Object with all context-sensitive properties requires at least one non-context-sensitive property for inference to work #64251

// problem: doesn't infer D correctly, context and state are any
createMachine({
  initial: "a",
  context: { foo: 1 },
  states: {
    a: {
      entry: (context, state) => {
        context
        // ^? any
        state
        // ^? any
      }
    }
  }
})

// solution: add a useless non-context-sensitive property `_: null` 
createMachine({
  initial: "a",
  context: { foo: 1 },
  states: {
    a: {
      entry: (context, state) => {
        context
        // ^? { foo: number }
        state
        // ^? "a"
      },
      _: null
    }
  }
})

declare const createMachine:
  <D extends {
    initial: keyof D["states"],
    context: object,
    states: {
      [S in keyof D["states"]]: {
        entry?: (context: D["context"], state: S) => void,
        _?: null
      }
    }
  }>
    (definition: IdentityObject<D>) =>
      D

type Identity<T> =
  T extends any
    ? ( T extends (...a: never) => unknown ? T :
        T extends object ? IdentityObject<T> :
        T
      )
    : never

type IdentityObject<T> =
  { [K in keyof T]: Identity<T[K]> }