add must_use for Future (#450)

core/src/connection_reuse.rs

@@ -562,6 +562,7 @@ where
 }
 
 /// Implementation of `Future` that yields the next incoming substream from a dialed connection.
+#[must_use = "futures do nothing unless polled"]
 pub struct ConnectionReuseIncoming<T, D, M>
 where
     T: Transport,

core/src/either.rs

@@ -213,6 +213,7 @@ where
 }
 
 #[derive(Debug, Copy, Clone)]
+#[must_use = "futures do nothing unless polled"]
 pub enum EitherOutbound<A: StreamMuxer, B: StreamMuxer> {
     A(A::OutboundSubstream),
     B(B::OutboundSubstream),
@@ -220,6 +221,7 @@ pub enum EitherOutbound<A: StreamMuxer, B: StreamMuxer> {
 
 /// Implements `Stream` and dispatches all method calls to either `First` or `Second`.
 #[derive(Debug, Copy, Clone)]
+#[must_use = "futures do nothing unless polled"]
 pub enum EitherListenStream<A, B> {
     First(A),
     Second(B),
@@ -248,6 +250,7 @@ where
 //         If Rust had impl Trait we could use the Either enum from the futures crate and add some
 //         modifiers to it. This custom enum is a combination of Either and these modifiers.
 #[derive(Debug, Copy, Clone)]
+#[must_use = "futures do nothing unless polled"]
 pub enum EitherListenUpgrade<A, B> {
     First(A),
     Second(B),

core/src/swarm.rs

@@ -222,6 +222,7 @@ where
 }
 
 /// Future that must be driven to completion in order for the swarm to work.
+#[must_use = "futures do nothing unless polled"]
 pub struct SwarmFuture<T, H>
 where
     T: MuxedTransport + 'static, // TODO: 'static :-/

core/src/transport/interruptible.rs

@@ -96,6 +96,7 @@ pub struct Interrupt {
     _tx: oneshot::Sender<()>,
 }
 
+#[must_use = "futures do nothing unless polled"]
 pub struct InterruptibleDial<F> {
     inner: F,
     rx: future::Shared<oneshot::Receiver<()>>,

core/src/unique.rs

@@ -342,6 +342,7 @@ impl<T> Drop for UniqueConnec<T> {
 }
 
 /// Future returned by `UniqueConnec::dial()`.
+#[must_use = "futures do nothing unless polled"]
 pub struct UniqueConnecFuture<T> {
     inner: Weak<Mutex<UniqueConnecInner<T>>>,
 }

core/src/upgrade/choice.rs

@@ -92,6 +92,7 @@ pub enum EitherUpgradeIdentifier<A, B> {
 //         If Rust had impl Trait we could use the Either enum from the futures crate and add some
 //         modifiers to it. This custom enum is a combination of Either and these modifiers.
 #[derive(Debug, Copy, Clone)]
+#[must_use = "futures do nothing unless polled"]
 pub enum EitherConnUpgrFuture<A, B> {
     First(A),
     Second(B),