[External] : Re: RFR: 8231436: Fix the applicability of a no- at Target annotation type

[Alex Buckley]

On 2/5/2021 4:18 PM, Liam Miller-Cushon wrote:
> I don't have a strong opinion either way about whether this change is 
> worth pursuing, or worth pursuing now. The simplicity of @Target-less 
> annotations applying to everything is appealing. I also think there's 
> going to be some noticeable compatibility impact, due to the number of 
> annotations that will start appearing in type contexts, and the number 
> of tools that process annotations that will need to become more robust 
> in their handling of type annotations.
Suppose that the no- at Target annotation @Foo is today a declaration 
annotation on a method declaration, but tomorrow (due to recompiling Foo 
and the aforementioned method declaration) @Foo becomes a declaration 
annotation _and a type annotation that applies to the return type of the 
method_. Hardly any annotation processor will care, because it'll be 
calling Method::getAnnotations that only exposes declaration 
annotations. Type annotations are exposed by a different API, 
Method::getAnnotatedReturnType & friends.

Of course a type-checking annotation processor might be calling 
Method::getAnnotatedReturnType to look for, say, @NonNull, but I have a 
hard time believing that such a processor will be unable to cope with 
@Foo's presence. And the owner of Foo can choose at any time to add an 
@Target that makes @Foo appear as both declaration and type annotation.

Is there a compatibility impact I am overlooking?

Alex