error[E0658]: `concat_idents` is not stable enough for use and is subject to change (see issue #29599)
  --> $DIR/feature-gate-concat_idents.rs:15:13
   |
LL |     let a = concat_idents!(X, Y_1); //~ ERROR `concat_idents` is not stable
   |             ^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: add #![feature(concat_idents)] to the crate attributes to enable

error[E0658]: `concat_idents` is not stable enough for use and is subject to change (see issue #29599)
  --> $DIR/feature-gate-concat_idents.rs:16:13
   |
LL |     let b = concat_idents!(X, Y_2); //~ ERROR `concat_idents` is not stable
   |             ^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: add #![feature(concat_idents)] to the crate attributes to enable

error: aborting due to 2 previous errors

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