forward-referenced-class trouble

[Nikodemus Siivola]

 reported by Bruno Haible on sbcl-devel
   (defclass c (a) ())
   (setf (class-name (find-class 'a)) 'b)
   (defclass a () (x))
   (defclass b () (y))
   (make-instance 'c)
 Expected: an instance of c, with a slot named x
 Got: debugger invoked on a SIMPLE-ERROR in thread 78906:
        While computing the class precedence list of the class named C.
        The class named B is a forward referenced class.
        The class named B is a direct superclass of the class named C.

  [ Is this actually a bug? DEFCLASS only replaces an existing class
    when the class name is the proper name of that class, and in the
    above code the class found by (FIND-CLASS 'A) does not have a
    proper name. CSR, 2006-08-07 ]