error: `#[derive(ArgEnum)]` only supports enums
 --> $DIR/arg_enum_on_struct.rs:3:10
  |
3 | #[derive(ArgEnum, Debug)]
  |          ^^^^^^^
  |
  = note: this error originates in the derive macro `ArgEnum` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0046]: not all trait items implemented, missing: `as_arg`
 --> $DIR/arg_enum_on_struct.rs:3:10
  |
3 | #[derive(ArgEnum, Debug)]
  |          ^^^^^^^ missing `as_arg` in implementation
  |
  = note: this error originates in the derive macro `ArgEnum` (in Nightly builds, run with -Z macro-backtrace for more info)
  = help: implement the missing item: `fn as_arg(&self) -> Option<&'static str> { todo!() }`