EntityTypeConstraint.php

<?php

namespace Drupal\Core\Entity\Plugin\Validation\Constraint;

use Drupal\Core\StringTranslation\TranslatableMarkup;
use Drupal\Core\Validation\Attribute\Constraint;
use Symfony\Component\Validator\Constraint as SymfonyConstraint;

/**
 * Checks if a value is a valid entity type.
 */
class EntityTypeConstraint extends SymfonyConstraint {
  
  /**
   * The default violation message.
   *
   * @var string
   */
  public $message = 'The entity must be of type %type.';
  
  /**
   * The entity type option.
   *
   * @var string
   */
  public $type;
  
  /**
   * {@inheritdoc}
   */
  public function getDefaultOption() : ?string {
    return 'type';
  }
  
  /**
   * {@inheritdoc}
   */
  public function getRequiredOptions() : array {
    return [
      'type',
    ];
  }

}