Issue #2839670 by mstef, pguillard, RajeevK: Add ability to select parent and...

    $fields['parent'] = BaseFieldDefinition::create('entity_reference')

      ->setLabel(t('Parent'))

      ->setDescription(t('The parent item'))

      ->setDescription(t('The parent menu item.'))

      ->setSetting('target_type', 'colossal_menu_link')

      ->setSetting('handler', 'default');

      ->setSetting('handler', 'default')

      ->setDisplayOptions('form', array(

        'type' => 'options_select',

        'weight' => 5,

      ))

      ->setDisplayConfigurable('form', TRUE);

    $fields['title'] = BaseFieldDefinition::create('string')

      ->setLabel(t('Title'))

    $fields['weight'] = BaseFieldDefinition::create('integer')

      ->setLabel(t('Weight'))

      ->setDescription(t('Link weight among links in the same menu at the same depth. In the menu, the links with high weight will sink and links with a low weight will be positioned nearer the top.'))

      ->setDefaultValue(0);

      ->setDefaultValue(0)

      ->setDisplayOptions('form', array(

        'type' => 'number',

        'weight' => 20,

      ))

      ->setDisplayConfigurable('form', TRUE);

    $fields['langcode'] = BaseFieldDefinition::create('language')

      ->setLabel(t('Language code'))

namespace Drupal\colossal_menu\Form;

use Drupal\colossal_menu\Menu\MenuLinkTree;

use Drupal\Core\Entity\ContentEntityForm;

use Drupal\Core\Entity\EntityRepositoryInterface;

use Drupal\Core\Form\FormStateInterface;

use Drupal\Core\Menu\Form\MenuLinkFormInterface;

use Drupal\Core\Menu\MenuLinkInterface;

use Drupal\Core\Entity\Display\EntityFormDisplayInterface;

use Drupal\Core\Entity\Entity\EntityFormDisplay;

use Drupal\Core\Entity\EntityTypeManagerInterface;

use Drupal\Component\Datetime\TimeInterface;

use Drupal\Core\Entity\EntityTypeBundleInfoInterface;

use Drupal\Core\Menu\MenuTreeParameters;

use Symfony\Component\DependencyInjection\ContainerInterface;

/**

 * Form controller for Link edit forms.

 */

class LinkForm extends ContentEntityForm implements MenuLinkFormInterface {

  /**

   * The link tree.

   *

   * @var \Drupal\colossal_menu\Menu\MenuLinkTree

   */

  protected $linkTree;

  /**

   * Constructs a LinkForm object.

   *

   * @param \Drupal\Core\Entity\EntityRepositoryInterface $entity_repository

   *   The entity repository service.

   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager

   *   The entity manager.

   * @param \Drupal\colossal_menu\Menu\MenuLinkTree $link_tree

   *   The colossal menu link tree.

   * @param \Drupal\Core\Entity\EntityTypeBundleInfoInterface $entity_type_bundle_info

   *   The entity type bundle service.

   * @param \Drupal\Component\Datetime\TimeInterface $time

   *   The time service.

   */

   public function __construct(EntityRepositoryInterface $entity_repository, EntityTypeManagerInterface $entity_type_manager, MenuLinkTree $link_tree, EntityTypeBundleInfoInterface $entity_type_bundle_info = NULL, TimeInterface $time = NULL) {

     parent::__construct($entity_repository, $entity_type_bundle_info, $time);

     $this->entityTypeManager = $entity_type_manager;

     $this->linkTree = $link_tree;

   }

   /**

    * {@inheritdoc}

    */

   public static function create(ContainerInterface $container) {

     return new static(

       $container->get('entity.repository'),

       $container->get('entity_type.manager'),

       $container->get('colossal_menu.link_tree'),

       $container->get('entity_type.bundle.info'),

       $container->get('datetime.time')

     );

   }

  /**

   * {@inheritdoc}

   */

      $form['#title'] = $this->t('Edit %label', ['%label' => $link->label()]);

    }

    return parent::form($form, $form_state, $link);

    $form = parent::form($form, $form_state, $link);

    // Override the parent select options to limit them to links of the

    // given menu and display the link hierarchy.

    $form['parent']['widget']['#options'] = $this->parentSelectOptions();

    return $form;

  }

  /**

   * {@inheritdoc}

   */

  public function validateForm(array &$form, FormStateInterface $form_state) {

    $entity = parent::validateForm($form, $form_state);

    // Check if a parent is present.

    if ($parent = $entity->get('parent')->entity) {

      // Check if the link ID and the parent ID are the same.

      if ($parent->id() == $entity->id()) {

        // Set an error.

        $form_state->setErrorByName('parent', $this->t('The parent cannot be set to the link being edited.'));

      }

    }

  }

  /**

    ]);

  }

  /**

   * Provide the select list options for the parent field.

   *

   * @return array

   *   An array of select list options, keyed by link ID.

   */

  public function parentSelectOptions() {

    // Start the options.

    $options = ['_none' => '- ' . $this->t('None') . ' -'];

    // Load the menu tree for the menu that the link is part of.

    $tree = $this->linkTree->load($this->entity->getMenuName(), new MenuTreeParameters);

    // Recursively add the parent options as a tree.

    $this->parentSelectOptionsRecursive($options, $tree);

    return $options;

  }

  /**

   * Recursive callback to generate the select list options for the link parent

   * as a tree with depth.

   *

   * @param array &$options

   *   The select list options array.

   * @param array $tree

   *   The menu link tree.

   * @param int $depth

   *   The depth of the menu tree.

   */

  protected function parentSelectOptionsRecursive(array &$options, array $tree, int $depth = 0) {

    // Iterate the tree.

    foreach ($tree as $id => $level) {

      // Add the parent link.

      $options[$id] = str_repeat('-', ($depth * 2)) . ' ' . $level->link->label();

      // Recursively add the children.

      $this->parentSelectOptionsRecursive($options, $level->subtree, ($depth + 1));

    }

  }

}