Move IoSlice and IoSliceMut to core::io

[bushrat011899]

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ACP: rust-lang/libs-team#755
Tracking issue: #154046
Related: #152918
Related: #155625

Description

Moves std::io::IoSlice and std::io::IoSliceMut into core::io. This is required for the Read and Write traits to be moved into alloc and/or core, as they contain stable methods which work with IO slices. Similar to #155574, this PR inlines the std::sys types required to create an ABI compatible type for the platforms where such compatibility is guaranteed.

Additionally, I've moved the relevant tests out of std::io::tests into coretests::io::io_slice.

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Notes

• This PR overlaps with Move OS-dependent parts of std::io to alloc #152918, but goes further than moving the IO slice types to alloc and instead moves them straight to core. Since these types have no interaction with allocation, and doing so will allow Write to move to core::io, I consider this a better home for these types.
• Some discussion around the decision to not use a core::sys module can be found here.
• I've renamed unsupported to generic to better reflect that IoSlice(Mut) is supported by all platforms, it just doesn't have a special ABI-compatible type. I don't want to imply that parts of core "don't work" depending on the target; IoSlice(Mut) works exactly as expected on all targets.
• I've made pub items within each platform-specific representation pub(super) to highlight that everything within core::io::io_slice is an internal implementation detail not meant for any other part of the crate to be aware of.
• No AI tooling of any kind was used during the creation of this PR.

[rustbot]

r? @jhpratt

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The reviewer was selected based on:

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[lygstate]

a long awating staff, thanks.

[bushrat011899]

I've split this PR into 3 commits to better highlight how little actually changes in order to facilitate this move. For reviewers, I recommend going through each commit individually.

[jhpratt]

As a heads up, I am currently exploring Europe and won't be home for a couple more weeks. If you'd like a review before then, feel free to reroll.

[bushrat011899]

As a heads up, I am currently exploring Europe and won't be home for a couple more weeks. If you'd like a review before then, feel free to reroll.

Thanks for the heads up, hope you have a great time!

r? libs

[nia-e]

I will probably also take a day or two before I can get to this, but given the stuff it's touching it's likely worth a perf run:

@bors try @rust-timer queue

[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.

[bushrat011899]

Failure caused by functions previously available internally to std through the io_slice_as_bytes feature now being inaccessible since they're now defined in core. Enabled the feature in std, and there are no other unstable features that may cause a similar issue.

@rustbot ready

[nia-e]

@bors r+ rollup=never

[rust-bors]

📌 Commit 1b9cd39 has been approved by nia-e

It is now in the queue for this repository.

🌲 The tree is currently closed for pull requests below priority 1. This pull request will be tested once the tree is reopened.

[rust-bors]

💔 Test for 27478a4 failed: CI. Failed job:

• auto - dist-x86_64-apple (web logs, enhanced plaintext logs)

[nia-e]

Let's do a try build after this is fixed.

@rustbot author

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[programmerjake]

Let's do a try build after this is fixed.

GitHub is being broken again, I can't see the logs where it failed since GitHub refuses to show the full logs and the show raw logs link 404s, they're stuck in the LLVM build portion (which is a GitHub problem, not a building-LLVM problem).

So, maybe we should do a try build now in hopes of actually getting some logs with which to deduce the problem.

[nia-e]

@bors try jobs=dist-x86_64-apple

[rust-bors]

☀️ Try build successful (CI)
Build commit: cc23296 (cc23296b0fd1d5a951df2b72a3c201a89d6d3b98, parent: b5d1746e7d25465729706ac5a0004b035e219d01)