class MenuTreeHierarchyConstraintValidator

class MenuTreeHierarchyConstraintValidator extends ConstraintValidator implements ContainerInjectionInterface {
  
  /**
   * The entity type manager.
   *
   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
   */
  private $entityTypeManager;
  
  /**
   * Creates a new MenuTreeHierarchyConstraintValidator 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($entity, Constraint $constraint) {
    if ($entity && !$entity->isNew() && !$entity->isDefaultRevision()) {
      $original = $this->entityTypeManager
        ->getStorage($entity->getEntityTypeId())
        ->loadUnchanged($entity->id());
      // Ensure that empty items do not affect the comparison checks below.
      // @todo Remove this filtering when
      //   https://www.drupal.org/project/drupal/issues/3039031 is fixed.
      $entity->parent
        ->filterEmptyItems();
      if ($entity->parent
        ->isEmpty() !== $original->parent
        ->isEmpty() || !$entity->parent
        ->equals($original->parent)) {
        $this->context
          ->buildViolation($constraint->message)
          ->atPath('menu_parent')
          ->addViolation();
      }
      if (!$entity->weight
        ->equals($original->weight)) {
        $this->context
          ->buildViolation($constraint->message)
          ->atPath('weight')
          ->addViolation();
      }
    }
  }

}