Support bindInterceptor on final classes

[reubenfirmin]

Since everything is final by default in kotlin, guice's interceptors don't immediately work, and in fact silently fail. This is not hard to google a solution to, assuming you have tests around the caching; however, the kotlin wrapper should either detect this and raise an error, or (ideally) provide a solution (perhaps an open delegating proxy) that allows aop to work.

[JLLeitschuh]

and in fact silently fail

Sounds like a bug in Guice?

[johnlcox]

I'm having trouble understanding the issue here, and I'm apt to agree with @JLLeitschuh that the silent failing sounds like an issue in Guice rather than kotlin-guice.

Could you provide a Minimal Complete Verifiable Example showing what you are trying to do with a final class?

[reubenfirmin]

Java is non-final by default. Kotlin is final by default.

bindInterceptor only works on non-final classes, and non-final methods (https://github.com/google/guice/wiki/AOP). When guice was written, this was a reasonable decision since you have to go out of your way to make classes/methods final. In Kotlin, the inverse is true; you have to go out of your way to make things non-final. Therefore I think it's reasonable that it'd be the job of kotlin-guice to make bindInterceptor (perhaps renamed - bindInterceptorProxy) work seamlessly while maintaining the final-by-default setup. Otherwise, the code ends up becoming marked with "open" throughout for no obvious good reason.

[johnlcox]

I'm not sure it's possible to make interceptors work with final classes. The reason Guice doesn't support final classes is because the interception is implemented with an AOP library like cglib, which generates a subclass dynamically.

It looks like there is an issue logged to Guice to detect binding final (and other invalid) classes as interceptors: google/guice#294

Do you have some idea in mind for working around the limitations of the underlying AOP library implementation for interceptors?

[reubenfirmin]

You could potentially use an InvocationHandler and proxy to the matched methods via the interceptor.

[johnlcox]

We could proxy final classes, but so could Guice.

As long as Guice doesn't allow binding final classes I don't intend to support it in this extension project.