fspec gen ignores :fn rather than not gen.

same as Clojure aa9b5677

Author: dnolen

src/main/cljs/cljs/spec.cljc

@@ -263,6 +263,10 @@
   See 'fdef' for a single operation that creates an fspec and
   registers it, as well as a full description of :args, :ret and :fn
 
+  fspecs can generate functions that validate the arguments and
+  fabricate a return value compliant with the :ret spec, ignoring
+  the :fn spec if present.
+
   Optionally takes :gen generator-fn, which must be a fn of no args
   that returns a test.check generator."
   [& {:keys [args ret fn gen]}]

src/main/cljs/cljs/spec.cljs

@@ -1075,11 +1075,10 @@
           {path {:pred 'ifn? :val f :via via :in in}}))
       (gen* [_ _ _ _] (if gfn
                         (gfn)
-                        (when-not fnspec
-                          (gen/return
-                            (fn [& args]
-                              (assert (valid? argspec args) (with-out-str (explain argspec args)))
-                              (gen/generate (gen retspec)))))))
+                        (gen/return
+                          (fn [& args]
+                            (assert (valid? argspec args) (with-out-str (explain argspec args)))
+                            (gen/generate (gen retspec))))))
       (with-gen* [_ gfn] (fspec-impl argspec aform retspec rform fnspec fform gfn))
       (describe* [_] `(fspec :args ~aform :ret ~rform :fn ~fform)))))