[Pkg-rust-maintainers] Rust for Linux and host-only libraries

[Miguel Ojeda]

Hi Ximin, Sylvestre, Fabian, all,

In Rust for Linux, we are considering using host-only/userspace Rust
libraries (e.g. `syn`), and we were asked to check whether it would be
possible to just pick them from the distribution (since, in principle,
they don't require kernel-specific changes).

What is the policy in Debian for those? I was told about
`debcargo-conf` by Zixing Liu, and indeed I can see e.g. `syn` there
in `librust-syn-dev`, which places the sources at
`/usr/share/cargo/registry/`, which is great for what we need. Is that
correct? This would be useful for kernel developers that do not trust
third-party repositories (not even Rust's/crates.io/the upstream
repository).

By the way, is there a way to query where the sources are (i.e. that
path) in a "standard" way (e.g. like `pkg-config`)? Or, at least, can
we assume it should be stable? (e.g. for automated detection and/or
instructions we may want to provide).

Thanks!

Cheers,
Miguel