From ad61ff4b817f8581ea4c12f897f5e6baafe27952 Mon Sep 17 00:00:00 2001
From: Keegan McAllister <kmcallister@mozilla.com>
Date: Tue, 18 Nov 2014 14:02:40 -0800
Subject: deriving: error out when used on a non-type

Besides being more helpful, this gives us the flexibility to later define
a meaning for something like

    #[deriving(...)]
    mod bar { ... }
---
 src/libsyntax/ext/deriving/generic/mod.rs | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

(limited to 'src/libsyntax')

diff --git a/src/libsyntax/ext/deriving/generic/mod.rs b/src/libsyntax/ext/deriving/generic/mod.rs
index dccc12e406b..eec3805721a 100644
--- a/src/libsyntax/ext/deriving/generic/mod.rs
+++ b/src/libsyntax/ext/deriving/generic/mod.rs
@@ -335,7 +335,7 @@ pub fn combine_substructure<'a>(f: CombineSubstructureFunc<'a>)
 impl<'a> TraitDef<'a> {
     pub fn expand(&self,
                   cx: &mut ExtCtxt,
-                  _mitem: &ast::MetaItem,
+                  mitem: &ast::MetaItem,
                   item: &ast::Item,
                   push: |P<ast::Item>|) {
         let newitem = match item.node {
@@ -351,7 +351,10 @@ impl<'a> TraitDef<'a> {
                                      item.ident,
                                      generics)
             }
-            _ => return
+            _ => {
+                cx.span_err(mitem.span, "`deriving` may only be applied to structs and enums");
+                return;
+            }
         };
         // Keep the lint attributes of the previous item to control how the
         // generated implementations are linted
-- 
cgit 1.4.1-3-g733a5