class FormTestController

class FormTestController extends ControllerBase {
  
  /**
   * Returns two instances of the node form.
   *
   * @return string
   *   A HTML-formatted string with the double node form page content.
   */
  public function twoFormInstances() {
    $user = $this->currentUser();
    $values = [
      'uid' => $user->id(),
      'name' => $user->getAccountName(),
      'type' => 'page',
      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
    ];
    $node1 = $this->entityTypeManager()
      ->getStorage('node')
      ->create($values);
    $node2 = clone $node1;
    $return['node_form_1'] = $this->entityFormBuilder()
      ->getForm($node1);
    $return['node_form_2'] = $this->entityFormBuilder()
      ->getForm($node2);
    return $return;
  }
  
  /**
   * Emulate legacy AHAH-style ajax callback.
   *
   * Drupal 6 AHAH callbacks used to operate directly on forms retrieved using
   * \Drupal::formBuilder()->getCache() and stored using
   * \Drupal::formBuilder()->setCache() after manipulation. This callback helps
   * testing whether \Drupal::formBuilder()->setCache() prevents resaving of
   * immutable forms.
   */
  public function storageLegacyHandler($form_build_id) {
    $form_state = new FormState();
    $form = $this->formBuilder()
      ->getCache($form_build_id, $form_state);
    $result = [
      'form' => $form,
      'form_state' => $form_state,
    ];
    $form['#poisoned'] = TRUE;
    $form_state->set('poisoned', TRUE);
    $this->formBuilder()
      ->setCache($form_build_id, $form, $form_state);
    return new JsonResponse($result);
  }

}