Bound Functions Referenced Before They're Initialized

[sebmarkbage]

I don't yet know where this happens in the code, nor do I have a small repro yet but I thought I'd flag it early. When I run #397 on Prepack itself I'm getting two cases where properties are added to a function before it is initialized.

_1mZ.resolve = _1n0;
...
var _1mZ = _2zX.bind(null, _1hY);

Maybe it has something to do with the normal serialization relying on hoisting but hoisting doesn't work with the .bind(...) optimization that tries to minimize duplicates.

[NTillmann]

We don't generally rely on function hoisting, but if you hit this there's certainly a bug somewhere in the cycle breaking. I need some help to reproduce it...

[sebmarkbage]

Ok, this isn't repro of the same exact issue. Instead of the function being assigned to this is reading the not-yet-bound function. Seems related.

(function() {

  function wrap(obj) {
    function A() {
      return obj.hello();
    }
    function B() {
      return obj.world();
    }
    A.B = B;
    return A;
  }

  let fooObj = {};
  let barObj = {};
  let fooFn = wrap(fooObj);
  let barFn = wrap(barObj);

  // Create a cycle  
  fooObj.bar = barFn;
  barObj.foo = fooFn;

  global.foo = fooFn;

})();

->

(function () {
  function _6(obj) {
    return obj.hello();
  }

  function _7(obj) {
    return obj.world();
  }

  var _3 = {
    foo: _0
  };

  var _2 = _6.bind(null, _3);

  var _4 = _7.bind(null, _3);

  _2.B = _4;
  var _1 = {
    bar: _2
  };

  var _0 = _6.bind(null, _1);

  var _5 = _7.bind(null, _1);

  _0.B = _5;
  foo = _0;
}).call(this);

[sebmarkbage]

Here's one that sort of repros the original issue:

(function() {

  function wrap(obj) {
    function A() {
      return obj.hello();
    }
    function B() {
      return obj.world();
    }
    A.B = B;
    return A;
  }

  let fooObj = {};
  let fooFn = wrap(fooObj);
  let barFn = wrap(fooObj);
  fooObj.bar = barFn;

  global.foo = fooFn;

})();

->

(function () {
  function _5() {
    return _1.hello();
  }

  function _6() {
    return _1.world();
  }

  _2.B = _3;
  var _1 = {
    bar: _2
  };

  var _0 = _5.bind(null);

  var _4 = _6.bind(null);

  _0.B = _4;

  var _2 = _5.bind(null);

  var _3 = _6.bind(null);

  foo = _0;
}).call(this);

[NTillmann]

Thanks for distilling the repro! That really helped.
Fixed by referenced merged pull request.