[records] Spec for next version of Record Classes JEP

[Brian Goetz]

I think we're reaching diminishing returns here.  Here's how I would 
think about this:

  - We do an applicability check to see if the annotation _could apply_ 
to any of the things we are going to generate.  If the target isn't one 
of param/method/field/component, we issue an error.
  - If there is an annotation on a component that only applies to method 
/ param, but the corresponding method/param is explicitly declare, oh 
well.  We promise to propagate well-formed annotations to all the places 
that it would apply, and "zero" is a valid value of all.

On 9/28/2020 6:21 AM, Gavin Bierman wrote:
> There’s one minor corner-case that I bring to your attention. Consider the
> following:
>
> @Target(ElementType.METHOD)
> @interface A { }
>
> record R(@A int x) {
>     int x() { return this.x; }
> }
>
> The new rules ensure that this is an error as the annotation on the record
> component is not propagated anywhere because of the explicit accessor
> declaration. However, what if the accessor was annotated with the same
> annotation?
>
> @Target(ElementType.METHOD)
> @interface A { }
>
> record R(@A int x) {
>     @A int x() { return this.x; }
> }
>
> As it stands, the spec rules this out as an error. For simple annotations,
> equality is simple to define, but do we want to attempt to define it for all
> kinds of annotations? This feels like it’s not worth the complexity, but I’d be
> happy to hear opinions.

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