New in Symfony 5.4: DependencyInjection Improvements

Inject tagged services in service locators

Contributed by Ion Bazan in #43015

In Symfony 5.4 you can use tagged iterators as arguments of service locators, which simplifies the injection of tagged services in other services. The following example shows how to use this feature when using YAML config (it works with XML and PHP config too):

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# config/services.yaml
services:
    _instanceof:
        App\Command\HandlerInterface:
            tags: ['app.command_handler']

    app.command_handlers:
        class: Symfony\Component\DependencyInjection\ServiceLocator
        arguments: [!tagged_iterator { tag: 'app.command_handler', default_index_method: 'getCommandName' }]

    App\CommandBus:
        arguments: ['@app.command_handlers']

    App\AnotherCommandBus:
        arguments: ['@app.command_handlers']

Autowire union and intersection types

Contributed by Nicolas Grekas in #43479

PHP 8.0 added union types (e.g. ClassA | ClassB $variable) and PHP 8.1 adds intersection types (ClassA & ClassB $variable). In Symfony 5.4 we've improved the DependencyInjection component to support both. For example:

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public function __construct(NormalizerInterface & DenormalizerInterface $serializer)
{
    // ...
}

Autowiring of intersection types works when both types have a corresponding autowiring alias, and if both aliases point to the very same service.

New config options for TaggedIterator and TaggedLocator attributes

Contributed by Mykhailo Shtanko in #43386

When using tagged iterators and locators for your services, you can define tagged services with priority and tagged services with index. In Symfony 5.4 we've improved the TaggedIterator and TaggedLocator attributes so you can define those options in the attributes too:

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use Psr\Container\ContainerInterface;
use Symfony\Component\DependencyInjection\Attribute\TaggedIterator;
use Symfony\Component\DependencyInjection\Attribute\TaggedLocator;

public function __construct(
    #[TaggedIterator(tag: '...', defaultPriorityMethod: 'getPriority')]
    private iterable $argument,
) {
}

public function __construct(
    #[TaggedLocator(tag: '...', defaultIndexMethod: 'getDefaultFooName')]
    private ContainerInterface $argument,
) {
}

Added a new SubscribedService attribute

Contributed by Kevin Bond in #42238

In previous Symfony versions, the ServiceSubscriberTrait could be used to inject services in some of your class methods. This trait looks for all methods in your class that have no arguments and a return type to provide a ServiceLocator for the services of those return types.

This behavior works well most of the times, but in some cases it's common to have such a method (no arguments but a return type) which shouldn't get any services injected. That's why in Symfony 5.4 we've deprecated that behavior and introduced a new SubscribedService PHP attribute.

Add that attribute to any method in which you want a service injected:

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use Psr\Log\LoggerInterface;
use Symfony\Component\Routing\RouterInterface;
use Symfony\Contracts\Service\Attribute\SubscribedService;
use Symfony\Contracts\Service\ServiceSubscriberInterface;

class MyService implements ServiceSubscriberInterface
{
    #[SubscribedService]
    private function router(): RouterInterface
    {
        return $this->container->get(__METHOD__);
    }

    #[SubscribedService]
    private function logger(): LoggerInterface
    {
        return $this->container->get(__METHOD__);
    }

    // ...
}

Autoconfigurable methods, properties and parameters

Contributed by Ruud Kamphuis in #42039

In Symfony you can autoconfigure classes annotated with attributes using some code like the following in your dependency injection extension:

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$container->registerAttributeForAutoconfiguration(
    MyAttribute::class,
    static function (ChildDefinition $definition, MyAttribute $attribute, \ReflectionClass $reflector): void {
        $definition->addTag('my_tag', ['some_property' => $attribute->someProperty]);
    }
);

In Symfony 5.4 we've improved this feature to allow you to also autoconfigure methods, properties and parameters. First, make sure that you have some PHP attribute defined in your application that allows using them on methods and properties.

Now, use that PHP attribute in some method and/or property:

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#[MyAttribute]
class MyService {
}

class MyOtherService {
    #[MyAttribute]
    public function myMethod() {}
}

You can now use the registerAttributeForAutoconfiguration() method in your extension, together with a union of the types that you want to search for. In this example, the extension only cares for classes and methods, so it uses \ReflectionClass|\ReflectionMethod $reflector:

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final class MyBundleExtension extends Extension
{
    public function load(array $configs, ContainerBuilder $container) : void
    {
        $container->registerAttributeForAutoconfiguration(
            MyAttribute::class,
            static function (ChildDefinition $definition, MyAttribute $attribute, \ReflectionClass|\ReflectionMethod $reflector) : void {
                $args = [];
                if ($reflector instanceof \ReflectionMethod) {
                    $args['method'] = $reflector->getName();
                }
                $definition->addTag('my.tag', $args);
            }
        );
    }
}