added #[must_use] for impl Future structs

examples/guessing.rs

@@ -63,7 +63,7 @@ async fn main() -> Result<(), failure::Error> {
 
     let mut incoming = listener.incoming();
     while let Some(stream) = incoming.next().await {
-        runtime::spawn(play(stream?));
+        runtime::spawn(play(stream?)).await?;
     }
     Ok(())
 }

examples/tcp-echo.rs

@@ -23,7 +23,8 @@ async fn main() -> std::io::Result<()> {
             let (reader, writer) = &mut stream.split();
             reader.copy_into(writer).await?;
             Ok::<(), std::io::Error>(())
-        });
+        })
+        .await?;
     }
     Ok(())
 }

rustfmt.toml

@@ -0,0 +1 @@
+unstable_features = true

src/net/tcp.rs

@@ -217,6 +217,7 @@ impl AsyncWrite for TcpStream {
 ///
 /// [`TcpStream::connect`]: struct.TcpStream.html#method.connect
 /// [`TcpStream`]: struct.TcpStream.html
+#[must_use = "futures do nothing unless polled"]
 pub struct Connect {
     addrs: Option<io::Result<VecDeque<SocketAddr>>>,
     last_err: Option<io::Error>,
@@ -452,6 +453,7 @@ impl TcpListener {
 ///
 /// [`TcpStream::accept`]: struct.TcpStream.html#method.accept
 /// [`TcpStream`]: struct.TcpStream.html
+#[must_use = "futures do nothing unless polled"]
 #[derive(Debug)]
 pub struct Accept<'stream> {
     inner: Incoming<'stream>,
@@ -479,6 +481,7 @@ impl<'stream> Future for Accept<'stream> {
 /// [`incoming`]: struct.TcpListener.html#method.incoming
 /// [`accept`]: struct.TcpStream.html#method.accept
 /// [`TcpListener`]: struct.TcpStream.html
+#[must_use = "streams do nothing unless polled"]
 #[derive(Debug)]
 pub struct Incoming<'listener> {
     inner: &'listener mut TcpListener,

src/net/udp.rs

@@ -358,6 +358,7 @@ impl UdpSocket {
 /// On success, returns the number of bytes written.
 ///
 /// [`UdpSocket::send_to`]: struct.UdpSocket.html#method.send_to
+#[must_use = "futures do nothing unless polled"]
 #[derive(Debug)]
 pub struct SendTo<'socket, 'buf> {
     /// The open socket we use to send the message from.
@@ -392,6 +393,7 @@ impl<'socket, 'buf> Future for SendTo<'socket, 'buf> {
 /// On success, returns the number of bytes read and the origin.
 ///
 /// [`UdpSocket::recv_from`]: struct.UdpSocket.html#method.recv_from
+#[must_use = "futures do nothing unless polled"]
 #[derive(Debug)]
 pub struct RecvFrom<'socket, 'buf> {
     socket: &'socket mut UdpSocket,

src/task.rs

@@ -45,6 +45,7 @@ where
 /// A handle that awaits the result of a [`spawn`]ed future.
 ///
 /// [`spawn`]: fn.spawn.html
+#[must_use = "futures do nothing unless polled"]
 #[derive(Debug)]
 pub struct JoinHandle<T> {
     pub(crate) rx: futures::channel::oneshot::Receiver<T>,