Throttle goes crazy in sync source, sync notifier scenario with trailing: true

[benlesh]

Originally reported here

Original Text (@OliverJAsh)

Another weird discovery: in v7.0.0-beta.10 this doesn't throw an error but it does still log 1 over 1000 times.

import * as Rx from "rxjs";
import { throttle } from "rxjs/operators";

const source = Rx.of(1).pipe(
  throttle(() => Rx.of(1), { leading: false, trailing: true })
);

source.subscribe(x => console.log(x));

https://stackblitz.com/edit/rxjs-compat-vswz6n

If someone can confirm this is not expected behaviour, I can try to send a PR with a test and a fix.

If I understand correctly, this is the expected behaviour as @josepot says:

If the source emits and completes synchronously, then I would expect for the operator to not capture any values during the durationSelector observable

So source should emit nothing and complete synchronously?

---

In RxJS v7 beta, the behaviour is different but still incorrect (at least in my mind): https://stackblitz.com/edit/rxjs-compat-mmjf6c. This never logs anything.

Ah, I believe this is because of this change: 4af0227. In my example the duration selector never emits anything, it only completes. That makes sense.