QuickEditController::fieldForm

public QuickEditController::fieldForm(EntityInterface $entity, $field_name, $langcode, $view_mode_id, Request $request)

public function fieldForm(EntityInterface $entity, $field_name, $langcode, $view_mode_id, Request $request) {
  $response = new AjaxResponse();

  // Replace entity with PrivateTempStore copy if available and not resetting,
  // init PrivateTempStore copy otherwise.
  $tempstore_entity = $this->tempStoreFactory->get('quickedit')->get($entity->uuid());
  if ($tempstore_entity && $request->request->get('reset') !== 'true') {
    $entity = $tempstore_entity;
  }
  else {
    $this->tempStoreFactory->get('quickedit')->set($entity->uuid(), $entity);
  }

  $form_state = (new FormState())
    ->set('langcode', $langcode)
    ->disableRedirect()
    ->addBuildInfo('args', [$entity, $field_name]);
  $form = $this->formBuilder()->buildForm('Drupal\quickedit\Form\QuickEditFieldForm', $form_state);

  if ($form_state->isExecuted()) {
    // The form submission saved the entity in PrivateTempStore. Return the
    // updated view of the field from the PrivateTempStore copy.
    $entity = $this->tempStoreFactory->get('quickedit')->get($entity->uuid());

    // Closure to render the field given a view mode.
    $render_field_in_view_mode = function($view_mode_id) use ($entity, $field_name, $langcode) {
      return $this->renderField($entity, $field_name, $langcode, $view_mode_id);
    };

    // Re-render the updated field.
    $output = $render_field_in_view_mode($view_mode_id);

    // Re-render the updated field for other view modes (i.e. for other
    // instances of the same logical field on the user's page).
    $other_view_mode_ids = $request->request->get('other_view_modes') ? : array();
    $other_view_modes = array_map($render_field_in_view_mode, array_combine($other_view_mode_ids, $other_view_mode_ids));

    $response->addCommand(new FieldFormSavedCommand($output, $other_view_modes));
  }
  else {
    $output = $this->renderer->renderRoot($form);
    // When working with a hidden form, we don't want its CSS/JS to be loaded.
    if ($request->request->get('nocssjs') !== 'true') {
      $response->setAttachments($form['#attached']);
    }
    $response->addCommand(new FieldFormCommand($output));

    $errors = $form_state->getErrors();
    if (count($errors)) {
      $status_messages = array(
        '#type' => 'status_messages'
      );
      $response->addCommand(new FieldFormValidationErrorsCommand($this->renderer->renderRoot($status_messages)));
    }
  }

  return $response;
}