UPGRADE FROM 5.x to 6.0

Config

The signature of method NodeDefinition::setDeprecated() has been updated to NodeDefinition::setDeprecation(string $package, string $version, string $message).
The signature of method BaseNode::setDeprecated() has been updated to BaseNode::setDeprecation(string $package, string $version, string $message).
Passing a null message to BaseNode::setDeprecated() to un-deprecate a node is not supported anymore.
Removed BaseNode::getDeprecationMessage(), use BaseNode::getDeprecation() instead.

The signature of method Definition::setDeprecated() has been updated to Definition::setDeprecation(string $package, string $version, string $message).
The signature of method Alias::setDeprecated() has been updated to Alias::setDeprecation(string $package, string $version, string $message).
The signature of method DeprecateTrait::deprecate() has been updated to DeprecateTrait::deprecation(string $package, string $version, string $message).
Removed the Psr\Container\ContainerInterface and Symfony\Component\DependencyInjection\ContainerInterface aliases of the service_container service, configure them explicitly instead.
Removed Definition::getDeprecationMessage(), use Definition::getDeprecation() instead.
Removed Alias::getDeprecationMessage(), use Alias::getDeprecation() instead.
The inline() function from the PHP-DSL has been removed, use service() instead

Removed argument $usePutenv from Dotenv's constructor, use Dotenv::usePutenv() instead.

Removed LegacyEventDispatcherProxy. Use the event dispatcher without the proxy.

Added the getIsEmptyCallback() method to the FormConfigInterface.
Added the setIsEmptyCallback() method to the FormConfigBuilderInterface.
Added argument callable|null $filter to ChoiceListFactoryInterface::createListFromChoices() and createListFromLoader().
The Symfony\Component\Form\Extension\Validator\Util\ServerParams class has been removed, use its parent Symfony\Component\Form\Util\ServerParams instead.

MicroKernelTrait::configureRoutes() is now always called with a RoutingConfigurator
The "framework.router.utf8" configuration option defaults to true
Removed session.attribute_bag service and session.flash_bag service.

Removed Response::create(), JsonResponse::create(), RedirectResponse::create(), and StreamedResponse::create() methods (use __construct() instead)

Made WarmableInterface::warmUp() return a list of classes or files to preload on PHP 7.4+
Removed support for service:action syntax to reference controllers. Use serviceOrFqcn::method instead.

Removed AmqpExt transport. Run composer require symfony/amqp-messenger to keep the transport in your application.
Removed Doctrine transport. Run composer require symfony/doctrine-messenger to keep the transport in your application.
Removed RedisExt transport. Run composer require symfony/redis-messenger to keep the transport in your application.
Use of invalid options in Redis and AMQP connections now throws an error.
The signature of method RetryStrategyInterface::isRetryable() has been updated to RetryStrategyInterface::isRetryable(Envelope $message, \Throwable $throwable = null).
The signature of method RetryStrategyInterface::getWaitingTime() has been updated to RetryStrategyInterface::getWaitingTime(Envelope $message, \Throwable $throwable = null).

The signature of method OptionsResolver::setDeprecated() has been updated to OptionsResolver::setDeprecated(string $option, string $package, string $version, $message).
Removed OptionsResolverIntrospector::getDeprecationMessage(), use OptionsResolverIntrospector::getDeprecation() instead.

Removed support for @expectedDeprecation annotations, use the ExpectDeprecationTrait::expectDeprecation() method instead.

Removed ROLE_PREVIOUS_ADMIN role in favor of IS_IMPERSONATOR attribute
Removed LogoutSuccessHandlerInterface and LogoutHandlerInterface, register a listener on the LogoutEvent event instead.
Removed DefaultLogoutSuccessHandler in favor of DefaultLogoutListener.