The presence of a generic signature in a XREF means that we should only find the result in a (further-constrained) extension with that generic signature. The absence of a generic signature in a XREF means that we should not find the result in a constrained extension. We implemented the former but not the latter, which would lead to deserialization failures if one had both constrained and unconstrained extensions with the same property in them. Methods/initializers weren’t a problem because the generic signature is (redundantly) encoded in their interface type.
We no longer allow extensions to provide generic parameters, and the
ability to parse the syntax
extension Array<String> { ... }
is causing confusion. Fixes rdar://problem/20873336.
Swift SVN r28468
