swift234

[Accessibility] Public classes may not have private superclasses.

In theory there's nothing wrong with this, but it makes it hard to see what
operations a class supports, and there's no obvious way to go to its nearest
public superclass.

Note that we have a similar issue with protocols, since private protocols can
refine public protocols, and then public classes can conform to private
protocols---the indirect conformance won't be listed in the inheritance
clause, but it is a public conformance nonetheless.

Swift SVN r19588