Towards cleaner nesting

[Dan Smith]

> On Jan 9, 2020, at 9:03 AM, Brian Goetz <brian.goetz at oracle.com> wrote:
> 
>> FWIW, I think it's helpful for case analysis to flatten the list of things that can be nested/contain nested things as follows:
>> - top-level/static classes
>> - inner classes* (I always forget whether this includes local classes, but turns out it does)
>> - interfaces
>> - records
>> - enums
>> - annotation types
>> - static methods/initializers
>> - instance methods/local methods/constructors/instance initializers*
>> 
>> The proposal is that each one of these can be nested in any of these.
> 
> Of course, some of these don't make sense, such as "constructors in field initializers", so it's not quite as simple as that, but yes, we should seek to bust the _gratuitous_ restrictions.

Yeah, thinking a bit more, I guess I'd refine my list like so:

Type declarations:
- top-level/static classes
- inner classes*
- interfaces
- records
- enums
- annotation types

Method declarations:
- static methods
- instance/local methods*
- static initializers
- instance initializers/constructors*

Variable declarations (leaf nodes, not containers):
- instance/local variables*
- static variables

And then "anything can be nested inside of anything" has the following exceptions:

- interfaces can't directly contain instance initializers/constructors, instance/local variables, or inner classes (maybe)

- records can't directly contain instance/local variables

- annotation types can't directly contain things prohibited in interfaces, or instance/local methods (maybe)

- method declarations of any kind can't directly contain static initializers, instance initializers/constructors, static methods (maybe), or static variables (maybe)

So, not quite "anything goes", but a much shorter and more refined list of prohibitions than we had previously.