UPGRADE FROM 6.0 to 6.1

All components

Deprecate requiring the "symfony/symfony" package; replace it with standalone components instead
Public and protected properties are now considered final; instead of overriding a property, consider setting its value in the constructor

Console

Deprecate Command::$defaultName and Command::$defaultDescription, use the AsCommand attribute instead
Add argument $suggestedValues to Command::addArgument and Command::addOption
Add argument $suggestedValues to InputArgument and InputOption constructors

DependencyInjection

Deprecate ReferenceSetArgumentTrait

FrameworkBundle

Deprecate the reset_on_message config option. It can be set to true only and does nothing now. To prevent services resetting after each message the "--no-reset" option in "messenger:consume" command can be set
Deprecate not setting the http_method_override config option. The default value will change to false in 7.0.

HttpKernel

Deprecate StreamedResponseListener, it's not needed anymore

Routing

Add argument $routeParameters to UrlMatcher::handleRouteRequirements()

Serializer

Deprecate ContextAwareNormalizerInterface, use NormalizerInterface instead
Deprecate ContextAwareDenormalizerInterface, use DenormalizerInterface instead
Deprecate ContextAwareEncoderInterface, use EncoderInterface instead
Deprecate ContextAwareDecoderInterface, use DecoderInterface instead
Deprecate supporting denormalization for AbstractUid in UidNormalizer, use one of AbstractUid child class instead
Deprecate denormalizing to an abstract class in UidNormalizer

Validator

Deprecate Constraint::$errorNames, use Constraint::ERROR_NAMES instead
Deprecate constraint ExpressionLanguageSyntax, use ExpressionSyntax instead
Implementing the ConstraintViolationInterface or ConstraintViolationListInterface without implementing the __toString() method is deprecated