JSON.stringify throws cyclic value! with cycle-avoiding replacer

[dckc]

I'm trying port the serialize ibid cycle from @agoric/SwingSet. xs throws cyclic value! at https://github.com/Agoric/marshal/blob/v0.0.1/marshal.js#L398

I reduced it to this function; if I run this in node, it works as expected. If I call it from a main.js under xs, it throws:

export function cycleFun() {
  const cycle = ['a', 'x', 'c'];
  cycle[1] = cycle;

  const seen = new Set();

  function skipSeen(k, v) {
    if (seen.has(v)) {
      return undefined;
    }
    seen.add(v);
    return v;
  }

  return JSON.stringify(cycle, skipSeen);
}

console.log(cycleFun());

I think the JSON.stringify spec says this should work.

I looked at xsJSON.c... is it checking for cycles before calling replacer or something? I'm struggling to see if the logic is quite the same as the spec.

cc @warner

[phoddie]

Curious. The snippet also works in Safari. We'll take a look. Thanks for the standalone test case. That will help.

[phoddie]

Fixed!