error[E0658]: attributes of the form `#[derive_*]` are reserved for the compiler (see issue #29644)
  --> $DIR/feature-gate-custom_derive.rs:11:1
   |
11 | #[derive_Clone]
   | ^^^^^^^^^^^^^^^
   |
   = help: add #![feature(custom_derive)] to the crate attributes to enable

error: aborting due to previous error