error[E0658]: the `#[ffi_const]` attribute is an experimental feature --> $DIR/feature-gate-ffi_const.rs:4:5 | LL | #[ffi_const] | ^^^^^^^^^^^^ | = note: see issue #58328 for more information = help: add `#![feature(ffi_const)]` to the crate attributes to enable = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0658`.