fix rescript-lang#4491

Author: bobzhang

jscomp/core/js_dump.ml

@@ -167,7 +167,7 @@ let exp_need_paren  (e : J.expression) =
 
   | Raw_js_code {code_info = Exp _}
   | Fun _ 
-  | Caml_block (_,_,_, (Blk_record _ | Blk_module _))
+  | Caml_block (_,_,_, (Blk_record _ | Blk_module _ | Blk_poly_var _ | Blk_extension | Blk_record_ext _ | Blk_record_inlined _ | Blk_constructor _ ))
   | Object _ -> true
   | Raw_js_code {code_info = Stmt _ }
   | Length _

jscomp/test/build.ninja

@@ -325,6 +325,7 @@ build test/gpr_4280_test.cmi test/gpr_4280_test.cmj : cc test/gpr_4280_test.ml |
 build test/gpr_4407_test.cmi test/gpr_4407_test.cmj : cc test/gpr_4407_test.ml | test/debug_mode_value.cmj test/mt.cmj $stdlib
 build test/gpr_441.cmi test/gpr_441.cmj : cc test/gpr_441.ml | $stdlib
 build test/gpr_4442_test.cmi test/gpr_4442_test.cmj : cc test/gpr_4442_test.ml | test/mt.cmj $stdlib
+build test/gpr_4491_test.cmi test/gpr_4491_test.cmj : cc test/gpr_4491_test.ml | $stdlib
 build test/gpr_459_test.cmi test/gpr_459_test.cmj : cc test/gpr_459_test.ml | test/mt.cmj $stdlib
 build test/gpr_627_test.cmi test/gpr_627_test.cmj : cc test/gpr_627_test.ml | test/mt.cmj $stdlib
 build test/gpr_658.cmi test/gpr_658.cmj : cc test/gpr_658.ml | $stdlib

jscomp/test/gpr_4491_test.js

@@ -0,0 +1,28 @@
+'use strict';
+
+
+function f(xs) {
+  if (xs !== undefined) {
+    console.log("side effect");
+    ({
+        hd: xs,
+        tl: {
+          hd: xs,
+          tl: /* [] */0
+        }
+      });
+  } else {
+    ({
+        hd: 1,
+        tl: {
+          hd: 2,
+          tl: /* [] */0
+        }
+      });
+  }
+  console.log("nothing to see here", xs);
+  
+}
+
+exports.f = f;
+/* No side effect */

jscomp/test/gpr_4491_test.ml

@@ -0,0 +1,7 @@
+let f xs =
+  let unused =
+    match xs with
+    | Some (l) -> Js.log "side effect"; [l; l]
+    | None  -> [1; 2]
+  in
+  Js.log2 "nothing to see here" xs