refactor(lib): Switch from pin-project to pin-project-lite (#2566)

Note the practical affects of this change:

- Dependency count with --features full dropped from 65 to 55.
- Time to compile after a clean dropped from 48s to 35s (on a pretty underpowered VM).

Closes #2388

Cargo.toml

@@ -34,7 +34,7 @@ httparse = "1.4"
 h2 = { version = "0.3.3", optional = true }
 itoa = "0.4.1"
 tracing = { version = "0.1", default-features = false, features = ["std"] }
-pin-project = "1.0"
+pin-project-lite = "0.2.4"
 tower-service = "0.3"
 tokio = { version = "1", features = ["sync"] }
 want = "0.3"

src/client/conn.rs

@@ -48,7 +48,7 @@
 
 use std::error::Error as StdError;
 use std::fmt;
-#[cfg(feature = "http2")]
+#[cfg(not(all(feature = "http1", feature = "http2")))]
 use std::marker::PhantomData;
 use std::sync::Arc;
 #[cfg(all(feature = "runtime", feature = "http2"))]
@@ -57,12 +57,14 @@ use std::time::Duration;
 use bytes::Bytes;
 use futures_util::future::{self, Either, FutureExt as _};
 use httparse::ParserConfig;
-use pin_project::pin_project;
+use pin_project_lite::pin_project;
 use tokio::io::{AsyncRead, AsyncWrite};
 use tower_service::Service;
 
 use super::dispatch;
 use crate::body::HttpBody;
+#[cfg(not(all(feature = "http1", feature = "http2")))]
+use crate::common::Never;
 use crate::common::{
     exec::{BoxSendFuture, Exec},
     task, Future, Pin, Poll,
@@ -74,17 +76,33 @@ use crate::upgrade::Upgraded;
 use crate::{Body, Request, Response};
 
 #[cfg(feature = "http1")]
-type Http1Dispatcher<T, B, R> = proto::dispatch::Dispatcher<proto::dispatch::Client<B>, B, T, R>;
+type Http1Dispatcher<T, B> =
+    proto::dispatch::Dispatcher<proto::dispatch::Client<B>, B, T, proto::h1::ClientTransaction>;
 
-#[pin_project(project = ProtoClientProj)]
+#[cfg(not(feature = "http1"))]
-enum ProtoClient<T, B>
+type Http1Dispatcher<T, B> = (Never, PhantomData<(T, Pin<Box<B>>)>);
-where
+
-    B: HttpBody,
+#[cfg(feature = "http2")]
-{
+type Http2ClientTask<B> = proto::h2::ClientTask<B>;
-    #[cfg(feature = "http1")]
+
-    H1(#[pin] Http1Dispatcher<T, B, proto::h1::ClientTransaction>),
+#[cfg(not(feature = "http2"))]
-    #[cfg(feature = "http2")]
+type Http2ClientTask<B> = (Never, PhantomData<Pin<Box<B>>>);
-    H2(#[pin] proto::h2::ClientTask<B>, PhantomData<fn(T)>),
+
+pin_project! {
+    #[project = ProtoClientProj]
+    enum ProtoClient<T, B>
+    where
+        B: HttpBody,
+    {
+        H1 {
+            #[pin]
+            h1: Http1Dispatcher<T, B>,
+        },
+        H2 {
+            #[pin]
+            h2: Http2ClientTask<B>,
+        },
+    }
 }
 
 /// Returns a handshake future over some IO.
@@ -405,7 +423,7 @@ where
     pub fn into_parts(self) -> Parts<T> {
         match self.inner.expect("already upgraded") {
             #[cfg(feature = "http1")]
-            ProtoClient::H1(h1) => {
+            ProtoClient::H1 { h1 } => {
                 let (io, read_buf, _) = h1.into_inner();
                 Parts {
                     io,
@@ -413,10 +431,12 @@ where
                     _inner: (),
                 }
             }
-            #[cfg(feature = "http2")]
+            ProtoClient::H2 { .. } => {
-            ProtoClient::H2(..) => {
                 panic!("http2 cannot into_inner");
             }
+
+            #[cfg(not(feature = "http1"))]
+            ProtoClient::H1 { h1 } => match h1.0 {},
         }
     }
 
@@ -434,9 +454,14 @@ where
     pub fn poll_without_shutdown(&mut self, cx: &mut task::Context<'_>) -> Poll<crate::Result<()>> {
         match *self.inner.as_mut().expect("already upgraded") {
             #[cfg(feature = "http1")]
-            ProtoClient::H1(ref mut h1) => h1.poll_without_shutdown(cx),
+            ProtoClient::H1 { ref mut h1 } => h1.poll_without_shutdown(cx),
             #[cfg(feature = "http2")]
-            ProtoClient::H2(ref mut h2, _) => Pin::new(h2).poll(cx).map_ok(|_| ()),
+            ProtoClient::H2 { ref mut h2, .. } => Pin::new(h2).poll(cx).map_ok(|_| ()),
+
+            #[cfg(not(feature = "http1"))]
+            ProtoClient::H1 { ref mut h1 } => match h1.0 {},
+            #[cfg(not(feature = "http2"))]
+            ProtoClient::H2 { ref mut h2, .. } => match h2.0 {},
         }
     }
 
@@ -465,7 +490,7 @@ where
             proto::Dispatched::Shutdown => Poll::Ready(Ok(())),
             #[cfg(feature = "http1")]
             proto::Dispatched::Upgrade(pending) => match self.inner.take() {
-                Some(ProtoClient::H1(h1)) => {
+                Some(ProtoClient::H1 { h1 }) => {
                     let (io, buf, _) = h1.into_inner();
                     pending.fulfill(Upgraded::new(io, buf));
                     Poll::Ready(Ok(()))
@@ -756,14 +781,14 @@ impl Builder {
                     }
                     let cd = proto::h1::dispatch::Client::new(rx);
                     let dispatch = proto::h1::Dispatcher::new(cd, conn);
-                    ProtoClient::H1(dispatch)
+                    ProtoClient::H1 { h1: dispatch }
                 }
                 #[cfg(feature = "http2")]
                 Proto::Http2 => {
                     let h2 =
                         proto::h2::client::handshake(io, rx, &opts.h2_builder, opts.exec.clone())
                             .await?;
-                    ProtoClient::H2(h2, PhantomData)
+                    ProtoClient::H2 { h2 }
                 }
             };
 
@@ -817,9 +842,14 @@ where
     fn poll(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
         match self.project() {
             #[cfg(feature = "http1")]
-            ProtoClientProj::H1(c) => c.poll(cx),
+            ProtoClientProj::H1 { h1 } => h1.poll(cx),
             #[cfg(feature = "http2")]
-            ProtoClientProj::H2(c, _) => c.poll(cx),
+            ProtoClientProj::H2 { h2, .. } => h2.poll(cx),
+
+            #[cfg(not(feature = "http1"))]
+            ProtoClientProj::H1 { h1 } => match h1.0 {},
+            #[cfg(not(feature = "http2"))]
+            ProtoClientProj::H2 { h2, .. } => match h2.0 {},
         }
     }
 }

src/client/connect/http.rs

@@ -11,7 +11,7 @@ use std::time::Duration;
 
 use futures_util::future::Either;
 use http::uri::{Scheme, Uri};
-use pin_project::pin_project;
+use pin_project_lite::pin_project;
 use tokio::net::{TcpSocket, TcpStream};
 use tokio::time::Sleep;
 
@@ -373,18 +373,19 @@ impl HttpInfo {
     }
 }
 
-// Not publicly exported (so missing_docs doesn't trigger).
+pin_project! {
-//
+    // Not publicly exported (so missing_docs doesn't trigger).
-// We return this `Future` instead of the `Pin<Box<dyn Future>>` directly
+    //
-// so that users don't rely on it fitting in a `Pin<Box<dyn Future>>` slot
+    // We return this `Future` instead of the `Pin<Box<dyn Future>>` directly
-// (and thus we can change the type in the future).
+    // so that users don't rely on it fitting in a `Pin<Box<dyn Future>>` slot
-#[must_use = "futures do nothing unless polled"]
+    // (and thus we can change the type in the future).
-#[pin_project]
+    #[must_use = "futures do nothing unless polled"]
-#[allow(missing_debug_implementations)]
+    #[allow(missing_debug_implementations)]
-pub struct HttpConnecting<R> {
+    pub struct HttpConnecting<R> {
-    #[pin]
+        #[pin]
-    fut: BoxConnecting,
+        fut: BoxConnecting,
-    _marker: PhantomData<R>,
+        _marker: PhantomData<R>,
+    }
 }
 
 type ConnectResult = Result<TcpStream, ConnectError>;

src/client/pool.rs

@@ -11,7 +11,7 @@ use futures_channel::oneshot;
 use tokio::time::{Duration, Instant, Interval};
 
 use super::client::Ver;
-use crate::common::{task, exec::Exec, Future, Pin, Poll, Unpin};
+use crate::common::{exec::Exec, task, Future, Pin, Poll, Unpin};
 
 // FIXME: allow() required due to `impl Trait` leaking types to this lint
 #[allow(missing_debug_implementations)]
@@ -714,16 +714,17 @@ impl Expiration {
 }
 
 #[cfg(feature = "runtime")]
-#[pin_project::pin_project]
+pin_project_lite::pin_project! {
-struct IdleTask<T> {
+    struct IdleTask<T> {
-    #[pin]
+        #[pin]
-    interval: Interval,
+        interval: Interval,
-    pool: WeakOpt<Mutex<PoolInner<T>>>,
+        pool: WeakOpt<Mutex<PoolInner<T>>>,
-    // This allows the IdleTask to be notified as soon as the entire
+        // This allows the IdleTask to be notified as soon as the entire
-    // Pool is fully dropped, and shutdown. This channel is never sent on,
+        // Pool is fully dropped, and shutdown. This channel is never sent on,
-    // but Err(Canceled) will be received when the Pool is dropped.
+        // but Err(Canceled) will be received when the Pool is dropped.
-    #[pin]
+        #[pin]
-    pool_drop_notifier: oneshot::Receiver<crate::common::Never>,
+        pool_drop_notifier: oneshot::Receiver<crate::common::Never>,
+    }
 }
 
 #[cfg(feature = "runtime")]
@@ -776,7 +777,7 @@ mod tests {
     use std::time::Duration;
 
     use super::{Connecting, Key, Pool, Poolable, Reservation, WeakOpt};
-    use crate::common::{task, exec::Exec, Future, Pin};
+    use crate::common::{exec::Exec, task, Future, Pin};
 
     /// Test unique reservations.
     #[derive(Debug, PartialEq, Eq)]

src/common/drain.rs

@@ -1,6 +1,6 @@
 use std::mem;
 
-use pin_project::pin_project;
+use pin_project_lite::pin_project;
 use tokio::sync::watch;
 
 use super::{task, Future, Pin, Poll};
@@ -21,14 +21,15 @@ pub(crate) struct Watch {
     rx: watch::Receiver<()>,
 }
 
-#[allow(missing_debug_implementations)]
+pin_project! {
-#[pin_project]
+    #[allow(missing_debug_implementations)]
-pub struct Watching<F, FN> {
+    pub struct Watching<F, FN> {
-    #[pin]
+        #[pin]
-    future: F,
+        future: F,
-    state: State<FN>,
+        state: State<FN>,
-    watch: Pin<Box<dyn Future<Output = ()> + Send + Sync>>,
+        watch: Pin<Box<dyn Future<Output = ()> + Send + Sync>>,
-    _rx: watch::Receiver<()>,
+        _rx: watch::Receiver<()>,
+    }
 }
 
 enum State<F> {

src/common/lazy.rs

@@ -1,4 +1,4 @@
-use pin_project::pin_project;
+use pin_project_lite::pin_project;
 
 use super::{task, Future, Pin, Poll};
 
@@ -12,23 +12,27 @@ where
     R: Future + Unpin,
 {
     Lazy {
-        inner: Inner::Init(func),
+        inner: Inner::Init { func },
     }
 }
 
 // FIXME: allow() required due to `impl Trait` leaking types to this lint
-#[allow(missing_debug_implementations)]
+pin_project! {
-#[pin_project]
+    #[allow(missing_debug_implementations)]
-pub(crate) struct Lazy<F, R> {
+    pub(crate) struct Lazy<F, R> {
-    #[pin]
+        #[pin]
-    inner: Inner<F, R>,
+        inner: Inner<F, R>,
+    }
 }
 
-#[pin_project(project = InnerProj, project_replace = InnerProjReplace)]
+pin_project! {
-enum Inner<F, R> {
+    #[project = InnerProj]
-    Init(F),
+    #[project_replace = InnerProjReplace]
-    Fut(#[pin] R),
+    enum Inner<F, R> {
-    Empty,
+        Init { func: F },
+        Fut { #[pin] fut: R },
+        Empty,
+    }
 }
 
 impl<F, R> Started for Lazy<F, R>
@@ -38,8 +42,8 @@ where
 {
     fn started(&self) -> bool {
         match self.inner {
-            Inner::Init(_) => false,
+            Inner::Init { .. } => false,
-            Inner::Fut(_) | Inner::Empty => true,
+            Inner::Fut { .. } | Inner::Empty => true,
         }
     }
 }
@@ -54,15 +58,15 @@ where
     fn poll(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
         let mut this = self.project();
 
-        if let InnerProj::Fut(f) = this.inner.as_mut().project() {
+        if let InnerProj::Fut { fut } = this.inner.as_mut().project() {
-            return f.poll(cx);
+            return fut.poll(cx);
         }
 
         match this.inner.as_mut().project_replace(Inner::Empty) {
-            InnerProjReplace::Init(func) => {
+            InnerProjReplace::Init { func } => {
-                this.inner.set(Inner::Fut(func()));
+                this.inner.set(Inner::Fut { fut: func() });
-                if let InnerProj::Fut(f) = this.inner.project() {
+                if let InnerProj::Fut { fut } = this.inner.project() {
-                    return f.poll(cx);
+                    return fut.poll(cx);
                 }
                 unreachable!()
             }

src/proto/h1/dispatch.rs

@@ -44,10 +44,13 @@ cfg_server! {
 }
 
 cfg_client! {
-    pub(crate) struct Client<B> {
+    pin_project_lite::pin_project! {
-        callback: Option<crate::client::dispatch::Callback<Request<B>, http::Response<Body>>>,
+        pub(crate) struct Client<B> {
-        rx: ClientRx<B>,
+            callback: Option<crate::client::dispatch::Callback<Request<B>, http::Response<Body>>>,
-        rx_closed: bool,
+            #[pin]
+            rx: ClientRx<B>,
+            rx_closed: bool,
+        }
     }
 
     type ClientRx<B> = crate::client::dispatch::Receiver<Request<B>, http::Response<Body>>;

src/proto/h2/mod.rs

@@ -5,7 +5,7 @@ use http::header::{
     TRANSFER_ENCODING, UPGRADE,
 };
 use http::HeaderMap;
-use pin_project::pin_project;
+use pin_project_lite::pin_project;
 use std::error::Error as StdError;
 use std::io::{self, Cursor, IoSlice};
 use std::mem;
@@ -88,15 +88,16 @@ fn strip_connection_headers(headers: &mut HeaderMap, is_request: bool) {
 
 // body adapters used by both Client and Server
 
-#[pin_project]
+pin_project! {
-struct PipeToSendStream<S>
+    struct PipeToSendStream<S>
-where
+    where
-    S: HttpBody,
+        S: HttpBody,
-{
+    {
-    body_tx: SendStream<SendBuf<S::Data>>,
+        body_tx: SendStream<SendBuf<S::Data>>,
-    data_done: bool,
+        data_done: bool,
-    #[pin]
+        #[pin]
-    stream: S,
+        stream: S,
+    }
 }
 
 impl<S> PipeToSendStream<S>

src/proto/h2/server.rs

@@ -7,7 +7,7 @@ use bytes::Bytes;
 use h2::server::{Connection, Handshake, SendResponse};
 use h2::{Reason, RecvStream};
 use http::{Method, Request};
-use pin_project::pin_project;
+use pin_project_lite::pin_project;
 use tokio::io::{AsyncRead, AsyncWrite};
 
 use super::{ping, PipeToSendStream, SendBuf};
@@ -62,15 +62,16 @@ impl Default for Config {
     }
 }
 
-#[pin_project]
+pin_project! {
-pub(crate) struct Server<T, S, B, E>
+    pub(crate) struct Server<T, S, B, E>
-where
+    where
-    S: HttpService<Body>,
+        S: HttpService<Body>,
-    B: HttpBody,
+        B: HttpBody,
-{
+    {
-    exec: E,
+        exec: E,
-    service: S,
+        service: S,
-    state: State<T, B>,
+        state: State<T, B>,
+    }
 }
 
 enum State<T, B>
@@ -348,24 +349,34 @@ where
     }
 }
 
-#[allow(missing_debug_implementations)]
+pin_project! {
-#[pin_project]
+    #[allow(missing_debug_implementations)]
-pub struct H2Stream<F, B>
+    pub struct H2Stream<F, B>
-where
+    where
-    B: HttpBody,
+        B: HttpBody,
-{
+    {
-    reply: SendResponse<SendBuf<B::Data>>,
+        reply: SendResponse<SendBuf<B::Data>>,
-    #[pin]
+        #[pin]
-    state: H2StreamState<F, B>,
+        state: H2StreamState<F, B>,
+    }
 }
 
-#[pin_project(project = H2StreamStateProj)]
+pin_project! {
-enum H2StreamState<F, B>
+    #[project = H2StreamStateProj]
-where
+    enum H2StreamState<F, B>
-    B: HttpBody,
+    where
-{
+        B: HttpBody,
-    Service(#[pin] F, Option<ConnectParts>),
+    {
-    Body(#[pin] PipeToSendStream<B>),
+        Service {
+            #[pin]
+            fut: F,
+            connect_parts: Option<ConnectParts>,
+        },
+        Body {
+            #[pin]
+            pipe: PipeToSendStream<B>,
+        },
+    }
 }
 
 struct ConnectParts {
@@ -385,7 +396,7 @@ where
     ) -> H2Stream<F, B> {
         H2Stream {
             reply: respond,
-            state: H2StreamState::Service(fut, connect_parts),
+            state: H2StreamState::Service { fut, connect_parts },
         }
     }
 }
@@ -415,7 +426,10 @@ where
         let mut me = self.project();
         loop {
             let next = match me.state.as_mut().project() {
-                H2StreamStateProj::Service(h, connect_parts) => {
+                H2StreamStateProj::Service {
+                    fut: h,
+                    connect_parts,
+                } => {
                     let res = match h.poll(cx) {
                         Poll::Ready(Ok(r)) => r,
                         Poll::Pending => {
@@ -476,13 +490,15 @@ where
 
                     if !body.is_end_stream() {
                         let body_tx = reply!(me, res, false);
-                        H2StreamState::Body(PipeToSendStream::new(body, body_tx))
+                        H2StreamState::Body {
+                            pipe: PipeToSendStream::new(body, body_tx),
+                        }
                     } else {
                         reply!(me, res, true);
                         return Poll::Ready(Ok(()));
                     }
                 }
-                H2StreamStateProj::Body(pipe) => {
+                H2StreamStateProj::Body { pipe } => {
                     return pipe.poll(cx);
                 }
             };

src/server/accept.rs

@@ -9,7 +9,7 @@
 #[cfg(feature = "stream")]
 use futures_core::Stream;
 #[cfg(feature = "stream")]
-use pin_project::pin_project;
+use pin_project_lite::pin_project;
 
 use crate::common::{
     task::{self, Poll},
@@ -86,8 +86,12 @@ pub fn from_stream<S, IO, E>(stream: S) -> impl Accept<Conn = IO, Error = E>
 where
     S: Stream<Item = Result<IO, E>>,
 {
-    #[pin_project]
+    pin_project! {
-    struct FromStream<S>(#[pin] S);
+        struct FromStream<S> {
+            #[pin]
+            stream: S,
+        }
+    }
 
     impl<S, IO, E> Accept for FromStream<S>
     where
@@ -99,9 +103,9 @@ where
             self: Pin<&mut Self>,
             cx: &mut task::Context<'_>,
         ) -> Poll<Option<Result<Self::Conn, Self::Error>>> {
-            self.project().0.poll_next(cx)
+            self.project().stream.poll_next(cx)
         }
     }
 
-    FromStream(stream)
+    FromStream { stream }
 }

src/server/conn.rs

@@ -45,7 +45,7 @@
 
 use std::error::Error as StdError;
 use std::fmt;
-#[cfg(feature = "http1")]
+#[cfg(not(all(feature = "http1", feature = "http2")))]
 use std::marker::PhantomData;
 #[cfg(feature = "tcp")]
 use std::net::SocketAddr;
@@ -53,7 +53,7 @@ use std::net::SocketAddr;
 use std::time::Duration;
 
 use bytes::Bytes;
-use pin_project::pin_project;
+use pin_project_lite::pin_project;
 use tokio::io::{AsyncRead, AsyncWrite};
 
 use super::accept::Accept;
@@ -61,6 +61,8 @@ use crate::body::{Body, HttpBody};
 use crate::common::exec::{ConnStreamExec, Exec, NewSvcExec};
 #[cfg(feature = "http2")]
 use crate::common::io::Rewind;
+#[cfg(not(all(feature = "http1", feature = "http2")))]
+use crate::common::Never;
 use crate::common::{task, Future, Pin, Poll, Unpin};
 #[cfg(all(feature = "http1", feature = "http2"))]
 use crate::error::{Kind, Parse};
@@ -111,77 +113,93 @@ enum ConnectionMode {
     Fallback,
 }
 
-/// A stream mapping incoming IOs to new services.
+pin_project! {
-///
+    /// A stream mapping incoming IOs to new services.
-/// Yields `Connecting`s that are futures that should be put on a reactor.
+    ///
-#[must_use = "streams do nothing unless polled"]
+    /// Yields `Connecting`s that are futures that should be put on a reactor.
-#[pin_project]
+    #[must_use = "streams do nothing unless polled"]
-#[derive(Debug)]
+    #[derive(Debug)]
-pub(super) struct Serve<I, S, E = Exec> {
+    pub(super) struct Serve<I, S, E = Exec> {
-    #[pin]
-    incoming: I,
-    make_service: S,
-    protocol: Http<E>,
-}
-
-/// A future building a new `Service` to a `Connection`.
-///
-/// Wraps the future returned from `MakeService` into one that returns
-/// a `Connection`.
-#[must_use = "futures do nothing unless polled"]
-#[pin_project]
-#[derive(Debug)]
-pub struct Connecting<I, F, E = Exec> {
-    #[pin]
-    future: F,
-    io: Option<I>,
-    protocol: Http<E>,
-}
-
-#[must_use = "futures do nothing unless polled"]
-#[pin_project]
-#[derive(Debug)]
-pub(super) struct SpawnAll<I, S, E> {
-    // TODO: re-add `pub(super)` once rustdoc can handle this.
-    //
-    // See https://github.com/rust-lang/rust/issues/64705
-    #[pin]
-    pub(super) serve: Serve<I, S, E>,
-}
-
-/// A future binding a connection with a Service.
-///
-/// Polling this future will drive HTTP forward.
-#[must_use = "futures do nothing unless polled"]
-#[pin_project]
-pub struct Connection<T, S, E = Exec>
-where
-    S: HttpService<Body>,
-{
-    pub(super) conn: Option<ProtoServer<T, S::ResBody, S, E>>,
-    #[cfg(all(feature = "http1", feature = "http2"))]
-    fallback: Fallback<E>,
-}
-
-#[pin_project(project = ProtoServerProj)]
-pub(super) enum ProtoServer<T, B, S, E = Exec>
-where
-    S: HttpService<Body>,
-    B: HttpBody,
-{
-    #[cfg(feature = "http1")]
-    H1(
         #[pin]
-        proto::h1::Dispatcher<
+        incoming: I,
-            proto::h1::dispatch::Server<S, Body>,
+        make_service: S,
-            B,
+        protocol: Http<E>,
-            T,
+    }
-            proto::ServerTransaction,
+}
-        >,
+
-        PhantomData<E>,
+pin_project! {
-    ),
+    /// A future building a new `Service` to a `Connection`.
-    #[cfg(feature = "http2")]
+    ///
-    H2(#[pin] proto::h2::Server<Rewind<T>, S, B, E>),
+    /// Wraps the future returned from `MakeService` into one that returns
+    /// a `Connection`.
+    #[must_use = "futures do nothing unless polled"]
+    #[derive(Debug)]
+    pub struct Connecting<I, F, E = Exec> {
+        #[pin]
+        future: F,
+        io: Option<I>,
+        protocol: Http<E>,
+    }
+}
+
+pin_project! {
+    #[must_use = "futures do nothing unless polled"]
+    #[derive(Debug)]
+    pub(super) struct SpawnAll<I, S, E> {
+        // TODO: re-add `pub(super)` once rustdoc can handle this.
+        //
+        // See https://github.com/rust-lang/rust/issues/64705
+        #[pin]
+        pub(super) serve: Serve<I, S, E>,
+    }
+}
+
+pin_project! {
+    /// A future binding a connection with a Service.
+    ///
+    /// Polling this future will drive HTTP forward.
+    #[must_use = "futures do nothing unless polled"]
+    pub struct Connection<T, S, E = Exec>
+    where
+        S: HttpService<Body>,
+    {
+        pub(super) conn: Option<ProtoServer<T, S::ResBody, S, E>>,
+        fallback: Fallback<E>,
+    }
+}
+
+#[cfg(feature = "http1")]
+type Http1Dispatcher<T, B, S> =
+    proto::h1::Dispatcher<proto::h1::dispatch::Server<S, Body>, B, T, proto::ServerTransaction>;
+
+#[cfg(not(feature = "http1"))]
+type Http1Dispatcher<T, B, S> = (Never, 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(not(feature = "http2"))]
+type Http2Server<T, B, S, E> = (
+    Never,
+    PhantomData<(T, Box<Pin<S>>, Box<Pin<B>>, Box<Pin<E>>)>,
+);
+
+pin_project! {
+    #[project = ProtoServerProj]
+    pub(super) enum ProtoServer<T, B, S, E = Exec>
+    where
+        S: HttpService<Body>,
+        B: HttpBody,
+    {
+        H1 {
+            #[pin]
+            h1: Http1Dispatcher<T, B, S>,
+        },
+        H2 {
+            #[pin]
+            h2: Http2Server<T, B, S, E>,
+        },
+    }
 }
 
 #[cfg(all(feature = "http1", feature = "http2"))]
@@ -191,6 +209,9 @@ enum Fallback<E> {
     Http1Only,
 }
 
+#[cfg(not(all(feature = "http1", feature = "http2")))]
+type Fallback<E> = PhantomData<E>;
+
 #[cfg(all(feature = "http1", feature = "http2"))]
 impl<E> Fallback<E> {
     fn to_h2(&self) -> bool {
@@ -557,7 +578,9 @@ impl<E> Http<E> {
                     conn.set_max_buf_size(max);
                 }
                 let sd = proto::h1::dispatch::Server::new(service);
-                ProtoServer::H1(proto::h1::Dispatcher::new(sd, conn), PhantomData)
+                ProtoServer::H1 {
+                    h1: proto::h1::Dispatcher::new(sd, conn),
+                }
             }};
         }
 
@@ -573,19 +596,20 @@ impl<E> Http<E> {
                 let rewind_io = Rewind::new(io);
                 let h2 =
                     proto::h2::Server::new(rewind_io, service, &self.h2_builder, self.exec.clone());
-                ProtoServer::H2(h2)
+                ProtoServer::H2 { h2 }
             }
         };
 
         Connection {
             conn: Some(proto),
-            #[cfg(feature = "http1")]
+            #[cfg(all(feature = "http1", feature = "http2"))]
-            #[cfg(feature = "http2")]
             fallback: if self.mode == ConnectionMode::Fallback {
                 Fallback::ToHttp2(self.h2_builder.clone(), self.exec.clone())
             } else {
                 Fallback::Http1Only
             },
+            #[cfg(not(all(feature = "http1", feature = "http2")))]
+            fallback: PhantomData,
         }
     }
 
@@ -628,17 +652,22 @@ where
     /// This should only be called while the `Connection` future is still
     /// pending. If called after `Connection::poll` has resolved, this does
     /// nothing.
-    pub fn graceful_shutdown(self: Pin<&mut Self>) {
+    pub fn graceful_shutdown(mut self: Pin<&mut Self>) {
-        match self.project().conn {
+        match self.conn {
             #[cfg(feature = "http1")]
-            Some(ProtoServer::H1(ref mut h1, _)) => {
+            Some(ProtoServer::H1 { ref mut h1, .. }) => {
                 h1.disable_keep_alive();
             }
             #[cfg(feature = "http2")]
-            Some(ProtoServer::H2(ref mut h2)) => {
+            Some(ProtoServer::H2 { ref mut h2 }) => {
                 h2.graceful_shutdown();
             }
             None => (),
+
+            #[cfg(not(feature = "http1"))]
+            Some(ProtoServer::H1 { ref mut h1, .. }) => match h1.0 {},
+            #[cfg(not(feature = "http2"))]
+            Some(ProtoServer::H2 { ref mut h2 }) => match h2.0 {},
         }
     }
 
@@ -662,7 +691,7 @@ where
     pub fn try_into_parts(self) -> Option<Parts<I, S>> {
         match self.conn.unwrap() {
             #[cfg(feature = "http1")]
-            ProtoServer::H1(h1, _) => {
+            ProtoServer::H1 { h1, .. } => {
                 let (io, read_buf, dispatch) = h1.into_inner();
                 Some(Parts {
                     io,
@@ -671,8 +700,10 @@ where
                     _inner: (),
                 })
             }
-            #[cfg(feature = "http2")]
+            ProtoServer::H2 { .. } => None,
-            ProtoServer::H2(_h2) => None,
+
+            #[cfg(not(feature = "http1"))]
+            ProtoServer::H1 { h1, .. } => match h1.0 {},
         }
     }
 
@@ -696,7 +727,7 @@ where
         loop {
             match *self.conn.as_mut().unwrap() {
                 #[cfg(feature = "http1")]
-                ProtoServer::H1(ref mut h1, _) => match ready!(h1.poll_without_shutdown(cx)) {
+                ProtoServer::H1 { ref mut h1, .. } => match ready!(h1.poll_without_shutdown(cx)) {
                     Ok(()) => return Poll::Ready(Ok(())),
                     Err(e) => {
                         #[cfg(feature = "http2")]
@@ -712,7 +743,12 @@ where
                     }
                 },
                 #[cfg(feature = "http2")]
-                ProtoServer::H2(ref mut h2) => return Pin::new(h2).poll(cx).map_ok(|_| ()),
+                ProtoServer::H2 { ref mut h2 } => return Pin::new(h2).poll(cx).map_ok(|_| ()),
+
+                #[cfg(not(feature = "http1"))]
+                ProtoServer::H1 { ref mut h1, .. } => match h1.0 {},
+                #[cfg(not(feature = "http2"))]
+                ProtoServer::H2 { ref mut h2 } => match h2.0 {},
             };
         }
     }
@@ -738,8 +774,8 @@ where
         let conn = self.conn.take();
 
         let (io, read_buf, dispatch) = match conn.unwrap() {
-            ProtoServer::H1(h1, _) => h1.into_inner(),
+            ProtoServer::H1 { h1, .. } => h1.into_inner(),
-            ProtoServer::H2(_h2) => {
+            ProtoServer::H2 { .. } => {
                 panic!("h2 cannot into_inner");
             }
         };
@@ -752,7 +788,7 @@ where
         let h2 = proto::h2::Server::new(rewind_io, dispatch.into_service(), builder, exec.clone());
 
         debug_assert!(self.conn.is_none());
-        self.conn = Some(ProtoServer::H2(h2));
+        self.conn = Some(ProtoServer::H2 { h2 });
     }
 
     /// Enable this connection to support higher-level HTTP upgrades.
@@ -986,9 +1022,14 @@ where
     fn poll(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
         match self.project() {
             #[cfg(feature = "http1")]
-            ProtoServerProj::H1(s, _) => s.poll(cx),
+            ProtoServerProj::H1 { h1, .. } => h1.poll(cx),
             #[cfg(feature = "http2")]
-            ProtoServerProj::H2(s) => s.poll(cx),
+            ProtoServerProj::H2 { h2 } => h2.poll(cx),
+
+            #[cfg(not(feature = "http1"))]
+            ProtoServerProj::H1 { h1, .. } => match h1.0 {},
+            #[cfg(not(feature = "http2"))]
+            ProtoServerProj::H2 { h2 } => match h2.0 {},
         }
     }
 }
@@ -1002,7 +1043,7 @@ pub(crate) mod spawn_all {
     use crate::common::exec::ConnStreamExec;
     use crate::common::{task, Future, Pin, Poll, Unpin};
     use crate::service::HttpService;
-    use pin_project::pin_project;
+    use pin_project_lite::pin_project;
 
     // Used by `SpawnAll` to optionally watch a `Connection` future.
     //
@@ -1047,23 +1088,36 @@ pub(crate) mod spawn_all {
     // Users cannot import this type, nor the associated `NewSvcExec`. Instead,
     // a blanket implementation for `Executor<impl Future>` is sufficient.
 
-    #[pin_project]
+    pin_project! {
-    #[allow(missing_debug_implementations)]
+        #[allow(missing_debug_implementations)]
-    pub struct NewSvcTask<I, N, S: HttpService<Body>, E, W: Watcher<I, S, E>> {
+        pub struct NewSvcTask<I, N, S: HttpService<Body>, E, W: Watcher<I, S, E>> {
-        #[pin]
+            #[pin]
-        state: State<I, N, S, E, W>,
+            state: State<I, N, S, E, W>,
+        }
     }
 
-    #[pin_project(project = StateProj)]
+    pin_project! {
-    pub(super) enum State<I, N, S: HttpService<Body>, E, W: Watcher<I, S, E>> {
+        #[project = StateProj]
-        Connecting(#[pin] Connecting<I, N, E>, W),
+        pub(super) enum State<I, N, S: HttpService<Body>, E, W: Watcher<I, S, E>> {
-        Connected(#[pin] W::Future),
+            Connecting {
+                #[pin]
+                connecting: Connecting<I, N, E>,
+                watcher: W,
+            },
+            Connected {
+                #[pin]
+                future: W::Future,
+            },
+        }
     }
 
     impl<I, N, S: HttpService<Body>, E, W: Watcher<I, S, E>> NewSvcTask<I, N, S, E, W> {
         pub(super) fn new(connecting: Connecting<I, N, E>, watcher: W) -> Self {
             NewSvcTask {
-                state: State::Connecting(connecting, watcher),
+                state: State::Connecting {
+                    connecting,
+                    watcher,
+                },
             }
         }
     }
@@ -1090,7 +1144,10 @@ pub(crate) mod spawn_all {
             loop {
                 let next = {
                     match me.state.as_mut().project() {
-                        StateProj::Connecting(connecting, watcher) => {
+                        StateProj::Connecting {
+                            connecting,
+                            watcher,
+                        } => {
                             let res = ready!(connecting.poll(cx));
                             let conn = match res {
                                 Ok(conn) => conn,
@@ -1100,10 +1157,10 @@ pub(crate) mod spawn_all {
                                     return Poll::Ready(());
                                 }
                             };
-                            let connected = watcher.watch(conn.with_upgrades());
+                            let future = watcher.watch(conn.with_upgrades());
-                            State::Connected(connected)
+                            State::Connected { future }
                         }
-                        StateProj::Connected(future) => {
+                        StateProj::Connected { future } => {
                             return future.poll(cx).map(|res| {
                                 if let Err(err) = res {
                                     debug!("connection error: {}", err);
@@ -1171,7 +1228,7 @@ mod upgrades {
                     #[cfg(feature = "http1")]
                     Ok(proto::Dispatched::Upgrade(pending)) => {
                         match self.inner.conn.take() {
-                            Some(ProtoServer::H1(h1, _)) => {
+                            Some(ProtoServer::H1 { h1, .. }) => {
                                 let (io, buf, _) = h1.into_inner();
                                 pending.fulfill(Upgraded::new(io, buf));
                                 return Poll::Ready(Ok(()));

src/server/server.rs

@@ -6,7 +6,7 @@ use std::net::{SocketAddr, TcpListener as StdTcpListener};
 #[cfg(feature = "tcp")]
 use std::time::Duration;
 
-use pin_project::pin_project;
+use pin_project_lite::pin_project;
 use tokio::io::{AsyncRead, AsyncWrite};
 
 use super::accept::Accept;
@@ -21,16 +21,17 @@ use super::shutdown::{Graceful, GracefulWatcher};
 #[cfg(feature = "tcp")]
 use super::tcp::AddrIncoming;
 
-/// A listening HTTP server that accepts connections in both HTTP1 and HTTP2 by default.
+pin_project! {
-///
+    /// A listening HTTP server that accepts connections in both HTTP1 and HTTP2 by default.
-/// `Server` is a `Future` mapping a bound listener with a set of service
+    ///
-/// handlers. It is built using the [`Builder`](Builder), and the future
+    /// `Server` is a `Future` mapping a bound listener with a set of service
-/// completes when the server has been shutdown. It should be run by an
+    /// handlers. It is built using the [`Builder`](Builder), and the future
-/// `Executor`.
+    /// completes when the server has been shutdown. It should be run by an
-#[pin_project]
+    /// `Executor`.
-pub struct Server<I, S, E = Exec> {
+    pub struct Server<I, S, E = Exec> {
-    #[pin]
+        #[pin]
-    spawn_all: SpawnAll<I, S, E>,
+        spawn_all: SpawnAll<I, S, E>,
+    }
 }
 
 /// A builder for a [`Server`](Server).

src/server/shutdown.rs

@@ -1,33 +1,36 @@
 use std::error::Error as StdError;
 
-use pin_project::pin_project;
+use pin_project_lite::pin_project;
 use tokio::io::{AsyncRead, AsyncWrite};
 
-use super::conn::{SpawnAll, UpgradeableConnection, Watcher};
 use super::accept::Accept;
+use super::conn::{SpawnAll, UpgradeableConnection, Watcher};
 use crate::body::{Body, HttpBody};
 use crate::common::drain::{self, Draining, Signal, Watch, Watching};
 use crate::common::exec::{ConnStreamExec, NewSvcExec};
 use crate::common::{task, Future, Pin, Poll, Unpin};
 use crate::service::{HttpService, MakeServiceRef};
 
-#[allow(missing_debug_implementations)]
+pin_project! {
-#[pin_project]
+    #[allow(missing_debug_implementations)]
-pub struct Graceful<I, S, F, E> {
+    pub struct Graceful<I, S, F, E> {
-    #[pin]
+        #[pin]
-    state: State<I, S, F, E>,
+        state: State<I, S, F, E>,
+    }
 }
 
-#[pin_project(project = StateProj)]
+pin_project! {
-pub(super) enum State<I, S, F, E> {
+    #[project = StateProj]
-    Running {
+    pub(super) enum State<I, S, F, E> {
-        drain: Option<(Signal, Watch)>,
+        Running {
-        #[pin]
+            drain: Option<(Signal, Watch)>,
-        spawn_all: SpawnAll<I, S, E>,
+            #[pin]
-        #[pin]
+            spawn_all: SpawnAll<I, S, E>,
-        signal: F,
+            #[pin]
-    },
+            signal: F,
-    Draining(Draining),
+        },
+        Draining { draining: Draining },
+    }
 }
 
 impl<I, S, F, E> Graceful<I, S, F, E> {
@@ -71,14 +74,16 @@ where
                         Poll::Ready(()) => {
                             debug!("signal received, starting graceful shutdown");
                             let sig = drain.take().expect("drain channel").0;
-                            State::Draining(sig.drain())
+                            State::Draining {
+                                draining: sig.drain(),
+                            }
                         }
                         Poll::Pending => {
                             let watch = drain.as_ref().expect("drain channel").1.clone();
                             return spawn_all.poll_watch(cx, &GracefulWatcher(watch));
                         }
                     },
-                    StateProj::Draining(ref mut draining) => {
+                    StateProj::Draining { ref mut draining } => {
                         return Pin::new(draining).poll(cx).map(Ok);
                     }
                 }

src/server/tcp.rs

@@ -199,13 +199,14 @@ mod addr_stream {
 
     use crate::common::{task, Pin, Poll};
 
-    /// A transport returned yieled by `AddrIncoming`.
+    pin_project_lite::pin_project! {
-    #[pin_project::pin_project]
+        /// A transport returned yieled by `AddrIncoming`.
-    #[derive(Debug)]
+        #[derive(Debug)]
-    pub struct AddrStream {
+        pub struct AddrStream {
-        #[pin]
+            #[pin]
-        inner: TcpStream,
+            inner: TcpStream,
-        pub(super) remote_addr: SocketAddr,
+            pub(super) remote_addr: SocketAddr,
+        }
     }
 
     impl AddrStream {

src/service/oneshot.rs

@@ -1,6 +1,6 @@
 // TODO: Eventually to be replaced with tower_util::Oneshot.
 
-use pin_project::pin_project;
+use pin_project_lite::pin_project;
 use tower_service::Service;
 
 use crate::common::{task, Future, Pin, Poll};
@@ -10,25 +10,35 @@ where
     S: Service<Req>,
 {
     Oneshot {
-        state: State::NotReady(svc, req),
+        state: State::NotReady { svc, req },
     }
 }
 
-// A `Future` consuming a `Service` and request, waiting until the `Service`
+pin_project! {
-// is ready, and then calling `Service::call` with the request, and
+    // A `Future` consuming a `Service` and request, waiting until the `Service`
-// waiting for that `Future`.
+    // is ready, and then calling `Service::call` with the request, and
-#[allow(missing_debug_implementations)]
+    // waiting for that `Future`.
-#[pin_project]
+    #[allow(missing_debug_implementations)]
-pub struct Oneshot<S: Service<Req>, Req> {
+    pub struct Oneshot<S: Service<Req>, Req> {
-    #[pin]
+        #[pin]
-    state: State<S, Req>,
+        state: State<S, Req>,
+    }
 }
 
-#[pin_project(project = StateProj, project_replace = StateProjOwn)]
+pin_project! {
-enum State<S: Service<Req>, Req> {
+    #[project = StateProj]
-    NotReady(S, Req),
+    #[project_replace = StateProjOwn]
-    Called(#[pin] S::Future),
+    enum State<S: Service<Req>, Req> {
-    Tmp,
+        NotReady {
+            svc: S,
+            req: Req,
+        },
+        Called {
+            #[pin]
+            fut: S::Future,
+        },
+        Tmp,
+    }
 }
 
 impl<S, Req> Future for Oneshot<S, Req>
@@ -42,19 +52,19 @@ where
 
         loop {
             match me.state.as_mut().project() {
-                StateProj::NotReady(ref mut svc, _) => {
+                StateProj::NotReady { ref mut svc, .. } => {
                     ready!(svc.poll_ready(cx))?;
                     // fallthrough out of the match's borrow
                 }
-                StateProj::Called(fut) => {
+                StateProj::Called { fut } => {
                     return fut.poll(cx);
                 }
                 StateProj::Tmp => unreachable!(),
             }
 
             match me.state.as_mut().project_replace(State::Tmp) {
-                StateProjOwn::NotReady(mut svc, req) => {
+                StateProjOwn::NotReady { mut svc, req } => {
-                    me.state.set(State::Called(svc.call(req)));
+                    me.state.set(State::Called { fut: svc.call(req) });
                 }
                 _ => unreachable!(),
             }