"Empty" Values Behave Strangely with getOwnPropertyDescriptor

[sebmarkbage]

  var c = __abstract('boolean', 'c');
  var x = {foo:1};
  if (c) x.bar = 2;
  result2 = Object.getOwnPropertyDescriptor(x, 'bar');
  
  var y = __abstract({foo:1}, 'y');
  __makeSimple(y);
  if (c) y.bar = 2;
  result4 = Object.getOwnPropertyDescriptor(y, 'bar');

  var _$1 = this;

  var __empty = {};
  var _0 = {
    value: void 0,
    writable: true,
    enumerable: true,
    configurable: true
  };
  var _4 = c;
  if (_4) _0.value = 2;else delete _0.value;
  _$1.result2 = _0;

  if (_4) {
    y.bar = 2;
  }

  var _$0 = _4 ? 2 : __empty;

  _$1.result4 = {
    value: _$0,
    writable: true,
    enumerable: true,
    configurable: true
  };

It effectively leaks when it doesn't go through a getter. In the first case it is as if the property on the descriptor is missing, not the descriptor itself. In the second case, it actually leaks the placeholder value.

[sebmarkbage]

I think this case is especially bad because you don't even need to use getOwnPropertyDescriptor for this one:

  var c = __abstract('boolean', 'c');
  var y = __abstract({foo:1}, 'y');
  __makeSimple(y);
  if (c) y.bar = 2;
  result = y.bar ? 'truthy' : 'falsy';

->

  var _$1 = this;

  var __empty = {};
  var _0 = c;

  if (_0) {
    y.bar = 2;
  }

  var _$0 = _0 ? 2 : __empty; // This turns into two truthy values. The second one should be `undefined`.

  _$1.result = _$0 ? "truthy" : "falsy";