error[E0658]: the `#[no_core]` attribute is an experimental feature --> $DIR/cfg-attr-crate-2.rs:6:21 | LL | #![cfg_attr(broken, no_core)] | ^^^^^^^ | = note: see issue #29639 for more information = help: add `#![feature(no_core)]` to the crate attributes to enable = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0658`.