swift234

Let the type checker decide which protocol members are visible via conforming types.

Deduced associated types are implemented by allowing name lookup into
a type to find the requirements in  the protocols to which that type
conforms. If the protocol conformance produced the witness for the
requirement via deduction (or, eventually, default definitions), we
use the deduced witness; otherwise, the actual declaration within the
type itself is used.

Previously, the AST-level lookup was deciding whether to filter out
protocol requirements based on the conformance information in the
AST. However, this lead to ordering dependencies, because the type
checker doesn't record the conformances in the AST until we've visited
all of the conformances for a given declaration. This lead to an
oddity where one could have one conformance depend on another's
deduced associated type, but only if that conformance was on a later
extension. Fixes <rdar://problem/14685674>.

As part of this, teach the type checker to re-use normal conformances
that get deserialized, rather than creating new ones. Otherwise, we'll
end up with two different copies of the same conformance running
around.


Swift SVN r7075