Enable statx on all Linux targets and short-circuit it for musl

[Gelbpunkt]

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This supersedes #154981. cc @strophy and sorry for taking a while to get around to this.

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The first patch is the original PR with the commit message slightly adjusted, which makes use of the statx runtime detection on all Linux targets.

Since we want to unconditionally use statx on musl targets (because we know statx is available on our supported musl versions), we can call it through libc::statx. Making use of that requires telling the libc crate that we are on a musl version recent enough for it, which I decided to do in bootstrap. If there's a better place to set the environment variable, let me know, but this is the most straightforward way I could come up with.

With that in place, we can then wire up a short circuit to libc::statx for musl targets and skip the detection logic that all other Linux targets use.

On my aarch64-unknown-linux-musl machine, ./x.py test library/std still passes with these changes.

r? @tgross35 since I presume you have opinions on how I'm holding libc here

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[tgross35]

@rustbot author

I think the thing to do here is un-gate statx in libc and avoid the complications here; if most users are using the bundled musl then there aren't any concerns there.

It would be good to set the libc_unstable_musl_v1_2_3 cfg but that should be a try build in r-l/r first then, once that works, update libc to set it if rustc-dep-of-std is enabled.

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[Darksonn]

libc PR: rust-lang/libc#5447

[strophy]

We're seeing multiple build failures in Alpine Linux due to a recent libc release breaking rustix: https://gitlab.alpinelinux.org/alpine/aports/-/work_items/18444

bytecodealliance/rustix#1675

I think some coordination is required between rustix, libc and rust, but it's opaque to me which order the dominoes need to fall for everything to work again.

[tgross35]

Is Alpine using unreleased libc? I'm not sure where an error would be coming from otherwise. I'm loosely holding off the libc release on that rustix issue but can't do so indefinitely, bytecodealliance/rustix#1496 has been around for a year...

Anyway that doesn't seem related to rust using statx, which is the PR here.

[xtqqczze]

bytecodealliance/rustix#1496 has been around for a year...

I think that issue might be fixed in rustix v1.1.5.

[tgross35]

There is now a new libc release out, which has statx on all musl targets. I don't have time to do the bump but if somebody wants to then do it in a separate PR and check the Apple iOS/watchOS/visionOS targets since there were some notable changes there.

[Gelbpunkt]

I'll try to get around to opening a PR for updating libc to 0.2.190 to move this forward on the weekend

[tgross35]

std now has a libc that has statx for all musl arches

[asder8215]

Just popping in here to say I appreciate you all for pushing statx on all musl arches. Was waiting for that change to be made to get #156269 across the line.

I'll update my PR to reflect that Metadata::from_statx is supported on Linux platforms (instead of it previously being supported on Linux platforms with a target env of gnu), but I'll likely wait for this PR to be merged since it changes cfg_has_statx to match on Linux unconditionally.

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.