Comment 1 for bug 1818142

What's the best way to do something like this? An issue is making code using it play well with earlier versions of SBCL. So if there's a symbol SB-EXT:*FOO* that controls the behavior, one might write (in the .sbclrc file, say):

(let ((sym (find-symbol "*FOO*" "SB-EXT")))
  (when sym (setf (symbol-value sym) t)))

With a declaration, one could use the DECLARATION declaration, but the problem there would be the package could be locked.

(declaim (declaration sb-ext:defmethod-warn))
(declaim (sb-ext:defmethod-warn))