add test for #24421

Fixes #24421.

src/test/ui/closure-expected-type/issue-24421.rs

@@ -0,0 +1,20 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-pass
+
+fn test<F: Fn(&u64, &u64)>(f: F) {}
+
+fn main() {
+    test(|x,      y     | {});
+    test(|x:&u64, y:&u64| {});
+    test(|x:&u64, y     | {});
+    test(|x,      y:&u64| {});
+}