UserNameValidator.php

<?php

declare (strict_types=1);
namespace Drupal\user;

use Drupal\Core\Validation\BasicRecursiveValidatorFactory;
use Drupal\Core\Validation\ConstraintManager;
use Symfony\Component\Validator\ConstraintViolationListInterface;

/**
 * Provides a username validator.
 *
 * This validator re-uses the UserName constraint plugin but does not require a
 * User entity.
 */
class UserNameValidator {
  public function __construct(protected readonly BasicRecursiveValidatorFactory $validatorFactory, protected readonly ConstraintManager $constraintManager) {
  }
  
  /**
   * Validates a user name.
   *
   * @return \Symfony\Component\Validator\ConstraintViolationListInterface
   *   The list of constraint violations.
   */
  public function validateName(string $name) : ConstraintViolationListInterface {
    $validator = $this->validatorFactory
      ->createValidator();
    $constraint = $this->constraintManager
      ->create('UserName', []);
    return $validator->validate($name, $constraint);
  }

}