mutable-proto-special-form.js

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// Any copyright is dedicated to the Public Domain.

// http://creativecommons.org/licenses/publicdomain/

//-----------------------------------------------------------------------------

var BUGNUMBER = 948583;

var summary =

  "Make __proto__ in object literals a special form not influenced by " +

  "|Object.prototype|";

print(BUGNUMBER + ": " + summary);

/**************

 * BEGIN TEST *

 **************/

var passed = true;

function performProtoTests(msg)

  print("Testing " + msg);

  assertEq(passed, true, "passed wrong at start of test set");

  assertEq(Object.getPrototypeOf({ __proto__: null }), null);

  assertEq(Object.getPrototypeOf({ __proto__: undefined }), Object.prototype);

  assertEq(Object.getPrototypeOf({ __proto__: 17 }), Object.prototype);

  var obj = {};

  assertEq(Object.getPrototypeOf({ __proto__: obj }), obj);

  assertEq(passed, true, "passed wrong at end of test set");

  print("Tests of " + msg + " passed!");

function poisonProto(obj)

  Object.defineProperty(obj, "__proto__",

                          configurable: true,

                          enumerable: true,

                          set: function(v) { passed = false; },

});

performProtoTests("initial behavior");

var desc = Object.getOwnPropertyDescriptor(Object.prototype, "__proto__");

var setProto = desc.set;

delete Object.prototype.__proto__;

performProtoTests("behavior after Object.prototype.__proto__ deletion");

Object.defineProperty(Object.prototype, "__proto__",

                        configurable: true,

                        enumerable: false,

                        set: function(v) { passed = false; },

});

performProtoTests("behavior after making Object.prototype.__proto__ a " +

                  "custom setter");

Object.defineProperty(Object.prototype, "__proto__", { set: undefined });

performProtoTests("behavior after making Object.prototype.__proto__'s " +

                  "[[Set]] === undefined");

try

  var superProto = Object.create(null);

  poisonProto(superProto);

  setProto.call(Object.prototype, superProto);

  performProtoTests("behavior after mutating Object.prototype.[[Prototype]]");

  // Note: The handler below will have to be updated to exempt a scriptable

  //       getPrototypeOf trap (to instead consult the target whose [[Prototype]]

  //       is safely non-recursive), if we ever implement one.

  var death = new Proxy(Object.create(null),

                        new Proxy({}, { get: function() { passed = false; } }));

  setProto.call(Object.prototype, death);

  performProtoTests("behavior after making Object.prototype.[[Prototype]] a " +

                    "proxy that throws for any access");

catch (e) {}

if (typeof reportCompare === "function")

  reportCompare(true, true);

print("Tests complete");