feat(lib): update to std::future::Future

BREAKING CHANGE: All usage of async traits (`Future`, `Stream`,
`AsyncRead`, `AsyncWrite`, etc) are updated to newer versions.

src/common/lazy.rs

@@ -1,6 +1,6 @@
 use std::mem;
 
-use futures::{Future, IntoFuture, Poll};
+use super::{Future, Pin, Poll, task};
 
 pub(crate) trait Started: Future {
     fn started(&self) -> bool;
@@ -9,7 +9,7 @@ pub(crate) trait Started: Future {
 pub(crate) fn lazy<F, R>(func: F) -> Lazy<F, R>
 where
     F: FnOnce() -> R,
-    R: IntoFuture,
+    R: Future + Unpin,
 {
     Lazy {
         inner: Inner::Init(func),
@@ -18,8 +18,8 @@ where
 
 // FIXME: allow() required due to `impl Trait` leaking types to this lint
 #[allow(missing_debug_implementations)]
-pub(crate) struct Lazy<F, R: IntoFuture> {
-    inner: Inner<F, R::Future>
+pub(crate) struct Lazy<F, R> {
+    inner: Inner<F, R>
 }
 
 enum Inner<F, R> {
@@ -31,7 +31,7 @@ enum Inner<F, R> {
 impl<F, R> Started for Lazy<F, R>
 where
     F: FnOnce() -> R,
-    R: IntoFuture,
+    R: Future + Unpin,
 {
     fn started(&self) -> bool {
         match self.inner {
@@ -45,21 +45,20 @@ where
 impl<F, R> Future for Lazy<F, R>
 where
     F: FnOnce() -> R,
-    R: IntoFuture,
+    R: Future + Unpin,
 {
-    type Item = R::Item;
-    type Error = R::Error;
+    type Output = R::Output;
 
-    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
+    fn poll(mut self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
         match self.inner {
-            Inner::Fut(ref mut f) => return f.poll(),
+            Inner::Fut(ref mut f) => return Pin::new(f).poll(cx),
             _ => (),
         }
 
         match mem::replace(&mut self.inner, Inner::Empty) {
             Inner::Init(func) => {
-                let mut fut = func().into_future();
-                let ret = fut.poll();
+                let mut fut = func();
+                let ret = Pin::new(&mut fut).poll(cx);
                 self.inner = Inner::Fut(fut);
                 ret
             },
@@ -68,3 +67,6 @@ where
     }
 }
 
+// The closure `F` is never pinned
+impl<F, R: Unpin> Unpin for Lazy<F, R> {}
+