Make Object.prototype an immutable prototype object (#317)

* make `Object.prototype` an immutable prototype object
* throw an exception on `Object.setPrototypeOf(Object.prototype, xxx)`
* do not throw an exception for `Reflect.setPrototypeOf(Object.prototype, xxx)`

Author: chqrlie

quickjs.c

@@ -6859,6 +6859,13 @@ static int JS_SetPrototypeInternal(JSContext *ctx, JSValue obj,
     sh = p->shape;
     if (sh->proto == proto)
         return TRUE;
+    if (p == JS_VALUE_GET_OBJ(ctx->class_proto[JS_CLASS_OBJECT])) {
+        if (throw_flag) {
+            JS_ThrowTypeError(ctx, "'Immutable prototype object \'Object.prototype\' cannot have their prototype set'");
+            return -1;
+        }
+        return FALSE;
+    }
     if (!p->extensible) {
         if (throw_flag) {
             JS_ThrowTypeError(ctx, "object is not extensible");

tests/test_builtin.js

@@ -220,6 +220,8 @@ function test()
     assert(Object.isExtensible(a), false, "extensible");
     assert(typeof a.y, "undefined", "extensible");
     assert(err, true, "extensible");
+
+    assert_throws(TypeError, () => Object.setPrototypeOf(Object.prototype, {}));
 }
 
 function test_enum()