Auto merge of #28009 - GuillaumeGomez:patch-1, r=Manishearth

r? @Manishearth

src/librustc_typeck/check/mod.rs

@@ -729,6 +729,9 @@ pub fn check_item_type<'a,'tcx>(ccx: &CrateCtxt<'a,'tcx>, it: &'tcx ast::Item) {
                 if !pty.generics.types.is_empty() {
                     span_err!(ccx.tcx.sess, item.span, E0044,
                         "foreign items may not have type parameters");
+                    span_help!(ccx.tcx.sess, item.span,
+                        "consider using specialization instead of \
+                        type parameters");
                 }
 
                 if let ast::ForeignItemFn(ref fn_decl, _) = item.node {