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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. |
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| .. | ||
| auxiliary | ||
| accidental-stable-in-unstable.rs | ||
| accidental-stable-in-unstable.stderr | ||
| allow-unstable-reexport.rs | ||
| allow-unstable-reexport.stderr | ||
| allowed-through-unstable.rs | ||
| allowed-through-unstable.stderr | ||
| const-stability-attribute-implies-missing.rs | ||
| const-stability-attribute-implies-missing.stderr | ||
| const-stability-attribute-implies-no-feature.rs | ||
| const-stability-attribute-implies-no-feature.stderr | ||
| const-stability-attribute-implies-using-stable.rs | ||
| const-stability-attribute-implies-using-stable.stderr | ||
| const-stability-attribute-implies-using-unstable.rs | ||
| const-stability-attribute-implies-using-unstable.stderr | ||
| ctor-stability.rs | ||
| default-body-stability-err.rs | ||
| default-body-stability-err.stderr | ||
| default-body-stability-ok-enables.rs | ||
| default-body-stability-ok-impls.rs | ||
| generics-default-stability-trait.rs | ||
| generics-default-stability-trait.stderr | ||
| generics-default-stability-where.rs | ||
| generics-default-stability-where.stderr | ||
| generics-default-stability.rs | ||
| generics-default-stability.stderr | ||
| issue-28075.rs | ||
| issue-28075.stderr | ||
| issue-28388-3.rs | ||
| issue-28388-3.stderr | ||
| issue-99286-stable-intrinsics.rs | ||
| issue-106589.rs | ||
| issue-106589.stderr | ||
| issue-109177.rs | ||
| issue-109177.stderr | ||
| missing-const-stability.rs | ||
| missing-const-stability.stderr | ||
| missing-stability-attr-at-top-level.rs | ||
| missing-stability-attr-at-top-level.stderr | ||
| stability-attribute-implies-missing.rs | ||
| stability-attribute-implies-missing.stderr | ||
| stability-attribute-implies-no-feature.rs | ||
| stability-attribute-implies-no-feature.stderr | ||
| stability-attribute-implies-using-stable.rs | ||
| stability-attribute-implies-using-stable.stderr | ||
| stability-attribute-implies-using-unstable.rs | ||
| stability-attribute-implies-using-unstable.stderr | ||
| stability-attribute-issue-43027.rs | ||
| stability-attribute-issue.rs | ||
| stability-attribute-issue.stderr | ||
| stability-attribute-non-staged-force-unstable.rs | ||
| stability-attribute-non-staged-force-unstable.stderr | ||
| stability-attribute-non-staged.rs | ||
| stability-attribute-non-staged.stderr | ||
| stability-attribute-sanity-2.rs | ||
| stability-attribute-sanity-2.stderr | ||
| stability-attribute-sanity-3.rs | ||
| stability-attribute-sanity-3.stderr | ||
| stability-attribute-sanity-4.rs | ||
| stability-attribute-sanity-4.stderr | ||
| stability-attribute-sanity.rs | ||
| stability-attribute-sanity.stderr | ||
| stability-attribute-trait-impl.rs | ||
| stability-attribute-trait-impl.stderr | ||
| stability-in-private-module.rs | ||
| stability-in-private-module.stderr | ||
| stable-in-unstable.rs | ||
| stable-in-unstable.stderr | ||
| suggest-vec-allocator-api.rs | ||
| suggest-vec-allocator-api.stderr | ||
| unresolved_stability_lint.rs | ||
| unresolved_stability_lint.stderr | ||