[AutoDiff] Fix incorrectly sorted members of synthesized 'TangentVector'.

[rxwei]

Do not mark synthesized TangentVector members as synthesized so that the type checker won't sort them. We would like tangent vector members to have the same order as the properties in the parent declaration.

Also add typealias TangentVector = Self to the synthesized TangentVector so that it will not need its own Differentiable conformance derivation.

Resolves SR-14241 / rdar://74659803.

[rxwei]

@CodaFi With this fix, things seems to work fine without the need to manually evaluate TangentVector's conformances to the inherited protocols. Let me know if you still think it's the right fix.

  struct TangentVector : AdditiveArithmetic, Differentiable {
    @_hasStorage var simd: Array<Float>.DifferentiableView { get set }
    @_hasStorage var scalar: Float { get set }
    init(simd: Array<Float>.DifferentiableView, scalar: Float)
    typealias TangentVector = Thing.TangentVector
    static var zero: Thing.TangentVector { get }
    static func + (lhs: Thing.TangentVector, rhs: Thing.TangentVector) -> Thing.TangentVector
    static func - (lhs: Thing.TangentVector, rhs: Thing.TangentVector) -> Thing.TangentVector
    static func __derived_struct_equals(_ a: Thing.TangentVector, _ b: Thing.TangentVector) -> Bool
  }

I also tried your other suggestion to call getABIMembers() instead of getStoredProperties(), but that didn't seem to fix it.

[rxwei]

@swift-ci please test

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 4f531c3f148f73ce3a60cd0629718d8cbb245f8b

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 4f531c3f148f73ce3a60cd0629718d8cbb245f8b

[rxwei]

@swift-ci please test

[DougGregor]

We should make this specific to TangentVector, not cover all implicit decls.

[slavapestov]

@rxwei Perhaps either the getParsedMembers() or getMembers() request on TangentVector should be where the stored properties are generated?

[rxwei]

@rxwei Perhaps either the getParsedMembers() or getMembers() request on TangentVector should be where the stored properties are generated?

They are generated by the parent decl's conformance request, since Differentiable conformance derivation generates the nested TangentVector and its properties. I think the getStoredProperties() that caused the bug is when the Differentiable conformance of the TangentVector itself gets requested.

[rxwei]

I attempted calling getParsedMembers() and getABIMembers() instead of calling getStoredProperties() in various places but it did not work; it looks like synthesized members are always sorted. What ended up working is marking TangentVector members as not synthesized. Thanks @CodaFi and @slavapestov for the suggestions!

[rxwei]

@swift-ci please test

[rxwei]

Since this change is now local to Differentiable derived conformances and does not touch other parts of the compiler, I'll go ahead and merge this in. Any additional feedback is welcome.