Move std::io::Error into core

[bushrat011899]

View all comments

ACP: rust-lang/libs-team#755
Tracking issue: #154046
Related: #155574
Related: #152918

Description

Moves std::io::Error into core, deferring Box-adjacent methods to incoherent implementations in alloc, and RawOsError methods to std. This requires some substantial changes to the internals of Error, but none of them are breaking changes or externally visible.

Notably, I've replaced usage of Box with a wrapper around a pointer and an appropriate drop function. This requires the addition of quite a few lines of unsafe, but is required to work around Box only being accessible from alloc. Additionally, an atomic pointer to a VTable is used for working with RawOsError in core, since we cannot know the required implementations without std.

As mention in this comment, there may be concern around having a static AtomicPtr in core for certain users. I've added a configuration option no_io_statics which (similar to no_sync/etc. in alloc) can be used to prevent their inclusion in core. When active, the fallback default implementation will always be used.

---

Notes

• This PR adopts the VTable technique from Move OS-dependent parts of std::io to alloc #152918
• This PR builds on my previous PR Move std::io::RawOsError to core::io #155574
• No AI tooling of any kind was used during the creation of this PR.

[programmerjake]

example of how to link from core's docs to std: https://doc.rust-lang.org/1.95.0/src/core/str/mod.rs.html#200

[bushrat011899]

example of how to link from core's docs to std: https://doc.rust-lang.org/1.95.0/src/core/str/mod.rs.html#200

That's a clever trick I never knew about! Looks like it's also required for linking to incoherent implementations even within the file that creates them too.

[programmerjake]

label -O-unix
See

maybe just leave it until you get the PR to work, that way there's less comment spam.

[Mark-Simulacrum]

@bors r+ rollup=never

[rust-bors]

📌 Commit 0a1de1d has been approved by Mark-Simulacrum

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.

[JonathanBrouwer]

@bors p=1
Scheduling

[rust-bors]

💔 Test for 281a1ae failed: CI. Failed job:

• auto - test-various (web logs, enhanced plaintext logs)

[bushrat011899]

Failure seems to be caused by the final WASM output of the wasm-panic-small make test being at least 2,281 bytes larger that previous (limit in the test is set to 40,000 bytes, but I'm unsure how lenient that limit was).

I'm pushing a commit which increases the limit to 45,000 bytes, as I'm unsure what could be done otherwise. The wasm-stringify-ints-small test has a limit of 50,000 bytes which does pass, so I suspect the 40,000 limit was just very close to being broken already, and this PR was the last straw.

[bushrat011899]

@rustbot ready

[jhpratt]

@bors r=Mark-Simulacrum

[rust-bors]

📌 Commit 3fa872c has been approved by Mark-Simulacrum

It is now in the queue for this repository.

[rust-bors]

☀️ Test successful - CI
Approved by: Mark-Simulacrum
Duration: 3h 7m 37s
Pushing 7fb284d to main...

[github-actions]

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing df6ee90 (parent) -> 7fb284d (this PR)

Test differences

Show 222 test diffs

222 doctest diffs were found. These are ignored, as they are noisy.

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 7fb284d9037fa54f6a9b24261c82b394472cbfd7 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

1. dist-x86_64-msvc-alt: 2h 4m -> 2h 42m (+30.2%)
2. dist-i586-gnu-i586-i686-musl: 1h 15m -> 1h 35m (+26.4%)
3. i686-msvc-1: 3h -> 2h 13m (-25.8%)
4. dist-powerpc64le-linux-gnu: 1h 34m -> 1h 17m (-17.7%)
5. dist-i686-mingw: 2h 31m -> 2h 8m (-15.0%)
6. dist-aarch64-msvc: 1h 39m -> 1h 50m (+11.1%)
7. dist-x86_64-apple: 1h 42m -> 1h 52m (+9.1%)
8. dist-x86_64-solaris: 1h 40m -> 1h 31m (-9.0%)
9. x86_64-msvc-ext1: 2h 3m -> 2h 13m (+8.3%)
10. aarch64-msvc-2: 1h 43m -> 1h 35m (-7.2%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

[rust-timer]

Finished benchmarking commit (7fb284d): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

Our benchmarks found a performance regression caused by this PR.
This might be an actual regression, but it can also be just noise.

Next Steps:

• If the regression was expected or you think it can be justified,
  please write a comment with sufficient written justification, and add
  @rustbot label: +perf-regression-triaged to it, to mark the regression as triaged.
• If you think that you know of a way to resolve the regression, try to create
  a new PR with a fix for the regression.
• If you do not understand the regression or you think that it is just noise,
  you can ask the @rust-lang/wg-compiler-performance working group for help (members of this group
  were already notified of this PR).

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	1.0%	[0.5%, 2.6%]	9
Regressions ❌ (secondary)	1.4%	[0.2%, 7.7%]	23
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.7%	[-6.0%, -3.2%]	6
All ❌✅ (primary)	1.0%	[0.5%, 2.6%]	9

Max RSS (memory usage)

Results (secondary -0.9%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.3%	[2.3%, 2.3%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.0%	[-2.4%, -1.7%]	3
All ❌✅ (primary)	-	-	0

Cycles

Results (primary 2.0%, secondary 0.4%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	2.0%	[2.0%, 2.0%]	1
Regressions ❌ (secondary)	5.2%	[2.4%, 6.9%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.4%	[-5.9%, -3.6%]	4
All ❌✅ (primary)	2.0%	[2.0%, 2.0%]	1

Binary size

Results (primary 0.8%, secondary 1.5%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.9%	[0.0%, 2.5%]	37
Regressions ❌ (secondary)	2.0%	[0.0%, 2.5%]	91
Improvements ✅ (primary)	-0.1%	[-0.3%, -0.1%]	5
Improvements ✅ (secondary)	-3.6%	[-7.2%, -0.9%]	8
All ❌✅ (primary)	0.8%	[-0.3%, 2.5%]	42

Bootstrap: 485.504s -> 486.093s (0.12%)
Artifact size: 393.08 MiB -> 393.66 MiB (0.15%)