// RUN: %target-swift-frontend %s -parse -verify

// Distributed under the terms of the MIT license
// Test case submitted to project by https://github.com/tmu (Teemu Kurppa)
// rdar://18175202

func d<b: Sequence, e where Optional<e> == b.Iterator.Element>(c : b) -> e? {
  for mx : e? in c { // expected-warning {{immutable value 'mx' was never used}}
  }
}