clojure.spec.alpha/exercise-fn should emit a bettor error message when no implementation is found for a symbol

Question

Here we get a NullPointerException because although we do have a spec for {{foo}}, we don't have an implementation for it, a more descriptive error message would help.

`
(require '[clojure.spec.alpha :as s])

(s/fdef foo :args (s/cat :x int?) :ret int?)
=> user/foo

(s/exercise-fn foo) NullPointerException clojure.core/apply (core.clj:657) ``

Proposed: Check for a nil function and throw.

Patch: clj-2190.patch

Answer 1

Comment made by: stu

If we are going to handle this case, can we also include the name of the offending symbol in the error message?

Answer 2

Comment made by: alexmiller

The sym-or-f arg is resolved to nil before exercise-fn is invoked, so we have no symbol to report by that point.

Answer 3

Reference: https://clojure.atlassian.net/browse/CLJ-2190 (reported by alex+import)