Compiler Passes

Compiler passes are components that hook into the container compilation process and add/modify service definitions. They're extremely handy to dynamically configure your services.

For example, if you want to automatically register all services tagged with event.listener to the event dispatcher, you may use the follow compiler pass:

<?php
declare(strict_types=1);

use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\DependencyInjection\Reference;
use Symfony\Component\EventDispatcher\EventDispatcherInterface;

final class EventListenerInjector implements CompilerPassInterface
{
    public function process(ContainerBuilder $container)
    {
        $dispatcher = $container->getDefinition(EventDispatcherInterface::class);   

        foreach ($container->findTaggedServiceIds('event.listener') as $service => $tags) {
            foreach ($tags as $tag) {
                $dispatcher->addMethodCall(
                    'addListener',
                    [$tag['event'], new Reference($service), $tag['priority']]
                );
            }
        }
    }
}

Type and priority

There are different types of compiler passes. You can see the available types on the PassConfig class.

You may also configure different priorities for the compiler passes.

Configuration

When setting up your container, you can call ContainerBuilder#addPass() or ContainerBuilder#addDelayedPass().

The type and priority are configured via these methods as well. The default values are PassConfig::TYPE_BEFORE_OPTIMIZATION as type and 0 as priority.