diff --git a/.github/patch-types.php b/.github/patch-types.php
index d5897449138cd..75963bb46e7f3 100644
--- a/.github/patch-types.php
+++ b/.github/patch-types.php
@@ -31,9 +31,9 @@
         case false !== strpos($file, '/src/Symfony/Component/DependencyInjection/Tests/Fixtures/Prototype/BadClasses/MissingParent.php'):
         case false !== strpos($file, '/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/'):
         case false !== strpos($file, '/src/Symfony/Component/ErrorHandler/Tests/Fixtures/'):
-        case false !== strpos($file, '/src/Symfony/Component/PropertyInfo/Tests/Fixtures/Dummy.php'):
-        case false !== strpos($file, '/src/Symfony/Component/PropertyInfo/Tests/Fixtures/ParentDummy.php'):
+        case false !== strpos($file, '/src/Symfony/Component/PropertyInfo/Tests/Fixtures/'):
         case false !== strpos($file, '/src/Symfony/Component/Runtime/Internal/ComposerPlugin.php'):
+        case false !== strpos($file, '/src/Symfony/Component/Serializer/Tests/Fixtures/'):
         case false !== strpos($file, '/src/Symfony/Component/Serializer/Tests/Normalizer/Features/ObjectOuter.php'):
         case false !== strpos($file, '/src/Symfony/Component/VarDumper/Tests/Fixtures/NotLoadableClass.php'):
         case false !== strpos($file, '/src/Symfony/Component/VarDumper/Tests/Fixtures/ReflectionIntersectionTypeFixture.php'):
diff --git a/src/Symfony/Bundle/FrameworkBundle/Kernel/MicroKernelTrait.php b/src/Symfony/Bundle/FrameworkBundle/Kernel/MicroKernelTrait.php
index ff269bcf1ea6b..3a63471c6f630 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Kernel/MicroKernelTrait.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Kernel/MicroKernelTrait.php
@@ -165,10 +165,8 @@ public function registerContainerConfiguration(LoaderInterface $loader)
 
     /**
      * @internal
-     *
-     * @return RouteCollection
      */
-    public function loadRoutes(LoaderInterface $loader)
+    public function loadRoutes(LoaderInterface $loader): RouteCollection
     {
         $file = (new \ReflectionObject($this))->getFileName();
         /* @var RoutingPhpFileLoader $kernelLoader */
diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/Command/TranslationUpdateCommandTest.php b/src/Symfony/Bundle/FrameworkBundle/Tests/Command/TranslationUpdateCommandTest.php
index 35ce89f63887c..5a3d70717bcca 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Tests/Command/TranslationUpdateCommandTest.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/Command/TranslationUpdateCommandTest.php
@@ -145,10 +145,7 @@ protected function tearDown(): void
         $this->fs->remove($this->translationDir);
     }
 
-    /**
-     * @return CommandTester
-     */
-    private function createCommandTester($extractedMessages = [], $loadedMessages = [], KernelInterface $kernel = null, array $transPaths = [], array $codePaths = [])
+    private function createCommandTester($extractedMessages = [], $loadedMessages = [], KernelInterface $kernel = null, array $transPaths = [], array $codePaths = []): CommandTester
     {
         $translator = $this->createMock(Translator::class);
         $translator
diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/Functional/app/AppKernel.php b/src/Symfony/Bundle/FrameworkBundle/Tests/Functional/app/AppKernel.php
index a666dfc4778fb..c66074b132695 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Tests/Functional/app/AppKernel.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/Functional/app/AppKernel.php
@@ -106,7 +106,7 @@ protected function getKernelParameters(): array
         return $parameters;
     }
 
-    public function getConfigTreeBuilder()
+    public function getConfigTreeBuilder(): TreeBuilder
     {
         $treeBuilder = new TreeBuilder('foo');
         $rootNode = $treeBuilder->getRootNode();
@@ -119,7 +119,7 @@ public function load(array $configs, ContainerBuilder $container)
     {
     }
 
-    public function getNamespace()
+    public function getNamespace(): string
     {
         return '';
     }
@@ -129,7 +129,7 @@ public function getXsdValidationBasePath()
         return false;
     }
 
-    public function getAlias()
+    public function getAlias(): string
     {
         return 'foo';
     }
diff --git a/src/Symfony/Bundle/SecurityBundle/Tests/DependencyInjection/Compiler/RegisterEntryPointsPassTest.php b/src/Symfony/Bundle/SecurityBundle/Tests/DependencyInjection/Compiler/RegisterEntryPointsPassTest.php
index 53f24a153efc7..b10b8a810bc7a 100644
--- a/src/Symfony/Bundle/SecurityBundle/Tests/DependencyInjection/Compiler/RegisterEntryPointsPassTest.php
+++ b/src/Symfony/Bundle/SecurityBundle/Tests/DependencyInjection/Compiler/RegisterEntryPointsPassTest.php
@@ -93,7 +93,7 @@ public function onAuthenticationFailure(Request $request, AuthenticationExceptio
         ], JsonResponse::HTTP_FORBIDDEN);
     }
 
-    public function start(Request $request, AuthenticationException $authException = null)
+    public function start(Request $request, AuthenticationException $authException = null): Response
     {
     }
 }
diff --git a/src/Symfony/Bundle/SecurityBundle/Tests/DependencyInjection/SecurityExtensionTest.php b/src/Symfony/Bundle/SecurityBundle/Tests/DependencyInjection/SecurityExtensionTest.php
index 14cd5c4271adb..8719112f2484b 100644
--- a/src/Symfony/Bundle/SecurityBundle/Tests/DependencyInjection/SecurityExtensionTest.php
+++ b/src/Symfony/Bundle/SecurityBundle/Tests/DependencyInjection/SecurityExtensionTest.php
@@ -36,6 +36,7 @@
 use Symfony\Component\Security\Core\User\UserInterface;
 use Symfony\Component\Security\Core\User\UserProviderInterface;
 use Symfony\Component\Security\Guard\AuthenticatorInterface as GuardAuthenticatorInterface;
+use Symfony\Component\Security\Guard\Token\GuardTokenInterface;
 use Symfony\Component\Security\Http\Authenticator\AuthenticatorInterface;
 use Symfony\Component\Security\Http\Authenticator\HttpBasicAuthenticator;
 use Symfony\Component\Security\Http\Authenticator\Passport\Passport;
@@ -865,11 +866,11 @@ public function createToken(Passport $passport, string $firewallName): TokenInte
 
 class NullAuthenticator implements GuardAuthenticatorInterface
 {
-    public function start(Request $request, AuthenticationException $authException = null)
+    public function start(Request $request, AuthenticationException $authException = null): Response
     {
     }
 
-    public function supports(Request $request)
+    public function supports(Request $request): bool
     {
     }
 
@@ -877,27 +878,27 @@ public function getCredentials(Request $request)
     {
     }
 
-    public function getUser($credentials, UserProviderInterface $userProvider)
+    public function getUser($credentials, UserProviderInterface $userProvider): ?UserInterface
     {
     }
 
-    public function checkCredentials($credentials, UserInterface $user)
+    public function checkCredentials($credentials, UserInterface $user): bool
     {
     }
 
-    public function createAuthenticatedToken(UserInterface $user, string $providerKey)
+    public function createAuthenticatedToken(UserInterface $user, string $providerKey): GuardTokenInterface
     {
     }
 
-    public function onAuthenticationFailure(Request $request, AuthenticationException $exception)
+    public function onAuthenticationFailure(Request $request, AuthenticationException $exception): ?Response
     {
     }
 
-    public function onAuthenticationSuccess(Request $request, TokenInterface $token, string $providerKey)
+    public function onAuthenticationSuccess(Request $request, TokenInterface $token, string $providerKey): ?Response
     {
     }
 
-    public function supportsRememberMe()
+    public function supportsRememberMe(): bool
     {
     }
 }
@@ -922,7 +923,7 @@ public function createListeners(ContainerBuilder $container, string $firewallNam
         return ['custom_firewall_listener_id'];
     }
 
-    public function create(ContainerBuilder $container, string $id, array $config, string $userProvider, ?string $defaultEntryPoint)
+    public function create(ContainerBuilder $container, string $id, array $config, string $userProvider, ?string $defaultEntryPoint): array
     {
         $container->register('provider_id', \stdClass::class);
         $container->register('listener_id', \stdClass::class);
@@ -930,12 +931,12 @@ public function create(ContainerBuilder $container, string $id, array $config, s
         return ['provider_id', 'listener_id', $defaultEntryPoint];
     }
 
-    public function getPosition()
+    public function getPosition(): string
     {
         return 'form';
     }
 
-    public function getKey()
+    public function getKey(): string
     {
         return 'custom_listener';
     }
diff --git a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/AnonymousBundle/AppCustomAuthenticator.php b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/AnonymousBundle/AppCustomAuthenticator.php
index 5069fa9cc7fa9..c1d38688ecd25 100644
--- a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/AnonymousBundle/AppCustomAuthenticator.php
+++ b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/AnonymousBundle/AppCustomAuthenticator.php
@@ -21,7 +21,7 @@
 
 class AppCustomAuthenticator extends AbstractGuardAuthenticator
 {
-    public function supports(Request $request)
+    public function supports(Request $request): bool
     {
         return false;
     }
@@ -30,28 +30,28 @@ public function getCredentials(Request $request)
     {
     }
 
-    public function getUser($credentials, UserProviderInterface $userProvider)
+    public function getUser($credentials, UserProviderInterface $userProvider): ?UserInterface
     {
     }
 
-    public function checkCredentials($credentials, UserInterface $user)
+    public function checkCredentials($credentials, UserInterface $user): bool
     {
     }
 
-    public function onAuthenticationFailure(Request $request, AuthenticationException $exception)
+    public function onAuthenticationFailure(Request $request, AuthenticationException $exception): ?Response
     {
     }
 
-    public function onAuthenticationSuccess(Request $request, TokenInterface $token, $providerKey)
+    public function onAuthenticationSuccess(Request $request, TokenInterface $token, $providerKey): ?Response
     {
     }
 
-    public function start(Request $request, AuthenticationException $authException = null)
+    public function start(Request $request, AuthenticationException $authException = null): Response
     {
         return new Response($authException->getMessage(), Response::HTTP_UNAUTHORIZED);
     }
 
-    public function supportsRememberMe()
+    public function supportsRememberMe(): bool
     {
     }
 }
diff --git a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/CsrfFormLoginBundle/Controller/LoginController.php b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/CsrfFormLoginBundle/Controller/LoginController.php
index f6f7aca9d5ec2..c77b1e204e0db 100644
--- a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/CsrfFormLoginBundle/Controller/LoginController.php
+++ b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/CsrfFormLoginBundle/Controller/LoginController.php
@@ -54,7 +54,7 @@ public function secureAction()
     /**
      * {@inheritdoc}
      */
-    public static function getSubscribedServices()
+    public static function getSubscribedServices(): array
     {
         return [
             'form.factory' => FormFactoryInterface::class,
diff --git a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/FormLoginBundle/Controller/LocalizedController.php b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/FormLoginBundle/Controller/LocalizedController.php
index 5904183581517..11d00e257e98a 100644
--- a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/FormLoginBundle/Controller/LocalizedController.php
+++ b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/FormLoginBundle/Controller/LocalizedController.php
@@ -71,7 +71,7 @@ public function homepageAction()
     /**
      * {@inheritdoc}
      */
-    public static function getSubscribedServices()
+    public static function getSubscribedServices(): array
     {
         return [
             'twig' => Environment::class,
diff --git a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/FormLoginBundle/Controller/LoginController.php b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/FormLoginBundle/Controller/LoginController.php
index 99183293fb1e8..db6aacca8cfc2 100644
--- a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/FormLoginBundle/Controller/LoginController.php
+++ b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/FormLoginBundle/Controller/LoginController.php
@@ -63,7 +63,7 @@ public function secureAction()
     /**
      * {@inheritdoc}
      */
-    public static function getSubscribedServices()
+    public static function getSubscribedServices(): array
     {
         return [
             'twig' => Environment::class,
diff --git a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/GuardedBundle/AppCustomAuthenticator.php b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/GuardedBundle/AppCustomAuthenticator.php
index 22d378835e4c0..43e439ecfa9bf 100644
--- a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/GuardedBundle/AppCustomAuthenticator.php
+++ b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/GuardedBundle/AppCustomAuthenticator.php
@@ -21,7 +21,7 @@
 
 class AppCustomAuthenticator extends AbstractGuardAuthenticator
 {
-    public function supports(Request $request)
+    public function supports(Request $request): bool
     {
         return '/manual_login' !== $request->getPathInfo() && '/profile' !== $request->getPathInfo();
     }
@@ -31,29 +31,29 @@ public function getCredentials(Request $request)
         throw new AuthenticationException('This should be hit');
     }
 
-    public function getUser($credentials, UserProviderInterface $userProvider)
+    public function getUser($credentials, UserProviderInterface $userProvider): ?UserInterface
     {
     }
 
-    public function checkCredentials($credentials, UserInterface $user)
+    public function checkCredentials($credentials, UserInterface $user): bool
     {
     }
 
-    public function onAuthenticationFailure(Request $request, AuthenticationException $exception)
+    public function onAuthenticationFailure(Request $request, AuthenticationException $exception): ?Response
     {
         return new Response('', 418);
     }
 
-    public function onAuthenticationSuccess(Request $request, TokenInterface $token, $providerKey)
+    public function onAuthenticationSuccess(Request $request, TokenInterface $token, $providerKey): ?Response
     {
     }
 
-    public function start(Request $request, AuthenticationException $authException = null)
+    public function start(Request $request, AuthenticationException $authException = null): Response
     {
         return new Response($authException->getMessage(), Response::HTTP_UNAUTHORIZED);
     }
 
-    public function supportsRememberMe()
+    public function supportsRememberMe(): bool
     {
     }
 }
diff --git a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/LoginLink/TestCustomLoginLinkSuccessHandler.php b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/LoginLink/TestCustomLoginLinkSuccessHandler.php
index a20866c8cfd91..0d1501508b58a 100644
--- a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/LoginLink/TestCustomLoginLinkSuccessHandler.php
+++ b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/LoginLink/TestCustomLoginLinkSuccessHandler.php
@@ -4,12 +4,13 @@
 
 use Symfony\Component\HttpFoundation\JsonResponse;
 use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpFoundation\Response;
 use Symfony\Component\Security\Core\Authentication\Token\TokenInterface;
 use Symfony\Component\Security\Http\Authentication\AuthenticationSuccessHandlerInterface;
 
 class TestCustomLoginLinkSuccessHandler implements AuthenticationSuccessHandlerInterface
 {
-    public function onAuthenticationSuccess(Request $request, TokenInterface $token)
+    public function onAuthenticationSuccess(Request $request, TokenInterface $token): Response
     {
         return new JsonResponse(['message' => sprintf('Welcome %s!', $token->getUserIdentifier())]);
     }
diff --git a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/RememberMeBundle/Security/StaticTokenProvider.php b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/RememberMeBundle/Security/StaticTokenProvider.php
index 43479ca9cfd4d..a51702eec15b6 100644
--- a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/RememberMeBundle/Security/StaticTokenProvider.php
+++ b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/RememberMeBundle/Security/StaticTokenProvider.php
@@ -29,7 +29,7 @@ public function __construct($kernel)
         }
     }
 
-    public function loadTokenBySeries(string $series)
+    public function loadTokenBySeries(string $series): PersistentTokenInterface
     {
         $token = self::$db[$series] ?? false;
         if (!$token) {
diff --git a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/RememberMeBundle/Security/UserChangingUserProvider.php b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/RememberMeBundle/Security/UserChangingUserProvider.php
index a5306b6bf1607..f28bfff393693 100644
--- a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/RememberMeBundle/Security/UserChangingUserProvider.php
+++ b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/RememberMeBundle/Security/UserChangingUserProvider.php
@@ -26,7 +26,7 @@ public function __construct(InMemoryUserProvider $inner)
         $this->inner = $inner;
     }
 
-    public function loadUserByUsername($username)
+    public function loadUserByUsername($username): UserInterface
     {
         return $this->inner->loadUserByUsername($username);
     }
@@ -36,7 +36,7 @@ public function loadUserByIdentifier(string $userIdentifier): UserInterface
         return $this->inner->loadUserByIdentifier($userIdentifier);
     }
 
-    public function refreshUser(UserInterface $user)
+    public function refreshUser(UserInterface $user): UserInterface
     {
         $user = $this->inner->refreshUser($user);
 
@@ -46,7 +46,7 @@ public function refreshUser(UserInterface $user)
         return $user;
     }
 
-    public function supportsClass($class)
+    public function supportsClass($class): bool
     {
         return $this->inner->supportsClass($class);
     }
diff --git a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/SecuredPageBundle/Security/Core/User/ArrayUserProvider.php b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/SecuredPageBundle/Security/Core/User/ArrayUserProvider.php
index a5ca99a41b6b7..db9d39e7d6e74 100644
--- a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/SecuredPageBundle/Security/Core/User/ArrayUserProvider.php
+++ b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/Bundle/SecuredPageBundle/Security/Core/User/ArrayUserProvider.php
@@ -29,7 +29,7 @@ public function getUser($username)
         return $this->users[$username];
     }
 
-    public function loadUserByUsername($username)
+    public function loadUserByUsername($username): UserInterface
     {
         return $this->loadUserByIdentifier($username);
     }
@@ -48,7 +48,7 @@ public function loadUserByIdentifier(string $identifier): UserInterface
         return $user;
     }
 
-    public function refreshUser(UserInterface $user)
+    public function refreshUser(UserInterface $user): UserInterface
     {
         if (!$user instanceof UserInterface) {
             throw new UnsupportedUserException(sprintf('Instances of "%s" are not supported.', get_debug_type($user)));
@@ -60,7 +60,7 @@ public function refreshUser(UserInterface $user)
         return new $class($storedUser->getUserIdentifier(), $storedUser->getPassword(), $storedUser->getRoles(), $storedUser->isEnabled());
     }
 
-    public function supportsClass($class)
+    public function supportsClass($class): bool
     {
         return InMemoryUser::class === $class || UserWithoutEquatable::class === $class;
     }
diff --git a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/SecurityTest.php b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/SecurityTest.php
index f435789f6f5f0..418bb55f14454 100644
--- a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/SecurityTest.php
+++ b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/SecurityTest.php
@@ -161,7 +161,7 @@ public function __toString()
     /**
      * {@inheritdoc}
      */
-    public function getRoles()
+    public function getRoles(): array
     {
         return $this->roles;
     }
diff --git a/src/Symfony/Bundle/WebProfilerBundle/Tests/Functional/WebProfilerBundleKernel.php b/src/Symfony/Bundle/WebProfilerBundle/Tests/Functional/WebProfilerBundleKernel.php
index 79b66a8fb23ca..28b85d916becd 100644
--- a/src/Symfony/Bundle/WebProfilerBundle/Tests/Functional/WebProfilerBundleKernel.php
+++ b/src/Symfony/Bundle/WebProfilerBundle/Tests/Functional/WebProfilerBundleKernel.php
@@ -23,7 +23,7 @@ public function __construct()
         parent::__construct('test', false);
     }
 
-    public function registerBundles()
+    public function registerBundles(): iterable
     {
         return [
             new FrameworkBundle(),
@@ -59,7 +59,7 @@ public function getCacheDir(): string
         return sys_get_temp_dir().'/cache-'.spl_object_hash($this);
     }
 
-    public function getLogDir()
+    public function getLogDir(): string
     {
         return sys_get_temp_dir().'/log-'.spl_object_hash($this);
     }
diff --git a/src/Symfony/Component/Config/Tests/Fixtures/Configuration/CustomNodeDefinition.php b/src/Symfony/Component/Config/Tests/Fixtures/Configuration/CustomNodeDefinition.php
index 9783947b9a229..d5f933a85f5bb 100644
--- a/src/Symfony/Component/Config/Tests/Fixtures/Configuration/CustomNodeDefinition.php
+++ b/src/Symfony/Component/Config/Tests/Fixtures/Configuration/CustomNodeDefinition.php
@@ -3,11 +3,12 @@
 
 namespace Symfony\Component\Config\Tests\Fixtures\Configuration;
 
+use Symfony\Component\Config\Definition\NodeInterface;
 use Symfony\Component\Config\Definition\Builder\NodeDefinition;
 
 class CustomNodeDefinition extends NodeDefinition
 {
-    protected function createNode()
+    protected function createNode(): NodeInterface
     {
         return new CustomNode();
     }
diff --git a/src/Symfony/Component/Console/Terminal.php b/src/Symfony/Component/Console/Terminal.php
index 5e5a3c2f767db..08c53535b1d35 100644
--- a/src/Symfony/Component/Console/Terminal.php
+++ b/src/Symfony/Component/Console/Terminal.php
@@ -57,10 +57,8 @@ public function getHeight()
 
     /**
      * @internal
-     *
-     * @return bool
      */
-    public static function hasSttyAvailable()
+    public static function hasSttyAvailable(): bool
     {
         if (null !== self::$stty) {
             return self::$stty;
diff --git a/src/Symfony/Component/Console/Tests/ApplicationTest.php b/src/Symfony/Component/Console/Tests/ApplicationTest.php
index 2b63dd1e42704..81dfe7e9a2b5b 100644
--- a/src/Symfony/Component/Console/Tests/ApplicationTest.php
+++ b/src/Symfony/Component/Console/Tests/ApplicationTest.php
@@ -1947,7 +1947,7 @@ public function handleSignal(int $signal): void
         $this->signaled = true;
     }
 
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): int
     {
         for ($i = 0; $i < $this->loop; ++$i) {
             usleep(100);
diff --git a/src/Symfony/Component/Console/Tests/Descriptor/ApplicationDescriptionTest.php b/src/Symfony/Component/Console/Tests/Descriptor/ApplicationDescriptionTest.php
index 33d5c3840f3e3..b3ba9d8482b0f 100644
--- a/src/Symfony/Component/Console/Tests/Descriptor/ApplicationDescriptionTest.php
+++ b/src/Symfony/Component/Console/Tests/Descriptor/ApplicationDescriptionTest.php
@@ -46,7 +46,7 @@ final class TestApplication extends Application
     /**
      * {@inheritdoc}
      */
-    protected function getDefaultCommands()
+    protected function getDefaultCommands(): array
     {
         return [];
     }
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Compiler/ResolveInstanceofConditionalsPassTest.php b/src/Symfony/Component/DependencyInjection/Tests/Compiler/ResolveInstanceofConditionalsPassTest.php
index d750ce69583d7..b7ea0f4ac84bb 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Compiler/ResolveInstanceofConditionalsPassTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Compiler/ResolveInstanceofConditionalsPassTest.php
@@ -376,15 +376,15 @@ public function reset()
     {
     }
 
-    public function supports(ResourceInterface $metadata)
+    public function supports(ResourceInterface $metadata): bool
     {
     }
 
-    public function isFresh(ResourceInterface $resource, $timestamp)
+    public function isFresh(ResourceInterface $resource, $timestamp): bool
     {
     }
 
-    public static function getSubscribedServices()
+    public static function getSubscribedServices(): array
     {
     }
 }
diff --git a/src/Symfony/Component/DependencyInjection/Tests/ServiceLocatorTest.php b/src/Symfony/Component/DependencyInjection/Tests/ServiceLocatorTest.php
index e03f9fc55585e..d8a3a0006dbc4 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/ServiceLocatorTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/ServiceLocatorTest.php
@@ -11,6 +11,7 @@
 
 namespace Symfony\Component\DependencyInjection\Tests;
 
+use Psr\Container\ContainerInterface;
 use Psr\Container\NotFoundExceptionInterface;
 use Symfony\Component\DependencyInjection\Container;
 use Symfony\Component\DependencyInjection\Exception\ServiceCircularReferenceException;
@@ -21,7 +22,7 @@
 
 class ServiceLocatorTest extends BaseServiceLocatorTest
 {
-    public function getServiceLocator(array $factories)
+    public function getServiceLocator(array $factories): ContainerInterface
     {
         return new ServiceLocator($factories);
     }
diff --git a/src/Symfony/Component/Form/ChoiceList/Factory/Cache/ChoiceLoader.php b/src/Symfony/Component/Form/ChoiceList/Factory/Cache/ChoiceLoader.php
index f0e1067b90710..83b2ca0aa2ab4 100644
--- a/src/Symfony/Component/Form/ChoiceList/Factory/Cache/ChoiceLoader.php
+++ b/src/Symfony/Component/Form/ChoiceList/Factory/Cache/ChoiceLoader.php
@@ -11,6 +11,7 @@
 
 namespace Symfony\Component\Form\ChoiceList\Factory\Cache;
 
+use Symfony\Component\Form\ChoiceList\ChoiceListInterface;
 use Symfony\Component\Form\ChoiceList\Loader\ChoiceLoaderInterface;
 use Symfony\Component\Form\FormTypeExtensionInterface;
 use Symfony\Component\Form\FormTypeInterface;
@@ -28,7 +29,7 @@ final class ChoiceLoader extends AbstractStaticOption implements ChoiceLoaderInt
     /**
      * {@inheritdoc}
      */
-    public function loadChoiceList(callable $value = null)
+    public function loadChoiceList(callable $value = null): ChoiceListInterface
     {
         return $this->getOption()->loadChoiceList($value);
     }
@@ -36,7 +37,7 @@ public function loadChoiceList(callable $value = null)
     /**
      * {@inheritdoc}
      */
-    public function loadChoicesForValues(array $values, callable $value = null)
+    public function loadChoicesForValues(array $values, callable $value = null): array
     {
         return $this->getOption()->loadChoicesForValues($values, $value);
     }
@@ -44,7 +45,7 @@ public function loadChoicesForValues(array $values, callable $value = null)
     /**
      * {@inheritdoc}
      */
-    public function loadValuesForChoices(array $choices, callable $value = null)
+    public function loadValuesForChoices(array $choices, callable $value = null): array
     {
         return $this->getOption()->loadValuesForChoices($choices, $value);
     }
diff --git a/src/Symfony/Component/Form/ChoiceList/Loader/AbstractChoiceLoader.php b/src/Symfony/Component/Form/ChoiceList/Loader/AbstractChoiceLoader.php
index ea736a52c683f..a30af63b1ab57 100644
--- a/src/Symfony/Component/Form/ChoiceList/Loader/AbstractChoiceLoader.php
+++ b/src/Symfony/Component/Form/ChoiceList/Loader/AbstractChoiceLoader.php
@@ -12,6 +12,7 @@
 namespace Symfony\Component\Form\ChoiceList\Loader;
 
 use Symfony\Component\Form\ChoiceList\ArrayChoiceList;
+use Symfony\Component\Form\ChoiceList\ChoiceListInterface;
 
 /**
  * @author Jules Pietri <jules@heahprod.com>
@@ -30,7 +31,7 @@ abstract class AbstractChoiceLoader implements ChoiceLoaderInterface
      *
      * {@inheritdoc}
      */
-    public function loadChoiceList(callable $value = null)
+    public function loadChoiceList(callable $value = null): ChoiceListInterface
     {
         return $this->choiceList ?? ($this->choiceList = new ArrayChoiceList($this->loadChoices(), $value));
     }
diff --git a/src/Symfony/Component/Form/Tests/Fixtures/ChoiceList/DeprecatedChoiceListFactory.php b/src/Symfony/Component/Form/Tests/Fixtures/ChoiceList/DeprecatedChoiceListFactory.php
index 6361c2eedc33f..89d4ec182ed74 100644
--- a/src/Symfony/Component/Form/Tests/Fixtures/ChoiceList/DeprecatedChoiceListFactory.php
+++ b/src/Symfony/Component/Form/Tests/Fixtures/ChoiceList/DeprecatedChoiceListFactory.php
@@ -5,18 +5,19 @@
 use Symfony\Component\Form\ChoiceList\ChoiceListInterface;
 use Symfony\Component\Form\ChoiceList\Factory\ChoiceListFactoryInterface;
 use Symfony\Component\Form\ChoiceList\Loader\ChoiceLoaderInterface;
+use Symfony\Component\Form\ChoiceList\View\ChoiceListView;
 
 class DeprecatedChoiceListFactory implements ChoiceListFactoryInterface
 {
-    public function createListFromChoices(iterable $choices, callable $value = null)
+    public function createListFromChoices(iterable $choices, callable $value = null): ChoiceListInterface
     {
     }
 
-    public function createListFromLoader(ChoiceLoaderInterface $loader, callable $value = null)
+    public function createListFromLoader(ChoiceLoaderInterface $loader, callable $value = null): ChoiceListInterface
     {
     }
 
-    public function createView(ChoiceListInterface $list, $preferredChoices = null, $label = null, callable $index = null, callable $groupBy = null, $attr = null)
+    public function createView(ChoiceListInterface $list, $preferredChoices = null, $label = null, callable $index = null, callable $groupBy = null, $attr = null): ChoiceListView
     {
     }
 }
diff --git a/src/Symfony/Component/HttpClient/CurlHttpClient.php b/src/Symfony/Component/HttpClient/CurlHttpClient.php
index 5ab0040db3be9..e4092005a900f 100644
--- a/src/Symfony/Component/HttpClient/CurlHttpClient.php
+++ b/src/Symfony/Component/HttpClient/CurlHttpClient.php
@@ -345,10 +345,7 @@ public function reset()
         $this->multi->reset();
     }
 
-    /**
-     * @return array
-     */
-    public function __sleep()
+    public function __sleep(): array
     {
         throw new \BadMethodCallException('Cannot serialize '.__CLASS__);
     }
diff --git a/src/Symfony/Component/HttpClient/HttplugClient.php b/src/Symfony/Component/HttpClient/HttplugClient.php
index 7be016da9d8e9..df0cca1ce9622 100644
--- a/src/Symfony/Component/HttpClient/HttplugClient.php
+++ b/src/Symfony/Component/HttpClient/HttplugClient.php
@@ -218,10 +218,7 @@ public function createUri($uri): UriInterface
         throw new \LogicException(sprintf('You cannot use "%s()" as the "nyholm/psr7" package is not installed. Try running "composer require nyholm/psr7".', __METHOD__));
     }
 
-    /**
-     * @return array
-     */
-    public function __sleep()
+    public function __sleep(): array
     {
         throw new \BadMethodCallException('Cannot serialize '.__CLASS__);
     }
diff --git a/src/Symfony/Component/HttpClient/Response/AmpResponse.php b/src/Symfony/Component/HttpClient/Response/AmpResponse.php
index 27ba36bdf8922..8d5ef3d131ec3 100644
--- a/src/Symfony/Component/HttpClient/Response/AmpResponse.php
+++ b/src/Symfony/Component/HttpClient/Response/AmpResponse.php
@@ -142,10 +142,7 @@ public function getInfo(string $type = null)
         return null !== $type ? $this->info[$type] ?? null : $this->info;
     }
 
-    /**
-     * @return array
-     */
-    public function __sleep()
+    public function __sleep(): array
     {
         throw new \BadMethodCallException('Cannot serialize '.__CLASS__);
     }
diff --git a/src/Symfony/Component/HttpClient/Response/CommonResponseTrait.php b/src/Symfony/Component/HttpClient/Response/CommonResponseTrait.php
index f3c8e149f77f7..bf947c69d1b32 100644
--- a/src/Symfony/Component/HttpClient/Response/CommonResponseTrait.php
+++ b/src/Symfony/Component/HttpClient/Response/CommonResponseTrait.php
@@ -127,10 +127,7 @@ public function toStream(bool $throw = true)
         return $stream;
     }
 
-    /**
-     * @return array
-     */
-    public function __sleep()
+    public function __sleep(): array
     {
         throw new \BadMethodCallException('Cannot serialize '.__CLASS__);
     }
diff --git a/src/Symfony/Component/HttpFoundation/Cookie.php b/src/Symfony/Component/HttpFoundation/Cookie.php
index bb42641c594ed..3c4192c522553 100644
--- a/src/Symfony/Component/HttpFoundation/Cookie.php
+++ b/src/Symfony/Component/HttpFoundation/Cookie.php
@@ -156,10 +156,8 @@ public function withExpires($expire = 0): self
      * Converts expires formats to a unix timestamp.
      *
      * @param int|string|\DateTimeInterface $expire
-     *
-     * @return int
      */
-    private static function expiresTimestamp($expire = 0)
+    private static function expiresTimestamp($expire = 0): int
     {
         // convert expiration time to a Unix timestamp
         if ($expire instanceof \DateTimeInterface) {
diff --git a/src/Symfony/Component/HttpFoundation/Request.php b/src/Symfony/Component/HttpFoundation/Request.php
index 1b705aa207925..2a9741e89e31a 100644
--- a/src/Symfony/Component/HttpFoundation/Request.php
+++ b/src/Symfony/Component/HttpFoundation/Request.php
@@ -912,7 +912,7 @@ public function getBaseUrl()
      *
      * @return string The raw URL (i.e. not urldecoded)
      */
-    private function getBaseUrlReal()
+    private function getBaseUrlReal(): string
     {
         if (null === $this->baseUrl) {
             $this->baseUrl = $this->prepareBaseUrl();
diff --git a/src/Symfony/Component/HttpKernel/Tests/CacheWarmer/CacheWarmerTest.php b/src/Symfony/Component/HttpKernel/Tests/CacheWarmer/CacheWarmerTest.php
index 28b7bdee06cfe..02d07fe1bcce9 100644
--- a/src/Symfony/Component/HttpKernel/Tests/CacheWarmer/CacheWarmerTest.php
+++ b/src/Symfony/Component/HttpKernel/Tests/CacheWarmer/CacheWarmerTest.php
@@ -57,7 +57,7 @@ public function __construct(string $file)
     /**
      * @return string[]
      */
-    public function warmUp(string $cacheDir)
+    public function warmUp(string $cacheDir): array
     {
         $this->writeCacheFile($this->file, 'content');
 
diff --git a/src/Symfony/Component/Lock/Lock.php b/src/Symfony/Component/Lock/Lock.php
index 98dc10ce23109..166b68681de0d 100644
--- a/src/Symfony/Component/Lock/Lock.php
+++ b/src/Symfony/Component/Lock/Lock.php
@@ -52,7 +52,7 @@ public function __construct(Key $key, PersistingStoreInterface $store, float $tt
     /**
      * @return array
      */
-    public function __sleep()
+    public function __sleep(): array
     {
         throw new \BadMethodCallException('Cannot serialize '.__CLASS__);
     }
diff --git a/src/Symfony/Component/Mailer/DataCollector/MessageDataCollector.php b/src/Symfony/Component/Mailer/DataCollector/MessageDataCollector.php
index a5b474c2b8aba..2200d9fe61804 100644
--- a/src/Symfony/Component/Mailer/DataCollector/MessageDataCollector.php
+++ b/src/Symfony/Component/Mailer/DataCollector/MessageDataCollector.php
@@ -53,7 +53,7 @@ public function reset()
     /**
      * {@inheritdoc}
      */
-    public function getName()
+    public function getName(): string
     {
         return 'mailer';
     }
diff --git a/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/PostgreSqlConnection.php b/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/PostgreSqlConnection.php
index 34fa328486e7a..37abd4313dcbe 100644
--- a/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/PostgreSqlConnection.php
+++ b/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/PostgreSqlConnection.php
@@ -38,7 +38,7 @@ final class PostgreSqlConnection extends Connection
     /**
      * @return array
      */
-    public function __sleep()
+    public function __sleep(): array
     {
         throw new \BadMethodCallException('Cannot serialize '.__CLASS__);
     }
diff --git a/src/Symfony/Component/Messenger/Transport/Serialization/Normalizer/FlattenExceptionNormalizer.php b/src/Symfony/Component/Messenger/Transport/Serialization/Normalizer/FlattenExceptionNormalizer.php
index 9be0bf178ea4f..d3e70d525d146 100644
--- a/src/Symfony/Component/Messenger/Transport/Serialization/Normalizer/FlattenExceptionNormalizer.php
+++ b/src/Symfony/Component/Messenger/Transport/Serialization/Normalizer/FlattenExceptionNormalizer.php
@@ -54,7 +54,7 @@ public function normalize($object, string $format = null, array $context = [])
     /**
      * {@inheritdoc}
      */
-    public function supportsNormalization($data, string $format = null, array $context = [])
+    public function supportsNormalization($data, string $format = null, array $context = []): bool
     {
         return $data instanceof FlattenException && ($context[Serializer::MESSENGER_SERIALIZATION_CONTEXT] ?? false);
     }
@@ -93,7 +93,7 @@ public function denormalize($data, string $type, string $format = null, array $c
     /**
      * {@inheritdoc}
      */
-    public function supportsDenormalization($data, string $type, string $format = null, array $context = [])
+    public function supportsDenormalization($data, string $type, string $format = null, array $context = []): bool
     {
         return FlattenException::class === $type && ($context[Serializer::MESSENGER_SERIALIZATION_CONTEXT] ?? false);
     }
diff --git a/src/Symfony/Component/Notifier/DataCollector/NotificationDataCollector.php b/src/Symfony/Component/Notifier/DataCollector/NotificationDataCollector.php
index 0bd03e919b2ab..0a0a70c990d69 100644
--- a/src/Symfony/Component/Notifier/DataCollector/NotificationDataCollector.php
+++ b/src/Symfony/Component/Notifier/DataCollector/NotificationDataCollector.php
@@ -53,7 +53,7 @@ public function reset()
     /**
      * {@inheritdoc}
      */
-    public function getName()
+    public function getName(): string
     {
         return 'notifier';
     }
diff --git a/src/Symfony/Component/PropertyInfo/Extractor/ConstructorExtractor.php b/src/Symfony/Component/PropertyInfo/Extractor/ConstructorExtractor.php
index 86dc43f13b9f5..f8ea6de18529d 100644
--- a/src/Symfony/Component/PropertyInfo/Extractor/ConstructorExtractor.php
+++ b/src/Symfony/Component/PropertyInfo/Extractor/ConstructorExtractor.php
@@ -34,7 +34,7 @@ public function __construct(iterable $extractors = [])
     /**
      * {@inheritdoc}
      */
-    public function getTypes(string $class, string $property, array $context = [])
+    public function getTypes(string $class, string $property, array $context = []): ?array
     {
         foreach ($this->extractors as $extractor) {
             $value = $extractor->getTypesFromConstructor($class, $property);
diff --git a/src/Symfony/Component/Routing/Tests/Loader/ObjectLoaderTest.php b/src/Symfony/Component/Routing/Tests/Loader/ObjectLoaderTest.php
index 54d3643b1f584..fcd679ead9e31 100644
--- a/src/Symfony/Component/Routing/Tests/Loader/ObjectLoaderTest.php
+++ b/src/Symfony/Component/Routing/Tests/Loader/ObjectLoaderTest.php
@@ -103,7 +103,7 @@ public function supports($resource, string $type = null): bool
         return 'service';
     }
 
-    protected function getObject(string $id)
+    protected function getObject(string $id): object
     {
         return $this->loaderMap[$id] ?? null;
     }
diff --git a/src/Symfony/Component/Security/Core/Tests/Authentication/AuthenticationTrustResolverTest.php b/src/Symfony/Component/Security/Core/Tests/Authentication/AuthenticationTrustResolverTest.php
index 9113d064aacdc..9500117f4f59c 100644
--- a/src/Symfony/Component/Security/Core/Tests/Authentication/AuthenticationTrustResolverTest.php
+++ b/src/Symfony/Component/Security/Core/Tests/Authentication/AuthenticationTrustResolverTest.php
@@ -11,6 +11,7 @@
 
 namespace Symfony\Component\Security\Core\Tests\Authentication;
 
+use Symfony\Component\Security\Core\User\UserInterface;
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\Security\Core\Authentication\AuthenticationTrustResolver;
 use Symfony\Component\Security\Core\Authentication\Token\AnonymousToken;
@@ -176,7 +177,7 @@ public function getCredentials()
     {
     }
 
-    public function getUser()
+    public function getUser(): UserInterface
     {
     }
 
diff --git a/src/Symfony/Component/Security/Core/Tests/Authentication/Provider/DaoAuthenticationProviderTest.php b/src/Symfony/Component/Security/Core/Tests/Authentication/Provider/DaoAuthenticationProviderTest.php
index 563c9db951962..63a9261fadf8a 100644
--- a/src/Symfony/Component/Security/Core/Tests/Authentication/Provider/DaoAuthenticationProviderTest.php
+++ b/src/Symfony/Component/Security/Core/Tests/Authentication/Provider/DaoAuthenticationProviderTest.php
@@ -391,5 +391,5 @@ public function loadUserByIdentifier(string $identifier): UserInterface;
 
 interface DaoAuthenticationProviderTest_UserProvider extends UserProviderInterface
 {
-    public function loadUserByUsername($username);
+    public function loadUserByUsername($username): string;
 }
diff --git a/src/Symfony/Component/Security/Core/Tests/Authentication/Token/AbstractTokenTest.php b/src/Symfony/Component/Security/Core/Tests/Authentication/Token/AbstractTokenTest.php
index be4ccf0989848..a52eb4753490d 100644
--- a/src/Symfony/Component/Security/Core/Tests/Authentication/Token/AbstractTokenTest.php
+++ b/src/Symfony/Component/Security/Core/Tests/Authentication/Token/AbstractTokenTest.php
@@ -268,22 +268,22 @@ public function __construct($name, array $roles = [])
         $this->roles = $roles;
     }
 
-    public function getUsername()
+    public function getUsername(): string
     {
         return $this->name;
     }
 
-    public function getUserIdentifier()
+    public function getUserIdentifier(): string
     {
         return $this->name;
     }
 
-    public function getPassword()
+    public function getPassword(): ?string
     {
         return '***';
     }
 
-    public function getRoles()
+    public function getRoles(): array
     {
         if (empty($this->roles)) {
             return ['ROLE_USER'];
@@ -296,7 +296,7 @@ public function eraseCredentials()
     {
     }
 
-    public function getSalt()
+    public function getSalt(): ?string
     {
         return null;
     }
diff --git a/src/Symfony/Component/Security/Http/Tests/EventListener/PasswordMigratingListenerTest.php b/src/Symfony/Component/Security/Http/Tests/EventListener/PasswordMigratingListenerTest.php
index b8062b268653a..da61fa59166fb 100644
--- a/src/Symfony/Component/Security/Http/Tests/EventListener/PasswordMigratingListenerTest.php
+++ b/src/Symfony/Component/Security/Http/Tests/EventListener/PasswordMigratingListenerTest.php
@@ -152,5 +152,5 @@ abstract class TestPasswordAuthenticatedUser implements UserInterface, PasswordA
 {
     abstract public function getPassword(): ?string;
 
-    abstract public function getSalt();
+    abstract public function getSalt(): ?string;
 }
diff --git a/src/Symfony/Component/Semaphore/Semaphore.php b/src/Symfony/Component/Semaphore/Semaphore.php
index 5614364c7bb86..8c1db61471b9a 100644
--- a/src/Symfony/Component/Semaphore/Semaphore.php
+++ b/src/Symfony/Component/Semaphore/Semaphore.php
@@ -49,7 +49,7 @@ public function __construct(Key $key, PersistingStoreInterface $store, float $tt
     /**
      * @return array
      */
-    public function __sleep()
+    public function __sleep(): array
     {
         throw new \BadMethodCallException('Cannot serialize '.__CLASS__);
     }
diff --git a/src/Symfony/Component/Serializer/CacheWarmer/CompiledClassMetadataCacheWarmer.php b/src/Symfony/Component/Serializer/CacheWarmer/CompiledClassMetadataCacheWarmer.php
index 360640e139723..de12fa1be299a 100644
--- a/src/Symfony/Component/Serializer/CacheWarmer/CompiledClassMetadataCacheWarmer.php
+++ b/src/Symfony/Component/Serializer/CacheWarmer/CompiledClassMetadataCacheWarmer.php
@@ -40,7 +40,7 @@ public function __construct(array $classesToCompile, ClassMetadataFactoryInterfa
     /**
      * {@inheritdoc}
      */
-    public function warmUp($cacheDir)
+    public function warmUp($cacheDir): array
     {
         $metadatas = [];
 
@@ -58,7 +58,7 @@ public function warmUp($cacheDir)
     /**
      * {@inheritdoc}
      */
-    public function isOptional()
+    public function isOptional(): bool
     {
         return true;
     }
diff --git a/src/Symfony/Component/Serializer/Encoder/ChainEncoder.php b/src/Symfony/Component/Serializer/Encoder/ChainEncoder.php
index 48722d21c1bcc..3cdc62a745216 100644
--- a/src/Symfony/Component/Serializer/Encoder/ChainEncoder.php
+++ b/src/Symfony/Component/Serializer/Encoder/ChainEncoder.php
@@ -35,7 +35,7 @@ public function __construct(array $encoders = [])
     /**
      * {@inheritdoc}
      */
-    final public function encode($data, string $format, array $context = [])
+    final public function encode($data, string $format, array $context = []): string
     {
         return $this->getEncoder($format, $context)->encode($data, $format, $context);
     }
diff --git a/src/Symfony/Component/Serializer/Mapping/Factory/CompiledClassMetadataFactory.php b/src/Symfony/Component/Serializer/Mapping/Factory/CompiledClassMetadataFactory.php
index 17daf9e66d2e8..3adf65f052106 100644
--- a/src/Symfony/Component/Serializer/Mapping/Factory/CompiledClassMetadataFactory.php
+++ b/src/Symfony/Component/Serializer/Mapping/Factory/CompiledClassMetadataFactory.php
@@ -14,6 +14,7 @@
 use Symfony\Component\Serializer\Mapping\AttributeMetadata;
 use Symfony\Component\Serializer\Mapping\ClassDiscriminatorMapping;
 use Symfony\Component\Serializer\Mapping\ClassMetadata;
+use Symfony\Component\Serializer\Mapping\ClassMetadataInterface;
 
 /**
  * @author Fabien Bourigault <bourigaultfabien@gmail.com>
@@ -44,7 +45,7 @@ public function __construct(string $compiledClassMetadataFile, ClassMetadataFact
     /**
      * {@inheritdoc}
      */
-    public function getMetadataFor($value)
+    public function getMetadataFor($value): ClassMetadataInterface
     {
         $className = \is_object($value) ? \get_class($value) : $value;
 
@@ -72,7 +73,7 @@ public function getMetadataFor($value)
     /**
      * {@inheritdoc}
      */
-    public function hasMetadataFor($value)
+    public function hasMetadataFor($value): bool
     {
         $className = \is_object($value) ? \get_class($value) : $value;
 
diff --git a/src/Symfony/Component/Serializer/Normalizer/BackedEnumNormalizer.php b/src/Symfony/Component/Serializer/Normalizer/BackedEnumNormalizer.php
index 808e046283356..b129bb6a81f03 100644
--- a/src/Symfony/Component/Serializer/Normalizer/BackedEnumNormalizer.php
+++ b/src/Symfony/Component/Serializer/Normalizer/BackedEnumNormalizer.php
@@ -40,7 +40,7 @@ public function normalize($object, $format = null, array $context = [])
     /**
      * {@inheritdoc}
      */
-    public function supportsNormalization($data, $format = null)
+    public function supportsNormalization($data, $format = null): bool
     {
         return $data instanceof \BackedEnum;
     }
@@ -70,7 +70,7 @@ public function denormalize($data, $type, $format = null, array $context = [])
     /**
      * {@inheritdoc}
      */
-    public function supportsDenormalization($data, $type, $format = null)
+    public function supportsDenormalization($data, $type, $format = null): bool
     {
         return is_subclass_of($type, \BackedEnum::class);
     }
diff --git a/src/Symfony/Component/Serializer/Normalizer/MimeMessageNormalizer.php b/src/Symfony/Component/Serializer/Normalizer/MimeMessageNormalizer.php
index 0708847bde0e5..5f3de19335473 100644
--- a/src/Symfony/Component/Serializer/Normalizer/MimeMessageNormalizer.php
+++ b/src/Symfony/Component/Serializer/Normalizer/MimeMessageNormalizer.php
@@ -100,7 +100,7 @@ public function denormalize($data, string $type, string $format = null, array $c
     /**
      * {@inheritdoc}
      */
-    public function supportsNormalization($data, string $format = null)
+    public function supportsNormalization($data, string $format = null): bool
     {
         return $data instanceof Message || $data instanceof Headers || $data instanceof HeaderInterface || $data instanceof Address || $data instanceof AbstractPart;
     }
@@ -108,7 +108,7 @@ public function supportsNormalization($data, string $format = null)
     /**
      * {@inheritdoc}
      */
-    public function supportsDenormalization($data, string $type, string $format = null)
+    public function supportsDenormalization($data, string $type, string $format = null): bool
     {
         return is_a($type, Message::class, true) || Headers::class === $type || AbstractPart::class === $type;
     }
diff --git a/src/Symfony/Component/Serializer/Normalizer/UidNormalizer.php b/src/Symfony/Component/Serializer/Normalizer/UidNormalizer.php
index 009d334895ee8..55508a962df4f 100644
--- a/src/Symfony/Component/Serializer/Normalizer/UidNormalizer.php
+++ b/src/Symfony/Component/Serializer/Normalizer/UidNormalizer.php
@@ -59,7 +59,7 @@ public function normalize($object, string $format = null, array $context = [])
     /**
      * {@inheritdoc}
      */
-    public function supportsNormalization($data, string $format = null)
+    public function supportsNormalization($data, string $format = null): bool
     {
         return $data instanceof AbstractUid;
     }
@@ -79,7 +79,7 @@ public function denormalize($data, string $type, string $format = null, array $c
     /**
      * {@inheritdoc}
      */
-    public function supportsDenormalization($data, string $type, string $format = null)
+    public function supportsDenormalization($data, string $type, string $format = null): bool
     {
         return is_a($type, AbstractUid::class, true);
     }
diff --git a/src/Symfony/Component/Serializer/Normalizer/UnwrappingDenormalizer.php b/src/Symfony/Component/Serializer/Normalizer/UnwrappingDenormalizer.php
index 6bc8df80bb3cd..9e9880d901167 100644
--- a/src/Symfony/Component/Serializer/Normalizer/UnwrappingDenormalizer.php
+++ b/src/Symfony/Component/Serializer/Normalizer/UnwrappingDenormalizer.php
@@ -54,7 +54,7 @@ public function denormalize($data, $class, string $format = null, array $context
     /**
      * {@inheritdoc}
      */
-    public function supportsDenormalization($data, $type, string $format = null, array $context = [])
+    public function supportsDenormalization($data, $type, string $format = null, array $context = []): bool
     {
         return \array_key_exists(self::UNWRAP_PATH, $context) && !isset($context['unwrapped']);
     }
diff --git a/src/Symfony/Component/Serializer/Serializer.php b/src/Symfony/Component/Serializer/Serializer.php
index d2c0741457d9e..29f829a3a6b0a 100644
--- a/src/Symfony/Component/Serializer/Serializer.php
+++ b/src/Symfony/Component/Serializer/Serializer.php
@@ -316,7 +316,7 @@ private function getDenormalizer($data, string $class, ?string $format, array $c
     /**
      * {@inheritdoc}
      */
-    final public function encode($data, string $format, array $context = [])
+    final public function encode($data, string $format, array $context = []): string
     {
         return $this->encoder->encode($data, $format, $context);
     }
diff --git a/src/Symfony/Component/Serializer/Tests/Encoder/ChainEncoderTest.php b/src/Symfony/Component/Serializer/Tests/Encoder/ChainEncoderTest.php
index d90163d2537a0..f447c684a39eb 100644
--- a/src/Symfony/Component/Serializer/Tests/Encoder/ChainEncoderTest.php
+++ b/src/Symfony/Component/Serializer/Tests/Encoder/ChainEncoderTest.php
@@ -95,7 +95,7 @@ public function supportsEncoding(string $format): bool
         return true;
     }
 
-    public function encode($data, string $format, array $context = [])
+    public function encode($data, string $format, array $context = []): string
     {
     }
 }
diff --git a/src/Symfony/Component/Serializer/Tests/Normalizer/AbstractObjectNormalizerTest.php b/src/Symfony/Component/Serializer/Tests/Normalizer/AbstractObjectNormalizerTest.php
index e8243b1609ff6..73fcea051c7dd 100644
--- a/src/Symfony/Component/Serializer/Tests/Normalizer/AbstractObjectNormalizerTest.php
+++ b/src/Symfony/Component/Serializer/Tests/Normalizer/AbstractObjectNormalizerTest.php
@@ -622,7 +622,7 @@ class NotSerializable
     /**
      * @return array
      */
-    public function __sleep()
+    public function __sleep(): array
     {
         if (class_exists(\Error::class)) {
             throw new \Error('not serializable');
diff --git a/src/Symfony/Component/Serializer/Tests/Normalizer/PropertyNormalizerTest.php b/src/Symfony/Component/Serializer/Tests/Normalizer/PropertyNormalizerTest.php
index b2a76656d76fe..14fe5382b3198 100644
--- a/src/Symfony/Component/Serializer/Tests/Normalizer/PropertyNormalizerTest.php
+++ b/src/Symfony/Component/Serializer/Tests/Normalizer/PropertyNormalizerTest.php
@@ -483,7 +483,7 @@ public function getChildren(): array
     /**
      * @return Dummy[][][]
      */
-    public function getGrandChildren()
+    public function getGrandChildren(): array
     {
         return $this->grandChildren;
     }
@@ -491,7 +491,7 @@ public function getGrandChildren()
     /**
      * @return array
      */
-    public function getIntMatrix()
+    public function getIntMatrix(): array
     {
         return $this->intMatrix;
     }
diff --git a/src/Symfony/Component/Translation/PseudoLocalizationTranslator.php b/src/Symfony/Component/Translation/PseudoLocalizationTranslator.php
index 49f122eb83b34..d5a1b29e2a04f 100644
--- a/src/Symfony/Component/Translation/PseudoLocalizationTranslator.php
+++ b/src/Symfony/Component/Translation/PseudoLocalizationTranslator.php
@@ -82,7 +82,7 @@ public function __construct(TranslatorInterface $translator, array $options = []
     /**
      * {@inheritdoc}
      */
-    public function trans(string $id, array $parameters = [], string $domain = null, string $locale = null)
+    public function trans(string $id, array $parameters = [], string $domain = null, string $locale = null): string
     {
         $trans = '';
         $visibleText = '';
diff --git a/src/Symfony/Component/Translation/Tests/IdentityTranslatorTest.php b/src/Symfony/Component/Translation/Tests/IdentityTranslatorTest.php
index 16945d38a293a..35389e5872505 100644
--- a/src/Symfony/Component/Translation/Tests/IdentityTranslatorTest.php
+++ b/src/Symfony/Component/Translation/Tests/IdentityTranslatorTest.php
@@ -13,6 +13,7 @@
 
 use Symfony\Component\Translation\IdentityTranslator;
 use Symfony\Contracts\Translation\Test\TranslatorTest;
+use Symfony\Contracts\Translation\TranslatorInterface;
 
 class IdentityTranslatorTest extends TranslatorTest
 {
@@ -33,7 +34,7 @@ protected function tearDown(): void
         \Locale::setDefault($this->defaultLocale);
     }
 
-    public function getTranslator()
+    public function getTranslator(): TranslatorInterface
     {
         return new IdentityTranslator();
     }
diff --git a/src/Symfony/Component/Translation/TranslatorBag.php b/src/Symfony/Component/Translation/TranslatorBag.php
index c6555782fdb70..6d98455e5b78a 100644
--- a/src/Symfony/Component/Translation/TranslatorBag.php
+++ b/src/Symfony/Component/Translation/TranslatorBag.php
@@ -38,7 +38,7 @@ public function addBag(TranslatorBagInterface $bag): void
     /**
      * {@inheritdoc}
      */
-    public function getCatalogue(string $locale = null)
+    public function getCatalogue(string $locale = null): MessageCatalogueInterface
     {
         if (null === $locale || !isset($this->catalogues[$locale])) {
             $this->catalogues[$locale] = new MessageCatalogue($locale);
diff --git a/src/Symfony/Component/Validator/Constraint.php b/src/Symfony/Component/Validator/Constraint.php
index a2974373d3cce..73c7c74dfee5f 100644
--- a/src/Symfony/Component/Validator/Constraint.php
+++ b/src/Symfony/Component/Validator/Constraint.php
@@ -297,7 +297,7 @@ public function getTargets()
      *
      * @internal
      */
-    public function __sleep()
+    public function __sleep(): array
     {
         // Initialize "groups" option if it is not set
         $this->groups;
diff --git a/src/Symfony/Component/Validator/Constraints/Compound.php b/src/Symfony/Component/Validator/Constraints/Compound.php
index 042da1dd5757b..54dcd6c86f9dd 100644
--- a/src/Symfony/Component/Validator/Constraints/Compound.php
+++ b/src/Symfony/Component/Validator/Constraints/Compound.php
@@ -35,12 +35,12 @@ public function __construct($options = null)
         parent::__construct($options);
     }
 
-    final protected function getCompositeOption()
+    final protected function getCompositeOption(): string
     {
         return 'constraints';
     }
 
-    final public function validatedBy()
+    final public function validatedBy(): string
     {
         return CompoundValidator::class;
     }
diff --git a/src/Symfony/Component/Validator/Tests/Constraints/CompoundTest.php b/src/Symfony/Component/Validator/Tests/Constraints/CompoundTest.php
index 5f8f8456ad7f1..d5cf9e9ceecbb 100644
--- a/src/Symfony/Component/Validator/Tests/Constraints/CompoundTest.php
+++ b/src/Symfony/Component/Validator/Tests/Constraints/CompoundTest.php
@@ -46,7 +46,7 @@ class ForwardingOptionCompound extends Compound
 {
     public $min;
 
-    public function getDefaultOption()
+    public function getDefaultOption(): ?string
     {
         return 'min';
     }
diff --git a/src/Symfony/Component/Validator/Tests/Mapping/ClassMetadataTest.php b/src/Symfony/Component/Validator/Tests/Mapping/ClassMetadataTest.php
index abab68d050bf5..df67a129f7006 100644
--- a/src/Symfony/Component/Validator/Tests/Mapping/ClassMetadataTest.php
+++ b/src/Symfony/Component/Validator/Tests/Mapping/ClassMetadataTest.php
@@ -373,12 +373,12 @@ class ClassCompositeConstraint extends Composite
 {
     public $nested;
 
-    public function getDefaultOption()
+    public function getDefaultOption(): ?string
     {
         return $this->getCompositeOption();
     }
 
-    protected function getCompositeOption()
+    protected function getCompositeOption(): string
     {
         return 'nested';
     }
diff --git a/src/Symfony/Component/Validator/Tests/Mapping/Factory/LazyLoadingMetadataFactoryTest.php b/src/Symfony/Component/Validator/Tests/Mapping/Factory/LazyLoadingMetadataFactoryTest.php
index 87dba42bf6e9b..f9b4381c65fbf 100644
--- a/src/Symfony/Component/Validator/Tests/Mapping/Factory/LazyLoadingMetadataFactoryTest.php
+++ b/src/Symfony/Component/Validator/Tests/Mapping/Factory/LazyLoadingMetadataFactoryTest.php
@@ -176,7 +176,7 @@ public function loadClassMetadata(ClassMetadata $metadata): bool
 
 class PropertyGetterInterfaceConstraintLoader implements LoaderInterface
 {
-    public function loadClassMetadata(ClassMetadata $metadata)
+    public function loadClassMetadata(ClassMetadata $metadata): bool
     {
         if (PropertyGetterInterface::class === $metadata->getClassName()) {
             $metadata->addGetterConstraint('property', new NotBlank());
diff --git a/src/Symfony/Component/Validator/Tests/Mapping/MemberMetadataTest.php b/src/Symfony/Component/Validator/Tests/Mapping/MemberMetadataTest.php
index 32e40a964b129..241f81468b971 100644
--- a/src/Symfony/Component/Validator/Tests/Mapping/MemberMetadataTest.php
+++ b/src/Symfony/Component/Validator/Tests/Mapping/MemberMetadataTest.php
@@ -121,12 +121,12 @@ class PropertyCompositeConstraint extends Composite
 {
     public $nested;
 
-    public function getDefaultOption()
+    public function getDefaultOption(): ?string
     {
         return $this->getCompositeOption();
     }
 
-    protected function getCompositeOption()
+    protected function getCompositeOption(): string
     {
         return 'nested';
     }
diff --git a/src/Symfony/Contracts/Tests/Service/ServiceSubscriberTraitTest.php b/src/Symfony/Contracts/Tests/Service/ServiceSubscriberTraitTest.php
index 09453d865f220..344bba8772dc6 100644
--- a/src/Symfony/Contracts/Tests/Service/ServiceSubscriberTraitTest.php
+++ b/src/Symfony/Contracts/Tests/Service/ServiceSubscriberTraitTest.php
@@ -42,9 +42,6 @@ public function aParentService(): Service1
     {
     }
 
-    /**
-     * @return ?ContainerInterface
-     */
     public function setContainer(ContainerInterface $container)
     {
         return $container;