Fix NoAccessLevelOnExtensionDeclaration to update members inside #if blocks.

[allevato]

Fixes #966.

This rewrites the rule entirely to take advantage of the natural recursion of visiting the extension's children instead of trying to rewrite and replace the member list at the extension level.

I've tended to avoid the idea of writing stateful format rules like this, because pushing state down from a node to its children would normally require maintaining a stack of information. But in this case, the problem is a lot simpler because extensions can't be nested, so there's never more than one level of state to track.

[ahoppen]

I’m sorry to disappoint you but nesting extensions is not a parser error. The following parsers fine

extension A {
  extension B {   
  }
}

Nested extensions only get diagnosed at type-checking time, so I think we do need to handle them…

[allevato]

I’m sorry to disappoint you but nesting extensions is not a parser error. The following parsers fine

extension A {
  extension B {   
  }
}

Nested extensions only get diagnosed at type-checking time, so I think we do need to handle them…

Ugh, yeah, you're right.

Do you have a preference for how you'd like them handled? We could manage the stack and do the same thing for nested extensions that we would for top-level ones, or we could just ignore nested extensions because they're obviously broken.

[ahoppen]

I would just not walk into nested extensions. Leaving them as-is is probably the best thing we can do.