1 error[E0658]: this is an internal attribute that will never be stable
2 --> $DIR/feature-gate-on-unimplemented.rs:3:1
4 LL | #[rustc_on_unimplemented = "test error `{Self}` with `{Bar}`"]
5 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7 = note: see issue #29642 <https://github.com/rust-lang/rust/issues/29642> for more information
8 = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
10 error: aborting due to previous error
12 For more information about this error, try `rustc --explain E0658`.