CLJS-1980: port CLJ-2100 (s/nilable form should retain original spec form)

Author: anmonteiro

src/main/cljs/cljs/spec.cljc

@@ -40,6 +40,11 @@
     (sequential? form) (walk/postwalk #(if (symbol? %) (res env %) %) (unfn form))
     :else form))
 
+(defmacro ^:private mres
+  "a compile time res, for use in cljs/spec.cljs"
+  [form]
+  (res &env form))
+
 (defn- ns-qualify
   "Qualify symbol s by resolving it or using the current *ns*."
   [env s]

src/main/cljs/cljs/spec.cljs

@@ -1369,7 +1369,7 @@
             [[1 (gen/delay (gen/return nil))]
              [9 (gen/delay (gensub pred overrides (conj path ::pred) rmap form))]])))
       (with-gen* [_ gfn] (nilable-impl form pred gfn))
-      (describe* [_] `(nilable ~(describe* spec))))))
+      (describe* [_] `(nilable ~(s/mres form))))))
 
 (defn exercise
   "generates a number (default 10) of values compatible with spec and maps conform over them,