Issue #3261777 by super_romeo: is-invalid class does not added to selectboxes

    $variables['safe_value_label'] = Xss::filter($variables['attributes']['value']);

  }

}

/**

 * Implements hook_preprocess_select() for adding classes to select boxes.

 */

function bootstrap_barrio_preprocess_select(&$variables) {

  if (isset($variables['attributes']['class'])) {

    if (is_object($variables['attributes']['class'])) {

      if (in_array('error', $variables['attributes']['class']->value())) {

        $variables['attributes']['class']->addClass('is-invalid');

      }

    }

    elseif (is_array($variables['attributes']['class'])) {

      if (in_array('error', $variables['attributes']['class'])) {

        $variables['attributes']['class'][] = 'is-invalid';

      }

    }

  }

}