d0029a47c2
Currently, if a `#![staged_api]` crate contains an exported item without a stability marker (or inherited stability), the item is useless. This change introduces a check to ensure that all exported items have a defined stability. it also introduces the `unmarked_api` feature, which lets users import unmarked features. While this PR should in theory forbid these from existing, in practice we can't be so sure; so this lets users bypass this check instead of having to wait for the library and/or compiler to be fixed (since otherwise this is a hard error). r? @aturon