Add check on find_best_match_for_name and improve help message for undefined macro

src/libsyntax/ext/base.rs

@@ -760,7 +760,12 @@ impl<'a> ExtCtxt<'a> {
                               err: &mut DiagnosticBuilder<'a>) {
         let names = &self.syntax_env.names;
         if let Some(suggestion) = find_best_match_for_name(names.iter(), name, None) {
-            err.fileline_help(span, &format!("did you mean `{}!`?", suggestion));
+            if suggestion != name {
+                err.fileline_help(span, &format!("did you mean `{}!`?", suggestion));
+            } else {
+                err.fileline_help(span, &format!("have you added the `#[macro_use]` on the \
+                                                  module/import?"));
+            }
         }
     }
 }