How do I alter the route defined by another module?

Question

In other words, what is the Drupal 8 equivalent of hook_menu_alter()?

Drupal 8 still uses hook_menu(), but for what I can see, the information returned by the hook is different from what the hook returned in Drupal 7. For example, the definition given in user_menu() for user is the following.

  $items['user'] = array(
    'title' => 'User account',
    'title callback' => 'user_menu_title',
    'weight' => -10,
    'route_name' => 'user_page',
    'menu_name' => 'account',
  );

The route_name property links to an entry in the user.routing.yml file.

user_page:
  pattern: '/user'
  defaults:
    _content: '\Drupal\user\Controller\UserController::userPage'
  requirements:
    _access: 'TRUE'

This is different from what done with Symphony, and it confuses me about how a module can alter the route defined from another user.

The only function that is still invoking hook_menu_alter() is menu_router_build(), but that function still contains code that needs to be updated, since it is still using the now deprecated drupal_alter().

  // Alter the menu as defined in modules, keys are like user/%user.
  drupal_alter('menu', $callbacks);
  foreach ($callbacks as $path => $router_item) {
    // If the menu item is a default local task and incorrectly references a
    // route, remove it.
    // @todo This may be removed later depending on the outcome of
    // http://drupal.org/node/1889790
    if (isset($router_item['type']) && $router_item['type'] == MENU_DEFAULT_LOCAL_TASK) {
      unset($callbacks[$path]['route_name']);
    }
    // If the menu item references a route, normalize the route information
    // into the old structure. Note that routes are keyed by name, not path,
    // so the path of the route takes precedence.
    if (isset($router_item['route_name'])) {
      $router_item['page callback'] = 'USES_ROUTE';
      $router_item['access callback'] = TRUE;
      $new_path = _menu_router_translate_route($router_item['route_name']);

      unset($callbacks[$path]);
      $callbacks[$new_path] = $router_item;
    }
  }

Answer 1

Allow views to override existing routing items just uses existing functionality.

If you want to change the information attached to a route, not the menu, like the actual used controller, or the requirements (permission/role etc.) you can use an event provided by Drupal:

  <?php

  use Drupal\Core\Routing\RouteBuildEvent;
  use Drupal\Core\Routing\RoutingEvents;
  use Symfony\Component\EventDispatcher\EventSubscriberInterface;

  class RouteSubscriber implements EventSubscriberInterface {
 
   /**
    * {@inheritdoc}
    */
   public static function getSubscribedEvents() {
      $events[RoutingEvents::ALTER] = 'alterRoutes';
     return $events;
   }

  /**
   * Alters existing routes.
   *
   * @param \Drupal\Core\Routing\RouteBuildEvent $event
   *   The route building event.
   */
  protected function alterRoutes(RouteBuildEvent $event) {
    // Fetch the collection which can be altered.
    $collection = $event->getRouteCollection();
    // The event is fired multiple times so ensure that the user_page route
    // is available.
    if ($route = $collection->get('user_page')) {
      // As example add a new requirement.
      $route->setRequirement('_role', 'anonymous');
    }
  }

  }

Additionally you have to register a service with the tag 'event_subscriber' for this class.

Answer 2

Since I asked the question, Drupal 8 core code has been changed. Some of the issues about routes have been fixed.

hook_menu() isn't used from Drupal 8 anymore; the routes a module uses are defined in a .routing.yml file (for example user.routing.yml). Alter hooks are still used, but since hook_menu() isn't invoked from Drupal core, hook_menu_alter() won't be invoked.

The steps necessary to alter a route defined from other modules are the following:

• Define a service tagged as event_subscriber (The tag is the important part, or the service would not work as expected.)

  services:
    mymodule.route_subscriber:
      class: Drupal\mymodule\Routing\RouteSubscriber
      tags:
        - { name: event_subscriber }
  

• Create a class that extends RouteSubscriberBase

  namespace Drupal\mymodule\Routing;
  
  use Drupal\Core\Routing\RouteSubscriberBase;
  use Symfony\Component\Routing\RouteCollection;
  
  /**
   * Listens to the dynamic route events.
   */
  class RouteSubscriber extends RouteSubscriberBase {
  
    /**
     * {@inheritdoc}
     */
    protected function alterRoutes(RouteCollection $collection) {
      // Change the route associated with the user profile page (/user, /user/{uid}).
      if ($route = $collection->get('user.page')) {
        $route->setDefault('_controller', '\Drupal\mymodule\Controller\UserController::userPage');
      }
    }
  
  }
  

  For real implementation examples of alterRoutes(), see AdminRouteSubscriber::alterRoutes() or RouteSubscriber::alterRoutes() .

  protected function alterRoutes(RouteCollection $collection) {
    foreach ($collection->all() as $route) {
      if (strpos($route->getPath(), '/admin') === 0 && !$route->hasOption('_admin_route') && static::isHtmlRoute($route)) {
        $route->setOption('_admin_route', TRUE);
      }
    }
  }
  

  protected function alterRoutes(RouteCollection $collection) {
    $mappers = $this->mapperManager->getMappers($collection);
    foreach ($mappers as $mapper) {
      $collection->add($mapper->getOverviewRouteName(), $mapper->getOverviewRoute());
      $collection->add($mapper->getAddRouteName(), $mapper->getAddRoute());
      $collection->add($mapper->getEditRouteName(), $mapper->getEditRoute());
      $collection->add($mapper->getDeleteRouteName(), $mapper
        ->getDeleteRoute());
    }
  }
  

Notice that compared with earlier Drupal 8 releases, some details are changed.

• The route name is changed from user_page to user.page
• The requirements for that route changed from _access: 'TRUE' to _user_is_logged_in: 'TRUE'
• The property to set a route controller changed from _content to _controller

Answer 3

See Altering existing routes and adding new routes based on dynamic ones; it worked nicely for me to remove /search handled by the Search module. In my case, I used the following code.

<?php
/**
 * @file
 * Contains \Drupal\ua_sc_module\Routing\SearchAlterRouteSubscriber.
 */

namespace Drupal\ua_sc_module\Routing;

use Drupal\Core\Routing\RouteSubscriberBase;
use Symfony\Component\Routing\RouteCollection;

/**
 * Listens to the dynamic route events.
 */
class SearchAlterRouteSubscriber extends RouteSubscriberBase {

  /**
   * {@inheritdoc}
   */
  protected function alterRoutes(RouteCollection $collection) {
    // Remove the /search route.
    if ($collection->get('search.view')) {
      $collection->remove('search.view');
    }
  }

}