CLJS-1685: Incorrectly lazy subvec when start param is nil

Author: dnolen

src/main/cljs/cljs/core.cljs

@@ -5516,9 +5516,10 @@ reduces them without incurring seq initialization"
   the resulting vector shares structure with the original and no
   trimming is done."
   ([v start]
-     (subvec v start (count v)))
+   (subvec v start (count v)))
   ([v start end]
-     (build-subvec nil v start end nil)))
+   (assert (and (not (nil? start)) (not (nil? end))))
+   (build-subvec nil v start end nil)))
 
 (defn- tv-ensure-editable [edit node]
   (if (identical? edit (.-edit node))

src/test/cljs/cljs/core_test.cljs

@@ -1320,6 +1320,13 @@
     (is (true?  (equiv-map (MapWithNoIKVReduce. {:a 1 :b 2 :c 3}) {:a 1 :b 2 :c 3})))
     (is (false? (equiv-map (MapWithNoIKVReduce. {:a 1 :b 2 :c 3}) {:a 1 :b 2 :c 4})))))
 
+(deftest test-cljs-1685
+  (testing "nil start or end param throws error"
+    (is (= :fail (try (subvec nil nil)
+                      (catch js/Error e :fail))))
+    (is (= :fail (try (subvec nil 1 nil)
+                      (catch js/Error e :fail))))))
+
 (comment
   ;; ObjMap
   ;; (let [ks (map (partial str "foo") (range 500))