Make non-power-of-two alignments a validity error in `Layout`
Inspired by the zulip conversation about how `Layout` should better enforce `size <= isize::MAX as usize`, this uses an N-variant enum on N-bit platforms to require at the validity level that the existing invariant of "must be a power of two" is upheld.
This was MIRI can catch it, and means there's a more-specific type for `Layout` to store than just `NonZeroUsize`.
It's left as `pub(crate)` here; a future PR could consider giving it a tracking issue for non-internal usage.
Inspired by the zulip conversation about how `Layout` should better enforce `size < isize::MAX as usize`, this uses an N-variant enum on N-bit platforms to require at the validity level that the existing invariant of "must be a power of two" is upheld.
This was MIRI can catch it, and means there's a more-specific type for `Layout` to store than just `NonZeroUsize`.
Handle rustc_const_stable attribute in library feature collector
The library feature collector in [compiler/rustc_passes/src/lib_features.rs](551b4fa395/compiler/rustc_passes/src/lib_features.rs) has only been looking at `#[stable(…)]`, `#[unstable(…)]`, and `#[rustc_const_unstable(…)]` attributes, while ignoring `#[rustc_const_stable(…)]`. The consequences of this were:
- When any const feature got stabilized (changing one or more `rustc_const_unstable` to `rustc_const_stable`), users who had previously enabled that unstable feature using `#![feature(…)]` would get told "unknown feature", rather than rustc's nicer "the feature … has been stable since … and no longer requires an attribute to enable".
This can be seen in the way that https://github.com/rust-lang/rust/pull/93957#issuecomment-1079794660 failed after rebase:
```console
error[E0635]: unknown feature `const_ptr_offset`
--> $DIR/offset_from_ub.rs:1:35
|
LL | #![feature(const_ptr_offset_from, const_ptr_offset)]
| ^^^^^^^^^^^^^^^^
```
- We weren't enforcing that a particular feature is either stable everywhere or unstable everywhere, and that a feature that has been stabilized has the same stabilization version everywhere, both of which we enforce for the other stability attributes.
This PR updates the library feature collector to handle `rustc_const_stable`, and fixes places in the standard library and test suite where `rustc_const_stable` was being used in a way that does not meet the rules for a stability attribute.
The current implementation is much more conservative than it needs to
be, because it's dealing with the size and alignment of a given `T`,
which are more restricted than an arbitrary `Layout`.
For example, imagine a struct with a `u32` and a `u4`. You can safely
create a `Layout { size_: 5, align_: 4 }` by hand, but
`Layout:🆕:<T>` will give `Layout { size_: 8, align_: 4}`, where the
size already has padding that accounts for the alignment. (And the
existing `debug_assert_eq!` in `Layout::array` already demonstrates that
no additional padding is required.)
Add #[must_use] to from_value conversions
I added two methods to the list myself. Clippy did not flag them because they take `mut` args, but neither modifies their argument.
```rust
core::str const unsafe fn from_utf8_unchecked_mut(v: &mut [u8]) -> &mut str;
std::ffi::CString unsafe fn from_raw(ptr: *mut c_char) -> CString;
```
I put a custom note on `from_raw`:
```rust
#[must_use = "call `drop(from_raw(ptr))` if you intend to drop the `CString`"]
pub unsafe fn from_raw(ptr: *mut c_char) -> CString {
```
Parent issue: #89692
r? ``@joshtriplett``
Since this is an example, this could really do with some review from
someone familiar with unsafe stuff !
I made the example no longer `no_run` since it works for me.
Fixes#81847
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
Co-authored-by: Amanieu d'Antras <amanieu@gmail.com>
Due to the std/alloc split, it is not possible to make
`alloc::collections::TryReserveError::AllocError` non-exhaustive without
having an unstable, doc-hidden method to construct (which negates the
benefits from `#[non_exhaustive]`.
Convert primitives in the standard library to intra-doc links
Blocked on https://github.com/rust-lang/rust/pull/80181. I forgot that this needs to wait for the beta bump so the standard library can be documented with `doc --stage 0`.
Notably I didn't convert `core::slice` because it's like 50 links and I got scared 😨
Update LayoutError/LayoutErr stability attributes
`LayoutError` ended up not making it into 1.49.0, updating the stability attributes to reflect that.
I also pushed `LayoutErr` deprecation back a release to allow 2 releases before the deprecation comes into effect.
This change should be backported to beta.
Rename/Deprecate LayoutErr in favor of LayoutError
Implements rust-lang/wg-allocators#73.
This patch renames LayoutErr to LayoutError, and uses a type alias to support users using the old name.
The new name will be instantly stable in release 1.49 (current nightly), the type alias will become deprecated in release 1.51 (so that when the current nightly is 1.51, 1.49 will be stable).
This is the only error type in `std` that ends in `Err` rather than `Error`, if this PR lands all stdlib error types will end in `Error` 🥰
