Merge branch '5.1' into 5.2

* 5.1:
  Listing possible values of storage_id
  Require preprocessor env name fix used in PHP snippet

Author: javiereguiluz

configuration/env_var_processors.rst

@@ -396,7 +396,7 @@ Symfony provides the following env var processors:
             // config/packages/framework.php
             $container->setParameter('env(PHP_FILE)', '../config/.runtime-evaluated.php');
             $container->loadFromExtension('app', [
-                'auth' => '%env(require:AUTH_FILE)%',
+                'auth' => '%env(require:PHP_FILE)%',
             ]);
 
 ``env(trim:FOO)``

reference/configuration/framework.rst

@@ -1448,9 +1448,14 @@ storage_id
 
 **type**: ``string`` **default**: ``'session.storage.native'``
 
-The service id used for session storage. The ``session.storage`` service
-alias will be set to this service id. This class has to implement
+The service ID used for storing the session. The ``session.storage`` service
+alias will be set to this service. The class has to implement
 :class:`Symfony\\Component\\HttpFoundation\\Session\\Storage\\SessionStorageInterface`.
+To see a list of all available storages, run:
+
+.. code-block:: terminal
+
+    $ php bin/console debug:container session.storage.
 
 .. _config-framework-session-handler-id: