Fix #1458 (allow paren'd exprs to be the operator in a do)

Closes #1458

Author: catamorphism

src/libsyntax/parse/parser.rs

@@ -1576,7 +1576,7 @@ impl Parser {
             @{node: expr_call(f, args, true),
               .. *e}
           }
-          expr_path(*) | expr_field(*) | expr_call(*) => {
+          expr_path(*) | expr_field(*) | expr_call(*) | expr_paren(*) => {
             let block = self.parse_lambda_block_expr();
             let last_arg = self.mk_expr(block.span.lo, block.span.hi,
                                     ctor(block));

src/test/run-pass/issue-1458.rs

@@ -0,0 +1,12 @@
+fn plus_one(f: fn() -> int) -> int {
+  return f() + 1;
+}
+
+fn ret_plus_one() -> fn(fn() -> int) -> int {
+  return plus_one;
+}
+
+fn main() {
+    let z = do (ret_plus_one()) || { 2 };
+    assert z == 3;
+}