todo!() "Indicates unfinished code" (https://doc.rust-lang.org/std/macro.todo.html)
Rust documentation provides further clarification:
> The difference between unimplemented! and todo! is that while todo!
> conveys an intent of implementing the functionality later and the
> message is "not yet implemented", unimplemented! makes no such claims.
todo!() seems more appropriate for assists that insert missing impls.
