add test for #20803

closes #20803

Author: apasel422

src/test/run-pass/issue-20803.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.
+
+use std::ops::Add;
+
+fn foo<T>(x: T) -> <i32 as Add<T>>::Output where i32: Add<T> {
+    42i32 + x
+}
+
+fn main() {
+    println!("{}", foo(0i32));
+}