Leave this to me!

@Vinccool96 your enthusiasm is noted and appreciated 😄 thanks! But, we generally try to avoid "cookie licking" in the issue tracker: https://typescript-eslint.io/contributing/issues#issue-claiming. Sometimes folks will claim an issue and then drop out, leaving it hanging ("licked").

Is it normal that, in the v8 version of the rule, this doesn't create an error?

interface Base {
  name: string;
}
interface Derived {
  age: number;
}
// valid because extending multiple interfaces can be used instead of a union type
interface Both extends Base, Derived {}

I know it says in the comment valid because extending multiple interfaces can be used instead of a union type, but (the default option of allowInterfaces is never, so why is this valid?

That would be a separate discussion or issue from this one 🙂. Off the top of my head I don't remember, and it would be good to have that as a standalone discoverable discussion/issue.

How do I make the playground use v8 for the issue?

https://v8--typescript-eslint.netlify.app/play