Autoconfigure service locator tag

src/Symfony/Bundle/FrameworkBundle/CHANGELOG.md

@@ -16,6 +16,7 @@ CHANGELOG
  * Deprecated `bundle:controller:action` syntax to reference controllers. Use `serviceOrFqcn::method` instead where `serviceOrFqcn`
    is either the service ID or the FQCN of the controller.
  * Deprecated `Symfony\Bundle\FrameworkBundle\Controller\ControllerNameParser`
+ * The `container.service_locator` tag of `ServiceLocator`s is now autoconfigured.
 
 4.0.0
 -----

src/Symfony/Bundle/FrameworkBundle/DependencyInjection/FrameworkExtension.php

@@ -42,6 +42,7 @@ use Symfony\Component\DependencyInjection\Parameter;
 use Symfony\Component\DependencyInjection\ParameterBag\ContainerBagInterface;
 use Symfony\Component\DependencyInjection\ParameterBag\ParameterBagInterface;
 use Symfony\Component\DependencyInjection\Reference;
+use Symfony\Component\DependencyInjection\ServiceLocator;
 use Symfony\Component\DependencyInjection\ServiceSubscriberInterface;
 use Symfony\Component\EventDispatcher\EventSubscriberInterface;
 use Symfony\Component\ExpressionLanguage\ExpressionLanguage;
@@ -288,6 +289,8 @@ class FrameworkExtension extends Extension
             ->addTag('config_cache.resource_checker');
         $container->registerForAutoconfiguration(EnvVarProcessorInterface::class)
             ->addTag('container.env_var_processor');
+        $container->registerForAutoconfiguration(ServiceLocator::class)
+            ->addTag('container.service_locator');
         $container->registerForAutoconfiguration(ServiceSubscriberInterface::class)
             ->addTag('container.service_subscriber');
         $container->registerForAutoconfiguration(ArgumentValueResolverInterface::class)