Once again something is at odds here. You give resounding "Yes" comments, but in the backwards compatibility discussions I had with language team members, those "Yes" comments were actually "not really our problem" answers.

I also don't know how current code running in a future compiler is forward-compatibility. And the Rust guarantee only kind-of holds if you define "code" as "crate". Everything outside of or crossing that boundary is not compatible.

To clarify and bring it to an example: Are you guaranteeing that `(a<b, c>(d))` will always be parsed as a tuple with two comparisons? Because if so I believe you're the only one.