add test for issue #20575

closes #20575

Author: Jorge Aparicio

src/test/run-pass/issue-20575.rs

@@ -0,0 +1,19 @@
+// Copyright 2015 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.
+
+// Test that overloaded calls work with zero arity closures
+
+#![feature(box_syntax)]
+
+fn main() {
+    let functions: [Box<Fn() -> Option<()>>; 1] = [box || None];
+
+    let _: Option<Vec<()>> = functions.iter().map(|f| (*f)()).collect();
+}