[SR-6232] Bogus diagnostic: 'X' does not have a member type named 'XXX'; did you mean 'XXX'

[slavapestov]

Previous ID	SR-6232
Radar	rdar://problem/35730965
Original Reporter	@slavapestov
Type	Bug

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug
Assignee	@DougGregor
Priority	Medium

md5: aeb9a0d8418dfab5ba0e77147f17e8f0

Issue Description:

extension Collection { typealias XXX = Int }

func foo<X : Collection>(_: X.XXX, _: X) {}

[belkadan]

This is hardly the only problem with typealiases in protocol extensions…

[airspeedswift]

This is blocking making #12641 source-compatible for people already writing IndexDistance == Int (unless there’s another way of giving access to IndexDistance to Collection adopters)

[slavapestov]

I think the problem is that when the GSB looks up members it passes 'ignoreNewExtensions' to lookupDirect(), to solve circularity issues. We could change this back if we solve the underlying circularity.

[airspeedswift]

@swift-ci create

[slavapestov]

This was fixed a while ago.