Tracking issue for release notes of #129401: Partially stabilize feature(new_uninit)

[rustbot]

This issue tracks the release notes text for #129401.

Steps

• Proposed text is drafted by PR author (or team) making the noteworthy change.
• Issue is nominated for release team review of clarity for wider audience.
• Release team includes text in release notes/blog posts.

Release notes text

The responsible team for the underlying change should edit this section to replace the automatically generated link with a succinct description of what changed, drawing upon text proposed by the author (either in discussion or through direct editing).

# API stabilization
- [Partially stabilize `feature(new_uninit)`](https://github.com/rust-lang/rust/pull/129401)

Tip

Use the previous releases categories to help choose which one(s) to use.
The category will be de-duplicated with all the other ones by the release team.

More than one section can be included if needed.

Release blog section

If the change is notable enough for inclusion in the blog post, the responsible team should add content to this section.
Otherwise leave it empty.

cc @workingjubilee, @dtolnay -- origin issue/PR authors and assignees for starting to draft text

[workingjubilee]

We actually basically stabilized the entire feature, honestly, as it was originally conceived.

If you want to keep it short you could phrase it like this:

• There is now AllocationType::new_uninit() and AllocationType::new_uninit_slice() for each dereferenceable allocation type or "smart pointer" (Box, Rc, and Arc), and the corresponding assume_inits.

But you could jam in the entire list of new fn if you feel the blog post needs padding:

impl<T> Box<T> { pub fn new_uninit() -> Box<MaybeUninit<T>> {…} }
impl<T> Rc<T> { pub fn new_uninit() -> Rc<MaybeUninit<T>> {…} }
impl<T> Arc<T> { pub fn new_uninit() -> Arc<MaybeUninit<T>> {…} }

impl<T> Box<[T]> { pub fn new_uninit_slice(len: usize) -> Box<[MaybeUninit<T>]> {…} }
impl<T> Rc<[T]> { pub fn new_uninit_slice(len: usize) -> Rc<[MaybeUninit<T>]> {…} }
impl<T> Arc<[T]> { pub fn new_uninit_slice(len: usize) -> Arc<[MaybeUninit<T>]> {…} }

impl<T> Box<MaybeUninit<T>> { pub unsafe fn assume_init(self) -> Box<T> {…} }
impl<T> Box<[MaybeUninit<T>]> { pub unsafe fn assume_init(self) -> Box<[T]> {…} }
impl<T> Rc<MaybeUninit<T>> { pub unsafe fn assume_init(self) -> Rc<T> {…} }
impl<T> Rc<[MaybeUninit<T>]> { pub unsafe fn assume_init(self) -> Rc<[T]> {…} }
impl<T> Arc<MaybeUninit<T>> { pub unsafe fn assume_init(self) -> Arc<T> {…} }
impl<T> Arc<[MaybeUninit<T>]> { pub unsafe fn assume_init(self) -> Arc<[T]> {…} }

It was a "partial" stabilization because after the feature was proposed a bunch of PRs were landed that added a zillion extra functions to be stabilized with it, and there wasn't consensus for stabilizing those also yet. So they weren't.

[Mark-Simulacrum]

Yeah, I think we'll just list this in the API stabilizations section, no dedicated blog section. Thanks!