Accept a LHS formed of a single sequence TT in macro_rules!.

This was already accepted when checking that a macro definition was well-formed but not handled during expansion.

Author: LeoTestard

src/libsyntax/ext/tt/macro_rules.rs

@@ -179,6 +179,7 @@ fn generic_extension<'cx>(cx: &'cx ExtCtxt,
     for (i, lhs) in lhses.iter().enumerate() { // try each arm's matchers
         let lhs_tt = match *lhs {
             TokenTree::Delimited(_, ref delim) => &delim.tts[..],
+            TokenTree::Sequence(..) => ref_slice(lhs),
             _ => cx.span_fatal(sp, "malformed macro lhs")
         };
 

src/test/run-pass/macro-lhs-sequence.rs

@@ -0,0 +1,17 @@
+// 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.
+
+macro_rules! foo(
+    $($i:ident),+ => ()
+);
+
+fn main() {
+    foo!(bar, baz);
+}