fix tests on stable

serde/src/ser/impls.rs

@@ -70,9 +70,11 @@ use super::{
     Error,
     Serialize,
     Serializer,
-    IteratorSerializer,
 };
 
+#[cfg(feature = "unstable")]
+use super::IteratorSerializer;
+
 ///////////////////////////////////////////////////////////////////////////////
 
 macro_rules! impl_visit {

serde/src/ser/mod.rs

@@ -18,7 +18,9 @@ use error;
 #[cfg(all(feature = "collections", not(feature = "std")))]
 use collections::String;
 
+#[cfg(feature = "unstable")]
 use core::marker::PhantomData;
+#[cfg(feature = "unstable")]
 use core::cell::RefCell;
 
 pub mod impls;
@@ -418,12 +420,14 @@ pub trait Serializer {
 /// A wrapper type for iterators that implements `Serialize` for iterators whose items implement
 /// `Serialize`. Don't use multiple times. Create new versions of this with the `iterator` function
 /// every time you want to serialize an iterator.
+#[cfg(feature = "unstable")]
 pub struct IteratorSerializer<I>(RefCell<Option<I>>)
     where <I as Iterator>::Item: Serialize,
           I: Iterator;
 
 /// Creates a temporary type that can be passed to any function expecting a `Serialize` and will
 /// serialize the given iterator as a sequence
+#[cfg(feature = "unstable")]
 pub fn iterator<I>(iter: I) -> IteratorSerializer<I>
     where <I as Iterator>::Item: Serialize,
           I: Iterator