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

🔎 Search Terms

object with all context-sensitive properties, self referencial types, xstate

🕗 Version & Regression Information

Tested with TypeScript 7.0.2, the issue exists even in versions as old as 4.4.4

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=6.0.3#code/PTAEAcCcHsCMBsCmBbAXKAJtRBnAdgOQAuoAlngGaKSgAioAxtJJIg0fAJ4A0j0eRRAA8SAQzwZQOIqMGhRreXk4AoBq1mIAsqIYALcogAUAbxWgyeUkVKj46AESiH3c3wHCi6E6ArRo6ACMoAC+rhbSmjjebhaiMRaJoIgCkJzoRkweIryRggCUoAC8AHygZklJWYIisZUgoAB6APx1SXmIbYkNLV0hdf0W-SH5KioNONDwAK42-OiiGJKioNM4iEg4OKB4-AC01Z5763g41qQAbogQMODURJygAAYA+uh40-DwT6BqGoI6fSGUxucjnOyOZzhdw1LzlXz+IKhaEdaLlOrxdGVZKpdKgTL8WG5GQFYplCrYmGeLoWHqtSlSEmdBl0vrQpJvHafeADNzDUYqDBseAKa5ZaSMf7aXQGPCIVBuAA89E8KQw2wpFjBNghoAA1ohONAKHQANoOVEOAC67KpInQcAAVmwiLbUQlKqaAMqWfWG41mi1MnDWq0e7EpIhpZoZQ72wNxojW4madBewqlUAXaCkDC2jkxrlfPq8oYlOpGIUUbWkeagACSQoE1k4AHlYM72MqShny9jaGMHncG02bA9FQAVMpFNwT5IiNXbcSqJLNfGgOeqiTbIwAOn3mLlV0gvdWeD1uwA7nhQGu5wqGZuF9vQE6XbeR5GW+3O0RJ2UH0pCculGJJ3kQY9B04YdGy-B4fxdf9ijcHxTQAaV9A0jRNCcw0-ZtxwndCrTKfogAOfEUiAA

💻 Code

// 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]> }

🙁 Actual behavior

The first createMachine invocation doesn't infer the type parameter correctly (it requires at least one non-context-sensitive property) and hence context and state parameters of entry are not inferred.

🙂 Expected behavior

The first createMachine invocation should infer the type parameter correctly without having to pass in a non-context-sensitive property leading to inference of context and state parameters of entry

Additional information about the issue

The premise is adding (or rather not adding) an extra useless property shouldn't make a difference to the inference

Empieza reproduciendo la diferencia de inferencia en el TypeScript Playground enlazado usando los dos ejemplos de createMachine. Lee la declaración genérica y el tipo IdentityObject en el issue, y luego sigue la inferencia de los parámetros de tipo del compilador para la propiedad entry sensible al contexto. Se considera terminado cuando la versión sin la propiedad _ adicional infiere context como { foo: number } y state como "a".