ArityException Wrong number of args (2) passed to: clojure.lang.PersistentVector about spec-tools

[Biserkov]

To answer my own question: wrapping the s/or in an st/spec seems to work?

(s/def ::d (st/spec (s/merge (st/spec (s/or :one (s/keys :req-un [::a])
                                            :two (s/keys :req-un [::b])))
                             (s/keys :req-un [::c]))))

[wandersoncferreira]

Hello @Biserkov , the problem is the following: there is a bug introduced with multi-spec support after version 0.10.0 at the parse-form function. Your spec is decomposed by parse-form which yields :type [:or [:map]]to the inner most portion of your spec.

When we look at the parse-form, we find (current-version):

(defmethod parse-form 'clojure.spec.alpha/merge [_ form]
  (let [type-priority #((:type %) {:map 0
                                   :multi-spec 1} 0)]
    (apply impl/deep-merge (->> (rest form)
                                (map parse-spec)
                                (sort-by type-priority)))))

The ArityException is thrown by this operation:

 #([:or [:map]] {:map 0
                 :multi-spec 1} 0)
 ;; => Wrong number of args (2) passed to: clojure.lang.PersistentVector

The same code in version 0.10.0 looks like this:

(defmethod parse-form 'clojure.spec.alpha/merge [_ form]
  (apply impl/deep-merge (map parse-spec (rest form))))

Does not contain the portion to sort by priority, thus no error. I opened a PR to change the type-priority function to be more defensive.