fix(debounceTime): synchronous reentrancy of debounceTime no longer swallows the second value

[jayphelps]

Currently the second value is swallowed because hasValue is set to false in between the scheduling of the second and its execution.

fixes #2748

const results = [];
const source = new Rx.Subject();
const scheduler = new VirtualTimeScheduler();

source.debounceTime(0, scheduler).subscribe(value => {
  results.push(value);

  if (value === 1) {
    source.next(2);
  }
});
source.next(1);
scheduler.flush();

expect(results).to.deep.equal([1, 2]);

@kwonoj you had mentioned in #2748 that rxjs doesn't guarantee reentrancy, though I think in this case the fix is simple. Are there reasons to explicitly not do it in this case?

FWIW the regular debounce operator already supports reentrancy, so I added a test for it too. This all seems so familiar so perhaps we discussed this years ago and fixed only debounce lol

[kwonoj]

@jayphelps as long as it doesn't hurts current code execution, I don't think there's strong reason to explicitly block changes to allow reentrancy. Still in v5 without scheduler reentrancy is not gauranteed, means might work but mostly not work in general - not sure just fixing single operator gives huge value. If someone chains another operator doesn't work with reentrancy with fixed debouncetime, then consumer still will be blocked and have to reschedule it.

[rxjs-bot]

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[coveralls]

Coverage increased (+0.03%) to 97.109% when pulling 1050a5d on jayphelps:debounceTime into c1721e3 on ReactiveX:master.

[jayphelps]

Hmm Travis can’t seem to find Node v4. Maybe they removed it? I googled a bit, can’t find confirmation

[kwonoj]

🤔 weird, nvm seems failing to look it up but I also couldn't see anything related.

[kwonoj]

seems it was one time glitch. restarting job makes it work.

[benlesh]

LGTM

[lock]

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