PathAliasConstraintValidator.php

<?php

namespace Drupal\path\Plugin\Validation\Constraint;

use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
use Drupal\Core\Entity\EntityTypeManagerInterface;
use Symfony\Component\DependencyInjection\ContainerInterface;
use Symfony\Component\Validator\Constraint;
use Symfony\Component\Validator\ConstraintValidator;

/**
 * Constraint validator for changing path aliases in pending revisions.
 */
class PathAliasConstraintValidator extends ConstraintValidator implements ContainerInjectionInterface {
    
    /**
     * The entity type manager.
     *
     * @var \Drupal\Core\Entity\EntityTypeManagerInterface
     */
    private $entityTypeManager;
    
    /**
     * Creates a new PathAliasConstraintValidator instance.
     *
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager.
     */
    public function __construct(EntityTypeManagerInterface $entity_type_manager) {
        $this->entityTypeManager = $entity_type_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('entity_type.manager'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function validate($value, Constraint $constraint) : void {
        $entity = !empty($value->getParent()) ? $value->getEntity() : NULL;
        if ($entity && !$entity->isNew() && !$entity->isDefaultRevision()) {
            
            /** @var \Drupal\Core\Entity\ContentEntityInterface $original */
            $original = $this->entityTypeManager
                ->getStorage($entity->getEntityTypeId())
                ->loadUnchanged($entity->id());
            $entity_langcode = $entity->language()
                ->getId();
            // Only add the violation if the current translation does not have the
            // same path alias.
            if ($original->hasTranslation($entity_langcode)) {
                if ($value->alias != $original->getTranslation($entity_langcode)->path->alias) {
                    $this->context
                        ->addViolation($constraint->message);
                }
            }
        }
    }

}