Rollup of 6 pull requests
Successful merges:
- #130289 (docs: Permissions.readonly() also ignores root user special permissions)
- #134583 (docs: `transmute<&mut T, &mut MaybeUninit<T>>` is unsound when exposed to safe code)
- #134611 (Align `{i686,x86_64}-win7-windows-msvc` to their parent targets)
- #134629 (compiletest: Allow using a specific debugger when running debuginfo tests)
- #134642 (Implement `PointerLike` for `isize`, `NonNull`, `Cell`, `UnsafeCell`, and `SyncUnsafeCell`.)
- #134660 (Fix spacing of markdown code block fences in compiler rustdoc)
r? `@ghost`
`@rustbot` modify labels: rollup
Implement `PointerLike` for `isize`, `NonNull`, `Cell`, `UnsafeCell`, and `SyncUnsafeCell`.
* Implementing `PointerLike` for `UnsafeCell` enables the possibility of interior mutable `dyn*` values. Since this means potentially exercising new codegen behavior, I added a test for it in `tests/ui/dyn-star/cell.rs`. Please let me know if there are further sorts of tests that should be written, or other care that should be taken with this change.
It is unfortunately not possible without compiler changes to implement `PointerLike` for `Atomic*` types, since they are not `repr(transparent)` (and, in theory if not in practice, `AtomicUsize`'s alignment may be greater than that of an ordinary pointer or `usize`).
* Implementing `PointerLike` for `NonNull` is useful for pointer types which wrap `NonNull`.
* Implementing `PointerLike` for `isize` is just for completeness; I have no use cases in mind, but I cannot think of any reason not to do this.
* Tracking issue: #102425
`@rustbot` label +F-dyn_star
(there is no label or tracking issue for F-pointer_like_trait)
docs: `transmute<&mut T, &mut MaybeUninit<T>>` is unsound when exposed to safe code
Closes#66699
On my system (Edit: And also in the [playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=90529e2a9900599cb759e4bfaa5b5efe)) the example program terminates with an unpredictable exit code:
```console
$ cargo +nightly build && target/debug/bin ; echo $?
255
$ cargo +nightly build && target/debug/bin ; echo $?
253
```
And miri considers the code to have undefined behavior:
```console
$ cargo +nightly miri run
error: Undefined Behavior: using uninitialized data, but this operation requires initialized memory
--> src/main.rs:12:24
|
12 | std::process::exit(*code); // UB! Accessing uninitialized memory
| ^^^^^ using uninitialized data, but this operation requires initialized memory
|
error: aborting due to 1 previous error
```
docs: Permissions.readonly() also ignores root user special permissions
The root user can write to files without any (write) permission bits set. But this is not taken into account by `std::fs::Permissions.readonly()`.
The rustdoc for `readonly()` also mentions shortcomings later:
> On Unix-based platforms this checks if any of the owner, group or others write permission bits are set. It does not check if the current user is in the file’s assigned group. It also does not check ACLs.
But since this part already clarifies how it works -- it checks write permission bits -- I think it's not necessary to repeat the root user shortcomings here.
Implementing `PointerLike` for `UnsafeCell` enables the possibility of
interior mutable `dyn*` values. Since this means potentially exercising
new codegen behavior, I added a test for it in `tests/ui/dyn-star/cell.rs`.
Also updated UI tests to account for the `isize` implementation changing
error messages.
Delete `Rvalue::Len` 🎉
Everything's moved to `PtrMetadata`, so we can get rid of the `Len` variant now.
~~Depends on #134326, so draft until that lands~~ Ready!
r? mir
Asserts the maximum value that can be returned from `Vec::len`
Currently, casting `Vec<i32>` to `Vec<u32>` takes O(1) time:
```rust
// See <https://godbolt.org/z/hxq3hnYKG> for assembly output.
pub fn cast(vec: Vec<i32>) -> Vec<u32> {
vec.into_iter().map(|e| e as _).collect()
}
```
But the generated assembly is not the same as the identity function, which prevents us from casting `Vec<Vec<i32>>` to `Vec<Vec<u32>>` within O(1) time:
```rust
// See <https://godbolt.org/z/7n48bxd9f> for assembly output.
pub fn cast(vec: Vec<Vec<i32>>) -> Vec<Vec<u32>> {
vec.into_iter()
.map(|e| e.into_iter().map(|e| e as _).collect())
.collect()
}
```
This change tries to fix the problem. You can see the comparison here: <https://godbolt.org/z/jdManrKvx>.
In the playground the example program terminates with an unpredictable exit
code. The undefined behavior is also detected by miri:
error: Undefined Behavior: using uninitialized data
Document `PointerLike` implementation restrictions.
Since <https://github.com/rust-lang/rust/pull/133226>, it is no longer automatically implemented, but must be manually implemented, with special restrictions. The documentation now (roughly) explains those special restrictions.
cc `@compiler-errors` (author of the previous PR)
Rollup of 6 pull requests
Successful merges:
- #134364 (Use E0665 for missing `#[default]` on enum and update doc)
- #134601 (Support pretty-printing `dyn*` trait objects)
- #134603 (Explain why a type is not eligible for `impl PointerLike`.)
- #134618 (coroutine_clone: add comments)
- #134630 (Use `&raw` for `ptr` primitive docs)
- #134637 (Flatten effects directory now that it doesn't really test anything specific)
r? `@ghost`
`@rustbot` modify labels: rollup
This behavior is worth documenting because there are other plausible
alternatives, such as panicking when a duplicate is encountered, and
it reminds the programmer to consider whether they should, for example,
coalesce duplicate keys first.
Optimize `is_ascii` for `str` and `[u8]` further
Replace the existing optimized function with one that enables auto-vectorization.
This is especially beneficial on x86-64 as `pmovmskb` can be emitted with careful structuring of the code. The instruction can detect non-ASCII characters one vector register width at a time instead of the current `usize` at a time check.
The resulting implementation is completely safe.
`case00_libcore` is the current implementation, `case04_while_loop` is this PR.
```
benchmarks:
ascii::is_ascii_slice::long::case00_libcore 22.25/iter +/- 1.09
ascii::is_ascii_slice::long::case04_while_loop 6.78/iter +/- 0.92
ascii::is_ascii_slice::medium::case00_libcore 2.81/iter +/- 0.39
ascii::is_ascii_slice::medium::case04_while_loop 1.56/iter +/- 0.78
ascii::is_ascii_slice::short::case00_libcore 5.55/iter +/- 0.85
ascii::is_ascii_slice::short::case04_while_loop 3.75/iter +/- 0.22
ascii::is_ascii_slice::unaligned_both_long::case00_libcore 26.59/iter +/- 0.66
ascii::is_ascii_slice::unaligned_both_long::case04_while_loop 5.78/iter +/- 0.16
ascii::is_ascii_slice::unaligned_both_medium::case00_libcore 2.97/iter +/- 0.32
ascii::is_ascii_slice::unaligned_both_medium::case04_while_loop 2.41/iter +/- 0.10
ascii::is_ascii_slice::unaligned_head_long::case00_libcore 23.71/iter +/- 0.79
ascii::is_ascii_slice::unaligned_head_long::case04_while_loop 7.83/iter +/- 1.31
ascii::is_ascii_slice::unaligned_head_medium::case00_libcore 3.69/iter +/- 0.54
ascii::is_ascii_slice::unaligned_head_medium::case04_while_loop 7.05/iter +/- 0.32
ascii::is_ascii_slice::unaligned_tail_long::case00_libcore 24.44/iter +/- 1.41
ascii::is_ascii_slice::unaligned_tail_long::case04_while_loop 5.12/iter +/- 0.18
ascii::is_ascii_slice::unaligned_tail_medium::case00_libcore 3.24/iter +/- 0.40
ascii::is_ascii_slice::unaligned_tail_medium::case04_while_loop 2.86/iter +/- 0.14
```
`unaligned_head_medium` is the main regression in the benchmarks. It is a 32 byte string being sliced `bytes[1..]`.
The first commit can be used to run the benchmarks against the current core implementation.
Previous implementation was done in #74066
---
Two potential drawbacks of this implementation are that it increases instruction count and may regress other platforms/architectures. The benches here may also be too artificial to glean much insight from.
https://rust.godbolt.org/z/G9znGfY36
Correctly document CTFE behavior of is_null and methods that call is_null.
The "panic in const if CTFE doesn't know the answer" behavior was discussed to be the desired behavior in #74939, and is currently how the function actually behaves.
I intentionally wrote this documentation to allow for the possibility that a panic might not occur even if the pointer is out of bounds, because of #133700 and other potential changes in the future.
This is beta-nominated since `const fn is_null` stabilization is in beta already but the docs there are wrong, and it seems better to have the docs be correct at the time of stabilization.
Win: Use POSIX rename semantics for `std::fs::rename` if available
Windows 10 1601 introduced `FileRenameInfoEx` as well as `FILE_RENAME_FLAG_POSIX_SEMANTICS`, allowing for atomic renaming and renaming if the target file is has already been opened with `FILE_SHARE_DELETE`, in which case the file gets renamed on disk while the open file handle still refers to the old file, just like in POSIX. This resolves#123985, where atomic renaming proved difficult to impossible due to race conditions.
If `FileRenameInfoEx` isn't available due to missing support from the underlying filesystem or missing OS support, the renaming is retried with `FileRenameInfo`, which matches the behavior of `MoveFileEx`.
This PR also manually replicates parts of `MoveFileEx`'s internal logic, as reverse-engineered from the disassembly: If the source file is a reparse point and said reparse point is a mount point, the mount point itself gets renamed; otherwise the reparse point is resolved and the result renamed.
Notes:
- Currently, the `win7` target doesn't bother with `FileRenameInfoEx` at all; it's probably desirable to remove that special casing and try `FileRenameInfoEx` anyway if it doesn't exist, in case the binary is run on newer OS versions.
Fixes#123985
The "panic in const if CTFE doesn't know the answer" behavior was discussed to be the desired behavior in #74939, and is currently how the function actually behaves.
I intentionally wrote this documentation to allow for the possibility that a panic might not occur even if the pointer is out of bounds, because of #133700 and other potential changes in the future.
Less unwrap() in documentation
I think the common use of `.unwrap()` in examples makes it overrepresented, looking like a more typical way of error handling than it really is in real programs.
Therefore, this PR changes a bunch of examples to use different error handling methods, primarily the `?` operator. Additionally, `unwrap()` docs warn that it might abort the program.
Improve prose around into_slice example of IterMut
Having a part without modification and one with seems redundant, since `into_slice` is only called for the part without. I have brought the modification into the remaining part, although it perhaps does not add much (or only distracts?).
Abstract `ProcThreadAttributeList` into its own struct
As extensively discussed in issue #114854, the current implementation of the unstable `windows_process_extensions_raw_attribute` features lacks support for passing a raw pointer.
This PR wants to explore the opportunity to abstract away the `ProcThreadAttributeList` into its own struct to for one improve safety and usability and secondly make it possible to maybe also use it to spawn new threads.
try-job: x86_64-mingw
unimplement `PointerLike` for trait objects
Values of type `dyn* PointerLike` or `dyn PointerLike` are not pointer-like so these types should not implement `PointerLike`.
After https://github.com/rust-lang/rust/pull/133226, `PointerLike` allows user implementations, so we can't just mark it with `#[rustc_deny_explicit_impl(implement_via_object = false)]`. Instead, this PR splits the `#[rustc_deny_explicit_impl(implement_via_object = ...)]` attribute into two separate attributes `#[rustc_deny_explicit_impl]` and `#[rustc_do_not_implement_via_object]` so that we opt out of the automatic `impl PointerLike for dyn PointerLike` and still allow user implementations.
For traits that are marked with `#[do_not_implement_via_object]` but not `#[rustc_deny_explicit_impl]` I've also made it possible to add a manual `impl Trait for dyn Trait`. There is no immediate need for this, but it was one line to implement and seems nice to have.
fixes https://github.com/rust-lang/rust/issues/134545
fixes https://github.com/rust-lang/rust/issues/134543
r? `@compiler-errors`
remove reference to dangling from slice::Iter
This aligns the comment with reality and with IterMut. Also dangling does not seem to take any arguments.
This commit splits the `#[rustc_deny_explicit_impl(implement_via_object = ...)]` attribute
into two attributes `#[rustc_deny_explicit_impl]` and `#[rustc_do_not_implement_via_object]`.
This allows us to have special traits that can have user-defined impls but do not have the
automatic trait impl for trait objects (`impl Trait for dyn Trait`).
