Accept any string but keep auto complete

index.ts

// Intersect string with {}:

export type StateWords = | 'first' | 'second' | 'third' | string & {}

// Record<never, never> can also work:

export type StateWords = | 'first' | 'second' | 'third' | string & Record<never, never>
  
// These intersections trick TypeScript into thinking that it is a "different" string type that literal string types are not assignable to (and thus the union won't get reduced to only string).

type StringAutoComplete<T> = T | string & {}