Register custom AttributeBag through CompilerPass

I am trying to tidy up my session variables by integrating custom AttributBags into the session. In Symfony < 6.0 you were able to inject a custom AttributBag into the session service.

See related questions

However this approach does not work anymore in Symfony >= 6.0. This blog article explains that the session service is deprecated and must now be accessed over the request_stack service. For controllers this works fine.

My current (not working) approach looks like this: Define a custom AttributBag class.

class ShoppingCartBag extends AttributeBag {
    public function __construct(string $storageKey = 'shoppingCart') {
        parent::__construct($storageKey);
    }
}

Add a custom CompilerPass in the Kernel class so that Symfony takes care of all changes while building the container.

class Kernel extends BaseKernel {
    use MicroKernelTrait;

    protected function build(ContainerBuilder $container): void {
        $container->addCompilerPass(new AddShoppingCartBagToSessionService());
    }
}

The custom CompilerPass looks like this.

class AddShoppingCartBagToSessionService implements CompilerPassInterface {

    public function process(ContainerBuilder $container) {
        $container->getDefinition('request_stack') //<- Works, but how to access the session?
            ->addMethodCall('getSession') // How to bridge the gap? This thought does not work. I assume it is because the session is not yet instantiated when the container is build.
            ->addMethodCall('registerBag', [new Reference('App\Session\CustomBag\ShoppingCartBag')]);
    }
}

Solution

As you correctly assumed, the session does not exist yet when doing this via the compiler pass.

Symfony uses a so called SessionFactory to create the session. So what you can do instead, is decorating the existing session.factory service with your own implementation of the SessionFactoryInterface and add your attribute bag there:

An implementation of this decorated session factory might look like this:

namespace App;

use Symfony\Component\HttpFoundation\Session\SessionFactoryInterface;
use Symfony\Component\HttpFoundation\Session\SessionInterface;

class SessionFactoryWithAttributeBag implements SessionFactoryInterface
{
    public function __construct(private SessionFactoryInterface $delegate)
    {
    }

    public function createSession(): SessionInterface
    {
        $session = $this->delegate->createSession();
        $session->registerBag(new ShoppingCartBag());

        return $session;
    }
}

And then you can decorate the session.factory via the services.yaml:

services:
    App\SessionFactoryWithAttributeBag:
        decorates: session.factory
        arguments: ['@.inner']

Now, whenever a session is created, your custom bag is also registered