FileUriUnique.php

<?php

namespace Drupal\file\Plugin\Validation\Constraint;

use Symfony\Component\Validator\Constraint;

/**
 * Supports validating file URIs.
 *
 * @Constraint(
 *   id = "FileUriUnique",
 *   label = @Translation("File URI", context = "Validation")
 * )
 */
class FileUriUnique extends Constraint {
    public $message = 'The file %value already exists. Enter a unique file URI.';
    
    /**
     * {@inheritdoc}
     */
    public function validatedBy() {
        return '\\Drupal\\Core\\Validation\\Plugin\\Validation\\Constraint\\UniqueFieldValueValidator';
    }

}