Move `std::io::Read` to `alloc::io` by bushrat011899 · Pull Request #158544 · rust-lang/rust

bushrat011899 · 2026-06-29T05:15:01Z

ACP: rust-lang/libs-team#755
Tracking issue: #154046
Split From: #156527
~~Blocked On: #158541~~

Description

Moves std::io::Read to alloc::io. This is mostly a direct cut and paste, but with a large diff due to how many implementations need to be moved into alloc. Blocked on #158541.

There is some new code written for some of the Read implementations to account for the no_global_oom_handling configuration, since Vec::extend_from_slice and String::push_str are unavailable. I've highlighted all of these such instances with review comments for clarity.

Notes

No AI tooling of any kind was used during the creation of this PR.
Please see Tracking Issue for alloc::io and core::io #154046 (comment) for a review order and broader context for this PR.

rustbot · 2026-06-29T05:15:06Z

r? @Mark-Simulacrum

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Owners of files modified in this PR: @ChrisDenton, libs
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bushrat011899 · 2026-06-29T05:15:11Z

@rustbot blocked

clarfonthey · 2026-07-14T00:16:05Z

I haven't fully reviewed this, but I'm going to mark this as blocked on figuring out the write regressions first. Since these all depend on each other, we probably want to figure out what to do there before continuing.

@rustbot blocked

JonathanBrouwer · 2026-07-14T13:53:31Z

@bors try @rust-timer queue

Move `std::io::Read` to `alloc::io`

rust-bors · 2026-07-14T16:05:01Z

☀️ Try build successful (CI)
Build commit: 234ef2c (234ef2c008a7112fbea2e9e8553bcb4c11f7e135)
Base parent: da80ed0 (da80ed0708a09dc096c184345d6eb42cbcd50a1e)

rust-timer · 2026-07-14T17:02:02Z

Finished benchmarking commit (234ef2c): comparison URL.

Overall result: ❌ regressions - no action needed

Benchmarking means the PR may be perf-sensitive. Consider adding rollup=never if this change is not fit for rolling up.

@rustbot label: -S-waiting-on-perf -perf-regression

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)	-	-	0
Regressions ❌ (secondary)	0.2%	[0.2%, 0.3%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 1.0%, secondary -4.8%)

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

	mean	range	count
Regressions ❌ (primary)	4.5%	[4.5%, 4.5%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.5%	[-2.5%, -2.5%]	1
Improvements ✅ (secondary)	-4.8%	[-7.4%, -2.1%]	2
All ❌✅ (primary)	1.0%	[-2.5%, 4.5%]	2

Cycles

Results (secondary -1.2%)

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)	2.9%	[2.5%, 3.4%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.3%	[-4.0%, -2.1%]	4
All ❌✅ (primary)	-	-	0

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 491.202s -> 490.122s (-0.22%)
Artifact size: 389.32 MiB -> 389.39 MiB (0.02%)

JonathanBrouwer · 2026-07-14T17:06:07Z

(The regressions are noise)

bushrat011899 · 2026-07-14T20:34:26Z

I'm surprised this had no real regressions. Pleasantly surprised, but still. I'll draft up a PR adding #[inline] to all the functions that were in std but are now accessed from core/alloc.

clarfonthey · 2026-07-15T00:59:36Z

Yeah, my best guess is that the regressions might be hiding in the code in alloc that depends on code in core, which is why the previous PR regressed and this one didn't.

clarfonthey · 2026-07-17T17:15:22Z

@rustbot review

Since the perf wasn't just a few inline attributes, we're going to just go ahead and we can figure it out later if necessary.

clarfonthey · 2026-07-17T17:16:05Z

@bors r+ rollup=iffy

Since this modifies a nontrivial amount of std::io code and might conflict with other I/O changes, just to keep in mind.

rust-bors · 2026-07-17T17:16:08Z

📌 Commit d1bdecc has been approved by clarfonthey

It is now in the queue for this repository.

…uwer Rollup of 5 pull requests Successful merges: - #158544 (Move `std::io::Read` to `alloc::io`) - #158668 (`DeeplyNormalize` and `normalize_with_depth_to` take `Unnormalized<T>` as input) - #157514 ([tiny] Use multipart suggestion for finding ident when literal was expected in attr) - #158748 (improve diagnostic suggestion when matching struct variants with tuple) - #159463 (triagebot: tweak wording for miri changes message) Failed merges: - #158916 (Emit all borrowck errors at the end of borrowck)

Rollup merge of #158544 - bushrat011899:core_io_read, r=clarfonthey Move `std::io::Read` to `alloc::io` ACP: rust-lang/libs-team#755 Tracking issue: #154046 Split From: #156527 ~~Blocked On: #158541 ## Description Moves `std::io::Read` to `alloc::io`. This is mostly a direct cut and paste, but with a large diff due to how many implementations need to be moved into `alloc`. Blocked on #158541. There is some new code written for some of the `Read` implementations to account for the `no_global_oom_handling` configuration, since `Vec::extend_from_slice` and `String::push_str` are unavailable. I've highlighted all of these such instances with review comments for clarity. --- ## Notes * No AI tooling of any kind was used during the creation of this PR. * Please see #154046 (comment) for a review order and broader context for this PR.

…ing, r=clarfonthey Move `std::io::read_to_string` to `alloc::io` ACP: rust-lang/libs-team#755 Tracking issue: rust-lang#154046 Split From: rust-lang#156527 ~~Blocked On: rust-lang#158544 ## Description Moves `std::io::read_to_string` to `alloc::io`. This is a trivial move. Blocked on rust-lang#158544. --- ## Notes * No AI tooling of any kind was used during the creation of this PR. * Please see rust-lang#154046 (comment) for a review order and broader context for this PR.

rustbot assigned Mark-Simulacrum Jun 29, 2026

rustbot added S-blocked Status: Blocked on something else such as an RFC or other implementation work. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 29, 2026

This was referenced Jun 29, 2026

Tracking Issue for alloc::io and core::io #154046

Open

Move std::io::read_to_string to alloc::io #158545

Open