UPGRADE FROM 3.0 to 3.1

DependencyInjection

* Using unsupported configuration keys in YAML configuration files has been

deprecated and will raise an exception in Symfony 4.0.

* Using unsupported options to configure service aliases has been deprecated

and will raise an exception in Symfony 4.0.

Form

* The `choices_as_values` option of the `ChoiceType` has been deprecated and

will be removed in Symfony 4.0.

Serializer

* Passing a Doctrine `Cache` instance to the `ClassMetadataFactory` has been

deprecated and will not be supported in Symfony 4.0. You should use the

`CacheClassMetadataFactory` class instead.

Yaml

* The `!!php/object` tag to indicate dumped PHP objects has been deprecated

and will be removed in Symfony 4.0. Use the `!php/object` tag instead.

UPGRADE FROM 3.x to 4.0

DependencyInjection

* Using unsupported configuration keys in YAML configuration files raises an

exception.

* Using unsupported options to configure service aliases raises an exception.

Form

* The `choices_as_values` option of the `ChoiceType` has been removed.

Serializer

* The ability to pass a Doctrine `Cache` instance to the `ClassMetadataFactory`

class has been removed. You should use the `CacheClassMetadataFactory` class

instead.

Yaml

* The `!!php/object` tag to indicate dumped PHP objects was removed in favor of

the `!php/object` tag.