New error: Type instantiation is excessively deep and possibly infinite.

[amcasey]

This one's actually new in 3.8. There are some additional errors in 3.9 - I'll post them below.

https://github.com/davidkpiano/xstate/blob/2e0bd5dcb11c8ffc5bfc9fba1d3c66fb7546c4bd/packages/core/src/stateUtils.ts#L157

packages/core/src/stateUtils.ts:157:36 - error TS2589: Type instantiation is excessively deep and possibly infinite.

157   return getValueFromAdj(rootNode, getAdjList(config));
                                       ~~~~~~~~~~~~~~~~~~

packages/core/src/State.ts:181:12 - error TS2589: Type instantiation is excessively deep and possibly infinite.

181     return new State(config);
               ~~~~~~~~~~~~~~~~~

packages/core/src/interpreter.ts:208:5 - error TS2589: Type instantiation is excessively deep and possibly infinite.

208     this.parent = parent;
        ~~~~~~~~~~~~~~~~~~~~

packages/core/src/interpreter.ts:783:13 - error TS2345: Argument of type '{ type: string; data: any; }' is not assignable to parameter of type 'string | EventObject | Event<EventObject>[] | Event<EventObject>'.
  Object literal may only specify known properties, and 'data' does not exist in type 'EventObject'.

783             data: err
                ~~~~~~~~~

To repro:

1. yarn
2. tsc -b -f tsconfig.monorepo.json

[amcasey]

3.9 errors:

packages/core/src/stateUtils.ts:157:36 - error TS2589: Type instantiation is excessively deep and possibly infinite.

157   return getValueFromAdj(rootNode, getAdjList(config));
                                       ~~~~~~~~~~~~~~~~~~

packages/core/src/actions.ts:108:9 - error TS2783: 'type' is specified more than once, so this usage will be overwritten.

108         type,
            ~~~~

  packages/core/src/actions.ts:109:9
    109         ...exec,
                ~~~~~~~
    This spread always overwrites this property.

packages/core/src/State.ts:181:12 - error TS2589: Type instantiation is excessively deep and possibly infinite.

181     return new State(config);
               ~~~~~~~~~~~~~~~~~

packages/core/src/interpreter.ts:208:5 - error TS2589: Type instantiation is excessively deep and possibly infinite.

208     this.parent = parent;
        ~~~~~~~~~~~~~~~~~~~~

packages/core/src/interpreter.ts:783:13 - error TS2345: Argument of type '{ type: string; data: any; }' is not assignable to parameter of type 'string | EventObject | Event<EventObject>[] | Event<EventObject>'.
  Object literal may only specify known properties, and 'data' does not exist in type 'EventObject'.

783             data: err
                ~~~~~~~~~

packages/core/src/StateNode.ts:285:5 - error TS2322: Type 'MachineOptions<TContext, any> & Partial<MachineOptions<TContext, TEvent>>' is not assignable to type 'MachineOptions<TContext, TEvent>'.
  Types of property '_parent' are incompatible.
    Type '(StateNode<TContext, any, any, any> & StateNode<TContext, any, TEvent, any>) | undefined' is not assignable to type 'StateNode<TContext, any, TEvent, any> | undefined'.
      Type 'StateNode<TContext, any, any, any> & StateNode<TContext, any, TEvent, any>' is not assignable to type 'StateNode<TContext, any, TEvent, any> | undefined'.
        Type 'StateNode<TContext, any, any, any> & StateNode<TContext, any, TEvent, any>' is not assignable to type 'StateNode<TContext, any, TEvent, any>'.
          Types of property 'parent' are incompatible.
            Type '(StateNode<TContext, any, any, any> & StateNode<TContext, any, TEvent, any>) | undefined' is not assignable to type 'StateNode<TContext, any, TEvent, any> | undefined'.
              Type 'StateNode<TContext, any, any, any> & StateNode<TContext, any, TEvent, any>' is not assignable to type 'StateNode<TContext, any, TEvent, any> | undefined'.

285     this.options = Object.assign(createDefaultOptions<TContext>(), options);
        ~~~~~~~~~~~~

packages/core/src/StateNode.ts:1824:7 - error TS2322: Type 'TransitionsConfigArray<TContext, TEvent>' is not assignable to type '(TransitionConfig<TContext, EventObject> & { event: string; })[]'.
  Type '(TransitionConfig<TContext, ActionTypes.NullEvent extends TEvent["type"] ? Extract<TEvent, { type: TEvent["type"] & ActionTypes.NullEvent; }> : EventObject> & { ...; }) | (TransitionConfig<...> & { ...; }) | (TransitionConfig<...> & { ...; })' is not assignable to type 'TransitionConfig<TContext, EventObject> & { event: string; }'.
    Type 'TransitionConfig<TContext, ActionTypes.NullEvent extends TEvent["type"] ? Extract<TEvent, { type: TEvent["type"] & ActionTypes.NullEvent; }> : EventObject> & { ...; }' is not assignable to type 'TransitionConfig<TContext, EventObject> & { event: string; }'.
      Type 'TransitionConfig<TContext, ActionTypes.NullEvent extends TEvent["type"] ? Extract<TEvent, { type: TEvent["type"] & ActionTypes.NullEvent; }> : EventObject> & { ...; }' is not assignable to type 'TransitionConfig<TContext, EventObject>'.
        Types of property 'target' are incompatible.
          Type 'string | StateNode<TContext, any, ActionTypes.NullEvent extends TEvent["type"] ? Extract<TEvent, { type: TEvent["type"] & ActionTypes.NullEvent; }> : EventObject, any> | (string | StateNode<...>)[] | undefined' is not assignable to type 'string | StateNode<TContext, any, EventObject, any> | (string | StateNode<TContext, any, EventObject, any>)[] | undefined'.
            Type 'StateNode<TContext, any, ActionTypes.NullEvent extends TEvent["type"] ? Extract<TEvent, { type: TEvent["type"] & ActionTypes.NullEvent; }> : EventObject, any>' is not assignable to type 'string | StateNode<TContext, any, EventObject, any> | (string | StateNode<TContext, any, EventObject, any>)[] | undefined'.
              Type 'StateNode<TContext, any, ActionTypes.NullEvent extends TEvent["type"] ? Extract<TEvent, { type: TEvent["type"] & ActionTypes.NullEvent; }> : EventObject, any>' is not assignable to type 'StateNode<TContext, any, EventObject, any>'.
                The types of 'config.on' are incompatible between these types.
                  Type 'TransitionsConfigMap<TContext, ActionTypes.NullEvent extends TEvent["type"] ? Extract<TEvent, { type: TEvent["type"] & ActionTypes.NullEvent; }> : EventObject> | TransitionsConfigArray<...> | undefined' is not assignable to type 'TransitionsConfigMap<TContext, EventObject> | TransitionsConfigArray<TContext, EventObject> | undefined'.
                    Type 'TransitionsConfigMap<TContext, ActionTypes.NullEvent extends TEvent["type"] ? Extract<TEvent, { type: TEvent["type"] & ActionTypes.NullEvent; }> : EventObject>' is not assignable to type 'TransitionsConfigMap<TContext, EventObject> | TransitionsConfigArray<TContext, EventObject> | undefined'.
                      Type 'TransitionsConfigMap<TContext, ActionTypes.NullEvent extends TEvent["type"] ? Extract<TEvent, { type: TEvent["type"] & ActionTypes.NullEvent; }> : EventObject>' is not assignable to type 'TransitionsConfigMap<TContext, EventObject>'.
                        Type 'SingleOrArray<string | StateNode<TContext, any, ActionTypes.NullEvent extends TEvent["type"] ? Extract<TEvent, { type: TEvent["type"] & ActionTypes.NullEvent; }> : EventObject, any> | (TransitionConfig<...> & { ...; }) | undefined>' is not assignable to type 'SingleOrArray<string | StateNode<TContext, any, EventObject, any> | (TransitionConfig<TContext, EventObject> & { ...; }) | undefined>'.
                          Type 'StateNode<TContext, any, ActionTypes.NullEvent extends TEvent["type"] ? Extract<TEvent, { type: TEvent["type"] & ActionTypes.NullEvent; }> : EventObject, any>' is not assignable to type 'SingleOrArray<string | StateNode<TContext, any, EventObject, any> | (TransitionConfig<TContext, EventObject> & { ...; }) | undefined>'.

1824       onConfig = this.config.on;
           ~~~~~~~~

packages/core/src/StateNode.ts:1824:7 - error TS2589: Type instantiation is excessively deep and possibly infinite.

1824       onConfig = this.config.on;
           ~~~~~~~~~~~~~~~~~~~~~~~~~

[ahejlsberg]

I took a quick look. The excessively depth errors are caused by these two types in src\types.ts:

type TransitionsConfigMap<TContext, TEvent extends EventObject> = {
  [K in TEvent['type'] | NullEvent['type'] | '*']?: SingleOrArray<
    | TransitionConfigTargetShortcut<TContext, TEvent>
    | (TransitionConfig<
        TContext,
        K extends TEvent['type'] ? Extract<TEvent, { type: K }> : EventObject
      > & {
        event?: undefined;
      })
  >;
};

type TransitionsConfigArray<TContext, TEvent extends EventObject> = Array<
  {
    [K in TEvent['type'] | NullEvent['type'] | '*']: TransitionConfig<
      TContext,
      K extends TEvent['type'] ? Extract<TEvent, { type: K }> : EventObject
    > & {
      event: K;
    };
  }[TEvent['type'] | NullEvent['type'] | '*']
>;

The problem appears to be exploration of the conditional type constrains that keep spiraling until we hit the depth limiter. When I change K extends TEvent['type'] ? Extract<TEvent, { type: K }> : EventObject to just EventObject in each of the types, the check time drops by 50% and the type count drops by 60-70%. I'm not exactly sure what these types are doing, but simplifying them definitely has a major effect.

[DanielRosenwasser]

FYI @davidkpiano

[davidkpiano]

Working on a fix for this, but I found some odd type behavior:

type ResolvedEvent = ({
    type: "CHANGE";
    value: string;
} & {
    type: "CHANGE";
}) | ({
    type: "SAVE";
} & {
    type: "CHANGE";
})

function assign(event: ResolvedEvent) {
    return event.value;
}

This will produce the following error for event.value:

Property 'value' does not exist on type 'ResolvedEvent'.
  Property 'value' does not exist on type '{ type: "SAVE"; } & { type: "CHANGE"; }'.(2339)

I would expect ResolvedEvent to be narrowed to { type: 'CHANGE'; value: string } since { type: 'SAVE' } & { type: 'CHANGE' } should be never.

[ahejlsberg]

Working on a fix for this, but I found some odd type behavior

Are you sure you're using the 3.9 compiler? There's no error with the nightly build:

https://www.typescriptlang.org/play/index.html?ts=Nightly#code/C4TwDgpgBAShDOB7ANgNwgEwKLoHbCgF4oAKAbwFgAoKWqUSALigCIBhACQEEA5AcSwsA3NTpRUAQ2QBXCM3jAATgEtcAcxFUAvlABkUSjToM5rTrwHDqWgJRQAPqUNiTzFgGUuANUGad+52NwU3Zufl9rG2pqADNpXABjYGVEXCgJeHhlNVwSCDxgZjgkNEwcCHw7QNpFCGBpRTT8iuAAOkkZCD8gA

[davidkpiano]

Ah, no, I was using 3.8.3. Glad to see it's fixed - was that specific issue tracked?

[ahejlsberg]

Glad to see it's fixed - was that specific issue tracked?

Yes, it was fixed by #36696.

[vasilii-kovalev]

I'm facing the error in such a case:

type GetLetters<Text> = Text extends `${infer Letter}${infer Rest}` ? Letter | GetLetters<Rest> : never;
type Letters = GetLetters<"some very, very long text">;

The error appears when the text is longer than or equal to 24 characters.

Playground.