> The first crate, foo, is in the 2024 edition, and defines a trait with a single generic method. The second crate, bar, is in the 2021 edition, depends on foo, and implements that trait for its own type.

I wasn’t aware that an early edition of rust can reference crates for a later edition. It doesn’t seem that terrible to prohibit this (Probably some very good reason to counter this though!). Editions give us the privilege of not having to constantly update crates that don’t really need to be changed whenever a new rust version comes out. If I do end up making changes to my crate and updating my dependencies then I don’t see it as such a pain to update the Rust Edition of my crate if said dependencies also happen to use a later edition.

I do, however, see one downside to this though and experienced it first hand in c# .net standard where it was way better to use the earliest version possible of .net standard for your library to maximise compatibility with things that use it. No incentive to use a later standard and therefore there was stagnation. May not be applicable because you normally distribute compiled binaries but food for thought.