futures: replace pin_utils with pin_project (#374)

This allows us to remove an unnecessary clone of the dispatcher or span
from poll impls. Also, it is commonly used in other crates (e.g.
`tokio`), so might make users' dependency graphs smaller.

Signed-off-by: Eliza Weisman <eliza@buoyant.io>

tracing-futures/Cargo.toml

@@ -21,18 +21,18 @@ license = "MIT"
 [features]
 default = ["futures-01", "tokio"]
 futures-01 = ["futures"]
-std-future = ["pin-utils"]
+std-future = ["pin-project"]
 futures-preview = ["std-future", "futures-core-preview"]
 tokio-alpha = ["std-future", "tokio_02"]
 
 [dependencies]
 futures = { version = "0.1", optional = true }
 futures-core-preview = { version = "0.3.0-alpha.18", optional = true }
-pin-utils = { version = "0.1.0-alpha.4", optional = true }
+pin-project = { version = "0.4", optional = true}
 tracing = "0.1"
 tokio-executor = { version = "0.1", optional = true }
 tokio = { version = "0.1", optional = true }
-tokio_02 = { package = "tokio", version = "0.2.0-alpha.4", optional = true }
+tokio_02 = { package = "tokio", version = "0.2.0-alpha.6", optional = true }
 
 [dev-dependencies]
 tokio = "0.1.22"

tracing-futures/src/lib.rs

@@ -35,13 +35,13 @@
 //! [`futures`]: https://crates.io/crates/futures
 #[cfg(feature = "futures-01")]
 extern crate futures;
-#[cfg(feature = "std-future")]
-extern crate pin_utils;
 #[cfg(feature = "tokio-executor")]
 extern crate tokio_executor;
 #[cfg_attr(test, macro_use)]
 extern crate tracing;
 
+#[cfg(feature = "std-future")]
+use pin_project::pin_project;
 #[cfg(feature = "std-future")]
 use std::{pin::Pin, task::Context};
 
@@ -87,41 +87,44 @@ pub trait WithSubscriber: Sized {
 }
 
 /// A future, stream, or sink that has been instrumented with a `tracing` span.
+#[cfg_attr(feature = "std-future", pin_project)]
 #[derive(Debug, Clone)]
 pub struct Instrumented<T> {
+    #[cfg(feature = "std-future")]
+    #[pin]
+    inner: T,
+    #[cfg(not(feature = "std-future"))]
     inner: T,
     span: Span,
 }
 
 /// A future, stream, sink, or executor that has been instrumented with a
 /// `tracing` subscriber.
+#[cfg_attr(feature = "std-future", pin_project)]
 #[derive(Clone, Debug)]
 pub struct WithDispatch<T> {
+    // cfg_attr doesn't work inside structs, apparently...
+    #[cfg(feature = "std-future")]
+    #[pin]
+    inner: T,
+    #[cfg(not(feature = "std-future"))]
     inner: T,
     dispatch: Dispatch,
 }
 
 impl<T: Sized> Instrument for T {}
 
-#[cfg(feature = "std-future")]
-impl<T: std::future::Future> Instrumented<T> {
-    pin_utils::unsafe_pinned!(inner: T);
-}
-
 #[cfg(feature = "std-future")]
 impl<T: std::future::Future> std::future::Future for Instrumented<T> {
     type Output = T::Output;
 
-    fn poll(mut self: Pin<&mut Self>, lw: &mut Context) -> std::task::Poll<Self::Output> {
+    fn poll(self: Pin<&mut Self>, cx: &mut Context) -> std::task::Poll<Self::Output> {
-        let span = self.as_ref().span.clone();
+        let this = self.project();
-        let _enter = span.enter();
+        let _enter = this.span.enter();
-        self.as_mut().inner().poll(lw)
+        this.inner.poll(cx)
     }
 }
 
-#[cfg(feature = "std-future")]
-impl<T: Unpin> Unpin for Instrumented<T> {}
-
 #[cfg(feature = "futures-01")]
 impl<T: futures::Future> futures::Future for Instrumented<T> {
     type Item = T::Item;
@@ -192,18 +195,15 @@ impl<T: futures::Future> futures::Future for WithDispatch<T> {
     }
 }
 
-#[cfg(feature = "std-future")]
-impl<T: std::future::Future> WithDispatch<T> {
-    pin_utils::unsafe_pinned!(inner: T);
-}
-
 #[cfg(feature = "std-future")]
 impl<T: std::future::Future> std::future::Future for WithDispatch<T> {
     type Output = T::Output;
 
-    fn poll(mut self: Pin<&mut Self>, lw: &mut Context) -> std::task::Poll<Self::Output> {
+    fn poll(self: Pin<&mut Self>, cx: &mut Context) -> std::task::Poll<Self::Output> {
-        let dispatch = self.as_ref().dispatch.clone();
+        let this = self.project();
-        dispatcher::with_default(&dispatch, || self.as_mut().inner().poll(lw))
+        let dispatch = this.dispatch;
+        let future = this.inner;
+        dispatcher::with_default(dispatch, || future.poll(cx))
     }
 }