minor #9385 Documented the smart URL redirection (javiereguiluz)

This PR was squashed before being merged into the master branch (closes #9385).

Discussion
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Documented the smart URL redirection

This fixes #9330.

Commits
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49cfb48 Documented the smart URL redirection

Author: javiereguiluz

routing.rst

@@ -493,6 +493,8 @@ that are special: each adds a unique piece of functionality inside your applicat
 ``_locale``
     Used to set the locale on the request (:ref:`read more <translation-locale-url>`).
 
+.. _routing-trailing-slash-redirection:
+
 Redirecting URLs with Trailing Slashes
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -508,14 +510,19 @@ slashes (but only for ``GET`` and ``HEAD`` requests):
 ----------  ----------------------------------------  ------------------------------------------
 Route path  If the requested URL is ``/foo``          If the requested URL is ``/foo/``
 ----------  ----------------------------------------  ------------------------------------------
-``/foo``    It matches (``200`` status response)      It doesn't match (``404`` status response)
+``/foo``    It matches (``200`` status response)      It makes a ``301`` redirect to ``/foo``
 ``/foo/``   It makes a ``301`` redirect to ``/foo/``  It matches (``200`` status response)
 ----------  ----------------------------------------  ------------------------------------------
 
-In summary, adding a trailing slash in the route path is the best way to ensure
-that both URLs work. Read the :doc:`/routing/redirect_trailing_slash` article to
-learn how to avoid the ``404`` error when the request URL contains a trailing
-slash and the route path does not.
+.. note::
+
+    If your application defines different routes for each path (``/foo`` and
+    ``/foo/``) this automatic redirection doesn't take place and the right
+    route is always matched.
+
+.. versionadded:: 4.1
+    The automatic ``301`` redirection from ``/foo/`` to ``/foo`` was introduced
+    in Symfony 4.1. In previous Symfony versions this results in a ``404`` response.
 
 .. index::
    single: Routing; Controllers

routing/redirect_trailing_slash.rst

@@ -4,103 +4,9 @@
 Redirect URLs with a Trailing Slash
 ===================================
 
-The goal of this article is to demonstrate how to redirect URLs with a
-trailing slash to the same URL without a trailing slash
-(for example ``/en/blog/`` to ``/en/blog``).
-
-Create a controller that will match any URL with a trailing slash, remove
-the trailing slash (keeping query parameters if any) and redirect to the
-new URL with a 308 (*HTTP Permanent Redirect*) response status code::
-
-    // src/Controller/RedirectingController.php
-    namespace App\Controller;
-
-    use Symfony\Bundle\FrameworkBundle\Controller\Controller;
-    use Symfony\Component\HttpFoundation\Request;
-
-    class RedirectingController extends Controller
-    {
-        public function removeTrailingSlash(Request $request)
-        {
-            $pathInfo = $request->getPathInfo();
-            $requestUri = $request->getRequestUri();
-
-            $url = str_replace($pathInfo, rtrim($pathInfo, ' /'), $requestUri);
-
-            // 308 (Permanent Redirect) is similar to 301 (Moved Permanently) except
-            // that it does not allow changing the request method (e.g. from POST to GET)
-            return $this->redirect($url, 308);
-        }
-    }
-
-After that, create a route to this controller that's matched whenever a URL
-with a trailing slash is requested. Be sure to put this route last in your
-system, as explained below:
-
-.. configuration-block::
-
-    .. code-block:: php-annotations
-
-        // src/Controller/RedirectingController.php
-        namespace App\Controller;
-
-        use Symfony\Bundle\FrameworkBundle\Controller\Controller;
-        use Symfony\Component\HttpFoundation\Request;
-        use Symfony\Component\Routing\Annotation\Route;
-
-        class RedirectingController extends Controller
-        {
-            /**
-             * @Route("/{url}", name="remove_trailing_slash",
-             *     requirements={"url" = ".*\/$"})
-             */
-            public function removeTrailingSlash(Request $request)
-            {
-                // ...
-            }
-        }
-
-    .. code-block:: yaml
-
-        # config/routes.yaml
-        remove_trailing_slash:
-            path: /{url}
-            controller: App\Controller\RedirectingController::removeTrailingSlash
-            requirements:
-                url: .*/$
-
-    .. code-block:: xml
-
-        <?xml version="1.0" encoding="UTF-8" ?>
-        <routes xmlns="http://symfony.com/schema/routing">
-            <route id="remove_trailing_slash" path="/{url}" methods="GET">
-                <default key="_controller">App\Controller\RedirectingController::removeTrailingSlash</default>
-                <requirement key="url">.*/$</requirement>
-            </route>
-        </routes>
-
-    .. code-block:: php
-
-        use Symfony\Component\Routing\RouteCollection;
-        use Symfony\Component\Routing\Route;
-
-        $routes = new RouteCollection();
-        $routes->add(
-            'remove_trailing_slash',
-            new Route(
-                '/{url}',
-                array(
-                    '_controller' => 'App\Controller\RedirectingController::removeTrailingSlash',
-                ),
-                array(
-                    'url' => '.*/$',
-                )
-            )
-        );
-
 .. caution::
 
-    Make sure to include this route in your routing configuration at the
-    very end of your route listing. Otherwise, you risk redirecting real
-    routes (including Symfony core routes) that actually *do* have a trailing
-    slash in their path.
+    In Symfony 4.1 the automatic URL redirection was improved as explained in
+    :ref:`routing-trailing-slash-redirection`. That's why you no longer need to
+    do that redirection yourself and this article has been removed because it's
+    no longer needed.