Stabilize feature `cstr_from_bytes_until_nul`
This PR seeks to stabilize `cstr_from_bytes_until_nul`.
Partially addresses #95027
This function has only been on nightly for about 10 months, but I think it is simple enough that there isn't harm discussing stabilization. It has also had at least a handful of mentions on both the user forum and the discord, so it seems like it's already in use or at least known.
This needs FCP still.
Comment on potential discussion points:
- eventual conversion of `CStr` to be a single thin pointer: this function will still be useful to provide a safe way to create a `CStr` after this change.
- should this return a length too, to address concerns about the `CStr` change? I don't see it as being particularly useful, and it seems less ergonomic (i.e. returning `Result<(&CStr, usize), FromBytesUntilNulError>`). I think users that also need this length without the additional `strlen` call are likely better off using a combination of other methods, but this is up for discussion
- `CString::from_vec_until_nul`: this is also useful, but it doesn't even have a nightly implementation merged yet. I propose feature gating that separately, as opposed to blocking this `CStr` implementation on that
Possible alternatives:
A user can use `from_bytes_with_nul` on a slice up to `my_slice[..my_slice.iter().find(|c| c == 0).unwrap()]`. However; that is significantly less ergonomic, and is a bit more work for the compiler to optimize compared the direct `memchr` call that this wraps.
## New stable API
```rs
// both in core::ffi
pub struct FromBytesUntilNulError(());
impl CStr {
pub const fn from_bytes_until_nul(
bytes: &[u8]
) -> Result<&CStr, FromBytesUntilNulError>
}
```
cc ```@ericseppanen``` original author, ```@Mark-Simulacrum``` original reviewer, ```@m-ou-se``` brought up some issues on the thin pointer CStr
```@rustbot``` modify labels: +T-libs-api +needs-fcp
Stop probing for statx unless necessary
As is the current toy program:
fn main() -> std::io::Result<()> {
use std::fs;
let metadata = fs::metadata("foo.txt")?;
assert!(!metadata.is_dir());
Ok(())
}
... observed under strace will issue:
[snip]
statx(0, NULL, AT_STATX_SYNC_AS_STAT, STATX_ALL, NULL) = -1 EFAULT (Bad address) statx(AT_FDCWD, "foo.txt", AT_STATX_SYNC_AS_STAT, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0644, stx_size=0, ...}) = 0
While statx is not necessarily always present, checking for it can be delayed to the first error condition. Said condition may very well never happen, in which case the check got avoided altogether.
Note this is still suboptimal as there still will be programs issuing it, but bulk of the problem is removed.
Tested by forbidding the syscall for the binary and observing it correctly falls back to newfstatat.
While here tidy up the commentary, in particular by denoting some problems with the current approach.
Harden the pre-tyctxt query system against accidental recomputation
While the current compiler has no issues where we `take` and then compute the query again, in https://github.com/rust-lang/rust/pull/105462 I accidentally introduced such a case.
I also took the opportunity to remove `peek_mut`, which is only ever used for `global_tcx` to then invoke `enter`. I added an `enter` method directly on the query.
The test relied on Error::last_os_error() coming from the stat call on
the passed file, but there is no guarantee this will be the case.
Instead extract errno from the error returned by the routine.
Patch de facto written by joboet.
Co-authored-by: joboet <jonasboettiger@icloud.com>
When this happens, we ignore the symbol from `compiler_builtins`
in favor of Miri's builtin support.
This allows Miri to target platforms like wasm32-unknown-unknown,
where functions like `memcmp` are provided by `compiler_builtins`.
Data race spans
Fixes https://github.com/rust-lang/miri/issues/2205
This adds output to data race errors very similar to the spans we emit for Stacked Borrows errors. For example, from our test suite:
```
help: The Atomic Load on thread `<unnamed>` is here
--> tests/fail/data_race/atomic_read_na_write_race1.rs:23:13
|
23 | ... (&*c.0).load(Ordering::SeqCst) //~ ERROR: Data race detected between Atomic Load on thread `<unnamed>` and Write o...
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: The Write on thread `<unnamed>` is here
--> tests/fail/data_race/atomic_read_na_write_race1.rs:19:13
|
19 | *(c.0 as *mut usize) = 32;
| ^^^^^^^^^^^^^^^^^^^^^^^^^```
```
Because of https://github.com/rust-lang/miri/pull/2647 this comes without a perf regression, according to our benchmarks.
