error[E0658]: `macro` is experimental
  --> $DIR/feature-gate-decl_macro.rs:3:1
   |
LL | macro m() {}
   | ^^^^^^^^^^^^
   |
   = note: for more information, see https://github.com/rust-lang/rust/issues/39412
   = help: add #![feature(decl_macro)] to the crate attributes to enable

error: aborting due to previous error

For more information about this error, try `rustc --explain E0658`.