From 2fd6ae69d1c79635896b643b1094b3805d1ec6c2 Mon Sep 17 00:00:00 2001
From: Jorge Aparicio <jorge@japaric.io>
Date: Sat, 23 Feb 2019 22:38:10 +0100
Subject: [PATCH] `binds` can only appear once in the argument list

---
 macros/src/syntax.rs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/macros/src/syntax.rs b/macros/src/syntax.rs
index ee03b2f5a3..23981d98d0 100644
--- a/macros/src/syntax.rs
+++ b/macros/src/syntax.rs
@@ -973,6 +973,13 @@ fn parse_args(
         let ident_s = ident.to_string();
         match &*ident_s {
             "binds" if accepts_binds => {
+                if binds.is_some() {
+                    return Err(parse::Error::new(
+                        ident.span(),
+                        "argument appears more than once",
+                    ));
+                }
+
                 // #ident
                 let ident = content.parse()?;