Add a message for when a . follows a macro invocation

src/libsyntax/parse/parser.rs

@@ -3592,6 +3592,16 @@ impl<'a> Parser<'a> {
             let hi = self.span.hi;
 
             if id.name == token::special_idents::invalid.name {
+                if self.token == token::Dot {
+                    let span = self.span;
+                    let token_string = self.this_token_to_string();
+                    self.span_err(span,
+                                  format!("expected statement, found `{}`",
+                                          token_string).as_slice());
+                    let mac_span = mk_sp(lo, hi);
+                    self.span_help(mac_span, "try parenthesizing this macro invocation");
+                    self.abort_if_errors();
+                }
                 P(spanned(lo, hi, StmtMac(
                     spanned(lo, hi, MacInvocTT(pth, tts, EMPTY_CTXT)), false)))
             } else {

src/test/compile-fail/macro-invocation-dot-help.rs

@@ -0,0 +1,14 @@
+// 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.
+
+fn main() {
+    foo!() //~ HELP try parenthesizing this macro invocation
+    .bar //~ ERROR expected statement
+}