Constrain Future::Output in supertrait of TryFuture

futures-core/src/future.rs

@@ -2,7 +2,6 @@
 
 use core::ops::DerefMut;
 use core::pin::Pin;
-use core::task::{Context, Poll};
 
 #[doc(no_inline)]
 pub use core::future::Future;
@@ -20,10 +19,10 @@ pub type LocalBoxFuture<'a, T> = Pin<alloc::boxed::Box<dyn Future<Output = T> +
 /// should no longer be polled.
 ///
 /// `is_terminated` will return `true` if a future should no longer be polled.
-/// Usually, this state occurs after `poll` (or `try_poll`) returned
-/// `Poll::Ready`. However, `is_terminated` may also return `true` if a future
-/// has become inactive and can no longer make progress and should be ignored
-/// or dropped rather than being `poll`ed again.
+/// Usually, this state occurs after `poll` returned `Poll::Ready`. However,
+/// `is_terminated` may also return `true` if a future has become inactive
+/// and can no longer make progress and should be ignored or dropped rather
+/// than being `poll`ed again.
 pub trait FusedFuture: Future {
     /// Returns `true` if the underlying future should no longer be polled.
     fn is_terminated(&self) -> bool;
@@ -45,29 +44,14 @@ where
     }
 }
 
-mod private_try_future {
-    use super::Future;
-
-    pub trait Sealed {}
-
-    impl<F, T, E> Sealed for F where F: ?Sized + Future<Output = Result<T, E>> {}
-}
-
 /// A convenience for futures that return `Result` values that includes
 /// a variety of adapters tailored to such futures.
-pub trait TryFuture: Future + private_try_future::Sealed {
+pub trait TryFuture: Future<Output = Result<Self::Ok, Self::Error>> {
     /// The type of successful values yielded by this future
     type Ok;
 
     /// The type of failures yielded by this future
     type Error;
-
-    /// Poll this `TryFuture` as if it were a `Future`.
-    ///
-    /// This method is a stopgap for a compiler limitation that prevents us from
-    /// directly inheriting from the `Future` trait; in the future it won't be
-    /// needed.
-    fn try_poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<Self::Ok, Self::Error>>;
 }
 
 impl<F, T, E> TryFuture for F
@@ -76,11 +60,6 @@ where
 {
     type Ok = T;
     type Error = E;
-
-    #[inline]
-    fn try_poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        self.poll(cx)
-    }
 }
 
 #[cfg(feature = "alloc")]

futures-util/src/compat/compat03as01.rs

@@ -102,7 +102,7 @@ where
     type Error = Fut::Error;
 
     fn poll(&mut self) -> Poll01<Self::Item, Self::Error> {
-        with_context(self, |inner, cx| poll_03_to_01(inner.try_poll(cx)))
+        with_context(self, |inner, cx| poll_03_to_01(inner.poll(cx)))
     }
 }
 

futures-util/src/future/mod.rs

@@ -40,8 +40,8 @@ pub use self::future::{Shared, WeakShared};
 
 mod try_future;
 pub use self::try_future::{
-    AndThen, ErrInto, InspectErr, InspectOk, IntoFuture, MapErr, MapOk, MapOkOrElse, OkInto,
-    OrElse, TryFlatten, TryFlattenStream, TryFutureExt, UnwrapOrElse,
+    AndThen, ErrInto, InspectErr, InspectOk, MapErr, MapOk, MapOkOrElse, OkInto, OrElse,
+    TryFlatten, TryFlattenStream, TryFutureExt, UnwrapOrElse,
 };
 
 #[cfg(feature = "sink")]

futures-util/src/future/select_ok.rs

@@ -1,5 +1,5 @@
 use super::assert_future;
-use crate::future::TryFutureExt;
+use crate::future::FutureExt;
 use alloc::vec::Vec;
 use core::iter::FromIterator;
 use core::mem;
@@ -49,7 +49,7 @@ impl<Fut: TryFuture + Unpin> Future for SelectOk<Fut> {
         // loop until we've either exhausted all errors, a success was hit, or nothing is ready
         loop {
             let item =
-                self.inner.iter_mut().enumerate().find_map(|(i, f)| match f.try_poll_unpin(cx) {
+                self.inner.iter_mut().enumerate().find_map(|(i, f)| match f.poll_unpin(cx) {
                     Poll::Pending => None,
                     Poll::Ready(e) => Some((i, e)),
                 });

futures-util/src/future/try_future/mod.rs

@@ -5,12 +5,7 @@
 
 #[cfg(feature = "compat")]
 use crate::compat::Compat;
-use core::pin::Pin;
-use futures_core::{
-    future::TryFuture,
-    stream::TryStream,
-    task::{Context, Poll},
-};
+use futures_core::{future::TryFuture, stream::TryStream};
 #[cfg(feature = "sink")]
 use futures_sink::Sink;
 
@@ -23,7 +18,6 @@ use crate::future::{assert_future, Inspect, Map};
 use crate::stream::assert_stream;
 
 // Combinators
-mod into_future;
 mod try_flatten;
 mod try_flatten_err;
 
@@ -89,46 +83,43 @@ delegate_all!(
 delegate_all!(
     /// Future for the [`inspect_ok`](super::TryFutureExt::inspect_ok) method.
     InspectOk<Fut, F>(
-        Inspect<IntoFuture<Fut>, InspectOkFn<F>>
-    ): Debug + Future + FusedFuture + New[|x: Fut, f: F| Inspect::new(IntoFuture::new(x), inspect_ok_fn(f))]
+        Inspect<Fut, InspectOkFn<F>>
+    ): Debug + Future + FusedFuture + New[|x: Fut, f: F| Inspect::new(x, inspect_ok_fn(f))]
 );
 
 delegate_all!(
     /// Future for the [`inspect_err`](super::TryFutureExt::inspect_err) method.
     InspectErr<Fut, F>(
-        Inspect<IntoFuture<Fut>, InspectErrFn<F>>
-    ): Debug + Future + FusedFuture + New[|x: Fut, f: F| Inspect::new(IntoFuture::new(x), inspect_err_fn(f))]
+        Inspect<Fut, InspectErrFn<F>>
+    ): Debug + Future + FusedFuture + New[|x: Fut, f: F| Inspect::new(x, inspect_err_fn(f))]
 );
 
-#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
-pub use self::into_future::IntoFuture;
-
 delegate_all!(
     /// Future for the [`map_ok`](TryFutureExt::map_ok) method.
     MapOk<Fut, F>(
-        Map<IntoFuture<Fut>, MapOkFn<F>>
-    ): Debug + Future + FusedFuture + New[|x: Fut, f: F| Map::new(IntoFuture::new(x), map_ok_fn(f))]
+        Map<Fut, MapOkFn<F>>
+    ): Debug + Future + FusedFuture + New[|x: Fut, f: F| Map::new(x, map_ok_fn(f))]
 );
 
 delegate_all!(
     /// Future for the [`map_err`](TryFutureExt::map_err) method.
     MapErr<Fut, F>(
-        Map<IntoFuture<Fut>, MapErrFn<F>>
-    ): Debug + Future + FusedFuture + New[|x: Fut, f: F| Map::new(IntoFuture::new(x), map_err_fn(f))]
+        Map<Fut, MapErrFn<F>>
+    ): Debug + Future + FusedFuture + New[|x: Fut, f: F| Map::new(x, map_err_fn(f))]
 );
 
 delegate_all!(
     /// Future for the [`map_ok_or_else`](TryFutureExt::map_ok_or_else) method.
     MapOkOrElse<Fut, F, G>(
-        Map<IntoFuture<Fut>, MapOkOrElseFn<F, G>>
-    ): Debug + Future + FusedFuture + New[|x: Fut, f: F, g: G| Map::new(IntoFuture::new(x), map_ok_or_else_fn(f, g))]
+        Map<Fut, MapOkOrElseFn<F, G>>
+    ): Debug + Future + FusedFuture + New[|x: Fut, f: F, g: G| Map::new(x, map_ok_or_else_fn(f, g))]
 );
 
 delegate_all!(
     /// Future for the [`unwrap_or_else`](TryFutureExt::unwrap_or_else) method.
     UnwrapOrElse<Fut, F>(
-        Map<IntoFuture<Fut>, UnwrapOrElseFn<F>>
-    ): Debug + Future + FusedFuture + New[|x: Fut, f: F| Map::new(IntoFuture::new(x), unwrap_or_else_fn(f))]
+        Map<Fut, UnwrapOrElseFn<F>>
+    ): Debug + Future + FusedFuture + New[|x: Fut, f: F| Map::new(x, unwrap_or_else_fn(f))]
 );
 
 impl<Fut: ?Sized + TryFuture> TryFutureExt for Fut {}
@@ -585,41 +576,4 @@ pub trait TryFutureExt: TryFuture {
     {
         Compat::new(self)
     }
-
-    /// Wraps a [`TryFuture`] into a type that implements
-    /// [`Future`](std::future::Future).
-    ///
-    /// [`TryFuture`]s currently do not implement the
-    /// [`Future`](std::future::Future) trait due to limitations of the
-    /// compiler.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use futures::future::{Future, TryFuture, TryFutureExt};
-    ///
-    /// # type T = i32;
-    /// # type E = ();
-    /// fn make_try_future() -> impl TryFuture<Ok = T, Error = E> { // ... }
-    /// # async { Ok::<i32, ()>(1) }
-    /// # }
-    /// fn take_future(future: impl Future<Output = Result<T, E>>) { /* ... */ }
-    ///
-    /// take_future(make_try_future().into_future());
-    /// ```
-    fn into_future(self) -> IntoFuture<Self>
-    where
-        Self: Sized,
-    {
-        assert_future::<Result<Self::Ok, Self::Error>, _>(IntoFuture::new(self))
-    }
-
-    /// A convenience method for calling [`TryFuture::try_poll`] on [`Unpin`]
-    /// future types.
-    fn try_poll_unpin(&mut self, cx: &mut Context<'_>) -> Poll<Result<Self::Ok, Self::Error>>
-    where
-        Self: Unpin,
-    {
-        Pin::new(self).try_poll(cx)
-    }
 }

futures-util/src/future/try_future/try_flatten.rs

@@ -43,15 +43,15 @@ where
     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
         Poll::Ready(loop {
             match self.as_mut().project() {
-                TryFlattenProj::First { f } => match ready!(f.try_poll(cx)) {
+                TryFlattenProj::First { f } => match ready!(f.poll(cx)) {
                     Ok(f) => self.set(Self::Second { f }),
                     Err(e) => {
                         self.set(Self::Empty);
                         break Err(e);
                     }
                 },
                 TryFlattenProj::Second { f } => {
-                    let output = ready!(f.try_poll(cx));
+                    let output = ready!(f.poll(cx));
                     self.set(Self::Empty);
                     break output;
                 }
@@ -81,7 +81,7 @@ where
     fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
         Poll::Ready(loop {
             match self.as_mut().project() {
-                TryFlattenProj::First { f } => match ready!(f.try_poll(cx)) {
+                TryFlattenProj::First { f } => match ready!(f.poll(cx)) {
                     Ok(f) => self.set(Self::Second { f }),
                     Err(e) => {
                         self.set(Self::Empty);
@@ -112,7 +112,7 @@ where
     fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
         Poll::Ready(loop {
             match self.as_mut().project() {
-                TryFlattenProj::First { f } => match ready!(f.try_poll(cx)) {
+                TryFlattenProj::First { f } => match ready!(f.poll(cx)) {
                     Ok(f) => self.set(Self::Second { f }),
                     Err(e) => {
                         self.set(Self::Empty);

futures-util/src/future/try_future/try_flatten_err.rs

@@ -40,15 +40,15 @@ where
     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
         Poll::Ready(loop {
             match self.as_mut().project() {
-                TryFlattenErrProj::First { f } => match ready!(f.try_poll(cx)) {
+                TryFlattenErrProj::First { f } => match ready!(f.poll(cx)) {
                     Err(f) => self.set(Self::Second { f }),
                     Ok(e) => {
                         self.set(Self::Empty);
                         break Ok(e);
                     }
                 },
                 TryFlattenErrProj::Second { f } => {
-                    let output = ready!(f.try_poll(cx));
+                    let output = ready!(f.poll(cx));
                     self.set(Self::Empty);
                     break output;
                 }

futures-util/src/future/try_join_all.rs

@@ -10,11 +10,10 @@ use core::mem;
 use core::pin::Pin;
 use core::task::{Context, Poll};
 
-use super::{assert_future, join_all, IntoFuture, TryFuture, TryMaybeDone};
+use super::{assert_future, join_all, TryFuture, TryMaybeDone};
 
 #[cfg(not(futures_no_atomic_cas))]
 use crate::stream::{FuturesOrdered, TryCollect, TryStreamExt};
-use crate::TryFutureExt;
 
 enum FinalState<E = ()> {
     Pending,
@@ -36,11 +35,11 @@ where
     F: TryFuture,
 {
     Small {
-        elems: Pin<Box<[TryMaybeDone<IntoFuture<F>>]>>,
+        elems: Pin<Box<[TryMaybeDone<F>]>>,
     },
     #[cfg(not(futures_no_atomic_cas))]
     Big {
-        fut: TryCollect<FuturesOrdered<IntoFuture<F>>, Vec<F::Ok>>,
+        fut: TryCollect<FuturesOrdered<F>, Vec<F::Ok>>,
     },
 }
 
@@ -119,7 +118,7 @@ where
     I: IntoIterator,
     I::Item: TryFuture,
 {
-    let iter = iter.into_iter().map(TryFutureExt::into_future);
+    let iter = iter.into_iter();
 
     #[cfg(futures_no_atomic_cas)]
     {
@@ -159,7 +158,7 @@ where
                 let mut state = FinalState::AllDone;
 
                 for elem in join_all::iter_pin_mut(elems.as_mut()) {
-                    match elem.try_poll(cx) {
+                    match elem.poll(cx) {
                         Poll::Pending => state = FinalState::Pending,
                         Poll::Ready(Ok(())) => {}
                         Poll::Ready(Err(e)) => {

futures-util/src/future/try_maybe_done.rs

@@ -76,7 +76,7 @@ impl<Fut: TryFuture> Future for TryMaybeDone<Fut> {
     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
         unsafe {
             match self.as_mut().get_unchecked_mut() {
-                TryMaybeDone::Future(f) => match ready!(Pin::new_unchecked(f).try_poll(cx)) {
+                TryMaybeDone::Future(f) => match ready!(Pin::new_unchecked(f).poll(cx)) {
                     Ok(res) => self.set(Self::Done(res)),
                     Err(e) => {
                         self.set(Self::Gone);

futures-util/src/future/try_select.rs

@@ -1,4 +1,4 @@
-use crate::future::{Either, TryFutureExt};
+use crate::future::{Either, FutureExt};
 use core::pin::Pin;
 use futures_core::future::{Future, TryFuture};
 use futures_core::task::{Context, Poll};
@@ -69,10 +69,10 @@ where
 
     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
         let (mut a, mut b) = self.inner.take().expect("cannot poll Select twice");
-        match a.try_poll_unpin(cx) {
+        match a.poll_unpin(cx) {
             Poll::Ready(Err(x)) => Poll::Ready(Err(Either::Left((x, b)))),
             Poll::Ready(Ok(x)) => Poll::Ready(Ok(Either::Left((x, b)))),
-            Poll::Pending => match b.try_poll_unpin(cx) {
+            Poll::Pending => match b.poll_unpin(cx) {
                 Poll::Ready(Err(x)) => Poll::Ready(Err(Either::Right((x, a)))),
                 Poll::Ready(Ok(x)) => Poll::Ready(Ok(Either::Right((x, a)))),
                 Poll::Pending => {

futures-util/src/stream/stream/try_fold.rs

@@ -70,7 +70,7 @@ where
         Poll::Ready(loop {
             if let Some(fut) = this.future.as_mut().as_pin_mut() {
                 // we're currently processing a future to produce a new accum value
-                let res = ready!(fut.try_poll(cx));
+                let res = ready!(fut.poll(cx));
                 this.future.set(None);
                 match res {
                     Ok(a) => *this.accum = Some(a),