BundleConstraintValidator.php

<?php

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

use Symfony\Component\Validator\Constraint;
use Symfony\Component\Validator\ConstraintValidator;

/**
 * Validates the Bundle constraint.
 */
class BundleConstraintValidator extends ConstraintValidator {
  
  /**
   * {@inheritdoc}
   */
  public function validate($entity, Constraint $constraint) {
    if (!isset($entity)) {
      return;
    }
    if (!in_array($entity->bundle(), $constraint->getBundleOption())) {
      $this->context
        ->addViolation($constraint->message, [
        '%bundle' => implode(', ', $constraint->getBundleOption()),
      ]);
    }
  }

}