CLJS-1650: cljs.reader/read-map now returns array-map/hash-map based on the size of the sequence.

Author: ducky427

src/main/cljs/cljs/reader.cljs

@@ -273,10 +273,13 @@ nil if the end of stream has been reached")
 
 (defn read-map
   [rdr _]
-  (let [l (read-delimited-list "}" rdr true)]
-    (when (odd? (count l))
+  (let [l (read-delimited-list "}" rdr true)
+        c (count l)]
+    (when (odd? c)
       (reader-error rdr "Map literal must contain an even number of forms"))
-    (apply hash-map l)))
+    (if (<= c (* 2 (.-HASHMAP-THRESHOLD PersistentArrayMap)))
+      (apply array-map l)
+      (apply hash-map l))))
 
 (defn read-number
   [reader initch]

src/test/cljs/cljs/reader_test.cljs

@@ -174,6 +174,14 @@
     (testing "Testing reading, CLJS-819"
       (is (= m " \u00a1")))))
 
+(deftest testing-map-type
+  (let [a  (reader/read-string "{:a 1 :b 2 :c 3}")
+        b  (reader/read-string "{:a 1 :b 2 :c 3 :d 4 :e 5 :f 6 :g 7 :h 8 :i 9}")]
+    (is (= a {:a 1 :b 2 :c 3}))
+    (is (instance? PersistentArrayMap a))
+    (is (= b {:a 1 :b 2 :c 3 :d 4 :e 5 :f 6 :g 7 :h 8 :i 9}))
+    (is (instance? PersistentHashMap b))))
+
 ;; NOTE: issue uncovered by test.check
 
 (deftest test-slash-reading