CLJS-3363: reduce-kv on seq of map entries

Author: mfikes

src/main/cljs/cljs/core.cljs

@@ -2624,9 +2624,11 @@ reduces them without incurring seq initialization"
   and f is not called. Note that reduce-kv is supported on vectors,
   where the keys will be the ordinals."
   ([f init coll]
-    (if-not (nil? coll)
+    (if (satisfies? IKVReduce coll)
       (-kv-reduce coll f init)
-      init)))
+      (reduce (fn [ret me]
+                (f ret (-key me) (-val me)))
+        init coll))))
 
 (defn identity
   "Returns its argument."

src/test/cljs/cljs/core_test.cljs

@@ -1975,6 +1975,12 @@
       {1 1 3 3}     (update-keys (array-map 0 1 2 3) inc)
       {1 1 3 3}     (update-keys (sorted-map 2 3 0 1) inc))))
 
+(deftest test-cljs-3363
+  (is (= {}
+        (reduce-kv #(assoc %1 %3 %2) {} nil)))
+  (is (= {1 :a 2 :b}
+        (reduce-kv #(assoc %1 %3 %2) {} (seq {:a 1 :b 2})))))
+
 (defn cljs-3386-test-fn
   ([x] x) ([_ _ & zs] zs))