chore: use poll_fn from std (#6810)

tokio-stream/src/lib.rs

@@ -74,9 +74,6 @@
 #[macro_use]
 mod macros;
 
-mod poll_fn;
-pub(crate) use poll_fn::poll_fn;
-
 pub mod wrappers;
 
 mod stream_ext;

tokio-stream/src/poll_fn.rs

@@ -1,35 +0,0 @@
-use std::future::Future;
-use std::pin::Pin;
-use std::task::{Context, Poll};
-
-pub(crate) struct PollFn<F> {
-    f: F,
-}
-
-pub(crate) fn poll_fn<T, F>(f: F) -> PollFn<F>
-where
-    F: FnMut(&mut Context<'_>) -> Poll<T>,
-{
-    PollFn { f }
-}
-
-impl<T, F> Future for PollFn<F>
-where
-    F: FnMut(&mut Context<'_>) -> Poll<T>,
-{
-    type Output = T;
-
-    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
-        // Safety: We never construct a `Pin<&mut F>` anywhere, so accessing `f`
-        // mutably in an unpinned way is sound.
-        //
-        // This use of unsafe cannot be replaced with the pin-project macro
-        // because:
-        //  * If we put `#[pin]` on the field, then it gives us a `Pin<&mut F>`,
-        //    which we can't use to call the closure.
-        //  * If we don't put `#[pin]` on the field, then it makes `PollFn` be
-        //    unconditionally `Unpin`, which we also don't want.
-        let me = unsafe { Pin::into_inner_unchecked(self) };
-        (me.f)(cx)
-    }
-}

tokio-stream/src/stream_map.rs

@@ -1,6 +1,7 @@
-use crate::{poll_fn, Stream};
+use crate::Stream;
 
 use std::borrow::Borrow;
+use std::future::poll_fn;
 use std::hash::Hash;
 use std::pin::Pin;
 use std::task::{ready, Context, Poll};