swift-mirror/test/Constraints/one_way_closure_params.swift

// RUN: %target-typecheck-verify-swift -swift-version 4 -experimental-one-way-closure-params

func testBasic() {
  let _: (Float) -> Float = { $0 + 1 }

  let _ = { $0 + 1 } // expected-error{{unable to infer type of a closure parameter '$0' in the current context}}
}