Add feature gate io

serde2/benches/bench_log.rs

@@ -1,4 +1,4 @@
-#![feature(plugin)]
+#![feature(plugin, io)]
 #![allow(non_camel_case_types)]
 
 #[plugin]

serde2/src/lib.rs

@@ -1,3 +1,5 @@
+#![feature(io)]
+
 extern crate unicode;
 
 //pub use ser::{Serialize, Serializer};