Add parse support for expr_ext.

Author: graydon

src/comp/front/ast.rs

@@ -164,6 +164,7 @@ tag expr_ {
     expr_field(@expr, ident, ann);
     expr_index(@expr, @expr, ann);
     expr_path(path, option.t[def], ann);
+    expr_ext(vec[@expr], option.t[@expr], ann);
 }
 
 type lit = spanned[lit_];

src/comp/front/parser.rs

@@ -586,6 +586,17 @@ impure fn parse_bottom_expr(parser p) -> @ast.expr {
             ex = ast.expr_bind(e, es.node, ast.ann_none);
         }
 
+        case (token.POUND) {
+            p.bump();
+            auto pf = parse_expr;
+            auto es = parse_seq[@ast.expr](token.LPAREN,
+                                           token.RPAREN,
+                                           some(token.COMMA),
+                                           pf, p);
+            hi = es.span;
+            ex = ast.expr_ext(es.node, none[@ast.expr], ast.ann_none);
+        }
+
         case (_) {
             auto lit = parse_lit(p);
             hi = lit.span;