LinkTypeConstraint.php

<?php

namespace Drupal\link\Plugin\Validation\Constraint;

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

/**
 * Validation constraint for links receiving data allowed by its settings.
 */
class LinkTypeConstraint extends SymfonyConstraint {
    public $message = "The path '@uri' is invalid.";

}