The current implementation of describe-symbol-for-emacs assumes that ccl::setf-function-spec-name will always return a symbol. Although this is true for short-form defsetf forms, when the long form has been used, an anonymous function is returned instead of a symbol, which then causes describe-symbol-for-emacs to fail. For example, doing an apropos on "sub" will cause an error because "subseq" has a long form defsetf.
Here is a fix:
Index: swank-openmcl.lisp =================================================================== RCS file: /project/slime/cvsroot/slime/swank-openmcl.lisp,v retrieving revision 1.101 diff -u -r1.101 swank-openmcl.lisp --- swank-openmcl.lisp 21 Sep 2005 11:43:47 -0000 1.101 +++ swank-openmcl.lisp 22 Sep 2005 02:18:52 -0000 @@ -634,7 +634,8 @@ (maybe-push :setf (let ((setf-function-name (ccl::setf-function-spec-name `(setf ,symbol)))) - (when (fboundp setf-function-name) + (when (or (functionp setf-function-name) ;; long form defsetf + (fboundp setf-function-name)) (doc 'function setf-function-name)))) result)))