Simplify extension traits using a macro

src/io/seek.rs

@@ -5,119 +5,114 @@ use cfg_if::cfg_if;
 use crate::future::Future;
 use crate::io::{self, SeekFrom};
 use crate::task::{Context, Poll};
+use crate::utils::extension_trait;
 
 cfg_if! {
     if #[cfg(feature = "docs")] {
         use std::ops::{Deref, DerefMut};
+    }
+}
 
-        #[doc(hidden)]
-        pub struct ImplFuture<T>(std::marker::PhantomData<T>);
-
-        /// Allows seeking through a byte stream.
-        ///
-        /// This trait is a re-export of [`futures::io::AsyncSeek`] and is an async version of
-        /// [`std::io::Seek`].
-        ///
-        /// The [provided methods] do not really exist in the trait itself, but they become
-        /// available when the prelude is imported:
-        ///
-        /// ```
-        /// # #[allow(unused_imports)]
-        /// use async_std::prelude::*;
-        /// ```
-        ///
-        /// [`std::io::Seek`]: https://doc.rust-lang.org/std/io/trait.Seek.html
-        /// [`futures::io::AsyncSeek`]:
-        /// https://docs.rs/futures-preview/0.3.0-alpha.17/futures/io/trait.AsyncSeek.html
-        /// [provided methods]: #provided-methods
-        pub trait Seek {
-            /// Attempt to seek to an offset, in bytes, in a stream.
-            fn poll_seek(
-                self: Pin<&mut Self>,
-                cx: &mut Context<'_>,
-                pos: SeekFrom,
-            ) -> Poll<io::Result<u64>>;
-
-            /// Seeks to a new position in a byte stream.
-            ///
-            /// Returns the new position in the byte stream.
-            ///
-            /// A seek beyond the end of stream is allowed, but behavior is defined by the
-            /// implementation.
-            ///
-            /// # Examples
-            ///
-            /// ```no_run
-            /// # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
-            /// #
-            /// use async_std::fs::File;
-            /// use async_std::io::SeekFrom;
-            /// use async_std::prelude::*;
-            ///
-            /// let mut file = File::open("a.txt").await?;
-            ///
-            /// let file_len = file.seek(SeekFrom::End(0)).await?;
-            /// #
-            /// # Ok(()) }) }
-            /// ```
-            fn seek(&mut self, pos: SeekFrom) -> ImplFuture<io::Result<u64>>
-            where
-                Self: Unpin
-            {
-                unreachable!()
-            }
-        }
+extension_trait! {
+    #[doc = r#"
+        Allows seeking through a byte stream.
 
-        impl<T: Seek + Unpin + ?Sized> Seek for Box<T> {
-            fn poll_seek(
-                self: Pin<&mut Self>,
-                cx: &mut Context<'_>,
-                pos: SeekFrom,
-            ) -> Poll<io::Result<u64>> {
-                unreachable!()
-            }
-        }
+        This trait is a re-export of [`futures::io::AsyncSeek`] and is an async version of
+        [`std::io::Seek`].
 
-        impl<T: Seek + Unpin + ?Sized> Seek for &mut T {
-            fn poll_seek(
-                self: Pin<&mut Self>,
-                cx: &mut Context<'_>,
-                pos: SeekFrom,
-            ) -> Poll<io::Result<u64>> {
-                unreachable!()
-            }
-        }
+        The [provided methods] do not really exist in the trait itself, but they become
+        available when the prelude is imported:
+
+        ```
+        # #[allow(unused_imports)]
+        use async_std::prelude::*;
+        ```
+
+        [`std::io::Seek`]: https://doc.rust-lang.org/std/io/trait.Seek.html
+        [`futures::io::AsyncSeek`]:
+        https://docs.rs/futures-preview/0.3.0-alpha.17/futures/io/trait.AsyncSeek.html
+        [provided methods]: #provided-methods
+    "#]
+    pub trait Seek [SeekExt: futures_io::AsyncSeek] {
+        #[doc = r#"
+            Attempt to seek to an offset, in bytes, in a stream.
+        "#]
+        fn poll_seek(
+            self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            pos: SeekFrom,
+        ) -> Poll<io::Result<u64>>;
+
+        #[doc = r#"
+            Seeks to a new position in a byte stream.
+
+            Returns the new position in the byte stream.
+
+            A seek beyond the end of stream is allowed, but behavior is defined by the
+            implementation.
+
+            # Examples
+
+            ```no_run
+            # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
+            #
+            use async_std::fs::File;
+            use async_std::io::SeekFrom;
+            use async_std::prelude::*;
 
-        impl<P> Seek for Pin<P>
+            let mut file = File::open("a.txt").await?;
+
+            let file_len = file.seek(SeekFrom::End(0)).await?;
+            #
+            # Ok(()) }) }
+            ```
+        "#]
+        fn seek(
+            &mut self,
+            pos: SeekFrom,
+        ) -> impl Future<Output = io::Result<u64>> [SeekFuture<'_, Self>]
         where
-            P: DerefMut + Unpin,
-            <P as Deref>::Target: Seek,
+            Self: Unpin,
         {
-            fn poll_seek(
-                self: Pin<&mut Self>,
-                cx: &mut Context<'_>,
-                pos: SeekFrom,
-            ) -> Poll<io::Result<u64>> {
-                unreachable!()
-            }
+            SeekFuture { seeker: self, pos }
         }
-    } else {
-        pub use futures_io::AsyncSeek as Seek;
     }
-}
 
-#[doc(hidden)]
-pub trait SeekExt: futures_io::AsyncSeek {
-    fn seek(&mut self, pos: SeekFrom) -> SeekFuture<'_, Self>
+    impl<T: Seek + Unpin + ?Sized> Seek for Box<T> {
+        fn poll_seek(
+            self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            pos: SeekFrom,
+        ) -> Poll<io::Result<u64>> {
+            unreachable!("this impl only appears in the rendered docs")
+        }
+    }
+
+    impl<T: Seek + Unpin + ?Sized> Seek for &mut T {
+        fn poll_seek(
+            self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            pos: SeekFrom,
+        ) -> Poll<io::Result<u64>> {
+            unreachable!("this impl only appears in the rendered docs")
+        }
+    }
+
+    impl<P> Seek for Pin<P>
     where
-        Self: Unpin,
+        P: DerefMut + Unpin,
+        <P as Deref>::Target: Seek,
     {
-        SeekFuture { seeker: self, pos }
+        fn poll_seek(
+            self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            pos: SeekFrom,
+        ) -> Poll<io::Result<u64>> {
+            unreachable!("this impl only appears in the rendered docs")
+        }
     }
 }
 
-impl<T: futures_io::AsyncSeek + ?Sized> SeekExt for T {}
-
 #[doc(hidden)]
 #[allow(missing_debug_implementations)]
 pub struct SeekFuture<'a, T: Unpin + ?Sized> {