menu_ui_form_node_form_alter

menu_ui_form_node_form_alter(&$form, FormStateInterface $form_state)

function menu_ui_form_node_form_alter(&$form, FormStateInterface $form_state) {
  // Generate a list of possible parents (not including this link or descendants).
  // @todo This must be handled in a #process handler.
  $node = $form_state->getFormObject()->getEntity();
  $defaults = menu_ui_get_menu_link_defaults($node);
  /** @var \Drupal\node\NodeTypeInterface $node_type */
  $node_type = $node->type->entity;
  /** @var \Drupal\Core\Menu\MenuParentFormSelectorInterface $menu_parent_selector */
  $menu_parent_selector = \Drupal::service('menu.parent_form_selector');
  $menu_names = menu_ui_get_menus();
  $type_menus = $node_type->getThirdPartySetting('menu_ui', 'available_menus', array('main'));
  $available_menus = array();
  foreach ($type_menus as $menu) {
    $available_menus[$menu] = $menu_names[$menu];
  }
  if ($defaults['id']) {
    $default = $defaults['menu_name'] . ':' . $defaults['parent'];
  }
  else {
    $default = $node_type->getThirdPartySetting('menu_ui', 'parent', 'main:');
  }
  $parent_element = $menu_parent_selector->parentSelectElement($default, $defaults['id'], $available_menus);
  // If no possible parent menu items were found, there is nothing to display.
  if (empty($parent_element)) {
    return;
  }

  $form['menu'] = array(
    '#type' => 'details',
    '#title' => t('Menu settings'),
    '#access' => \Drupal::currentUser()->hasPermission('administer menu'),
    '#open' => (bool) $defaults['id'],
    '#group' => 'advanced',
    '#attached' => array(
      'library' => array('menu_ui/drupal.menu_ui'),
    ),
    '#tree' => TRUE,
    '#weight' => -2,
    '#attributes' => array('class' => array('menu-link-form')),
  );
  $form['menu']['enabled'] = array(
    '#type' => 'checkbox',
    '#title' => t('Provide a menu link'),
    '#default_value' => (int) (bool) $defaults['id'],
  );
  $form['menu']['link'] = array(
    '#type' => 'container',
    '#parents' => array('menu'),
    '#states' => array(
      'invisible' => array(
        'input[name="menu[enabled]"]' => array('checked' => FALSE),
      ),
    ),
  );

  // Populate the element with the link data.
  foreach (array('id', 'entity_id') as $key) {
    $form['menu']['link'][$key] = array('#type' => 'value', '#value' => $defaults[$key]);
  }

  $form['menu']['link']['title'] = array(
    '#type' => 'textfield',
    '#title' => t('Menu link title'),
    '#default_value' => $defaults['title'],
    '#maxlength' => $defaults['title_max_length'],
  );

  $form['menu']['link']['description'] = array(
    '#type' => 'textarea',
    '#title' => t('Description'),
    '#default_value' => $defaults['description'],
    '#rows' => 1,
    '#description' => t('Shown when hovering over the menu link.'),
  );

  $form['menu']['link']['menu_parent'] = $parent_element;
  $form['menu']['link']['menu_parent']['#title'] = t('Parent item');
  $form['menu']['link']['menu_parent']['#attributes']['class'][] = 'menu-parent-select';

  $form['menu']['link']['weight'] = array(
    '#type' => 'number',
    '#title' => t('Weight'),
    '#default_value' => $defaults['weight'],
    '#description' => t('Menu links with lower weights are displayed before links with higher weights.'),
  );

  foreach (array_keys($form['actions']) as $action) {
    if ($action != 'preview' && isset($form['actions'][$action]['#type']) && $form['actions'][$action]['#type'] === 'submit') {
      $form['actions'][$action]['#submit'][] = 'menu_ui_form_node_form_submit';
    }
  }
}