Fix Unpin impl of (Try)MaybeDone (#2317)

Author: taiki-e

futures-util/src/future/either.rs

@@ -10,9 +10,9 @@ use futures_sink::Sink;
 #[derive(Debug, Clone)]
 pub enum Either<A, B> {
     /// First branch of the type
-    Left(A),
+    Left(/* #[pin] */ A),
     /// Second branch of the type
-    Right(B),
+    Right(/* #[pin] */ B),
 }
 
 impl<A, B> Either<A, B> {

futures-util/src/future/maybe_done.rs

@@ -12,14 +12,16 @@ use futures_core::task::{Context, Poll};
 #[derive(Debug)]
 pub enum MaybeDone<Fut: Future> {
     /// A not-yet-completed future
-    Future(Fut),
+    Future(/* #[pin] */ Fut),
     /// The output of the completed future
     Done(Fut::Output),
     /// The empty variant after the result of a [`MaybeDone`] has been
     /// taken using the [`take_output`](MaybeDone::take_output) method.
     Gone,
 }
 
+impl<Fut: Future + Unpin> Unpin for MaybeDone<Fut> {}
+
 /// Wraps a future into a `MaybeDone`
 ///
 /// # Examples

futures-util/src/future/try_maybe_done.rs

@@ -12,7 +12,7 @@ use futures_core::task::{Context, Poll};
 #[derive(Debug)]
 pub enum TryMaybeDone<Fut: TryFuture> {
     /// A not-yet-completed future
-    Future(Fut),
+    Future(/* #[pin] */ Fut),
     /// The output of the completed future
     Done(Fut::Ok),
     /// The empty variant after the result of a [`TryMaybeDone`] has been
@@ -21,6 +21,8 @@ pub enum TryMaybeDone<Fut: TryFuture> {
     Gone,
 }
 
+impl<Fut: TryFuture + Unpin> Unpin for TryMaybeDone<Fut> {}
+
 /// Wraps a future into a `TryMaybeDone`
 pub fn try_maybe_done<Fut: TryFuture>(future: Fut) -> TryMaybeDone<Fut> {
     TryMaybeDone::Future(future)