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);
    }

}