retry(0) behavior changed in RxJS 7 and it is inconsitent with expectations (and documentation)

[vteslenko]

Bug Report

Current Behavior
Calling retry(0) will produce EMPTY obervable, so upstream will never be subscribed to.

retry(0) => 0 upstream subscriptions.
retry(1) => 1 upstream subscription and up to 1 resubscription.
retry(2) => 1 upstream subscription and up to 2 resubscriptions.

This breaks the scenario when retries can be turned on and off with a parameter.

Expected behavior
Calling retry(0) will produce an operator that subscribes to upstream only once.

retry(0) => 1 upstream subscription.
retry(1) => 1 upstream subscription and up to 1 resubscription.
retry(2) => 1 upstream subscription and up to 2 resubscriptions.

With previos behavior retry(param) where param=0 just turns retries off.

Reproduction

import { of } from "rxjs";
import { map, retry } from "rxjs/operators";

const source = of("World").pipe(
  map(x => `Hello ${x}!`),
  retry(0)
);

source.subscribe(console.log);

Ver 6.6.7: https://rxjs-fdhbub.stackblitz.io
You will see "Hello World" in the console once.

Ver 7.0.0: https://rxjs-xeymgx.stackblitz.io
The console will be empty.

Possible Solution
retry(0) should work as in 6.6.7, as it aligns with expectations that there always will be one upstream subscription.

[josepot]

Yep, I also think that this is a bug, because the following test currently fails:

  it('should not alter the source when the number of retries is smaller than 1', () => {
    const source = cold('--1-2-3-#');
    const subs =       ['^       !'];

    const expected =    '--1-2-3-#';
    const unsub =       '         !';

    const result = source.pipe(retry(0));

    expectObservable(result, unsub).toBe(expected);
    expectSubscriptions(source.subscriptions).toBe(subs);
  })

It's an easy fix. I'm pretty sure that the PR that I've opened fixes the issue.