Resource Leak Checker: warn of @MustCall on class declaration

[mernst]

Usually, writing @MustCall on a class declaration is the wrong thing. Instead, one should write @InheritableMustCall. However, it is an easy error to make.

I suggest that writing @MustCall on a class declaration should result in a warning or errror, but one that can be suppressed.

[msridhar]

Do you think it would be better for @MustCall itself to be inheritable? Or does that go against some standard design principles? We could also have an optional boolean parameter inheritable for @MustCall, which defaults to true but could be configured as needed.

[kelloggm]

As I recall, we needed @InheritableMustCall because for an annotation to be inheritable, it must be a declaration annotation - type annotations are not inheritable, and @MustCall itself is a type annotation. So, we needed @InheritableMustCall for technical reasons.

I propose that @MustCall on a class declaration should always be an error, with new error text instructing the user to write @InheritableMustCall instead. This would require a few additional warning suppressions in code that already requires warning suppressions (e.g., when @MustCall({}) is written on a particular sub-class of a super class that generally is @MustCall("close"), such as ByteArrayOutputStream), but otherwise I think that it would be fine. And, those @MustCall({}) annotations could just as easily (and maybe should be?) @InheritableMustCall annotations instead.

[msridhar]

@kelloggm that sounds good to me.