defer type doesn't handle void correctly

[mhverbakel]

Bug Report

Current Behavior
When using defer with a () => void factory, the return type will be Observable<any>.

Reproduction
https://stackblitz.com/edit/rxjs-gm1wy5

import { defer } from 'rxjs';

const example = defer(() => {});

// Type of example is Observable<any> but should be Observable<never>.

Expected behavior
When using defer with a () => void factory, the return type will be Observable<never>.

Possible Solution
Adding the following to the declaration:

function defer(observableFactory: () => void): Observable<never>;

[cartant]

I don't agree with the expected behaviour. defer should return an ObservableInput and void is not an ObservableInput.

[mhverbakel]

Fine with me, but then | void should be removed from https:/ReactiveX/rxjs/blob/6.5.2/src/internal/observable/defer.ts#L55.

[cartant]

Yikes. I didn't even realise that was there. This should definitely have two signatures.