Override clojure.spec.alpha/gensub for friendly exceptions for failed such-that - see https://clojure.atlassian.net/browse/CLJ-2097

clojure.spec.alpha.clj

;; Normally the exception thrown by such-that does not point to the failed spec, which makes it useless
;; Eval this to override it and include `path` to the spec (and `form`, not sure which better)
(in-ns 'clojure.spec.alpha)
(defn- gensub
  [spec overrides path rmap form]
  ;;(prn {:spec spec :over overrides :path path :form form})
  (let [spec (specize spec)]
    (if-let [g (c/or (when-let [gfn (c/or (get overrides (c/or (spec-name spec) spec))
                                          (get overrides path))]
                       (gfn))
                     (gen* spec overrides path rmap))]
      (gen/such-that #(valid? spec %) g {:max-tries 100
                                   :ex-fn     (fn [{:keys [max-tries]}]
                                                (ex-info (str "Couldn't satisfy " (spec-name spec) "  after " max-tries " tries.")
                                                         {:max  max-tries
                                                          :path path
                                                          :sample-explain (->> (first (gen/sample g 1))
                                                                               (explain-data spec)
                                                                               :clojure.spec.alpha/problems)}))}
      (let [abbr (abbrev form)]
        (throw (ex-info (str "Unable to construct gen at: " path " for: " abbr)
                        {::path path ::form form ::failure :no-gen}))))))