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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.
128 lines
5.4 KiB
Plaintext
128 lines
5.4 KiB
Plaintext
error[E0658]: use of unstable library feature 'unstable'
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--> $DIR/const-unstable-intrinsic.rs:17:9
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LL | unstable_intrinsic::old_way::size_of_val(&x);
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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= note: see issue #42 <https://github.com/rust-lang/rust/issues/42> for more information
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= help: add `#![feature(unstable)]` to the crate attributes to enable
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= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
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error[E0658]: use of unstable library feature 'unstable'
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--> $DIR/const-unstable-intrinsic.rs:20:9
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LL | unstable_intrinsic::old_way::min_align_of_val(&x);
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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= note: see issue #42 <https://github.com/rust-lang/rust/issues/42> for more information
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= help: add `#![feature(unstable)]` to the crate attributes to enable
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= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
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error[E0658]: use of unstable library feature 'unstable'
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--> $DIR/const-unstable-intrinsic.rs:23:9
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LL | unstable_intrinsic::new_way::size_of_val(&x);
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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= note: see issue #42 <https://github.com/rust-lang/rust/issues/42> for more information
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= help: add `#![feature(unstable)]` to the crate attributes to enable
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= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
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error[E0658]: use of unstable library feature 'unstable'
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--> $DIR/const-unstable-intrinsic.rs:26:9
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LL | unstable_intrinsic::new_way::min_align_of_val(&x);
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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= note: see issue #42 <https://github.com/rust-lang/rust/issues/42> for more information
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= help: add `#![feature(unstable)]` to the crate attributes to enable
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= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
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error: cannot call non-const intrinsic `size_of_val` in constant functions
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--> $DIR/const-unstable-intrinsic.rs:17:9
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LL | unstable_intrinsic::old_way::size_of_val(&x);
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: `min_align_of_val` is not yet stable as a const intrinsic
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--> $DIR/const-unstable-intrinsic.rs:20:9
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LL | unstable_intrinsic::old_way::min_align_of_val(&x);
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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= help: add `#![feature(unstable)]` to the crate attributes to enable
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error: intrinsic `unstable_intrinsic::new_way::size_of_val` cannot be (indirectly) exposed to stable
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--> $DIR/const-unstable-intrinsic.rs:23:9
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LL | unstable_intrinsic::new_way::size_of_val(&x);
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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= help: mark the caller as `#[rustc_const_unstable]`, or mark the intrinsic `#[rustc_const_stable_indirect]` (but this requires team approval)
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error: `min_align_of_val` is not yet stable as a const intrinsic
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--> $DIR/const-unstable-intrinsic.rs:26:9
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LL | unstable_intrinsic::new_way::min_align_of_val(&x);
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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= help: add `#![feature(unstable)]` to the crate attributes to enable
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error: cannot call non-const intrinsic `size_of_val` in constant functions
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--> $DIR/const-unstable-intrinsic.rs:30:9
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LL | old_way::size_of_val(&x);
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| ^^^^^^^^^^^^^^^^^^^^^^^^
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error: const function that might be (indirectly) exposed to stable cannot use `#[feature(local)]`
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--> $DIR/const-unstable-intrinsic.rs:32:9
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LL | old_way::min_align_of_val(&x);
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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help: if the function is not (yet) meant to be exposed to stable, add `#[rustc_const_unstable]` (this is what you probably want to do)
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LL + #[rustc_const_unstable(feature = "...", issue = "...")]
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LL | const fn const_main() {
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help: otherwise, as a last resort `#[rustc_allow_const_fn_unstable]` can be used to bypass stability checks (this requires team approval)
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LL + #[rustc_allow_const_fn_unstable(local)]
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LL | const fn const_main() {
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error: intrinsic `new_way::size_of_val` cannot be (indirectly) exposed to stable
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--> $DIR/const-unstable-intrinsic.rs:34:9
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LL | new_way::size_of_val(&x);
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| ^^^^^^^^^^^^^^^^^^^^^^^^
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= help: mark the caller as `#[rustc_const_unstable]`, or mark the intrinsic `#[rustc_const_stable_indirect]` (but this requires team approval)
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error: const function that might be (indirectly) exposed to stable cannot use `#[feature(local)]`
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--> $DIR/const-unstable-intrinsic.rs:36:9
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LL | new_way::min_align_of_val(&x);
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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help: if the function is not (yet) meant to be exposed to stable, add `#[rustc_const_unstable]` (this is what you probably want to do)
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LL + #[rustc_const_unstable(feature = "...", issue = "...")]
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LL | const fn const_main() {
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help: otherwise, as a last resort `#[rustc_allow_const_fn_unstable]` can be used to bypass stability checks (this requires team approval)
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LL + #[rustc_allow_const_fn_unstable(local)]
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LL | const fn const_main() {
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error: cannot call non-const intrinsic `copy` in constant functions
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--> $DIR/const-unstable-intrinsic.rs:74:14
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LL | unsafe { copy(src, dst, count) }
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| ^^^^^^^^^^^^^^^^^^^^^
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error: aborting due to 13 previous errors
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For more information about this error, try `rustc --explain E0658`.
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