> I think the way you do this is set things up so that no bits that are written in Rust are built by default, and make sure that the build system is set up such that Rust bindings for C code are only built when there's Rust code that's enabled that requires them.

Which is currently the only way possible and it will stay that way for a long time because remember that clang support less targets than gcc and gcc cannot compile Rust.

Once gcc can /reliably/ compile Rust, then and only then Rust could be "upgraded" to a first class citizen in Linux. The "C-maintainers don't want to learn Rust" issue, will still be here of course, but there will already be many years of having a mixed code base..