Way to make a configuration struct stable across versions?

Ok, that is extremely weird that you cannot have an expression with that type, but FRU still works with it, so it's no longer the equivalent of just desugaring to all the field assignments. EDIT: skimming https://rust-lang.github.io/rfcs/2145-type-privacy.html and the rfc/tracking issues I don't actually see any mention of how it relates to FRU.