RegisterKernelListenersPass.php

<?php

/**
 * @file
 * Definition of Drupal\Core\DependencyInjection\Compiler\RegisterKernelListenersPass.
 */
namespace Drupal\Core\DependencyInjection\Compiler;

use InvalidArgumentException;
use ReflectionClass;
use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
class RegisterKernelListenersPass implements CompilerPassInterface {
  public function process(ContainerBuilder $container) {
    if (!$container
      ->hasDefinition('dispatcher')) {
      return;
    }
    $definition = $container
      ->getDefinition('dispatcher');
    foreach ($container
      ->findTaggedServiceIds('event_subscriber') as $id => $attributes) {

      // We must assume that the class value has been correcly filled, even if the service is created by a factory
      $class = $container
        ->getDefinition($id)
        ->getClass();
      $refClass = new ReflectionClass($class);
      $interface = 'Symfony\\Component\\EventDispatcher\\EventSubscriberInterface';
      if (!$refClass
        ->implementsInterface($interface)) {
        throw new InvalidArgumentException(sprintf('Service "%s" must implement interface "%s".', $id, $interface));
      }
      $definition
        ->addMethodCall('addSubscriberService', array(
        $id,
        $class,
      ));
    }
  }

}