fix: use event generic in ServiceConfig type

[christianchown]

Hi. Ran into a typing problem when using MachineConfig. The following code does not compile in TypeScript with "strict": true

type TestContext = {};
type TestEvent =
  | { type: 'EVENT_WITH_PAYLOAD'; payload: string }
  | { type: 'OTHER_EVENT_WITH_PAYLOAD'; payload: number };

const services = {
  testService: (_context: TestContext, _event: TestEvent) => Promise.resolve(),
  testService2: (_context: TestContext, _event: TestEvent) => Promise.resolve(),
};

const partialMachineOptions: Partial<MachineOptions<TestContext, TestEvent>> = {
  services, 
  // Type ... is not assignable to type 'Record<string, ServiceConfig<TestContext, AnyEventObject>>'
  // ...
  // Types of parameters '_event' and 'event' are incompatible. 
  // Type 'AnyEventObject' is not assignable to type 'TestEvent'.
};

This is because ServiceConfig expects an InvokeCreator that uses AnyEventObject.

In TypeScript's strict mode, TestEvent is not compatible with AnyEventObject as all TestEvents are inferred as having a payload property.

This PR fixes the problem by having ServiceConfig (like the other types in MachineOptions) use the supplied event generic.

[changeset-bot]

🦋 Changeset is good to go

Latest commit: 8270d5a

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[davidkpiano]

Thanks! Would you mind adding a quick changeset?

[christianchown]

thanks for reviewing so swiftly @davidkpiano, changeset added!