Exactly, this is poor SWE. If you need a new feature from a latest rustc or an upstream, and can stomach losing users, then perhaps you mark things #[deprecated

Exactly, this is poor SWE. If you need a new feature from a latest rustc or an upstream, and can stomach losing users, then perhaps you mark things #[deprecated] for a release or two (which should be months, not days). AND don't bundle bugfixes with API breaks if it can be avoided. Otherwise, just don't bother! This is hype-driven development at its worst.