If future Rust versions do make semantic changes to existing language constructs, that will presumably only apply to crates built with the new edition, and crat

If future Rust versions do make semantic changes to existing language constructs, that will presumably only apply to crates built with the new edition, and crates built with the old will get the old semantics. If we’re talking ABI-level stuff, that doesn’t require an edition because you build all your crates with the same compiler, so it can use a consistent ABI. Swift’s ABI stability has nothing to do with semantic changes and everything to do with they wanted binary compatibility, so they could start using Swift in the system frameworks that your app links against.