diff --git a/.github/patch-types.php b/.github/patch-types.php
new file mode 100644
index 000000000000..d64325f6c8b4
--- /dev/null
+++ b/.github/patch-types.php
@@ -0,0 +1,45 @@
+<?php
+
+if (false === getenv('SYMFONY_PATCH_TYPE_DECLARATIONS')) {
+    putenv('SYMFONY_PATCH_TYPE_DECLARATIONS=force=1&php71-compat=0');
+}
+
+require __DIR__.'/../.phpunit/phpunit-8.3-0/vendor/autoload.php';
+
+file_put_contents(__DIR__.'/../vendor/autoload.php', preg_replace('/^return (Composer.*);/m', <<<'EOTXT'
+$loader = \1;
+$loader->addClassMap(['Symfony\Component\Debug\Exception\FlattenException' => \dirname(__DIR__).'/src/Symfony/Component/Debug/Exception/FlattenException.php']);
+
+return $loader;
+
+EOTXT
+, file_get_contents(__DIR__.'/../vendor/autoload.php')));
+
+$loader = require __DIR__.'/../vendor/autoload.php';
+
+Symfony\Component\ErrorHandler\DebugClassLoader::enable();
+
+foreach ($loader->getClassMap() as $class => $file) {
+    switch (true) {
+        case false !== strpos(realpath($file), '/vendor/'):
+        case false !== strpos($file, '/src/Symfony/Bridge/PhpUnit/'):
+        case false !== strpos($file, '/src/Symfony/Bundle/FrameworkBundle/Tests/Fixtures/Validation/Article.php'):
+        case false !== strpos($file, '/src/Symfony/Component/Config/Tests/Fixtures/BadParent.php'):
+        case false !== strpos($file, '/src/Symfony/Component/Debug/Tests/Fixtures/'):
+        case false !== strpos($file, '/src/Symfony/Component/DependencyInjection/Tests/Compiler/OptionalServiceClass.php'):
+        case false !== strpos($file, '/src/Symfony/Component/DependencyInjection/Tests/Fixtures/ParentNotExists.php'):
+        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/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/Php74.php') && \PHP_VERSION_ID < 70400:
+            continue 2;
+    }
+
+    class_exists($class);
+}
+
+Symfony\Component\ErrorHandler\DebugClassLoader::disable();
diff --git a/.travis.yml b/.travis.yml
index 184398c68f5a..3627aaf18d34 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -26,7 +26,7 @@ env:
 matrix:
     include:
         - php: 7.1
-          env: php_extra="7.2"
+          env: php_extra="7.2 7.4snapshot"
         - php: 7.3
           env: deps=high
         - php: 7.4snapshot
@@ -79,10 +79,8 @@ before_install:
       export COMPONENTS=$(find src/Symfony -mindepth 2 -type f -name phpunit.xml.dist -printf '%h\n')
       find ~/.phpenv -name xdebug.ini -delete
 
-      if [[ $TRAVIS_PHP_VERSION = 7.4* && $deps ]]; then
+      if [[ $TRAVIS_PHP_VERSION = 7.4* ]]; then
           export PHPUNIT_X="$PHPUNIT_X,issue-32995"
-      elif [[ $TRAVIS_PHP_VERSION = 7.4* ]]; then
-          export PHPUNIT_X="$PHPUNIT --group issue-32995"
       fi
 
       nanoseconds () {
@@ -150,7 +148,7 @@ before_install:
     - |
       # php.ini configuration
       for PHP in $TRAVIS_PHP_VERSION $php_extra; do
-          phpenv global $PHP 2>/dev/null || (cd / && wget https://s3.amazonaws.com/travis-php-archives/binaries/ubuntu/14.04/x86_64/php-$PHP.tar.bz2 -O - | tar -xj)
+          phpenv global $PHP 2>/dev/null || (cd / && wget https://storage.googleapis.com/travis-ci-language-archives/php/binaries/ubuntu/16.04/x86_64/php-$PHP.tar.bz2 -O - | tar -xj)
           INI=~/.phpenv/versions/$PHP/etc/conf.d/travis.ini
           echo date.timezone = Europe/Paris >> $INI
           echo memory_limit = -1 >> $INI
@@ -262,7 +260,7 @@ install:
       run_tests () {
           set -e
           export PHP=$1
-          if [[ $PHP != $TRAVIS_PHP_VERSION && $TRAVIS_PULL_REQUEST != false ]]; then
+          if [[ $PHP != 7.4* && $PHP != $TRAVIS_PHP_VERSION && $TRAVIS_PULL_REQUEST != false ]]; then
               echo -e "\\n\\e[1;34mIntermediate PHP version $PHP is skipped for pull requests.\\e[0m"
               break
           fi
@@ -279,6 +277,17 @@ install:
               echo "$COMPONENTS" | parallel --gnu "tfold {} 'cd {} && ([ -e composer.lock ] && ${COMPOSER_UP/update/install} || $COMPOSER_UP --prefer-lowest --prefer-stable) && $PHPUNIT_X'"
               echo "$COMPONENTS" | xargs -n1 -I{} tar --append -f ~/php-ext/composer-lowest.lock.tar {}/composer.lock
           else
+              if [[ $PHP = 7.4* ]]; then
+                  # add return types before running the test suite
+                  rm vendor/symfony/contracts -Rf
+                  ln -sd $(realpath src/Symfony/Contracts) vendor/symfony/contracts
+                  sed -i 's/"\*\*\/Tests\/"//' composer.json
+                  composer install --optimize-autoloader
+                  php .github/patch-types.php
+                  php .github/patch-types.php # ensure the script is idempotent
+                  export PHPUNIT_X="$PHPUNIT_X,issue-32995,legacy"
+              fi
+
               echo "$COMPONENTS" | parallel --gnu "tfold {} $PHPUNIT_X {}"
               tfold src/Symfony/Component/Console.tty $PHPUNIT src/Symfony/Component/Console --group tty
               if [[ $PHP = ${MIN_PHP%.*} ]]; then
diff --git a/src/Symfony/Component/HttpFoundation/Session/Storage/Handler/MongoDbSessionHandler.php b/src/Symfony/Component/HttpFoundation/Session/Storage/Handler/MongoDbSessionHandler.php
index ad1bd24d4ff9..27e08002155b 100644
--- a/src/Symfony/Component/HttpFoundation/Session/Storage/Handler/MongoDbSessionHandler.php
+++ b/src/Symfony/Component/HttpFoundation/Session/Storage/Handler/MongoDbSessionHandler.php
@@ -100,7 +100,7 @@ protected function doDestroy($sessionId)
     }
 
     /**
-     * @return int
+     * @return bool
      */
     public function gc($maxlifetime)
     {