https://github.com/rust-lang/rustc-guide/blob/master/src/stabilization_guide.md#removing-existing-uses-of-the-feature-gate still mentions `#![cfg_attr(stage0, feature(XXX))]`, but as of https://github.com/rust-lang/rust/pull/61494, it's `bootstrap` instead of `stage0`.
https://github.com/rust-lang/rustc-guide/blob/master/src/stabilization_guide.md#removing-existing-uses-of-the-feature-gate still mentions
#![cfg_attr(stage0, feature(XXX))], but as of rust-lang/rust#61494, it'sbootstrapinstead ofstage0.