Clean up error types

futures-channel/src/mpsc/mod.rs

@@ -81,8 +81,6 @@
 use futures_core::stream::{FusedStream, Stream};
 use futures_core::task::{Context, Poll, Waker};
 use futures_core::task::__internal::AtomicWaker;
-use std::any::Any;
-use std::error::Error;
 use std::fmt;
 use std::pin::Pin;
 use std::sync::{Arc, Mutex};
@@ -166,7 +164,7 @@ enum SendErrorKind {
 
 /// The error type returned from [`try_next`](Receiver::try_next).
 pub struct TryRecvError {
-    _inner: (),
+    _priv: (),
 }
 
 impl fmt::Display for SendError {
@@ -179,7 +177,7 @@ impl fmt::Display for SendError {
     }
 }
 
-impl Error for SendError {}
+impl std::error::Error for SendError {}
 
 impl SendError {
     /// Returns true if this error is a result of the channel being full.
@@ -217,7 +215,7 @@ impl<T> fmt::Display for TrySendError<T> {
     }
 }
 
-impl<T: Any> Error for TrySendError<T> {}
+impl<T: core::any::Any> std::error::Error for TrySendError<T> {}
 
 impl<T> TrySendError<T> {
     /// Returns true if this error is a result of the channel being full.
@@ -254,7 +252,7 @@ impl fmt::Display for TryRecvError {
     }
 }
 
-impl Error for TryRecvError {}
+impl std::error::Error for TryRecvError {}
 
 #[derive(Debug)]
 struct Inner<T> {
@@ -834,7 +832,7 @@ impl<T> Receiver<T> {
             Poll::Ready(msg) => {
                 Ok(msg)
             },
-            Poll::Pending => Err(TryRecvError { _inner: () }),
+            Poll::Pending => Err(TryRecvError { _priv: () }),
         }
     }
 

futures-core/src/task/spawn.rs

@@ -55,7 +55,7 @@ pub trait LocalSpawn {
 
 /// An error that occurred during spawning.
 pub struct SpawnError {
-    _hidden: (),
+    _priv: (),
 }
 
 impl fmt::Debug for SpawnError {
@@ -78,7 +78,7 @@ impl std::error::Error for SpawnError {}
 impl SpawnError {
     /// Spawning failed because the executor has been shut down.
     pub fn shutdown() -> Self {
-        Self { _hidden: () }
+        Self { _priv: () }
     }
 
     /// Check whether spawning failed to the executor being shut down.

futures-executor/src/enter.rs

@@ -7,16 +7,29 @@ thread_local!(static ENTERED: Cell<bool> = Cell::new(false));
 ///
 /// For more details, see [`enter` documentation](enter()).
 pub struct Enter {
-    _a: ()
+    _priv: (),
 }
 
 /// An error returned by `enter` if an execution scope has already been
 /// entered.
-#[derive(Debug)]
 pub struct EnterError {
-    _a: (),
+    _priv: (),
 }
 
+impl fmt::Debug for EnterError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("EnterError").finish()
+    }
+}
+
+impl fmt::Display for EnterError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "an execution scope has already been entered")
+    }
+}
+
+impl std::error::Error for EnterError {}
+
 /// Marks the current thread as being within the dynamic extent of an
 /// executor.
 ///
@@ -42,11 +55,11 @@ pub struct EnterError {
 pub fn enter() -> Result<Enter, EnterError> {
     ENTERED.with(|c| {
         if c.get() {
-            Err(EnterError { _a: () })
+            Err(EnterError { _priv: () })
         } else {
             c.set(true);
 
-            Ok(Enter { _a: () })
+            Ok(Enter { _priv: () })
         }
     })
 }

futures-util/src/future/abortable.rs

@@ -2,6 +2,7 @@ use crate::task::AtomicWaker;
 use futures_core::future::Future;
 use futures_core::task::{Context, Poll};
 use pin_utils::unsafe_pinned;
+use core::fmt;
 use core::pin::Pin;
 use core::sync::atomic::{AtomicBool, Ordering};
 use alloc::sync::Arc;
@@ -124,6 +125,15 @@ pub fn abortable<Fut>(future: Fut) -> (Abortable<Fut>, AbortHandle)
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub struct Aborted;
 
+impl fmt::Display for Aborted {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "`Abortable` future has been aborted")
+    }
+}
+
+#[cfg(feature = "std")]
+impl std::error::Error for Aborted {}
+
 impl<Fut> Future for Abortable<Fut> where Fut: Future {
     type Output = Result<Fut::Output, Aborted>;
 

futures-util/src/lock/bilock.rs

@@ -11,10 +11,6 @@ use core::sync::atomic::AtomicUsize;
 use core::sync::atomic::Ordering::SeqCst;
 use alloc::boxed::Box;
 use alloc::sync::Arc;
-#[cfg(feature = "std")]
-use std::any::Any;
-#[cfg(feature = "std")]
-use std::error::Error;
 
 /// A type of futures-powered synchronization primitive which is a mutex between
 /// two possible owners.
@@ -218,7 +214,7 @@ impl<T> fmt::Display for ReuniteError<T> {
 }
 
 #[cfg(feature = "std")]
-impl<T: Any> Error for ReuniteError<T> {}
+impl<T: core::any::Any> std::error::Error for ReuniteError<T> {}
 
 /// Returned RAII guard from the `poll_lock` method.
 ///

futures-util/src/stream/split.rs

@@ -3,10 +3,6 @@ use futures_core::task::{Context, Poll};
 use futures_sink::Sink;
 use core::fmt;
 use core::pin::Pin;
-#[cfg(feature = "std")]
-use std::any::Any;
-#[cfg(feature = "std")]
-use std::error::Error;
 
 use crate::lock::BiLock;
 
@@ -47,12 +43,12 @@ fn SplitSink<S: Sink<Item>, Item>(lock: BiLock<S>) -> SplitSink<S, Item> {
 /// A `Sink` part of the split pair
 #[derive(Debug)]
 #[must_use = "sinks do nothing unless polled"]
-pub struct SplitSink<S: Sink<Item>, Item> {
+pub struct SplitSink<S, Item> {
     lock: BiLock<S>,
     slot: Option<Item>,
 }
 
-impl<S: Sink<Item>, Item> Unpin for SplitSink<S, Item> {}
+impl<S, Item> Unpin for SplitSink<S, Item> {}
 
 impl<S: Sink<Item> + Unpin, Item> SplitSink<S, Item> {
     /// Attempts to put the two "halves" of a split `Stream + Sink` back
@@ -112,21 +108,21 @@ pub(super) fn split<S: Stream + Sink<Item>, Item>(s: S) -> (SplitSink<S, Item>,
 
 /// Error indicating a `SplitSink<S>` and `SplitStream<S>` were not two halves
 /// of a `Stream + Split`, and thus could not be `reunite`d.
-pub struct ReuniteError<T: Sink<Item>, Item>(pub SplitSink<T, Item>, pub SplitStream<T>);
+pub struct ReuniteError<T, Item>(pub SplitSink<T, Item>, pub SplitStream<T>);
 
-impl<T: Sink<Item>, Item> fmt::Debug for ReuniteError<T, Item> {
+impl<T, Item> fmt::Debug for ReuniteError<T, Item> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_tuple("ReuniteError")
             .field(&"...")
             .finish()
     }
 }
 
-impl<T: Sink<Item>, Item> fmt::Display for ReuniteError<T, Item> {
+impl<T, Item> fmt::Display for ReuniteError<T, Item> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(f, "tried to reunite a SplitStream and SplitSink that don't form a pair")
     }
 }
 
 #[cfg(feature = "std")]
-impl<T: Any + Sink<Item>, Item> Error for ReuniteError<T, Item> {}
+impl<T: core::any::Any, Item> std::error::Error for ReuniteError<T, Item> {}