With the pending CL 321689, interfaces that contain constraints are not different anymore from interfaces that have embedded types. There's one new type(set), called a Union. I believe we simply need to export the explicitly declared methods and embedded elements, some of which may be unions. A union in turn is simply a list of types, together with a bit for each type indicating whether it's a "~" or not. Upon import, we should construct the internal representation lazily.

Thanks, that sounds good to me.

NewUnion looks good for importers. I think Union will need term/tilde accessors for exporters though; I don't see any at https://go-review.googlesource.com/c/go/+/321689/8/src/cmd/compile/internal/types2/union.go.

I'm going to close this issue. We have the APIs needed in types2 on the dev.typeparams, and I expect the corresponding go/types APIs will be included as part of @findleyr 's go/types API extensions proposals.