collectRoutesAndDefinitions example

$cache = $this->menuCacheBackend->get($tree_cid);
    if ($cache && isset($cache->data)) {
      $data = $cache->data;
      // Cache the definitions in memory so they don't need to be loaded again.       $this->definitions += $data['definitions'];
      unset($data['definitions']);
    }
    else {
      $links = $this->loadLinks($menu_name, $parameters);
      $data['tree'] = $this->doBuildTreeData($links, $parameters->activeTrail, $parameters->minDepth);
      $data['definitions'] = [];
      $data['route_names'] = $this->collectRoutesAndDefinitions($data['tree'], $data['definitions']);
      $this->menuCacheBackend->set($tree_cid, $data, Cache::PERMANENT, ['config:system.menu.' . $menu_name]);
      // The definitions were already added to $this->definitions in       // $this->doBuildTreeData()       unset($data['definitions']);
    }
    return $data;
  }

  /** * Loads links in the given menu, according to the given tree parameters. * * @param string $menu_name * A menu name. * @param \Drupal\Core\Menu\MenuTreeParameters $parameters * The parameters to determine which menu links to be loaded into a tree. * This method will set the absolute minimum depth, which is used in * MenuTreeStorage::doBuildTreeData(). * * @return array * A flat array of menu links that are part of the menu. Each array element * is an associative array of information about the menu link, containing * the fields from the {menu_tree} table. This array must be ordered * depth-first. */