From fc60797f7f3079288bdd1717dedbb885eaf1dbfa Mon Sep 17 00:00:00 2001
From: Vadim Chugunov <vadimcn@gmail.com>
Date: Mon, 6 Oct 2014 23:15:12 -0700
Subject: [PATCH] Fix the most egregious instances of "local ambiguity:
 multiple parsing options..." error in macros, which often occurs when trying
 to match parts of Rust syntax. For example, this matcher: `fn $name:ident(
 $($param:ident : $pty:ty),* )` would fail when parsing `fn foo()`, because
 macro parser wouldn't realize that an ident cannot start with `)`.

This resolves #5902, and at least partially mitigates #9364 and #3232.
---
 src/libsyntax/ext/tt/macro_parser.rs | 11 +++++++++-
 src/test/run-pass/macro-nt-list.rs   | 30 ++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)
 create mode 100644 src/test/run-pass/macro-nt-list.rs

diff --git a/src/libsyntax/ext/tt/macro_parser.rs b/src/libsyntax/ext/tt/macro_parser.rs
index 090b39eee47..88376108fec 100644
--- a/src/libsyntax/ext/tt/macro_parser.rs
+++ b/src/libsyntax/ext/tt/macro_parser.rs
@@ -350,7 +350,16 @@ pub fn parse(sess: &ParseSess,
                         sp_lo: sp.lo
                     });
                   }
-                  MatchNonterminal(_,_,_) => { bb_eis.push(ei) }
+                  MatchNonterminal(_,_,_) => {
+                    // Built-in nonterminals never start with these tokens,
+                    // so we can eliminate them from consideration.
+                    match tok {
+                        token::RPAREN |
+                        token::RBRACE |
+                        token::RBRACKET => {},
+                        _ => bb_eis.push(ei)
+                    }
+                  }
                   MatchTok(ref t) => {
                     let mut ei_t = ei.clone();
                     if token_name_eq(t,&tok) {
diff --git a/src/test/run-pass/macro-nt-list.rs b/src/test/run-pass/macro-nt-list.rs
new file mode 100644
index 00000000000..2a00e5b8616
--- /dev/null
+++ b/src/test/run-pass/macro-nt-list.rs
@@ -0,0 +1,30 @@
+// Copyright 2014 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.
+
+#![feature(macro_rules)]
+
+macro_rules! list (
+    ( ($($id:ident),*) ) => (());
+    ( [$($id:ident),*] ) => (());
+    ( {$($id:ident),*} ) => (());
+)
+
+macro_rules! tt_list (
+    ( ($($tt:tt),*) ) => (());
+)
+
+pub fn main() {
+    list!( () );
+    list!( [] );
+    list!( {} );
+
+    tt_list!( (a, b, c) );
+    tt_list!( () );
+}