Lazy services - Final classes cannot be proxied by ProxyManager

[vhejda]

I am testing the 3.0.0@RC in a Symfony 3.4 project, and after installing, I am getting:

PHP Fatal error:  Uncaught ProxyManager\Exception\InvalidProxiedClassException: 
Provided class "JMS\Serializer\Handler\FormErrorHandler" is final and cannot be proxied

It is coming from ocramius/proxy-manager, as the FormErrorHandler is a final class and the service is registered as lazy="true". ocramius/proxy-manager is a dev-dependency of symfony/symfony, so I suppose I will not be the only affected person.

Related issue on Symfony/Symfony suggest dropping the final keyword:
symfony/symfony#20392

This might be fixing the problem, but looks like it's only merged to Symfony 4.x:
symfony/symfony#27697

I'd be happy to give a hand here, but not sure what the solution in here should be. Dropping the final on the affected classes in jms/serializer, or dropping the lazy=true here in bundle? Or something else?

Thanks for looking into this!

[goetas]

My preferred solution here is to remove lazy=true from the handlers.
But I'm curious about the performance difference...

[goetas]

Curious to know if is worth keeping the final keyword in the classes...

The reason for adding the final keyword is that many devs were extending handlers and re implementating 100% of them. More than once inherentance introduced problems that without will not arise