diff --git a/core/lib/Drupal/Core/Config/ConfigFactory.php b/core/lib/Drupal/Core/Config/ConfigFactory.php
index 112cd9f311..852f1d07b4 100644
--- a/core/lib/Drupal/Core/Config/ConfigFactory.php
+++ b/core/lib/Drupal/Core/Config/ConfigFactory.php
@@ -382,7 +382,7 @@ public function onConfigDelete(ConfigCrudEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[ConfigEvents::SAVE][] = ['onConfigSave', 255];
     $events[ConfigEvents::DELETE][] = ['onConfigDelete', 255];
     return $events;
diff --git a/core/lib/Drupal/Core/Config/Development/ConfigSchemaChecker.php b/core/lib/Drupal/Core/Config/Development/ConfigSchemaChecker.php
index acd39b49fe..428428d5c1 100644
--- a/core/lib/Drupal/Core/Config/Development/ConfigSchemaChecker.php
+++ b/core/lib/Drupal/Core/Config/Development/ConfigSchemaChecker.php
@@ -99,7 +99,7 @@ public function onConfigSave(ConfigCrudEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[ConfigEvents::SAVE][] = ['onConfigSave', 255];
     return $events;
   }
diff --git a/core/lib/Drupal/Core/Config/Entity/Query/QueryFactory.php b/core/lib/Drupal/Core/Config/Entity/Query/QueryFactory.php
index 15d18cfc00..889a535a12 100644
--- a/core/lib/Drupal/Core/Config/Entity/Query/QueryFactory.php
+++ b/core/lib/Drupal/Core/Config/Entity/Query/QueryFactory.php
@@ -249,7 +249,7 @@ public function onConfigDelete(ConfigCrudEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[ConfigEvents::SAVE][] = ['onConfigSave', 128];
     $events[ConfigEvents::DELETE][] = ['onConfigDelete', 128];
     return $events;
diff --git a/core/lib/Drupal/Core/Config/Importer/FinalMissingContentSubscriber.php b/core/lib/Drupal/Core/Config/Importer/FinalMissingContentSubscriber.php
index 3dca3fbf00..186aa95ae1 100644
--- a/core/lib/Drupal/Core/Config/Importer/FinalMissingContentSubscriber.php
+++ b/core/lib/Drupal/Core/Config/Importer/FinalMissingContentSubscriber.php
@@ -30,7 +30,7 @@ public function onMissingContent(MissingContentEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // This should always be the final event as it will mark all content
     // dependencies as resolved.
     $events[ConfigEvents::IMPORT_MISSING_CONTENT][] = ['onMissingContent', -1024];
diff --git a/core/lib/Drupal/Core/Database/ReplicaKillSwitch.php b/core/lib/Drupal/Core/Database/ReplicaKillSwitch.php
index 584a97c67b..d5ac045d8a 100644
--- a/core/lib/Drupal/Core/Database/ReplicaKillSwitch.php
+++ b/core/lib/Drupal/Core/Database/ReplicaKillSwitch.php
@@ -105,7 +105,7 @@ public function checkReplicaServer(RequestEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::REQUEST][] = ['checkReplicaServer'];
     return $events;
   }
diff --git a/core/lib/Drupal/Core/EventSubscriber/ActiveLinkResponseFilter.php b/core/lib/Drupal/Core/EventSubscriber/ActiveLinkResponseFilter.php
index d70f2ce074..7fdf31912a 100644
--- a/core/lib/Drupal/Core/EventSubscriber/ActiveLinkResponseFilter.php
+++ b/core/lib/Drupal/Core/EventSubscriber/ActiveLinkResponseFilter.php
@@ -245,7 +245,7 @@ public static function setLinkActiveClass($html_markup, $current_path, $is_front
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Should run after any other response subscriber that modifies the markup.
     $events[KernelEvents::RESPONSE][] = ['onResponse', -512];
 
diff --git a/core/lib/Drupal/Core/EventSubscriber/AjaxResponseSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/AjaxResponseSubscriber.php
index 5f730dcf4d..266dfc6a82 100644
--- a/core/lib/Drupal/Core/EventSubscriber/AjaxResponseSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/AjaxResponseSubscriber.php
@@ -109,7 +109,7 @@ public function onResponse(ResponseEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::RESPONSE][] = ['onResponse', -100];
     $events[KernelEvents::REQUEST][] = ['onRequest', 50];
 
diff --git a/core/lib/Drupal/Core/EventSubscriber/AnonymousUserResponseSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/AnonymousUserResponseSubscriber.php
index efb26ac7a5..be4505f539 100644
--- a/core/lib/Drupal/Core/EventSubscriber/AnonymousUserResponseSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/AnonymousUserResponseSubscriber.php
@@ -71,7 +71,7 @@ public function onRespond(ResponseEvent $event) {
    * @return array
    *   An array of event listener definitions.
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Priority 5, so that it runs before FinishResponseSubscriber, but after
     // event subscribers that add the associated cacheability metadata (which
     // have priority 10). This one is conditional, so must run after those.
diff --git a/core/lib/Drupal/Core/EventSubscriber/AuthenticationSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/AuthenticationSubscriber.php
index b592c1ad09..d2b82a1ab6 100644
--- a/core/lib/Drupal/Core/EventSubscriber/AuthenticationSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/AuthenticationSubscriber.php
@@ -139,7 +139,7 @@ public function onExceptionAccessDenied(ExceptionEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // The priority for authentication must be higher than the highest event
     // subscriber accessing the current user. Especially it must be higher than
     // LanguageRequestSubscriber as LanguageManager accesses the current user if
diff --git a/core/lib/Drupal/Core/EventSubscriber/CacheRouterRebuildSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/CacheRouterRebuildSubscriber.php
index c1f532799e..c65fd87c45 100644
--- a/core/lib/Drupal/Core/EventSubscriber/CacheRouterRebuildSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/CacheRouterRebuildSubscriber.php
@@ -23,7 +23,7 @@ public function onRouterFinished() {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events = [];
     // Act only when the router rebuild is finished.
     $events[RoutingEvents::FINISHED][] = ['onRouterFinished', 200];
diff --git a/core/lib/Drupal/Core/EventSubscriber/ClientErrorResponseSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/ClientErrorResponseSubscriber.php
index ea5b046781..0e37c1e96e 100644
--- a/core/lib/Drupal/Core/EventSubscriber/ClientErrorResponseSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/ClientErrorResponseSubscriber.php
@@ -39,7 +39,7 @@ public function onRespond(ResponseEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Priority 10, so that it runs before FinishResponseSubscriber, which will
     // expose the cacheability metadata in the form of headers.
     $events[KernelEvents::RESPONSE][] = ['onRespond', 10];
diff --git a/core/lib/Drupal/Core/EventSubscriber/ConfigSnapshotSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/ConfigSnapshotSubscriber.php
index 20e0cd6773..1cd5162ac2 100644
--- a/core/lib/Drupal/Core/EventSubscriber/ConfigSnapshotSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/ConfigSnapshotSubscriber.php
@@ -66,7 +66,7 @@ public function onConfigImporterImport(ConfigImporterEvent $event) {
    * @return array
    *   An array of event listener definitions.
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[ConfigEvents::IMPORT][] = ['onConfigImporterImport', 40];
     return $events;
   }
diff --git a/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php
index f904bc5f7a..56ff7b1379 100644
--- a/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php
@@ -166,7 +166,7 @@ protected function wrapControllerExecutionInRenderContext($controller, array $ar
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::CONTROLLER][] = ['onController'];
 
     return $events;
diff --git a/core/lib/Drupal/Core/EventSubscriber/EnforcedFormResponseSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/EnforcedFormResponseSubscriber.php
index e3c4a87203..19a156d7ca 100644
--- a/core/lib/Drupal/Core/EventSubscriber/EnforcedFormResponseSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/EnforcedFormResponseSubscriber.php
@@ -36,7 +36,7 @@ public function onKernelResponse(ResponseEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::EXCEPTION] = ['onKernelException', 128];
     $events[KernelEvents::RESPONSE] = ['onKernelResponse', 128];
 
diff --git a/core/lib/Drupal/Core/EventSubscriber/EntityRouteAlterSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/EntityRouteAlterSubscriber.php
index bca8f684b1..5aaafc170a 100644
--- a/core/lib/Drupal/Core/EventSubscriber/EntityRouteAlterSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/EntityRouteAlterSubscriber.php
@@ -52,7 +52,7 @@ public function onRoutingRouteAlterSetType(RouteBuildEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[RoutingEvents::ALTER][] = ['onRoutingRouteAlterSetType', -150];
     return $events;
   }
diff --git a/core/lib/Drupal/Core/EventSubscriber/EntityRouteProviderSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/EntityRouteProviderSubscriber.php
index 8246f784dd..f00395433e 100644
--- a/core/lib/Drupal/Core/EventSubscriber/EntityRouteProviderSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/EntityRouteProviderSubscriber.php
@@ -62,7 +62,7 @@ public function onDynamicRouteEvent(RouteBuildEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[RoutingEvents::DYNAMIC][] = ['onDynamicRouteEvent'];
     return $events;
   }
diff --git a/core/lib/Drupal/Core/EventSubscriber/ExceptionDetectNeedsInstallSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/ExceptionDetectNeedsInstallSubscriber.php
index ae0fcbebdb..9c75d90b85 100644
--- a/core/lib/Drupal/Core/EventSubscriber/ExceptionDetectNeedsInstallSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/ExceptionDetectNeedsInstallSubscriber.php
@@ -57,7 +57,7 @@ public function onException(ExceptionEvent $event) {
    * @return array
    *   An array of event listener definitions.
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::EXCEPTION][] = ['onException', 100];
     return $events;
   }
diff --git a/core/lib/Drupal/Core/EventSubscriber/ExceptionLoggingSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/ExceptionLoggingSubscriber.php
index 6b4bd1f14e..83e22bf9d2 100644
--- a/core/lib/Drupal/Core/EventSubscriber/ExceptionLoggingSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/ExceptionLoggingSubscriber.php
@@ -100,7 +100,7 @@ public function onException(ExceptionEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::EXCEPTION][] = ['onException', 50];
     return $events;
   }
diff --git a/core/lib/Drupal/Core/EventSubscriber/ExcludedModulesEventSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/ExcludedModulesEventSubscriber.php
index 93884d2b28..4f18c888dd 100644
--- a/core/lib/Drupal/Core/EventSubscriber/ExcludedModulesEventSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/ExcludedModulesEventSubscriber.php
@@ -54,7 +54,7 @@ public function __construct(StorageInterface $active_storage, Settings $settings
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // React early on export and late on import.
     return [
       'config.transform.import' => ['onConfigTransformImport', -500],
diff --git a/core/lib/Drupal/Core/EventSubscriber/FinalExceptionSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/FinalExceptionSubscriber.php
index 7c641fbc73..c940fea3ba 100644
--- a/core/lib/Drupal/Core/EventSubscriber/FinalExceptionSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/FinalExceptionSubscriber.php
@@ -141,7 +141,7 @@ public function onException(ExceptionEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Run as the final (very late) KernelEvents::EXCEPTION subscriber.
     $events[KernelEvents::EXCEPTION][] = ['onException', -256];
     return $events;
diff --git a/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php
index d00270f793..886749c790 100644
--- a/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php
@@ -314,7 +314,7 @@ protected function setExpiresNoCache(Response $response) {
    * @return array
    *   An array of event listener definitions.
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::RESPONSE][] = ['onRespond'];
     // There is no specific reason for choosing 16 beside it should be executed
     // before ::onRespond().
diff --git a/core/lib/Drupal/Core/EventSubscriber/HtmlResponsePlaceholderStrategySubscriber.php b/core/lib/Drupal/Core/EventSubscriber/HtmlResponsePlaceholderStrategySubscriber.php
index 7db706f3b0..8b9ab1d016 100644
--- a/core/lib/Drupal/Core/EventSubscriber/HtmlResponsePlaceholderStrategySubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/HtmlResponsePlaceholderStrategySubscriber.php
@@ -61,7 +61,7 @@ public function onRespond(ResponseEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Run shortly before HtmlResponseSubscriber.
     $events[KernelEvents::RESPONSE][] = ['onRespond', 5];
     return $events;
diff --git a/core/lib/Drupal/Core/EventSubscriber/HtmlResponseSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/HtmlResponseSubscriber.php
index 0526bbcc9b..df02677d69 100644
--- a/core/lib/Drupal/Core/EventSubscriber/HtmlResponseSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/HtmlResponseSubscriber.php
@@ -48,7 +48,7 @@ public function onRespond(ResponseEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::RESPONSE][] = ['onRespond'];
     return $events;
   }
diff --git a/core/lib/Drupal/Core/EventSubscriber/KernelDestructionSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/KernelDestructionSubscriber.php
index 331a5d5948..dfc7ab30b2 100644
--- a/core/lib/Drupal/Core/EventSubscriber/KernelDestructionSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/KernelDestructionSubscriber.php
@@ -59,7 +59,7 @@ public function onKernelTerminate(TerminateEvent $event) {
    * @return array
    *   An array of event listener definitions.
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::TERMINATE][] = ['onKernelTerminate', 100];
     return $events;
   }
diff --git a/core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php
index 8ad4aadae8..a4c42695b9 100644
--- a/core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php
@@ -101,7 +101,7 @@ public function onViewRenderArray(ViewEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::VIEW][] = ['onViewRenderArray'];
 
     return $events;
diff --git a/core/lib/Drupal/Core/EventSubscriber/MaintenanceModeSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/MaintenanceModeSubscriber.php
index 06a1263334..579d07d438 100644
--- a/core/lib/Drupal/Core/EventSubscriber/MaintenanceModeSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/MaintenanceModeSubscriber.php
@@ -154,7 +154,7 @@ protected function getSiteMaintenanceMessage() {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::REQUEST][] = ['onKernelRequestMaintenance', 30];
     $events[KernelEvents::EXCEPTION][] = ['onKernelRequestMaintenance'];
     return $events;
diff --git a/core/lib/Drupal/Core/EventSubscriber/MenuRouterRebuildSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/MenuRouterRebuildSubscriber.php
index 621cdeb7e5..b94aa9fa5b 100644
--- a/core/lib/Drupal/Core/EventSubscriber/MenuRouterRebuildSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/MenuRouterRebuildSubscriber.php
@@ -101,7 +101,7 @@ protected function menuLinksRebuild() {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Run after CachedRouteRebuildSubscriber.
     $events[RoutingEvents::FINISHED][] = ['onRouterRebuild', 100];
     return $events;
diff --git a/core/lib/Drupal/Core/EventSubscriber/OptionsRequestSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/OptionsRequestSubscriber.php
index 018ab6575d..66f5571081 100644
--- a/core/lib/Drupal/Core/EventSubscriber/OptionsRequestSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/OptionsRequestSubscriber.php
@@ -60,7 +60,7 @@ public function onRequest(RequestEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Set a high priority so it is executed before routing.
     $events[KernelEvents::REQUEST][] = ['onRequest', 1000];
     return $events;
diff --git a/core/lib/Drupal/Core/EventSubscriber/ParamConverterSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/ParamConverterSubscriber.php
index 3b12516853..0e3952753e 100644
--- a/core/lib/Drupal/Core/EventSubscriber/ParamConverterSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/ParamConverterSubscriber.php
@@ -43,7 +43,7 @@ public function onRoutingRouteAlterSetParameterConverters(RouteBuildEvent $event
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Run after \Drupal\system\EventSubscriber\AdminRouteSubscriber.
     $events[RoutingEvents::ALTER][] = ['onRoutingRouteAlterSetParameterConverters', -220];
     return $events;
diff --git a/core/lib/Drupal/Core/EventSubscriber/PathRootsSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/PathRootsSubscriber.php
index 0ded041a26..508e111650 100644
--- a/core/lib/Drupal/Core/EventSubscriber/PathRootsSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/PathRootsSubscriber.php
@@ -64,7 +64,7 @@ public function onRouteFinished() {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events = [];
     // Try to set a low priority to ensure that all routes are already added.
     $events[RoutingEvents::ALTER][] = ['onRouteAlter', -1024];
diff --git a/core/lib/Drupal/Core/EventSubscriber/PsrResponseSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/PsrResponseSubscriber.php
index e5d920900d..85c788aa30 100644
--- a/core/lib/Drupal/Core/EventSubscriber/PsrResponseSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/PsrResponseSubscriber.php
@@ -49,7 +49,7 @@ public function onKernelView(ViewEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::VIEW][] = ['onKernelView'];
     return $events;
   }
diff --git a/core/lib/Drupal/Core/EventSubscriber/RedirectLeadingSlashesSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/RedirectLeadingSlashesSubscriber.php
index 2b4eb93b39..dce347bcf7 100644
--- a/core/lib/Drupal/Core/EventSubscriber/RedirectLeadingSlashesSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/RedirectLeadingSlashesSubscriber.php
@@ -41,7 +41,7 @@ public function redirect(RequestEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::REQUEST][] = ['redirect', 1000];
     return $events;
   }
diff --git a/core/lib/Drupal/Core/EventSubscriber/RedirectResponseSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/RedirectResponseSubscriber.php
index afd22cda3b..6add632887 100644
--- a/core/lib/Drupal/Core/EventSubscriber/RedirectResponseSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/RedirectResponseSubscriber.php
@@ -134,7 +134,7 @@ protected function getDestinationAsAbsoluteUrl($destination, $scheme_and_host) {
    * @return array
    *   An array of event listener definitions.
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::RESPONSE][] = ['checkRedirectUrl'];
     return $events;
   }
diff --git a/core/lib/Drupal/Core/EventSubscriber/RenderArrayNonHtmlSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/RenderArrayNonHtmlSubscriber.php
index f88b91b3f2..c6f20372cd 100644
--- a/core/lib/Drupal/Core/EventSubscriber/RenderArrayNonHtmlSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/RenderArrayNonHtmlSubscriber.php
@@ -34,7 +34,7 @@ public function onRespond(ViewEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::VIEW][] = ['onRespond', -10];
     return $events;
   }
diff --git a/core/lib/Drupal/Core/EventSubscriber/RequestCloseSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/RequestCloseSubscriber.php
index 88a77dba29..bfde31939b 100644
--- a/core/lib/Drupal/Core/EventSubscriber/RequestCloseSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/RequestCloseSubscriber.php
@@ -48,7 +48,7 @@ public function onTerminate(TerminateEvent $event) {
    * @return array
    *   An array of event listener definitions.
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::TERMINATE][] = ['onTerminate', 100];
 
     return $events;
diff --git a/core/lib/Drupal/Core/EventSubscriber/ResponseGeneratorSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/ResponseGeneratorSubscriber.php
index bf45269588..c1ae3ae1a2 100644
--- a/core/lib/Drupal/Core/EventSubscriber/ResponseGeneratorSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/ResponseGeneratorSubscriber.php
@@ -32,7 +32,7 @@ public function onRespond(ResponseEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::RESPONSE][] = ['onRespond'];
     return $events;
   }
diff --git a/core/lib/Drupal/Core/EventSubscriber/RouteAccessResponseSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/RouteAccessResponseSubscriber.php
index add077dea5..1ccde84e87 100644
--- a/core/lib/Drupal/Core/EventSubscriber/RouteAccessResponseSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/RouteAccessResponseSubscriber.php
@@ -47,7 +47,7 @@ public function onRespond(ResponseEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Priority 10, so that it runs before FinishResponseSubscriber, which will
     // expose the cacheability metadata in the form of headers.
     $events[KernelEvents::RESPONSE][] = ['onRespond', 10];
diff --git a/core/lib/Drupal/Core/EventSubscriber/RouteMethodSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/RouteMethodSubscriber.php
index 3188835213..de7e60c100 100644
--- a/core/lib/Drupal/Core/EventSubscriber/RouteMethodSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/RouteMethodSubscriber.php
@@ -35,7 +35,7 @@ public function onRouteBuilding(RouteBuildEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Set a higher priority to ensure that routes get the default HTTP methods
     // as early as possible.
     $events[RoutingEvents::ALTER][] = ['onRouteBuilding', 5000];
diff --git a/core/lib/Drupal/Core/EventSubscriber/RssResponseRelativeUrlFilter.php b/core/lib/Drupal/Core/EventSubscriber/RssResponseRelativeUrlFilter.php
index 5da62bd823..593ea902bb 100644
--- a/core/lib/Drupal/Core/EventSubscriber/RssResponseRelativeUrlFilter.php
+++ b/core/lib/Drupal/Core/EventSubscriber/RssResponseRelativeUrlFilter.php
@@ -70,7 +70,7 @@ protected function transformRootRelativeUrlsToAbsolute($rss_markup, Request $req
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Should run after any other response subscriber that modifies the markup.
     // @see \Drupal\Core\EventSubscriber\ActiveLinkResponseFilter
     $events[KernelEvents::RESPONSE][] = ['onResponse', -512];
diff --git a/core/lib/Drupal/Core/Form/EventSubscriber/FormAjaxSubscriber.php b/core/lib/Drupal/Core/Form/EventSubscriber/FormAjaxSubscriber.php
index a224b891ae..f21cefae65 100644
--- a/core/lib/Drupal/Core/Form/EventSubscriber/FormAjaxSubscriber.php
+++ b/core/lib/Drupal/Core/Form/EventSubscriber/FormAjaxSubscriber.php
@@ -156,7 +156,7 @@ protected function formatSize($size) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Run before exception.logger.
     $events[KernelEvents::EXCEPTION] = ['onException', 51];
     // Run before main_content_view_subscriber.
diff --git a/core/lib/Drupal/Core/Routing/Enhancer/ParamConversionEnhancer.php b/core/lib/Drupal/Core/Routing/Enhancer/ParamConversionEnhancer.php
index 3d268e4816..704ee12a66 100644
--- a/core/lib/Drupal/Core/Routing/Enhancer/ParamConversionEnhancer.php
+++ b/core/lib/Drupal/Core/Routing/Enhancer/ParamConversionEnhancer.php
@@ -84,7 +84,7 @@ public function onException(ExceptionEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::EXCEPTION][] = ['onException', 75];
     return $events;
   }
diff --git a/core/lib/Drupal/Core/Routing/RoutePreloader.php b/core/lib/Drupal/Core/Routing/RoutePreloader.php
index 9a8fba810c..3d2b697227 100644
--- a/core/lib/Drupal/Core/Routing/RoutePreloader.php
+++ b/core/lib/Drupal/Core/Routing/RoutePreloader.php
@@ -117,7 +117,7 @@ public function onFinishedRoutes() {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Set a really low priority to catch as many as possible routes.
     $events[RoutingEvents::ALTER] = ['onAlterRoutes', -1024];
     $events[RoutingEvents::FINISHED] = ['onFinishedRoutes'];
diff --git a/core/lib/Drupal/Core/Routing/RouteProvider.php b/core/lib/Drupal/Core/Routing/RouteProvider.php
index 24c6f6ea05..beb302f72a 100644
--- a/core/lib/Drupal/Core/Routing/RouteProvider.php
+++ b/core/lib/Drupal/Core/Routing/RouteProvider.php
@@ -424,7 +424,7 @@ public function reset() {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[RoutingEvents::FINISHED][] = ['reset'];
     return $events;
   }
diff --git a/core/lib/Drupal/Core/Routing/RouteProviderLazyBuilder.php b/core/lib/Drupal/Core/Routing/RouteProviderLazyBuilder.php
index 0b3f9fd109..2621722712 100644
--- a/core/lib/Drupal/Core/Routing/RouteProviderLazyBuilder.php
+++ b/core/lib/Drupal/Core/Routing/RouteProviderLazyBuilder.php
@@ -171,7 +171,7 @@ public function hasRebuilt() {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[RoutingEvents::DYNAMIC][] = ['routerRebuilding', 3000];
     $events[RoutingEvents::FINISHED][] = ['routerRebuildFinished', -3000];
     return $events;
diff --git a/core/lib/Drupal/Core/Test/PerformanceTestRecorder.php b/core/lib/Drupal/Core/Test/PerformanceTestRecorder.php
index 8be037bdf5..e896df4737 100644
--- a/core/lib/Drupal/Core/Test/PerformanceTestRecorder.php
+++ b/core/lib/Drupal/Core/Test/PerformanceTestRecorder.php
@@ -81,7 +81,7 @@ public function onRouteBuilderFinish() {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events = [];
     $events[RoutingEvents::FINISHED][] = ['onRouteBuilderFinish', -9999999];
     return $events;
diff --git a/core/modules/automated_cron/src/EventSubscriber/AutomatedCron.php b/core/modules/automated_cron/src/EventSubscriber/AutomatedCron.php
index 634ff5f6a4..c237f07ea3 100644
--- a/core/modules/automated_cron/src/EventSubscriber/AutomatedCron.php
+++ b/core/modules/automated_cron/src/EventSubscriber/AutomatedCron.php
@@ -73,7 +73,7 @@ public function onTerminate(TerminateEvent $event) {
    * @return array
    *   An array of event listener definitions.
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     return [KernelEvents::TERMINATE => [['onTerminate', 100]]];
   }
 
diff --git a/core/modules/big_pipe/src/EventSubscriber/HtmlResponseBigPipeSubscriber.php b/core/modules/big_pipe/src/EventSubscriber/HtmlResponseBigPipeSubscriber.php
index 08b03f97dc..e818522a69 100644
--- a/core/modules/big_pipe/src/EventSubscriber/HtmlResponseBigPipeSubscriber.php
+++ b/core/modules/big_pipe/src/EventSubscriber/HtmlResponseBigPipeSubscriber.php
@@ -112,7 +112,7 @@ protected function getBigPipeService(ResponseEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Run after HtmlResponsePlaceholderStrategySubscriber (priority 5), i.e.
     // after BigPipeStrategy has been applied, but before normal (priority 0)
     // response subscribers have been applied, because by then it'll be too late
diff --git a/core/modules/big_pipe/src/EventSubscriber/NoBigPipeRouteAlterSubscriber.php b/core/modules/big_pipe/src/EventSubscriber/NoBigPipeRouteAlterSubscriber.php
index 8b3c9c23a7..1ba1702e3c 100644
--- a/core/modules/big_pipe/src/EventSubscriber/NoBigPipeRouteAlterSubscriber.php
+++ b/core/modules/big_pipe/src/EventSubscriber/NoBigPipeRouteAlterSubscriber.php
@@ -40,7 +40,7 @@ public function onRoutingRouteAlterSetNoBigPipe(RouteBuildEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[RoutingEvents::ALTER][] = ['onRoutingRouteAlterSetNoBigPipe'];
     return $events;
   }
diff --git a/core/modules/big_pipe/tests/modules/big_pipe_test/src/EventSubscriber/BigPipeTestSubscriber.php b/core/modules/big_pipe/tests/modules/big_pipe_test/src/EventSubscriber/BigPipeTestSubscriber.php
index 5bf8d5a3b3..c21d153ace 100644
--- a/core/modules/big_pipe/tests/modules/big_pipe_test/src/EventSubscriber/BigPipeTestSubscriber.php
+++ b/core/modules/big_pipe/tests/modules/big_pipe_test/src/EventSubscriber/BigPipeTestSubscriber.php
@@ -71,7 +71,7 @@ public function onRespondSetBigPipeDebugPlaceholderHeaders(ResponseEvent $event)
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Run just before \Drupal\big_pipe\EventSubscriber\HtmlResponseBigPipeSubscriber::onRespond().
     $events[KernelEvents::RESPONSE][] = ['onRespondSetBigPipeDebugPlaceholderHeaders', -9999];
 
diff --git a/core/modules/block/src/EventSubscriber/BlockPageDisplayVariantSubscriber.php b/core/modules/block/src/EventSubscriber/BlockPageDisplayVariantSubscriber.php
index 89f361f440..c7dc9fc81a 100644
--- a/core/modules/block/src/EventSubscriber/BlockPageDisplayVariantSubscriber.php
+++ b/core/modules/block/src/EventSubscriber/BlockPageDisplayVariantSubscriber.php
@@ -26,7 +26,7 @@ public function onSelectPageDisplayVariant(PageDisplayVariantSelectionEvent $eve
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[RenderEvents::SELECT_PAGE_DISPLAY_VARIANT][] = ['onSelectPageDisplayVariant'];
     return $events;
   }
diff --git a/core/modules/color/src/EventSubscriber/ColorConfigCacheInvalidator.php b/core/modules/color/src/EventSubscriber/ColorConfigCacheInvalidator.php
index 46b67a1d23..b39af35e9d 100644
--- a/core/modules/color/src/EventSubscriber/ColorConfigCacheInvalidator.php
+++ b/core/modules/color/src/EventSubscriber/ColorConfigCacheInvalidator.php
@@ -46,7 +46,7 @@ public function onChange(ConfigCrudEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[ConfigEvents::SAVE][] = ['onChange'];
     $events[ConfigEvents::DELETE][] = ['onChange'];
 
diff --git a/core/modules/config/src/ConfigSubscriber.php b/core/modules/config/src/ConfigSubscriber.php
index 779bab67dd..b42999a712 100644
--- a/core/modules/config/src/ConfigSubscriber.php
+++ b/core/modules/config/src/ConfigSubscriber.php
@@ -33,7 +33,7 @@ public function onConfigImporterValidate(ConfigImporterEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[ConfigEvents::IMPORT_VALIDATE][] = ['onConfigImporterValidate', 20];
     return $events;
   }
diff --git a/core/modules/config/tests/config_collection_install_test/src/EventSubscriber.php b/core/modules/config/tests/config_collection_install_test/src/EventSubscriber.php
index ae38661284..7f6a60f237 100644
--- a/core/modules/config/tests/config_collection_install_test/src/EventSubscriber.php
+++ b/core/modules/config/tests/config_collection_install_test/src/EventSubscriber.php
@@ -42,7 +42,7 @@ public function addCollections(ConfigCollectionInfo $collection_info) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[ConfigEvents::COLLECTION_INFO][] = ['addCollections'];
     return $events;
   }
diff --git a/core/modules/config/tests/config_events_test/src/EventSubscriber.php b/core/modules/config/tests/config_events_test/src/EventSubscriber.php
index 0cdc4416c3..8a79b8b606 100644
--- a/core/modules/config/tests/config_events_test/src/EventSubscriber.php
+++ b/core/modules/config/tests/config_events_test/src/EventSubscriber.php
@@ -47,7 +47,7 @@ public function configEventRecorder(ConfigCrudEvent $event, $name) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[ConfigEvents::SAVE][] = ['configEventRecorder'];
     $events[ConfigEvents::DELETE][] = ['configEventRecorder'];
     $events[ConfigEvents::RENAME][] = ['configEventRecorder'];
diff --git a/core/modules/config/tests/config_import_test/src/EventSubscriber.php b/core/modules/config/tests/config_import_test/src/EventSubscriber.php
index 6b72b8ac99..ad6b52b361 100644
--- a/core/modules/config/tests/config_import_test/src/EventSubscriber.php
+++ b/core/modules/config/tests/config_import_test/src/EventSubscriber.php
@@ -131,7 +131,7 @@ public function onConfigDelete(ConfigCrudEvent $event) {
    * @return array
    *   An array of event listener definitions.
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[ConfigEvents::SAVE][] = ['onConfigSave', 40];
     $events[ConfigEvents::DELETE][] = ['onConfigDelete', 40];
     $events[ConfigEvents::IMPORT_VALIDATE] = ['onConfigImporterValidate'];
diff --git a/core/modules/config/tests/config_transformer_test/src/EventSubscriber.php b/core/modules/config/tests/config_transformer_test/src/EventSubscriber.php
index 1370020abd..bec371642f 100644
--- a/core/modules/config/tests/config_transformer_test/src/EventSubscriber.php
+++ b/core/modules/config/tests/config_transformer_test/src/EventSubscriber.php
@@ -105,7 +105,7 @@ public function onExportTransform(StorageTransformEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[ConfigEvents::STORAGE_TRANSFORM_IMPORT][] = ['onImportTransform'];
     $events[ConfigEvents::STORAGE_TRANSFORM_EXPORT][] = ['onExportTransform'];
     return $events;
diff --git a/core/modules/config_translation/src/Routing/RouteSubscriber.php b/core/modules/config_translation/src/Routing/RouteSubscriber.php
index 10044aa7f8..5897212cd6 100644
--- a/core/modules/config_translation/src/Routing/RouteSubscriber.php
+++ b/core/modules/config_translation/src/Routing/RouteSubscriber.php
@@ -46,7 +46,7 @@ protected function alterRoutes(RouteCollection $collection) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Come after field_ui.
     $events[RoutingEvents::ALTER] = ['onAlterRoutes', -110];
     return $events;
diff --git a/core/modules/config_translation/tests/modules/config_translation_test/src/EventSubscriber/ConfigTranslationTestSubscriber.php b/core/modules/config_translation/tests/modules/config_translation_test/src/EventSubscriber/ConfigTranslationTestSubscriber.php
index 15fc6ac40a..305dbb0eca 100644
--- a/core/modules/config_translation/tests/modules/config_translation_test/src/EventSubscriber/ConfigTranslationTestSubscriber.php
+++ b/core/modules/config_translation/tests/modules/config_translation_test/src/EventSubscriber/ConfigTranslationTestSubscriber.php
@@ -14,7 +14,7 @@ class ConfigTranslationTestSubscriber implements EventSubscriberInterface {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     return [
       ConfigTranslationEvents::POPULATE_MAPPER => [
         ['addConfigNames'],
diff --git a/core/modules/content_moderation/src/Routing/ContentModerationRouteSubscriber.php b/core/modules/content_moderation/src/Routing/ContentModerationRouteSubscriber.php
index 934734da3c..9dfe9612ca 100644
--- a/core/modules/content_moderation/src/Routing/ContentModerationRouteSubscriber.php
+++ b/core/modules/content_moderation/src/Routing/ContentModerationRouteSubscriber.php
@@ -102,7 +102,7 @@ protected function getModeratedEntityTypes() {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events = parent::getSubscribedEvents();
     // This needs to run after that EntityResolverManager has set the route
     // entity type.
diff --git a/core/modules/content_translation/src/Routing/ContentTranslationRouteSubscriber.php b/core/modules/content_translation/src/Routing/ContentTranslationRouteSubscriber.php
index 6cd3b350df..8e68d69591 100644
--- a/core/modules/content_translation/src/Routing/ContentTranslationRouteSubscriber.php
+++ b/core/modules/content_translation/src/Routing/ContentTranslationRouteSubscriber.php
@@ -173,7 +173,7 @@ protected function alterRoutes(RouteCollection $collection) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events = parent::getSubscribedEvents();
     // Should run after AdminRouteSubscriber so the routes can inherit admin
     // status of the edit routes on entities. Therefore priority -210.
diff --git a/core/modules/dynamic_page_cache/src/EventSubscriber/DynamicPageCacheSubscriber.php b/core/modules/dynamic_page_cache/src/EventSubscriber/DynamicPageCacheSubscriber.php
index 22b51b9ea5..2f75ccfaff 100644
--- a/core/modules/dynamic_page_cache/src/EventSubscriber/DynamicPageCacheSubscriber.php
+++ b/core/modules/dynamic_page_cache/src/EventSubscriber/DynamicPageCacheSubscriber.php
@@ -304,7 +304,7 @@ protected function renderArrayToResponse(array $render_array) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events = [];
 
     // Run after AuthenticationSubscriber (necessary for the 'user' cache
diff --git a/core/modules/editor/src/EventSubscriber/EditorConfigTranslationSubscriber.php b/core/modules/editor/src/EventSubscriber/EditorConfigTranslationSubscriber.php
index eb43ddc6b5..d505ef224e 100644
--- a/core/modules/editor/src/EventSubscriber/EditorConfigTranslationSubscriber.php
+++ b/core/modules/editor/src/EventSubscriber/EditorConfigTranslationSubscriber.php
@@ -33,7 +33,7 @@ public function __construct(ConfigFactoryInterface $config_factory) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events = [];
     if (class_exists('Drupal\config_translation\Event\ConfigTranslationEvents')) {
       $events[ConfigTranslationEvents::POPULATE_MAPPER][] = ['addConfigNames'];
diff --git a/core/modules/field_ui/src/Routing/RouteSubscriber.php b/core/modules/field_ui/src/Routing/RouteSubscriber.php
index 046176a83b..75e6b4b691 100644
--- a/core/modules/field_ui/src/Routing/RouteSubscriber.php
+++ b/core/modules/field_ui/src/Routing/RouteSubscriber.php
@@ -161,7 +161,7 @@ protected function alterRoutes(RouteCollection $collection) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events = parent::getSubscribedEvents();
     $events[RoutingEvents::ALTER] = ['onAlterRoutes', -100];
     return $events;
diff --git a/core/modules/jsonapi/src/EventSubscriber/JsonApiRequestValidator.php b/core/modules/jsonapi/src/EventSubscriber/JsonApiRequestValidator.php
index db33f307e1..43b16a1055 100644
--- a/core/modules/jsonapi/src/EventSubscriber/JsonApiRequestValidator.php
+++ b/core/modules/jsonapi/src/EventSubscriber/JsonApiRequestValidator.php
@@ -83,7 +83,7 @@ protected function validateQueryParams(Request $request) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::REQUEST][] = ['onRequest'];
     return $events;
   }
diff --git a/core/modules/jsonapi/src/EventSubscriber/ResourceObjectNormalizationCacher.php b/core/modules/jsonapi/src/EventSubscriber/ResourceObjectNormalizationCacher.php
index 667eb83d25..cd63e1d80f 100644
--- a/core/modules/jsonapi/src/EventSubscriber/ResourceObjectNormalizationCacher.php
+++ b/core/modules/jsonapi/src/EventSubscriber/ResourceObjectNormalizationCacher.php
@@ -173,7 +173,7 @@ protected static function generateLookupRenderArray(ResourceObject $object) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::TERMINATE][] = ['onTerminate'];
     return $events;
   }
diff --git a/core/modules/jsonapi/src/EventSubscriber/ResourceResponseSubscriber.php b/core/modules/jsonapi/src/EventSubscriber/ResourceResponseSubscriber.php
index edf81cb677..6d47e9d234 100644
--- a/core/modules/jsonapi/src/EventSubscriber/ResourceResponseSubscriber.php
+++ b/core/modules/jsonapi/src/EventSubscriber/ResourceResponseSubscriber.php
@@ -61,7 +61,7 @@ public function __construct(SerializerInterface $serializer) {
    * @see \Drupal\rest\EventSubscriber\ResourceResponseSubscriber::getSubscribedEvents()
    * @see \Drupal\dynamic_page_cache\EventSubscriber\DynamicPageCacheSubscriber
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Run before the dynamic page cache subscriber (priority 100), so that
     // Dynamic Page Cache can cache flattened responses.
     $events[KernelEvents::RESPONSE][] = ['onResponse', 128];
diff --git a/core/modules/jsonapi/src/EventSubscriber/ResourceResponseValidator.php b/core/modules/jsonapi/src/EventSubscriber/ResourceResponseValidator.php
index 1ba0cd0196..3f08f56a8a 100644
--- a/core/modules/jsonapi/src/EventSubscriber/ResourceResponseValidator.php
+++ b/core/modules/jsonapi/src/EventSubscriber/ResourceResponseValidator.php
@@ -76,7 +76,7 @@ public function __construct(LoggerInterface $logger, ModuleHandlerInterface $mod
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::RESPONSE][] = ['onResponse'];
     return $events;
   }
diff --git a/core/modules/jsonapi/tests/modules/jsonapi_test_resource_type_building/src/EventSubscriber/ResourceTypeBuildEventSubscriber.php b/core/modules/jsonapi/tests/modules/jsonapi_test_resource_type_building/src/EventSubscriber/ResourceTypeBuildEventSubscriber.php
index 658ac0afc0..f97df3ee84 100644
--- a/core/modules/jsonapi/tests/modules/jsonapi_test_resource_type_building/src/EventSubscriber/ResourceTypeBuildEventSubscriber.php
+++ b/core/modules/jsonapi/tests/modules/jsonapi_test_resource_type_building/src/EventSubscriber/ResourceTypeBuildEventSubscriber.php
@@ -16,7 +16,7 @@ class ResourceTypeBuildEventSubscriber implements EventSubscriberInterface {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     return [
       ResourceTypeBuildEvents::BUILD => [
         ['disableResourceType'],
diff --git a/core/modules/language/src/EventSubscriber/ConfigSubscriber.php b/core/modules/language/src/EventSubscriber/ConfigSubscriber.php
index 5fd08e6b65..ff35d9b6d6 100644
--- a/core/modules/language/src/EventSubscriber/ConfigSubscriber.php
+++ b/core/modules/language/src/EventSubscriber/ConfigSubscriber.php
@@ -140,7 +140,7 @@ public function setPathProcessorLanguage(PathProcessorLanguage $path_processor_l
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[ConfigEvents::SAVE][] = ['onConfigSave', 0];
     return $events;
   }
diff --git a/core/modules/language/src/EventSubscriber/LanguageRequestSubscriber.php b/core/modules/language/src/EventSubscriber/LanguageRequestSubscriber.php
index e7320f34a5..e43680bf3a 100644
--- a/core/modules/language/src/EventSubscriber/LanguageRequestSubscriber.php
+++ b/core/modules/language/src/EventSubscriber/LanguageRequestSubscriber.php
@@ -103,7 +103,7 @@ private function setLanguageOverrides() {
    * @return array
    *   An array of event listener definitions.
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::REQUEST][] = ['onKernelRequestLanguage', 255];
     $events[DrupalKernelInterface::CONTAINER_INITIALIZE_SUBREQUEST_FINISHED][] = ['onContainerInitializeSubrequestFinished', 255];
 
diff --git a/core/modules/layout_builder/src/EventSubscriber/BlockComponentRenderArray.php b/core/modules/layout_builder/src/EventSubscriber/BlockComponentRenderArray.php
index 8ed8137f25..083de3983d 100644
--- a/core/modules/layout_builder/src/EventSubscriber/BlockComponentRenderArray.php
+++ b/core/modules/layout_builder/src/EventSubscriber/BlockComponentRenderArray.php
@@ -47,7 +47,7 @@ public function __construct(AccountInterface $current_user) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[LayoutBuilderEvents::SECTION_COMPONENT_BUILD_RENDER_ARRAY] = ['onBuildRender', 100];
     return $events;
   }
diff --git a/core/modules/layout_builder/src/EventSubscriber/PrepareLayout.php b/core/modules/layout_builder/src/EventSubscriber/PrepareLayout.php
index e335b87ab8..ec8122b2fd 100644
--- a/core/modules/layout_builder/src/EventSubscriber/PrepareLayout.php
+++ b/core/modules/layout_builder/src/EventSubscriber/PrepareLayout.php
@@ -51,7 +51,7 @@ public function __construct(LayoutTempstoreRepositoryInterface $layout_tempstore
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[LayoutBuilderEvents::PREPARE_LAYOUT][] = ['onPrepareLayout', 10];
     return $events;
   }
diff --git a/core/modules/layout_builder/src/EventSubscriber/SetInlineBlockDependency.php b/core/modules/layout_builder/src/EventSubscriber/SetInlineBlockDependency.php
index d1ff4ad3dc..a1fb950be7 100644
--- a/core/modules/layout_builder/src/EventSubscriber/SetInlineBlockDependency.php
+++ b/core/modules/layout_builder/src/EventSubscriber/SetInlineBlockDependency.php
@@ -79,7 +79,7 @@ public function __construct(EntityTypeManagerInterface $entity_type_manager, Con
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     return [
       BlockContentEvents::BLOCK_CONTENT_GET_DEPENDENCY => 'onGetDependency',
     ];
diff --git a/core/modules/layout_builder/src/Routing/LayoutBuilderRoutes.php b/core/modules/layout_builder/src/Routing/LayoutBuilderRoutes.php
index 60d0937968..6039e24247 100644
--- a/core/modules/layout_builder/src/Routing/LayoutBuilderRoutes.php
+++ b/core/modules/layout_builder/src/Routing/LayoutBuilderRoutes.php
@@ -48,7 +48,7 @@ public function onAlterRoutes(RouteBuildEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Run after \Drupal\field_ui\Routing\RouteSubscriber.
     $events[RoutingEvents::ALTER] = ['onAlterRoutes', -110];
     return $events;
diff --git a/core/modules/layout_builder/tests/modules/layout_builder_element_test/src/EventSubscriber/TestPrepareLayout.php b/core/modules/layout_builder/tests/modules/layout_builder_element_test/src/EventSubscriber/TestPrepareLayout.php
index cec4af43bb..0d9c1afd50 100644
--- a/core/modules/layout_builder/tests/modules/layout_builder_element_test/src/EventSubscriber/TestPrepareLayout.php
+++ b/core/modules/layout_builder/tests/modules/layout_builder_element_test/src/EventSubscriber/TestPrepareLayout.php
@@ -52,7 +52,7 @@ public function __construct(LayoutTempstoreRepositoryInterface $layout_tempstore
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Act before core's layout builder subscriber.
     $events[LayoutBuilderEvents::PREPARE_LAYOUT][] = ['onBeforePrepareLayout', 20];
     // Act after core's layout builder subscriber.
diff --git a/core/modules/locale/src/EventSubscriber/LocaleTranslationCacheTag.php b/core/modules/locale/src/EventSubscriber/LocaleTranslationCacheTag.php
index 4968097906..0faa7e3250 100644
--- a/core/modules/locale/src/EventSubscriber/LocaleTranslationCacheTag.php
+++ b/core/modules/locale/src/EventSubscriber/LocaleTranslationCacheTag.php
@@ -38,7 +38,7 @@ public function saveTranslation() {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[LocaleEvents::SAVE_TRANSLATION][] = ['saveTranslation'];
     return $events;
   }
diff --git a/core/modules/locale/src/LocaleConfigSubscriber.php b/core/modules/locale/src/LocaleConfigSubscriber.php
index 289e838e05..1763eb2952 100644
--- a/core/modules/locale/src/LocaleConfigSubscriber.php
+++ b/core/modules/locale/src/LocaleConfigSubscriber.php
@@ -63,7 +63,7 @@ public function __construct(ConfigFactoryInterface $config_factory, LocaleConfig
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[LanguageConfigOverrideEvents::SAVE_OVERRIDE] = 'onOverrideChange';
     $events[LanguageConfigOverrideEvents::DELETE_OVERRIDE] = 'onOverrideChange';
     $events[ConfigEvents::SAVE] = 'onConfigSave';
diff --git a/core/modules/media/src/EventSubscriber/MediaConfigSubscriber.php b/core/modules/media/src/EventSubscriber/MediaConfigSubscriber.php
index 82721e02b3..21efa1a1f7 100644
--- a/core/modules/media/src/EventSubscriber/MediaConfigSubscriber.php
+++ b/core/modules/media/src/EventSubscriber/MediaConfigSubscriber.php
@@ -84,7 +84,7 @@ public function onSave(ConfigCrudEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[ConfigEvents::SAVE][] = ['onSave'];
     return $events;
   }
diff --git a/core/modules/migrate/src/Plugin/PluginEventSubscriber.php b/core/modules/migrate/src/Plugin/PluginEventSubscriber.php
index d503638269..1e839faf0c 100644
--- a/core/modules/migrate/src/Plugin/PluginEventSubscriber.php
+++ b/core/modules/migrate/src/Plugin/PluginEventSubscriber.php
@@ -81,7 +81,7 @@ public function postRollback(MigrateRollbackEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events = [];
     $events[MigrateEvents::PRE_IMPORT][] = ['preImport'];
     $events[MigrateEvents::POST_IMPORT][] = ['postImport'];
diff --git a/core/modules/node/src/EventSubscriber/NodeAdminRouteSubscriber.php b/core/modules/node/src/EventSubscriber/NodeAdminRouteSubscriber.php
index 722c70549d..2b53991e55 100644
--- a/core/modules/node/src/EventSubscriber/NodeAdminRouteSubscriber.php
+++ b/core/modules/node/src/EventSubscriber/NodeAdminRouteSubscriber.php
@@ -68,7 +68,7 @@ public function onConfigSave(ConfigCrudEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events = parent::getSubscribedEvents();
     $events[ConfigEvents::SAVE][] = ['onConfigSave', 0];
     return $events;
diff --git a/core/modules/node/src/EventSubscriber/NodeTranslationExceptionSubscriber.php b/core/modules/node/src/EventSubscriber/NodeTranslationExceptionSubscriber.php
index 7d93e7201a..2aa2b42fc0 100644
--- a/core/modules/node/src/EventSubscriber/NodeTranslationExceptionSubscriber.php
+++ b/core/modules/node/src/EventSubscriber/NodeTranslationExceptionSubscriber.php
@@ -117,7 +117,7 @@ public function onException(ExceptionEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events = [];
 
     $events[KernelEvents::EXCEPTION] = ['onException'];
diff --git a/core/modules/node/src/EventSubscriber/NodeTranslationMigrateSubscriber.php b/core/modules/node/src/EventSubscriber/NodeTranslationMigrateSubscriber.php
index 5911f0e05f..39e1f5aceb 100644
--- a/core/modules/node/src/EventSubscriber/NodeTranslationMigrateSubscriber.php
+++ b/core/modules/node/src/EventSubscriber/NodeTranslationMigrateSubscriber.php
@@ -101,7 +101,7 @@ public function onPostImport(MigrateImportEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events = [];
 
     $events[MigrateEvents::POST_ROW_SAVE] = ['onPostRowSave'];
diff --git a/core/modules/path_alias/src/EventSubscriber/PathAliasSubscriber.php b/core/modules/path_alias/src/EventSubscriber/PathAliasSubscriber.php
index 6ed435a0b5..3dce19b18b 100644
--- a/core/modules/path_alias/src/EventSubscriber/PathAliasSubscriber.php
+++ b/core/modules/path_alias/src/EventSubscriber/PathAliasSubscriber.php
@@ -69,7 +69,7 @@ public function onKernelTerminate(TerminateEvent $event) {
    * @return array
    *   An array of event listener definitions.
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::CONTROLLER][] = ['onKernelController', 200];
     $events[KernelEvents::TERMINATE][] = ['onKernelTerminate', 200];
     return $events;
diff --git a/core/modules/rest/src/EventSubscriber/EntityResourcePostRouteSubscriber.php b/core/modules/rest/src/EventSubscriber/EntityResourcePostRouteSubscriber.php
index 80d29dc3f4..42830f66b2 100644
--- a/core/modules/rest/src/EventSubscriber/EntityResourcePostRouteSubscriber.php
+++ b/core/modules/rest/src/EventSubscriber/EntityResourcePostRouteSubscriber.php
@@ -64,7 +64,7 @@ public function onDynamicRouteEvent(RouteBuildEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Priority -10, to run after \Drupal\rest\Routing\ResourceRoutes, which has
     // priority 0.
     $events[RoutingEvents::DYNAMIC][] = ['onDynamicRouteEvent', -10];
diff --git a/core/modules/rest/src/EventSubscriber/ResourceResponseSubscriber.php b/core/modules/rest/src/EventSubscriber/ResourceResponseSubscriber.php
index 47ea8800ae..2fe460fce3 100644
--- a/core/modules/rest/src/EventSubscriber/ResourceResponseSubscriber.php
+++ b/core/modules/rest/src/EventSubscriber/ResourceResponseSubscriber.php
@@ -200,7 +200,7 @@ protected function flattenResponse(ResourceResponseInterface $response) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Run before \Drupal\dynamic_page_cache\EventSubscriber\DynamicPageCacheSubscriber
     // (priority 100), so that Dynamic Page Cache can cache flattened responses.
     $events[KernelEvents::RESPONSE][] = ['onResponse', 128];
diff --git a/core/modules/rest/src/Routing/ResourceRoutes.php b/core/modules/rest/src/Routing/ResourceRoutes.php
index f8ebbff151..f4628130f8 100644
--- a/core/modules/rest/src/Routing/ResourceRoutes.php
+++ b/core/modules/rest/src/Routing/ResourceRoutes.php
@@ -140,7 +140,7 @@ protected function getRoutesForResourceConfig(RestResourceConfigInterface $rest_
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[RoutingEvents::DYNAMIC] = 'onDynamicRouteEvent';
     return $events;
   }
diff --git a/core/modules/serialization/src/EventSubscriber/UserRouteAlterSubscriber.php b/core/modules/serialization/src/EventSubscriber/UserRouteAlterSubscriber.php
index 147b593aa1..8f84eb5462 100644
--- a/core/modules/serialization/src/EventSubscriber/UserRouteAlterSubscriber.php
+++ b/core/modules/serialization/src/EventSubscriber/UserRouteAlterSubscriber.php
@@ -31,7 +31,7 @@ public function __construct(array $serializer_formats) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[RoutingEvents::ALTER][] = 'onRoutingAlterAddFormats';
     return $events;
   }
diff --git a/core/modules/system/src/EventSubscriber/AdminRouteSubscriber.php b/core/modules/system/src/EventSubscriber/AdminRouteSubscriber.php
index 06a6ba4890..7c1d9a30a5 100644
--- a/core/modules/system/src/EventSubscriber/AdminRouteSubscriber.php
+++ b/core/modules/system/src/EventSubscriber/AdminRouteSubscriber.php
@@ -27,7 +27,7 @@ protected function alterRoutes(RouteCollection $collection) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events = parent::getSubscribedEvents();
 
     // Use a lower priority than \Drupal\field_ui\Routing\RouteSubscriber or
diff --git a/core/modules/system/src/EventSubscriber/ConfigCacheTag.php b/core/modules/system/src/EventSubscriber/ConfigCacheTag.php
index 68050aa85a..8202edd2e7 100644
--- a/core/modules/system/src/EventSubscriber/ConfigCacheTag.php
+++ b/core/modules/system/src/EventSubscriber/ConfigCacheTag.php
@@ -79,7 +79,7 @@ public function onSave(ConfigCrudEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[ConfigEvents::SAVE][] = ['onSave'];
     return $events;
   }
diff --git a/core/modules/system/src/EventSubscriber/SecurityFileUploadEventSubscriber.php b/core/modules/system/src/EventSubscriber/SecurityFileUploadEventSubscriber.php
index 4aeeb574d3..e90959e325 100644
--- a/core/modules/system/src/EventSubscriber/SecurityFileUploadEventSubscriber.php
+++ b/core/modules/system/src/EventSubscriber/SecurityFileUploadEventSubscriber.php
@@ -34,7 +34,7 @@ public function __construct(ConfigFactoryInterface $config_factory) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // This event must be run last to ensure the filename obeys the security
     // rules.
     $events[FileUploadSanitizeNameEvent::class][] = ['sanitizeName', PHP_INT_MIN];
diff --git a/core/modules/system/src/SystemConfigSubscriber.php b/core/modules/system/src/SystemConfigSubscriber.php
index 0ab0d15fc6..c51a1bf166 100644
--- a/core/modules/system/src/SystemConfigSubscriber.php
+++ b/core/modules/system/src/SystemConfigSubscriber.php
@@ -83,7 +83,7 @@ public function onConfigImporterValidateSiteUUID(ConfigImporterEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[ConfigEvents::SAVE][] = ['onConfigSave', 0];
     // The empty check has a high priority so that it can stop propagation if
     // there is no configuration to import.
diff --git a/core/modules/system/src/TimeZoneResolver.php b/core/modules/system/src/TimeZoneResolver.php
index 551a8d5cda..050b843e99 100644
--- a/core/modules/system/src/TimeZoneResolver.php
+++ b/core/modules/system/src/TimeZoneResolver.php
@@ -71,7 +71,7 @@ public function onConfigSave(ConfigCrudEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[ConfigEvents::SAVE][] = ['onConfigSave', 0];
     // The priority for this must run directly after the authentication
     // subscriber.
diff --git a/core/modules/system/tests/modules/display_variant_test/src/EventSubscriber/TestPageDisplayVariantSubscriber.php b/core/modules/system/tests/modules/display_variant_test/src/EventSubscriber/TestPageDisplayVariantSubscriber.php
index e24266e033..01900c2ed1 100644
--- a/core/modules/system/tests/modules/display_variant_test/src/EventSubscriber/TestPageDisplayVariantSubscriber.php
+++ b/core/modules/system/tests/modules/display_variant_test/src/EventSubscriber/TestPageDisplayVariantSubscriber.php
@@ -31,7 +31,7 @@ public function onSelectPageDisplayVariant(PageDisplayVariantSelectionEvent $eve
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[RenderEvents::SELECT_PAGE_DISPLAY_VARIANT][] = ['onSelectPageDisplayVariant'];
     return $events;
   }
diff --git a/core/modules/system/tests/modules/early_rendering_controller_test/src/TestDomainObjectViewSubscriber.php b/core/modules/system/tests/modules/early_rendering_controller_test/src/TestDomainObjectViewSubscriber.php
index c251d581d0..560d17e1a1 100644
--- a/core/modules/system/tests/modules/early_rendering_controller_test/src/TestDomainObjectViewSubscriber.php
+++ b/core/modules/system/tests/modules/early_rendering_controller_test/src/TestDomainObjectViewSubscriber.php
@@ -37,7 +37,7 @@ public function onViewTestDomainObject(ViewEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::VIEW][] = ['onViewTestDomainObject'];
 
     return $events;
diff --git a/core/modules/system/tests/modules/entity_test/src/EntityTestDefinitionSubscriber.php b/core/modules/system/tests/modules/entity_test/src/EntityTestDefinitionSubscriber.php
index 63a2618ec5..d00395ac58 100644
--- a/core/modules/system/tests/modules/entity_test/src/EntityTestDefinitionSubscriber.php
+++ b/core/modules/system/tests/modules/entity_test/src/EntityTestDefinitionSubscriber.php
@@ -79,7 +79,7 @@ public function __construct(StateInterface $state, EntityLastInstalledSchemaRepo
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     return static::getEntityTypeEvents() + static::getFieldStorageDefinitionEvents();
   }
 
diff --git a/core/modules/system/tests/modules/entity_test_update/src/EventSubscriber/EntitySchemaSubscriber.php b/core/modules/system/tests/modules/entity_test_update/src/EventSubscriber/EntitySchemaSubscriber.php
index a53aff8a82..45a1d1f35d 100644
--- a/core/modules/system/tests/modules/entity_test_update/src/EventSubscriber/EntitySchemaSubscriber.php
+++ b/core/modules/system/tests/modules/entity_test_update/src/EventSubscriber/EntitySchemaSubscriber.php
@@ -48,7 +48,7 @@ public function __construct(EntityDefinitionUpdateManagerInterface $entityDefini
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     return static::getEntityTypeEvents();
   }
 
diff --git a/core/modules/system/tests/modules/form_test/src/EventSubscriber/FormTestEventSubscriber.php b/core/modules/system/tests/modules/form_test/src/EventSubscriber/FormTestEventSubscriber.php
index 410b3e7f44..0d3b204049 100644
--- a/core/modules/system/tests/modules/form_test/src/EventSubscriber/FormTestEventSubscriber.php
+++ b/core/modules/system/tests/modules/form_test/src/EventSubscriber/FormTestEventSubscriber.php
@@ -38,7 +38,7 @@ public function onKernelResponse(ResponseEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::REQUEST][] = ['onKernelRequest'];
     $events[KernelEvents::RESPONSE][] = ['onKernelResponse'];
     return $events;
diff --git a/core/modules/system/tests/modules/hold_test/src/EventSubscriber/HoldTestSubscriber.php b/core/modules/system/tests/modules/hold_test/src/EventSubscriber/HoldTestSubscriber.php
index c5264ba1d6..523e257f70 100644
--- a/core/modules/system/tests/modules/hold_test/src/EventSubscriber/HoldTestSubscriber.php
+++ b/core/modules/system/tests/modules/hold_test/src/EventSubscriber/HoldTestSubscriber.php
@@ -67,7 +67,7 @@ protected function hold($type) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::REQUEST][] = ['onRequest'];
     $events[KernelEvents::RESPONSE][] = ['onRespond'];
     return $events;
diff --git a/core/modules/system/tests/modules/module_install_class_loader_test1/src/EventSubscriber.php b/core/modules/system/tests/modules/module_install_class_loader_test1/src/EventSubscriber.php
index ce0ef4981a..e9e851799f 100644
--- a/core/modules/system/tests/modules/module_install_class_loader_test1/src/EventSubscriber.php
+++ b/core/modules/system/tests/modules/module_install_class_loader_test1/src/EventSubscriber.php
@@ -13,7 +13,7 @@ class EventSubscriber implements EventSubscriberInterface {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events = [];
     // If the autoloader is not fixed during module install when the modules
     // module_install_class_loader_test1 and module_install_class_loader_test2
diff --git a/core/modules/system/tests/modules/module_install_class_loader_test2/src/EventSubscriber.php b/core/modules/system/tests/modules/module_install_class_loader_test2/src/EventSubscriber.php
index d994ca3d27..edcf1b409d 100644
--- a/core/modules/system/tests/modules/module_install_class_loader_test2/src/EventSubscriber.php
+++ b/core/modules/system/tests/modules/module_install_class_loader_test2/src/EventSubscriber.php
@@ -12,7 +12,7 @@ class EventSubscriber implements EventSubscriberInterface {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     return [];
   }
 
diff --git a/core/modules/system/tests/modules/service_provider_test/src/TestClass.php b/core/modules/system/tests/modules/service_provider_test/src/TestClass.php
index 5724af1c02..14de650795 100644
--- a/core/modules/system/tests/modules/service_provider_test/src/TestClass.php
+++ b/core/modules/system/tests/modules/service_provider_test/src/TestClass.php
@@ -57,7 +57,7 @@ public function onKernelResponseTest(ResponseEvent $event) {
    * @return array
    *   An array of event listener definitions.
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::REQUEST][] = ['onKernelRequestTest'];
     $events[KernelEvents::RESPONSE][] = ['onKernelResponseTest'];
     return $events;
diff --git a/core/modules/system/tests/modules/session_test/src/EventSubscriber/SessionTestSubscriber.php b/core/modules/system/tests/modules/session_test/src/EventSubscriber/SessionTestSubscriber.php
index 13d1b711ad..38b797a8a2 100644
--- a/core/modules/system/tests/modules/session_test/src/EventSubscriber/SessionTestSubscriber.php
+++ b/core/modules/system/tests/modules/session_test/src/EventSubscriber/SessionTestSubscriber.php
@@ -48,7 +48,7 @@ public function onKernelResponseSessionTest(ResponseEvent $event) {
    * @return array
    *   An array of event listener definitions.
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::RESPONSE][] = ['onKernelResponseSessionTest'];
     $events[KernelEvents::REQUEST][] = ['onKernelRequestSessionTest'];
     return $events;
diff --git a/core/modules/system/tests/modules/theme_test/src/EventSubscriber/ThemeTestSubscriber.php b/core/modules/system/tests/modules/theme_test/src/EventSubscriber/ThemeTestSubscriber.php
index 2cc0d36976..a4e3ba7115 100644
--- a/core/modules/system/tests/modules/theme_test/src/EventSubscriber/ThemeTestSubscriber.php
+++ b/core/modules/system/tests/modules/theme_test/src/EventSubscriber/ThemeTestSubscriber.php
@@ -92,7 +92,7 @@ public function onView(RequestEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::REQUEST][] = ['onRequest'];
     $events[KernelEvents::VIEW][] = ['onView', -1000];
     return $events;
diff --git a/core/modules/user/src/Authentication/Provider/Cookie.php b/core/modules/user/src/Authentication/Provider/Cookie.php
index 0fcac24a0d..d15093ec45 100644
--- a/core/modules/user/src/Authentication/Provider/Cookie.php
+++ b/core/modules/user/src/Authentication/Provider/Cookie.php
@@ -147,7 +147,7 @@ public function addCheckToUrl(ResponseEvent $event) {
    * @return array
    *   An array of event listener definitions.
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::RESPONSE][] = ['addCheckToUrl', -1000];
     return $events;
   }
diff --git a/core/modules/user/src/EventSubscriber/AccessDeniedSubscriber.php b/core/modules/user/src/EventSubscriber/AccessDeniedSubscriber.php
index 9a80dc9c22..54d5275997 100644
--- a/core/modules/user/src/EventSubscriber/AccessDeniedSubscriber.php
+++ b/core/modules/user/src/EventSubscriber/AccessDeniedSubscriber.php
@@ -78,7 +78,7 @@ public function onException(ExceptionEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Use a higher priority than
     // \Drupal\Core\EventSubscriber\ExceptionLoggingSubscriber, because there's
     // no need to log the exception if we can redirect.
diff --git a/core/modules/user/src/EventSubscriber/MaintenanceModeSubscriber.php b/core/modules/user/src/EventSubscriber/MaintenanceModeSubscriber.php
index dbaf637ce7..e805162c08 100644
--- a/core/modules/user/src/EventSubscriber/MaintenanceModeSubscriber.php
+++ b/core/modules/user/src/EventSubscriber/MaintenanceModeSubscriber.php
@@ -67,7 +67,7 @@ public function onKernelRequestMaintenance(RequestEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[KernelEvents::REQUEST][] = ['onKernelRequestMaintenance', 31];
     return $events;
   }
diff --git a/core/modules/user/src/EventSubscriber/UserFloodSubscriber.php b/core/modules/user/src/EventSubscriber/UserFloodSubscriber.php
index ba0c324c1a..83538025d6 100644
--- a/core/modules/user/src/EventSubscriber/UserFloodSubscriber.php
+++ b/core/modules/user/src/EventSubscriber/UserFloodSubscriber.php
@@ -33,7 +33,7 @@ public function __construct(LoggerInterface $logger = NULL) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events[UserEvents::FLOOD_BLOCKED_USER][] = ['blockedUser'];
     $events[UserEvents::FLOOD_BLOCKED_IP][] = ['blockedIp'];
     return $events;
diff --git a/core/modules/user/src/EventSubscriber/UserRequestSubscriber.php b/core/modules/user/src/EventSubscriber/UserRequestSubscriber.php
index 6fb12a65c8..11fe4ec730 100644
--- a/core/modules/user/src/EventSubscriber/UserRequestSubscriber.php
+++ b/core/modules/user/src/EventSubscriber/UserRequestSubscriber.php
@@ -59,7 +59,7 @@ public function onKernelTerminate(TerminateEvent $event) {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Should go before other subscribers start to write their caches. Notably
     // before \Drupal\Core\EventSubscriber\KernelDestructionSubscriber to
     // prevent instantiation of destructed services.
diff --git a/core/modules/views/src/EventSubscriber/RouteSubscriber.php b/core/modules/views/src/EventSubscriber/RouteSubscriber.php
index 2f5b52c8ee..07a6fcc7f2 100644
--- a/core/modules/views/src/EventSubscriber/RouteSubscriber.php
+++ b/core/modules/views/src/EventSubscriber/RouteSubscriber.php
@@ -74,7 +74,7 @@ public function reset() {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     $events = parent::getSubscribedEvents();
     $events[RoutingEvents::FINISHED] = ['routeRebuildFinished'];
     // Ensure to run after the entity resolver subscriber
diff --git a/core/modules/views/src/EventSubscriber/ViewsEntitySchemaSubscriber.php b/core/modules/views/src/EventSubscriber/ViewsEntitySchemaSubscriber.php
index 52d112d840..15a1f6c79f 100644
--- a/core/modules/views/src/EventSubscriber/ViewsEntitySchemaSubscriber.php
+++ b/core/modules/views/src/EventSubscriber/ViewsEntitySchemaSubscriber.php
@@ -99,7 +99,7 @@ public function __construct(EntityTypeManagerInterface $entity_type_manager, Log
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     return static::getEntityTypeEvents();
   }
 
diff --git a/core/modules/workspaces/src/EventSubscriber/EntitySchemaSubscriber.php b/core/modules/workspaces/src/EventSubscriber/EntitySchemaSubscriber.php
index 6f521014a2..5882d49b77 100644
--- a/core/modules/workspaces/src/EventSubscriber/EntitySchemaSubscriber.php
+++ b/core/modules/workspaces/src/EventSubscriber/EntitySchemaSubscriber.php
@@ -60,7 +60,7 @@ public function __construct(EntityDefinitionUpdateManagerInterface $entityDefini
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     return static::getEntityTypeEvents();
   }
 
diff --git a/core/modules/workspaces/src/EventSubscriber/WorkspaceRequestSubscriber.php b/core/modules/workspaces/src/EventSubscriber/WorkspaceRequestSubscriber.php
index 09f391d504..2852f30365 100644
--- a/core/modules/workspaces/src/EventSubscriber/WorkspaceRequestSubscriber.php
+++ b/core/modules/workspaces/src/EventSubscriber/WorkspaceRequestSubscriber.php
@@ -95,7 +95,7 @@ public function onKernelRequest(RequestEvent $event) {
   /**
    * {@inheritDoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     // Use a priority of 190 in order to run after the generic core subscriber.
     // @see \Drupal\Core\EventSubscriber\PathSubscriber::getSubscribedEvents()
     $events[KernelEvents::CONTROLLER][] = ['onKernelController', 190];
diff --git a/core/tests/Drupal/Tests/Component/EventDispatcher/ContainerAwareEventDispatcherTest.php b/core/tests/Drupal/Tests/Component/EventDispatcher/ContainerAwareEventDispatcherTest.php
index f60e2b9a47..d8a99cd704 100644
--- a/core/tests/Drupal/Tests/Component/EventDispatcher/ContainerAwareEventDispatcherTest.php
+++ b/core/tests/Drupal/Tests/Component/EventDispatcher/ContainerAwareEventDispatcherTest.php
@@ -621,7 +621,7 @@ public function foo(Event $e, $name, $dispatcher) {
 
 class TestEventSubscriber implements EventSubscriberInterface {
 
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     return ['pre.foo' => 'preFoo', 'post.foo' => 'postFoo'];
   }
 
@@ -629,7 +629,7 @@ public static function getSubscribedEvents() {
 
 class TestEventSubscriberWithPriorities implements EventSubscriberInterface {
 
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     return [
       'pre.foo' => ['preFoo', 10],
       'post.foo' => ['postFoo'],
@@ -640,7 +640,7 @@ public static function getSubscribedEvents() {
 
 class TestEventSubscriberWithMultipleListeners implements EventSubscriberInterface {
 
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     return [
       'pre.foo' => [
         ['preFoo1'],
