remove remnants of const_box feature
This feature requires major design work, and the few methods it gates currently aren't actually useful. Let's reset to a clean slate so when a design materializes, we can start from scratch.
Closes https://github.com/rust-lang/rust/issues/92521 by removing the feature it tracks.
r? ````@oli-obk````
document capacity for ZST as example
The main text already covers this, although it provides weaker guarantees, but I think an example in the right spot does not hurt. Fixes#80747
Fix Ptr inconsistency in {Rc,Arc}
### PR Description
This pr aims to address the problem discussed on [zulip](504259637).
### Problem Clarification
As this post presents, the `{Rc, Arc}::{in/de-crement_strong_count_/in}` do not limit the layout of the memory that `ptr` points to, while internally `Rc::from_raw_in` is called directly.
UB doesn't just appear when the strong count is decremented to zero. Miri also detects the UB of `out-of-bounds pointer use` when increment strong count is called on a pointer with an incorrect layout(shown as below).
```rust
use std::rc::Rc;
#[repr(align(8))]
struct Aligned8(u64);
#[repr(align(16))]
struct Aligned16(u64);
fn main() {
let rc: Rc<Aligned8> = Rc::new(Aligned8(42));
let raw_ptr = Rc::into_raw(rc);
unsafe {
Rc::increment_strong_count(raw_ptr as *const Aligned16);
}
}
```
Miri output:
```
error: Undefined Behavior: out-of-bounds pointer use: expected a pointer to 32 bytes of memory, but got alloc954 which is only 24 bytes from the end of the allocation
```
Update the standard library to Rust 2024
This updates the standard library to Rust 2024. This includes the following notable changes:
- Macros are updated to use new expression fragment specifiers. This PR includes a test to illustrate the changes, primarily allowing `const {...}` expressions now.
- Some tests show a change in MIR drop order. We do not believe this will be an observable change ([see zulip discussion](500972873)).
Fixes https://github.com/rust-lang/rust/issues/133081
Add PeekMut::refresh
I'm not sure if this should go through ACP or not. BinaryHeap is not the most critical data structure in the standard library and it would be understandable if maintainer throughput is thus too limited to accept this PR without a proper design phase that ensures the required understanding of consequence over a longer time period.
This aims to improve the useability of heaps for priority-based work queues. In certain scenarios, modifications on the most relevant or critical items are performed until a condition that determines the work items have been sufficiently addressed. For instance the criticality could be a deadline that is relaxed whenever some part of a work item is completed. Such a loop will repeatedly access the most critical item and put it back in a sorted position when it is complete. Crucially, due to the ordering invariant we know that all necessary work was performed when the completed item remains the most critical. Getting this information from the heap position avoids a (potentially more costly) check on the item state itself.
A customized `drop` with boolean result would avoid up to two more comparisons performed in both the last no-op refresh and Drop code but this occurs once in each execution of the above scenario whereas refresh occurs any number of times. Also note that the comparison overhead of Drop is only taken if the element is mutably inspected to determine the end condition, i.e. not when refresh itself is the break condition.
This improves the useability of heaps for priority-based work queues. In
certain scenarios, modifications on the most relevant or critical items are
performed until a condition that determines the work items have been
sufficiently addressed. The loop will repeatedly access the most critical
item and put it back in a sorted position when it is complete. Crucially,
due to the ordering invariant we know that all work was performed when the
completed item remains the most critical. Getting this information from the
heap position avoids a (potentially more costly) check on the item state
itself.
A customized `drop` with boolean result would avoid up to two more
comparisons performed in both the last no-op refresh and Drop code but this
occurs once in each execution of the above scenario whereas refresh occurs
any number of times. Also note that the comparison overhead of Drop is only
taken if the element is mutably inspected to determine the end condition,
i.e. not when refresh itself is the break condition.
Put the alloc unit tests in a separate alloctests package
Same rationale as https://github.com/rust-lang/rust/pull/135937. This PR has some extra complexity though as a decent amount of tests are testing internal implementation details rather than the public api. As such I opted to include the modules containing the types under test using `#[path]` into the alloctests package. This means that those modules still need `#[cfg(test)]`, but the rest of liballoc no longer need it.
library: Use `size_of` from the prelude instead of imported
Use `std::mem::{size_of, size_of_val, align_of, align_of_val}` from the prelude instead of importing or qualifying them.
These functions were added to all preludes in Rust 1.80.
try-job: test-various
try-job: x86_64-gnu
try-job: x86_64-msvc-1
Use `std::mem::{size_of, size_of_val, align_of, align_of_val}` from the
prelude instead of importing or qualifying them.
These functions were added to all preludes in Rust 1.80.
Update `compiler-builtins` to 0.1.149
Includes a change to make a subset of math symbols available on all platforms [1], and disables `f16` on aarch64 without neon [2].
[1]: https://github.com/rust-lang/compiler-builtins/pull/763
[2]: https://github.com/rust-lang/compiler-builtins/pull/775
try-job: aarch64-gnu
try-job: aarch64-gnu-debug
try-job: armhf-gnu
try-job: dist-various-1
try-job: dist-various-2
try-job: dist-aarch64-linux
try-job: dist-arm-linux
try-job: dist-armv7-linux
try-job: dist-x86_64-linux
try-job: test-various
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.
Rollup of 8 pull requests
Successful merges:
- #137370 (adjust_abi: make fallback logic for ABIs a bit easier to read)
- #137444 (Improve behavior of `IF_LET_RESCOPE` around temporaries and place expressions)
- #137464 (Fix invalid suggestion from type error for derive macro)
- #137539 ( Add rustdoc-gui regression test for #137082 )
- #137576 (Don't doc-comment BTreeMap<K, SetValZST, A>)
- #137595 (remove `simd_fpow` and `simd_fpowi`)
- #137600 (type_ir: remove redundant part of comment)
- #137602 (feature: fix typo in attribute description)
r? `@ghost`
`@rustbot` modify labels: rollup
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
