refactor(common): replace Never with Infallible (#3392)

src/body/body.rs

@@ -1,4 +1,6 @@
 use std::borrow::Cow;
+#[cfg(all(feature = "client", any(feature = "http1", feature = "http2")))]
+use std::convert::Infallible;
 #[cfg(feature = "stream")]
 use std::error::Error as StdError;
 use std::fmt;
@@ -19,8 +21,6 @@ use super::DecodedLength;
 #[cfg(feature = "stream")]
 use crate::common::sync_wrapper::SyncWrapper;
 use crate::common::watch;
-#[cfg(all(feature = "client", any(feature = "http1", feature = "http2")))]
-use crate::common::Never;
 #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
 use crate::proto::h2::ping;
 
@@ -79,7 +79,7 @@ struct Extra {
 }
 
 #[cfg(all(feature = "client", any(feature = "http1", feature = "http2")))]
-type DelayEofUntil = oneshot::Receiver<Never>;
+type DelayEofUntil = oneshot::Receiver<Infallible>;
 
 enum DelayEof {
     /// Initial state, stream hasn't seen EOF yet.

src/client/conn.rs

@@ -59,6 +59,8 @@ pub mod http1;
 #[cfg(all(feature = "backports", feature = "http2"))]
 pub mod http2;
 
+#[cfg(not(all(feature = "http1", feature = "http2")))]
+use std::convert::Infallible;
 use std::error::Error as StdError;
 use std::fmt;
 use std::future::Future;
@@ -82,8 +84,6 @@ use tracing::{debug, trace};
 use super::dispatch;
 use crate::body::HttpBody;
 use crate::common::exec::{BoxSendFuture, Exec};
-#[cfg(not(all(feature = "http1", feature = "http2")))]
-use crate::common::Never;
 use crate::proto;
 use crate::rt::Executor;
 #[cfg(feature = "http1")]
@@ -95,13 +95,13 @@ type Http1Dispatcher<T, B> =
     proto::dispatch::Dispatcher<proto::dispatch::Client<B>, B, T, proto::h1::ClientTransaction>;
 
 #[cfg(not(feature = "http1"))]
-type Http1Dispatcher<T, B> = (Never, PhantomData<(T, Pin<Box<B>>)>);
+type Http1Dispatcher<T, B> = (Infallible, PhantomData<(T, Pin<Box<B>>)>);
 
 #[cfg(feature = "http2")]
 type Http2ClientTask<B> = proto::h2::ClientTask<B>;
 
 #[cfg(not(feature = "http2"))]
-type Http2ClientTask<B> = (Never, PhantomData<Pin<Box<B>>>);
+type Http2ClientTask<B> = (Infallible, PhantomData<Pin<Box<B>>>);
 
 pin_project! {
     #[project = ProtoClientProj]

src/client/pool.rs

@@ -83,7 +83,7 @@ struct PoolInner<T> {
     // A oneshot channel is used to allow the interval to be notified when
     // the Pool completely drops. That way, the interval can cancel immediately.
     #[cfg(feature = "runtime")]
-    idle_interval_ref: Option<oneshot::Sender<crate::common::Never>>,
+    idle_interval_ref: Option<oneshot::Sender<std::convert::Infallible>>,
     #[cfg(feature = "runtime")]
     exec: Exec,
     timeout: Option<Duration>,
@@ -741,7 +741,7 @@ pin_project_lite::pin_project! {
         // Pool is fully dropped, and shutdown. This channel is never sent on,
         // but Err(Canceled) will be received when the Pool is dropped.
         #[pin]
-        pool_drop_notifier: oneshot::Receiver<crate::common::Never>,
+        pool_drop_notifier: oneshot::Receiver<std::convert::Infallible>,
     }
 }
 

src/common/mod.rs

@@ -17,7 +17,6 @@ pub(crate) mod exec;
 pub(crate) mod io;
 #[cfg(all(feature = "client", any(feature = "http1", feature = "http2")))]
 mod lazy;
-mod never;
 #[cfg(any(
     feature = "stream",
     all(feature = "client", any(feature = "http1", feature = "http2"))
@@ -29,5 +28,3 @@ pub(crate) mod watch;
 
 #[cfg(all(feature = "client", any(feature = "http1", feature = "http2")))]
 pub(crate) use self::lazy::{lazy, Started as Lazy};
-#[cfg(any(feature = "http1", feature = "http2", feature = "runtime"))]
-pub(crate) use self::never::Never;

src/common/task.rs

@@ -1,11 +1,12 @@
-use std::task::{Context, Poll};
-
-use super::Never;
+use std::{
+    convert::Infallible,
+    task::{Context, Poll},
+};
 
 /// A function to help "yield" a future, such that it is re-scheduled immediately.
 ///
 /// Useful for spin counts, so a future doesn't hog too much time.
-pub(crate) fn yield_now(cx: &mut Context<'_>) -> Poll<Never> {
+pub(crate) fn yield_now(cx: &mut Context<'_>) -> Poll<Infallible> {
     cx.waker().wake_by_ref();
     Poll::Pending
 }

src/proto/h1/dispatch.rs

@@ -566,13 +566,13 @@ cfg_client! {
     {
         type PollItem = RequestHead;
         type PollBody = B;
-        type PollError = crate::common::Never;
+        type PollError = std::convert::Infallible;
         type RecvItem = crate::proto::ResponseHead;
 
         fn poll_msg(
             mut self: Pin<&mut Self>,
             cx: &mut Context<'_>,
-        ) -> Poll<Option<Result<(Self::PollItem, Self::PollBody), crate::common::Never>>> {
+        ) -> Poll<Option<Result<(Self::PollItem, Self::PollBody), Self::PollError>>> {
             let mut this = self.as_mut();
             debug_assert!(!this.rx_closed);
             match this.rx.poll_recv(cx) {

src/proto/h2/client.rs

@@ -1,3 +1,4 @@
+use std::convert::Infallible;
 use std::error::Error as StdError;
 use std::future::Future;
 use std::marker::Unpin;
@@ -19,7 +20,7 @@ use tracing::{debug, trace, warn};
 use super::{ping, H2Upgraded, PipeToSendStream, SendBuf};
 use crate::body::HttpBody;
 use crate::client::dispatch::Callback;
-use crate::common::{exec::Exec, Never};
+use crate::common::exec::Exec;
 use crate::ext::Protocol;
 use crate::headers;
 use crate::proto::h2::UpgradedSendStream;
@@ -32,11 +33,11 @@ type ClientRx<B> = crate::client::dispatch::Receiver<Request<B>, Response<Body>>
 
 ///// An mpsc channel is used to help notify the `Connection` task when *all*
 ///// other handles to it have been dropped, so that it can shutdown.
-type ConnDropRef = mpsc::Sender<Never>;
+type ConnDropRef = mpsc::Sender<Infallible>;
 
 ///// A oneshot channel watches the `Connection` task, and when it completes,
 ///// the "dispatch" task will be notified and can shutdown sooner.
-type ConnEof = oneshot::Receiver<Never>;
+type ConnEof = oneshot::Receiver<Infallible>;
 
 // Our defaults are chosen for the "majority" case, which usually are not
 // resource constrained, and so the spec default of 64kb can be too limiting
@@ -181,7 +182,7 @@ where
     })
 }
 
-async fn conn_task<C, D>(conn: C, drop_rx: D, cancel_tx: oneshot::Sender<Never>)
+async fn conn_task<C, D>(conn: C, drop_rx: D, cancel_tx: oneshot::Sender<Infallible>)
 where
     C: Future + Unpin,
     D: Future<Output = ()> + Unpin,

src/server/conn.rs

@@ -72,6 +72,8 @@ cfg_feature! {
     use std::pin::Pin;
     use std::future::Future;
     use std::marker::Unpin;
+    #[cfg(not(all(feature = "http1", feature = "http2")))]
+    use std::convert::Infallible;
 
     use bytes::Bytes;
     use pin_project_lite::pin_project;
@@ -80,8 +82,6 @@ cfg_feature! {
 
     pub use super::server::Connecting;
     use crate::body::{Body, HttpBody};
-    #[cfg(not(all(feature = "http1", feature = "http2")))]
-    use crate::common::Never;
     use crate::common::exec::{ConnStreamExec, Exec};
     use crate::proto;
     use crate::service::HttpService;
@@ -159,14 +159,14 @@ type Http1Dispatcher<T, B, S> =
     proto::h1::Dispatcher<proto::h1::dispatch::Server<S, Body>, B, T, proto::ServerTransaction>;
 
 #[cfg(all(not(feature = "http1"), feature = "http2"))]
-type Http1Dispatcher<T, B, S> = (Never, PhantomData<(T, Box<Pin<B>>, Box<Pin<S>>)>);
+type Http1Dispatcher<T, B, S> = (Infallible, PhantomData<(T, Box<Pin<B>>, Box<Pin<S>>)>);
 
 #[cfg(feature = "http2")]
 type Http2Server<T, B, S, E> = proto::h2::Server<Rewind<T>, S, B, E>;
 
 #[cfg(all(not(feature = "http2"), feature = "http1"))]
 type Http2Server<T, B, S, E> = (
-    Never,
+    Infallible,
     PhantomData<(T, Box<Pin<S>>, Box<Pin<B>>, Box<Pin<E>>)>,
 );