Rollup merge of rust-lang#27131 - apasel422:issue-20162, r=arielb1

closes rust-lang#20162

Author: steveklabnik

src/test/compile-fail/issue-20162.rs

@@ -0,0 +1,17 @@
+// 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.
+
+struct X { x: i32 }
+
+fn main() {
+    let mut b: Vec<X> = vec![];
+    b.sort();
+    //~^ ERROR the trait `core::cmp::Ord` is not implemented for the type `X`
+}