error[E0658]: transparent unions are unstable --> $DIR/feature-gate-transparent_unions.rs:2:1 | LL | union OkButUnstableUnion { | ^^^^^^^^^^^^^^^^^^^^^^^^ | = note: see issue #60405 for more information = help: add `#![feature(transparent_unions)]` to the crate attributes to enable = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0658`.