Snapcraft rust plugin doesn't suport workspaces

[Chris Holcombe]

Rust has support for what's called a workspace: https://doc.rust-lang.org/book/second-edition/ch14-03-cargo-workspaces.html. It allows several crates to share the same Cargo.lock. Snapcraft could have support for this by just calling `cargo build --all`. That would build all crates in the project.

[Leo Arias (elopio)]

I have had this same problem before. Thanks for reporting it. Marking as triaged, with medium importance.