Symfony 8.1 is a minor release. According to the Symfony release process, there should be no significant backward compatibility breaks. Minor backward compatibility breaks are prefixed in this document with [BC BREAK], make sure your code is compatible with these entries before upgrading. Read more about this in the Symfony documentation.

If you're upgrading from a version below 8.0, follow the 8.0 upgrade guide first.

• [BC BREAK] Add object support to input options and arguments' default by changing the $default type to mixed in InputArgument, InputOption, #[Argument] and #[Option]

• Deprecate configuring options alias, parent, synthetic, file, arguments, properties, configurator or calls when using from_callable
• Deprecate default index/priority methods when defining tagged locators/iterators; use the #[AsTaggedItem] attribute instead

• Deprecate setting an $aliasMap in RegisterMappingsPass. Namespace aliases are no longer supported in Doctrine.

• Deprecate setting the framework.profiler.collect_serializer_data config option
• Deprecate parameters router.request_context.scheme and router.request_context.host; use the router.request_context.base_url parameter or the framework.router.default_uri config option instead

• Deprecate passing a non-flat list of attributes to Controller::setController()

• Deprecate the Symfony\Component\HttpKernel\DependencyInjection\Extension class, use the parent Symfony\Component\DependencyInjection\Extension\Extension class instead:

  - use Symfony\Component\HttpKernel\DependencyInjection\Extension;
  + use Symfony\Component\DependencyInjection\Extension\Extension;
  
  class ExampleExtension extends Extension
  {
      // ...
  }

• Deprecate passing a ControllerArgumentsEvent to the ViewEvent constructor; pass a ControllerArgumentsMetadata instead

• Add getParentRoleNames() method to RoleHierarchyInterface
• Make RoleHierarchyInterface::getReachableRoleNames() return roles as both keys and values
• Deprecate SameOriginCsrfTokenManager::onKernelResponse(), SameOriginCsrfTokenManager::clearCookies() and SameOriginCsrfTokenManager::persistStrategy(); this logic is now handled automatically by SameOriginCsrfListener

• Deprecate datetime constructor as a fallback, in version 9.0 a Symfony\Component\Serializer\Exception\NotNormalizableValueException will be thrown when a date could not be parsed using the default format

• Add argument $format to Ulid::isValid()