error: a WIP interface trait must be public
 --> tests/ui/private_trait.rs:3:1
  |
3 | #[interface]
  | ^^^^^^^^^^^^
  |
  = note: this error originates in the attribute macro `interface` (in Nightly builds, run with -Z macro-backtrace for more info)

warning: unused import: `OperationResult`
 --> tests/ui/private_trait.rs:1:21
  |
1 | use wip_interface::{OperationResult, interface};
  |                     ^^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` (part of `#[warn(unused)]`) on by default