More precisely document `Global::deallocate()`'s safety.
There is a subtlety which "other conditions must be upheld by the caller" does not capture: `GlobalAlloc`/`alloc::dealloc()` require that the provided layout will be *equal*, not just that it "fits", the layout used to allocate. This is always true here due to how `allocate()`, `grow()`, and `shrink()` are implemented (they never return a larger allocation than requested), but that is a non-local property of the implementation, so it should be documented explicitly.
r? libs
`@rustbot` label A-allocators
There is a subtlety which "other conditions must be upheld by the caller"
does not capture: `GlobalAlloc`/`alloc::dealloc()` require that the
provided layout will be *equal*, not just that it "fits", the layout
used to allocate. This is always true here due to how `allocate()`,
`grow()`, and `shrink()` are implemented (they never return a larger
allocation than requested), but that is a non-local property of the
implementation, so it should be documented explicitly.
Don't doc-comment BTreeMap<K, SetValZST, A>
This otherwise shows up in documentation as an empty impl block (worse, at the *top* of the docs above the public impls).
Update `String::from_raw_parts` safety requirements
These have become out of sync with `Vec::from_raw_part`'s safety requirements, and are likely to diverge again. I think it's safest to just point at `Vec`'s requirements.
https://github.com/rust-lang/rust/issues/119206#issuecomment-2180116680
Reduce `Box::default` stack copies in debug mode
The `Box::new(T::default())` implementation of `Box::default` only
had two stack copies in debug mode, compared to the current version,
which has four. By avoiding creating any `MaybeUninit<T>`'s and just writing
`T` directly to the `Box` pointer, the stack usage in debug mode remains
the same as the old version.
Another option would be to mark `Box::write` as `#[inline(always)]`,
and change it's implementation to to avoid calling `MaybeUninit::write`
(which creates a `MaybeUninit<T>` on the stack) and to use `ptr::write` instead.
Fixes: #136043
Impl TryFrom<Vec<u8>> for String
I think this is useful enough to have :)
As a general question, is there any policy around adding "missing" trait implementations? (like adding `AsRef<T> for T` for std types), I mostly stumble upon them when using a lot of "impl Trait in argument position" like (`foo: impl Into<String>`)
Add `MAX_LEN_UTF8` and `MAX_LEN_UTF16` Constants
This pull request adds the `MAX_LEN_UTF8` and `MAX_LEN_UTF16` constants as per #45795, gated behind the `char_max_len` feature.
The constants are currently applied in the `alloc`, `core` and `std` libraries.
Restrict DerefPure for Cow<T> impl to T = impl Clone, [impl Clone], str.
Fixes#136046
`feature(deref_patterns)` tracking issue: https://github.com/rust-lang/rust/issues/87121
`Cow<'_, T>` should only implement `DerefPure` if its `Deref` impl is pure, which requires `<T::Owned as Borrow<T>>::borrow` to be pure. This PR restricts `impl DerefPure for Cow<'_, T>` to `T: Sized + Clone`, `T = [U: Clone]`, and `T = str` (for all of whom `<T::Owned as Borrow<T>>::borrow` is implemented in the stdlib and is pure).
cc ``@Nadrieril``
------
An alternate approach would be to introduce a new `unsafe trait BorrowPure<T>` analogous to `DerefPure` that could be implemented for `T: Sized`, `&T`, `&mut T`, `String`, `Vec`, `Box`, `PathBuf`, `OsString`, etc. https://github.com/rust-lang/rust/compare/master...zachs18:borrow-pure-trait
Implement Extend<AsciiChar> for String
Implement `Extend<AsciiChar>` for `String` as suggested in https://github.com/rust-lang/rust/issues/110998#issuecomment-2590122968. Also implements `Extend<&AsciiChar>` since there's an analogous impl for `Extend<&char>`, but happy to remove if not thought useful.
r? `@scottmcm`
since you requested it, but no pressure to review!
Prepare standard library for Rust 2024 migration
This includes a variety of commits preparing the standard library for migration to Rust 2024.
The actual migration is blocked on a few things, so I wanted to get this out of the way in a relatively digestable PR.
alloc boxed: docs: use MaybeUninit::write instead of as_mut_ptr
In the deferred initialization pattern, the docs were needlessly going through `as_mut_ptr().write()` to initialize, which is unnecessary use of a pointer, needs to be inside an `unsafe` block, and may weaken alias analysis.
A small workaround for https://github.com/rust-lang/rust/issues/136899,
rustdoc's invalid_rust_codeblocks was not handling this well in 2024.
This may be needed when migrating to 2024 when building with stage0.
In the deferred initialization pattern, the docs were needlessly going
through as_mut_ptr().write() to initialize, which is unnecessary use of
a pointer, needs to be inside an unsafe block, and may weaken alias
analysis.
Some miscellaneous edition-related library tweaks
Some library edition tweaks that can be done separately from upgrading the whole standard library to edition 2024 (which is blocked on getting the submodules upgraded, for example)
Update bootstrap compiler and rustfmt
The rustfmt version we previously used formats things differently from what the latest nightly rustfmt does. This causes issues for subtrees that get formatted both in-tree and in their own repo. Updating the rustfmt used in-tree solves those issues. Also bumped the bootstrap compiler as the stage0 update command always updates both at the same
time.
Optimize `Rc::<str>::default()` implementation
This PR lets `impl Default for Rc<str>` re-use the implementation for `Rc::<[u8]>::default()`. The previous version only calculted the memory layout at runtime, even though it should be known at compile time, resulting in an additional function call.
The same optimization is done for `Rc<CStr>`.
Generated byte code: <https://godbolt.org/z/dfq73jsoP>.
Resolves <https://github.com/rust-lang/rust/issues/135784>.
Cc `@Billy-Sheppard.`
