[SR-7304] typealias overriding associated type ... is better expressed as same-type constraint

[swift-ci]

Previous ID	SR-7304
Radar	rdar://problem/39040799
Original Reporter	tannernelson (JIRA User)
Type	Bug
Status	Resolved
Resolution	Duplicate

Attachment: Download

Environment

confirmed on Swift 4.1 branch 03-18 and 03-26
macOS sierra 10.12.6
Xcode 9.3 beta 4

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: 2e2170ea1da2050209f5105ba6dcd674

duplicates:

• [SR-4685] Can't infer associatedtypes with where clause #47262

Issue Description:

This warning cropped up recently in the Swift 4.1 pre-releases.

Swift either needs to "generate" these type-aliases when there is a same-type constraint or let users add them in extensions. Right now, Swift just generates this warning then still requires a concrete type-alias to be defined to use any associated types that may reference that type.

See the twitter thread here: https://twitter.com/UINT_MIN/status/979381922009825280

[belkadan]

cc @DougGregor

(that isn't the solution I'm after; there should be no typealias needed at all)

[belkadan]

@swift-ci create