anchor.diff:  
   (cl:in-package #:bazel.warning)
   
  +(defun format-control-string-or-nil (simple-condition)
  +  "Return the control slot of SIMPLE-CONDITION only if it is a string."
  +  (let ((control (simple-condition-format-control simple-condition)))
  +    (typecase control
  +      (string control)
  +      #+sbcl ;; needs SBCL version here.
  +      (sb-format::fmt-control
  +       (sb-format::fmt-control-string control))
  +      (t nil))))
  +
   (deftype style ()
     "A generic style warning."
     'cl:style-warning)
  
positive.code:     #+sbcl
      (sb-ext:deprecation-condition t)
      ((and warning simple-condition)
       (search "deprecated" (simple-condition-format-control c)
               :test #'char-equal))))
  
  (deftype deprecation ()
  
negative.code: (defun optional-and-key-p (warning)
    "Is WARNING a bad style warning about &optional and &key present in the same lambda list?"
    (when (typep warning 'simple-condition)
      (equal (format-control-string-or-nil warning)
             "&OPTIONAL and &KEY found in the same lambda list: ~S")))
  
  (deftype optional-and-key ()
  