Fix some Unpin implementations

Author: taiki-e

futures-util/src/future/chain.rs

@@ -10,6 +10,8 @@ pub(crate) enum Chain<Fut1, Fut2, Data> {
     Empty,
 }
 
+impl<Fut1: Unpin, Fut2: Unpin, Data> Unpin for Chain<Fut1, Fut2, Data> {}
+
 impl<Fut1, Fut2, Data> Chain<Fut1, Fut2, Data> {
     pub(crate)fn is_terminated(&self) -> bool {
         if let Chain::Empty = *self { true } else { false }

futures-util/src/sink/close.rs

@@ -12,6 +12,8 @@ pub struct Close<'a, Si: Sink<Item> + Unpin + ?Sized, Item> {
     _phantom: PhantomData<fn(Item)>,
 }
 
+impl<Si: Sink<Item> + Unpin + ?Sized, Item> Unpin for Close<'_, Si, Item> {}
+
 /// A future that completes when the sink has finished closing.
 ///
 /// The sink itself is returned after closeing is complete.

futures-util/src/sink/drain.rs

@@ -30,6 +30,8 @@ pub fn drain<T>() -> Drain<T> {
     Drain { marker: PhantomData }
 }
 
+impl<T> Unpin for Drain<T> {}
+
 impl<T> Sink<T> for Drain<T> {
     type Error = Never;
 

futures-util/src/stream/pending.rs

@@ -17,6 +17,8 @@ pub fn pending<T>() -> Pending<T> {
     Pending { _data: marker::PhantomData }
 }
 
+impl<T> Unpin for Pending<T> {}
+
 impl<T> FusedStream for Pending<T> {
     fn is_terminated(&self) -> bool {
         true

futures-util/src/try_future/try_chain.rs

@@ -10,6 +10,8 @@ pub(crate) enum TryChain<Fut1, Fut2, Data> {
     Empty,
 }
 
+impl<Fut1: Unpin, Fut2: Unpin, Data> Unpin for TryChain<Fut1, Fut2, Data> {}
+
 pub(crate) enum TryChainAction<Fut2>
     where Fut2: TryFuture,
 {