book-2.0.x-dev/src/Plugin/Validation/Constraint/ExistsInConstraint.php

<?php

declare(strict_types=1);

namespace Drupal\book\Plugin\Validation\Constraint;

use Drupal\Core\StringTranslation\TranslatableMarkup;
use Symfony\Component\Validator\Constraint;

/**
 * Checks that a value in this config exists in a list in the same config.
 */
#[\Drupal\Core\Validation\Attribute\Constraint(
  id: 'ExistsIn',
  label: new TranslatableMarkup('Value must match value in a list in the same config', [], ['context' => 'Validation'])
)]
class ExistsInConstraint extends Constraint {

  /**
   * The error message if the string does not match.
   *
   * @var string
   */
  public string $message = "'@value' is not a valid choice. Valid choices are: @choices.";

  /**
   * An expression to select a different property path in the same config.
   *
   * @var string
   */
  public string $selector;

  /**
   * Treat the values or the keys as the valid choices: "keys" or "values".
   *
   * @var string
   */
  public string $which;

  /**
   * {@inheritdoc}
   */
  public function getRequiredOptions(): array {
    return ['selector', 'which'];
  }

}