|  | error[E0658]: rustc_allow_const_fn_unstable side-steps feature gating and stability checks | 
|  | --> $DIR/feature-gate-rustc-allow-const-fn-unstable.rs:3:1 | 
|  | | | 
|  | LL | #[rustc_allow_const_fn_unstable()] | 
|  | | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | 
|  | | | 
|  | = note: see issue #69399 <https://github.com/rust-lang/rust/issues/69399> for more information | 
|  | = help: add `#![feature(rustc_allow_const_fn_unstable)]` 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|  | = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date | 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`. |