pluginreference-2.0.0/src/Plugin/Validation/Constraint/ValidPluginReferenceConstraint.php

<?php

namespace Drupal\pluginreference\Plugin\Validation\Constraint;

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

/**
 * Plugin Reference valid reference constraint.
 *
 * Verifies that referenced plugins are valid.
 */
#[ConstraintAnnotation(
  id: 'ValidPluginReference',
  label: new TranslatableMarkup('Plugin Reference valid reference', [], ['context' => 'Validation']),
)]
class ValidPluginReferenceConstraint extends Constraint {

  /**
   * The default violation message.
   *
   * @var string
   */
  public $message = 'This plugin (%type: %id) cannot be referenced.';

  /**
   * Violation message when the plugin does not exist.
   *
   * @var string
   */
  public $nonExistingMessage = 'The referenced plugin (%type: %id) does not exist.';

}