Be smart about span of parenthesized expression in macro

Author: sanxiyn

src/librustc/hir/lowering.rs

@@ -1261,7 +1261,10 @@ impl<'a> LoweringContext<'a> {
                 }
                 ExprKind::Paren(ref ex) => {
                     return self.lower_expr(ex).map(|mut ex| {
-                        ex.span = e.span;
+                        // include parens in span, but only if it is a super-span.
+                        if e.span.contains(ex.span) {
+                            ex.span = e.span;
+                        }
                         // merge attributes into the inner expression.
                         ex.attrs.update(|attrs| {
                             attrs.prepend(e.attrs.clone())

src/test/compile-fail/paren-span.rs

@@ -0,0 +1,31 @@
+// Copyright 2016 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.
+
+// Be smart about span of parenthesized expression in macro.
+
+macro_rules! paren {
+    ($e:expr) => (($e))
+    //            ^^^^ do not highlight here
+}
+
+mod m {
+    pub struct S {
+        x: i32
+    }
+    pub fn make() -> S {
+        S { x: 0 }
+    }
+}
+
+fn main() {
+    let s = m::make();
+    paren!(s.x); //~ ERROR field `x` of struct `m::S` is private
+    //     ^^^ highlight here
+}