[v5] Remove Typestate

.changeset/small-papayas-wait.md

@@ -0,0 +1,5 @@
+---
+'xstate': major
+---
+
+Typings for `Typestate` have been removed. The reason for this is that types for typestates needed to be manually specified, which is unsound because it is possible to specify _impossible_ typestates; i.e., typings for a state's `value` and `context` that are impossible to achieve.

packages/core/actions/ExecutableAction.ts

@@ -34,7 +34,7 @@ export class ExecutableAction<
     this.type = actionObject.type;
     this.params = actionObject.params ?? {};
   }
-  public execute(state: State<TContext, TEvent, any>) {
+  public execute(state: State<TContext, TEvent>) {
     const context = this.context ?? state.context;
 
     return this._exec?.(context, state.event, {

packages/core/src/Machine.ts

@@ -3,29 +3,23 @@ import {
   MachineConfig,
   EventObject,
   AnyEventObject,
-  Typestate,
   MachineContext
 } from './types';
 import { StateMachine } from './StateMachine';
 
 export function createMachine<
   TContext extends MachineContext,
-  TEvent extends EventObject = AnyEventObject,
-  TTypestate extends Typestate<TContext> = { value: any; context: TContext }
+  TEvent extends EventObject = AnyEventObject
 >(
   config: MachineConfig<TContext, TEvent>,
   options?: Partial<MachineImplementations<TContext, TEvent>>
-): StateMachine<TContext, TEvent, TTypestate>;
+): StateMachine<TContext, TEvent>;
 export function createMachine<
   TContext extends MachineContext,
-  TEvent extends EventObject = AnyEventObject,
-  TTypestate extends Typestate<TContext> = { value: any; context: TContext }
+  TEvent extends EventObject = AnyEventObject
 >(
   definition: MachineConfig<TContext, TEvent>,
   implementations?: Partial<MachineImplementations<TContext, TEvent>>
-): StateMachine<TContext, TEvent, TTypestate> {
-  return new StateMachine<TContext, TEvent, TTypestate>(
-    definition,
-    implementations
-  );
+): StateMachine<TContext, TEvent> {
+  return new StateMachine<TContext, TEvent>(definition, implementations);
 }

packages/core/src/State.ts

@@ -5,7 +5,6 @@ import type {
   StateConfig,
   SCXML,
   TransitionDefinition,
-  Typestate,
   HistoryValue,
   ActorRef,
   MachineContext,
@@ -26,9 +25,8 @@ import type { StateMachine } from './StateMachine';
 
 export function isState<
   TContext extends MachineContext,
-  TEvent extends EventObject,
-  TTypestate extends Typestate<TContext> = { value: any; context: TContext }
->(state: object | string): state is State<TContext, TEvent, TTypestate> {
+  TEvent extends EventObject
+>(state: object | string): state is State<TContext, TEvent> {
   if (isString(state)) {
     return false;
   }
@@ -38,12 +36,11 @@ export function isState<
 
 export class State<
   TContext extends MachineContext,
-  TEvent extends EventObject = EventObject,
-  TTypestate extends Typestate<TContext> = { value: any; context: TContext }
+  TEvent extends EventObject = EventObject
 > {
   public value: StateValue;
   public context: TContext;
-  public history?: State<TContext, TEvent, TTypestate>;
+  public history?: State<TContext, TEvent>;
   public historyValue: HistoryValue<TContext, TEvent> = {};
   public actions: BaseActionObject[] = [];
   public meta: any = {};
@@ -79,7 +76,7 @@ export class State<
    */
   public children: Record<string, ActorRef<any>>;
   public tags: Set<string>;
-  public machine: StateMachine<TContext, TEvent, TTypestate> | undefined;
+  public machine: StateMachine<TContext, TEvent> | undefined;
   /**
    * Creates a new State instance for the given `stateValue` and `context`.
    * @param stateValue
@@ -89,9 +86,9 @@ export class State<
     TContext extends MachineContext,
     TEvent extends EventObject = EventObject
   >(
-    stateValue: State<TContext, TEvent, any> | StateValue,
+    stateValue: State<TContext, TEvent> | StateValue,
     context: TContext = {} as TContext
-  ): State<TContext, TEvent, any> {
+  ): State<TContext, TEvent> {
     if (stateValue instanceof State) {
       if (stateValue.context !== context) {
         return new State<TContext, TEvent>({
@@ -133,17 +130,15 @@ export class State<
   public static create<
     TContext extends MachineContext,
     TEvent extends EventObject = EventObject
-  >(config: StateConfig<TContext, TEvent>): State<TContext, TEvent, any> {
+  >(config: StateConfig<TContext, TEvent>): State<TContext, TEvent> {
     return new State(config);
   }
   /**
    * Creates a new `State` instance for the given `stateValue` and `context` with no actions (side-effects).
    * @param stateValue
    * @param context
    */
-  public static inert<TState extends State<any, any, any>>(
-    state: TState
-  ): TState;
+  public static inert<TState extends State<any, any>>(state: TState): TState;
   public static inert<
     TContext extends MachineContext,
     TEvent extends EventObject = EventObject
@@ -241,17 +236,9 @@ export class State<
    * Whether the current state value is a subset of the given parent state value.
    * @param parentStateValue
    */
-  public matches<TSV extends TTypestate['value']>(
+  public matches<TSV extends StateValue>(
     parentStateValue: TSV
-  ): this is State<
-    (TTypestate extends any
-      ? { value: TSV; context: any } extends TTypestate
-        ? TTypestate
-        : never
-      : never)['context'],
-    TEvent,
-    TTypestate
-  > & { value: TSV } {
+  ): this is State<TContext, TEvent> & { value: TSV } {
     return matchesState(parentStateValue as StateValue, this.value);
   }
 

packages/core/src/StateMachine.ts

@@ -6,7 +6,6 @@ import type {
   EventObject,
   MachineConfig,
   SCXML,
-  Typestate,
   Transitions,
   MachineSchema,
   StateNodeDefinition,
@@ -59,8 +58,7 @@ function resolveContext<TContext>(
 
 export class StateMachine<
   TContext extends MachineContext = any,
-  TEvent extends EventObject = EventObject,
-  TTypestate extends Typestate<TContext> = any
+  TEvent extends EventObject = EventObject
 > {
   private _context: () => TContext;
   public get context(): TContext {
@@ -172,7 +170,7 @@ export class StateMachine<
    *
    * @param state The state to resolve
    */
-  public resolveState(state: State<TContext, TEvent, any>): typeof state {
+  public resolveState(state: State<TContext, TEvent>): typeof state {
     const configuration = Array.from(
       getConfiguration(getStateNodes(this.root, state.value))
     );
@@ -191,9 +189,9 @@ export class StateMachine<
    * @param event The received event
    */
   public transition(
-    state: StateValue | State<TContext, TEvent, TTypestate> = this.initialState,
+    state: StateValue | State<TContext, TEvent> = this.initialState,
     event: Event<TEvent> | SCXML.Event<TEvent>
-  ): State<TContext, TEvent, TTypestate> {
+  ): State<TContext, TEvent> {
     const currentState = toState(state, this);
 
     return macrostep(currentState, event, this);
@@ -207,9 +205,9 @@ export class StateMachine<
    * @param event The received event
    */
   public microstep(
-    state: StateValue | State<TContext, TEvent, TTypestate> = this.initialState,
+    state: StateValue | State<TContext, TEvent> = this.initialState,
     event: Event<TEvent> | SCXML.Event<TEvent>
-  ): State<TContext, TEvent, TTypestate> {
+  ): State<TContext, TEvent> {
     const resolvedState = toState(state, this);
     const _event = toSCXMLEvent(event);
 
@@ -240,7 +238,7 @@ export class StateMachine<
     return transitionNode(this.root, state.value, state, _event) || [];
   }
 
-  public get first(): State<TContext, TEvent, TTypestate> {
+  public get first(): State<TContext, TEvent> {
     const pseudoinitial = this.resolveState(
       State.from(
         getStateValue(this.root, getConfiguration([this.root])),
@@ -256,21 +254,17 @@ export class StateMachine<
    * The initial State instance, which includes all actions to be executed from
    * entering the initial state.
    */
-  public get initialState(): State<TContext, TEvent, TTypestate> {
+  public get initialState(): State<TContext, TEvent> {
     const nextState = resolveMicroTransition(this, [], this.first, undefined);
     return macrostep(nextState, null as any, this);
   }
 
   /**
    * Returns the initial `State` instance, with reference to `self` as an `ActorRef`.
    */
-  public getInitialState(): State<TContext, TEvent, TTypestate> {
+  public getInitialState(): State<TContext, TEvent> {
     const nextState = resolveMicroTransition(this, [], this.first, undefined);
-    return macrostep(nextState, null as any, this) as State<
-      TContext,
-      TEvent,
-      TTypestate
-    >;
+    return macrostep(nextState, null as any, this) as State<TContext, TEvent>;
   }
 
   public getStateNodeById(stateId: string): StateNode<TContext, TEvent> {
@@ -297,11 +291,11 @@ export class StateMachine<
 
   public createState(
     stateConfig: State<TContext, TEvent> | StateConfig<TContext, TEvent>
-  ): State<TContext, TEvent, TTypestate> {
+  ): State<TContext, TEvent> {
     const state =
       stateConfig instanceof State
         ? stateConfig
-        : (new State(stateConfig) as State<TContext, TEvent, TTypestate>);
+        : (new State(stateConfig) as State<TContext, TEvent>);
     state.machine = this;
     return state;
   }

packages/core/src/actor.ts

@@ -104,10 +104,7 @@ export function spawnObservable<T extends EventObject>(
   return spawn(createObservableBehavior(lazyObservable), name);
 }
 
-export function spawnMachine(
-  machine: StateMachine<any, any, any>,
-  name?: string
-) {
+export function spawnMachine(machine: StateMachine<any, any>, name?: string) {
   return spawn(createMachineBehavior(machine), name);
 }
 
@@ -130,7 +127,7 @@ export function spawnFrom<
   TEvent extends EventObject,
   TEmitted extends State<any, any>
 >(
-  entity: StateMachine<TEmitted['context'], any, TEmitted['event']>,
+  entity: StateMachine<TEmitted['context'], TEmitted['event']>,
   name?: string
 ): ObservableActorRef<TEvent, TEmitted>;
 export function spawnFrom<TEvent extends EventObject>(

packages/core/src/behaviors.ts

@@ -492,7 +492,7 @@ export function createBehaviorFrom<
   TEvent extends EventObject,
   TEmitted extends State<any, any>
 >(
-  entity: StateMachine<TEmitted['context'], any, TEmitted['event']>
+  entity: StateMachine<TEmitted['context'], TEmitted['event']>
 ): Behavior<TEvent, TEmitted>;
 export function createBehaviorFrom<TEvent extends EventObject>(
   entity: InvokeCallback