how does this work for abstract classes that don't have only abstract methods or that have mandatory constructor arguments ?

how does this work for abstract classes that don't have only abstract methods or that have mandatory constructor arguments ?

Methods, whether abstract or not, are forwarded to the instance returned by the lazy-factory. Then, it's the job of the lazy-factory to do whatever is needed to create such instances.

@nicolas-grekas does it handle the case of a constructor with required arguments properly ? and what happens for final methods ?

For constructors: not our job. The service definition has to be correct.
Final methods on abstract classes will throw an exception saying this is not compatible.

@nicolas-grekas the service definition won't provide constructor arguments for the proxy instance, only for the actual instance.
So we should probably detect the case where the abstract class has a constructor to throw as unsupported (maybe first trying to override it and throwing only if not possible)

Ah sorry I misunderstood your question. We don't call the constructor, see newInstanceWithoutConstructor here:
https://github.com/symfony/symfony/blob/7.4/src/Symfony/Component/VarExporter/Internal/LazyDecoratorTrait.php