import TensorFlow

protocol Foo {
  func foo(_ x: Int) -> Self
}

protocol Bar: Foo, Differentiable {
  @differentiable(wrt: self)
  func foo(_ x: Int) -> Self
}

extension KeyPathIterable {
  func foo(_ x: Int) -> Self { self }
}

// This allows KeyPathIterable things to conform to Bar easily.
extension KeyPathIterable where Self: Differentiable {
  // Note: thanks to retroactive conformances, you don't even need this,
  // but if you do accidentally (or intentionally) write it, we should give
  // a nicer compiler error message.
  @differentiable(wrt: self)
  func foo(_ x: Int) -> Self { self }


  @derivative(of: foo(_:), wrt: self)
  func _vjpFoo(_ x: Int) -> (value: Self, pullback: (TangentVector) -> TangentVector) {
    fatalError("Unimplemented")
  }
}

saeta@saeta:~/tmp/repros$ swiftc  foo.swift 
foo.swift:25:19: error: ambiguous reference to 'foo' in '@derivative' attribute
  @derivative(of: foo(_:), wrt: self)
                  ^

foo.swift:25:19: error: ambiguous reference to 'foo' in '@derivative' attribute
  @derivative(of: foo(_:), wrt: self)
                  ^
foo.swift:13:8: note: first potential reference here:
  func foo(_ x: Int) -> Self { self }
       ^
foo.swift:22:8: note: second potential reference here:
  func foo(_ x: Int) -> Self { self }
       ^