edlp_d8/core/modules/menu_link_content/menu_link_content.module

<?php

/**
 * @file
 * Allows administrators to create custom menu links.
 */

use Drupal\Core\Entity\EntityInterface;
use Drupal\Core\Routing\RouteMatchInterface;
use Drupal\system\MenuInterface;

/**
 * Implements hook_help().
 */
function menu_link_content_help($route_name, RouteMatchInterface $route_match) {
  switch ($route_name) {
    case 'help.page.menu_link_content':
      $output = '';
      $output .= '<h3>' . t('About') . '</h3>';
      $output .= '<p>' . t('The Custom Menu Links module allows users to create menu links. These links can be translated if multiple languages are used for the site.');
      if (\Drupal::moduleHandler()->moduleExists('menu_ui')) {
        $output .= ' ' . t('It is required by the Menu UI module, which provides an interface for managing menus and menu links. For more information, see the <a href=":menu-help">Menu UI module help page</a> and the <a href=":drupal-org-help">online documentation for the Custom Menu Links module</a>.', [':menu-help' => \Drupal::url('help.page', ['name' => 'menu_ui']), ':drupal-org-help' => 'https://www.drupal.org/documentation/modules/menu_link']);
      }
      else {
        $output .= ' ' . t('For more information, see the <a href=":drupal-org-help">online documentation for the Custom Menu Links module</a>. If you enable the Menu UI module, it provides an interface for managing menus and menu links.', [':drupal-org-help' => 'https://www.drupal.org/documentation/modules/menu_link']);
      }
      $output .= '</p>';
      return $output;
  }
}

/**
 * Implements hook_menu_delete().
 */
function menu_link_content_menu_delete(MenuInterface $menu) {
  $storage = \Drupal::entityManager()->getStorage('menu_link_content');
  $menu_links = $storage->loadByProperties(['menu_name' => $menu->id()]);
  $storage->delete($menu_links);
}

/**
 * Implements hook_path_insert().
 */
function menu_link_content_path_insert($path) {
  _menu_link_content_update_path_alias($path['alias']);
}

/**
 * Helper function to update plugin definition using internal scheme.
 *
 * @param string $path
 *   The path alias.
 */
function _menu_link_content_update_path_alias($path) {
  /** @var \Drupal\Core\Menu\MenuLinkManagerInterface $menu_link_manager */
  $menu_link_manager = \Drupal::service('plugin.manager.menu.link');
  /** @var \Drupal\menu_link_content\MenuLinkContentInterface[] $entities */
  $entities = \Drupal::entityManager()
    ->getStorage('menu_link_content')
    ->loadByProperties(['link.uri' => 'internal:' . $path]);
  foreach ($entities as $menu_link) {
    $menu_link_manager->updateDefinition($menu_link->getPluginId(), $menu_link->getPluginDefinition(), FALSE);
  }
}

/**
 * Implements hook_path_update().
 */
function menu_link_content_path_update($path) {
  if ($path['alias'] != $path['original']['alias']) {
    _menu_link_content_update_path_alias($path['alias']);
    _menu_link_content_update_path_alias($path['original']['alias']);
  }
  elseif ($path['source'] != $path['original']['source']) {
    _menu_link_content_update_path_alias($path['alias']);
  }
}

/**
 * Implements hook_path_delete().
 */
function menu_link_content_path_delete($path) {
  _menu_link_content_update_path_alias($path['alias']);
}

/**
 * Implements hook_entity_predelete().
 */
function menu_link_content_entity_predelete(EntityInterface $entity) {
  /** @var \Drupal\Core\Menu\MenuLinkManagerInterface $menu_link_manager */
  $menu_link_manager = \Drupal::service('plugin.manager.menu.link');
  $entity_type_id = $entity->getEntityTypeId();
  foreach ($entity->uriRelationships() as $rel) {
    $url = $entity->toUrl($rel);
    $route_parameters = $url->getRouteParameters();
    if (!isset($route_parameters[$entity_type_id])) {
      // Do not delete links which do not relate to this exact entity. For
      // example, "collection", "add-form", etc.
      continue;
    }
    // Delete all MenuLinkContent links that point to this entity route.
    $result = $menu_link_manager->loadLinksByRoute($url->getRouteName(), $route_parameters);

    if ($result) {
      foreach ($result as $id => $instance) {
        if ($instance->isDeletable() && strpos($id, 'menu_link_content:') === 0) {
          $instance->deleteLink();
        }
      }
    }
  }
}