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Stabilize `const_option`
This makes the following API stable in const contexts:
```rust
impl<T> Option<T> {
pub const fn as_mut(&mut self) -> Option<&mut T>;
pub const fn expect(self, msg: &str) -> T;
pub const fn unwrap(self) -> T;
pub const unsafe fn unwrap_unchecked(self) -> T;
pub const fn take(&mut self) -> Option<T>;
pub const fn replace(&mut self, value: T) -> Option<T>;
}
impl<T> Option<&T> {
pub const fn copied(self) -> Option<T>
where T: Copy;
}
impl<T> Option<&mut T> {
pub const fn copied(self) -> Option<T>
where T: Copy;
}
impl<T, E> Option<Result<T, E>> {
pub const fn transpose(self) -> Result<Option<T>, E>
}
impl<T> Option<Option<T>> {
pub const fn flatten(self) -> Option<T>;
}
```
The following functions make use of the unstable `const_precise_live_drops` feature:
- `expect`
- `unwrap`
- `unwrap_unchecked`
- `transpose`
- `flatten`
Fixes: <https://github.com/rust-lang/rust/issues/67441>
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This makes the following API stable in const contexts:
impl<T> Option<T> {
pub const fn as_mut(&mut self) -> Option<&mut T>;
pub const fn expect(self, msg: &str) -> T;
pub const fn unwrap(self) -> T;
pub const unsafe fn unwrap_unchecked(self) -> T;
pub const fn take(&mut self) -> Option<T>;
pub const fn replace(&mut self, value: T) -> Option<T>;
}
impl<T> Option<&T> {
pub const fn copied(self) -> Option<T>
where T: Copy;
}
impl<T> Option<&mut T> {
pub const fn copied(self) -> Option<T>
where T: Copy;
}
impl<T, E> Option<Result<T, E>> {
pub const fn transpose(self) -> Result<Option<T>, E>
}
impl<T> Option<Option<T>> {
pub const fn flatten(self) -> Option<T>;
}
The following functions make use of the unstable
`const_precise_live_drops` feature:
- `expect`
- `unwrap`
- `unwrap_unchecked`
- `transpose`
- `flatten`
Fixes: <https://github.com/rust-lang/rust/issues/67441>
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remove const_cow_is_borrowed feature gate
The two functions guarded by this are still unstable, and there's no reason to require a separate feature gate for their const-ness -- we can just have `cow_is_borrowed` cover both kinds of stability.
Cc #65143
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Const-stabilizes:
- `write`
- `write_bytes`
- `write_unaligned`
In the following paths:
- `core::ptr`
- `core::ptr::NonNull`
- pointer `<*mut T>`
Const-stabilizes the internal `core::intrinsics`:
- `write_bytes`
- `write_via_move`
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liballoc: introduce String, Vec const-slicing
This change `const`-qualifies many methods on `Vec` and `String`, notably `as_slice`, `as_str`, `len`. These changes are made behind the unstable feature flag `const_vec_string_slice`.
## Motivation
This is to support simultaneous variance over ownership and constness. I have an enum type that may contain either `String` or `&str`, and I want to produce a `&str` from it in a possibly-`const` context.
```rust
enum StrOrString<'s> {
Str(&'s str),
String(String),
}
impl<'s> StrOrString<'s> {
const fn as_str(&self) -> &str {
match self {
// In a const-context, I really only expect to see this variant, but I can't switch the implementation
// in some mode like #[cfg(const)] -- there has to be a single body
Self::Str(s) => s,
// so this is a problem, since it's not `const`
Self::String(s) => s.as_str(),
}
}
}
```
Currently `String` and `Vec` don't support this, but can without functional changes. Similar logic applies for `len`, `capacity`, `is_empty`.
## Changes
The essential thing enabling this change is that `Unique::as_ptr` is `const`. This lets us convert `RawVec::ptr` -> `Vec::as_ptr` -> `Vec::as_slice` -> `String::as_str`.
I had to move the `Deref` implementations into `as_{str,slice}` because `Deref` isn't `#[const_trait]`, but I would expect this change to be invisible up to inlining. I moved the `DerefMut` implementations as well for uniformity.
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This change `const`-qualifies many methods on Vec and String, notably
`as_slice`, `as_str`, `len`. These changes are made behind the unstable
feature flag `const_vec_string_slice` with the following tracking issue:
https://github.com/rust-lang/rust/issues/129041
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Apply size optimizations to panic machinery and some cold functions
* std dependencies gimli and addr2line are now built with opt-level=s
* various panic-related methods and `#[cold]` methods are now marked `#[optimize(size)]`
Panics should be cold enough that it doesn't make sense to optimize them for speed. The only tradeoff here is if someone does a lot of backtrace captures (without panics) and printing then the opt-level change might impact their perf.
Seems to be the first use of the optimize attribute. Tracking issue #54882
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A partial stabilization that only affects:
- AllocType<T>::new_uninit
- AllocType<T>::assume_init
- AllocType<[T]>::new_uninit_slice
- AllocType<[T]>::assume_init
where "AllocType" is Box, Rc, or Arc
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Bump bootstrap compiler to new beta
https://forge.rust-lang.org/release/process.html#master-bootstrap-update-t-2-day-tuesday
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They are all clean now, so enable the lint to keep them clean going forward.
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
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Stabilize `const_waker`
Closes: https://github.com/rust-lang/rust/issues/102012.
For `local_waker` and `context_ext` related things, I just ~~moved them to dedicated feature gates and reused their own tracking issue (maybe it's better to open a new one later, but at least they should not be tracked under https://github.com/rust-lang/rust/issues/102012 from the beginning IMO.)~~ reused their own feature gates as suggested by ``@tgross35.``
``@rustbot`` label: +T-libs-api
r? libs-api
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Mark format! with must_use hint
Uses unstable feature https://github.com/rust-lang/rust/issues/94745
Part of #126475
First contribution to rust, please let me know if the blessing of tests is correct
Thanks `@bjorn3` for the help
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Don't check the capacity every time (and also for `Extend` for tuples, as this is how `unzip()` is implemented).
I did this with an unsafe method on `Extend` that doesn't check for growth (`extend_one_unchecked()`). I've marked it as perma-unstable currently, although we may want to expose it in the future so collections outside of std can benefit from it. Then specialize `Extend for (A, B)` for `TrustedLen` to call it.
It may seem that an alternative way of implementing this is to have a semi-public trait (`#[doc(hidden)]` public, so collections outside of core can implement it) for `extend()` inside tuples, and specialize it from collections. However, it is impossible due to limitations of `min_specialization`.
A concern that may arise with the current approach is that implementing `extend_one_unchecked()` correctly must also incur implementing `extend_reserve()`, otherwise you can have UB. This is a somewhat non-local safety invariant. However, I believe this is fine, since to have actual UB you must have unsafe code inside your `extend_one_unchecked()` that makes incorrect assumption, *and* not implement `extend_reserve()`. I've also documented this requirement.
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Stabilize `hint::assert_unchecked`
Make the following API stable, including const:
```rust
// core::hint, std::hint
pub const unsafe fn assert_unchecked(p: bool);
```
This PR also reworks some of the documentation and adds an example.
Tracking issue: https://github.com/rust-lang/rust/issues/119131
FCP: https://github.com/rust-lang/rust/issues/119131#issuecomment-1906394087. The docs update should resolve the remaining concern.
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This is possible now that inline const blocks are stable; the idea was
even mentioned as an alternative when `uninit_array()` was added:
<https://github.com/rust-lang/rust/pull/65580#issuecomment-544200681>
> if it’s stabilized soon enough maybe it’s not worth having a
> standard library method that will be replaceable with
> `let buffer = [MaybeUninit::<T>::uninit(); $N];`
Const array repetition and inline const blocks are now stable (in the
next release), so that circumstance has come to pass, and we no longer
have reason to want `uninit_array()` other than convenience. Therefore,
let’s evaluate the inconvenience by not using `uninit_array()` in
the standard library, before potentially deleting it entirely.
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Rollup of 3 pull requests
Successful merges:
- #126140 (Rename `std::fs::try_exists` to `std::fs::exists` and stabilize fs_try_exists)
- #126318 (Add a `x perf` command for integrating bootstrap with `rustc-perf`)
- #126552 (Remove use of const traits (and `feature(effects)`) from stdlib)
r? `@ghost`
`@rustbot` modify labels: rollup
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Make both `hint_assert_unchecked` and `const_hint_assert_unchecked`
stable as `hint_assert_unchecked`.
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Fully stabilize the following API, including const where applicable:
impl <T> NonNull<T> {
pub const unsafe fn offset(self, count: isize) -> Self;
pub const unsafe fn add(self, count: usize) -> Self;
pub const unsafe fn sub(self, count: usize) -> Self;
pub const unsafe fn offset_from(self, origin: NonNull<T>) -> isize;
pub const unsafe fn read(self) -> T;
pub unsafe fn read_volatile(self) -> T;
pub const unsafe fn read_unaligned(self) -> T;
pub unsafe fn write_volatile(self, val: T);
pub unsafe fn replace(self, src: T) -> T;
}
impl<T: ?Sized> NonNull<T> {
pub const unsafe fn byte_offset(self, count: isize) -> Self;
pub const unsafe fn byte_add(self, count: usize) -> Self;
pub const unsafe fn byte_sub(self, count: usize) -> Self;
pub const unsafe fn byte_offset_from<U: ?Sized>(self, origin: NonNull<U>) -> isize;
pub unsafe fn drop_in_place(self);
}
Stabilize the following without const:
impl <T> NonNull<T> {
// const under `const_intrinsic_copy`
pub const unsafe fn copy_to(self, dest: NonNull<T>, count: usize);
pub const unsafe fn copy_to_nonoverlapping(self, dest: NonNull<T>, count: usize);
pub const unsafe fn copy_from(self, src: NonNull<T>, count: usize);
pub const unsafe fn copy_from_nonoverlapping(self, src: NonNull<T>, count: usize);
// const under `const_ptr_write`
pub const unsafe fn write(self, val: T);
pub const unsafe fn write_bytes(self, val: u8, count: usize);
pub const unsafe fn write_unaligned(self, val: T);
// const under `const_swap`
pub const unsafe fn swap(self, with: NonNull<T>);
// const under `const_align_offset`
pub const fn align_offset(self, align: usize) -> usize;
// const under `const_pointer_is_aligned`
pub const fn is_aligned(self) -> bool;
}
Left the following unstable:
impl <T> NonNull<T> {
// moved gate to `ptr_sub_ptr`
pub const unsafe fn sub_ptr(self, subtracted: NonNull<T>) -> usize;
}
impl <T: ?Sized> NonNull<T> {
// moved gate to `pointer_is_aligned_to`
pub const fn is_aligned_to(self, align: usize) -> bool;
}
Fixes: https://github.com/rust-lang/rust/issues/117691
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Stabilize `Utf8Chunks`
Pending FCP in https://github.com/rust-lang/rust/issues/99543.
This PR includes the proposed modification in https://github.com/rust-lang/libs-team/issues/190 as agreed in https://github.com/rust-lang/rust/issues/99543#issuecomment-2050406568.
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Do not allocate for ZST ThinBox (attempt 2 using const_allocate)
There's PR https://github.com/rust-lang/rust/pull/123184 which avoids allocation for ZST ThinBox.
That PR has an issue with unsoundness with padding in `MaybeUninit` (see comments in that PR). Also that PR relies on `Freeze` trait.
This PR is much simpler implementation which does not have this problem, but it uses `const_allocate` feature.
`@oli-obk` suggested that `const_allocate` should not be used for that feature. But I like how easy it to do this feature with `const_allocate`. Maybe it's OK to use `const_allocate` while `ThinBox` is unstable? Or, well, we can abandon this PR.
r? `@oli-obk`
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There's PR https://github.com/rust-lang/rust/pull/123184
which avoids allocation for ZST ThinBox.
That PR has an issue with unsoundness with misuse of `MaybeUninit`
(see comments in that PR).
This PR is much simpler implementation which does not have this
problem, but it uses `const_allocate` feature.
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This is an alternative to #121920
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Stabilize `unchecked_{add,sub,mul}`
Tracking issue: #85122
I think we might as well just stabilize these basic three. They're the ones that have `nuw`/`nsw` flags in LLVM.
Notably, this doesn't include the potentially-more-complex or -more-situational things like `unchecked_neg` or `unchecked_shr` that are under different feature flags.
To quote Ralf https://github.com/rust-lang/rust/issues/85122#issuecomment-1681669646,
> Are there any objections to stabilizing at least `unchecked_{add,sub,mul}`? For those there shouldn't be any surprises about what their safety requirements are.
*Semantially* these are [already available on stable, even in `const`, via](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=bdb1ff889b61950897f1e9f56d0c9a36) `checked_*`+`unreachable_unchecked`. So IMHO we might as well just let people write them directly, rather than try to go through a `let Some(x) = x.checked_add(y) else { unsafe { hint::unreachable_unchecked() }};` dance.
I added additional text to each method to attempt to better describe the behaviour and encourage `wrapping_*` instead.
r? rust-lang/libs-api
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