stream: update features and doc for broadcast/watch stream (#3504)

tokio-stream/src/macros.rs

@@ -38,6 +38,16 @@ macro_rules! cfg_time {
     }
 }
 
+macro_rules! cfg_sync {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "sync")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "sync")))]
+            $item
+        )*
+    }
+}
+
 macro_rules! ready {
     ($e:expr $(,)?) => {
         match $e {

tokio-stream/src/wrappers.rs

@@ -1,17 +1,25 @@
 //! Wrappers for Tokio types that implement `Stream`.
 
+/// Error types for the wrappers.
+pub mod errors {
+    cfg_sync! {
+        pub use crate::wrappers::broadcast::BroadcastStreamRecvError;
+    }
+}
+
 mod mpsc_bounded;
 pub use mpsc_bounded::ReceiverStream;
 
 mod mpsc_unbounded;
 pub use mpsc_unbounded::UnboundedReceiverStream;
 
-mod broadcast;
-pub use broadcast::BroadcastStream;
-pub use broadcast::BroadcastStreamRecvError;
+cfg_sync! {
+    mod broadcast;
+    pub use broadcast::BroadcastStream;
 
-mod watch;
-pub use watch::WatchStream;
+    mod watch;
+    pub use watch::WatchStream;
+}
 
 cfg_time! {
     mod interval;

tokio-stream/src/wrappers/broadcast.rs

@@ -12,6 +12,7 @@ use std::task::{Context, Poll};
 ///
 /// [`tokio::sync::broadcast::Receiver`]: struct@tokio::sync::broadcast::Receiver
 /// [`Stream`]: trait@crate::Stream
+#[cfg_attr(docsrs, doc(cfg(feature = "sync")))]
 pub struct BroadcastStream<T> {
     inner: ReusableBoxFuture<(Result<T, RecvError>, Receiver<T>)>,
 }

tokio-stream/src/wrappers/watch.rs

@@ -12,6 +12,7 @@ use tokio::sync::watch::error::RecvError;
 ///
 /// [`tokio::sync::watch::Receiver`]: struct@tokio::sync::watch::Receiver
 /// [`Stream`]: trait@crate::Stream
+#[cfg_attr(docsrs, doc(cfg(feature = "sync")))]
 pub struct WatchStream<T> {
     inner: ReusableBoxFuture<(Result<(), RecvError>, Receiver<T>)>,
 }