zip() throws (swallowed) error when closed synchronously in next() handler

[chrisguttandin]

Describe the bug

After enabling logging for notifications on stopped observables with config.onStoppedNotification I noticed that zip() sometimes throws an error which can't be delivered anymore in case the observable gets closed from within the next handler.

Firefox: TypeError: buffers is null
Chrome: TypeError: Cannot read properties of null (reading 'some')

The error originates from here:

rxjs/src/internal/observable/zip.ts

Line 91 in 081ca2b

if (buffers.some((buffer, i) => !buffer.length && completed[i])) {

Expected behavior

I would not expect this to happen. I think this case should be handled internally.

Reproduction code

import { NEVER, concat, config, first, of, zip } from 'rxjs';

config.onStoppedNotification = (notification) => {
  if (notification.kind === 'E') {
    throw notification.error;
  }
};

const source$ = concat(of(1), NEVER);

zip(source$).pipe(first()).subscribe();

Reproduction URL

https://stackblitz.com/edit/rxjs-qxrbts?devtoolsheight=60&file=index.ts

Version

7.4.0

Environment

I discovered this in an Angular App (v13.1) which also uses NgRx (v13) but I guess it's not relevant for this issue.

Additional context

I think adding a simple check if buffers is already null before calling buffers.some() should fix the issue. I would be happy to provide a PR with this fix.

[truebden]

I just faced this issue in my code too and it would be great to have the PR merged 😉