pub fn diff_packages(old: &Package, new: &Package) -> DiffReportExpand description
Compares two resolved packages. Matched packages share a name; the new package’s name is used as the path prefix.
Only the pair is in hand, so a type from another package does not resolve,
and a type the diff cannot resolve is reported as breaking: a struct field
appended with such a type classifies breaking (driftsys/ridl#598).
diff_sets_in resolves it.