error[E0658]: the `#[marker]` attribute is an experimental feature --> $DIR/feature-gate-marker_trait_attr.rs:3:1 | LL | #[marker] trait ExplicitMarker {} | ^^^^^^^^^ | = note: see issue #29864 for more information = help: add `#![feature(marker_trait_attr)]` to the crate attributes to enable = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0658`.