impl FusedStream for Buffered (#2676)

Author: arcnmx

futures-util/src/stream/stream/buffered.rs

@@ -1,4 +1,4 @@
-use crate::stream::{Fuse, FuturesOrdered, StreamExt};
+use crate::stream::{Fuse, FusedStream, FuturesOrdered, StreamExt};
 use core::fmt;
 use core::num::NonZeroUsize;
 use core::pin::Pin;
@@ -100,6 +100,16 @@ where
     }
 }
 
+impl<St> FusedStream for Buffered<St>
+where
+    St: Stream,
+    St::Item: Future,
+{
+    fn is_terminated(&self) -> bool {
+        self.stream.is_done() && self.in_progress_queue.is_terminated()
+    }
+}
+
 // Forwarding impl of Sink from the underlying stream
 #[cfg(feature = "sink")]
 impl<S, Item> Sink<Item> for Buffered<S>