From c4d12cba88de290cc5ef6b64ef0c12ab4995e640 Mon Sep 17 00:00:00 2001
From: Zac Harrold <zac@harrold.com.au>
Date: Fri, 22 May 2026 08:38:41 +1000
Subject: [PATCH 1/9] Setup `core::io::prelude`

---
 library/core/src/io/mod.rs     |  2 ++
 library/core/src/io/prelude.rs | 12 ++++++++++++
 2 files changed, 14 insertions(+)
 create mode 100644 library/core/src/io/prelude.rs

diff --git a/library/core/src/io/mod.rs b/library/core/src/io/mod.rs
index 0134540ae86c8..a44d271535a9e 100644
--- a/library/core/src/io/mod.rs
+++ b/library/core/src/io/mod.rs
@@ -5,6 +5,8 @@ mod cursor;
 mod error;
 mod impls;
 mod io_slice;
+#[unstable(feature = "core_io", issue = "154046")]
+pub mod prelude;
 mod seek;
 mod size_hint;
 mod util;
diff --git a/library/core/src/io/prelude.rs b/library/core/src/io/prelude.rs
new file mode 100644
index 0000000000000..15dacaa3a4fa0
--- /dev/null
+++ b/library/core/src/io/prelude.rs
@@ -0,0 +1,12 @@
+//! The I/O Prelude.
+//!
+//! The purpose of this module is to alleviate imports of many common I/O traits
+//! by adding a glob import to the top of I/O heavy modules:
+//!
+//! ```
+//! # #![allow(unused_imports)]
+//! use std::io::prelude::*;
+//! ```
+
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use crate::io::{Seek, Write};

From 0791c08ecbef1e98f72fcf42792e6017d8a4684b Mon Sep 17 00:00:00 2001
From: Zac Harrold <zac@harrold.com.au>
Date: Fri, 22 May 2026 08:38:58 +1000
Subject: [PATCH 2/9] Setup `alloc::io::prelude`

---
 library/alloc/src/io/mod.rs     |  2 ++
 library/alloc/src/io/prelude.rs | 12 ++++++++++++
 2 files changed, 14 insertions(+)
 create mode 100644 library/alloc/src/io/prelude.rs

diff --git a/library/alloc/src/io/mod.rs b/library/alloc/src/io/mod.rs
index 5c043240daba8..be2d17bb5a9e6 100644
--- a/library/alloc/src/io/mod.rs
+++ b/library/alloc/src/io/mod.rs
@@ -6,6 +6,8 @@ mod copy;
 mod cursor;
 mod error;
 mod impls;
+#[unstable(feature = "alloc_io", issue = "154046")]
+pub mod prelude;
 mod read;
 mod util;
 
diff --git a/library/alloc/src/io/prelude.rs b/library/alloc/src/io/prelude.rs
new file mode 100644
index 0000000000000..86ae040d1d6f6
--- /dev/null
+++ b/library/alloc/src/io/prelude.rs
@@ -0,0 +1,12 @@
+//! The I/O Prelude.
+//!
+//! The purpose of this module is to alleviate imports of many common I/O traits
+//! by adding a glob import to the top of I/O heavy modules:
+//!
+//! ```
+//! # #![allow(unused_imports)]
+//! use std::io::prelude::*;
+//! ```
+
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use crate::io::{BufRead, Read, Seek, Write};

From d95198739c2623c9e0b4f26d26c54ccd70d8e0a9 Mon Sep 17 00:00:00 2001
From: Zac Harrold <zac@harrold.com.au>
Date: Sun, 19 Jul 2026 21:13:23 +1000
Subject: [PATCH 3/9] Expand documentation for `alloc::io`

---
 library/alloc/src/io/mod.rs | 175 ++++++++++++++++++++++++++++++++++++
 1 file changed, 175 insertions(+)

diff --git a/library/alloc/src/io/mod.rs b/library/alloc/src/io/mod.rs
index be2d17bb5a9e6..44d780292317f 100644
--- a/library/alloc/src/io/mod.rs
+++ b/library/alloc/src/io/mod.rs
@@ -1,4 +1,179 @@
 //! Traits, helpers, and type definitions for core I/O functionality.
+//!
+//! The `io` module contains a number of common things you'll need
+//! when doing input and output. The most core part of this module is
+//! the [`Read`] and [`Write`] traits, which provide the
+//! most general interface for reading and writing input and output.
+//!
+//! ## Read and Write
+//!
+//! Because they are traits, [`Read`] and [`Write`] are implemented by a number
+//! of other types, and you can implement them for your types too. As such,
+//! you'll see a few different types of I/O throughout the documentation in
+//! this module: [`File`]s, [`TcpStream`]s, and sometimes even [`Vec<T>`]s. For
+//! example, [`Read`] adds a [`read`][`Read::read`] method, which we can use on
+//! [`File`]s:
+//!
+//! ```no_run
+//! use std::io;
+//! use std::io::prelude::*;
+//! use std::fs::File;
+//!
+//! fn main() -> io::Result<()> {
+//!     let mut f = File::open("foo.txt")?;
+//!     let mut buffer = [0; 10];
+//!
+//!     // read up to 10 bytes
+//!     let n = f.read(&mut buffer)?;
+//!
+//!     println!("The bytes: {:?}", &buffer[..n]);
+//!     Ok(())
+//! }
+//! ```
+//!
+//! [`Read`] and [`Write`] are so important, implementors of the two traits have a
+//! nickname: readers and writers. So you'll sometimes see 'a reader' instead
+//! of 'a type that implements the [`Read`] trait'. Much easier!
+//!
+//! ## Seek and BufRead
+//!
+//! Beyond that, there are two important traits that are provided: [`Seek`]
+//! and [`BufRead`]. Both of these build on top of a reader to control
+//! how the reading happens. [`Seek`] lets you control where the next byte is
+//! coming from:
+//!
+//! ```no_run
+//! use std::io;
+//! use std::io::prelude::*;
+//! use std::io::SeekFrom;
+//! use std::fs::File;
+//!
+//! fn main() -> io::Result<()> {
+//!     let mut f = File::open("foo.txt")?;
+//!     let mut buffer = [0; 10];
+//!
+//!     // skip to the last 10 bytes of the file
+//!     f.seek(SeekFrom::End(-10))?;
+//!
+//!     // read up to 10 bytes
+//!     let n = f.read(&mut buffer)?;
+//!
+//!     println!("The bytes: {:?}", &buffer[..n]);
+//!     Ok(())
+//! }
+//! ```
+//!
+//! [`BufRead`] uses an internal buffer to provide a number of other ways to read, but
+//! to show it off, we'll need to talk about buffers in general. Keep reading!
+//!
+//! ## BufReader and BufWriter
+//!
+//! Byte-based interfaces are unwieldy and can be inefficient, as we'd need to be
+//! making near-constant calls to the operating system. To help with this,
+//! `std::io` comes with two structs, [`BufReader`] and [`BufWriter`], which wrap
+//! readers and writers. The wrapper uses a buffer, reducing the number of
+//! calls and providing nicer methods for accessing exactly what you want.
+//!
+//! For example, [`BufReader`] works with the [`BufRead`] trait to add extra
+//! methods to any reader:
+//!
+//! ```no_run
+//! use std::io;
+//! use std::io::prelude::*;
+//! use std::io::BufReader;
+//! use std::fs::File;
+//!
+//! fn main() -> io::Result<()> {
+//!     let f = File::open("foo.txt")?;
+//!     let mut reader = BufReader::new(f);
+//!     let mut buffer = String::new();
+//!
+//!     // read a line into buffer
+//!     reader.read_line(&mut buffer)?;
+//!
+//!     println!("{buffer}");
+//!     Ok(())
+//! }
+//! ```
+//!
+//! [`BufWriter`] doesn't add any new ways of writing; it just buffers every call
+//! to [`write`][`Write::write`]:
+//!
+//! ```no_run
+//! use std::io;
+//! use std::io::prelude::*;
+//! use std::io::BufWriter;
+//! use std::fs::File;
+//!
+//! fn main() -> io::Result<()> {
+//!     let f = File::create("foo.txt")?;
+//!     {
+//!         let mut writer = BufWriter::new(f);
+//!
+//!         // write a byte to the buffer
+//!         writer.write(&[42])?;
+//!
+//!     } // the buffer is flushed once writer goes out of scope
+//!
+//!     Ok(())
+//! }
+//! ```
+//!
+//! ## Iterator types
+//!
+//! A large number of the structures provided by `std::io` are for various
+//! ways of iterating over I/O. For example, [`Lines`] is used to split over
+//! lines:
+//!
+//! ```no_run
+//! use std::io;
+//! use std::io::prelude::*;
+//! use std::io::BufReader;
+//! use std::fs::File;
+//!
+//! fn main() -> io::Result<()> {
+//!     let f = File::open("foo.txt")?;
+//!     let reader = BufReader::new(f);
+//!
+//!     for line in reader.lines() {
+//!         println!("{}", line?);
+//!     }
+//!     Ok(())
+//! }
+//! ```
+//!
+//! ## io::Result
+//!
+//! Last, but certainly not least, is [`io::Result`]. This type is used
+//! as the return type of many `std::io` functions that can cause an error, and
+//! can be returned from your own functions as well. Many of the examples in this
+//! module use the [`?` operator]:
+//!
+//! ```no_run
+//! use std::io;
+//!
+//! # #[allow(dead_code)]
+//! fn read_input() -> io::Result<()> {
+//!     let mut input = String::new();
+//!
+//!     io::stdin().read_line(&mut input)?;
+//!
+//!     println!("You typed: {}", input.trim());
+//!
+//!     Ok(())
+//! }
+//! ```
+//!
+//! The return type of `read_input()`, [`io::Result<()>`][`io::Result`], is a very
+//! common type for functions which don't have a 'real' return value, but do want to
+//! return errors if they happen. In this case, the only purpose of this function is
+//! to read the line and print it, so we use `()`.
+//!
+//! [`File`]: ../../std/fs/struct.File.html
+//! [`TcpStream`]: ../../std/net/struct.TcpStream.html
+//! [`Vec<T>`]: crate::vec::Vec
+//! [`io::Result`]: self::Result
+//! [`?` operator]: ../../book/appendix-02-operators.html
 
 mod buf_read;
 mod buffered;

From 32117cda49c21aecbe8d0430f766b53211e73094 Mon Sep 17 00:00:00 2001
From: Zac Harrold <zac@harrold.com.au>
Date: Thu, 21 May 2026 11:18:11 +1000
Subject: [PATCH 4/9] Move general IO tests to `alloctests`

---
 .../io/tests.rs => alloctests/tests/io/mod.rs}   | 16 ++++++++++------
 library/alloctests/tests/lib.rs                  | 12 ++++++++++++
 library/std/src/io/mod.rs                        |  3 ---
 3 files changed, 22 insertions(+), 9 deletions(-)
 rename library/{std/src/io/tests.rs => alloctests/tests/io/mod.rs} (98%)

diff --git a/library/std/src/io/tests.rs b/library/alloctests/tests/io/mod.rs
similarity index 98%
rename from library/std/src/io/tests.rs
rename to library/alloctests/tests/io/mod.rs
index 3b4f871268cd1..fcc27dbbd73f7 100644
--- a/library/std/src/io/tests.rs
+++ b/library/alloctests/tests/io/mod.rs
@@ -1,7 +1,11 @@
-use super::{BorrowedBuf, Cursor, SeekFrom, repeat};
-use crate::cmp::{self, min};
-use crate::io::{self, BufRead, BufReader, DEFAULT_BUF_SIZE, IoSlice, Read, Seek, Write};
-use crate::mem::MaybeUninit;
+use alloc::io::{
+    self, BorrowedBuf, BufRead, BufReader, Cursor, DEFAULT_BUF_SIZE, IoSlice, Read, Seek, SeekFrom,
+    Write, repeat,
+};
+use core::cmp::{self, min};
+use core::mem::MaybeUninit;
+
+extern crate test;
 
 #[test]
 fn read_until() {
@@ -270,7 +274,7 @@ fn chain_bufread() {
 #[test]
 fn chain_splitted_char() {
     let chain = b"\xc3".chain(b"\xa9".as_slice());
-    assert_eq!(crate::io::read_to_string(chain).unwrap(), "é");
+    assert_eq!(alloc::io::read_to_string(chain).unwrap(), "é");
 
     let mut chain = b"\xc3".chain(b"\xa9\n".as_slice());
     let mut buf = String::new();
@@ -360,7 +364,7 @@ fn bench_read_to_end(b: &mut test::Bencher) {
     b.iter(|| {
         let mut lr = repeat(1).take(10000000);
         let mut vec = Vec::with_capacity(1024);
-        super::default_read_to_end(&mut lr, &mut vec, None)
+        alloc::io::default_read_to_end(&mut lr, &mut vec, None)
     });
 }
 
diff --git a/library/alloctests/tests/lib.rs b/library/alloctests/tests/lib.rs
index 7ccc8d9c6a115..e787e3af9b636 100644
--- a/library/alloctests/tests/lib.rs
+++ b/library/alloctests/tests/lib.rs
@@ -2,23 +2,30 @@
 #![allow(internal_features)]
 #![deny(implicit_provenance_casts)]
 #![deny(unsafe_op_in_unsafe_fn)]
+#![feature(alloc_io)]
 #![feature(allocator_api)]
 #![feature(binary_heap_drain_sorted)]
 #![feature(binary_heap_into_iter_sorted)]
 #![feature(binary_heap_pop_if)]
+#![feature(borrowed_buf_init)]
+#![feature(buf_read_has_data_left)]
 #![feature(casefold)]
 #![feature(const_btree_len)]
 #![feature(const_cmp)]
 #![feature(const_heap)]
 #![feature(const_trait_impl)]
 #![feature(core_intrinsics)]
+#![feature(core_io_borrowed_buf)]
+#![feature(core_io_internals)]
 #![feature(cow_is_borrowed)]
+#![feature(cursor_split)]
 #![feature(deque_extend_front)]
 #![feature(downcast_unchecked)]
 #![feature(drain_keep_rest)]
 #![feature(exact_size_is_empty)]
 #![feature(hashmap_internals)]
 #![feature(inplace_iteration)]
+#![feature(io_const_error)]
 #![feature(iter_advance_by)]
 #![feature(iter_array_chunks)]
 #![feature(iter_next_chunk)]
@@ -28,6 +35,9 @@
 #![feature(map_try_insert)]
 #![feature(pattern)]
 #![feature(ptr_cast_slice)]
+#![feature(read_buf)]
+#![feature(seek_io_take_position)]
+#![feature(seek_stream_len)]
 #![feature(slice_partial_sort_unstable)]
 #![feature(slice_partition_dedup)]
 #![feature(slice_ptr_get)]
@@ -48,6 +58,7 @@
 #![feature(vec_deque_retain_range)]
 #![feature(vec_peek_mut)]
 #![feature(vec_try_remove)]
+#![feature(write_all_vectored)]
 // tidy-alphabetical-end
 
 extern crate alloc;
@@ -67,6 +78,7 @@ mod const_fns;
 mod cow_str;
 mod fmt;
 mod heap;
+mod io;
 mod linked_list;
 mod misc_tests;
 mod num;
diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index 203572c9067b6..d9cbe15c1d4f6 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -294,9 +294,6 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-#[cfg(test)]
-mod tests;
-
 use alloc_crate::io::OsFunctions;
 #[unstable(feature = "raw_os_error_ty", issue = "107792")]
 pub use alloc_crate::io::RawOsError;

From 125be4beff372ce676908a5e7de60c6bcac7daa7 Mon Sep 17 00:00:00 2001
From: Zac Harrold <zac@harrold.com.au>
Date: Thu, 21 May 2026 11:31:20 +1000
Subject: [PATCH 5/9] Move `std::io::util` tests to `alloctests`

---
 library/alloctests/tests/io/mod.rs                     |  2 ++
 .../io/util/tests.rs => alloctests/tests/io/util.rs}   | 10 +++++-----
 library/alloctests/tests/lib.rs                        |  1 +
 library/std/src/io/mod.rs                              |  1 -
 library/std/src/io/util.rs                             |  2 --
 5 files changed, 8 insertions(+), 8 deletions(-)
 rename library/{std/src/io/util/tests.rs => alloctests/tests/io/util.rs} (96%)
 delete mode 100644 library/std/src/io/util.rs

diff --git a/library/alloctests/tests/io/mod.rs b/library/alloctests/tests/io/mod.rs
index fcc27dbbd73f7..77fd3723ff158 100644
--- a/library/alloctests/tests/io/mod.rs
+++ b/library/alloctests/tests/io/mod.rs
@@ -1,3 +1,5 @@
+mod util;
+
 use alloc::io::{
     self, BorrowedBuf, BufRead, BufReader, Cursor, DEFAULT_BUF_SIZE, IoSlice, Read, Seek, SeekFrom,
     Write, repeat,
diff --git a/library/std/src/io/util/tests.rs b/library/alloctests/tests/io/util.rs
similarity index 96%
rename from library/std/src/io/util/tests.rs
rename to library/alloctests/tests/io/util.rs
index ed1d6891577da..52e0c3013dde7 100644
--- a/library/std/src/io/util/tests.rs
+++ b/library/alloctests/tests/io/util.rs
@@ -1,9 +1,9 @@
-use crate::fmt;
-use crate::io::prelude::*;
-use crate::io::{
-    BorrowedBuf, Empty, ErrorKind, IoSlice, IoSliceMut, Repeat, SeekFrom, Sink, empty, repeat, sink,
+use alloc::io::{
+    BorrowedBuf, Empty, ErrorKind, IoSlice, IoSliceMut, Read, Repeat, Seek, SeekFrom, Sink, Write,
+    empty, repeat, sink,
 };
-use crate::mem::MaybeUninit;
+use core::fmt;
+use core::mem::MaybeUninit;
 
 struct ErrorDisplay;
 
diff --git a/library/alloctests/tests/lib.rs b/library/alloctests/tests/lib.rs
index e787e3af9b636..eb9ea287d950f 100644
--- a/library/alloctests/tests/lib.rs
+++ b/library/alloctests/tests/lib.rs
@@ -9,6 +9,7 @@
 #![feature(binary_heap_pop_if)]
 #![feature(borrowed_buf_init)]
 #![feature(buf_read_has_data_left)]
+#![feature(can_vector)]
 #![feature(casefold)]
 #![feature(const_btree_len)]
 #![feature(const_cmp)]
diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index d9cbe15c1d4f6..385b8081a33ff 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -349,4 +349,3 @@ mod impls;
 mod pipe;
 pub mod prelude;
 mod stdio;
-mod util;
diff --git a/library/std/src/io/util.rs b/library/std/src/io/util.rs
deleted file mode 100644
index 87c2771955a9d..0000000000000
--- a/library/std/src/io/util.rs
+++ /dev/null
@@ -1,2 +0,0 @@
-#[cfg(test)]
-mod tests;

From 39bf757d697baad2fae42fc2df9d59bd8e1d7a55 Mon Sep 17 00:00:00 2001
From: Zac Harrold <zac@harrold.com.au>
Date: Thu, 21 May 2026 11:42:23 +1000
Subject: [PATCH 6/9] Move `std::io::cursor` tests to `alloctests`

---
 .../src/io/cursor/tests.rs => alloctests/tests/io/cursor.rs} | 5 +++--
 library/alloctests/tests/io/mod.rs                           | 1 +
 library/std/src/io/cursor.rs                                 | 2 --
 library/std/src/io/mod.rs                                    | 1 -
 4 files changed, 4 insertions(+), 5 deletions(-)
 rename library/{std/src/io/cursor/tests.rs => alloctests/tests/io/cursor.rs} (99%)
 delete mode 100644 library/std/src/io/cursor.rs

diff --git a/library/std/src/io/cursor/tests.rs b/library/alloctests/tests/io/cursor.rs
similarity index 99%
rename from library/std/src/io/cursor/tests.rs
rename to library/alloctests/tests/io/cursor.rs
index d7c203c297fe6..5e863f29af53c 100644
--- a/library/std/src/io/cursor/tests.rs
+++ b/library/alloctests/tests/io/cursor.rs
@@ -1,5 +1,6 @@
-use crate::io::prelude::*;
-use crate::io::{Cursor, IoSlice, IoSliceMut, SeekFrom};
+use alloc::io::{Cursor, IoSlice, IoSliceMut, Read, Seek, SeekFrom, Write};
+
+extern crate test;
 
 #[test]
 fn test_vec_writer() {
diff --git a/library/alloctests/tests/io/mod.rs b/library/alloctests/tests/io/mod.rs
index 77fd3723ff158..a3fbbf96653cb 100644
--- a/library/alloctests/tests/io/mod.rs
+++ b/library/alloctests/tests/io/mod.rs
@@ -1,3 +1,4 @@
+mod cursor;
 mod util;
 
 use alloc::io::{
diff --git a/library/std/src/io/cursor.rs b/library/std/src/io/cursor.rs
deleted file mode 100644
index 87c2771955a9d..0000000000000
--- a/library/std/src/io/cursor.rs
+++ /dev/null
@@ -1,2 +0,0 @@
-#[cfg(test)]
-mod tests;
diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index 385b8081a33ff..9cb63ebe9cd72 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -343,7 +343,6 @@ pub use self::stdio::{set_output_capture, try_set_output_capture};
 
 mod buffered;
 mod copy;
-mod cursor;
 mod error;
 mod impls;
 mod pipe;

From f67f57d68c00f11620ddaf7736d86e199a341583 Mon Sep 17 00:00:00 2001
From: Zac Harrold <zac@harrold.com.au>
Date: Thu, 21 May 2026 11:45:18 +1000
Subject: [PATCH 7/9] Move `std::io::buffered` tests to `alloctests`

---
 .../tests/io/buffered.rs}                     | 31 ++++++++++---------
 library/alloctests/tests/io/mod.rs            |  1 +
 library/std/src/io/buffered/mod.rs            |  4 ---
 library/std/src/io/mod.rs                     |  1 -
 4 files changed, 18 insertions(+), 19 deletions(-)
 rename library/{std/src/io/buffered/tests.rs => alloctests/tests/io/buffered.rs} (98%)
 delete mode 100644 library/std/src/io/buffered/mod.rs

diff --git a/library/std/src/io/buffered/tests.rs b/library/alloctests/tests/io/buffered.rs
similarity index 98%
rename from library/std/src/io/buffered/tests.rs
rename to library/alloctests/tests/io/buffered.rs
index ff4585a60cae9..0abaa63870e15 100644
--- a/library/std/src/io/buffered/tests.rs
+++ b/library/alloctests/tests/io/buffered.rs
@@ -1,10 +1,14 @@
-use crate::io::prelude::*;
-use crate::io::{
-    self, BorrowedBuf, BufReader, BufWriter, ErrorKind, IoSlice, LineWriter, SeekFrom,
+//! Tests for buffering wrappers for I/O traits
+
+use alloc::io::{
+    self, BorrowedBuf, BufRead, BufReader, BufWriter, ErrorKind, IoSlice, LineWriter, Read, Seek,
+    SeekFrom, Write,
 };
-use crate::mem::MaybeUninit;
-use crate::sync::atomic::{AtomicUsize, Ordering};
-use crate::{panic, thread};
+use core::mem::MaybeUninit;
+use core::sync::atomic::{AtomicUsize, Ordering};
+use std::{panic, thread};
+
+extern crate test;
 
 /// A dummy reader intended at testing short-reads propagation.
 pub struct ShortReader {
@@ -488,7 +492,7 @@ fn dont_panic_in_drop_on_panicked_flush() {
 }
 
 #[test]
-#[cfg_attr(any(target_os = "emscripten", target_os = "wasi"), ignore)] // no threads
+#[cfg_attr(not(panic = "unwind"), ignore = "test requires unwinding support")]
 fn panic_in_write_doesnt_flush_in_drop() {
     static WRITES: AtomicUsize = AtomicUsize::new(0);
 
@@ -504,12 +508,11 @@ fn panic_in_write_doesnt_flush_in_drop() {
         }
     }
 
-    thread::spawn(|| {
+    panic::catch_unwind(panic::AssertUnwindSafe(|| {
         let mut writer = BufWriter::new(PanicWriter);
         let _ = writer.write(b"hello world");
         let _ = writer.flush();
-    })
-    .join()
+    }))
     .unwrap_err();
 
     assert_eq!(WRITES.load(Ordering::SeqCst), 1);
@@ -681,7 +684,7 @@ fn line_vectored() {
 
 #[test]
 fn line_vectored_partial_and_errors() {
-    use crate::collections::VecDeque;
+    use alloc::collections::VecDeque;
 
     enum Call {
         Write { inputs: Vec<&'static [u8]>, output: io::Result<usize> },
@@ -1150,7 +1153,7 @@ struct WriteRecorder {
 
 impl Write for WriteRecorder {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
-        use crate::str::from_utf8;
+        use core::str::from_utf8;
 
         self.events.push(RecordedEvent::Write(from_utf8(buf).unwrap().to_string()));
         Ok(buf.len())
@@ -1183,7 +1186,7 @@ fn single_formatted_write() {
 fn bufreader_full_initialize() {
     struct OneByteReader;
     impl Read for OneByteReader {
-        fn read(&mut self, buf: &mut [u8]) -> crate::io::Result<usize> {
+        fn read(&mut self, buf: &mut [u8]) -> alloc::io::Result<usize> {
             if buf.len() > 0 {
                 buf[0] = 0;
                 Ok(1)
@@ -1206,7 +1209,7 @@ fn bufreader_full_initialize() {
 /// This is a regression test for https://github.com/rust-lang/rust/issues/127584.
 #[test]
 fn bufwriter_aliasing() {
-    use crate::io::{BufWriter, Cursor};
+    use alloc::io::{BufWriter, Cursor};
     let mut v = vec![0; 1024];
     let c = Cursor::new(&mut v);
     let w = BufWriter::new(Box::new(c));
diff --git a/library/alloctests/tests/io/mod.rs b/library/alloctests/tests/io/mod.rs
index a3fbbf96653cb..b0df3b51094ca 100644
--- a/library/alloctests/tests/io/mod.rs
+++ b/library/alloctests/tests/io/mod.rs
@@ -1,3 +1,4 @@
+mod buffered;
 mod cursor;
 mod util;
 
diff --git a/library/std/src/io/buffered/mod.rs b/library/std/src/io/buffered/mod.rs
deleted file mode 100644
index 1d09ff7d8dc1c..0000000000000
--- a/library/std/src/io/buffered/mod.rs
+++ /dev/null
@@ -1,4 +0,0 @@
-//! Buffering wrappers for I/O traits
-
-#[cfg(test)]
-mod tests;
diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index 9cb63ebe9cd72..945de19424f3b 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -341,7 +341,6 @@ pub(crate) use self::stdio::{attempt_print_to_stderr, cleanup};
 #[doc(no_inline, hidden)]
 pub use self::stdio::{set_output_capture, try_set_output_capture};
 
-mod buffered;
 mod copy;
 mod error;
 mod impls;

From 29da936fe337721cdb5c320e2229339cdaa6dd7f Mon Sep 17 00:00:00 2001
From: Zac Harrold <zac@harrold.com.au>
Date: Mon, 25 May 2026 13:29:57 +1000
Subject: [PATCH 8/9] Move `std::io::impls` benchmarks to `alloctests`

---
 library/{std/src/io/impls/tests.rs => alloctests/benches/io.rs} | 2 +-
 library/alloctests/benches/lib.rs                               | 1 +
 library/std/src/io/impls.rs                                     | 2 --
 library/std/src/io/mod.rs                                       | 1 -
 4 files changed, 2 insertions(+), 4 deletions(-)
 rename library/{std/src/io/impls/tests.rs => alloctests/benches/io.rs} (97%)
 delete mode 100644 library/std/src/io/impls.rs

diff --git a/library/std/src/io/impls/tests.rs b/library/alloctests/benches/io.rs
similarity index 97%
rename from library/std/src/io/impls/tests.rs
rename to library/alloctests/benches/io.rs
index d1cd84a67ada5..5ee8263b8cea4 100644
--- a/library/std/src/io/impls/tests.rs
+++ b/library/alloctests/benches/io.rs
@@ -1,4 +1,4 @@
-use crate::io::prelude::*;
+use std::io::prelude::*;
 
 #[bench]
 fn bench_read_slice(b: &mut test::Bencher) {
diff --git a/library/alloctests/benches/lib.rs b/library/alloctests/benches/lib.rs
index 4b7139d943593..974b389a765d5 100644
--- a/library/alloctests/benches/lib.rs
+++ b/library/alloctests/benches/lib.rs
@@ -12,6 +12,7 @@ extern crate test;
 
 mod binary_heap;
 mod btree;
+mod io;
 mod linked_list;
 mod slice;
 mod str;
diff --git a/library/std/src/io/impls.rs b/library/std/src/io/impls.rs
deleted file mode 100644
index 87c2771955a9d..0000000000000
--- a/library/std/src/io/impls.rs
+++ /dev/null
@@ -1,2 +0,0 @@
-#[cfg(test)]
-mod tests;
diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index 945de19424f3b..ebd69e93fa98f 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -343,7 +343,6 @@ pub use self::stdio::{set_output_capture, try_set_output_capture};
 
 mod copy;
 mod error;
-mod impls;
 mod pipe;
 pub mod prelude;
 mod stdio;

From 5b49a9daf874ea1779139d9bf48bec98e9bc4b62 Mon Sep 17 00:00:00 2001
From: Zac Harrold <zac@harrold.com.au>
Date: Sun, 2 Aug 2026 07:08:45 +1000
Subject: [PATCH 9/9] Move `std::io::copy` tests to `alloctests`

---
 library/alloctests/benches/io.rs              | 23 +++++++++++
 .../tests.rs => alloctests/tests/io/copy.rs}  | 40 +++----------------
 library/alloctests/tests/io/mod.rs            |  1 +
 library/std/src/io/copy.rs                    |  2 -
 library/std/src/io/mod.rs                     |  1 -
 5 files changed, 29 insertions(+), 38 deletions(-)
 rename library/{std/src/io/copy/tests.rs => alloctests/tests/io/copy.rs} (74%)
 delete mode 100644 library/std/src/io/copy.rs

diff --git a/library/alloctests/benches/io.rs b/library/alloctests/benches/io.rs
index 5ee8263b8cea4..f2e3f2cd3c998 100644
--- a/library/alloctests/benches/io.rs
+++ b/library/alloctests/benches/io.rs
@@ -55,3 +55,26 @@ fn bench_write_vec(b: &mut test::Bencher) {
         }
     })
 }
+
+#[bench]
+#[cfg(unix)]
+#[cfg_attr(target_os = "emscripten", ignore)] // no /dev
+fn bench_copy_buf_reader(b: &mut test::Bencher) {
+    use std::fs::{File, OpenOptions};
+
+    let mut file_in = File::open("/dev/zero").expect("opening /dev/zero failed");
+    // use dyn to avoid specializations unrelated to readbuf
+    let dyn_in = &mut file_in as &mut dyn Read;
+    let mut reader = std::io::BufReader::with_capacity(256 * 1024, dyn_in.take(0));
+    let mut writer =
+        OpenOptions::new().write(true).open("/dev/null").expect("opening /dev/null failed");
+
+    const BYTES: u64 = 1024 * 1024;
+
+    b.bytes = BYTES;
+
+    b.iter(|| {
+        reader.get_mut().set_limit(BYTES);
+        std::io::copy(&mut reader, &mut writer).unwrap()
+    });
+}
diff --git a/library/std/src/io/copy/tests.rs b/library/alloctests/tests/io/copy.rs
similarity index 74%
rename from library/std/src/io/copy/tests.rs
rename to library/alloctests/tests/io/copy.rs
index 7bdba3a04416e..485deeaea80e7 100644
--- a/library/std/src/io/copy/tests.rs
+++ b/library/alloctests/tests/io/copy.rs
@@ -1,7 +1,6 @@
-use crate::cmp::{max, min};
-use crate::collections::VecDeque;
-use crate::io;
-use crate::io::*;
+use alloc::collections::VecDeque;
+use alloc::io::{self, *};
+use core::cmp::{max, min};
 
 #[test]
 fn copy_copies() {
@@ -65,7 +64,7 @@ fn copy_specializes_bufreader() {
     let mut buffered = BufReader::with_capacity(256 * 1024, Cursor::new(&mut source));
 
     let mut sink = Vec::new();
-    assert_eq!(crate::io::copy(&mut buffered, &mut sink).unwrap(), source.len() as u64);
+    assert_eq!(io::copy(&mut buffered, &mut sink).unwrap(), source.len() as u64);
     assert_eq!(source.as_slice(), sink.as_slice());
 
     let buf_sz = 71 * 1024;
@@ -73,7 +72,7 @@ fn copy_specializes_bufreader() {
 
     let mut buffered = BufReader::with_capacity(buf_sz, Cursor::new(&mut source));
     let mut sink = WriteObserver { observed_buffer: 0 };
-    assert_eq!(crate::io::copy(&mut buffered, &mut sink).unwrap(), source.len() as u64);
+    assert_eq!(io::copy(&mut buffered, &mut sink).unwrap(), source.len() as u64);
     assert_eq!(
         sink.observed_buffer, buf_sz,
         "expected a large buffer to be provided to the writer"
@@ -117,32 +116,3 @@ fn copy_specializes_from_slice() {
     assert_eq!(60 * 1024u64, io::copy(&mut source, &mut sink).unwrap());
     assert_eq!(60 * 1024, sink.observed_buffer);
 }
-
-#[cfg(unix)]
-mod io_benches {
-    use test::Bencher;
-
-    use crate::fs::{File, OpenOptions};
-    use crate::io::BufReader;
-    use crate::io::prelude::*;
-
-    #[bench]
-    #[cfg_attr(target_os = "emscripten", ignore)] // no /dev
-    fn bench_copy_buf_reader(b: &mut Bencher) {
-        let mut file_in = File::open("/dev/zero").expect("opening /dev/zero failed");
-        // use dyn to avoid specializations unrelated to readbuf
-        let dyn_in = &mut file_in as &mut dyn Read;
-        let mut reader = BufReader::with_capacity(256 * 1024, dyn_in.take(0));
-        let mut writer =
-            OpenOptions::new().write(true).open("/dev/null").expect("opening /dev/null failed");
-
-        const BYTES: u64 = 1024 * 1024;
-
-        b.bytes = BYTES;
-
-        b.iter(|| {
-            reader.get_mut().set_limit(BYTES);
-            crate::io::copy(&mut reader, &mut writer).unwrap()
-        });
-    }
-}
diff --git a/library/alloctests/tests/io/mod.rs b/library/alloctests/tests/io/mod.rs
index b0df3b51094ca..712e322d79f1c 100644
--- a/library/alloctests/tests/io/mod.rs
+++ b/library/alloctests/tests/io/mod.rs
@@ -1,4 +1,5 @@
 mod buffered;
+mod copy;
 mod cursor;
 mod util;
 
diff --git a/library/std/src/io/copy.rs b/library/std/src/io/copy.rs
deleted file mode 100644
index 87c2771955a9d..0000000000000
--- a/library/std/src/io/copy.rs
+++ /dev/null
@@ -1,2 +0,0 @@
-#[cfg(test)]
-mod tests;
diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index ebd69e93fa98f..c0ed06d5311bc 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -341,7 +341,6 @@ pub(crate) use self::stdio::{attempt_print_to_stderr, cleanup};
 #[doc(no_inline, hidden)]
 pub use self::stdio::{set_output_capture, try_set_output_capture};
 
-mod copy;
 mod error;
 mod pipe;
 pub mod prelude;