error[E0658]: the `#[register_tool]` attribute is an experimental feature --> $DIR/feature-gate-register_tool.rs:1:1 | LL | #![register_tool(tool)] | ^^^^^^^^^^^^^^^^^^^^^^^ | = note: see issue #66079 for more information = help: add `#![feature(register_tool)]` to the crate attributes to enable error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0658`.