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Fix gap in const stability checks around intrinsics - #162409

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RalfJung:intrinsic-const-stab
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Fix gap in const stability checks around intrinsics#162409
RalfJung wants to merge 2 commits into
rust-lang:mainfrom
RalfJung:intrinsic-const-stab

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@RalfJung

@RalfJung RalfJung commented Sep 7, 2026

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@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.

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rustbot commented Sep 7, 2026

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⚠️ #[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 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
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r? @mati865

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@N1ark

N1ark commented Sep 7, 2026

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sorry about that 😓

N1ark
N1ark reviewed Sep 7, 2026
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Comment thread compiler/rustc_const_eval/src/check_consts/mod.rs Outdated
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RalfJung force-pushed the intrinsic-const-stab branch from 2d64547 to bc0851a Compare September 7, 2026 09:17
@RalfJung

RalfJung commented Sep 7, 2026

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sorry about that 😓

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

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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 b3a8050 to 9d60be8 Compare September 7, 2026 09:30
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RalfJung force-pushed the intrinsic-const-stab branch from 9d60be8 to 022d14a Compare September 7, 2026 10:15
RalfJung
RalfJung commented Sep 7, 2026
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Comment thread library/core/src/intrinsics/mod.rs Outdated
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[miri::intrinsic_fallback_is_spec]
#[rustc_allow_const_fn_unstable(const_ops, const_trait_impl, core_intrinsics)] // FIXME these got accidentally exposed

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The interpreter has an implementation for this, right? So we can just use do_not_const_check.

@N1ark N1ark mentioned this pull request Sep 7, 2026
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@RalfJung
RalfJung force-pushed the intrinsic-const-stab branch from 022d14a to 4896f11 Compare September 7, 2026 10:25
@RalfJung
RalfJung force-pushed the intrinsic-const-stab branch from 4896f11 to 64752fb Compare September 7, 2026 10:28
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