Fix polymorphic compare on nullables.

Polymorphic compare could crash when the second argument is null.

Author: Cristiano Calcagno

jscomp/runtime/caml_obj.ml

@@ -167,6 +167,8 @@ let unsafe_js_compare x y =
 let rec caml_compare (a : Obj.t) (b : Obj.t) : int =
   if a == b then 0 else
   (*front and formoest, we do not compare function values*)
+  if a == (Obj.repr Js_null.empty) then -1 else
+  if b == (Obj.repr Js_null.empty) then 1 else
   let a_type = Js.typeof a in 
   let b_type = Js.typeof b in 
   if a_type = "string" then
@@ -182,7 +184,6 @@ let rec caml_compare (a : Obj.t) (b : Obj.t) : int =
     | false, false -> 
       if a_type = "boolean"
       || a_type = "undefined"
-      || a == (Obj.repr Js_null.empty)
       then (* TODO: refine semantics when comparing with [null] *)
         unsafe_js_compare a b
       else if a_type = "function" || b_type = "function"

jscomp/test/caml_compare_test.js

@@ -883,7 +883,35 @@ var suites_001 = /* :: */[
                                                                                                   ]);
                                                                                         })
                                                                                     ],
-                                                                                    /* [] */0
+                                                                                    /* :: */[
+                                                                                      /* tuple */[
+                                                                                        "File \"caml_compare_test.ml\", line 81, characters 4-11",
+                                                                                        (function () {
+                                                                                            return /* Eq */Block.__(0, [
+                                                                                                      Caml_obj.caml_compare(null, /* :: */[
+                                                                                                            3,
+                                                                                                            /* [] */0
+                                                                                                          ]),
+                                                                                                      -1
+                                                                                                    ]);
+                                                                                          })
+                                                                                      ],
+                                                                                      /* :: */[
+                                                                                        /* tuple */[
+                                                                                          "File \"caml_compare_test.ml\", line 84, characters 4-11",
+                                                                                          (function () {
+                                                                                              return /* Eq */Block.__(0, [
+                                                                                                        Caml_obj.caml_compare(/* :: */[
+                                                                                                              3,
+                                                                                                              /* [] */0
+                                                                                                            ], null),
+                                                                                                        1
+                                                                                                      ]);
+                                                                                            })
+                                                                                        ],
+                                                                                        /* [] */0
+                                                                                      ]
+                                                                                    ]
                                                                                   ]
                                                                                 ]
                                                                               ]

jscomp/test/caml_compare_test.ml

@@ -77,6 +77,14 @@ let suites = Mt.[
     "eq_in_list2", (fun _ -> Eq ([[%bs.obj {x=2}]] = [[%bs.obj {x=2}]], true));
     "eq_with_list", (fun _ -> Eq ([%bs.obj {x=[0]}] = [%bs.obj {x=[0]}], true));
     "eq_with_list2", (fun _ -> Eq ([%bs.obj {x=[0]}] = [%bs.obj {x=[1]}], false));
+
+    __LOC__ , begin fun _ ->
+        Eq(compare Js.null (Js.Null.return [3]), -1)
+    end;
+    __LOC__ , begin fun _ ->
+        Eq(compare (Js.Null.return [3]) Js.null, 1)
+    end;
+
 ]
 ;;
 

lib/js/caml_obj.js

@@ -66,6 +66,10 @@ function caml_compare(_a, _b) {
     var a = _a;
     if (a === b) {
       return 0;
+    } else if (a === null) {
+      return -1;
+    } else if (b === null) {
+      return 1;
     } else {
       var a_type = typeof a;
       var b_type = typeof b;
@@ -82,7 +86,7 @@ function caml_compare(_a, _b) {
           }
         } else if (is_b_number) {
           return 1;
-        } else if (a_type === "boolean" || a_type === "undefined" || a === null) {
+        } else if (a_type === "boolean" || a_type === "undefined") {
           var x = a;
           var y = b;
           if (x === y) {