[malezjaa]

Closes #135758

Public API:

impl u8/.../u128/usize/i8/.../i128/isize/bool {
    pub const unsafe fn unchecked_disjoint_bitor(self, other: Self) -> Self;
}

Implementation prs: #135760, #147368

Could we get a FCP started for this ^^?

r? @clarfonthey (since you've expressed interest in stabilization)

[rustbot]

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

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

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

cc @rust-lang/wg-const-eval

⚠️ #[rustc_intrinsic_const_stable_indirect] controls whether intrinsics can be exposed to stable const
code; adding it needs t-lang approval.

cc @rust-lang/wg-const-eval

[tgross35]

#147368 only merged a few days ago, those are trivial but we should still allow them to soak for at least a release cycle.

[RalfJung]

This is not great, it means we are not checking that the fallback impl actually only needs stable const stuff. Can we do without core_intrinsics_fallbacks?

Suggested change

	#[rustc_allow_const_fn_unstable(const_trait_impl, core_intrinsics_fallbacks)]
	#[rustc_allow_const_fn_unstable(const_trait_impl)]

View changes since the review

[RalfJung]

Okay currently this does not work.

I am not comfortable stabilizing more intrinsics with trait-based fallback impls when we cannot actually do const stability checks in those fallback impls. So this is blocked on supporting #[rustc_const_stable_indirect] on traits.

[clarfonthey]

cc discussion on funnel shifts: #161015 (comment)

[RalfJung]

To avoid blocking on const stability checking improvements, I'd suggest to make this PR only stabilize unchecked_disjoint_bitor for non-const callers.