class PluginExistsConstraintValidator

class PluginExistsConstraintValidator extends ConstraintValidator {
  
  /**
   * {@inheritdoc}
   */
  public function validate(mixed $plugin_id, Constraint $constraint) {
    assert($constraint instanceof PluginExistsConstraint);
    if ($plugin_id === NULL) {
      return;
    }
    $definition = $constraint->pluginManager
      ->getDefinition($plugin_id, FALSE);
    // Some plugin managers provide fallbacks. In most cases, the use of a
    // fallback plugin ID suggests that the given plugin ID is invalid in some
    // way, so by default, we don't consider fallback plugin IDs as valid,
    // although that can be overridden by the `allowFallback` option if needed.
    if ($constraint->pluginManager instanceof FallbackPluginManagerInterface && $constraint->allowFallback) {
      $fallback_plugin_id = $constraint->pluginManager
        ->getFallbackPluginId($plugin_id);
      $definition = $constraint->pluginManager
        ->getDefinition($fallback_plugin_id, FALSE);
    }
    if (empty($definition)) {
      $this->context
        ->addViolation($constraint->unknownPluginMessage, [
        '@plugin_id' => $plugin_id,
      ]);
      return;
    }
    // If we don't need to validate the plugin class's interface, we're done.
    if (empty($constraint->interface)) {
      return;
    }
    if (!is_a(DefaultFactory::getPluginClass($plugin_id, $definition), $constraint->interface, TRUE)) {
      $this->context
        ->addViolation($constraint->invalidInterfaceMessage, [
        '@plugin_id' => $plugin_id,
        '@interface' => $constraint->interface,
      ]);
    }
  }

}