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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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| .. | ||
| auxiliary | ||
| always-extern.rs | ||
| always-extern.stderr | ||
| always-gets-overridden.rs | ||
| bad-intrinsic-monomorphization.rs | ||
| bad-intrinsic-monomorphization.stderr | ||
| const-eval-select-backtrace-std.rs | ||
| const-eval-select-backtrace-std.run.stderr | ||
| const-eval-select-backtrace.rs | ||
| const-eval-select-backtrace.run.stderr | ||
| const-eval-select-bad.rs | ||
| const-eval-select-bad.stderr | ||
| const-eval-select-stability.rs | ||
| const-eval-select-stability.stderr | ||
| const-eval-select-x86_64.rs | ||
| const-eval-select.rs | ||
| feature-gate-safe-intrinsic.rs | ||
| feature-gate-safe-intrinsic.stderr | ||
| incorrect-read_via_copy-defn.rs | ||
| incorrect-read_via_copy-defn.stderr | ||
| incorrect-transmute.rs | ||
| incorrect-transmute.stderr | ||
| intrinsic-alignment.rs | ||
| intrinsic-assume.rs | ||
| intrinsic-atomics-cc.rs | ||
| intrinsic-atomics.rs | ||
| intrinsic-fmuladd.rs | ||
| intrinsic-nearby.rs | ||
| intrinsic-raw_eq-const-bad.rs | ||
| intrinsic-raw_eq-const-bad.stderr | ||
| intrinsic-raw_eq-const.rs | ||
| intrinsic-unreachable.rs | ||
| intrinsic-volatile.rs | ||
| intrinsics-integer.rs | ||
| intrinsics-math.rs | ||
| issue-28575.rs | ||
| issue-28575.stderr | ||
| issue-84297-reifying-copy.rs | ||
| non-integer-atomic.rs | ||
| non-integer-atomic.stderr | ||
| not-overridden.rs | ||
| not-overridden.stderr | ||
| panic-uninitialized-zeroed.rs | ||
| reify-intrinsic.rs | ||
| reify-intrinsic.stderr | ||
| safe-intrinsic-mismatch.effects.stderr | ||
| safe-intrinsic-mismatch.rs | ||
| safe-intrinsic-mismatch.stock.stderr | ||
| unchecked_math_unsafe.rs | ||
| unchecked_math_unsafe.stderr | ||
| unchecked_math_unstable.rs | ||
| unchecked_math_unstable.stderr | ||