menu.inc

<?php

/**
 * @file
 * API for the Drupal menu system.
 */

use Drupal\Component\Utility\NestedArray;
use Drupal\Core\Cache\CacheBackendInterface;
use Drupal\Core\Language\Language;
use Drupal\Core\Template\Attribute;
use Drupal\menu_link\Entity\MenuLink;
use Drupal\menu_link\MenuLinkStorageController;
use Symfony\Cmf\Component\Routing\RouteObjectInterface;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
use Symfony\Component\Routing\Route;

/**
 * @defgroup menu Menu system
 * @{
 * Define the navigation menus, and route page requests to code based on URLs.
 *
 * The Drupal menu system drives both the navigation system from a user
 * perspective and the callback system that Drupal uses to respond to URLs
 * passed from the browser. For this reason, a good understanding of the
 * menu system is fundamental to the creation of complex modules. As a note,
 * this is related to, but separate from menu.module, which allows menus
 * (which in this context are hierarchical lists of links) to be customized from
 * the Drupal administrative interface.
 *
 * Drupal's menu system follows a simple hierarchy defined by paths.
 * Implementations of hook_menu() define menu items and assign them to
 * paths (which should be unique). The menu system aggregates these items
 * and determines the menu hierarchy from the paths. For example, if the
 * paths defined were a, a/b, e, a/b/c/d, f/g, and a/b/h, the menu system
 * would form the structure:
 * - a
 *   - a/b
 *     - a/b/c/d
 *     - a/b/h
 * - e
 * - f/g
 * Note that the number of elements in the path does not necessarily
 * determine the depth of the menu item in the tree.
 *
 * When responding to a page request, the menu system looks to see if the
 * path requested by the browser is registered as a menu item with a
 * callback. If not, the system searches up the menu tree for the most
 * complete match with a callback it can find. If the path a/b/i is
 * requested in the tree above, the callback for a/b would be used.
 *
 * The found callback function is called with any arguments specified
 * in the "page arguments" attribute of its menu item. The
 * attribute must be an array. After these arguments, any remaining
 * components of the path are appended as further arguments. In this
 * way, the callback for a/b above could respond to a request for
 * a/b/i differently than a request for a/b/j.
 *
 * For an illustration of this process, see page_example.module.
 *
 * Access to the callback functions is also protected by the menu system.
 * The "access callback" with an optional "access arguments" of each menu
 * item is called before the page callback proceeds. If this returns TRUE,
 * then access is granted; if FALSE, then access is denied. Default local task
 * menu items (see next paragraph) may omit this attribute to use the value
 * provided by the parent item.
 *
 * In the default Drupal interface, you will notice many links rendered as
 * tabs. These are known in the menu system as "local tasks", and they are
 * rendered as tabs by default, though other presentations are possible.
 * Local tasks function just as other menu items in most respects. It is
 * convention that the names of these tasks should be short verbs if
 * possible. In addition, a "default" local task should be provided for
 * each set. When visiting a local task's parent menu item, the default
 * local task will be rendered as if it is selected; this provides for a
 * normal tab user experience. This default task is special in that it
 * links not to its provided path, but to its parent item's path instead.
 * The default task's path is only used to place it appropriately in the
 * menu hierarchy.
 *
 * Everything described so far is stored in the menu_router table. The
 * menu_links table holds the visible menu links. By default these are
 * derived from the same hook_menu definitions, however you are free to
 * add more with menu_link_save().
 */

/**
 * @defgroup menu_flags Menu flags
 * @{
 * Flags for use in the "type" attribute of menu items.
 */

/**
 * Internal menu flag -- menu item is the root of the menu tree.
 */
const MENU_IS_ROOT = 0x0001;

/**
 * Internal menu flag -- menu item is visible in the menu tree.
 */
const MENU_VISIBLE_IN_TREE = 0x0002;

/**
 * Internal menu flag -- menu item is visible in the breadcrumb.
 */
const MENU_VISIBLE_IN_BREADCRUMB = 0x0004;

/**
 * Internal menu flag -- menu item links back to its parent.
 */
const MENU_LINKS_TO_PARENT = 0x0008;

/**
 * Internal menu flag -- menu item can be modified by administrator.
 */
const MENU_MODIFIED_BY_ADMIN = 0x0020;

/**
 * Internal menu flag -- menu item was created by administrator.
 */
const MENU_CREATED_BY_ADMIN = 0x0040;

/**
 * Internal menu flag -- menu item is a local task.
 */
const MENU_IS_LOCAL_TASK = 0x0080;

/**
 * Internal menu flag -- menu item is a local action.
 */
const MENU_IS_LOCAL_ACTION = 0x0100;

/**
 * @} End of "defgroup menu_flags".
 */

/**
 * @defgroup menu_item_types Menu item types
 * @{
 * Definitions for various menu item types.
 *
 * Menu item definitions provide one of these constants, which are shortcuts for
 * combinations of @link menu_flags Menu flags @endlink.
 */

/**
 * Menu type -- A "normal" menu item that's shown in menu and breadcrumbs.
 *
 * Normal menu items show up in the menu tree and can be moved/hidden by
 * the administrator. Use this for most menu items. It is the default value if
 * no menu item type is specified.
 */
define('MENU_NORMAL_ITEM', MENU_VISIBLE_IN_TREE | MENU_VISIBLE_IN_BREADCRUMB);

/**
 * Menu type -- A hidden, internal callback, typically used for API calls.
 *
 * Callbacks simply register a path so that the correct function is fired
 * when the URL is accessed. They do not appear in menus or breadcrumbs.
 */
const MENU_CALLBACK = 0x0000;

/**
 * Menu type -- A normal menu item, hidden until enabled by an administrator.
 *
 * Modules may "suggest" menu items that the administrator may enable. They act
 * just as callbacks do until enabled, at which time they act like normal items.
 * Note for the value: 0x0010 was a flag which is no longer used, but this way
 * the values of MENU_CALLBACK and MENU_SUGGESTED_ITEM are separate.
 */
define('MENU_SUGGESTED_ITEM', MENU_VISIBLE_IN_BREADCRUMB | 0x0010);

/**
 * Menu type -- A task specific to the parent item, usually rendered as a tab.
 *
 * Local tasks are menu items that describe actions to be performed on their
 * parent item. An example is the path "node/52/edit", which performs the
 * "edit" task on "node/52".
 */
define('MENU_LOCAL_TASK', MENU_IS_LOCAL_TASK | MENU_VISIBLE_IN_BREADCRUMB);

/**
 * Menu type -- The "default" local task, which is initially active.
 *
 * Every set of local tasks should provide one "default" task, that links to the
 * same path as its parent when clicked.
 */
define('MENU_DEFAULT_LOCAL_TASK', MENU_IS_LOCAL_TASK | MENU_LINKS_TO_PARENT | MENU_VISIBLE_IN_BREADCRUMB);

/**
 * Menu type -- An action specific to the parent, usually rendered as a link.
 *
 * Local actions are menu items that describe actions on the parent item such
 * as adding a new user, taxonomy term, etc.
 */
define('MENU_LOCAL_ACTION', MENU_IS_LOCAL_TASK | MENU_IS_LOCAL_ACTION | MENU_VISIBLE_IN_BREADCRUMB);

/**
 * Menu type -- A task specific to the parent, which is never rendered.
 *
 * Sibling local tasks are not rendered themselves, but affect the breadcrumb
 * trail and need their sibling tasks rendered as tabs.
 */
define('MENU_SIBLING_LOCAL_TASK', MENU_IS_LOCAL_TASK | MENU_IS_LOCAL_ACTION | MENU_VISIBLE_IN_BREADCRUMB);

/**
 * @} End of "defgroup menu_item_types".
 */

/**
 * @defgroup menu_context_types Menu context types
 * @{
 * Flags for use in the "context" attribute of menu router items.
 */

/**
 * Internal menu flag: Invisible local task.
 *
 * This flag may be used for local tasks like "Delete", so custom modules and
 * themes can alter the default context and expose the task by altering menu.
 */
const MENU_CONTEXT_NONE = 0x0000;

/**
 * Internal menu flag: Local task should be displayed in page context.
 */
const MENU_CONTEXT_PAGE = 0x0001;

/**
 * Internal menu flag: Local task should be displayed inline.
 */
const MENU_CONTEXT_INLINE = 0x0002;

/**
 * @} End of "defgroup menu_context_types".
 */

/**
 * @defgroup menu_status_codes Menu status codes
 * @{
 * Status codes for menu callbacks.
 */

/**
 * Internal menu status code -- Menu item was not found.
 */
const MENU_NOT_FOUND = 404;

/**
 * Internal menu status code -- Menu item access is denied.
 */
const MENU_ACCESS_DENIED = 403;

/**
 * Internal menu status code -- Menu item inaccessible because site is offline.
 */
const MENU_SITE_OFFLINE = 4;

/**
 * Internal menu status code -- Everything is working fine.
 */
const MENU_SITE_ONLINE = 5;

/**
 * @} End of "defgroup menu_status_codes".
 */

/**
 * @defgroup menu_tree_parameters Menu tree parameters
 * @{
 * Parameters for a menu tree.
 */

 /**
 * The maximum number of path elements for a menu callback
 */
const MENU_MAX_PARTS = 9;


/**
 * The maximum depth of a menu links tree - matches the number of p columns.
 *
 * @todo Move this constant to MenuLinkStorageController along with all the tree
 * functionality.
 */
const MENU_MAX_DEPTH = 9;


/**
 * @} End of "defgroup menu_tree_parameters".
 */

/**
 * Reserved key to identify the most specific menu link for a given path.
 *
 * The value of this constant is a hash of the constant name. We use the hash
 * so that the reserved key is over 32 characters in length and will not
 * collide with allowed menu names:
 * @code
 * sha1('MENU_PREFERRED_LINK') = 1cf698d64d1aa4b83907cf6ed55db3a7f8e92c91
 * @endcode
 *
 * @see menu_link_get_preferred()
 */
const MENU_PREFERRED_LINK = '1cf698d64d1aa4b83907cf6ed55db3a7f8e92c91';

/**
 * Returns the ancestors (and relevant placeholders) for any given path.
 *
 * For example, the ancestors of node/12345/edit are:
 * - node/12345/edit
 * - node/12345/%
 * - node/%/edit
 * - node/%/%
 * - node/12345
 * - node/%
 * - node
 *
 * To generate these, we will use binary numbers. Each bit represents a
 * part of the path. If the bit is 1, then it represents the original
 * value while 0 means wildcard. If the path is node/12/edit/foo
 * then the 1011 bitstring represents node/%/edit/foo where % means that
 * any argument matches that part. We limit ourselves to using binary
 * numbers that correspond the patterns of wildcards of router items that
 * actually exists. This list of 'masks' is built in menu_router_rebuild().
 *
 * @param $parts
 *   An array of path parts, for the above example
 *   array('node', '12345', 'edit').
 *
 * @return
 *   An array which contains the ancestors and placeholders. Placeholders
 *   simply contain as many '%s' as the ancestors.
 */
function menu_get_ancestors($parts) {
  $number_parts = count($parts);
  $ancestors = array();
  $length =  $number_parts - 1;
  $end = (1 << $number_parts) - 1;
  $masks = Drupal::state()->get('menu.masks');
  // If the optimized menu.masks array is not available use brute force to get
  // the correct $ancestors and $placeholders returned. Do not use this as the
  // default value of the menu.masks variable to avoid building such a big
  // array.
  if (!$masks) {
    $masks = range(511, 1);
  }
  // Only examine patterns that actually exist as router items (the masks).
  foreach ($masks as $i) {
    if ($i > $end) {
      // Only look at masks that are not longer than the path of interest.
      continue;
    }
    elseif ($i < (1 << $length)) {
      // We have exhausted the masks of a given length, so decrease the length.
      --$length;
    }
    $current = '';
    for ($j = $length; $j >= 0; $j--) {
      // Check the bit on the $j offset.
      if ($i & (1 << $j)) {
        // Bit one means the original value.
        $current .= $parts[$length - $j];
      }
      else {
        // Bit zero means means wildcard.
        $current .= '%';
      }
      // Unless we are at offset 0, add a slash.
      if ($j) {
        $current .= '/';
      }
    }
    $ancestors[] = $current;
  }
  return $ancestors;
}

/**
 * Unserializes menu data, using a map to replace path elements.
 *
 * The menu system stores various path-related information (such as the 'page
 * arguments' and 'access arguments' components of a menu item) in the database
 * using serialized arrays, where integer values in the arrays represent
 * arguments to be replaced by values from the path. This function first
 * unserializes such menu information arrays, and then does the path
 * replacement.
 *
 * The path replacement acts on each integer-valued element of the unserialized
 * menu data array ($data) using a map array ($map, which is typically an array
 * of path arguments) as a list of replacements. For instance, if there is an
 * element of $data whose value is the number 2, then it is replaced in $data
 * with $map[2]; non-integer values in $data are left alone.
 *
 * As an example, an unserialized $data array with elements ('node_load', 1)
 * represents instructions for calling the node_load() function. Specifically,
 * this instruction says to use the path component at index 1 as the input
 * parameter to node_load(). If the path is 'node/123', then $map will be the
 * array ('node', 123), and the returned array from this function will have
 * elements ('node_load', 123), since $map[1] is 123. This return value will
 * indicate specifically that node_load(123) is to be called to load the node
 * whose ID is 123 for this menu item.
 *
 * @param $data
 *   A serialized array of menu data, as read from the database.
 * @param $map
 *   A path argument array, used to replace integer values in $data; an integer
 *   value N in $data will be replaced by value $map[N]. Typically, the $map
 *   array is generated from a call to the arg() function.
 *
 * @return
 *   The unserialized $data array, with path arguments replaced.
 */
function menu_unserialize($data, $map) {
  if ($data = unserialize($data)) {
    foreach ($data as $k => $v) {
      if (is_int($v)) {
        $data[$k] = isset($map[$v]) ? $map[$v] : '';
      }
    }
    return $data;
  }
  else {
    return array();
  }
}



/**
 * Replaces the statically cached item for a given path.
 *
 * @param $path
 *   The path.
 * @param $router_item
 *   The router item. Usually a router entry from menu_get_item() is either
 *   modified or set to a different path. This allows the navigation block,
 *   the page title, the breadcrumb, and the page help to be modified in one
 *   call.
 */
function menu_set_item($path, $router_item) {
  menu_get_item($path, $router_item);
}

/**
 * Gets a router item.
 *
 * @param $path
 *   The path; for example, 'node/5'. The function will find the corresponding
 *   node/% item and return that.
 * @param $router_item
 *   Internal use only.
 *
 * @return
 *   The router item or, if an error occurs in _menu_translate(), FALSE. A
 *   router item is an associative array corresponding to one row in the
 *   menu_router table. The value corresponding to the key 'map' holds the
 *   loaded objects. The value corresponding to the key 'access' is TRUE if the
 *   current user can access this page. The values corresponding to the keys
 *   'title', 'page_arguments', 'access_arguments', and 'theme_arguments' will
 *   be filled in based on the database values and the objects loaded.
 */
function menu_get_item($path = NULL, $router_item = NULL) {
  $router_items = &drupal_static(__FUNCTION__);
  if (!isset($path)) {
    $path = current_path();
  }
  if (isset($router_item)) {
    $router_items[$path] = $router_item;
  }
  if (!isset($router_items[$path])) {
    // Rebuild if we know it's needed, or if the menu masks are missing which
    // occurs rarely, likely due to a race condition of multiple rebuilds.
    if (Drupal::state()->get('menu_rebuild_needed') || !Drupal::state()->get('menu.masks')) {
      menu_router_rebuild();
    }
    $original_map = arg(NULL, $path);

    $parts = array_slice($original_map, 0, MENU_MAX_PARTS);
    $ancestors = menu_get_ancestors($parts);
    $router_item = db_query_range('SELECT * FROM {menu_router} WHERE path IN (:ancestors) ORDER BY fit DESC', 0, 1, array(':ancestors' => $ancestors))->fetchAssoc();

    if ($router_item) {
      // Allow modules to alter the router item before it is translated and
      // checked for access.
      drupal_alter('menu_get_item', $router_item, $path, $original_map);

      $map = _menu_translate($router_item, $original_map);
      $router_item['original_map'] = $original_map;
      if ($map === FALSE) {
        $router_items[$path] = FALSE;
        return FALSE;
      }
      if ($router_item['access']) {
        $router_item['map'] = $map;
        $router_item['page_arguments'] = array_merge(menu_unserialize($router_item['page_arguments'], $map), array_slice($map, $router_item['number_parts']));
        $router_item['theme_arguments'] = array_merge(menu_unserialize($router_item['theme_arguments'], $map), array_slice($map, $router_item['number_parts']));
      }
    }
    $router_items[$path] = $router_item;
  }
  return $router_items[$path];
}

/**
 * Loads objects into the map as defined in the $item['load_functions'].
 *
 * @param $item
 *   A menu router or menu link item
 * @param $map
 *   An array of path arguments; for example, array('node', '5').
 *
 * @return
 *   Returns TRUE for success, FALSE if an object cannot be loaded.
 *   Names of object loading functions are placed in $item['load_functions'].
 *   Loaded objects are placed in $map[]; keys are the same as keys in the
 *   $item['load_functions'] array.
 *   $item['access'] is set to FALSE if an object cannot be loaded.
 */
function _menu_load_objects(&$item, &$map) {
  if ($load_functions = $item['load_functions']) {
    // If someone calls this function twice, then unserialize will fail.
    if (!is_array($load_functions)) {
      $load_functions = unserialize($load_functions);
    }
    $path_map = $map;
    foreach ($load_functions as $index => $function) {
      if ($function) {
        $value = isset($path_map[$index]) ? $path_map[$index] : '';
        if (is_array($function)) {
          // Set up arguments for the load function. These were pulled from
          // 'load arguments' in the hook_menu() entry, but they need
          // some processing. In this case the $function is the key to the
          // load_function array, and the value is the list of arguments.
          list($function, $args) = each($function);
          $load_functions[$index] = $function;

          // Some arguments are placeholders for dynamic items to process.
          foreach ($args as $i => $arg) {
            if ($arg === '%index') {
              // Pass on argument index to the load function, so multiple
              // occurrences of the same placeholder can be identified.
              $args[$i] = $index;
            }
            if ($arg === '%map') {
              // Pass on menu map by reference. The accepting function must
              // also declare this as a reference if it wants to modify
              // the map.
              $args[$i] = &$map;
            }
            if (is_int($arg)) {
              $args[$i] = isset($path_map[$arg]) ? $path_map[$arg] : '';
            }
          }
          array_unshift($args, $value);
          $return = call_user_func_array($function, $args);
        }
        else {
          $return = $function($value);
        }
        // If callback returned an error or there is no callback, trigger 404.
        if (empty($return)) {
          $item['access'] = FALSE;
          $map = FALSE;
          return FALSE;
        }
        $map[$index] = $return;
      }
    }
    $item['load_functions'] = $load_functions;
  }
  return TRUE;
}

/**
 * Checks access to a menu item using the access callback.
 *
 * @param $item
 *   A menu router or menu link item
 * @param $map
 *   An array of path arguments; for example, array('node', '5').
 *
 * @return
 *   $item['access'] becomes TRUE if the item is accessible, FALSE otherwise.
 */
function _menu_check_access(&$item, $map) {
  // Determine access callback, which will decide whether or not the current
  // user has access to this path.
  $callback = empty($item['access_callback']) ? 0 : trim($item['access_callback']);
  // Check for a TRUE or FALSE value.
  if (is_numeric($callback)) {
    $item['access'] = (bool) $callback;
  }
  else {
    $arguments = menu_unserialize($item['access_arguments'], $map);
    // As call_user_func_array is quite slow and user_access is a very common
    // callback, it is worth making a special case for it.
    if ($callback == 'user_access') {
      $item['access'] = (count($arguments) == 1) ? user_access($arguments[0]) : user_access($arguments[0], $arguments[1]);
    }
    else {
      $item['access'] = call_user_func_array($callback, $arguments);
    }
  }
}

/**
 * Localizes the router item title using t() or another callback.
 *
 * Translate the title and description to allow storage of English title
 * strings in the database, yet display of them in the language required
 * by the current user.
 *
 * @param $item
 *   A menu router item or a menu link item.
 * @param $map
 *   The path as an array with objects already replaced. E.g., for path
 *   node/123 $map would be array('node', $node) where $node is the node
 *   object for node 123.
 * @param $link_translate
 *   TRUE if we are translating a menu link item; FALSE if we are
 *   translating a menu router item.
 *
 * @return
 *   No return value.
 *   $item['title'] is localized according to $item['title_callback'].
 *   If an item's callback is check_plain(), $item['options']['html'] becomes
 *   TRUE.
 *   $item['description'] is computed using $item['description_callback'] if
 *   specified; otherwise it is translated using t().
 *   When doing link translation and the $item['options']['attributes']['title']
 *   (link title attribute) matches the description, it is translated as well.
 */
function _menu_item_localize(&$item, $map, $link_translate = FALSE) {
  $title_callback = $item['title_callback'];
  $item['localized_options'] = $item['options'];
  // All 'class' attributes are assumed to be an array during rendering, but
  // links stored in the database may use an old string value.
  // @todo In order to remove this code we need to implement a database update
  //   including unserializing all existing link options and running this code
  //   on them, as well as adding validation to menu_link_save().
  if (isset($item['options']['attributes']['class']) && is_string($item['options']['attributes']['class'])) {
    $item['localized_options']['attributes']['class'] = explode(' ', $item['options']['attributes']['class']);
  }
  // If we are translating the title of a menu link, and its title is the same
  // as the corresponding router item, then we can use the title information
  // from the router. If it's customized, then we need to use the link title
  // itself; can't localize.
  // If we are translating a router item (tabs, page, breadcrumb), then we
  // can always use the information from the router item.
  if (!$link_translate || ($item['title'] == $item['link_title'])) {
    // t() is a special case. Since it is used very close to all the time,
    // we handle it directly instead of using indirect, slower methods.
    if ($title_callback == 't') {
      if (empty($item['title_arguments'])) {
        $item['title'] = t($item['title']);
      }
      else {
        $item['title'] = t($item['title'], menu_unserialize($item['title_arguments'], $map));
      }
    }
    elseif ($title_callback) {
      if (empty($item['title_arguments'])) {
        $item['title'] = $title_callback($item['title']);
      }
      else {
        $item['title'] = call_user_func_array($title_callback, menu_unserialize($item['title_arguments'], $map));
      }
      // Avoid calling check_plain again on l() function.
      if ($title_callback == 'check_plain') {
        $item['localized_options']['html'] = TRUE;
      }
    }
  }
  elseif ($link_translate) {
    $item['title'] = $item['link_title'];
  }

  // Translate description, see the motivation above.
  if (!empty($item['description'])) {
    $original_description = $item['description'];
  }
  if (!empty($item['description_arguments']) || !empty($item['description'])) {
    $description_callback = $item['description_callback'];
    // If the description callback is t(), call it directly.
    if ($description_callback == 't') {
      if (empty($item['description_arguments'])) {
        $item['description'] = t($item['description']);
      }
      else {
        $item['description'] = t($item['description'], menu_unserialize($item['description_arguments'], $map));
      }
    }
    elseif ($description_callback) {
      // If there are no arguments, call the description callback directly.
      if (empty($item['description_arguments'])) {
        $item['description'] = $description_callback($item['description']);
      }
      // Otherwise, use call_user_func_array() to pass the arguments.
      else {
        $item['description'] = call_user_func_array($description_callback, menu_unserialize($item['description_arguments'], $map));
      }
    }
  }
  // If the title and description are the same, use the translated description
  // as a localized title.
  if ($link_translate && isset($original_description) && isset($item['options']['attributes']['title']) && $item['options']['attributes']['title'] == $original_description) {
    $item['localized_options']['attributes']['title'] = $item['description'];
  }
}

/**
 * Handles dynamic path translation and menu access control.
 *
 * When a user arrives on a page such as node/5, this function determines
 * what "5" corresponds to, by inspecting the page's menu path definition,
 * node/%node. This will call node_load(5) to load the corresponding node
 * object.
 *
 * It also works in reverse, to allow the display of tabs and menu items which
 * contain these dynamic arguments, translating node/%node to node/5.
 *
 * Translation of menu item titles and descriptions are done here to
 * allow for storage of English strings in the database, and translation
 * to the language required to generate the current page.
 *
 * @param $router_item
 *   A menu router item
 * @param $map
 *   An array of path arguments; for example, array('node', '5').
 * @param $to_arg
 *   Execute $item['to_arg_functions'] or not. Use only if you want to render a
 *   path from the menu table, for example tabs.
 *
 * @return
 *   Returns the map with objects loaded as defined in the
 *   $item['load_functions']. $item['access'] becomes TRUE if the item is
 *   accessible, FALSE otherwise. $item['href'] is set according to the map.
 *   If an error occurs during calling the load_functions (like trying to load
 *   a non-existent node) then this function returns FALSE.
 */
function _menu_translate(&$router_item, $map, $to_arg = FALSE) {
  if ($to_arg && !empty($router_item['to_arg_functions'])) {
    // Fill in missing path elements, such as the current uid.
    _menu_link_map_translate($map, $router_item['to_arg_functions']);
  }
  // The $path_map saves the pieces of the path as strings, while elements in
  // $map may be replaced with loaded objects.
  $path_map = $map;
  if (!empty($router_item['load_functions']) && !_menu_load_objects($router_item, $map)) {
    // An error occurred loading an object.
    $router_item['access'] = FALSE;
    return FALSE;
  }

  // Generate the link path for the page request or local tasks.
  $link_map = explode('/', $router_item['path']);
  if (isset($router_item['tab_root'])) {
    $tab_root_map = explode('/', $router_item['tab_root']);
  }
  if (isset($router_item['tab_parent'])) {
    $tab_parent_map = explode('/', $router_item['tab_parent']);
  }
  for ($i = 0; $i < $router_item['number_parts']; $i++) {
    if ($link_map[$i] == '%') {
      $link_map[$i] = $path_map[$i];
    }
    if (isset($tab_root_map[$i]) && $tab_root_map[$i] == '%') {
      $tab_root_map[$i] = $path_map[$i];
    }
    if (isset($tab_parent_map[$i]) && $tab_parent_map[$i] == '%') {
      $tab_parent_map[$i] = $path_map[$i];
    }
  }
  $router_item['href'] = implode('/', $link_map);
  $router_item['tab_root_href'] = implode('/', $tab_root_map);
  $router_item['tab_parent_href'] = implode('/', $tab_parent_map);
  $router_item['options'] = array();
  if (!empty($router_item['route_name'])) {
    // Route-provided menu items do not have menu loaders, so replace the map
    // with the link map.
    $map = $link_map;

    $route_provider = Drupal::getContainer()->get('router.route_provider');
    $route = $route_provider->getRouteByName($router_item['route_name']);
    $router_item['access'] = menu_item_route_access($route, $router_item['href'], $map);
  }
  else {
    // @todo: Remove once all routes are converted.
    _menu_check_access($router_item, $map);
  }

  // For performance, don't localize an item the user can't access.
  if ($router_item['access']) {
    _menu_item_localize($router_item, $map);
  }

  return $map;
}

/**
 * Translates the path elements in the map using any to_arg helper function.
 *
 * @param $map
 *   An array of path arguments; for example, array('node', '5').
 * @param $to_arg_functions
 *   An array of helper functions; for example, array(2 => 'menu_tail_to_arg').
 *
 * @see hook_menu()
 */
function _menu_link_map_translate(&$map, $to_arg_functions) {
  $to_arg_functions = unserialize($to_arg_functions);
  foreach ($to_arg_functions as $index => $function) {
    // Translate place-holders into real values.
    $arg = $function(!empty($map[$index]) ? $map[$index] : '', $map, $index);
    if (!empty($map[$index]) || isset($arg)) {
      $map[$index] = $arg;
    }
    else {
      unset($map[$index]);
    }
  }
}

/**
 * Returns a string containing the path relative to the current index.
 */
function menu_tail_to_arg($arg, $map, $index) {
  return implode('/', array_slice($map, $index));
}

/**
 * Loads the path as one string relative to the current index.
 *
 * To use this load function, you must specify the load arguments
 * in the router item as:
 * @code
 * $item['load arguments'] = array('%map', '%index');
 * @endcode
 *
 * @see search_menu().
 */
function menu_tail_load($arg, &$map, $index) {
  $arg = implode('/', array_slice($map, $index));
  $map = array_slice($map, 0, $index);
  return $arg;
}

/**
 * Provides menu link access control, translation, and argument handling.
 *
 * This function is similar to _menu_translate(), but it also does
 * link-specific preparation (such as always calling to_arg() functions).
 *
 * @param $item
 *   A menu link.
 * @param $translate
 *   (optional) Whether to try to translate a link containing dynamic path
 *   argument placeholders (%) based on the menu router item of the current
 *   path. Defaults to FALSE. Internally used for breadcrumbs.
 *
 * @return
 *   Returns the map of path arguments with objects loaded as defined in the
 *   $item['load_functions'].
 *   $item['access'] becomes TRUE if the item is accessible, FALSE otherwise.
 *   $item['href'] is generated from link_path, possibly by to_arg functions.
 *   $item['title'] is generated from link_title, and may be localized.
 *   $item['options'] is unserialized; it is also changed within the call here
 *   to $item['localized_options'] by _menu_item_localize().
 */
function _menu_link_translate(&$item, $translate = FALSE) {
  if (!is_array($item['options'])) {
    $item['options'] = unserialize($item['options']);
  }
  if ($item['external']) {
    $item['access'] = 1;
    $map = array();
    $item['href'] = $item['link_path'];
    $item['title'] = $item['link_title'];
    $item['localized_options'] = $item['options'];
  }
  else {
    // Complete the path of the menu link with elements from the current path,
    // if it contains dynamic placeholders (%).
    $map = explode('/', $item['link_path']);
    if (strpos($item['link_path'], '%') !== FALSE) {
      // Invoke registered to_arg callbacks.
      if (!empty($item['to_arg_functions'])) {
        _menu_link_map_translate($map, $item['to_arg_functions']);
      }
      // Or try to derive the path argument map from the current router item,
      // if this $item's path is within the router item's path. This means
      // that if we are on the current path 'foo/%/bar/%/baz', then
      // menu_get_item() will have translated the menu router item for the
      // current path, and we can take over the argument map for a link like
      // 'foo/%/bar'. This inheritance is only valid for breadcrumb links.
      // @see _menu_tree_check_access()
      // @see menu_get_active_breadcrumb()
      elseif ($translate && ($current_router_item = menu_get_item())) {
        // If $translate is TRUE, then this link is in the active trail.
        // Only translate paths within the current path.
        if (strpos($current_router_item['path'], $item['link_path']) === 0) {
          $count = count($map);
          $map = array_slice($current_router_item['original_map'], 0, $count);
          $item['original_map'] = $map;
          if (isset($current_router_item['map'])) {
            $item['map'] = array_slice($current_router_item['map'], 0, $count);
          }
          // Reset access to check it (for the first time).
          unset($item['access']);
        }
      }
    }
    $item['href'] = implode('/', $map);

    // Skip links containing untranslated arguments.
    if (strpos($item['href'], '%') !== FALSE) {
      $item['access'] = FALSE;
      return FALSE;
    }
    // menu_tree_check_access() may set this ahead of time for links to nodes.
    if (!isset($item['access'])) {
      if ($route = $item->getRoute()) {
        $item['access'] = menu_item_route_access($route, $item['href'], $map);
      }
      elseif (!empty($item['load_functions']) && !_menu_load_objects($item, $map)) {
        // An error occurred loading an object.
        $item['access'] = FALSE;
        return FALSE;
      }
      // Apply the access check defined in hook_menu() if there is not route
      // defined.
      else {
        _menu_check_access($item, $map);
      }
    }
    // For performance, don't localize a link the user can't access.
    if ($item['access']) {
      _menu_item_localize($item, $map, TRUE);
    }
  }

  // Allow other customizations - e.g. adding a page-specific query string to the
  // options array. For performance reasons we only invoke this hook if the link
  // has the 'alter' flag set in the options array.
  if (!empty($item['options']['alter'])) {
    drupal_alter('translated_menu_link', $item, $map);
  }

  return $map;
}

/**
 * Checks access to a menu item by mocking a request for a path.
 *
 * @param \Symfony\Component\Routing\Route $route
 *   Router for the given menu item.
 * @param string $href
 *   Menu path as returned by $item['href'] of menu_get_item().
 * @param array $map