Fixed issues with TEvent narrowing

.changeset/few-pianos-begin.md

@@ -0,0 +1,5 @@
+---
+'xstate': patch
+---
+
+Fixed an issue with `EventFrom` not being able to extract events that had a union of strings as their `type` (such as `{ type: 'INC' | 'DEC'; value: number; }`).

.changeset/thin-tools-repair.md

@@ -0,0 +1,5 @@
+---
+'xstate': patch
+---
+
+Fixed an issue with default `TEvent` (`{ type: string }`) not being correctly provided to inline transition actions.

packages/core/src/model.types.ts

@@ -5,7 +5,6 @@ import {
   BaseActionObject,
   Compute,
   EventObject,
-  ExtractEvent,
   MachineConfig,
   Prop,
   PropertyAssigner,
@@ -19,6 +18,12 @@ import {
   TypegenDisabled
 } from './typegenTypes';
 
+// real `ExtractEvent` breaks `model.assign` inference within transition actions
+type SimplisticExtractEvent<
+  TEvent extends EventObject,
+  TEventType extends TEvent['type']
+> = TEvent extends { type: TEventType } ? TEvent : never;
+
 export interface Model<
   TContext,
   TEvent extends EventObject,
@@ -28,10 +33,10 @@ export interface Model<
   initialContext: TContext;
   assign: <TEventType extends TEvent['type'] = TEvent['type']>(
     assigner:
-      | Assigner<TContext, ExtractEvent<TEvent, TEventType>>
-      | PropertyAssigner<TContext, ExtractEvent<TEvent, TEventType>>,
+      | Assigner<TContext, SimplisticExtractEvent<TEvent, TEventType>>
+      | PropertyAssigner<TContext, SimplisticExtractEvent<TEvent, TEventType>>,
     eventType?: TEventType
-  ) => AssignAction<TContext, ExtractEvent<TEvent, TEventType>>;
+  ) => AssignAction<TContext, SimplisticExtractEvent<TEvent, TEventType>>;
   events: Prop<TModelCreators, 'events'>;
   actions: Prop<TModelCreators, 'actions'>;
   reset: () => AssignAction<TContext, any>;

packages/core/src/types.ts

@@ -455,10 +455,7 @@ export type TransitionConfigOrTarget<
 export type TransitionsConfigMap<TContext, TEvent extends EventObject> = {
   [K in TEvent['type'] | '' | '*']?: K extends '' | '*'
     ? TransitionConfigOrTarget<TContext, TEvent>
-    : TransitionConfigOrTarget<
-        TContext,
-        TEvent extends { type: K } ? TEvent : never
-      >;
+    : TransitionConfigOrTarget<TContext, ExtractEvent<TEvent, K>>;
 };
 
 type TransitionsConfigArray<TContext, TEvent extends EventObject> = Array<
@@ -1657,7 +1654,11 @@ export type Spawnable =
 export type ExtractEvent<
   TEvent extends EventObject,
   TEventType extends TEvent['type']
-> = TEvent extends { type: TEventType } ? TEvent : never;
+> = TEvent extends any
+  ? TEventType extends TEvent['type']
+    ? TEvent
+    : never
+  : never;
 
 export interface BaseActorRef<TEvent extends EventObject> {
   send: (event: TEvent) => void;
@@ -1840,8 +1841,8 @@ type ResolveEventType<T> = ReturnTypeOrValue<T> extends infer R
 export type EventFrom<
   T,
   K extends Prop<TEvent, 'type'> = never,
-  TEvent = ResolveEventType<T>
-> = IsNever<K> extends true ? TEvent : Extract<TEvent, { type: K }>;
+  TEvent extends EventObject = ResolveEventType<T>
+> = IsNever<K> extends true ? TEvent : ExtractEvent<TEvent, K>;
 
 export type ContextFrom<T> = ReturnTypeOrValue<T> extends infer R
   ? R extends StateMachine<

packages/core/test/typeHelpers.test.ts

@@ -183,6 +183,20 @@ describe('EventFrom', () => {
     // @ts-expect-error
     acceptUserModelEventSubset({ type: 'eventThatDoesNotExist' });
   });
+
+  it('should correctly extract events from events having union of strings as their `type`', () => {
+    const machine = createMachine({
+      schema: {
+        events: {} as { type: 'INC' | 'DEC' }
+      }
+    });
+
+    type MachineEvent = EventFrom<typeof machine, 'INC'>;
+
+    const acceptEvent = (_event: MachineEvent) => {};
+
+    acceptEvent({ type: 'INC' });
+  });
 });
 
 describe('MachineOptionsFrom', () => {

packages/core/test/types.test.ts

@@ -565,6 +565,23 @@ describe('events', () => {
       }
     });
   });
+
+  it('should provide the default TEvent to transition actions when there is no specific TEvent configured', () => {
+    createMachine({
+      schema: {
+        context: {} as {
+          count: number;
+        }
+      },
+      on: {
+        FOO: {
+          actions: (_context, event) => {
+            ((_accept: string) => {})(event.type);
+          }
+        }
+      }
+    });
+  });
 });
 
 describe('interpreter', () => {