error[E0015]: cannot call non-const fn `::func` in constant functions --> $DIR/cross-crate.rs:20:11 | LL | Const.func(); | ^^^^^^ | = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants = help: add `#![feature(const_trait_impl)]` to the crate attributes to enable error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0015`.