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.
76 lines
2.6 KiB
Rust
76 lines
2.6 KiB
Rust
//! Ensure that unstable intrinsics can actually not be called,
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//! neither within a crate nor cross-crate.
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//@ aux-build:unstable_intrinsic.rs
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#![feature(staged_api, rustc_attrs, intrinsics)]
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#![stable(since="1.0.0", feature = "stable")]
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#![feature(local)]
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extern crate unstable_intrinsic;
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fn main() {
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const_main();
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}
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const fn const_main() {
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let x = 42;
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unsafe {
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unstable_intrinsic::old_way::size_of_val(&x);
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//~^ERROR: unstable library feature 'unstable'
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//~|ERROR: cannot call non-const intrinsic
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unstable_intrinsic::old_way::min_align_of_val(&x);
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//~^ERROR: unstable library feature 'unstable'
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//~|ERROR: not yet stable as a const intrinsic
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unstable_intrinsic::new_way::size_of_val(&x);
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//~^ERROR: unstable library feature 'unstable'
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//~|ERROR: cannot be (indirectly) exposed to stable
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unstable_intrinsic::new_way::min_align_of_val(&x);
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//~^ERROR: unstable library feature 'unstable'
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//~|ERROR: not yet stable as a const intrinsic
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old_way::size_of_val(&x);
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//~^ERROR: cannot call non-const intrinsic
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old_way::min_align_of_val(&x);
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//~^ERROR: cannot use `#[feature(local)]`
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new_way::size_of_val(&x);
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//~^ERROR: cannot be (indirectly) exposed to stable
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new_way::min_align_of_val(&x);
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//~^ERROR: cannot use `#[feature(local)]`
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}
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}
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#[stable(since="1.0.0", feature = "stable")]
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pub mod old_way {
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extern "rust-intrinsic" {
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#[unstable(feature = "local", issue = "42")]
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pub fn size_of_val<T>(x: *const T) -> usize;
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#[unstable(feature = "local", issue = "42")]
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#[rustc_const_unstable(feature = "local", issue = "42")]
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pub fn min_align_of_val<T>(x: *const T) -> usize;
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}
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}
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#[stable(since="1.0.0", feature = "stable")]
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pub mod new_way {
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#[unstable(feature = "local", issue = "42")]
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#[rustc_intrinsic]
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pub const unsafe fn size_of_val<T>(x: *const T) -> usize { 42 }
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#[unstable(feature = "local", issue = "42")]
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#[rustc_const_unstable(feature = "local", issue = "42")]
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#[rustc_intrinsic]
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pub const unsafe fn min_align_of_val<T>(x: *const T) -> usize { 42 }
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
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#[inline]
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pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
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// Const stability attributes are not inherited from parent items.
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extern "rust-intrinsic" {
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fn copy<T>(src: *const T, dst: *mut T, count: usize);
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}
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unsafe { copy(src, dst, count) }
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//~^ ERROR cannot call non-const intrinsic
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}
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