struct W<T> {}

struct S<C1: Collection> {
  init<C2>(_ c2: W<C2>) where C2: Collection, C1.Element == W<C2.Element> {
    fatalError("implementation not relevant to bug report")
  }
}

let _ = S<[W<String>]>(W<[Int]>())

// Actual diagnostic:
//   error: type of expression is ambiguous without more context
//   let _ = S<[W<String>]>(W<[Int]>())
//           ^~~~~~~~~~~~~~~~~~~~~~~~~

// Desired diagnostic: anything informative about the type mismatch. Maybe:
//   error: initializer requires "W<String>" and "W<Int>" to be equivalent
//   let _ = S<[W<String>]>(W<[Int]>())
//           ^
//
//   note: where C1 == [W<String>] and C2 == [Int]
//   init<C2>(_ c2: W<C2>) where C2: Collection, C1.Element == W<C2.Element> {
//   ^