bartik_theme_suggestions_form_alter(array &$suggestions, array $variabl
 /**
  * Implements hook_form_alter() to add classes to the search form.
  */
-function bartik_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
+function bartik_form_alter(&$form, FormStateInterface $form_state, $form_id) {
   if (in_array($form_id, ['search_block_form', 'search_form'])) {
     $key = ($form_id == 'search_block_form') ? 'actions' : 'basic';
     if (!isset($form[$key]['submit']['#attributes'])) {