Status report on optional Rust in FreeBSD support

Shawn Webb has published a status
report on work to provide basic support in FreeBSD for userland components
written in Rust.

We introduced a new BSD makefile, located at share/mk/bsd.rust.mk,
that enables building a Rust application during buildworld. As of this
writing, we only support building and installing Rust
applications. Supporting library crates is planned (we would like to
be able to build/install library crates that expose an FFI, like for
C/C++ compatibility). Normal library crates build and install just
fine. Support for cdylib Rust library crates specifically is what's
missing, but is desired and planned.

We do NOT currently support Rust in the kernel. Kernel support
requires more work that we deemed out-of-scope for this initial
proof-of-concept/work-in-progress patchset. We also do NOT support
building multiple programs in the same BSD Makefile (like with
bsd.progs.mk), though that is also a desired feature.

LWN covered a
discussion about including Rust in the FreeBSD base system in August
2024.