go/types, types2: fix overlap test for union termlist
Per the spec, "the type sets of all non-interface terms must be
pairwise disjoint (the pairwise intersection of the type sets must
be empty)" in a union.
For the overlap test, the existing implementation casually mixed
syntactic union terms (which may have interface type) with type set
terms (which are normalized/expanded and must not have interface
type). As a consequence, in some cases the overlap test failed.
This change skips terms with interface types in the overlap test.
Fixes #51607.
Change-Id: I8ae9953db31f0a0428389c6a45a6696aa2450219
Reviewed-on: https://go-review.googlesource.com/c/go/+/397695
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org> Reviewed-by: Robert Findley <rfindley@google.com>