Rollup merge of rust-lang#29537 - bltavares:issue-24954, r=steveklabnik

Closes rust-lang#24954

src/test/run-pass/issue-24954.rs

@@ -0,0 +1,22 @@
+// 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.
+
+macro_rules! foo {
+    ($y:expr) => ({
+        $y = 2;
+    })
+}
+
+#[allow(unused_variables)]
+#[allow(unused_assignments)]
+fn main() {
+    let mut x = 1;
+    foo!(x);
+}