Make annotations class retention only

[laeubi]

I noticed some annotations are marked with RUNTIME retention policy. For the purpose of checking the code it seems enough to have CLASS retention policy.

[eamonnmcmanus]

The current situation is a bit haphazard: some annotations have RUNTIME retention and some have CLASS. For example, @CheckReturnValue is RUNTIME but @CanIgnoreReturnValue (CIRV) is CLASS. We've tried promoting CIRV to RUNTIME in the past but ran into some issues with it causing extra classes to be retained when stripping Android apps.

Anyway, we are unlikely to change the retention of any annotation from RUNTIME to CLASS since that is an incompatible change. It seems quite likely that client code is relying on being able to detect at least some of these annotations at runtime. For example, Mockito checks its own @DoNotMock annotation at runtime, and code could be doing the same for Error Prone's.

[cushon]

There is some related discussion about RUNTIME vs. CLASS for JSpecify (jspecify/jspecify#28), I think the plan there is to generally use RUNTIME for new annotations

[laeubi]

It seems quite likely that client code is relying on being able to detect at least some of these annotations at runtime.

I can actually not think of any case where it is useful... Mockito is working on the runtime so it needs RUNTIME but for compiler or tool scoped annotation like error prone there is no benefit I can think of.

We've tried promoting CIRV to RUNTIME in the past but ran into some issues with it causing extra classes to be retained when stripping Android apps.

That's why I propose to put everything to CLASS, as RUNTIME has some unwanted implications and actually makes erroprone dripping into the runtime for no good reasons.