It turns out that this is a thing that can happen. Catch it early
rather than waiting for a less helpful message during CPL construction.
(continue ()
(setf duff t)
(list (find-sod-class "SodObject"))))))
- superclasses))
+ (find-duplicates (lambda (first second)
+ (declare (ignore second))
+ (setf duff t)
+ (cerror* "Class `~A' has duplicate ~
+ direct superclass `~A'"
+ name first))
+ superclasses)
+ (delete-duplicates superclasses)))
(synthetic-name (or name
(let ((var (synthetic-name)))
(unless pset