Rollup of 16 pull requests
Successful merges:
- #123374 (DOC: Add FFI example for slice::from_raw_parts())
- #124514 (Recommend to never display zero disambiguators when demangling v0 symbols)
- #125978 (Cleanup: HIR ty lowering: Consolidate the places that do assoc item probing & access checking)
- #125980 (Nvptx remove direct passmode)
- #126187 (For E0277 suggest adding `Result` return type for function when using QuestionMark `?` in the body.)
- #126210 (docs(core): make more const_ptr doctests assert instead of printing)
- #126249 (Simplify `[T; N]::try_map` signature)
- #126256 (Add {{target}} substitution to compiletest)
- #126263 (Make issue-122805.rs big endian compatible)
- #126281 (set_env: State the conclusion upfront)
- #126286 (Make `storage-live.rs` robust against rustc internal changes.)
- #126287 (Update a cranelift patch file for formatting changes.)
- #126301 (Use `tidy` to sort crate attributes for all compiler crates.)
- #126305 (Make PathBuf less Ok with adding UTF-16 then `into_string`)
- #126310 (Migrate run make prefer rlib)
- #126314 (fix RELEASES: we do not support upcasting to auto traits)
r? `@ghost`
`@rustbot` modify labels: rollup
Simplify `[T; N]::try_map` signature
People keep making fun of this signature for being so gnarly.
Associated type bounds admit a much simpler scribbling.
r? ````@scottmcm````
People keep making fun of this signature for being so gnarly.
Associated type bounds lend it a much simpler scribbling.
ChangeOutputType can also come along for the ride.
Fix `NonZero` doctest inconsistencies
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`NonZero`'s doctests contain both `?` and `.unwrap()` with no obvious reason for the difference, so this changes all of them to `?`. Also removes an explicit `std::num::NonZero`.
Clarify that they always have the same alignment as u8/i8, (unlike other atomic types).
Clarify in from_ptr that alignment is never an issue because of this.
Add `FRAC_1_SQRT_2PI` constant to f16/f32/f64/f128
This adds the `FRAC_1_SQRT_2PI` to the `f16`, `f32`, `f64` and `f128` as [`1/√(2π)`](https://www.wolframalpha.com/input?i=1%2Fsqrt%282*pi%29). The rationale is that while `FRAC_1_SQRT_PI` already exists, [Gaussian calculations](https://en.wikipedia.org/wiki/Gaussian_function) for random normal distributions require a `1/(σ√(2π))` term, which could then be directly expressed e.g. as `f32::FRAC_1_SQRT_2PI / sigma`.
The actual value is approximately `1/√(2π) = 0.3989422804014326779399460599343818684758586311649346576659258296…`. Truncated/rounded forms were used for the individual types.
---
~~I did not any of the `#[unstable]` attributes since I am not aware of their implications.~~
**Edit:** I applied the stability attributes from the surrounding types according to what seemed most likely correct. I believe the `more_float_constants` feature marker is incorrectly applied, but I wasn't sure how to proceed.
Size optimize int formatting
Let's use the new feature flag!
This uses a simpler algorithm to format integers.
It is slower, but also smaller.
It also saves having to import the 200 byte rodata lookup table.
In a test of mine this saves ~300 bytes total of a cortex-m binary that does integer formatting.
For a 16KB device, that's almost 2%.
Note though that for opt-level 3 the text size actually grows by 116 bytes.
Still a win in total. I'm not sure why the generated code is bigger than the more fancy algo. Maybe the smaller algo lends itself more to inlining and duplicating?
Use inline const blocks to create arrays of `MaybeUninit`.
This PR contains 2 changes enabled by the fact that [`inline_const` is now stable](https://github.com/rust-lang/rust/pull/104087), and was split out of #125082.
1. Use inline const instead of `unsafe` to construct arrays in `MaybeUninit` examples.
Rationale: Demonstrate good practice of avoiding `unsafe` code where it is not strictly necessary.
4. Use inline const instead of `unsafe` to implement `MaybeUninit::uninit_array()`.
This is arguably giving the compiler more work to do, in exchange for eliminating just one single internal unsafe block, so it's less certain that this is good on net.
r? `@Nilstrieb`
Add `size_of` and `size_of_val` and `align_of` and `align_of_val` to the prelude
(Note: need to update the PR to add `align_of` and `align_of_val`, and remove the second commit with the myriad changes to appease the lint.)
Many, many projects use `size_of` to get the size of a type. However,
it's also often equally easy to hardcode a size (e.g. `8` instead of
`size_of::<u64>()`). Minimizing friction in the use of `size_of` helps
ensure that people use it and make code more self-documenting.
The name `size_of` is unambiguous: the name alone, without any prefix or
path, is self-explanatory and unmistakeable for any other functionality.
Adding it to the prelude cannot produce any name conflicts, as any local
definition will silently shadow the one from the prelude. Thus, we don't
need to wait for a new edition prelude to add it.
Explain differences between `{Once,Lazy}{Cell,Lock}` types
The question of "which once-ish cell-ish type should I use?" has been raised multiple times, and is especially important now that we have stabilized the `LazyCell` and `LazyLock` types. The answer for the `Lazy*` types is that you would be better off using them if you want to use what is by far the most common pattern: initialize it with a single nullary function that you would call at every `get_or_init` site. For everything else there's the `Once*` types.
"For everything else" is a somewhat weak motivation, as it only describes by negation. While contrasting them is inevitable, I feel positive motivations are more understandable. For this, I now offer a distinct example that helps explain why `OnceLock` can be useful, despite `LazyLock` existing: you can do some cool stuff with it that `LazyLock` simply can't support due to its mere definition.
The pair of `std::sync::*Lock`s are usable inside a `static`, and can serve roles in async or multithreaded (or asynchronously multithreaded) programs that `*Cell`s cannot. Because of this, they received most of my attention.
Fixes#124696Fixes#125615
Add function `core::iter::chain`
The addition of `core::iter::zip` (#82917) set a precedent for adding plain functions for iterator adaptors. Adding `chain` makes it a little easier to `chain` two iterators.
```rust
for (x, y) in chain(xs, ys) {}
// vs.
for (x, y) in xs.into_iter().chain(ys) {}
```
There is prior art for the utility of this in [`itertools::chain`](https://docs.rs/itertools/latest/itertools/fn.chain.html).
Approved ACP https://github.com/rust-lang/libs-team/issues/154
The addition of `core::iter::zip` (#82917) set a precedent for adding
plain functions for iterator adaptors. Adding `chain` makes it a little
easier to `chain` two iterators.
```
for (x, y) in chain(xs, ys) {}
// vs.
for (x, y) in xs.into_iter().chain(ys) {}
```
Change pedantically incorrect OnceCell/OnceLock wording
While the semantic intent of a OnceCell/OnceLock is that it can only be written to once (upon init), the fact of the matter is that both these types offer a `take(&mut self) -> Option<T>` mechanism that, when successful, resets the cell to its initial state, thereby [technically allowing it to be written to again](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=415c023a6ae1ef35f371a2d3bb1aa735)
Despite the fact that this can only happen with a mutable reference (generally only used during the construction of the OnceCell/OnceLock), it would be incorrect to say that the type itself as a whole *categorically* prevents being initialized or written to more than once (since it is possible to imagine an identical type only without the `take()` method that actually fulfills that contract).
To clarify, change "that cannot be.." to "that nominally cannot.." and add a note to OnceCell about what can be done with an `&mut Self` reference.
```@rustbot``` label +A-rustdocs
The `mir!` macro has multiple parts:
- An optional return type annotation.
- A sequence of zero or more local declarations.
- A mandatory starting anonymous basic block, which is brace-delimited.
- A sequence of zero of more additional named basic blocks.
Some `mir!` invocations use braces with a "block" style, like so:
```
mir! {
let _unit: ();
{
let non_copy = S(42);
let ptr = std::ptr::addr_of_mut!(non_copy);
// Inside `callee`, the first argument and `*ptr` are basically
// aliasing places!
Call(_unit = callee(Move(*ptr), ptr), ReturnTo(after_call), UnwindContinue())
}
after_call = {
Return()
}
}
```
Some invocations use parens with a "block" style, like so:
```
mir!(
let x: [i32; 2];
let one: i32;
{
x = [42, 43];
one = 1;
x = [one, 2];
RET = Move(x);
Return()
}
)
```
And some invocations uses parens with a "tighter" style, like so:
```
mir!({
SetDiscriminant(*b, 0);
Return()
})
```
This last style is generally used for cases where just the mandatory
starting basic block is present. Its braces are placed next to the
parens.
This commit changes all `mir!` invocations to use braces with a "block"
style. Why?
- Consistency is good.
- The contents of the invocation is a block of code, so it's odd to use
parens. They are more normally used for function-like macros.
- Most importantly, the next commit will enable rustfmt for
`tests/mir-opt/`. rustfmt is more aggressive about formatting macros
that use parens than macros that use braces. Without this commit's
changes, rustfmt would break a couple of `mir!` macro invocations that
use braces within `tests/mir-opt` by inserting an extraneous comma.
E.g.:
```
mir!(type RET = (i32, bool);, { // extraneous comma after ';'
RET.0 = 1;
RET.1 = true;
Return()
})
```
Switching those `mir!` invocations to use braces avoids that problem,
resulting in this, which is nicer to read as well as being valid
syntax:
```
mir! {
type RET = (i32, bool);
{
RET.0 = 1;
RET.1 = true;
Return()
}
}
```
Implement feature `integer_sign_cast`
Tracking issue: https://github.com/rust-lang/rust/issues/125882
Since this is my first time making a library addition I wasn't sure where to place the new code relative to existing code. I decided to place it near the top where there are already some other basic bitwise manipulation functions. If there is an official guideline for the ordering of functions, please let me know.
Change f32::midpoint to upcast to f64
This has been verified by kani as a correct optimization
see: https://github.com/rust-lang/rust/issues/110840#issuecomment-1942587398
The new implementation is branchless and only differs in which NaN values are produced (if any are produced at all), which is fine to change. Aside from NaN handling, this implementation produces bitwise identical results to the original implementation.
Question: do we need a codegen test for this? I didn't add one, since the original PR #92048 didn't have any codegen tests.
This has been verified by kani as a correct optimization
see: https://github.com/rust-lang/rust/issues/110840#issuecomment-1942587398
The new implementation is branchless, and only differs in which NaN
values are produced (if any are produced at all). Which is fine to change.
Aside from NaN handling, this implementation produces bitwise identical
results to the original implementation.
The new implementation is gated on targets that have a fast 64-bit
floating point implementation in hardware, and on WASM.
Unroll first iteration of checked_ilog loop
This follows the optimization of #115913. As shown in https://github.com/rust-lang/rust/pull/115913#issuecomment-2066788006, the performance was improved in all important cases, but some regressions were introduced for the benchmarks `u32_log_random_small`, `u8_log_random` and `u8_log_random_small`.
Basically, #115913 changed the implementation from one division per iteration to one multiplication per iteration plus one division. When there are zero iterations, this is a regression from zero divisions to one division.
This PR avoids this by avoiding the division if we need zero iterations by returning `Some(0)` early. It also reduces the number of multiplications by one in all other cases.
Implement `needs_async_drop` in rustc and optimize async drop glue
This PR expands on #121801 and implements `Ty::needs_async_drop` which works almost exactly the same as `Ty::needs_drop`, which is needed for #123948.
Also made compiler's async drop code to look more like compiler's regular drop code, which enabled me to write an optimization where types which do not use `AsyncDrop` can simply forward async drop glue to `drop_in_place`. This made size of the async block from the [async_drop test](67980dd6fb/tests/ui/async-await/async-drop.rs) to decrease by 12%.
drop_in_place: weaken the claim of equivalence with drop(ptr.read())
The two are *not* semantically equivalent in all cases, so let's not be so definite about this.
Fixes https://github.com/rust-lang/rust/issues/112015
Add lang items for `AsyncFn*`, `Future`, `AsyncFnKindHelper`'s associated types
Adds lang items for `AsyncFnOnce::Output`, `AsyncFnOnce::CallOnceFuture`, `AsyncFnMut::CallRefFuture`, and uses them in the new solver. I'm mostly interested in doing this to help accelerate uplifting the new trait solver into a separate crate.
The old solver is kind of spaghetti, so I haven't moved that to use these lang items (i.e. it still uses `item_name`-based comparisons).
update: Also adds lang items for `Future::Output` and `AsyncFnKindHelper::Upvars`.
cc ``@lcnr``
This is create symmetry between the already existing TAU constant (2pi)
and the newly-introduced FRAC_1_SQRT_2PI, keeping the more common
name while increasing visibility.
rustfmt fixes
The `rmake.rs` entries in `rustfmt.toml` are causing major problems for `x fmt`. This PR removes them and does some minor related cleanups.
r? ``@GuillaumeGomez``
It's reasonable to want to, but in the current implementation this
causes multiple problems.
- All the `rmake.rs` files are formatted every time even when they
haven't changed. This is because they get whitelisted unconditionally
in the `OverrideBuilder`, before the changed files get added.
- The way `OverrideBuilder` works, if any files gets whitelisted then no
unmentioned files will get traversed. This is surprising, and means
that the `rmake.rs` entries broke the use of explicit paths to `x
fmt`, and also broke `GITHUB_ACTIONS=true git check --fmt`.
The commit removes the `rmake.rs` entries, fixes the formatting of a
couple of files that were misformatted (not previously caught due to the
`GITHUB_ACTIONS` breakage), and bans `!`-prefixed entries in
`rustfmt.toml` because they cause all these problems.
update tracking issue for lazy_cell_consume
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Always use the general case char count with `optimize_for_size`
The faster algo is really expensive, over a kilobyte if the full algo is present in a binary.
With this PR the general case algo is picked always instead of only for small strings.
In a test of mine this change makes the total binary go from 3116 bytes to 2032 bytes in opt-level 3 and from 1652 bytes to 1428 bytes in opt-level z. I've seen it much worse in real application, so the savings (especially on 'z') will be higher in many cases.
This is the second pr of this kind after #125606
Stabilize `LazyCell` and `LazyLock`
Closes#109736
This stabilizes the [`LazyLock`](https://doc.rust-lang.org/stable/std/sync/struct.LazyLock.html) and [`LazyCell`](https://doc.rust-lang.org/stable/std/cell/struct.LazyCell.html) types:
```rust
static HASHMAP: LazyLock<HashMap<i32, String>> = LazyLock::new(|| {
println!("initializing");
let mut m = HashMap::new();
m.insert(13, "Spica".to_string());
m.insert(74, "Hoyten".to_string());
m
});
let lazy: LazyCell<i32> = LazyCell::new(|| {
println!("initializing");
92
});
```
r? libs-api
Add assert_unsafe_precondition to unchecked_{add,sub,neg,mul,shl,shr} methods
(Old PR is haunted, opening a new one. See #117494 for previous discussion.)
This ensures that these preconditions are actually checked in debug mode, and hopefully should let people know if they messed up. I've also replaced the calls (I could find) in the code that use these intrinsics directly with those that use these methods, so that the asserts actually apply.
More discussions on people misusing these methods in the tracking issue: https://github.com/rust-lang/rust/issues/85122.
Bump bootstrap compiler to the latest beta compiler
This PR updates the bootstrap compiler, aka stage0 to the latest beta version, since it contains rust-lang/cargo#13925.
It removes those unconditional Cargo warnings:
```
warning: [...]/rust/library/core/Cargo.toml: unused manifest key: lints.rust.unexpected_cfgs.check-cfg
warning: [...]/rust/library/std/Cargo.toml: unused manifest key: lints.rust.unexpected_cfgs.check-cfg
warning: [...]/rust/library/alloc/Cargo.toml: unused manifest key: lints.rust.unexpected_cfgs.check-cfg
```
for all contributors/users of this repository (including CI).
I don't know if that's something we do, or if it's even advisable, feel free to close.
r? `@Mark-Simulacrum`
While the semantic intent of a OnceCell/OnceLock is that it can only be written
to once (upon init), the fact of the matter is that both these types offer a
`take(&mut self) -> Option<T>` mechanism that, when successful, resets the cell
to its initial state, thereby technically allowing it to be written to again.
Despite the fact that this can only happen with a mutable reference (generally
only used during the construction of the OnceCell/OnceLock), it would be
incorrect to say that the type itself as a whole categorically prevents being
initialized or written to more than once (since it is possible to imagine an
identical type only without the `take()` method that actually fulfills that
contract).
To clarify, change "that cannot be.." to "that nominally cannot.." and add a
note to OnceCell about what can be done with an `&mut Self` reference.
Make `clamp` inline
Context: rust-lang/rust-clippy#12826
This results in slightly more optimized assembly. (And most important, it's now less than lines than just manually clamping a value)
Add a fast-path to `Debug` ASCII `&str`
Instead of going through the `EscapeDebug` machinery, we can just skip over ASCII chars that don’t need any escaping.
---
This is an alternative / a companion to https://github.com/rust-lang/rust/pull/121138.
The other PR is adding the fast path deep within `EscapeDebug`, whereas this skips as early as possible.
Validate the special layout restriction on `DynMetadata`
If you look at <https://stdrs.dev/nightly/x86_64-unknown-linux-gnu/std/ptr/struct.DynMetadata.html>, you'd think that `DynMetadata` is a struct with fields.
But it's actually not, because the lang item is special-cased in rustc_middle layout:
7601adcc76/compiler/rustc_middle/src/ty/layout.rs (L861-L864)
That explains the very confusing codegen ICEs I was getting in https://github.com/rust-lang/rust/pull/124251#issuecomment-2128543265
> Tried to extract_field 0 from primitive OperandRef(Immediate((ptr: %5 = load ptr, ptr %4, align 8, !nonnull !3, !align !5, !noundef !3)) @ TyAndLayout { ty: DynMetadata<dyn Callsite>, layout: Layout { size: Size(8 bytes), align: AbiAndPrefAlign { abi: Align(8 bytes), pref: Align(8 bytes) }, abi: Scalar(Initialized { value: Pointer(AddressSpace(0)), valid_range: 1..=18446744073709551615 }), fields: Primitive, largest_niche: Some(Niche { offset: Size(0 bytes), value: Pointer(AddressSpace(0)), valid_range: 1..=18446744073709551615 }), variants: Single { index: 0 }, max_repr_align: None, unadjusted_abi_align: Align(8 bytes) } })
because there was a `Field` projection despite the layout clearly saying it's [`Primitive`](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_target/abi/enum.FieldsShape.html#variant.Primitive).
Thus this PR updates the MIR validator to check for such a projection, and changes `libcore` to not ever emit any projections into `DynMetadata`, just to transmute the whole thing when it wants a pointer.
Cleanup check-cfg handling in core and std
Follow-up to https://github.com/rust-lang/rust/pull/125296 where we:
- expect any feature cfg in std, due to `#[path]` imports
- move some check-cfg args inside the `build.rs` as per Cargo recommendation
- and replace the fake Cargo feature `"restricted-std"` by the custom cfg `restricted_std`
Fixes https://github.com/rust-lang/rust/pull/125296#issuecomment-2127009301
r? `@bjorn3` (maybe, feel free to re-roll)
Actually use TAIT instead of emulating it
`core`'s `impl_fn_for_zst` macro is just a hacky way of emulating TAIT. TAIT has become stable enough to be used [in other places](e8fbd99128/library/std/src/backtrace.rs (L431)) inside the standard library, so let's use it in `core` as well.
Expand `for_loops_over_fallibles` lint to lint on fallibles behind references.
Extends the scope of the (warn-by-default) lint `for_loops_over_fallibles` from just `for _ in x` where `x: Option<_>/Result<_, _>` to also cover `x: &(mut) Option<_>/Result<_>`
```rs
fn main() {
// Current lints
for _ in Some(42) {}
for _ in Ok::<_, i32>(42) {}
// New lints
for _ in &Some(42) {}
for _ in &mut Some(42) {}
for _ in &Ok::<_, i32>(42) {}
for _ in &mut Ok::<_, i32>(42) {}
// Should not lint
for _ in Some(42).into_iter() {}
for _ in Some(42).iter() {}
for _ in Some(42).iter_mut() {}
for _ in Ok::<_, i32>(42).into_iter() {}
for _ in Ok::<_, i32>(42).iter() {}
for _ in Ok::<_, i32>(42).iter_mut() {}
}
```
<details><summary><code>cargo build</code> diff</summary>
```diff
diff --git a/old.out b/new.out
index 84215aa..ca195a7 100644
--- a/old.out
+++ b/new.out
`@@` -1,33 +1,93 `@@`
warning: for loop over an `Option`. This is more readably written as an `if let` statement
--> src/main.rs:3:14
|
3 | for _ in Some(42) {}
| ^^^^^^^^
|
= note: `#[warn(for_loops_over_fallibles)]` on by default
help: to check pattern in a loop use `while let`
|
3 | while let Some(_) = Some(42) {}
| ~~~~~~~~~~~~~~~ ~~~
help: consider using `if let` to clear intent
|
3 | if let Some(_) = Some(42) {}
| ~~~~~~~~~~~~ ~~~
warning: for loop over a `Result`. This is more readably written as an `if let` statement
--> src/main.rs:4:14
|
4 | for _ in Ok::<_, i32>(42) {}
| ^^^^^^^^^^^^^^^^
|
help: to check pattern in a loop use `while let`
|
4 | while let Ok(_) = Ok::<_, i32>(42) {}
| ~~~~~~~~~~~~~ ~~~
help: consider using `if let` to clear intent
|
4 | if let Ok(_) = Ok::<_, i32>(42) {}
| ~~~~~~~~~~ ~~~
-warning: `for-loops-over-fallibles` (bin "for-loops-over-fallibles") generated 2 warnings
- Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.04s
+warning: for loop over a `&Option`. This is more readably written as an `if let` statement
+ --> src/main.rs:7:14
+ |
+7 | for _ in &Some(42) {}
+ | ^^^^^^^^^
+ |
+help: to check pattern in a loop use `while let`
+ |
+7 | while let Some(_) = &Some(42) {}
+ | ~~~~~~~~~~~~~~~ ~~~
+help: consider using `if let` to clear intent
+ |
+7 | if let Some(_) = &Some(42) {}
+ | ~~~~~~~~~~~~ ~~~
+
+warning: for loop over a `&mut Option`. This is more readably written as an `if let` statement
+ --> src/main.rs:8:14
+ |
+8 | for _ in &mut Some(42) {}
+ | ^^^^^^^^^^^^^
+ |
+help: to check pattern in a loop use `while let`
+ |
+8 | while let Some(_) = &mut Some(42) {}
+ | ~~~~~~~~~~~~~~~ ~~~
+help: consider using `if let` to clear intent
+ |
+8 | if let Some(_) = &mut Some(42) {}
+ | ~~~~~~~~~~~~ ~~~
+
+warning: for loop over a `&Result`. This is more readably written as an `if let` statement
+ --> src/main.rs:9:14
+ |
+9 | for _ in &Ok::<_, i32>(42) {}
+ | ^^^^^^^^^^^^^^^^^
+ |
+help: to check pattern in a loop use `while let`
+ |
+9 | while let Ok(_) = &Ok::<_, i32>(42) {}
+ | ~~~~~~~~~~~~~ ~~~
+help: consider using `if let` to clear intent
+ |
+9 | if let Ok(_) = &Ok::<_, i32>(42) {}
+ | ~~~~~~~~~~ ~~~
+
+warning: for loop over a `&mut Result`. This is more readably written as an `if let` statement
+ --> src/main.rs:10:14
+ |
+10 | for _ in &mut Ok::<_, i32>(42) {}
+ | ^^^^^^^^^^^^^^^^^^^^^
+ |
+help: to check pattern in a loop use `while let`
+ |
+10 | while let Ok(_) = &mut Ok::<_, i32>(42) {}
+ | ~~~~~~~~~~~~~ ~~~
+help: consider using `if let` to clear intent
+ |
+10 | if let Ok(_) = &mut Ok::<_, i32>(42) {}
+ | ~~~~~~~~~~ ~~~
+
+warning: `for-loops-over-fallibles` (bin "for-loops-over-fallibles") generated 6 warnings
+ Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.02s
```
</details>
-----
Question:
* ~~Currently, the article `an` is used for `&Option`, and `&mut Option` in the lint diagnostic, since that's what `Option` uses. Is this okay or should it be changed? (likewise, `a` is used for `&Result` and `&mut Result`)~~ The article `a` is used for `&Option`, `&mut Option`, `&Result`, `&mut Result` and (as before) `Result`. Only `Option` uses `an` (as before).
`@rustbot` label +A-lint
Rollup of 7 pull requests
Successful merges:
- #125043 (reference type safety invariant docs: clarification)
- #125306 (Force the inner coroutine of an async closure to `move` if the outer closure is `move` and `FnOnce`)
- #125355 (Use Backtrace::force_capture instead of Backtrace::capture in rustc_log)
- #125382 (rustdoc: rename `issue-\d+.rs` tests to have meaningful names (part 7))
- #125391 (Minor serialize/span tweaks)
- #125395 (Remove unnecessary `.md` from the documentation sidebar)
- #125399 (Stop using `to_hir_binop` in codegen)
r? `@ghost`
`@rustbot` modify labels: rollup
reference type safety invariant docs: clarification
The old text could have been read as saying that you can call a function if these requirements are upheld, which is definitely not true as they are an underapproximation of the actual safety invariant.
I removed the part about functions relaxing the requirements via their documentation... this seems incoherent with saying that it may actually be unsound to ever temporarily violate the requirement. Furthermore, a function *cannot* just relax this for its return value, that would in general be unsound. And the part about "unsafe code in a safe function may assume these invariants are ensured of arguments passed by the caller" also interacts with relaxing things: clearly, if the invariant has been relaxed, unsafe code cannot rely on it any more. There may be a place to give general guidance on what kinds of function contracts can exist, but the reference type is definitely not the right place to write that down.
I also took a clarification from https://github.com/rust-lang/rust/pull/121965 that is orthogonal to the rest of that PR.
Cc ```@joshlf``` ```@scottmcm```
miri: rename intrinsic_fallback_checks_ub to intrinsic_fallback_is_spec
Checking UB is not the only concern, we also have to make sure we are not losing out on non-determinism.
r? ``@oli-obk`` (not urgent, take your time)
offset: allow zero-byte offset on arbitrary pointers
As per prior `@rust-lang/opsem` [discussion](https://github.com/rust-lang/opsem-team/issues/10) and [FCP](https://github.com/rust-lang/unsafe-code-guidelines/issues/472#issuecomment-1793409130):
- Zero-sized reads and writes are allowed on all sufficiently aligned pointers, including the null pointer
- Inbounds-offset-by-zero is allowed on all pointers, including the null pointer
- `offset_from` on two pointers derived from the same allocation is always allowed when they have the same address
This removes surprising UB (in particular, even C++ allows "nullptr + 0", which we currently disallow), and it brings us one step closer to an important theoretical property for our semantics ("provenance monotonicity": if operations are valid on bytes without provenance, then adding provenance can't make them invalid).
The minimum LLVM we require (v17) includes https://reviews.llvm.org/D154051, so we can finally implement this.
The `offset_from` change is needed to maintain the equivalence with `offset`: if `let ptr2 = ptr1.offset(N)` is well-defined, then `ptr2.offset_from(ptr1)` should be well-defined and return N. Now consider the case where N is 0 and `ptr1` dangles: we want to still allow offset_from here.
I think we should change offset_from further, but that's a separate discussion.
Fixes https://github.com/rust-lang/rust/issues/65108
[Tracking issue](https://github.com/rust-lang/rust/issues/117945) | [T-lang summary](https://github.com/rust-lang/rust/pull/117329#issuecomment-1951981106)
Cc `@nikic`
Add opt-for-size core lib feature flag
Adds a feature flag to the core library that enables the possibility to have smaller implementations for certain algorithms.
So far, the core lib has traded performance for binary size. This is likely what most people want since they have big simd-capable machines. However, people on small machines, like embedded devices, don't enjoy the potential speedup of the bigger algorithms, but do have to pay for them. These microcontrollers often only have 16-1024kB of flash memory.
This PR is the result of some talks with project members like `@Amanieu` at RustNL.
There are some open questions of how this is eventually stabilized, but it's a similar question as with the existing `panic_immediate_abort` feature.
Speaking as someone from the embedded side, we'd rather have this unstable for a while as opposed to not having it at all. In the meantime we can try to use it and also add additional PRs to the core lib that uses the feature flag in areas where we find benefit.
Open questions from my side:
- Is this a good feature name?
- `panic_immediate_abort` is fairly verbose, so I went with something equally verbose
- It's easy to refactor later
- I've added the feature to `std` and `alloc` as well as they might benefit too. Do we agree?
- I expect these to get less usage out of the flag since most size-constraint projects don't use these libraries often.
Instead of having a single loop that works on utf-8 `char`s,
this splits the implementation into a loop that quickly skips over
printable ASCII, falling back to per-char iteration for other chunks.
Instead of writing each `char` of an escape sequence one by one,
this delegates to `Display`, which uses `write_str` internally
in order to write the whole escape sequence at once.
Re-add `From<f16> for f64`
This impl was originally added in #122470 before being removed in #123830 due to #123831. However, the issue only affects `f32` (which currently only has one `From<{float}>` impl, `From<f32>`) as `f64` already has two `From<{float}>` impls (`From<f32>` and `From<f64>`) and is also the float literal fallback type anyway. Therefore it is safe to re-add `From<f16> for f64`.
This PR also updates the FIXME link to point to the open issue #123831 rather than the closed issue #123824.
Tracking issue: #116909
`@rustbot` label +F-f16_and_f128 +T-libs-api
- `slice::sort` -> driftsort
https://github.com/Voultapher/sort-research-rs/blob/main/writeup/driftsort_introduction/text.md
- `slice::sort_unstable` -> ipnsort
https://github.com/Voultapher/sort-research-rs/blob/main/writeup/ipnsort_introduction/text.md
Replaces the sort implementations with tailor made ones that strike a
balance of run-time, compile-time and binary-size, yielding run-time and
compile-time improvements. Regressing binary-size for `slice::sort`
while improving it for `slice::sort_unstable`. All while upholding the
existing soft and hard safety guarantees, and even extending the soft
guarantees, detecting strict weak ordering violations with a high chance
and reporting it to users via a panic.
In addition the implementation of `select_nth_unstable` is also adapted
as it uses `slice::sort_unstable` internals.
Refactor examples and enhance documentation in result.rs
- Replaced `map` with `map_err` in the error handling example for correctness
- Reordered example code to improve readability and logical flow
- Added assertions to examples to demonstrate expected outcomes
Invert comparison in `uN::checked_sub`
After #124114, LLVM no longer combines the comparison and subtraction in `uN::checked_sub` when either operand is a constant (demo: https://rust.godbolt.org/z/MaeoYbsP1). The difference is more pronounced when the expression is slightly more complex (https://rust.godbolt.org/z/4rPavsYdc).
This is due to the use of `>=` here:
ee97564e3a/library/core/src/num/uint_macros.rs (L581-L593)
For constant `C`, LLVM eagerly converts `a >= C` into `a > C - 1`, but the backend can only combine `a < C` with `a - C`, not `C - 1 < a` and `a - C`: e586556e37/llvm/lib/CodeGen/CodeGenPrepare.cpp (L1697-L1742)
This PR[^1] simply inverts the `>=` into `<` to restore the LLVM magic, and somewhat align this with the implementation of `uN::overflowing_sub` from #103299.
When the result is stored as an `Option` (rather than being branched/cmoved on), the discriminant is `self >= rhs`. This PR doesn't affect the codegen (and relevant tests) of that since LLVM will negate `self < rhs` to `self >= rhs` when necessary.
[^1]: Note to `self`: My very first contribution to publicly-used code. Hopefully like what I should learn to always be, tiny and humble.
Many, many projects use `size_of` to get the size of a type. However,
it's also often equally easy to hardcode a size (e.g. `8` instead of
`size_of::<u64>()`). Minimizing friction in the use of `size_of` helps
ensure that people use it and make code more self-documenting.
The name `size_of` is unambiguous: the name alone, without any prefix or
path, is self-explanatory and unmistakeable for any other functionality.
Adding it to the prelude cannot produce any name conflicts, as any local
definition will silently shadow the one from the prelude. Thus, we don't
need to wait for a new edition prelude to add it.
Add `size_of_val`, `align_of`, and `align_of_val` as well, with similar
justification: widely useful, self-explanatory, unmistakeable for
anything else, won't produce conflicts.
Document proper usage of `fmt::Error` and `fmt()`'s `Result`.
I've seen several newcomers wonder why `fmt::Error` doesn't have any error detail information, or propose to return it in response to an error condition found inside a `impl fmt::Display for MyType`.
That is incorrect, per [a lone paragraph of the `fmt` module's documentation](https://doc.rust-lang.org/1.78.0/std/fmt/index.html#formatting-traits). However, users looking to implement a formatting trait won't necessarily look there. Therefore, let's add the critical information (that formatting per se is infallible) to all the involved items: every `fmt()` method, and `fmt::Error`.
This PR is not intended to make any novel claims about `fmt`; only to repeat an existing one in places where it will be more visible.
Remove feature from documentation examples
Add rustc_const_stable attribute to stabilized functions
Update intra-doc link for `u8::is_ascii_whitespace` on `&[u8]` functions
from_str_radix: outline only the panic function
In the `{integer}::from_str_radix` function, the radix check is labeled as `cold` and `inline(never)`, along with its corresponding panic. It probably was intended to apply these attributes only to the panic function.
Add benchmarks for `impl Debug for str`
In order to inform future perf improvements and prevent regressions, lets add some benchmarks that stress `impl Debug for str`.
---
As I am currently working on improving the perf in https://github.com/rust-lang/rust/pull/121150, its nice to have these benchmarks.
Writing them, I also saw that escapes are written out one char at a time, even though other parts of the code are already optimizing that via `as_str`, which I intend to do as well as a followup improvement.
r? ``@cuviper``
☝🏻 as you were also assigned to https://github.com/rust-lang/rust/pull/121150, CC ``@the8472`` if you want to steal the review :-)
Documentation of these properties previously existed in a lone paragraph
in the `fmt` module's documentation:
<https://doc.rust-lang.org/1.78.0/std/fmt/index.html#formatting-traits>
However, users looking to implement a formatting trait won't necessarily
look there. Therefore, let's add the critical information (that
formatting per se is infallible) to all the involved items.
When encountering a move conflict, on an expression that is `!Copy` passed as an argument to an `fn` that is `impl AsRef`, suggest borrowing the expression.
```
error[E0382]: use of moved value: `bar`
--> f204.rs:14:15
|
12 | let bar = Bar;
| --- move occurs because `bar` has type `Bar`, which does not implement the `Copy` trait
13 | foo(bar);
| --- value moved here
14 | let baa = bar;
| ^^^ value used here after move
|
help: borrow the value to avoid moving it
|
13 | foo(&bar);
| +
```
Fix#41708
Implement `as_chunks` with `split_at_unchecked`
We were discussing various ways to do [this on Discord](https://discord.com/channels/273534239310479360/273541522815713281/1236946363120619521), and in the process I noticed that <https://rust.godbolt.org/z/1P16P37Go> is emitting a panic path inside `as_chunks`. It optimizes out in release, but we could just not do that in the first place.
We're already doing unsafe code that depends on this value being calculated correctly, so might as well call `split_at_unchecked` instead of `split_at`.
Rollup of 8 pull requests
Successful merges:
- #123344 (Remove braces when fixing a nested use tree into a single item)
- #124587 (Generic `NonZero` post-stabilization changes.)
- #124775 (crashes: add lastest batch of crash tests)
- #124869 (Make sure we don't deny macro vars w keyword names)
- #124876 (Simplify `use crate::rustc_foo::bar` occurrences.)
- #124892 (Update cc crate to v1.0.97)
- #124903 (Ignore empty RUSTC_WRAPPER in bootstrap)
- #124909 (Reapply the part of #124548 that bors forgot)
r? `@ghost`
`@rustbot` modify labels: rollup
Avoid a cast in `ptr::slice_from_raw_parts(_mut)`
Casting to `*const ()` or `*mut ()` is no longer needed after https://github.com/rust-lang/rust/pull/123840 so let's make the MIR smaller (and more inline-able, as seen in the tests).
If [ACP#362](https://github.com/rust-lang/libs-team/issues/362) goes through we can keep calling `ptr::from_raw_parts(_mut)` in these also without the cast, but that hasn't had any libs-api attention yet, so I'm not waiting on it.
Correct the const stabilization of `last_chunk` for slices
`<[T]>::last_chunk` should have become const stable as part of <https://github.com/rust-lang/rust/pull/117561>. Update the const stability gate to reflect this.
Add constants for f16 and f128
- Commit 1 adds associated constants for `f16`, excluding NaN and infinities as these are implemented using arithmetic for `f32` and `f64`.
- Commit 2 adds associated constants for `f128`, excluding NaN and infinities.
- Commit 3 adds constants in `std::f16::consts`.
- Commit 4 adds constants in `std::f128::consts`.
Casting to `*const ()` or `*mut ()` just bloats the MIR, so let's not.
If ACP#362 goes through we can keep calling `ptr::from_raw_parts(_mut)` in these also without the cast, but that hasn't had any libs-api attention yet, so I'm not waiting on it.
Document That `f16` And `f128` Hardware Support is Limited (v2)
This PR is identical to #123892, which was approved and merged but then removed from master by a force-push due to a [CI bug](https://rust-lang.zulipchat.com/#narrow/stream/242791-t-infra/topic/ci.20broken.3F).
r? ghost
Original PR description:
---
This adds a small paragraph to the recently added f16 and f128 types explaining that hardware support may be limited, and that performance may suffer as a result of that.
I mainly wrote this because I felt it may be useful to express in some form; as a launchpoint for readers of the documentation if they have issues with performance.
I tried to word the documentation in a way that doesn't create false assumptions (that f16/f128 is too slow to use, for instance), removing the software implementation part could mislead people to thinking that f16/f128 is only available on some platforms, not all, so I believe it is important to keep in.\
"not all *major* platforms" is specifically said so as to not be redundant, because not all platforms implement many things, but the average rustacean is probably going to be using x86_64 or aarch64 derived ISA's, which is who this documentation is targeted towards.
I'm not sure of the best way to word the documentation, or if it should even be added, but I feel like it may be useful to have (potentially in a reworded way, I'm not very confident in the current wording and cannot decide if that is because it is too vague to be useful or too specific to be generally correct).
Co-authored-by: Jubilee <46493976+workingjubilee@users.noreply.github.com>
Update library/core/src/primitive_docs.rs
Remove orphaned doc link and clean up grammar a bit
Update library/core/src/primitive_docs.rs
Co-authored-by: Jubilee <46493976+workingjubilee@users.noreply.github.com>
Update library/core/src/primitive_docs.rs
Rewrite f16 and f128 hw support comments to match PR feedback
I wrote RISC-V allcaps in all cases, and wrote amd64 lowercase in all
cases, im not sure if either is the more correct way for either
platform, thats just how I normally write them, if theres a precedent
elsewhere it should probably be changed to match though.
Update library/core/src/primitive_docs.rs
Co-authored-by: Jubilee <46493976+workingjubilee@users.noreply.github.com>
Update library/core/src/primitive_docs.rs
Co-authored-by: Jubilee <46493976+workingjubilee@users.noreply.github.com>
Update library/core/src/primitive_docs.rs
Use `unchecked_sub` in `split_at`
LLVM currently isn't figuring it out on its own, even in the checked version where it hypothetically could.
Before: <https://rust.godbolt.org/z/PEY38YrKs>
```llvm
bb1: ; preds = %start
%4 = getelementptr inbounds float, ptr %x.0, i64 %n
%5 = sub i64 %x.1, %n
```
After:
```llvm
bb1: ; preds = %start
%4 = getelementptr inbounds float, ptr %x.0, i64 %n
%5 = sub nuw i64 %x.1, %n
```
This is not using the wrapper because there's already a ubcheck covering it, so I don't want this to get a second one once #121571 lands.
---
This is basically the same as #108763, since `split_at` is essentially doing two `get_unchecked`s.
Docs: suggest `uN::checked_sub` instead of check-then-unchecked
As of #124114 it's exactly the same in codegen, so might as well not use `unsafe`.
Note that this is only for *unsigned*, since the overflow conditions for `iN::checked_sub` are more complicated.
Remove an unnecessary cast
Very minor thing, obviously, but I randomly saw this unnecessary cast showing up in the UbChecks, so might as well get rid of it.
As of 124114 it's exactly the same in codegen, so might as well not use `unsafe`.
Note that this is only for *unsigned*, since the overflow conditions for `iN::checked_sub` are more complicated.
Stabilize `split_at_checked`
Closes#119128
For the const version of `slice::split_at_mut_checked`, I'm reusing the `const_slice_split_at_mut` feature flag (#101804). I don't if it okay to reuse tracking issues or if it preferred to create new ones...
Describe and use CStr literals in CStr and CString docs
Mention CStr literals in the description of both types, and use them in some of the code samples for CStr. This is intended to make C string literals more discoverable.
Additionally, I don't think the orange "This example is not tested" warnings are very encouraging, so I have made the examples on `CStr` build.
Implement ptr_as_ref_unchecked
Implementation of #122034.
Prefixed the feature name with `ptr_` for clarity.
Linked const-unstability to #91822, so the post there should probably be updated to mentions the 3 new methods when/if this PR is merged.
deref patterns: impl `DerefPure` for more std types
Context: [deref patterns](https://github.com/rust-lang/rust/issues/87121). The requirements of `DerefPure` aren't precise yet, but these types unambiguously satisfy them.
Interestingly, a hypothetical `impl DerefMut for Cow` that does a `Clone` would *not* be eligible for `DerefPure` if we allow mixing deref patterns with normal patterns. If the following is exhaustive then the `DerefMut` would cause UB:
```rust
match &mut Cow::Borrowed(&()) {
Cow::Owned(_) => ..., // Doesn't match
deref!(_x) if false => ..., // Causes the variant to switch to `Owned`
Cow::Borrowed(_) => ..., // Doesn't match
// We reach unreachable
}
```
Document never type fallback in `!`'s docs
Pulled the documentation I've written for #123939.
I want a single place where never type fallback is explained, which can be referred in all the lints and migration materials.
Use `target_vendor = "apple"` instead of `target_os = "..."`
Use `target_vendor = "apple"` instead of `all(target_os = "macos", target_os = "ios", target_os = "tvos", target_os = "watchos", target_os = "visionos")`.
The apple targets are quite close to being identical, with iOS, tvOS, watchOS and visionOS being even closer, so using `target_vendor` when possible makes it clearer when something is actually OS-specific, or just Apple-specific.
Note that `target_vendor` will [be deprecated in the future](https://github.com/rust-lang/rust/issues/100343), but not before an alternative (like `target_family = "apple"`) is available.
While doing this, I found various inconsistencies and small mistakes in the standard library, see the commits for details. Will follow-up with an extra PR for a similar issue that need a bit more discussion. EDIT: https://github.com/rust-lang/rust/pull/124494
Since you've talked about using `target_vendor = "apple"` in the past:
r? workingjubilee
CC `@simlay,` `@thomcc`
`@rustbot` label O-macos O-ios O-tvos O-watchos O-visionos
Fix#124478 - offset_of! returns a temporary
This was due to the must_use() call. Adding HIR's `OffsetOf` to the must_use checking within the compiler avoids this issue while maintaining the lint output.
Fixes#124478. `@tgross35`
Update `is_val_statically_known` Docs
* Add `Type Requirements` section, listing the allowed inputs, as requested by #121115
* Add `Pointers` subsection, explaining is_val_statically_known handles pointers.
* Add `Stability concerns` section, referring to other documentation relating to consistency in `const` functions.
Fixes#121115
Sorry this took so long.
Abort a process when FD ownership is violated
When an owned FD has already been closed before it's dropped that means something else touched an FD in ways it is not allowed to. At that point things can already be arbitrarily bad, e.g. clobbered mmaps. Recovery is not possible.
All we can do is hasten the fire.
Unlike the previous attempt in #124130 this shouldn't suffer from the possibility that FUSE filesystems can return arbitrary errors.
Convert some iter macros to normal functions
With all the MIR optimization changes that have happened since these were written, let's see if they still actually matter.
\*perf comes back\*
Well, it looks like it's not longer relevant for instruction, cycle, nor wall-time perf. Looks like a bunch of things are maybe 10kb bigger in debug, but some are also 50k *smaller* in debug.
So I think they should switch to being normal functions as the "greatly improves performance" justification for them being macros seems to no longer be true -- probably thanks to us always building `core` with `-Z inline-mir` so the difference is negligible.
Add diagnostic item for `std::iter::Enumerate`
This adds a diagnostic item for `std::iter::Enumerate`. The change will be used by the clippy `unused_enumerate_index` lint to move away from type paths to using diagnostic items.
see: https://github.com/rust-lang/rust-clippy/issues/5393
Rollup of 3 pull requests
Successful merges:
- #124003 (Dellvmize some intrinsics (use `u32` instead of `Self` in some integer intrinsics))
- #124169 (Don't fatal when calling `expect_one_of` when recovering arg in `parse_seq`)
- #124286 (Subtree sync for rustc_codegen_cranelift)
r? `@ghost`
`@rustbot` modify labels: rollup
Dellvmize some intrinsics (use `u32` instead of `Self` in some integer intrinsics)
This implements https://github.com/rust-lang/compiler-team/issues/693 minus what was implemented in #123226.
Note: I decided to _not_ change `shl`/... builder methods, as it just doesn't seem worth it.
r? ``@scottmcm``
alloc::Layout: explicitly document size invariant on the type level
https://github.com/rust-lang/rust/pull/95295 added this to the constructor, but it seems worth documenting the type invariant at the type level.
panic_str only exists for the migration to 2021 panic macros
The only caller is `expect_failed`, which is already a cold inline(never) function, so inlining into that function should be fine. (And indeed `panic_str` was `#[inline]` anyway.)
The existence of panic_str risks someone calling it when they should call `panic` instead, and I can't see a reason why this footgun should exist.
I also extended the comment in `panic` to explain why it needs a `'static` string -- I know I've wondered about this in the past and it took me quite a while to understand.
Add simple async drop glue generation
This is a prototype of the async drop glue generation for some simple types. Async drop glue is intended to behave very similar to the regular drop glue except for being asynchronous. Currently it does not execute synchronous drops but only calls user implementations of `AsyncDrop::async_drop` associative function and awaits the returned future. It is not complete as it only recurses into arrays, slices, tuples, and structs and does not have same sensible restrictions as the old `Drop` trait implementation like having the same bounds as the type definition, while code assumes their existence (requires a future work).
This current design uses a workaround as it does not create any custom async destructor state machine types for ADTs, but instead uses types defined in the std library called future combinators (deferred_async_drop, chain, ready_unit).
Also I recommend reading my [explainer](https://zetanumbers.github.io/book/async-drop-design.html).
This is a part of the [MCP: Low level components for async drop](https://github.com/rust-lang/compiler-team/issues/727) work.
Feature completeness:
- [x] `AsyncDrop` trait
- [ ] `async_drop_in_place_raw`/async drop glue generation support for
- [x] Trivially destructible types (integers, bools, floats, string slices, pointers, references, etc.)
- [x] Arrays and slices (array pointer is unsized into slice pointer)
- [x] ADTs (enums, structs, unions)
- [x] tuple-like types (tuples, closures)
- [ ] Dynamic types (`dyn Trait`, see explainer's [proposed design](https://github.com/zetanumbers/posts/blob/main/async-drop-design.md#async-drop-glue-for-dyn-trait))
- [ ] coroutines (https://github.com/rust-lang/rust/pull/123948)
- [x] Async drop glue includes sync drop glue code
- [x] Cleanup branch generation for `async_drop_in_place_raw`
- [ ] Union rejects non-trivially async destructible fields
- [ ] `AsyncDrop` implementation requires same bounds as type definition
- [ ] Skip trivially destructible fields (optimization)
- [ ] New [`TyKind::AdtAsyncDestructor`](https://github.com/zetanumbers/posts/blob/main/async-drop-design.md#adt-async-destructor-types) and get rid of combinators
- [ ] [Synchronously undroppable types](https://github.com/zetanumbers/posts/blob/main/async-drop-design.md#exclusively-async-drop)
- [ ] Automatic async drop at the end of the scope in async context
checked_ilog: improve performance
Addresses #115874.
(This PR replicates the original #115875, which I accidentally closed by deleting my forked repository...)
Use fake libc in core test
The war on libc continues.
Some platforms may not need to link to the libc crate (and it's possible some may not even have a libc), therefore we shouldn't require it for tests. This creates dummy `malloc` and `free` implementations for use in the pointer docs, but, keeps the public documentation looking the same as before.
Add a lower bound check to `unicode-table-generator` output
This adds a dedicated check for the lower bound
(if it is outside of ASCII range) to the output of the `unicode-table-generator` tool.
This generalized the ASCII-only fast-path, but only for the `Grapheme_Extend` property for now, as that is the only one with a lower bound outside of ASCII.
This adds a dedicated check for the lower bound
(if it is outside of ASCII range) to the output of the `unicode-table-generator` tool.
This generalized the ASCII-only fast-path, but only for the `Grapheme_Extend` property for now,
as that is the only one with a lower bound outside of ASCII.
Make `checked` ops emit *unchecked* LLVM operations where feasible
For things with easily pre-checked overflow conditions -- shifts and unsigned subtraction -- write the checked methods in such a way that we stop emitting wrapping versions of them.
For example, today <https://rust.godbolt.org/z/qM9YK8Txb> neither
```rust
a.checked_sub(b).unwrap()
```
nor
```rust
a.checked_sub(b).unwrap_unchecked()
```
actually optimizes to `sub nuw`. After this PR they do.
cc #103299
For things with easily pre-checked overflow conditions -- shifts and unsigned subtraction -- write then checked methods in such a way that we stop emitting wrapping versions of them.
For example, today <https://rust.godbolt.org/z/qM9YK8Txb> neither
```rust
a.checked_sub(b).unwrap()
```
nor
```rust
a.checked_sub(b).unwrap_unchecked()
```
actually optimizes to `sub nuw`. After this PR they do.
Add support for Arm64EC to the Standard Library
Adds the final pieces so that the standard library can be built for arm64ec-pc-windows-msvc (initially added in #119199)
* Bumps `windows-sys` to 0.56.0, which adds support for Arm64EC.
* Correctly set the `isEC` parameter for LLVM's `writeArchive` function.
* Add `#![feature(asm_experimental_arch)]` to library crates where Arm64EC inline assembly is used, as it is currently unstable.
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.
Link MSVC default lib in core
## The Problem
On Windows MSVC, Rust invokes the linker directly. This means only the objects and libraries Rust explicitly passes to the linker are used. In short, this is equivalent to passing `-nodefaultlibs`, `-nostartfiles`, etc for gnu compilers.
To compensate for this [the libc crate links to the necessary libraries](a0f5b4b213/src/windows/mod.rs (L258-L261)). The libc crate is then linked from std, thus when you use std you get the defaults back.or integrate with C/C++.
However, this has a few problems:
- For `no_std`, users are left to manually pass the default lib to the linker
- Whereas `std` has the opposite problem, using [`/nodefaultlib`](https://learn.microsoft.com/en-us/cpp/build/reference/nodefaultlib-ignore-libraries?view=msvc-170) doesn't work as expected because Rust treats them as normal libs. This is a particular problem when you want to use e.g. the debug CRT libraries in their place or integrate with C/C++..
## The solution
This PR fixes this in two ways:
- moves linking the default lib into `core`
- passes the lib to the linker using [`/defaultlib`](https://learn.microsoft.com/en-us/cpp/build/reference/defaultlib-specify-default-library?view=msvc-170). This allows users to override it in the normal way (i.e. with [`/nodefaultlib`](https://learn.microsoft.com/en-us/cpp/build/reference/nodefaultlib-ignore-libraries?view=msvc-170)).
This is more or less equivalent to what the MSVC C compiler does. You can see what this looks like in my second commit, which I'll reproduce here for convenience:
```rust
// In library/core
#[cfg(all(windows, target_env = "msvc"))]
#[link(
name = "/defaultlib:msvcrt",
modifiers = "+verbatim",
cfg(not(target_feature = "crt-static"))
)]
#[link(name = "/defaultlib:libcmt", modifiers = "+verbatim", cfg(target_feature = "crt-static"))]
extern "C" {}
```
## Alternatives
- Add the above to `unwind` and `std` but not `core`
- The status quo
- Some other kind of compiler magic maybe
This bares some discussion so I've t-libs nominated it.
Doc: replace x with y for hexa-decimal fmt
I found it a bit unintuitive to know which is variable and which is the format string in `format!("{x:x}")`, so I switched it to `y`.
Get rid of `USIZE_MARKER` in formatting infrastructure
An alternative to #123780.
The `USIZE_MARKER` function used to differentiate between placeholder and count arguments is never called anyway, so we can just replace the function-pointer-comparison hack with an `enum` and an `unreachable_unchecked`, hopefully without causing a regression.
CC `@RalfJung`
Update stdarch submodule
`asm_experimental_arch` is required in `core` as we're now using unstable inline assembly when building Arm64EC.
Brings in the fix for <https://github.com/rust-lang/stdarch/issues/1555> (cc `@tslnc04).`
r? `@Amanieu`
Add a `Debug` impl and some basic functions to `f16` and `f128`
`compiler_builtins` uses some convenience functions like `is_nan` and `is_sign_positive`. Add these, as well as a temporary implementation for `Debug` that prints the bit representation.
Rollup of 8 pull requests
Successful merges:
- #122882 (Avoid a panic in `set_output_capture` in the default panic handler)
- #123523 (Account for trait/impl difference when suggesting changing argument from ref to mut ref)
- #123744 (Silence `unused_imports` for redundant imports)
- #123784 (Replace `document.write` with `document.head.insertAdjacent`)
- #123798 (Avoid invalid socket address in length calculation)
- #123804 (Stop using `HirId` for fn-like parents since closures are not `OwnerNode`s)
- #123806 (Panic on overflow in `BorrowedCursor::advance`)
- #123820 (Add my former address to .mailmap)
r? `@ghost`
`@rustbot` modify labels: rollup
Panic on overflow in `BorrowedCursor::advance`
Passing `usize::MAX` to `advance` clearly isn't correct, but the current assertion fails to detect this when overflow checks are disabled. This isn't unsound, but should probably be fixed regardless.
`compiler_builtins` uses some convenience functions like `is_nan` and
`is_sign_positive`. Add these, as well as a temporary implementation for
`Debug` that prints the bit representation.
