I was just following the example from the docs, my use case is more like this:

  .
  ├── lib.rs
  └── foo/
    └── mod.rs
    └── one.rs
    └── two.rs
    └── three.rs
    └── four.rs
  └── bar/
    └── mod.rs
    └── one.rs
    └── two.rs
    └── three.rs
    └── four.rs

Which feels to me like a very common folder structure in other languages.