diff --git a/core/lib/Drupal/Core/Extension/ModuleInstaller.php b/core/lib/Drupal/Core/Extension/ModuleInstaller.php
index 1c1d68b823..c3dbcc86ac 100644
--- a/core/lib/Drupal/Core/Extension/ModuleInstaller.php
+++ b/core/lib/Drupal/Core/Extension/ModuleInstaller.php
@@ -175,13 +175,12 @@ public function install(array $module_list, $enable_dependencies = TRUE) {
 
         // Update the module handler in order to load the module's code.
         // This allows the module to participate in hooks and its existence to
-        // be discovered by other modules. The module code ("$module.module" and
-        // "$module.install" files) are loaded only after the kernel rebuild in
-        // order to make the PSR4 namespaces provided by this module available
-        // to its own code.
+        // be discovered by other modules.
         // The current ModuleHandler instance is obsolete with the kernel
         // rebuild below.
         $this->moduleHandler->setModuleList($module_filenames);
+        $this->moduleHandler->load($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
@@ -191,10 +190,6 @@ public function install(array $module_list, $enable_dependencies = TRUE) {
         // Update the kernel to include it.
         $this->updateKernel($module_filenames);
 
-        // Load the module code ("$module.module" and "$module.install" files).
-        $this->moduleHandler->load($module);
-        module_load_install($module);
-
         // Allow modules to react prior to the installation of a module.
         $this->moduleHandler->invokeAll('module_preinstall', array($module));
 
diff --git a/core/modules/aggregator/aggregator.module b/core/modules/aggregator/aggregator.module
index 5180b758c6..d4adae4edd 100644
--- a/core/modules/aggregator/aggregator.module
+++ b/core/modules/aggregator/aggregator.module
@@ -6,7 +6,6 @@
  */
 
 use Drupal\aggregator\Entity\Feed;
-use Drupal\aggregator\FeedStorageInterface;
 use Drupal\Core\Routing\RouteMatchInterface;
 
 /**
@@ -15,7 +14,7 @@
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x.
  *   Use \Drupal\aggregator\FeedStorageInterface::CLEAR_NEVER instead.
  */
-const AGGREGATOR_CLEAR_NEVER = FeedStorageInterface::CLEAR_NEVER;
+const AGGREGATOR_CLEAR_NEVER = 0;
 
 /**
  * Implements hook_help().
diff --git a/core/modules/comment/comment.module b/core/modules/comment/comment.module
index 1719f2f6d6..33af00ae88 100644
--- a/core/modules/comment/comment.module
+++ b/core/modules/comment/comment.module
@@ -32,7 +32,7 @@
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x.
  *   Use \Drupal\comment\CommentInterface::ANONYMOUS_MAYNOT_CONTACT instead.
  */
-const COMMENT_ANONYMOUS_MAYNOT_CONTACT = CommentInterface::ANONYMOUS_MAYNOT_CONTACT;
+const COMMENT_ANONYMOUS_MAYNOT_CONTACT = 0;
 
 /**
  * Anonymous posters may leave their contact information.
@@ -40,7 +40,7 @@
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x.
  *   Use \Drupal\comment\CommentInterface::ANONYMOUS_MAY_CONTACT instead.
  */
-const COMMENT_ANONYMOUS_MAY_CONTACT = CommentInterface::ANONYMOUS_MAY_CONTACT;
+const COMMENT_ANONYMOUS_MAY_CONTACT = 1;
 
 /**
  * Anonymous posters are required to leave their contact information.
@@ -48,7 +48,7 @@
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x.
  *   Use \Drupal\comment\CommentInterface::ANONYMOUS_MUST_CONTACT instead.
  */
-const COMMENT_ANONYMOUS_MUST_CONTACT = CommentInterface::ANONYMOUS_MUST_CONTACT;
+const COMMENT_ANONYMOUS_MUST_CONTACT = 2;
 
 /**
  * The time cutoff for comments marked as read for entity types other node.
diff --git a/core/modules/menu_ui/menu_ui.module b/core/modules/menu_ui/menu_ui.module
index 79cdcabdb5..bbd8669e29 100644
--- a/core/modules/menu_ui/menu_ui.module
+++ b/core/modules/menu_ui/menu_ui.module
@@ -17,7 +17,6 @@
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Routing\RouteMatchInterface;
 use Drupal\menu_link_content\Entity\MenuLinkContent;
-use Drupal\Core\Menu\MenuLinkManagerInterface;
 use Drupal\node\NodeTypeInterface;
 use Drupal\system\Entity\Menu;
 use Drupal\node\NodeInterface;
@@ -31,7 +30,7 @@
  *   Use \Drupal\Core\Menu\MenuLinkManagerInterface::MAX_MENU_NAME_LENGTH_UI
  *   instead.
  */
-const MENU_MAX_MENU_NAME_LENGTH_UI = MenuLinkManagerInterface::MAX_MENU_NAME_LENGTH_UI;
+const MENU_MAX_MENU_NAME_LENGTH_UI = 27;
 
 /**
  * Implements hook_help().
diff --git a/core/modules/responsive_image/responsive_image.module b/core/modules/responsive_image/responsive_image.module
index bea657a630..927c6106d9 100644
--- a/core/modules/responsive_image/responsive_image.module
+++ b/core/modules/responsive_image/responsive_image.module
@@ -11,7 +11,6 @@
 use Drupal\Core\Routing\RouteMatchInterface;
 use Drupal\image\Entity\ImageStyle;
 use Drupal\responsive_image\Entity\ResponsiveImageStyle;
-use Drupal\responsive_image\ResponsiveImageStyleInterface;
 use Drupal\Core\Image\ImageInterface;
 use Drupal\breakpoint\BreakpointInterface;
 
@@ -23,8 +22,8 @@
  *   and \Drupal\responsive_image\ResponsiveImageStyleInterface::ORIGINAL_IMAGE
  *   instead.
  */
-const RESPONSIVE_IMAGE_EMPTY_IMAGE = ResponsiveImageStyleInterface::EMPTY_IMAGE;
-const RESPONSIVE_IMAGE_ORIGINAL_IMAGE = ResponsiveImageStyleInterface::ORIGINAL_IMAGE;
+const RESPONSIVE_IMAGE_EMPTY_IMAGE = '_empty image_';
+const RESPONSIVE_IMAGE_ORIGINAL_IMAGE = '_original image_';
 
 /**
  * Implements hook_help().
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 01523f0391..473bdfabf4 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -13,7 +13,6 @@
 use Drupal\Core\Database\Query\AlterableInterface;
 use Drupal\Core\Extension\Extension;
 use Drupal\Core\Extension\ExtensionDiscovery;
-use Drupal\Core\Form\FormInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\KeyValueStore\KeyValueDatabaseExpirableFactory;
 use Drupal\Core\PageCache\RequestPolicyInterface;
@@ -59,7 +58,7 @@
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x.
  *   Use \Drupal\Core\Form\FormInterface::DISABLED instead.
  */
-const DRUPAL_DISABLED = FormInterface::DISABLED;
+const DRUPAL_DISABLED = 0;
 
 /**
  * Optional option on forms and settings.
@@ -67,7 +66,7 @@
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x.
  *   Use \Drupal\Core\Form\FormInterface::OPTIONAL instead.
  */
-const DRUPAL_OPTIONAL = FormInterface::OPTIONAL;
+const DRUPAL_OPTIONAL = 1;
 
 /**
  * Required option on forms and settings.
@@ -75,7 +74,7 @@
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x.
  *   Use \Drupal\Core\Form\FormInterface::REQUIRED instead.
  */
-const DRUPAL_REQUIRED = FormInterface::REQUIRED;
+const DRUPAL_REQUIRED = 2;
 
 /**
  * Return only visible regions.
diff --git a/core/modules/update/update.module b/core/modules/update/update.module
index 1a5711bf2a..f280e019ca 100644
--- a/core/modules/update/update.module
+++ b/core/modules/update/update.module
@@ -15,8 +15,6 @@
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Routing\RouteMatchInterface;
 use Drupal\Core\Site\Settings;
-use Drupal\update\UpdateFetcherInterface;
-use Drupal\update\UpdateManagerInterface;
 
 /*
  * These are internally used constants for this code, do not modify.
@@ -28,7 +26,7 @@
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x.
  *   Use \Drupal\update\UpdateManagerInterface::NOT_SECURE instead.
  */
-const UPDATE_NOT_SECURE = UpdateManagerInterface::NOT_SECURE;
+const UPDATE_NOT_SECURE = 1;
 
 /**
  * Current release has been unpublished and is no longer available.
@@ -36,7 +34,7 @@
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x.
  *   Use \Drupal\update\UpdateManagerInterface::REVOKED instead.
  */
-const UPDATE_REVOKED = UpdateManagerInterface::REVOKED;
+const UPDATE_REVOKED = 2;
 
 /**
  * Current release is no longer supported by the project maintainer.
@@ -44,7 +42,7 @@
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x.
  *   Use \Drupal\update\UpdateManagerInterface::NOT_SUPPORTED instead.
  */
-const UPDATE_NOT_SUPPORTED = UpdateManagerInterface::NOT_SUPPORTED;
+const UPDATE_NOT_SUPPORTED = 3;
 
 /**
  * Project has a new release available, but it is not a security release.
@@ -52,7 +50,7 @@
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x.
  *   Use \Drupal\update\UpdateManagerInterface::NOT_CURRENT instead.
  */
-const UPDATE_NOT_CURRENT = UpdateManagerInterface::NOT_CURRENT;
+const UPDATE_NOT_CURRENT = 4;
 
 /**
  * Project is up to date.
@@ -60,7 +58,7 @@
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x.
  *   Use \Drupal\update\UpdateManagerInterface::CURRENT instead.
  */
-const UPDATE_CURRENT = UpdateManagerInterface::CURRENT;
+const UPDATE_CURRENT = 5;
 
 /**
  * Project's status cannot be checked.
@@ -68,7 +66,7 @@
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x.
  *   Use \Drupal\update\UpdateFetcherInterface::NOT_CHECKED instead.
  */
-const UPDATE_NOT_CHECKED = UpdateFetcherInterface::NOT_CHECKED;
+const UPDATE_NOT_CHECKED = -1;
 
 /**
  * No available update data was found for project.
@@ -76,7 +74,7 @@
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x.
  *   Use \Drupal\update\UpdateFetcherInterface::UNKNOWN instead.
  */
-const UPDATE_UNKNOWN = UpdateFetcherInterface::UNKNOWN;
+const UPDATE_UNKNOWN = -2;
 
 /**
  * There was a failure fetching available update data for this project.
@@ -84,7 +82,7 @@
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x.
  *   Use \Drupal\update\UpdateFetcherInterface::NOT_FETCHED instead.
  */
-const UPDATE_NOT_FETCHED = UpdateFetcherInterface::NOT_FETCHED;
+const UPDATE_NOT_FETCHED = -3;
 
 /**
  * We need to (re)fetch available update data for this project.
@@ -92,7 +90,7 @@
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x.
  *   Use \Drupal\update\UpdateFetcherInterface::FETCH_PENDING instead.
  */
-const UPDATE_FETCH_PENDING = UpdateFetcherInterface::FETCH_PENDING;
+const UPDATE_FETCH_PENDING = -4;
 
 /**
  * Implements hook_help().
diff --git a/core/modules/user/user.module b/core/modules/user/user.module
index 26f768580e..969ef89c97 100644
--- a/core/modules/user/user.module
+++ b/core/modules/user/user.module
@@ -32,7 +32,7 @@
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x.
  *   Use \Drupal\user\UserInterface::USERNAME_MAX_LENGTH instead.
  */
-const USERNAME_MAX_LENGTH = UserInterface::USERNAME_MAX_LENGTH;
+const USERNAME_MAX_LENGTH = 60;
 
 /**
  * Only administrators can create user accounts.
@@ -40,7 +40,7 @@
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x.
  *   Use \Drupal\user\UserInterface::REGISTER_ADMINISTRATORS_ONLY instead.
  */
-const USER_REGISTER_ADMINISTRATORS_ONLY = UserInterface::REGISTER_ADMINISTRATORS_ONLY;
+const USER_REGISTER_ADMINISTRATORS_ONLY = 'admin_only';
 
 /**
  * Visitors can create their own accounts.
@@ -48,7 +48,7 @@
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x.
  *   Use \Drupal\user\UserInterface::REGISTER_VISITORS instead.
  */
-const USER_REGISTER_VISITORS = UserInterface::REGISTER_VISITORS;
+const USER_REGISTER_VISITORS = 'visitors';
 
 /**
  * Visitors can create accounts, but they don't become active without
@@ -58,7 +58,7 @@
  *   Use \Drupal\user\UserInterface::REGISTER_VISITORS_ADMINISTRATIVE_APPROVAL
  * instead.
  */
-const USER_REGISTER_VISITORS_ADMINISTRATIVE_APPROVAL = UserInterface::REGISTER_VISITORS_ADMINISTRATIVE_APPROVAL;
+const USER_REGISTER_VISITORS_ADMINISTRATIVE_APPROVAL = 'visitors_admin_approval';
 
 /**
  * Implements hook_help().