Editions aren't that clear-cut- crates targeting old editions can still use most new language features, and all new library features. For example, the NLL borrow checker was originally enabled in the 2018 edition, but it's now available in 2015 as well.
Editions are more designed to manage backwards-incompatible changes, like new keywords or tweaks to corner cases in the type system.
Editions are more designed to manage backwards-incompatible changes, like new keywords or tweaks to corner cases in the type system.