auto merge of #16632 : pcwalton/rust/unboxed-closures-euv, r=luqmana

expression use visitor.

Closes #16166.

r? @huonw

src/test/run-pass/unboxed-closures-direct-sugary-call.rs

@@ -0,0 +1,17 @@
+// Copyright 2014 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.
+
+#![feature(unboxed_closures, overloaded_calls)]
+
+fn main() {
+    let mut unboxed = |&mut:| {};
+    unboxed();
+}
+