[Pre-RFC] Crate/item stability

language design
12

Features are supposed to be additive, so a feature to disable parts of a crate doesn’t make much sense. I like the idea of not building unstable items at all, though! I’m currently imagining something like this:

  • rustc gains awareness of item stability. Up to one stability attribute per item, and the fields are just documentation.
  • Everything that belongs to a top-level crate is built no matter what (otherwise main() would have to be #[stable], for example).
  • By default, dependencies only have their stable and unspecified items built. Rust gains a new extern crate attribute, #[unstable_use], which is basically #[macro_use] but for unstable items.
  • rustc does not gain awareness of crate stability. Instead, Cargo is responsible for ensuring that >= 1.0.0 crates are sound (i.e. contain either no publically-visible items, or at least one publically-visible stable item; eventually unspecified items will be banned as well).

Thoughts?