It's from here: https://github.com/symfony/symfony/blob/master/src/Symfony/Component/Routing/Loader/PhpFileLoader.php#L42.
Notice that `$container` is not available. It would be available, if this one was used: https://github.com/symfony/symfony/blob/master/src/Symfony/Component/DependencyInjection/Loader/PhpFileLoader.php#L35, but I don't know how to tell Symfony to use the `Symfony/Component/DependencyInjection/Loader/PhpFileLoader` instead of the `Symfony/Component/Routing/Loader/PhpFileLoader` loader.