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a0215d8e46
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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| .. | ||
| aarch64-neon-works.rs | ||
| asm-implied-features-issue-128125.rs | ||
| feature-hierarchy.rs | ||
| gate.rs | ||
| gate.stderr | ||
| implicit-features-cli.rs | ||
| implicit-features.rs | ||
| implied-features.rs | ||
| invalid-attribute.rs | ||
| invalid-attribute.stderr | ||
| missing-plusminus-2.rs | ||
| missing-plusminus-2.stderr | ||
| missing-plusminus.rs | ||
| missing-plusminus.stderr | ||
| no-llvm-leaks.rs | ||
| rust-specific-name-no-warnings.rs | ||
| similar-feature-suggestion.rs | ||
| similar-feature-suggestion.stderr | ||
| tied-features-cli.one.stderr | ||
| tied-features-cli.rs | ||
| tied-features-cli.three.stderr | ||
| tied-features-cli.two.stderr | ||
| tied-features-no-implication-1.paca.stderr | ||
| tied-features-no-implication-1.pacg.stderr | ||
| tied-features-no-implication-1.rs | ||
| tied-features-no-implication.paca.stderr | ||
| tied-features-no-implication.pacg.stderr | ||
| tied-features-no-implication.rs | ||
| tied-features.rs | ||
| tied-features.stderr | ||
| unstable-feature.rs | ||
| unstable-feature.stderr | ||
| wasm-relaxed-simd.rs | ||
| wasm-safe.rs | ||