rust/tests/ui/consts/auxiliary/unstable_intrinsic.rs

#![feature(staged_api, rustc_attrs, intrinsics)]
#![stable(since="1.0.0", feature = "stable")]

#[unstable(feature = "unstable", issue = "42")]
#[rustc_intrinsic]
#[rustc_intrinsic_must_be_overridden]
pub const unsafe fn size_of_val<T>(x: *const T) -> usize { 42 }

#[unstable(feature = "unstable", issue = "42")]
#[rustc_const_unstable(feature = "unstable", issue = "42")]
#[rustc_intrinsic]
#[rustc_intrinsic_must_be_overridden]
pub const unsafe fn min_align_of_val<T>(x: *const T) -> usize { 42 }
Re-do recursive const stability checks Fundamentally, we have three disjoint categories of functions: 1. const-stable functions 2. private/unstable functions that are meant to be callable from const-stable functions 3. functions that can make use of unstable const features This PR implements the following system: - `#[rustc_const_stable]` puts functions in the first category. It may only be applied to `#[stable]` functions. - `#[rustc_const_unstable]` by default puts functions in the third category. The new attribute `#[rustc_const_stable_indirect]` can be added to such a function to move it into the second category. - `const fn` without a const stability marker are in the second category if they are still unstable. They automatically inherit the feature gate for regular calls, it can now also be used for const-calls. Also, several holes in recursive const stability checking are being closed. There's still one potential hole that is hard to avoid, which is when MIR building automatically inserts calls to a particular function in stable functions -- which happens in the panic machinery. Those need to not be `rustc_const_unstable` (or manually get a `rustc_const_stable_indirect`) to be sure they follow recursive const stability. But that's a fairly rare and special case so IMO it's fine. The net effect of this is that a `#[unstable]` or unmarked function can be constified simply by marking it as `const fn`, and it will then be const-callable from stable `const fn` and subject to recursive const stability requirements. If it is publicly reachable (which implies it cannot be unmarked), it will be const-unstable under the same feature gate. Only if the function ever becomes `#[stable]` does it need a `#[rustc_const_unstable]` or `#[rustc_const_stable]` marker to decide if this should also imply const-stability. Adding `#[rustc_const_unstable]` is only needed for (a) functions that need to use unstable const lang features (including intrinsics), or (b) `#[stable]` functions that are not yet intended to be const-stable. Adding `#[rustc_const_stable]` is only needed for functions that are actually meant to be directly callable from stable const code. `#[rustc_const_stable_indirect]` is used to mark intrinsics as const-callable and for `#[rustc_const_unstable]` functions that are actually called from other, exposed-on-stable `const fn`. No other attributes are required. 2024-10-06 12:59:19 -05:00			`#![feature(staged_api, rustc_attrs, intrinsics)]`
			`#![stable(since="1.0.0", feature = "stable")]`

remove support for extern-block const intrinsics 2024-11-01 16:19:42 -05:00			`#[unstable(feature = "unstable", issue = "42")]`
			`#[rustc_intrinsic]`
when an intrinsic has a const-stable fallback body, we can easily expose it on stable 2024-11-02 02:49:49 -05:00			`#[rustc_intrinsic_must_be_overridden]`
remove support for extern-block const intrinsics 2024-11-01 16:19:42 -05:00			`pub const unsafe fn size_of_val<T>(x: *const T) -> usize { 42 }`

			`#[unstable(feature = "unstable", issue = "42")]`
			`#[rustc_const_unstable(feature = "unstable", issue = "42")]`
			`#[rustc_intrinsic]`
when an intrinsic has a const-stable fallback body, we can easily expose it on stable 2024-11-02 02:49:49 -05:00			`#[rustc_intrinsic_must_be_overridden]`
remove support for extern-block const intrinsics 2024-11-01 16:19:42 -05:00			`pub const unsafe fn min_align_of_val<T>(x: *const T) -> usize { 42 }`