error[E0658]: `macro` is experimental --> $DIR/feature-gate-decl_macro.rs:3:1 | LL | macro m() {} | ^^^^^^^^^^^^ | = note: see issue #39412 for more information = help: add `#![feature(decl_macro)]` to the crate attributes to enable error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0658`.