error[E0658]: unless otherwise specified, attributes with the prefix `rustc_` are reserved for internal compiler diagnostics (see issue #29642) | |
--> $DIR/expand-to-unstable-2.rs:18:10 | |
| | |
LL | #[derive(Unstable)] | |
| ^^^^^^^^ | |
| | |
= help: add #![feature(rustc_attrs)] to the crate attributes to enable | |
error: aborting due to previous error | |
For more information about this error, try `rustc --explain E0658`. |