untitled

~/src/swank-clojure/swank/commands/basic.clj:299

The following function is used in slime-edit-definition.
It blows up on namespace 'user' and thus thwarts jumping to
definitions in the user namespace.

(defn- namespace-to-path [ns]
  (let [#^String ns-str (name (ns-name ns))]
    (-> ns-str
        (.substring 0 (.lastIndexOf ns-str ".")) <------ 'user' contains no '.'
        (.replace \- \_)
        (.replace \. \/))))

My amateurish fix:
(defn- namespace-to-path [ns]
  (let [#^String ns-str (name (ns-name ns))]
    (let [last-dot (.lastIndexOf ns-str ".")]
      (when (pos? last-dot)
       (-> ns-str
           (.substring 0 last-dot)
           (.replace \- \_)
           (.replace \. \/))))))