ConfigExistsConstraint.php

<?php

declare (strict_types=1);
namespace Drupal\Core\Config\Plugin\Validation\Constraint;

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

/**
 * Checks that the value is the name of an existing config object.
 */
class ConfigExistsConstraint extends SymfonyConstraint {
  
  /**
   * Optional prefix, to be specified when this contains a config entity ID.
   *
   * Every config entity type can have multiple instances, all with unique IDs
   * but the same config prefix. When config refers to a config entity,
   * typically only the ID is stored, not the prefix.
   *
   * @var string
   */
  public string $prefix = '';
  public function __construct(mixed $options = NULL, ?string $prefix = NULL, public string $message = "The '@name' config does not exist.", ?array $groups = NULL, mixed $payload = NULL) {
    parent::__construct($options, $groups, $payload);
    $this->prefix = $prefix ?? $this->prefix;
  }

}