Describe the bug

function handleObservableOrNext<T>(
  observable: Observable<T>,
  observerOrNext?: Partial<Observer<T>> | ((value: T) => void)
) {
  observable.subscribe(observerOrNext);
  // type error here
}

Expected behavior

no type error

Reproduction code

As described above

Reproduction URL

https://stackblitz.com/edit/typescript-vrgcva

Version

latest

Environment

No response

Additional context

• Should the next param here be optional?
  

  rxjs/src/internal/Observable.ts

  Line 78 in 081ca2b

  subscribe(next: (value: T) => void): Subscription;

  
  I think this param should be optional, since the implements of the overload support optional
  

  rxjs/src/internal/Observable.ts

  Line 214 in 081ca2b

  observerOrNext?: Partial<Observer<T>> | ((value: T) => void) | null,

• Are the overloads here good overloads?
  According to Writing Good Overloads in typescript handbook, with the same argument count and same return type, I don't think 2 different overloads here is good overloads.

Always prefer parameters with union types instead of overloads when possible.

could be merged into one overload function like

subscribe(observer?: Partial<Observer<T>> | ((value: T) => void)): Subscription;

ref: https://www.typescriptlang.org/docs/handbook/2/functions.html#writing-good-overloads