CLJS-1763: Defining a var that clashes with cljs.core throws a comp…

…iler error instead of warning

src/main/clojure/cljs/analyzer.cljc

@@ -1892,7 +1892,7 @@
     (fn [s [k & filters]]
       (if (= k :refer-clojure)
         (do
-          (when (seq s)
+          (when (seq (:excludes s))
             (throw (error env "Only one :refer-clojure form is allowed per namespace definition")))
           (let [valid-kws #{:exclude :rename}
                 xs
@@ -1924,7 +1924,8 @@
                     :else ret))]
             (merge-with into s xs)))
         s))
-    {} args))
+    {:excludes #{}
+     :renames {}} args))
 
 (defn use->require [env [lib & filters :as spec]]
   (when-not (and (symbol? lib) (odd? (count spec)))

src/test/clojure/cljs/analyzer_tests.clj

@@ -449,3 +449,10 @@
       (is (thrown-with-msg? Exception #"Can't def ns-qualified name in namespace foo.core"
             (a/analyze test-env '(def foo.core/foo 43))))
       (is (a/analyze test-env '(def cljs.user/foo 43))))))
+
+(deftest test-cljs-1763
+  (let [parsed (a/parse-ns-excludes {} '())]
+    (is (= parsed
+           {:excludes #{}
+            :renames {}}))
+    (is (set? (:excludes parsed)))))