CLJS-1642: cljs.core/reductions does not respect 'reduced'

Apply CLJ-1185 patch to ClojureScript

Author: dnolen

src/main/cljs/cljs/core.cljs

@@ -8858,15 +8858,17 @@ reduces them without incurring seq initialization"
   "Returns a lazy seq of the intermediate values of the reduction (as
   per reduce) of coll by f, starting with init."
   ([f coll]
-     (lazy-seq
-      (if-let [s (seq coll)]
-        (reductions f (first s) (rest s))
-        (list (f)))))
+   (lazy-seq
+     (if-let [s (seq coll)]
+       (reductions f (first s) (rest s))
+       (list (f)))))
   ([f init coll]
+   (if (reduced? init)
+     (list @init)
      (cons init
-           (lazy-seq
-            (when-let [s (seq coll)]
-              (reductions f (f init (first s)) (rest s)))))))
+       (lazy-seq
+         (when-let [s (seq coll)]
+           (reductions f (f init (first s)) (rest s))))))))
 
 (defn juxt
   "Takes a set of functions and returns a fn that is the juxtaposition

src/test/cljs/cljs/core_test.cljs

@@ -3150,6 +3150,21 @@
   (is (= [""] (s/split-lines "")))
   (is (= [] (s/split-lines "\n\n\n"))))
 
+(deftest test-reductions-obeys-reduced
+  (is (= [0 :x]
+        (reductions (constantly (reduced :x))
+          (range))))
+  (is (= [:x]
+        (reductions (fn [acc x] x)
+          (reduced :x)
+          (range))))
+  (is (= [2 6 12 12]
+        (reductions (fn [acc x]
+                      (if (= x :stop)
+                        (reduced acc)
+                        (+ acc x)))
+          [2 4 6 :stop 8 10]))))
+
 (comment
   ;; ObjMap
   ;; (let [ks (map (partial str "foo") (range 500))