fix some edge cases of recursive value

Author: bobzhang

jscomp/bin/whole_compiler.ml

@@ -66373,9 +66373,9 @@ let method_
     comment
   }
 
-
+(** This is coupuled with {!Caml_obj.caml_update_dummy} *)
 let dummy_obj ?comment ()  : t = 
-  {comment  ; expression_desc = Object []}
+  {comment  ; expression_desc = J.Array ([],Mutable)}
 
 let is_instance_array ?comment e : t = 
   {comment; expression_desc = Bin(InstanceOf, e , str L.js_array_ctor) }

jscomp/core/js_exp_make.ml

@@ -212,9 +212,9 @@ let method_
     comment
   }
 
-
+(** This is coupuled with {!Caml_obj.caml_update_dummy} *)
 let dummy_obj ?comment ()  : t = 
-  {comment  ; expression_desc = Object []}
+  {comment  ; expression_desc = J.Array ([],Mutable)}
 
 let is_instance_array ?comment e : t = 
   {comment; expression_desc = Bin(InstanceOf, e , str L.js_array_ctor) }

jscomp/runtime/caml_obj.ml

@@ -98,15 +98,32 @@ let caml_obj_truncate (x : Obj.t) (new_size : int) =
 
 let caml_lazy_make_forward x = lazy x
 
-(** TODO: the dummy one should be [{}] *)
+(** 
+  For the empty dummy object, whether it's 
+  `[]` or `{}` depends on how 
+  runtime encoding works, and will affect 
+  js polymorphic comparison(Js.(=)) (fine with caml polymoprhic comparison (Pervasives.equal))
+  In most cases, rec value comes from record/modules, 
+  whose tag is 0, we optimize that case
+ *)
 let caml_update_dummy x y =
+  (* let len = Bs_obj.length y in   
+  for i = 0 to len - 1 do 
+    Array.unsafe_set x i (Obj.field y i)
+  done;
+  Obj.set_tag (Obj.magic x) (Obj.tag y)
+  *)
   let len = Bs_obj.length y in
   for i = 0 to len - 1 do
     Obj.set_field x i (Obj.field y i)
-  done  ;
-  Obj.set_tag x (Obj.tag y);
-  Bs_obj.set_length x   (Bs_obj.length y)
-
+  done ; 
+  let y_tag = Obj.tag y in 
+  if y_tag <> 0 then
+    Obj.set_tag x y_tag
+  
+  (* Bs_obj.set_length x   (Bs_obj.length y) *)
+  (* [set_length] seems redundant here given that it is initialized as an array 
+  *)
 let caml_int_compare (x : int) (y: int) : int =
   if  x < y then -1 else if x = y then 0 else  1
 

jscomp/test/class3_test.js

@@ -305,7 +305,7 @@ eq('File "class3_test.ml", line 81, characters 12-19', v, /* int array */[
       3
     ]);
 
-var abstract_point = { };
+var abstract_point = [];
 
 Caml_obj.caml_update_dummy(abstract_point, [
       0,
@@ -363,7 +363,7 @@ var v$1 = Curry.js1(-792262820, 9, h);
 
 eq('File "class3_test.ml", line 107, characters 12-19', v$1, 32);
 
-var abstract_point2 = { };
+var abstract_point2 = [];
 
 Caml_obj.caml_update_dummy(abstract_point2, [
       0,

jscomp/test/class4_test.js

@@ -97,7 +97,7 @@ var restricted_point$prime$1 = restricted_point;
 
 var Point = /* module */[/* restricted_point' */restricted_point$prime$1];
 
-var abstract_point = { };
+var abstract_point = [];
 
 Caml_obj.caml_update_dummy(abstract_point, [
       0,

jscomp/test/class6_test.js

@@ -174,7 +174,7 @@ var d = [
   0
 ];
 
-var c2$prime = { };
+var c2$prime = [];
 
 Caml_obj.caml_update_dummy(c2$prime, [
       0,

jscomp/test/class8_test.js

@@ -35,7 +35,7 @@ function eq(loc, x, y) {
   return /* () */0;
 }
 
-var comparable = { };
+var comparable = [];
 
 Caml_obj.caml_update_dummy(comparable, [
       0,

jscomp/test/hamming_test.js

@@ -214,13 +214,13 @@ function iter_interval(f, _l, _param) {
   };
 }
 
-var hamming = { };
+var hamming = [];
 
-var ham2 = { };
+var ham2 = [];
 
-var ham3 = { };
+var ham3 = [];
 
-var ham5 = { };
+var ham5 = [];
 
 Caml_obj.caml_update_dummy(hamming, Block.__(246, [function () {
           return /* Cons */[