MenuForm::submitOverviewForm

protected MenuForm::submitOverviewForm(array $complete_form, FormStateInterface $form_state)

protected function submitOverviewForm(array $complete_form, FormStateInterface $form_state) {
  // Form API supports constructing and validating self-contained sections
  // within forms, but does not allow to handle the form section's submission
  // equally separated yet. Therefore, we use a $form_state key to point to
  // the parents of the form section.
  $parents = $form_state->get('menu_overview_form_parents');
  $input = NestedArray::getValue($form_state->getUserInput(), $parents);
  $form = &NestedArray::getValue($complete_form, $parents);

  // When dealing with saving menu items, the order in which these items are
  // saved is critical. If a changed child item is saved before its parent,
  // the child item could be saved with an invalid path past its immediate
  // parent. To prevent this, save items in the form in the same order they
  // are sent, ensuring parents are saved first, then their children.
  // See https://www.drupal.org/node/181126#comment-632270.
  $order = is_array($input) ? array_flip(array_keys($input)) : array();
  // Update our original form with the new order.
  $form = array_intersect_key(array_merge($order, $form), $form);

  $fields = array('weight', 'parent', 'enabled');
  $form_links = $form['links'];
  foreach (Element::children($form_links) as $id) {
    if (isset($form_links[$id]['#item'])) {
      $element = $form_links[$id];
      $updated_values = array();
      // Update any fields that have changed in this menu item.
      foreach ($fields as $field) {
        if ($element[$field]['#value'] != $element[$field]['#default_value']) {
          $updated_values[$field] = $element[$field]['#value'];
        }
      }
      if ($updated_values) {
        // Use the ID from the actual plugin instance since the hidden value
        // in the form could be tampered with.
        $this->menuLinkManager->updateDefinition($element['#item']->link->getPLuginId(), $updated_values);
      }
    }
  }
}