CLJ-1187 Support retrieval of metadata from quoted empty literals

Signed-off-by: Stuart Halloway <stu@cognitect.com>

Author: Bronsa

src/jvm/clojure/lang/Compiler.java

@@ -2022,7 +2022,9 @@ else if(v == Boolean.FALSE)
 				return NumberExpr.parse((Number)v);
 			else if(v instanceof String)
 				return new StringExpr((String) v);
-			else if(v instanceof IPersistentCollection && ((IPersistentCollection) v).count() == 0)
+			else if(v instanceof IPersistentCollection
+					&& (((IPersistentCollection) v).count() == 0)
+					&& (!(v instanceof IObj) || ((IObj) v).meta() == null))
 				return new EmptyExpr(v);
 			else
 				return new ConstantExpr(v);

test/clojure/test_clojure/metadata.clj

@@ -51,6 +51,13 @@
              (def ^{:a 1} foo 0)
              #'foo)]
       (is (= 1 (-> v meta :a)))))
+  (testing "const vars preserve metadata"
+    (let [[v1 v2] (eval-in-temp-ns
+                   (def ^:const foo ^:foo [])
+                   (def ^:const bar ^:foo [:bar])
+                   [(meta foo) (meta bar)])]
+      (is (= {:foo true} v1))
+      (is (= {:foo true} v2))))
   #_(testing "subsequent declare doesn't overwrite metadata"
     (let [v (eval-in-temp-ns
              (def ^{:b 2} bar 0)