Add `type_ascribe!` macro as placeholder syntax for type ascription
This makes it still possible to test the internal semantics of type ascription even once the `:`-syntax is removed from the parser. The macro now gets used in a bunch of UI tests that test the semantics and not syntax of type ascription.
I might have forgotten a few tests but this should hopefully be most of them. The remaining ones will certainly be found once type ascription is removed from the parser altogether.
Part of #101728
`#![custom_mir]`: Various improvements
This PR makes a bunch of improvements to `#![custom_mir]`. Ideally this would be 4 PRs, one for each commit, but those would take forever to get merged and be a pain to juggle. Should still be reviewed one commit at a time though.
### Commit 1: Support arbitrary `let`
Before this change, all locals used in the body need to be declared at the top of the `mir!` invocation, which is rather annoying. We attempt to change that.
Unfortunately, we still have the requirement that the output of the `mir!` macro must resolve, typecheck, etc. Because of that, we can't just accept this in the THIR -> MIR parser because something like
```rust
{
let x = 0;
Goto(other)
}
other = {
RET = x;
Return()
}
```
will fail to resolve. Instead, the implementation does macro shenanigans to find the let declarations and extract them as part of the `mir!` macro. That *works*, but it is fairly complicated and degrades debuginfo by quite a bit. Specifically, the spans for any statements and declarations that are affected by this are completely wrong. My guess is that this is a net improvement though.
One way to recover some of the debuginfo would be to not support type annotations in the `let` statements, which would allow us to parse like `let $stmt:stmt`. That seems quite surprising though.
### Commit 2: Parse consts
Reuses most of the const parsing from regular Mir building for building custom mir
### Commit 3: Parse statics
Statics are slightly weird because the Mir primitive associated with them is a reference/pointer to them, so this is factored out separately.
### Commit 4: Fix some spans
A bunch of the spans were non-ideal, so we adjust them to be much more helpful.
r? `@oli-obk`
Pointer-integer casts are required for conversion between `EXINF` (ITRON
task entry point parameter) and `*const ThreadInner`. Addresses the
deny-level lint `fuzzy_provenance_casts`.
Extract WStrUnits to sys_common::wstr
This commit extracts WStrUnits from sys::windows::args to sys_common::wstr. This allows using the same structure for other targets which use wtf8 (example UEFI).
This was originally a part of https://github.com/rust-lang/rust/pull/100316
Signed-off-by: Ayush Singh <ayushsingh1325@gmail.com>
Add slice to the stack allocated string comment
Precise that the "stack allocated string" is not a string but a string slice.
``@rustbot`` label +A-docs
Since it's O(1) to convert between them now, might as well reuse the logic.
Mostly for the various specializations it does, but might also save some monomorphization work if, say, people collect slice iterators into both `Vec`s and `VecDeque`s.
This commit extracts WStrUnits from sys::windows::args to sys_common::wstr. This
allows using the same structure for other targets which use wtf8 (example UEFI).
This was originally a part of https://github.com/rust-lang/rust/pull/100316
Signed-off-by: Ayush Singh <ayushsingh1325@gmail.com>
Update VecDeque implementation to use head+len instead of head+tail
(See #99805)
This changes `alloc::collections::VecDeque`'s internal representation from using head and tail indices to using a head index and a length field. It has a few advantages over the current design:
* It allows the buffer to be of length 0, which means the `VecDeque::new` new longer has to allocate and could be changed to a `const fn`
* It allows the `VecDeque` to fill the buffer completely, unlike the old implementation, which always had to leave a free space
* It removes the restriction for the size to be a power of two, allowing it to properly `shrink_to_fit`, unlike the old `VecDeque`
* The above points also combine to allow the `Vec<T> -> VecDeque<T>` conversion to be very cheap and guaranteed O(1). I mention this in the `From<Vec<T>>` impl, but it's not a strong guarantee just yet, as that would likely need some form of API change proposal.
All the tests seem to pass for the new `VecDeque`, with some slight adjustments.
r? `@scottmcm`
Remove redundant `all` in cfg
This appears to have been accidentally left in after removing the other branches 45bf1ed1a1
(hat tip to kangalioo for the git archaeology)
Stop peeling the last iteration of the loop in `Vec::resize_with`
`resize_with` uses the `ExtendWith` code that peels the last iteration:
341d8b8a2c/library/alloc/src/vec/mod.rs (L2525-L2529)
But that's kinda weird for `ExtendFunc` because it does the same thing on the last iteration anyway:
341d8b8a2c/library/alloc/src/vec/mod.rs (L2494-L2502)
So this just has it use the normal `extend`-from-`TrustedLen` code instead.
r? `@ghost`
Manually implement PartialEq for Option<T> and specialize non-nullable types
This PR manually implements `PartialEq` and `StructuralPartialEq` for `Option`, which seems to produce slightly better codegen than the automatically derived implementation.
It also allows specializing on the `core::num::NonZero*` and `core::ptr::NonNull` types, taking advantage of the niche optimization by transmuting the `Option<T>` to `T` to be compared directly, which can be done in just two instructions.
A comparison of the original, new and specialized code generation is available [here](https://godbolt.org/z/dE4jxdYsa).
Revert "Forbid inlining `thread_local!`'s `__getit` function on Windows"
Revert of #101368, fixes#104852.
I'd rather not do this since that's a soundness fix and this is hitting some compiler bug, but I don't really know an alternative.
r? `@ChrisDenton`
Previously, async constructs would be lowered to "normal" generators,
with an additional `from_generator` / `GenFuture` shim in between to
convert from `Generator` to `Future`.
The compiler will now special-case these generators internally so that
async constructs will *directly* implement `Future` without the need
to go through the `from_generator` / `GenFuture` shim.
The primary motivation for this change was hiding this implementation
detail in stack traces and debuginfo, but it can in theory also help
the optimizer as there is less abstractions to see through.
Forbid inlining `thread_local!`'s `__getit` function on Windows
Sadly, this will make things slower to avoid UB in an edge case, but it seems hard to avoid... and really whenever I look at this code I can't help but think we're asking for trouble.
It's pretty dodgy for us to leave this as a normal function rather than `#[inline(never)]`, given that if it *does* get inlined into a dynamically linked component, it's extremely unsafe (you get some other thread local, or if you're lucky, crash). Given that it's pretty rare for people to use dylibs on Windows, the fact that we haven't gotten bug reports about it isn't really that convincing. Ideally we'd come up with some kind of compiler solution (that avoids paying for this cost when static linking, or *at least* for use within the same crate...), but it's not clear what that looks like.
Oh, and because all this is only needed when we're implementing `thread_local!` with `#[thread_local]`, this patch adjusts the `cfg_attr` to be `all(windows, target_thread_local)` as well.
r? ``@ChrisDenton``
See also #84933, which is about improving the situation.
disable strict-provenance-violating doctests in Miri
Most of these are on deprecated unstable functions anyway. This lets us run the remaining doctests with `-Zmiri-strict-provenance`, which I think is a win.
r? `@thomcc`
Constify remaining `Layout` methods
Makes the methods on `Layout` that aren't yet unstably const, under the same feature and issue, #67521. Most of them required no changes, only non-trivial change is probably constifying `ValidAlignment` which may affect #102072
Deprecate the unstable `ptr_to_from_bits` feature
I propose that we deprecate the (unstable!) `to_bits` and `from_bits` methods on raw pointers. (With the intent to ~~remove them once `addr` has been around long enough to make the transition easy on people -- maybe another 6 weeks~~ remove them fairly soon after, as the strict and expose versions have been around for a while already.)
The APIs that came from the strict provenance explorations (#95228) are a more holistic version of these, and things like `.expose_addr()` work for the "that cast looks sketchy" case even if the full strict provenance stuff never happens. (As a bonus, `addr` is even shorter than `to_bits`, though it is only applicable if people can use full strict provenance! `addr` is *not* a direct replacement for `to_bits`.) So I think it's fine to move away from the `{to|from}_bits` methods, and encourage the others instead.
That also resolves the worry that was brought up (I forget where) that `q.to_bits()` and `(*q).to_bits()` both work if `q` is a pointer-to-floating-point, as they also have a `to_bits` method.
Tracking issue #91126
Code search: https://github.com/search?l=Rust&p=1&q=ptr_to_from_bits&type=Code
For potential pushback, some users in case they want to chime in
- `@RSSchermer` 365bb68541/arwa/src/html/custom_element.rs (L105)
- `@strax` 99616d1dbf/openexr/src/core/alloc.rs (L36)
- `@MiSawa` 577c622358/crates/kernel/src/timer.rs (L50)
Add slice methods for indexing via an array of indices.
Disclaimer: It's been a while since I contributed to the main Rust repo, apologies in advance if this is large enough already that it should've been an RFC.
---
# Update:
- Based on feedback, removed the `&[T]` variant of this API, and removed the requirements for the indices to be sorted.
# Description
This adds the following slice methods to `core`:
```rust
impl<T> [T] {
pub unsafe fn get_many_unchecked_mut<const N: usize>(&mut self, indices: [usize; N]) -> [&mut T; N];
pub fn get_many_mut<const N: usize>(&mut self, indices: [usize; N]) -> Option<[&mut T; N]>;
}
```
This allows creating multiple mutable references to disjunct positions in a slice, which previously required writing some awkward code with `split_at_mut()` or `iter_mut()`. For the bound-checked variant, the indices are checked against each other and against the bounds of the slice, which requires `N * (N + 1) / 2` comparison operations.
This has a proof-of-concept standalone implementation here: https://crates.io/crates/index_many
Care has been taken that the implementation passes miri borrow checks, and generates straight-forward assembly (though this was only checked on x86_64).
# Example
```rust
let v = &mut [1, 2, 3, 4];
let [a, b] = v.get_many_mut([0, 2]).unwrap();
std::mem::swap(a, b);
*v += 100;
assert_eq!(v, &[3, 2, 101, 4]);
```
# Codegen Examples
<details>
<summary>Click to expand!</summary>
Disclaimer: Taken from local tests with the standalone implementation.
## Unchecked Indexing:
```rust
pub unsafe fn example_unchecked(slice: &mut [usize], indices: [usize; 3]) -> [&mut usize; 3] {
slice.get_many_unchecked_mut(indices)
}
```
```nasm
example_unchecked:
mov rcx, qword, ptr, [r9]
mov r8, qword, ptr, [r9, +, 8]
mov r9, qword, ptr, [r9, +, 16]
lea rcx, [rdx, +, 8*rcx]
lea r8, [rdx, +, 8*r8]
lea rdx, [rdx, +, 8*r9]
mov qword, ptr, [rax], rcx
mov qword, ptr, [rax, +, 8], r8
mov qword, ptr, [rax, +, 16], rdx
ret
```
## Checked Indexing (Option):
```rust
pub unsafe fn example_option(slice: &mut [usize], indices: [usize; 3]) -> Option<[&mut usize; 3]> {
slice.get_many_mut(indices)
}
```
```nasm
mov r10, qword, ptr, [r9, +, 8]
mov rcx, qword, ptr, [r9, +, 16]
cmp rcx, r10
je .LBB0_7
mov r9, qword, ptr, [r9]
cmp rcx, r9
je .LBB0_7
cmp rcx, r8
jae .LBB0_7
cmp r10, r9
je .LBB0_7
cmp r9, r8
jae .LBB0_7
cmp r10, r8
jae .LBB0_7
lea r8, [rdx, +, 8*r9]
lea r9, [rdx, +, 8*r10]
lea rcx, [rdx, +, 8*rcx]
mov qword, ptr, [rax], r8
mov qword, ptr, [rax, +, 8], r9
mov qword, ptr, [rax, +, 16], rcx
ret
.LBB0_7:
mov qword, ptr, [rax], 0
ret
```
## Checked Indexing (Panic):
```rust
pub fn example_panic(slice: &mut [usize], indices: [usize; 3]) -> [&mut usize; 3] {
let len = slice.len();
match slice.get_many_mut(indices) {
Some(s) => s,
None => {
let tmp = indices;
index_many::sorted_bound_check_failed(&tmp, len)
}
}
}
```
```nasm
example_panic:
sub rsp, 56
mov rax, qword, ptr, [r9]
mov r10, qword, ptr, [r9, +, 8]
mov r9, qword, ptr, [r9, +, 16]
cmp r9, r10
je .LBB0_6
cmp r9, rax
je .LBB0_6
cmp r9, r8
jae .LBB0_6
cmp r10, rax
je .LBB0_6
cmp rax, r8
jae .LBB0_6
cmp r10, r8
jae .LBB0_6
lea rax, [rdx, +, 8*rax]
lea r8, [rdx, +, 8*r10]
lea rdx, [rdx, +, 8*r9]
mov qword, ptr, [rcx], rax
mov qword, ptr, [rcx, +, 8], r8
mov qword, ptr, [rcx, +, 16], rdx
mov rax, rcx
add rsp, 56
ret
.LBB0_6:
mov qword, ptr, [rsp, +, 32], rax
mov qword, ptr, [rsp, +, 40], r10
mov qword, ptr, [rsp, +, 48], r9
lea rcx, [rsp, +, 32]
mov edx, 3
call index_many::bound_check_failed
ud2
```
</details>
# Extensions
There are multiple optional extensions to this.
## Indexing With Ranges
This could easily be expanded to allow indexing with `[I; N]` where `I: SliceIndex<Self>`. I wanted to keep the initial implementation simple, so I didn't include it yet.
## Panicking Variant
We could also add this method:
```rust
impl<T> [T] {
fn index_many_mut<const N: usize>(&mut self, indices: [usize; N]) -> [&mut T; N];
}
```
This would work similar to the regular index operator and panic with out-of-bound indices. The advantage would be that we could more easily ensure good codegen with a useful panic message, which is non-trivial with the `Option` variant.
This is implemented in the standalone implementation, and used as basis for the codegen examples here and there.
Pin::new_unchecked: discuss pinning closure captures
Regardless of how the discussion in https://github.com/rust-lang/rust/pull/102737 turns out, pinning closure captures is super subtle business and probably worth discussing separately.
Fix doc example for `wrapping_abs`
The `max` variable is unused. This change introduces the `min_plus` variable, to make the example similar to the one from `saturating_abs`. An alternative would be to remove the unused variable.
add examples to chunks remainder methods.
add examples to chunks remainder methods.
my motivation for adding the examples was to make it very clear that the state of the iterator (in terms of where its cursor lies) has no effect on what remainder returns.
Also fixed some links to rchunk remainder methods.
Clarify and restrict when `{Arc,Rc}::get_unchecked_mut` is allowed.
(Tracking issue for `{Arc,Rc}::get_unchecked_mut`: #63292)
(I'm using `Rc` in this comment, but it applies for `Arc` all the same).
As currently documented, `Rc::get_unchecked_mut` can lead to unsoundness when multiple `Rc`/`Weak` pointers to the same allocation exist. The current documentation only requires that other `Rc`/`Weak` pointers to the same allocation "must not be dereferenced for the duration of the returned borrow". This can lead to unsoundness in (at least) two ways: variance, and `Rc<str>`/`Rc<[u8]>` aliasing. ([playground link](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=d7e2d091c389f463d121630ab0a37320)).
This PR changes the documentation of `Rc::get_unchecked_mut` to restrict usage to when all `Rc<T>`/`Weak<T>` have the exact same `T` (including lifetimes). I believe this is sufficient to prevent unsoundness, while still allowing `get_unchecked_mut` to be called on an aliased `Rc` as long as the safety contract is upheld by the caller.
## Alternatives
* A less strict, but still sound alternative would be to say that the caller must only write values which are valid for all aliased `Rc`/`Weak` inner types. (This was [mentioned](https://github.com/rust-lang/rust/issues/63292#issuecomment-568284090) in the tracking issue). This may be too complicated to clearly express in the documentation.
* A more strict alternative would be to say that there must not be any aliased `Rc`/`Weak` pointers, i.e. it is required that get_mut would return `Some(_)`. (This was also mentioned in the tracking issue). There is at least one codebase that this would cause to become unsound ([here](be5a164d77/src/memtable.rs (L166)), where additional locking is used to ensure unique access to an aliased `Rc<T>`; I saw this because it was linked on the tracking issue).
