[SR-9278] Unable to constrain a nested type which introduces no new generics

[djehrlich]

Previous ID	SR-9278
Radar	None
Original Reporter	@djehrlich
Type	Bug
Status	Closed
Resolution	Done

Environment

Xcode 10.1

Apple Swift version 4.2.1 (swiftlang-100.11.42 clang-1000.11.45.1)

Additional Detail from JIRA

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

md5: 7b4c5a4e94c7c3bf6e58535d54334a90

Issue Description:

class Outer<Channel> {
    class Generic<T> where Channel == Int {}
    class Nongeneric where Channel == Int {}
}

Should the “Nongeneric” inner class compile?

The “Generic” inner class compiles, but the “Nongeneric” inner class fails to compile with the error:

‘where’ clause cannot be attached to a non-generic declaration

[belkadan]

I'm not sure either of them should compile. @slavapestov, @DougGregor?

[slavapestov]

I agree we should revisit this. I'm in favor of allowing both to compile, but in the meantime, you can define Nongeneric inside a constrained extension of Outer instead.

[DougGregor]

I agree that it should be consistent either way, and I'd be fine with pursuing an extension to allow both to compile.

[slavapestov]

This is going through swift evolution now: https://forums.swift.org/t/where-clauses-on-contextually-generic-declarations/22449

[AnthonyLatsis]

#23489

[AnthonyLatsis]

Implemented (Swift 5.3)