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First, I think it might make sense to share the use cases we have for nestmates in Kotlin (those that will work out):
- same as Java: nested/inner classes
- multi-file classes (this is how we emulate free functions that are logically direct members of a package in Kotlin)
Now, there's one issue that does not seem entirely clear to me: does this proposal imply making nested classes truly private? It does not mention allowing ACC\_PRIVATE on classes, so I'm not sure whether this was intended.
In any case it would make sense, I think. I haven't given it much thought yet, but we could probably legalize the ACC\_PRIVATE flag on classes that have a NestChild entry, and check that they are only accessed from their nestmates, right?
(This would only work with Java's every-which-way treatment of access between the nested classes: in Kotlin, for example, nested classes can not access private members of their enclosing class, but such extra restrictions don't seem to be a security concern, because all these classes are in the same compilation unit anyway.)
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