Fix gap in const stability checks around intrinsics by RalfJung · Pull Request #162409 · rust-lang/rust

RalfJung · 2026-09-07T09:04:51Z

@N1ark managed to find a gap in our const stability checks around intrinsics. This PR fixes that gap.

Sadly the standard library already relies on the gap, so for now I added a rustc_allow_const_fn_unstable but that attribute usually needs some process to be approved.

Also fixes #150961 by properly supporting & testing rustc_do_not_const_check on intrinsics.

rustbot · 2026-09-07T09:04:54Z

⚠️ #[rustc_allow_const_fn_unstable] needs careful audit to avoid accidentally exposing unstable
implementation details on stable.

cc @rust-lang/wg-const-eval

Some changes occurred to constck

cc @fee1-dead

Some changes occurred to the CTFE machinery

cc @oli-obk, @lcnr

Some changes occurred to the intrinsics. Make sure the CTFE / Miri interpreter
gets adapted for the changes, if necessary.

cc @rust-lang/miri, @oli-obk, @lcnr

rustbot · 2026-09-07T09:04:57Z

r? @mati865

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N1ark · 2026-09-07T09:07:30Z

sorry about that 😓

RalfJung · 2026-09-07T09:21:36Z

sorry about that 😓

It was me who introduced this bug, you just found it. ;)

mati865 · 2026-09-07T10:32:02Z

@rustbot reroll

…lity-checked

RalfJung · 2026-09-14T13:20:51Z

r? @oli-obk

oli-obk

@bors r+

oh fun... so much nuance. I hope we'll reach the point where const stability is not really a common thing anymore soon

View changes since this review

rust-bors · 2026-09-14T14:00:18Z

📌 Commit fb46c1d has been approved by oli-obk

It is now in the queue for this repository.

rust-bors · 2026-09-14T16:29:12Z

⌛ Testing commit fb46c1d with merge 903b7fc...

Workflow: https://github.com/rust-lang/rust/actions/runs/34868907183

@N1ark

Fix gap in const stability checks around intrinsics @N1ark managed to find a gap in our const stability checks around intrinsics. This PR fixes that gap. Sadly the standard library already relies on the gap, so for now I added a `rustc_allow_const_fn_unstable` but that attribute usually needs some process to be approved. Also fixes #150961 by properly supporting & testing `rustc_do_not_const_check` on intrinsics.

JonathanBrouwer · 2026-09-14T17:23:59Z

@bors yield
Yielding to enclosing rollup

rust-bors · 2026-09-14T17:24:02Z

Auto build was cancelled. Cancelled workflows:

https://github.com/rust-lang/rust/actions/runs/34868907183

The next pull request likely to be tested is #162775.

…uwer Rollup of 3 pull requests Successful merges: - #162409 (Fix gap in const stability checks around intrinsics) - #162763 (Remove `Box::into_unique`) - #162766 (stop unleaking `&mut`s in std and the compiler)

@N1ark

Rollup merge of #162409 - RalfJung:intrinsic-const-stab, r=oli-obk Fix gap in const stability checks around intrinsics @N1ark managed to find a gap in our const stability checks around intrinsics. This PR fixes that gap. Sadly the standard library already relies on the gap, so for now I added a `rustc_allow_const_fn_unstable` but that attribute usually needs some process to be approved. Also fixes #150961 by properly supporting & testing `rustc_do_not_const_check` on intrinsics.

…uwer Rollup of 3 pull requests Successful merges: - rust-lang/rust#162409 (Fix gap in const stability checks around intrinsics) - rust-lang/rust#162763 (Remove `Box::into_unique`) - rust-lang/rust#162766 (stop unleaking `&mut`s in std and the compiler)

rust-timer · 2026-09-15T16:29:27Z

Note

This PR was benchmarked as part of triage of its containing rollup: triage URL.

Finished benchmarking commit (537ff44): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -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)	0.3%	[0.3%, 0.3%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

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

Cycles

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Binary size

Results (secondary -0.1%)

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)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.1%]	3
All ❌✅ (primary)	-	-	0

Bootstrap: missing data
Artifact size: 406.86 MiB -> 408.85 MiB (0.49%)

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Sep 7, 2026

rustbot assigned mati865 Sep 7, 2026

N1ark reviewed Sep 7, 2026

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Comment thread compiler/rustc_const_eval/src/check_consts/mod.rs Outdated

RalfJung force-pushed the intrinsic-const-stab branch from 2d64547 to bc0851a Compare September 7, 2026 09:17

RalfJung force-pushed the intrinsic-const-stab branch from bc0851a to b3a8050 Compare September 7, 2026 09:22

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RalfJung force-pushed the intrinsic-const-stab branch from 9d60be8 to 022d14a Compare September 7, 2026 10:15

RalfJung commented Sep 7, 2026

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Comment thread library/core/src/intrinsics/mod.rs Outdated

N1ark mentioned this pull request Sep 7, 2026

Make min/max and copysign intrinsics generic #162414

Open

RalfJung force-pushed the intrinsic-const-stab branch 2 times, most recently from 4896f11 to 64752fb Compare September 7, 2026 10:28

rustbot assigned fee1-dead and unassigned mati865 Sep 7, 2026

RalfJung force-pushed the intrinsic-const-stab branch 3 times, most recently from a6cc2c2 to 3bbe9af Compare September 8, 2026 07:42

RalfJung added 3 commits September 8, 2026 09:43

fallback body of indirectly-stable intrinsics needs to be const-stabi…

472fc3b

…lity-checked

avoid suggesting adding an attribute that's already there

4f967c1

de-constify FloatPrimitive fallback trait

fb46c1d

RalfJung force-pushed the intrinsic-const-stab branch from 3bbe9af to fb46c1d Compare September 8, 2026 07:43

rustbot assigned oli-obk and unassigned fee1-dead Sep 14, 2026

oli-obk approved these changes Sep 14, 2026

View reviewed changes

rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Sep 14, 2026

JonathanBrouwer mentioned this pull request Sep 14, 2026

Rollup of 3 pull requests #162775

Merged

rust-bors Bot merged commit 727e080 into rust-lang:main Sep 14, 2026
13 of 14 checks passed

rustbot added this to the 1.100.0 milestone Sep 14, 2026

RalfJung deleted the intrinsic-const-stab branch September 16, 2026 06:03

github-actions Bot mentioned this pull request Oct 2, 2026

Toolchain upgrade to nightly-2026-09-25 flux-rs/flux#1803

Merged

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rust-timer commented Sep 15, 2026

Overall result: ❌ regressions - no action needed

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