clojure.spec.alpha/form should return ::undefined for anonym functions

[mathesz]

The clojure.spec.alpha/form function calls fn-sym which returns a wrong value for anonym functions:

(defn- fn-sym [^Object f]
  (let [[_ f-ns f-n] (re-matches #"(.*)\$(.*?)(__[0-9]+)?" (.. f getClass getName))]
    ;; check for anonymous function
    (when (not= "fn" f-n)
      (symbol (demunge f-ns) (demunge f-n)))))

https://github.com/babashka/spec.alpha/blob/babashka/src/main/clojure/clojure/spec/alpha.clj#L146-L150
Expected behavior:

The function should return nil for anonym functions.

Current behavior:

Symbolic value of the function is returned, such as sci.impl.fns/fun/arity-0

The regular expression and the when condition fails to ignore sci anonym functions.

(re-matches #"(.*)\$(.*?)(__[-1-9]+)?" "sci.impl.fns$fun$arity_-1__7418@31425281")
=> ["sci.impl.fns$fun$arity_-1__7418@31425281" "sci.impl.fns$fun" "arity_-1__7418@31425281" nil]

The string "arity_-1__7418@31425281" becomes f-n which is not= "fn" , therefore the when condition returns a demunged symbol for the anonym function insted of the correct nil value.

Impact

(clojure.spec.alpha/form (fn [] true)) => sci.impl.fns/fun/arity-0

This should be :clojure.spec.alpha/undefined as per
https://github.com/babashka/spec.alpha/blob/babashka/src/main/clojure/clojure/spec/alpha.clj#L169

[borkdude]

Thanks.