Guard against infinite loops

[ForbesLindesay]

This guards against infinite loops using the halting-problem module.

It catches simple cases like the following statically:

export default function ({Plugin, types: t}) {
  return new Plugin('ast-transform', {
    visitor: {
      Identifier(node) {
        var n = 100;
        while (true) n++;
        return t.identifier(node.name.split('').reverse().join(''));
      }
    }
  });
}

results in

while statement on line 6 has a constant test. Either it is always false (making the statement redundant) or it is an infinite loop.

It can catch more subtle infinite loops like the following by checking for a timeout (of say 5 seconds) in all loops. In this case it will just give you a message of "Infinite loop detected on line 6"

export default function ({Plugin, types: t}) {
  return new Plugin('ast-transform', {
    visitor: {
      Identifier(node) {
        var n = 100;
        while (n > 0) n++;
        return t.identifier(node.name.split('').reverse().join(''));
      }
    }
  });
}

[fkling]

This is great, thank you!

[kyldvs]

Awesome!

[cpojer]

This is awesome, thank you @ForbesLindesay !