Type checking discriminated unions with adding new types

Question

Lets say I have the following typescript types:

enum EntityKind {
  Foo = 'foo',
  Bar = 'bar',
}

type Foo = {
  kind: EntityKind.Foo,
  foo: string
}

type Bar = {
  kind: EntityKind.Bar,
  bar: number
}

type Entity = (Foo | Bar) & {
  id: string,
  name: string
}

What I want is to be able to have the type checker fail when I add a new type to my enum. So what I'm hoping for is:

enum EntityKind {
  Foo = 'foo',
  Bar = 'bar',
  Baz = 'baz',
}

and I would get some kind of error that would require me to define a new type Baz and add it to the union.

Is this possible?

Answer 1

If you want an error in the type Entity you could add another type to the intersection that requires EntityKind to extend EntityUnion['kind']:

enum EntityKind {
  Foo = 'foo',
  Bar = 'bar',
}

type Foo = {
  kind: EntityKind.Foo,
  foo: string
}

type Bar = {
  kind: EntityKind.Bar,
  bar: number
}
type Check<T, U extends T> = {}

type EntityUnion = Foo | Bar 
type Entity = EntityUnion & {
  id: string,
  name: string
} & Check<EntityUnion['kind'], EntityKind>