io: remove poll_{read,write}_buf from traits (#2882)

These functions have object safety issues. It also has been decided to
avoid vectored operations on the I/O traits. A later PR will bring back
vectored operations on specific types that support them.

Refs: #2879, #2716

tokio/tests/io_async_read.rs

@@ -1,113 +1,10 @@
 #![warn(rust_2018_idioms)]
 #![cfg(feature = "full")]
 
-use tokio::io::{AsyncRead, ReadBuf};
-use tokio_test::task;
-use tokio_test::{assert_ready_err, assert_ready_ok};
-
-use bytes::BytesMut;
-use std::io;
-use std::pin::Pin;
-use std::task::{Context, Poll};
+use tokio::io::AsyncRead;
 
 #[test]
 fn assert_obj_safe() {
     fn _assert<T>() {}
     _assert::<Box<dyn AsyncRead>>();
 }
-
-#[test]
-fn read_buf_success() {
-    struct Rd;
-
-    impl AsyncRead for Rd {
-        fn poll_read(
-            self: Pin<&mut Self>,
-            _cx: &mut Context<'_>,
-            buf: &mut ReadBuf<'_>,
-        ) -> Poll<io::Result<()>> {
-            buf.append(b"hello world");
-            Poll::Ready(Ok(()))
-        }
-    }
-
-    let mut buf = BytesMut::with_capacity(65);
-
-    task::spawn(Rd).enter(|cx, rd| {
-        let n = assert_ready_ok!(rd.poll_read_buf(cx, &mut buf));
-
-        assert_eq!(11, n);
-        assert_eq!(buf[..], b"hello world"[..]);
-    });
-}
-
-#[test]
-fn read_buf_error() {
-    struct Rd;
-
-    impl AsyncRead for Rd {
-        fn poll_read(
-            self: Pin<&mut Self>,
-            _cx: &mut Context<'_>,
-            _buf: &mut ReadBuf<'_>,
-        ) -> Poll<io::Result<()>> {
-            let err = io::ErrorKind::Other.into();
-            Poll::Ready(Err(err))
-        }
-    }
-
-    let mut buf = BytesMut::with_capacity(65);
-
-    task::spawn(Rd).enter(|cx, rd| {
-        let err = assert_ready_err!(rd.poll_read_buf(cx, &mut buf));
-        assert_eq!(err.kind(), io::ErrorKind::Other);
-    });
-}
-
-#[test]
-fn read_buf_no_capacity() {
-    struct Rd;
-
-    impl AsyncRead for Rd {
-        fn poll_read(
-            self: Pin<&mut Self>,
-            _cx: &mut Context<'_>,
-            _buf: &mut ReadBuf<'_>,
-        ) -> Poll<io::Result<()>> {
-            unimplemented!();
-        }
-    }
-
-    let mut buf = [0u8; 0];
-
-    task::spawn(Rd).enter(|cx, rd| {
-        let n = assert_ready_ok!(rd.poll_read_buf(cx, &mut &mut buf[..]));
-        assert_eq!(0, n);
-    });
-}
-
-#[test]
-fn read_buf_uninitialized_ok() {
-    struct Rd;
-
-    impl AsyncRead for Rd {
-        fn poll_read(
-            self: Pin<&mut Self>,
-            _cx: &mut Context<'_>,
-            buf: &mut ReadBuf<'_>,
-        ) -> Poll<io::Result<()>> {
-            assert_eq!(buf.remaining(), 64);
-            assert_eq!(buf.filled().len(), 0);
-            assert_eq!(buf.initialized().len(), 0);
-            Poll::Ready(Ok(()))
-        }
-    }
-
-    // Can't create BytesMut w/ zero capacity, so fill it up
-    let mut buf = BytesMut::with_capacity(64);
-
-    task::spawn(Rd).enter(|cx, rd| {
-        let n = assert_ready_ok!(rd.poll_read_buf(cx, &mut buf));
-        assert_eq!(0, n);
-    });
-}