RegisterEntityResolversCompilerPass.php

<?php

namespace Drupal\serialization;

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

/**
 * Adds services tagged 'entity_resolver' to the Serializer.
 */
class RegisterEntityResolversCompilerPass implements CompilerPassInterface {
    
    /**
     * Adds services to the Serializer.
     *
     * @param \Symfony\Component\DependencyInjection\ContainerBuilder $container
     *   The container to process.
     */
    public function process(ContainerBuilder $container) {
        $definition = $container->getDefinition('serializer.entity_resolver');
        $resolvers = [];
        // Retrieve registered Normalizers and Encoders from the container.
        foreach ($container->findTaggedServiceIds('entity_resolver') as $id => $attributes) {
            $priority = isset($attributes[0]['priority']) ? $attributes[0]['priority'] : 0;
            $resolvers[$priority][] = new Reference($id);
        }
        // Add the registered concrete EntityResolvers to the ChainEntityResolver.
        foreach ($this->sort($resolvers) as $resolver) {
            $definition->addMethodCall('addResolver', [
                $resolver,
            ]);
        }
    }
    
    /**
     * Sorts by priority.
     *
     * Order services from highest priority number to lowest (reverse sorting).
     *
     * @param array $services
     *   A nested array keyed on priority number. For each priority number, the
     *   value is an array of Symfony\Component\DependencyInjection\Reference
     *   objects, each a reference to a normalizer or encoder service.
     *
     * @return array
     *   A flattened array of Reference objects from $services, ordered from high
     *   to low priority.
     */
    protected function sort($services) {
        $sorted = [];
        krsort($services);
        // Flatten the array.
        foreach ($services as $a) {
            $sorted = array_merge($sorted, $a);
        }
        return $sorted;
    }

}