Move BorrowedBuf and BorrowedCursor from std:io to core::io

Assigned new feature name `core_io_borrowed_buf` to distinguish from the
`Read::read_buf` functionality in `std::io`.

Author: jmillikin

compiler/rustc_span/src/lib.rs

@@ -24,6 +24,7 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![feature(array_windows)]
 #![feature(cfg_match)]
+#![feature(core_io_borrowed_buf)]
 #![feature(if_let_guard)]
 #![feature(let_chains)]
 #![feature(min_specialization)]

library/std/src/io/readbuf.rs renamed to library/core/src/io/borrowed_buf.rs

@@ -1,10 +1,9 @@
-#![unstable(feature = "read_buf", issue = "78485")]
+#![unstable(feature = "core_io_borrowed_buf", issue = "117693")]
 
 #[cfg(test)]
 mod tests;
 
 use crate::fmt::{self, Debug, Formatter};
-use crate::io::{Result, Write};
 use crate::mem::{self, MaybeUninit};
 use crate::{cmp, ptr};
 
@@ -303,15 +302,3 @@ impl<'a> BorrowedCursor<'a> {
         self.buf.filled += buf.len();
     }
 }
-
-impl<'a> Write for BorrowedCursor<'a> {
-    fn write(&mut self, buf: &[u8]) -> Result<usize> {
-        self.append(buf);
-        Ok(buf.len())
-    }
-
-    #[inline]
-    fn flush(&mut self) -> Result<()> {
-        Ok(())
-    }
-}

library/std/src/io/readbuf/tests.rs renamed to library/core/src/io/borrowed_buf/tests.rs

@@ -0,0 +1,6 @@
+//! Traits, helpers, and type definitions for core I/O functionality.
+
+mod borrowed_buf;
+
+#[unstable(feature = "core_io_borrowed_buf", issue = "117693")]
+pub use self::borrowed_buf::{BorrowedBuf, BorrowedCursor};

library/core/src/io/mod.rs

@@ -369,6 +369,8 @@ pub mod async_iter;
 pub mod cell;
 pub mod char;
 pub mod ffi;
+#[unstable(feature = "core_io_borrowed_buf", issue = "117693")]
+pub mod io;
 pub mod iter;
 pub mod net;
 pub mod option;

library/core/src/lib.rs

@@ -528,3 +528,16 @@ impl<A: Allocator> Write for VecDeque<u8, A> {
         Ok(())
     }
 }
+
+#[unstable(feature = "read_buf", issue = "78485")]
+impl<'a> io::Write for core::io::BorrowedCursor<'a> {
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        self.append(buf);
+        Ok(buf.len())
+    }
+
+    #[inline]
+    fn flush(&mut self) -> io::Result<()> {
+        Ok(())
+    }
+}

library/std/src/io/impls.rs

@@ -330,7 +330,7 @@ pub use self::{
 };
 
 #[unstable(feature = "read_buf", issue = "78485")]
-pub use self::readbuf::{BorrowedBuf, BorrowedCursor};
+pub use core::io::{BorrowedBuf, BorrowedCursor};
 pub(crate) use error::const_io_error;
 
 mod buffered;
@@ -339,7 +339,6 @@ mod cursor;
 mod error;
 mod impls;
 pub mod prelude;
-mod readbuf;
 mod stdio;
 mod util;
 

library/std/src/io/mod.rs

@@ -310,6 +310,7 @@
 // tidy-alphabetical-start
 #![feature(char_internals)]
 #![feature(core_intrinsics)]
+#![feature(core_io_borrowed_buf)]
 #![feature(duration_constants)]
 #![feature(error_generic_member_access)]
 #![feature(error_in_core)]