Move `std::io::util` to `core::io`
ACP: https://github.com/rust-lang/libs-team/issues/755
Tracking issue: https://github.com/rust-lang/rust/issues/154046
Subset of: https://github.com/rust-lang/rust/pull/154684
## Description
Moves utility types and functions from `std::io::util` and `std::io` to `core::io`, leaving any IO trait implementations behind. They will be moved along with the traits themselves. Certain documentation links had to be amended.
- `Chain`
- `Empty`
- `Repeat`
- `Sink`
- `Take`
- `empty`
- `repeat`
- `sink`
---
## Notes
* This can be reviewed independently of the other PRs tracked in rust-lang/rust#154046.
* `Chain` and `Take` were previously in the main `mod.rs` file for `std::io`, but I've chosen to move them into the `util.rs` file in `core::io` instead. I think they make more sense in that file, but I'm happy to move them into `mod.rs` if that's a controversial decision.
* No AI tooling of any kind was used during the creation of this PR.
Move `std::io::Cursor` to `core::io`
ACP: https://github.com/rust-lang/libs-team/issues/755
Tracking issue: https://github.com/rust-lang/rust/issues/154046
Subset of: https://github.com/rust-lang/rust/pull/154684
## Description
Moves `std::io::Cursor` to `core::io`, leaving the IO trait implementations behind. They will be moved along with the traits themselves. Certain documentation links had to be amended, and a private/unstable `into_parts_mut` method was added to allow the internals to remain private.
---
## Notes
* This can be reviewed independently of the other PRs tracked in rust-lang/rust#154046.
* No AI tooling of any kind was used during the creation of this PR.
enable more f16/f128 tests in Miri
See the individual commit messages for details.
The last commit is a drive-by comment fix that was not worth its own PR.
r? @tgross35
Show intrinsics::gpu in docs
It was previously not visible (unless compiling docs for amdgpu, which I guess nobody does).
Follow other specific intrinsics and always include them in docs.
Now looks like this:
<img width="1220" height="446" alt="2026-05-11_10-51-05" src="https://github.com/user-attachments/assets/c3a98f0e-2803-4697-87a8-1cc8ff01815c" />
r? @ZuseZ4 (I hope you are fine with reviewing this, please re-assign if not :))
It was previously not visible (unless compiling docs for amdgpu, which
I guess nobody does).
Follow other specific intrinsics and always include them in docs.
Improve doc comments for f32::ceil() and f32::floor()
Previously ::floor() included an example showing behaviour for negative values, but ::ceil() did not. Ensure both have examples of the negative case, for both f32 and f64.
Whilst we're here, tweak the wording slightly so it reads better.
kernel_copy tests: properly join background threads
This helps Miri because when there are threads just hanging in the background, we cannot check for memory leaks.
I think even without Miri this currently leads to 100% CPU load on one core for each of these threads: once the test function returns and `sink` gets dropped, the `read` in the thread will always immediately return `0`, and then we just loop with that forever until the process exits.
tests: ip*_properties: avoid parsing the IP over and over again
This test somehow takes 12s to execute in Miri (on CI, i.e. on a slow machine), despite not having any loop. I suspect it's caused by us for some reason re-parsing the same string again and again. Let's just not do that.
remove forever-deprecated and hidden `f64` methods
The methods `f64::is_positive` and `f64::is_negative` were deprecated since 1.0 and marked as `#[doc(hidden)]` in favor of `f64::is_sign_positive` and `f64::is_sign_negative`. They also only exist on `f64`, not on `f32`. But for some unknown reason, they have been marked as stable.
This PR proposes to remove both methods as they were never a part of the documented API, assuming that a crater run finds no significant breakage.
stream_send_recv_stress tests: wait for threads to finish
These tests currently fail in Miri (when run with nextest) because all they do is spawn a lot of threads that will do stuff, but they don't wait for the threads to actually finish. Miri by default errors when there are background threads lingering when `main` is done (since that can indicate a leak, and since it makes it impossible to check for memory leaks). Miri gives background threads a bit of time to finish when `main` is done, but for these tests that's nowhere near enough since basically the entire test runs after `main` is done.
Outside Miri, this could also still mean that the test doesn't actually run to completion, it might get abort when `main` finishes.
So let's use `thread::scope` to ensure all threads are done before the test is considered done.
Add `Drop::pin_drop` for pinned drops
This PR is part of the `pin_ergonomics` experiment (the tracking issue is rust-lang/rust#130494). It allows implementing `Drop` with a pinned `self` receiver, which is required for safe pin-projection.
Implementations:
- [x] At least and at most one of `drop` and `pin_drop` should be implemented.
- [x] No direct call of `drop` or `pin_drop`. They should only be called by the drop glue.
- [x] `pin_drop` must and must only be used with types that support pin-projection (i.e. types with `#[pin_v2]`).
- [ ] Allows writing `fn drop(&pin mut self)` and desugars to `fn pin_drop(&pin mut self)`. (Will be in the next PRs)
Previously ::floor() included an example showing behaviour for
negative values, but ::ceil() did not. Ensure both have examples of
the negative case, for both f32 and f64.
Whilst we're here, tweak the wording slightly so it reads better.
mark some panicking methods around Duration as track_caller
Currently when they panic it looks like this
```
0.005045 ---- instant_checked_duration_since_nopanic stdout ----
0.000039
0.000009 thread 'instant_checked_duration_since_nopanic' (2) panicked at /home/runner/work/miri-test-libstd/miri-test-libstd/rust-src-patched/library/std/src/time.rs:445:33:
0.000007 overflow when subtracting duration from instant
0.000006 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
0.000007 note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
```
That's pretty useless.
Also fix the panic message while we are at it.
Add mention of sendfile(2) and splice(2) to fs::copy() documentation.
Fixesrust-lang/rust#155968 by adding mention of sendfile(2) and splice(2) from io::copy()
Add `str::word_to_titlecase()` to `alloc`
A small addition to https://github.com/rust-lang/rust/issues/153892.
Hasn't gone through ACP, so needs libs-API signoff.
@rustbot label A-Unicode T-libs-api
`BufWriter`: Make the soundness of `BorrowedBuf` usage clearer.
The previous safety comment was outdated as it was written before `BorrowedBuf::set_init` was changed to be a boolean. It also failed to address the possibility that `flush_buf` invalidated the assumption.
core: drop unmapped ZSTs in array `map`
Fixes https://github.com/rust-lang/rust/issues/152211.
Alternative to rust-lang/rust#152220 and rust-lang/rust#152248.
This makes the `Drain` type use the same ZST-handling strategy as `slice::IterMut`, which stores the remaining length instead of a one-past-the-end pointer when the type is a ZST. I've also removed the const-generic `N` parameter from `Drain` to avoid unnecessary monomorphizations.
Experiment: Reborrow traits
With this PR we now have basic functional Reborrow and CoerceShared traits. The current limitations are:
1. Reborrowable types can only have one lifetime parameter, so as to avoid having to figure out and store in rmeta the information of which lifetimes weaken during reborrowing.
2. Reborrowing of `&mut` wrappers is working (though I've not tested generic wrappers like `Option<&mut T>` yet), but CoerceShared of `&mut` wrappers currently causes an ICE.
The remaining tasks to complete before I'd consider this PR mergeable are:
- [x] Fix ICE on CoerceShared. Unfortunately this might require dipping into rmeta.
- [x] Expand the tests to give a more complete view of the current state of the experiment.
Reborrow traits experiment: rust-lang/rust#145612
Co-authored by @dingxiangfei2009
John Millikin