RegisterEventSubscribersPass.php

<?php

namespace Drupal\Core\DependencyInjection\Compiler;

use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;

/**
 * Registers all event subscribers to the event dispatcher.
 */
class RegisterEventSubscribersPass implements CompilerPassInterface {
    
    /**
     * {@inheritdoc}
     */
    public function process(ContainerBuilder $container) {
        if (!$container->hasDefinition('event_dispatcher')) {
            return;
        }
        $definition = $container->getDefinition('event_dispatcher');
        $event_subscriber_info = [];
        foreach ($container->findTaggedServiceIds('event_subscriber') as $id => $attributes) {
            // We must assume that the class value has been correctly 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, $interface));
            }
            // Get all subscribed events.
            foreach ($class::getSubscribedEvents() as $event_name => $params) {
                if (is_string($params)) {
                    $priority = 0;
                    $event_subscriber_info[$event_name][$priority][] = [
                        'service' => [
                            $id,
                            $params,
                        ],
                    ];
                }
                elseif (is_string($params[0])) {
                    $priority = isset($params[1]) ? $params[1] : 0;
                    $event_subscriber_info[$event_name][$priority][] = [
                        'service' => [
                            $id,
                            $params[0],
                        ],
                    ];
                }
                else {
                    foreach ($params as $listener) {
                        $priority = isset($listener[1]) ? $listener[1] : 0;
                        $event_subscriber_info[$event_name][$priority][] = [
                            'service' => [
                                $id,
                                $listener[0],
                            ],
                        ];
                    }
                }
            }
        }
        foreach (array_keys($event_subscriber_info) as $event_name) {
            krsort($event_subscriber_info[$event_name]);
        }
        $definition->addArgument($event_subscriber_info);
    }

}