CLJS-2033: set-validator! should check current state

Author: mfikes

src/main/cljs/cljs/core.cljs

@@ -4325,6 +4325,9 @@ reduces them without incurring seq initialization"
   is not acceptable to the new validator, an Error will be thrown and the
   validator will not be changed."
   [iref val]
+  (when (and (some? val)
+             (not (val (-deref iref))))
+    (throw (js/Error. "Validator rejected reference state")))
   (set! (.-validator iref) val))
 
 (defn get-validator

src/test/cljs/cljs/core_test.cljs

@@ -47,6 +47,15 @@
     (testing "Testing atom validators"
       (is (= coll? (get-validator a)))
       (is (thrown? js/Error (reset! a 1)))
+      (is (thrown? js/Error (set-validator! a number?)))
+      (is (some? (get-validator a)))
+      (set-validator! a nil)
+      (is (nil? (get-validator a)))
+      (let [e1 (ex-info "" {})]
+        (try
+          (set-validator! a (fn [_] (throw e1)))
+          (catch :default e2
+            (is (identical? e1 e2)))))
       (is (= {:a 1} (meta a)))
       (alter-meta! a assoc :b 2)
       (is (= {:a 1 :b 2} (meta a)))))