OK, sure, but again what breaking changes editions do/don't currently allow is independent from what SkiFire13/I was responding to, which was the "requires full access to source code" bit.
Depends on the change. Obviously the compiler doesn't need to care about cross-edition compatibility between crates if the changes in question don't impact the public API. Otherwise, I'd expect the compiler to canonicalize the changes, and from what I understand that is precisely how edition changes are chosen/designed/implemented.
