error[E0658]: C-variadic functions are unstable --> $DIR/feature-gate-c_variadic.rs:3:1 | LL | pub unsafe extern "C" fn test(_: i32, ap: ...) { } | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | = note: see issue #44930 for more information = help: add `#![feature(c_variadic)]` to the crate attributes to enable error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0658`.