Not adding types will cause trouble in other scenarios. We should probably document how to use the trait in untyped codebases.

Instead, we could generate the method in ProxyHelper maybe?
Something like

use LazyProxyTrait {
    __unserialize as __doUnserialize;
}

public function __unserialize($data): void { $this->__doUnserialize($data); }

wouldn't this cause issues in those other cases mentioned above ? And if no, why not updating the trait directly ?

Not adding types will cause trouble in other scenarios

as a curiosity, which would be these scenarios?

Instead, we could generate the method in ProxyHelper maybe?

done!

why not updating the trait directly ?

for correctness and also to allow child classes to add the type hint I'd say

Tests are failing so there are some details to fix but this looks good to me so far, thanks.

yes, I saw this... any hints about the failure?
It occurs in doctrine bridge tests: variable $service here seems to be a stdClass_c562334 (hence the failure). But I have the same behavior on branch6.4 🤔

The PR title does not reflect the proposed change anymore though.

Thank you @nikophil.