From 0d1ab4e9e4e1a6b481a3cf32088ab7d7e7e673ef Mon Sep 17 00:00:00 2001
From: Anthony Ramine <n.oxyde@gmail.com>
Date: Sat, 8 Oct 2016 01:42:58 +0200
Subject: [PATCH] Do not add an empty #[derive()] list in expand_derive (fixes
 #37033)

---
 src/libsyntax_ext/deriving/mod.rs | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/libsyntax_ext/deriving/mod.rs b/src/libsyntax_ext/deriving/mod.rs
index 111596cfe88..fdb10a2beb2 100644
--- a/src/libsyntax_ext/deriving/mod.rs
+++ b/src/libsyntax_ext/deriving/mod.rs
@@ -154,11 +154,13 @@ pub fn expand_derive(cx: &mut ExtCtxt,
     });
     if new_attributes.len() > 0 {
         item = item.map(|mut i| {
-            let list = cx.meta_list(mitem.span,
-                                    intern_and_get_ident("derive"),
-                                    traits);
             i.attrs.extend(new_attributes);
-            i.attrs.push(cx.attribute(mitem.span, list));
+            if traits.len() > 0 {
+                let list = cx.meta_list(mitem.span,
+                                        intern_and_get_ident("derive"),
+                                        traits);
+                i.attrs.push(cx.attribute(mitem.span, list));
+            }
             i
         });
         return vec![Annotatable::Item(item)]
-- 
2.44.0