[SR-14229] [AutoDiff] conformance of synthesized TangentVector doesn't work

[83b09dda-53f5-4663-b44c-87fd2a9a8717]

Previous ID	SR-14229
Radar	rdar://problem/81170168
Original Reporter	@marcrasi
Type	Bug

Additional Detail from JIRA

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

md5: 02544c29a1fa7eb644c287b7535e0342

is duplicated by:

• SR-14959 [AutoDiff] Declaring protocol conformances for synthesized TangentVectors sometimes doesn't do anything

Issue Description:

Code:

public protocol P {}

public struct S: Differentiable {
  var x: Float = 0
  public init() {}

  //public struct TangentVector: AdditiveArithmetic, Differentiable {
  //  var x: Float = 0
  //}
  //public func move(along direction: TangentVector) { fatalError() }
}

extension S.TangentVector: P {}

func f<T: Differentiable>(_ t: T) where T.TangentVector: P {}

f(S())

Error:

module.swift:17:1: error: global function 'f' requires that 'S.TangentVector' conform to 'P'
f(S())
^
module.swift:15:6: note: where 'T.TangentVector' = 'S.TangentVector'
func f<T: Differentiable>(_ t: T) where T.TangentVector: P {}
     ^

This seems related to the synthesis because if you uncomment the custom TangentVector it compiles successfully.

[rxwei]

@swift-ci create

[jkshtj]

Issue still exists on 05/24 toolchain.