Document overrides of `clone_from()` in core/std
As mentioned in https://github.com/rust-lang/rust/pull/96979#discussion_r1379502413
Specifically, when an override doesn't just forward to an inner type, document the behavior and that it's preferred over simply assigning a clone of source. Also, change instances where the second parameter is "other" to "source".
I reused some of the wording over and over for similar impls, but I'm not sure that the wording is actually *good*. Would appreciate feedback about that.
Also, now some of these seem to provide pretty specific guarantees about behavior (e.g. will reuse the exact same allocation iff the len is the same), but I was basing it off of the docs for [`Box::clone_from`](https://doc.rust-lang.org/1.75.0/std/boxed/struct.Box.html#method.clone_from-1) - I'm not sure if providing those strong guarantees is actually good or not.
Avoid more NonNull-raw-NonNull roundtrips in Vec
r? the8472
The standard library in general has a lot of these round-trips from niched types to their raw innards and back. Such round-trips have overhead in debug builds since https://github.com/rust-lang/rust/pull/120594. I removed some such round-trips in that initial PR and I've been meaning to come back and hunt down more such examples (this is the last item on https://github.com/rust-lang/rust/issues/120848).
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`
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.
Support running library tests in Miri
This adds a new bootstrap subcommand `./x.py miri` which can test libraries in Miri. This is in preparation for eventually doing that as part of bors CI, but this PR only adds the infrastructure, and doesn't enable it yet.
`@rust-lang/bootstrap` should this be `x.py test --miri library/core` or `x.py miri library/core`? The flag has the advantage that we don't have to copy all the arguments from `Subcommand::Test`. It has the disadvantage that most test steps just ignore `--miri` and still run tests the regular way. For clippy you went the route of making it a separate subcommand. ~~I went with a flag now as that seemed easier, but I can change this.~~ I made it a new subcommand. Note however that the regular cargo invocation would be `cargo miri test ...`, so `x.py` is still going to be different in that the `test` is omitted. That said, we could also make it `./x.py miri-test` to make that difference smaller -- that's in fact more consistent with the internal name of the command when bootstrap invokes cargo.
`@rust-lang/libs` ~~unfortunately this PR does some unholy things to the `lib.rs` files of our library crates.~~
`@m-ou-se` found a way that entirely avoids library-level hacks, except for some new small `lib.miri.rs` files that hopefully you will never have to touch. There's a new hack in cargo-miri but there it is in good company...
Remove len argument from RawVec::reserve_for_push
Removes `RawVec::reserve_for_push`'s `len` argument since it's always the same as capacity.
Also makes `Vec::insert` use `RawVec::reserve_for_push`.
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
Eliminate `UbChecks` for non-standard libraries
The purpose of this PR is to allow other passes to treat `UbChecks` as constants in MIR for optimization after #122629.
r? RalfJung
Implement `Vec::pop_if`
This PR adds `Vec::pop_if` to the public API, behind the `vec_pop_if` feature.
```rust
impl<T> Vec<T> {
pub fn pop_if<F>(&mut self, f: F) -> Option<T>
where F: FnOnce(&mut T) -> bool;
}
```
Tracking issue: #122741
## Open questions
- [ ] Should the first unit test be split up?
- [ ] I don't see any guidance on ordering of methods in impl blocks, should I move the method elsewhere?
warning: casting raw pointers to the same type and constness is unnecessary (`*mut V` -> `*mut V`)
--> library\alloc\src\collections\btree\map\entry.rs:357:31
|
357 | let val_ptr = root.borrow_mut().push(self.key, value) as *mut V;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `root.borrow_mut().push
(self.key, value)`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast
warning: casting to the same type is unnecessary (`usize` -> `usize`)
--> library\alloc\src\ffi\c_str.rs:411:56
|
411 | let slice = slice::from_raw_parts_mut(ptr, len as usize);
| ^^^^^^^^^^^^ help: try: `len`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast
warning: casting raw pointers to the same type and constness is unnecessary (`*mut T` -> `*mut T`)
--> library\alloc\src\slice.rs:516:25
|
516 | (buf.as_mut_ptr() as *mut T).add(buf.len()),
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `buf.as_mut_ptr()`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast
warning: casting raw pointers to the same type and constness is unnecessary (`*mut T` -> `*mut T`)
--> library\alloc\src\slice.rs:537:21
|
537 | (buf.as_mut_ptr() as *mut T).add(buf.len()),
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `buf.as_mut_ptr()`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast
warning: casting raw pointers to the same type and constness is unnecessary (`*const ()` -> `*const ()`)
--> library\alloc\src\task.rs:151:13
|
151 | waker as *const (),
| ^^^^^^^^^^^^^^^^^^ help: try: `waker`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast
warning: casting raw pointers to the same type and constness is unnecessary (`*const ()` -> `*const ()`)
--> library\alloc\src\task.rs:323:13
|
323 | waker as *const (),
| ^^^^^^^^^^^^^^^^^^ help: try: `waker`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast
warning: casting to the same type is unnecessary (`usize` -> `usize`)
--> library\std\src\sys_common\net.rs:110:21
|
110 | assert!(len as usize >= mem::size_of::<c::sockaddr_in>());
| ^^^^^^^^^^^^ help: try: `len`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast
warning: casting to the same type is unnecessary (`usize` -> `usize`)
--> library\std\src\sys_common\net.rs:116:21
|
116 | assert!(len as usize >= mem::size_of::<c::sockaddr_in6>());
| ^^^^^^^^^^^^ help: try: `len`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast
Doc Guarantee: BTree(Set|Map): `IntoIter` Iterate in Sorted by key Order
This Doc-only PR adds text to the IntoIterator implementation and IntoIter type for both BTreeMap and BTreeSet that states that the returned items will be in sorted-by-key order, this is a guarantee that is made by the iter() and iter_mut() methods of BTreeMap/Set and BTreeMap respectively, but not on into_iter methods or types.
I don't know how the IntoIter iteration would not be sorted by key, and I would like to rely on that behavior for my prefix_array crate.
The text appended to IntoIter documentation is based on each types respective iter() method documentation, as is the text used in the IntoIterator documentation; they are slightly inconsistent between Set/Map, but they are consistent within their own types documentation.
select Vec::from_iter impls in a const block to optimize compile times
Ignoring whitespace diffs should make this easier to review.
This relies on the trick from #122301
Split out from #120682
Add `usize::MAX` arg tests for Vec
Tests to prevent recurrence of the UB from the rust-lang/rust#122760 issue.
I skipped the `with_capacity`, `drain`, `reserve`, etc. APIs because they actually had a good assortment of tests earlier in the same file.
r? Nilstrieb
Relax SeqCst ordering in standard library.
Every single SeqCst in the standard library is unnecessary. In all cases, Relaxed or Release+Acquire was sufficient.
As I [wrote](https://marabos.nl/atomics/memory-ordering.html#common-misconceptions) in my book on atomics:
> [..] when reading code, SeqCst basically tells the reader: "this operation depends on the total order of every single SeqCst operation in the program," which is an incredibly far-reaching claim. The same code would likely be easier to review and verify if it used weaker memory ordering instead, if possible. For example, Release effectively tells the reader: "this relates to an acquire operation on the same variable," which involves far fewer considerations when forming an understanding of the code.
>
> It is advisable to see SeqCst as a warning sign. Seeing it in the wild often means that either something complicated is going on, or simply that the author did not take the time to analyze their memory ordering related assumptions, both of which are reasons for extra scrutiny.
r? ````@Amanieu```` ````@joboet````
fix OOB pointer formed in Vec::index
Move the length check to before using `index` with `ptr::add` to prevent an out of bounds pointer from being formed.
Fixes#122760
Stabilize associated type bounds (RFC 2289)
This PR stabilizes associated type bounds, which were laid out in [RFC 2289]. This gives us a shorthand to express nested type bounds that would otherwise need to be expressed with nested `impl Trait` or broken into several `where` clauses.
### What are we stabilizing?
We're stabilizing the associated item bounds syntax, which allows us to put bounds in associated type position within other bounds, i.e. `T: Trait<Assoc: Bounds...>`. See [RFC 2289] for motivation.
In all position, the associated type bound syntax expands into a set of two (or more) bounds, and never anything else (see "How does this differ[...]" section for more info).
Associated type bounds are stabilized in four positions:
* **`where` clauses (and APIT)** - This is equivalent to breaking up the bound into two (or more) `where` clauses. For example, `where T: Trait<Assoc: Bound>` is equivalent to `where T: Trait, <T as Trait>::Assoc: Bound`.
* **Supertraits** - Similar to above, `trait CopyIterator: Iterator<Item: Copy> {}`. This is almost equivalent to breaking up the bound into two (or more) `where` clauses; however, the bound on the associated item is implied whenever the trait is used. See #112573/#112629.
* **Associated type item bounds** - This allows constraining the *nested* rigid projections that are associated with a trait's associated types. e.g. `trait Trait { type Assoc: Trait2<Assoc2: Copy>; }`.
* **opaque item bounds (RPIT, TAIT)** - This allows constraining associated types that are associated with the opaque without having to *name* the opaque. For example, `impl Iterator<Item: Copy>` defines an iterator whose item is `Copy` without having to actually name that item bound.
The latter three are not expressible in surface Rust (though for associated type item bounds, this will change in #120752, which I don't believe should block this PR), so this does represent a slight expansion of what can be expressed in trait bounds.
### How does this differ from the RFC?
Compared to the RFC, the current implementation *always* desugars associated type bounds to sets of `ty::Clause`s internally. Specifically, it does *not* introduce a position-dependent desugaring as laid out in [RFC 2289], and in particular:
* It does *not* desugar to anonymous associated items in associated type item bounds.
* It does *not* desugar to nested RPITs in RPIT bounds, nor nested TAITs in TAIT bounds.
This position-dependent desugaring laid out in the RFC existed simply to side-step limitations of the trait solver, which have mostly been fixed in #120584. The desugaring laid out in the RFC also added unnecessary complication to the design of the feature, and introduces its own limitations to, for example:
* Conditionally lowering to nested `impl Trait` in certain positions such as RPIT and TAIT means that we inherit the limitations of RPIT/TAIT, namely lack of support for higher-ranked opaque inference. See this code example: https://github.com/rust-lang/rust/pull/120752#issuecomment-1979412531.
* Introducing anonymous associated types makes traits no longer object safe, since anonymous associated types are not nameable, and all associated types must be named in `dyn` types.
This last point motivates why this PR is *not* stabilizing support for associated type bounds in `dyn` types, e.g, `dyn Assoc<Item: Bound>`. Why? Because `dyn` types need to have *concrete* types for all associated items, this would necessitate a distinct lowering for associated type bounds, which seems both complicated and unnecessary compared to just requiring the user to write `impl Trait` themselves. See #120719.
### Implementation history:
Limited to the significant behavioral changes and fixes and relevant PRs, ping me if I left something out--
* #57428
* #108063
* #110512
* #112629
* #120719
* #120584Closes#52662
[RFC 2289]: https://rust-lang.github.io/rfcs/2289-associated-type-bounds.html
Add slice::try_range
This adds a fallible version of the unstable `slice::range` (tracking: #76393) which is highly requested in the tracking issue.
Hoping this can slide by without an ACP (since the feature is already being tracked), but let me know otherwise.
Vec::try_with_capacity
Related to #91913
Implements try_with_capacity for `Vec`, `VecDeque`, and `String`. I can follow it up with more collections if desired.
`Vec::try_with_capacity()` is functionally equivalent to the current stable:
```rust
let mut v = Vec::new();
v.try_reserve_exact(n)?
```
However, `try_reserve` calls non-inlined `finish_grow`, which requires old and new `Layout`, and is designed to reallocate memory. There is benefit to using `try_with_capacity`, besides syntax convenience, because it generates much smaller code at the call site with a direct call to the allocator. There's codegen test included.
It's also a very desirable functionality for users of `no_global_oom_handling` (Rust-for-Linux), since it makes a very commonly used function available in that environment (`with_capacity` is used much more frequently than all `(try_)reserve(_exact)`).
Specifically, when an override doesn't just forward to an inner type,
document the behavior and that it's preferred over simply assigning
a clone of source. Also, change instances where the second parameter is
"other" to "source".
Add `#[inline]` to `BTreeMap::new` constructor
This PR add the `#[inline]` attribute to `BTreeMap::new` constructor as to make it eligible for inlining.
<details>
For some context: I was profiling `rustc --check-cfg` with callgrind and due to the way we currently setup all the targets and we end-up calling `BTreeMap::new` multiple times for (nearly) all the targets. Adding the `#[inline]` attribute reduced the number of instructions needed.
</details>
only set noalias on Box with the global allocator
As discovered in https://github.com/rust-lang/miri/issues/3341, `noalias` and custom allocators don't go well together.
rustc can now check whether a Box uses the global allocator. This replaces the previous ad-hoc and rather unprincipled check for a zero-sized allocator.
This is the rustc part of fixing that; Miri will also need a patch.
const_eval_select: make it safe but be careful with what we expose on stable for now
As this is all still nightly-only I think `````@rust-lang/wg-const-eval````` can do that without involving t-lang.
r? `````@oli-obk`````
Cc `````@Nilstrieb````` -- the updated version of your RFC would basically say that we can remove these comments about not making behavior differences visible in stable `const fn`
Clarify/add `must_use` message for Rc/Arc/Weak::into_raw.
The current `#[must_use]` messages for `{sync,rc}::Weak::into_raw` ("`self` will be dropped if the result is not used") are misleading, as `self` is consumed and will *not* be dropped.
This PR changes their `#[must_use]` message to the same as `Arc::into_raw`'s[ current `#[must_use]` message](d573564575/library/alloc/src/sync.rs (L1482)) ("losing the pointer will leak memory"), and also adds it to `Rc::into_raw`, which is not currently `#[must_use]`.
Preserve same vtable pointer when cloning raw waker, to fix Waker::will_wake
Fixes#121600.
As `@jkarneges` identified in https://github.com/rust-lang/rust/issues/121600#issuecomment-1963041051, the issue is two different const promotions produce two statics at different addresses, which may or may not later be deduplicated by the linker (in this case not).
Prior to #119863, the content of the statics was compared, and they were equal. After, the address of the statics are compared and they are not equal.
It is documented that `will_wake` _"works on a best-effort basis, and may return false even when the Wakers would awaken the same task"_ so this PR fixes a quality-of-implementation issue, not a correctness issue.
Have `String` use `SliceIndex` impls from `str`
This PR simplifies the implementation of `Index` and `IndexMut` on `String`, and in the process enables indexing `String` by any user types that implement `SliceIndex<str>`.
Similar to #47832
r? libs
Not sure if this warrants a crater run.
