Using `retry()` with `Rx.Observable.spawn()` results in undefined values

[eschwartz]

RxJS version: 4.1.0

Code to reproduce:

Rx.Observable
  .spawn(function*() {
    return 'A';
  })
  .map((val) => {
    console.log(`map: ${val}`)
    throw new Error('fail');
  })
  .retry(2)
  .subscribe(
    (val) => console.log(`onNext: ${val}`),
    (err) => console.log(`onError: ${err.message}`),
    (complete) => console.log('complete')
  );

Expected behavior:

map: A
map: A
onError: fail

Actual behavior:

map: A
map: undefined
onError: fail

Additional information:

Using Rx.Observable.spawn causes the second attempt to emit undefined instead of "A".

Note that this works as expected, if using Rx.Observable.fromPromise instead:

Rx.Observable
  .fromPromise(() => Promise.resolve('A'))
  .map((val) => {
    console.log(`map: ${val}`)
    throw new Error('fail');
  })
  .retry(2)
  .subscribe(
    (val) => console.log(`onNext: ${val}`),
    (err) => console.log(`onError: ${err.message}`),
    (complete) => console.log('complete')
  );

// map: A
// map: A
// onError: fail

[eschwartz]

I noticed when running this in CodePen, that it works as expected with TypeScript, but it fails when using plain JS.

This may explain why it's not caught by existing test coverage.