IssueTracker

I think there are a number of existing issues already requesting this (particularly for the nullability annotations). The blocker for this is that metalava needs to support typeuse annotations, and it doesn't yet (and it's a nontrivial amount of work; there is partial support in there behind a compile-time flag, but it's not complete.)

Kotlin's AnnotationTarget.TYPE maps to Java's ElementType.TYPE_USE, which was added in SDK 26. If we use this in Java code, we will likely need to do one of the following:

1. Require minSdkVersion=26 -- which is too high at this point in time
2. Advise clients to enable core library desugaring -- which I think still has client usability issues
3. Advise clients to ignore javac class resolution warnings -- which we're already getting flak for with Kotlin

Tor, do you see any better option here?

And, of course, that Metalava doesn't support typeuse annotations yet. But we (AndroidX) have more control over when that happens.

I think all of the androidx annotations are compile or class retention, not runtime retention, so there probably aren't any minSdkVersion requirements?

Ah, yes, good point -- the errors I saw for other annotations were due to Kotlin's Metadata which is runtime retention. We may still need to add Proguard rules, though, to avoid resolution warnings coming out of bytecode optimizers.