add experimental oneshot channel

The `oneshot` channel is gated under the `oneshot_channel` feature.

Signed-off-by: Connor Tsui <connor.tsui20@gmail.com>

Author: connortsui20

library/std/src/sync/mod.rs

@@ -184,6 +184,8 @@ pub use alloc_crate::sync::{Arc, Weak};
 #[unstable(feature = "mpmc_channel", issue = "126840")]
 pub mod mpmc;
 pub mod mpsc;
+#[unstable(feature = "oneshot_channel", issue = "143674")]
+pub mod oneshot;
 
 pub(crate) mod once; // `pub(crate)` for the `sys::sync::once` implementations and `LazyLock`.
 

library/std/src/sync/mpmc/mod.rs

@@ -654,7 +654,7 @@ impl<T> Clone for Sender<T> {
 #[unstable(feature = "mpmc_channel", issue = "126840")]
 impl<T> fmt::Debug for Sender<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.pad("Sender { .. }")
+        f.debug_struct("Sender").finish_non_exhaustive()
     }
 }
 
@@ -1380,7 +1380,7 @@ impl<T> Clone for Receiver<T> {
 #[unstable(feature = "mpmc_channel", issue = "126840")]
 impl<T> fmt::Debug for Receiver<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.pad("Receiver { .. }")
+        f.debug_struct("Receiver").finish_non_exhaustive()
     }
 }
 

library/std/src/sync/mpsc.rs

@@ -1114,8 +1114,10 @@ impl<T> error::Error for SendError<T> {}
 impl<T> fmt::Debug for TrySendError<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match *self {
-            TrySendError::Full(..) => "Full(..)".fmt(f),
-            TrySendError::Disconnected(..) => "Disconnected(..)".fmt(f),
+            TrySendError::Full(..) => f.debug_tuple("TrySendError::Full").finish_non_exhaustive(),
+            TrySendError::Disconnected(..) => {
+                f.debug_tuple("TrySendError::Disconnected").finish_non_exhaustive()
+            }
         }
     }
 }