The manifest.rs has the structs and enums that define most of the Cargo.toml
That could be really helpful for other build/dev tools like cargo-make
For now, I also have internally mapped the relevant items in an internal data structs and enums, but would be happier if I would have just had a standard crate to use to pull those definitions from (naturally with serde support).
The manifest.rs seems like exactly the thing I was looking for but I would prefer a standalone lightweight crate only holding definitions instead of depending on entire cargo crate.
It would also help making your codebase more modular and reusable.