rustfmt is not a library, and folks don’t depend on it as one. The only nightly features it uses are “hey let me use compiler as a library please,” which is also not, in my experience, common in the ecosystem. Even furthermore, it’s distributed precompiled in your rust installation, so that doesn’t end up giving you a nightly dependency to use it.

Anyway, thanks. Nightly does exist to be used, but our users largely report using stable, so when people say things like this, I am trying to see if there’s any blind spots.