diff --git a/src/Symfony/Bridge/Doctrine/Tests/Fixtures/BaseUser.php b/src/Symfony/Bridge/Doctrine/Tests/Fixtures/BaseUser.php
index 49c13e0d31..aa24cd6894 100644
--- a/src/Symfony/Bridge/Doctrine/Tests/Fixtures/BaseUser.php
+++ b/src/Symfony/Bridge/Doctrine/Tests/Fixtures/BaseUser.php
@@ -31,10 +31,7 @@ class BaseUser
         $this->username = $username;
     }
 
-    /**
-     * @return int
-     */
-    public function getId()
+    public function getId(): int
     {
         return $this->id;
     }
diff --git a/src/Symfony/Bridge/Monolog/Tests/LoggerTest.php b/src/Symfony/Bridge/Monolog/Tests/LoggerTest.php
index be4781d67f..3cf8d40e0b 100644
--- a/src/Symfony/Bridge/Monolog/Tests/LoggerTest.php
+++ b/src/Symfony/Bridge/Monolog/Tests/LoggerTest.php
@@ -153,8 +153,8 @@ class ClassThatInheritLogger extends Logger
         return parent::getLogs();
     }
 
-    public function countErrors()
+    public function countErrors(): int
     {
-        parent::countErrors();
+        return parent::countErrors();
     }
 }
diff --git a/src/Symfony/Bridge/Monolog/Tests/Processor/DebugProcessorTest.php b/src/Symfony/Bridge/Monolog/Tests/Processor/DebugProcessorTest.php
index ef859df0cd..7bd149c705 100644
--- a/src/Symfony/Bridge/Monolog/Tests/Processor/DebugProcessorTest.php
+++ b/src/Symfony/Bridge/Monolog/Tests/Processor/DebugProcessorTest.php
@@ -104,8 +104,8 @@ class ClassThatInheritDebugProcessor extends DebugProcessor
         return parent::getLogs();
     }
 
-    public function countErrors()
+    public function countErrors(): int
     {
-        parent::countErrors();
+        return parent::countErrors();
     }
 }
diff --git a/src/Symfony/Bundle/DebugBundle/Command/ServerDumpPlaceholderCommand.php b/src/Symfony/Bundle/DebugBundle/Command/ServerDumpPlaceholderCommand.php
index ae69edfff7..7df85c70c9 100644
--- a/src/Symfony/Bundle/DebugBundle/Command/ServerDumpPlaceholderCommand.php
+++ b/src/Symfony/Bundle/DebugBundle/Command/ServerDumpPlaceholderCommand.php
@@ -43,7 +43,7 @@ class ServerDumpPlaceholderCommand extends Command
         $this->setDescription($this->replacedCommand->getDescription());
     }
 
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): int
     {
         (new SymfonyStyle($input, $output))->getErrorStyle()->warning('In order to use the VarDumper server, set the "debug.dump_destination" config option to "tcp://%env(VAR_DUMPER_SERVER)%"');
 
diff --git a/src/Symfony/Bundle/FrameworkBundle/Command/AssetsInstallCommand.php b/src/Symfony/Bundle/FrameworkBundle/Command/AssetsInstallCommand.php
index 111ed815c7..d38e89f0e9 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Command/AssetsInstallCommand.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Command/AssetsInstallCommand.php
@@ -95,7 +95,7 @@ EOT
     /**
      * {@inheritdoc}
      */
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): int
     {
         /** @var KernelInterface $kernel */
         $kernel = $this->getApplication()->getKernel();
diff --git a/src/Symfony/Bundle/FrameworkBundle/Command/ConfigDumpReferenceCommand.php b/src/Symfony/Bundle/FrameworkBundle/Command/ConfigDumpReferenceCommand.php
index 05a5559171..60445e4063 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Command/ConfigDumpReferenceCommand.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Command/ConfigDumpReferenceCommand.php
@@ -74,7 +74,7 @@ EOF
      *
      * @throws \LogicException
      */
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): int
     {
         $io = new SymfonyStyle($input, $output);
         $errorIo = $io->getErrorStyle();
@@ -86,7 +86,7 @@ EOF
                 'For dumping a specific option, add its path as the second argument of this command. (e.g. <comment>config:dump-reference FrameworkBundle profiler.matcher</comment> to dump the <comment>framework.profiler.matcher</comment> configuration)',
             ]);
 
-            return null;
+            return 0;
         }
 
         $extension = $this->findExtension($name);
@@ -130,6 +130,6 @@ EOF
 
         $io->writeln(null === $path ? $dumper->dump($configuration, $extension->getNamespace()) : $dumper->dumpAtPath($configuration, $path));
 
-        return null;
+        return 0;
     }
 }
diff --git a/src/Symfony/Bundle/FrameworkBundle/Command/DebugAutowiringCommand.php b/src/Symfony/Bundle/FrameworkBundle/Command/DebugAutowiringCommand.php
index a7bec8c146..04d391da17 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Command/DebugAutowiringCommand.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Command/DebugAutowiringCommand.php
@@ -69,7 +69,7 @@ EOF
     /**
      * {@inheritdoc}
      */
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): int
     {
         $io = new SymfonyStyle($input, $output);
         $errorIo = $io->getErrorStyle();
@@ -146,7 +146,7 @@ EOF
 
         $io->newLine();
 
-        return null;
+        return 0;
     }
 
     private function getFileLink(string $class): string
diff --git a/src/Symfony/Bundle/FrameworkBundle/Command/RouterMatchCommand.php b/src/Symfony/Bundle/FrameworkBundle/Command/RouterMatchCommand.php
index e7306b94b6..454767e6a8 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Command/RouterMatchCommand.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Command/RouterMatchCommand.php
@@ -71,7 +71,7 @@ EOF
     /**
      * {@inheritdoc}
      */
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): int
     {
         $io = new SymfonyStyle($input, $output);
 
@@ -114,6 +114,6 @@ EOF
             return 1;
         }
 
-        return null;
+        return 0;
     }
 }
diff --git a/src/Symfony/Bundle/FrameworkBundle/Command/TranslationUpdateCommand.php b/src/Symfony/Bundle/FrameworkBundle/Command/TranslationUpdateCommand.php
index 645bedfe0e..cc704ab5e4 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Command/TranslationUpdateCommand.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Command/TranslationUpdateCommand.php
@@ -102,7 +102,7 @@ EOF
     /**
      * {@inheritdoc}
      */
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): int
     {
         $io = new SymfonyStyle($input, $output);
         $errorIo = $io->getErrorStyle();
@@ -236,7 +236,7 @@ EOF
         if (!\count($operation->getDomains())) {
             $errorIo->warning('No translation messages were found.');
 
-            return null;
+            return 0;
         }
 
         $resultMessage = 'Translation files were successfully updated';
@@ -302,7 +302,7 @@ EOF
 
         $errorIo->success($resultMessage.'.');
 
-        return null;
+        return 0;
     }
 
     private function filterCatalogue(MessageCatalogue $catalogue, string $domain): MessageCatalogue
diff --git a/src/Symfony/Bundle/SecurityBundle/Command/UserPasswordEncoderCommand.php b/src/Symfony/Bundle/SecurityBundle/Command/UserPasswordEncoderCommand.php
index 01f2b82356..c80e3c4bb1 100644
--- a/src/Symfony/Bundle/SecurityBundle/Command/UserPasswordEncoderCommand.php
+++ b/src/Symfony/Bundle/SecurityBundle/Command/UserPasswordEncoderCommand.php
@@ -101,7 +101,7 @@ EOF
     /**
      * {@inheritdoc}
      */
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): int
     {
         $io = new SymfonyStyle($input, $output);
         $errorIo = $output instanceof ConsoleOutputInterface ? new SymfonyStyle($input, $output->getErrorOutput()) : $io;
@@ -163,7 +163,7 @@ EOF
 
         $errorIo->success('Password encoding succeeded');
 
-        return null;
+        return 0;
     }
 
     /**
diff --git a/src/Symfony/Component/Cache/Traits/FilesystemCommonTrait.php b/src/Symfony/Component/Cache/Traits/FilesystemCommonTrait.php
index 237c726822..0e183ced99 100644
--- a/src/Symfony/Component/Cache/Traits/FilesystemCommonTrait.php
+++ b/src/Symfony/Component/Cache/Traits/FilesystemCommonTrait.php
@@ -131,6 +131,9 @@ trait FilesystemCommonTrait
         throw new \ErrorException($message, 0, $type, $file, $line);
     }
 
+    /**
+     * @return array
+     */
     public function __sleep()
     {
         throw new \BadMethodCallException('Cannot serialize '.__CLASS__);
diff --git a/src/Symfony/Component/Console/Command/Command.php b/src/Symfony/Component/Console/Command/Command.php
index 18d683de93..1420eda667 100644
--- a/src/Symfony/Component/Console/Command/Command.php
+++ b/src/Symfony/Component/Console/Command/Command.php
@@ -150,7 +150,7 @@ class Command
      * execute() method, you set the code to execute by passing
      * a Closure to the setCode() method.
      *
-     * @return int|null null or 0 if everything went fine, or an error code
+     * @return int|void void or 0 if everything went fine, or an exit code
      *
      * @throws LogicException When this abstract method is not implemented
      *
diff --git a/src/Symfony/Component/CssSelector/Node/Specificity.php b/src/Symfony/Component/CssSelector/Node/Specificity.php
index 9b35cb4116..d0ac8aa1d7 100644
--- a/src/Symfony/Component/CssSelector/Node/Specificity.php
+++ b/src/Symfony/Component/CssSelector/Node/Specificity.php
@@ -53,10 +53,8 @@ class Specificity
     /**
      * Returns -1 if the object specificity is lower than the argument,
      * 0 if they are equal, and 1 if the argument is lower.
-     *
-     * @return int
      */
-    public function compareTo(self $specificity)
+    public function compareTo(self $specificity): int
     {
         if ($this->a !== $specificity->a) {
             return $this->a > $specificity->a ? 1 : -1;
diff --git a/src/Symfony/Component/EventDispatcher/LegacyEventDispatcherProxy.php b/src/Symfony/Component/EventDispatcher/LegacyEventDispatcherProxy.php
index a3efdf31c6..09b58f00ed 100644
--- a/src/Symfony/Component/EventDispatcher/LegacyEventDispatcherProxy.php
+++ b/src/Symfony/Component/EventDispatcher/LegacyEventDispatcherProxy.php
@@ -124,7 +124,7 @@ final class LegacyEventDispatcherProxy implements EventDispatcherInterface
     /**
      * {@inheritdoc}
      */
-    public function getListenerPriority($eventName, $listener)
+    public function getListenerPriority($eventName, $listener): ?int
     {
         return $this->dispatcher->getListenerPriority($eventName, $listener);
     }
diff --git a/src/Symfony/Component/HttpFoundation/Session/Session.php b/src/Symfony/Component/HttpFoundation/Session/Session.php
index 0c7e9cc5ca..9738189b40 100644
--- a/src/Symfony/Component/HttpFoundation/Session/Session.php
+++ b/src/Symfony/Component/HttpFoundation/Session/Session.php
@@ -137,11 +137,9 @@ class Session implements SessionInterface, \IteratorAggregate, \Countable
     }
 
     /**
-     * @return int
-     *
      * @internal
      */
-    public function getUsageIndex()
+    public function getUsageIndex(): int
     {
         return $this->usageIndex;
     }
diff --git a/src/Symfony/Component/HttpKernel/Tests/EventListener/ExceptionListenerTest.php b/src/Symfony/Component/HttpKernel/Tests/EventListener/ExceptionListenerTest.php
index 7c2cb9d192..968429b8f7 100644
--- a/src/Symfony/Component/HttpKernel/Tests/EventListener/ExceptionListenerTest.php
+++ b/src/Symfony/Component/HttpKernel/Tests/EventListener/ExceptionListenerTest.php
@@ -159,7 +159,7 @@ class ExceptionListenerTest extends TestCase
 
 class TestLogger extends Logger implements DebugLoggerInterface
 {
-    public function countErrors()
+    public function countErrors(): int
     {
         return \count($this->logs['critical']);
     }
diff --git a/src/Symfony/Component/Intl/Tests/DateFormatter/AbstractIntlDateFormatterTest.php b/src/Symfony/Component/Intl/Tests/DateFormatter/AbstractIntlDateFormatterTest.php
index cf7a563b25..cee6b548a2 100644
--- a/src/Symfony/Component/Intl/Tests/DateFormatter/AbstractIntlDateFormatterTest.php
+++ b/src/Symfony/Component/Intl/Tests/DateFormatter/AbstractIntlDateFormatterTest.php
@@ -967,10 +967,7 @@ abstract class AbstractIntlDateFormatterTest extends TestCase
 
     abstract protected function getIntlErrorMessage(): string;
 
-    /**
-     * @return int
-     */
-    abstract protected function getIntlErrorCode();
+    abstract protected function getIntlErrorCode(): int;
 
     /**
      * @param int $errorCode
diff --git a/src/Symfony/Component/Intl/Tests/DateFormatter/IntlDateFormatterTest.php b/src/Symfony/Component/Intl/Tests/DateFormatter/IntlDateFormatterTest.php
index 2c043e235f..10f95c013b 100644
--- a/src/Symfony/Component/Intl/Tests/DateFormatter/IntlDateFormatterTest.php
+++ b/src/Symfony/Component/Intl/Tests/DateFormatter/IntlDateFormatterTest.php
@@ -188,7 +188,7 @@ class IntlDateFormatterTest extends AbstractIntlDateFormatterTest
         return IntlGlobals::getErrorMessage();
     }
 
-    protected function getIntlErrorCode()
+    protected function getIntlErrorCode(): int
     {
         return IntlGlobals::getErrorCode();
     }
diff --git a/src/Symfony/Component/Intl/Tests/DateFormatter/Verification/IntlDateFormatterTest.php b/src/Symfony/Component/Intl/Tests/DateFormatter/Verification/IntlDateFormatterTest.php
index a993ace5cb..50cccd993b 100644
--- a/src/Symfony/Component/Intl/Tests/DateFormatter/Verification/IntlDateFormatterTest.php
+++ b/src/Symfony/Component/Intl/Tests/DateFormatter/Verification/IntlDateFormatterTest.php
@@ -73,7 +73,7 @@ class IntlDateFormatterTest extends AbstractIntlDateFormatterTest
         return intl_get_error_message();
     }
 
-    protected function getIntlErrorCode()
+    protected function getIntlErrorCode(): int
     {
         return intl_get_error_code();
     }
diff --git a/src/Symfony/Component/Intl/Tests/NumberFormatter/AbstractNumberFormatterTest.php b/src/Symfony/Component/Intl/Tests/NumberFormatter/AbstractNumberFormatterTest.php
index 6a6e4ef628..9802a66b9a 100644
--- a/src/Symfony/Component/Intl/Tests/NumberFormatter/AbstractNumberFormatterTest.php
+++ b/src/Symfony/Component/Intl/Tests/NumberFormatter/AbstractNumberFormatterTest.php
@@ -842,10 +842,7 @@ abstract class AbstractNumberFormatterTest extends TestCase
 
     abstract protected function getIntlErrorMessage(): string;
 
-    /**
-     * @return int
-     */
-    abstract protected function getIntlErrorCode();
+    abstract protected function getIntlErrorCode(): int;
 
     /**
      * @param int $errorCode
diff --git a/src/Symfony/Component/Intl/Tests/NumberFormatter/NumberFormatterTest.php b/src/Symfony/Component/Intl/Tests/NumberFormatter/NumberFormatterTest.php
index 8faca56818..058e03756c 100644
--- a/src/Symfony/Component/Intl/Tests/NumberFormatter/NumberFormatterTest.php
+++ b/src/Symfony/Component/Intl/Tests/NumberFormatter/NumberFormatterTest.php
@@ -178,7 +178,7 @@ class NumberFormatterTest extends AbstractNumberFormatterTest
         return IntlGlobals::getErrorMessage();
     }
 
-    protected function getIntlErrorCode()
+    protected function getIntlErrorCode(): int
     {
         return IntlGlobals::getErrorCode();
     }
diff --git a/src/Symfony/Component/Intl/Tests/NumberFormatter/Verification/NumberFormatterTest.php b/src/Symfony/Component/Intl/Tests/NumberFormatter/Verification/NumberFormatterTest.php
index 1209180e89..edec2e9639 100644
--- a/src/Symfony/Component/Intl/Tests/NumberFormatter/Verification/NumberFormatterTest.php
+++ b/src/Symfony/Component/Intl/Tests/NumberFormatter/Verification/NumberFormatterTest.php
@@ -49,7 +49,7 @@ class NumberFormatterTest extends AbstractNumberFormatterTest
         return intl_get_error_message();
     }
 
-    protected function getIntlErrorCode()
+    protected function getIntlErrorCode(): int
     {
         return intl_get_error_code();
     }
diff --git a/src/Symfony/Component/Ldap/Adapter/ExtLdap/ConnectionOptions.php b/src/Symfony/Component/Ldap/Adapter/ExtLdap/ConnectionOptions.php
index 4f01c6f3ca..949770e88f 100644
--- a/src/Symfony/Component/Ldap/Adapter/ExtLdap/ConnectionOptions.php
+++ b/src/Symfony/Component/Ldap/Adapter/ExtLdap/ConnectionOptions.php
@@ -73,11 +73,9 @@ final class ConnectionOptions
      *
      * @param string $name
      *
-     * @return int
-     *
      * @throws LdapException
      */
-    public static function getOption($name)
+    public static function getOption($name): int
     {
         // Convert
         $constantName = self::getOptionName($name);
diff --git a/src/Symfony/Component/Security/Core/Authorization/Voter/TraceableVoter.php b/src/Symfony/Component/Security/Core/Authorization/Voter/TraceableVoter.php
index e5ce1f696b..d5fec633ab 100644
--- a/src/Symfony/Component/Security/Core/Authorization/Voter/TraceableVoter.php
+++ b/src/Symfony/Component/Security/Core/Authorization/Voter/TraceableVoter.php
@@ -34,7 +34,7 @@ class TraceableVoter implements VoterInterface
         $this->eventDispatcher = LegacyEventDispatcherProxy::decorate($eventDispatcher);
     }
 
-    public function vote(TokenInterface $token, $subject, array $attributes)
+    public function vote(TokenInterface $token, $subject, array $attributes): int
     {
         $result = $this->voter->vote($token, $subject, $attributes);
 
diff --git a/src/Symfony/Component/VarExporter/Internal/Exporter.php b/src/Symfony/Component/VarExporter/Internal/Exporter.php
index c0b7fa17f4..1b0bda7118 100644
--- a/src/Symfony/Component/VarExporter/Internal/Exporter.php
+++ b/src/Symfony/Component/VarExporter/Internal/Exporter.php
@@ -31,7 +31,7 @@ class Exporter
      * @param int               &$objectsCount
      * @param bool              &$valuesAreStatic
      *
-     * @return int
+     * @return array
      *
      * @throws NotInstantiableTypeException When a value cannot be serialized
      */
diff --git a/src/Symfony/Component/Workflow/Tests/WorkflowTest.php b/src/Symfony/Component/Workflow/Tests/WorkflowTest.php
index 26f58a1fa5..58caa122ea 100644
--- a/src/Symfony/Component/Workflow/Tests/WorkflowTest.php
+++ b/src/Symfony/Component/Workflow/Tests/WorkflowTest.php
@@ -601,7 +601,7 @@ class EventDispatcherMock implements \Symfony\Component\EventDispatcher\EventDis
     {
     }
 
-    public function getListenerPriority($eventName, $listener)
+    public function getListenerPriority($eventName, $listener): ?int
     {
     }