Should `@AnnotatedFor` on a package apply to subpackages?

[aosen-xiong]

QualifierDefaults had a // TODO: should AnnotatedFor apply to subpackages?? comment from #708 until #1331 removed it. The question was never answered, and modelling JSpecify's @NullMarked now requires thinking about it.

In #1304, I want to add aliasing between @AnnotatedFor("nullness") and @Nullmarked.

@DefaultQualifier on a package applies to subpackages, and had applyToSubpackages element (default true) so a default can opt out. @AnnotatedFor has no such element.

JSpecify specifies that @NullMarked on a package does not cover its subpackages, and #1304 aliases @NullMarked to both annotations:

@DefaultQualifier(NonNull, locations=UPPER_BOUND, applyToSubpackages=false) — can opt out, and does.
@AnnotatedFor("nullness") — cannot opt out, so the scope reaches subpackages.

Should we change @AnnotatedFor's behaviour or document this inconsistency with @Nullmarked semantics?

@wmdietl Do you have ideas on how to deal with this issue?

[wmdietl]

I think we should audit all our annotations and see whether we should add applyToSubpackages as a way to opt out of applying to sub-packages.
Unfortunately, for convenience, currently annotations like AnnotatedFor and DefaultQualifier apply to sub-packages.
We added the applyToSubpackages=false mechanism for the JSpecify reference checker, which wants to precisely model the JSpecify semantics. There, we didn't need AnnotatedFor, so we didn't consider that.

Could you go through the remaining qualifiers and see for which ones we need an "opt out"? When implementing this, we should make sure to not break on checker-qual inconsistencies, see #1906 .