Object.getOwnPropertyDescriptor can return just about anything

[Jason Orendorff]

On Tue, Apr 29, 2014 at 8:08 PM, Mark S. Miller <erights at google.com> wrote:
>> There aren’t any internal invariant sensitivities that I could find.  Once
>> such a non-standard descriptor is never directly used by any of the ordinary
>> object MOP operations
>
> I'm surprised and alarmed by this, and it seems wrong. It is also not what I
> think I remember. What about, for example, the invariant that an object
> cannot both claim that a property is non-configurable but then later change
> its alleged configuration?

As specified, proxies can do this:

  js> Object.isFrozen(proxy)
  true
  js> Object.getOwnPropertyDescriptor(proxy).configurable
  true

Of course the property is not really configurable. The extent of the
issue is that Object.getOwnPropertyDescriptor is not a reliable
reflection API.

-j