non final methods check

[marandaneto]

hey @JakeWharton first of all thanks for the great work.

I'd love to see nopen also checking non-final methods when they should be. I believe it makes sense to be within this lib, but this is you to say.

The idea is pretty much similar to @Open, but for methods. A method should be final (when possible) or annotated.

I've made a Draft PR (more like a POC), #8 and happy to chat about. If you are willing to bring this in and accept a PR, I'd gladly work on it.

Thanks a lot :)

[JakeWharton]

So this would require that any public or protected function in an @Open class was annotated or marked final?

[marandaneto]

yes, I'd like to double-check on compile-time that I'm not making an accidental overriding. on the same line as Item 19 of Effective Java, I believe a method should explicitly be marked as overridable/open or be final. This is a very handy check on compile-time when you ship a public API as a standalone library (binary).