UPGRADE FROM 5.1 to 5.2

Console

Application now runs pcntl_async_signals(true) when constucted; if the code of your CLI application depends on pcntl signals being synchronous, you should either call pcntl_async_signals(false) or implement SignalableCommandInterface::handleSignal()

DependencyInjection

Deprecated Definition::setPrivate() and Alias::setPrivate(), use setPublic() instead

FrameworkBundle

Deprecated the public form.factory, form.type.file, translator, security.csrf.token_manager, serializer, cache_clearer, filesystem and validator services to private.
If you configured the framework.cache.prefix_seed option, you might want to add the %kernel.environment% to its value to keep cache namespaces separated by environment of the app. The %kernel.container_class% (which includes the environment) used to be added by default to the seed, which is not the case anymore. This allows sharing caches between apps or different environments.
Deprecated the lock.RESOURCE_NAME and lock.RESOURCE_NAME.store services and the lock, LockInterface, lock.store and PersistingStoreInterface aliases, use lock.RESOURCE_NAME.factory, lock.factory or LockFactory instead.

Form

Deprecated PropertyPathMapper in favor of DataMapper and PropertyPathAccessor.

Before:

use Symfony\Component\Form\Extension\Core\DataMapper\PropertyPathMapper;

$builder->setDataMapper(new PropertyPathMapper());

After:

use Symfony\Component\Form\Extension\Core\DataAccessor\PropertyPathAccessor;
use Symfony\Component\Form\Extension\Core\DataMapper\DataMapper;

$builder->setDataMapper(new DataMapper(new PropertyPathAccessor()));

HttpFoundation

Deprecated not passing a Closure together with FILTER_CALLBACK to ParameterBag::filter(); wrap your filter in a closure instead.
Deprecated the Request::HEADER_X_FORWARDED_ALL constant, use either Request::HEADER_X_FORWARDED_FOR | Request::HEADER_X_FORWARDED_HOST | Request::HEADER_X_FORWARDED_PORT | Request::HEADER_X_FORWARDED_PROTO or Request::HEADER_X_FORWARDED_AWS_ELB or Request::HEADER_X_FORWARDED_TRAEFIKconstants instead.
Deprecated BinaryFileResponse::create(), use __construct() instead

Lock

MongoDbStore does not implement BlockingStoreInterface anymore, typehint against PersistingStoreInterface instead.
deprecated NotSupportedException, it shouldn't be thrown anymore.
deprecated RetryTillSaveStore, logic has been moved in Lock and is not needed anymore.

Mime

Deprecated Address::fromString(), use Address::create() instead

Monolog

The $actionLevel constructor argument of Symfony\Bridge\Monolog\Handler\FingersCrossed\NotFoundActivationStrategy has been deprecated and replaced by the $inner one which expects an ActivationStrategyInterface to decorate instead. Symfony\Bridge\Monolog\Handler\FingersCrossed\NotFoundActivationStrategy will become final in 6.0.
The $actionLevel constructor argument of Symfony\Bridge\Monolog\Handler\FingersCrossed\HttpCodeActivationStrategy has been deprecated and replaced by the $inner one which expects an ActivationStrategyInterface to decorate instead. Symfony\Bridge\Monolog\Handler\FingersCrossed\HttpCodeActivationStrategy will become final in 6.0

Notifier

[BC BREAK] The TransportInterface::send() and AbstractTransport::doSend() methods changed to return a ?SentMessage instance instead of void.
[BC BREAK] Changed the type-hint of the $recipient argument in the as*Message() method of EmailNotificationInterface and SmsNotificationInterface to EmailRecipientInterface and SmsRecipientInterface.
[BC BREAK] Removed the AdminRecipient.
[BC BREAK] Changed the type-hint of the $recipient argument in NotifierInterface::send(), Notifier::getChannels(), ChannelInterface::notifiy() and ChannelInterface::supports() to RecipientInterface.

PropertyAccess

Deprecated passing a boolean as the first argument of PropertyAccessor::__construct(). Pass a combination of bitwise flags instead.

PropertyInfo

Deprecated the enable_magic_call_extraction context option in ReflectionExtractor::getWriteInfo() and ReflectionExtractor::getReadInfo() in favor of enable_magic_methods_extraction.

TwigBundle

Deprecated the public twig service to private.

TwigBridge

Changed 2nd argument type of TranslationExtension::__construct() to TranslationNodeVisitor

Validator

Deprecated the allowEmptyString option of the Length constraint.

Before:

use Symfony\Component\Validator\Constraints as Assert;

/**
 * @Assert\Length(min=5, allowEmptyString=true)
 */

After:

use Symfony\Component\Validator\Constraints as Assert;

/**
 * @Assert\AtLeastOneOf({
 *     @Assert\Blank(),
 *     @Assert\Length(min=5)
 * })
 */

Deprecated the NumberConstraintTrait trait.

Deprecated setting a Doctrine annotation reader via ValidatorBuilder::enableAnnotationMapping()

Before:

$builder->enableAnnotationMapping($reader);

After:

$builder->enableAnnotationMapping(true)
    ->setDoctrineAnnotationReader($reader);

Deprecated creating a Doctrine annotation reader via ValidatorBuilder::enableAnnotationMapping()

Before:

$builder->enableAnnotationMapping();

After:

$builder->enableAnnotationMapping(true)
    ->addDefaultDoctrineAnnotationReader();

Security

[BC break] In the experimental authenticator-based system, * TokenInterface::getUser() returns null in case of unauthenticated session.
[BC break] AccessListener::PUBLIC_ACCESS has been removed in favor of AuthenticatedVoter::PUBLIC_ACCESS.
Deprecated setProviderKey()/getProviderKey() in favor of setFirewallName()/getFirewallName() in PreAuthenticatedToken, RememberMeToken, SwitchUserToken, UsernamePasswordToken, DefaultAuthenticationSuccessHandler, the old methods will be removed in 6.0.
Deprecated the AbstractRememberMeServices::$providerKey property in favor of AbstractRememberMeServices::$firewallName, the old property will be removed in 6.0.