First, thanks for your answer!
However, it seems I didn't express myself well enough.
The problem is that the Cargo.toml lies in rust-package and as far as I know this defines the package root.
Ah I see, I'm not sure how you can do this without moving the Cargo.toml file. Pretty sure the Cargo.toml file must always be the at the root of the published package. What is the reason for wanting to include the other packages? Does the Rust package depend on them?
yes, in lib/src is the library located I'm writing the binding for.
It's not my preferred project structure but as I said, the project owner would like to keep it like that - which is likely not possible.
Maybe it would work if I add the repo itself as a submodule of itself but that would be a mean circular dependency...