I think in almost 100% of cases, not having any license file(s) in a published crate is a mistake. Most licenses (especially the MIT and Apache-2.0 ones most used in the Rust ecosystem) require redistributed sources to contain a copy of the license text.

So, rust2rpm should print a warning when it finds zero license files, and make users file issues with upstream projects.

This would prevent lots of busywork during package review ...

I also opened a similar RFE against cargo: https://github.com/rust-lang/cargo/issues/10277