Propagate @GwtIncompatible to generated Factory classes?

[cpovirk]

(This is the Dagger equivalent to google/auto#187)

Motivation: I am trying to get Guava to start relying on the GWT compiler's new automatic stripping, rather than doing its own @GwtIncompatible stripping. This means that the Java compilation that we do for GWT is now seeing @GwtIncompatible classes. The GWT compiler proper then ignores then. But because javac saw them, Dagger generated Factory classes for those with @Inject constructors. Those Factory classes refer back to the @GwtIncompatible original, which the GWT compiler can't see. We get a compilation error:

[ERROR] Errors in 'blahblah.jar/com/google/common/time/DefaultSleeper$$Factory.java'
   [ERROR] Line 12: The constructor DefaultSleeper() is not visible

(Google developers can check out the full results.)

A solution (I think) is for Dagger to annotate the Factory class as @GwtIncompatible if the original class (or any enclosing class) is so annotated. Does this sound reasonable?

[cgruber]

This does sound reasonable as an approach.

[cgruber]

I'm going to mark this as a 2.1 milestone though, but we can chat about it if we need it for our 2.0 release shortly. I think the solution here is sort of subtle - we could special case gwt, but i'm hesitant to do that, since we have the same problem with j2objc, etc. But a comprehensive solution seems like it requires some semantic clarity I not fully certain we can get in time to fix it for 2.0.

2.1 should follow fairly soon after, though.

[gk5885]

This is pretty trivial and we should absolutely do that.