Richard Wei e29c19cf8b [AutoDiff] [Sema] Fix '@differentiable' witness matching regression. (#34533) ...

When checking protocol conformances with `@differentiable` requirements, the type checker is supposed to accept omissions of `@differentiable` attributes when there exsits an attribute that covers a superset of the differentiation configuration. This was accidentally regressed in apple/swift#33776 which made the following test case fail to compile. This is fixed by adjusting the witness matching conditions.

```swift
// rdar://70348904 reproducer:
public protocol P: Differentiable {
    @differentiable(wrt: self)
    @differentiable(wrt: (self, x))
    func foo(_ x: Float) -> Float
}

public struct S: P {}

extension S {
    // This had worked until apple/swift#33776.
    @differentiable(wrt: (self, x))
    public func foo(_ x: Float) -> Float { x }
}
```

Also fix some suboptimal diagnostics where more information could be shown.

Resolves rdar://70348904.

2020-11-01 17:10:03 -08:00

..

Inputs

…

main.swift

…

protocol_default_implementation_witness.swift

…