[Webkit-unassigned] [Bug 189030] For-in over a proxy with ownKeys handler hits non-enumerable keys

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=189030

--- Comment #1 from bakkot at gmail.com ---
This is probably related, so I'm going to add it as a comment here:

JSC can also print the same key twice. According to Allen Wirfs-Brock [1], "no duplicate names" is the most important property required by the spec, so this seems especially bad.

Sample code:

```
let a = {
  x: 0,
};

let b = {
  x: 0,
};


let pb = new Proxy(b, {
  ownKeys(target) {
    return Reflect.ownKeys(target);
  },
});

Object.setPrototypeOf(a, pb);


for (let key in a) {
  console.log(key);
}
```

This prints `x` twice.



[1] https://github.com/tc39/ecma262/issues/1281#issuecomment-411133580

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