CLJS-2787: Record comparison is broken when instance is constructed from another record instance via map factory

If map->Foo argument is a record, pour the extension map contents into
a plain map

Author: swannodette

src/main/clojure/cljs/core.cljc

@@ -1887,7 +1887,9 @@
              ks (map keyword fields)
              getters (map (core/fn [k] `(~k ~ms)) ks)]
     `(defn ~fn-name ~docstring [~ms]
-       (new ~rname ~@getters nil (not-empty (dissoc ~ms ~@ks)) nil))))
+       (let [extmap# (cond->> (dissoc ~ms ~@ks)
+                        (record? ~ms) (into {}))]
+         (new ~rname ~@getters nil (not-empty extmap#) nil)))))
 
 (core/defmacro defrecord
   "(defrecord name [fields*]  options* specs*)

src/test/cljs/cljs/core_test.cljs

@@ -1586,3 +1586,10 @@
     (is (uri? (goog.Uri. "")))
     (is (uri? (goog.Uri. "http://clojurescript.org")))
     (is (uri? (goog.Uri. "some string")))))
+
+(defrecord CLJS-2787 [])
+
+(deftest test-cljs-2787
+  (let [x (map->CLJS-2787 {1 2})
+        y (map->CLJS-2787 x)]
+    (= x y)))