Do not require Unpin for some trait impls (#7204)

Author: a1phyr

tokio/src/io/async_buf_read.rs

@@ -84,15 +84,15 @@ impl<T: ?Sized + AsyncBufRead + Unpin> AsyncBufRead for &mut T {
 
 impl<P> AsyncBufRead for Pin<P>
 where
-    P: DerefMut + Unpin,
+    P: DerefMut,
     P::Target: AsyncBufRead,
 {
     fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
-        self.get_mut().as_mut().poll_fill_buf(cx)
+        crate::util::pin_as_deref_mut(self).poll_fill_buf(cx)
     }
 
     fn consume(self: Pin<&mut Self>, amt: usize) {
-        self.get_mut().as_mut().consume(amt);
+        crate::util::pin_as_deref_mut(self).consume(amt);
     }
 }
 

tokio/src/io/async_read.rs

@@ -80,15 +80,15 @@ impl<T: ?Sized + AsyncRead + Unpin> AsyncRead for &mut T {
 
 impl<P> AsyncRead for Pin<P>
 where
-    P: DerefMut + Unpin,
+    P: DerefMut,
     P::Target: AsyncRead,
 {
     fn poll_read(
         self: Pin<&mut Self>,
         cx: &mut Context<'_>,
         buf: &mut ReadBuf<'_>,
     ) -> Poll<io::Result<()>> {
-        self.get_mut().as_mut().poll_read(cx, buf)
+        crate::util::pin_as_deref_mut(self).poll_read(cx, buf)
     }
 }
 

tokio/src/io/async_seek.rs

@@ -68,15 +68,15 @@ impl<T: ?Sized + AsyncSeek + Unpin> AsyncSeek for &mut T {
 
 impl<P> AsyncSeek for Pin<P>
 where
-    P: DerefMut + Unpin,
+    P: DerefMut,
     P::Target: AsyncSeek,
 {
     fn start_seek(self: Pin<&mut Self>, pos: SeekFrom) -> io::Result<()> {
-        self.get_mut().as_mut().start_seek(pos)
+        crate::util::pin_as_deref_mut(self).start_seek(pos)
     }
 
     fn poll_complete(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
-        self.get_mut().as_mut().poll_complete(cx)
+        crate::util::pin_as_deref_mut(self).poll_complete(cx)
     }
 }
 

tokio/src/io/async_write.rs

@@ -224,35 +224,35 @@ impl<T: ?Sized + AsyncWrite + Unpin> AsyncWrite for &mut T {
 
 impl<P> AsyncWrite for Pin<P>
 where
-    P: DerefMut + Unpin,
+    P: DerefMut,
     P::Target: AsyncWrite,
 {
     fn poll_write(
         self: Pin<&mut Self>,
         cx: &mut Context<'_>,
         buf: &[u8],
     ) -> Poll<io::Result<usize>> {
-        self.get_mut().as_mut().poll_write(cx, buf)
+        crate::util::pin_as_deref_mut(self).poll_write(cx, buf)
     }
 
     fn poll_write_vectored(
         self: Pin<&mut Self>,
         cx: &mut Context<'_>,
         bufs: &[IoSlice<'_>],
     ) -> Poll<io::Result<usize>> {
-        self.get_mut().as_mut().poll_write_vectored(cx, bufs)
+        crate::util::pin_as_deref_mut(self).poll_write_vectored(cx, bufs)
     }
 
     fn is_write_vectored(&self) -> bool {
         (**self).is_write_vectored()
     }
 
     fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-        self.get_mut().as_mut().poll_flush(cx)
+        crate::util::pin_as_deref_mut(self).poll_flush(cx)
     }
 
     fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-        self.get_mut().as_mut().poll_shutdown(cx)
+        crate::util::pin_as_deref_mut(self).poll_shutdown(cx)
     }
 }
 

tokio/src/util/mod.rs

@@ -96,3 +96,11 @@ pub(crate) mod cacheline;
 cfg_io_driver_impl! {
     pub(crate) mod ptr_expose;
 }
+
+use std::{ops::DerefMut, pin::Pin};
+
+/// Copy of [`std::pin::Pin::as_deref_mut`].
+// TODO: Remove this once we bump the MSRV to 1.84.
+pub(crate) fn pin_as_deref_mut<P: DerefMut>(ptr: Pin<&mut Pin<P>>) -> Pin<&mut P::Target> {
+    unsafe { ptr.get_unchecked_mut() }.as_mut()
+}