7 files changed, 91 insertions, 23 deletions
diff --git a/library/std/src/io/cursor.rs b/library/std/src/io/cursor.rs
index b2ffeb0f95d..08832bbc1e3 100644
--- a/library/std/src/io/cursor.rs
+++ b/library/std/src/io/cursor.rs
@@ -153,7 +153,7 @@ impl<T> Cursor<T> {
     /// let reference = buff.get_mut();
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_mut_cursor", issue = "130801")]
+    #[rustc_const_stable(feature = "const_mut_cursor", since = "1.86.0")]
     pub const fn get_mut(&mut self) -> &mut T {
         &mut self.inner
     }
@@ -201,7 +201,7 @@ impl<T> Cursor<T> {
     /// assert_eq!(buff.position(), 4);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_mut_cursor", issue = "130801")]
+    #[rustc_const_stable(feature = "const_mut_cursor", since = "1.86.0")]
     pub const fn set_position(&mut self, pos: u64) {
         self.pos = pos;
     }
diff --git a/library/std/src/io/error.rs b/library/std/src/io/error.rs
index 38b72336617..30bc0e3b088 100644
--- a/library/std/src/io/error.rs
+++ b/library/std/src/io/error.rs
@@ -83,7 +83,7 @@ impl Error {
 
     pub(crate) const UNKNOWN_THREAD_COUNT: Self = const_error!(
         ErrorKind::NotFound,
-        "The number of hardware threads is not known for the target platform"
+        "The number of hardware threads is not known for the target platform",
     );
 
     pub(crate) const UNSUPPORTED_PLATFORM: Self =
diff --git a/library/std/src/io/impls.rs b/library/std/src/io/impls.rs
index b952c85addf..8239b29884e 100644
--- a/library/std/src/io/impls.rs
+++ b/library/std/src/io/impls.rs
@@ -45,6 +45,7 @@ impl<R: Read + ?Sized> Read for &mut R {
     fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
         (**self).read_exact(buf)
     }
+
     #[inline]
     fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
         (**self).read_buf_exact(cursor)
@@ -78,6 +79,11 @@ impl<W: Write + ?Sized> Write for &mut W {
     }
 
     #[inline]
+    fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> io::Result<()> {
+        (**self).write_all_vectored(bufs)
+    }
+
+    #[inline]
     fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> io::Result<()> {
         (**self).write_fmt(fmt)
     }
@@ -90,9 +96,24 @@ impl<S: Seek + ?Sized> Seek for &mut S {
     }
 
     #[inline]
+    fn rewind(&mut self) -> io::Result<()> {
+        (**self).rewind()
+    }
+
+    #[inline]
+    fn stream_len(&mut self) -> io::Result<u64> {
+        (**self).stream_len()
+    }
+
+    #[inline]
     fn stream_position(&mut self) -> io::Result<u64> {
         (**self).stream_position()
     }
+
+    #[inline]
+    fn seek_relative(&mut self, offset: i64) -> io::Result<()> {
+        (**self).seek_relative(offset)
+    }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<B: BufRead + ?Sized> BufRead for &mut B {
@@ -107,11 +128,21 @@ impl<B: BufRead + ?Sized> BufRead for &mut B {
     }
 
     #[inline]
+    fn has_data_left(&mut self) -> io::Result<bool> {
+        (**self).has_data_left()
+    }
+
+    #[inline]
     fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> io::Result<usize> {
         (**self).read_until(byte, buf)
     }
 
     #[inline]
+    fn skip_until(&mut self, byte: u8) -> io::Result<usize> {
+        (**self).skip_until(byte)
+    }
+
+    #[inline]
     fn read_line(&mut self, buf: &mut String) -> io::Result<usize> {
         (**self).read_line(buf)
     }
@@ -153,6 +184,7 @@ impl<R: Read + ?Sized> Read for Box<R> {
     fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
         (**self).read_exact(buf)
     }
+
     #[inline]
     fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
         (**self).read_buf_exact(cursor)
@@ -186,6 +218,11 @@ impl<W: Write + ?Sized> Write for Box<W> {
     }
 
     #[inline]
+    fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> io::Result<()> {
+        (**self).write_all_vectored(bufs)
+    }
+
+    #[inline]
     fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> io::Result<()> {
         (**self).write_fmt(fmt)
     }
@@ -198,9 +235,24 @@ impl<S: Seek + ?Sized> Seek for Box<S> {
     }
 
     #[inline]
+    fn rewind(&mut self) -> io::Result<()> {
+        (**self).rewind()
+    }
+
+    #[inline]
+    fn stream_len(&mut self) -> io::Result<u64> {
+        (**self).stream_len()
+    }
+
+    #[inline]
     fn stream_position(&mut self) -> io::Result<u64> {
         (**self).stream_position()
     }
+
+    #[inline]
+    fn seek_relative(&mut self, offset: i64) -> io::Result<()> {
+        (**self).seek_relative(offset)
+    }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<B: BufRead + ?Sized> BufRead for Box<B> {
@@ -215,11 +267,21 @@ impl<B: BufRead + ?Sized> BufRead for Box<B> {
     }
 
     #[inline]
+    fn has_data_left(&mut self) -> io::Result<bool> {
+        (**self).has_data_left()
+    }
+
+    #[inline]
     fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> io::Result<usize> {
         (**self).read_until(byte, buf)
     }
 
     #[inline]
+    fn skip_until(&mut self, byte: u8) -> io::Result<usize> {
+        (**self).skip_until(byte)
+    }
+
+    #[inline]
     fn read_line(&mut self, buf: &mut String) -> io::Result<usize> {
         (**self).read_line(buf)
     }
diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index cfd03b8e3d6..980ea1478e0 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -344,7 +344,7 @@ pub mod prelude;
 mod stdio;
 mod util;
 
-const DEFAULT_BUF_SIZE: usize = crate::sys_common::io::DEFAULT_BUF_SIZE;
+const DEFAULT_BUF_SIZE: usize = crate::sys::io::DEFAULT_BUF_SIZE;
 
 pub(crate) use stdio::cleanup;
 
@@ -2249,6 +2249,7 @@ fn skip_until<R: BufRead + ?Sized>(r: &mut R, delim: u8) -> Result<usize> {
 /// }
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "IoBufRead")]
 pub trait BufRead: Read {
     /// Returns the contents of the internal buffer, filling it with more data
     /// from the inner reader if it is empty.
diff --git a/library/std/src/io/stdio.rs b/library/std/src/io/stdio.rs
index 318c3508221..017862c7f3a 100644
--- a/library/std/src/io/stdio.rs
+++ b/library/std/src/io/stdio.rs
@@ -20,7 +20,7 @@ type LocalStream = Arc<Mutex<Vec<u8>>>;
 
 thread_local! {
     /// Used by the test crate to capture the output of the print macros and panics.
-    static OUTPUT_CAPTURE: Cell<Option<LocalStream>> = {
+    static OUTPUT_CAPTURE: Cell<Option<LocalStream>> = const {
         Cell::new(None)
     }
 }
@@ -239,6 +239,7 @@ fn handle_ebadf_lazy<T>(r: io::Result<T>, default: impl FnOnce() -> T) -> io::Re
 /// }
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "Stdin")]
 pub struct Stdin {
     inner: &'static Mutex<BufReader<StdinRaw>>,
 }
diff --git a/library/std/src/io/stdio/tests.rs b/library/std/src/io/stdio/tests.rs
index bf8f3a5adfb..e68d8c29fbc 100644
--- a/library/std/src/io/stdio/tests.rs
+++ b/library/std/src/io/stdio/tests.rs
@@ -159,7 +159,8 @@ where
     assert_eq!(rx2.recv().unwrap(), Release2); // release th2
     th2.join().unwrap();
     th1.join().unwrap();
-    assert_eq!(*log.lock().unwrap(), [
-        Start1, Acquire1, Start2, Release1, Acquire2, Release2, Acquire1, Release1
-    ]);
+    assert_eq!(
+        *log.lock().unwrap(),
+        [Start1, Acquire1, Start2, Release1, Acquire2, Release2, Acquire1, Release1]
+    );
 }
diff --git a/library/std/src/io/util.rs b/library/std/src/io/util.rs
index b4c4dffc371..cb3f864fd4e 100644
--- a/library/std/src/io/util.rs
+++ b/library/std/src/io/util.rs
@@ -7,6 +7,7 @@ use crate::fmt;
 use crate::io::{
     self, BorrowedCursor, BufRead, IoSlice, IoSliceMut, Read, Seek, SeekFrom, SizeHint, Write,
 };
+use crate::mem::MaybeUninit;
 
 /// `Empty` ignores any data written via [`Write`], and will always be empty
 /// (returning zero bytes) when read via [`Read`].
@@ -182,28 +183,30 @@ pub const fn repeat(byte: u8) -> Repeat {
 impl Read for Repeat {
     #[inline]
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
-        for slot in &mut *buf {
-            *slot = self.byte;
-        }
+        buf.fill(self.byte);
         Ok(buf.len())
     }
 
-    fn read_buf(&mut self, mut buf: BorrowedCursor<'_>) -> io::Result<()> {
-        // SAFETY: No uninit bytes are being written
-        for slot in unsafe { buf.as_mut() } {
-            slot.write(self.byte);
-        }
-
-        let remaining = buf.capacity();
-
-        // SAFETY: the entire unfilled portion of buf has been initialized
-        unsafe {
-            buf.advance_unchecked(remaining);
-        }
+    #[inline]
+    fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
+        buf.fill(self.byte);
+        Ok(())
+    }
 
+    #[inline]
+    fn read_buf(&mut self, mut buf: BorrowedCursor<'_>) -> io::Result<()> {
+        // SAFETY: No uninit bytes are being written.
+        MaybeUninit::fill(unsafe { buf.as_mut() }, self.byte);
+        // SAFETY: the entire unfilled portion of buf has been initialized.
+        unsafe { buf.advance_unchecked(buf.capacity()) };
         Ok(())
     }
 
+    #[inline]
+    fn read_buf_exact(&mut self, buf: BorrowedCursor<'_>) -> io::Result<()> {
+        self.read_buf(buf)
+    }
+
     /// This function is not supported by `io::Repeat`, because there's no end of its data
     fn read_to_end(&mut self, _: &mut Vec<u8>) -> io::Result<usize> {
         Err(io::Error::from(io::ErrorKind::OutOfMemory))