Merge pull request #967 from andrewgordstewart/andrewgordstewart/add-tcontext-type-to-invoke-config

[andrewgordstewart]

With this change, the invoke.src property of a StateNodeConfig can perform type inference:

type UserContext = { foo: 'bar' };
type UserEvent = { type: 'READY' | 'SET' | 'GO' };
export const stateNode: StateNodeConfig<UserContext, any, UserEvent> = {
  invoke: {
    src: (ctx, event) => {
      switch (event.type) {
        case 'READY':
          // Property 'Foo' does not exist on type 'UserContext'. Did you mean 'foo'?ts(2551)
          return Promise.resolve(ctx.Foo);
        case 'SET':
          return Promise.resolve('SET');
        /// Type '"Go"' is not comparable to type '"READY" | "SET" | "GO"'.ts(2678)
        case 'Go':
          return Promise.resolve();
      }
    }
  }
};

See discussion starting here

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[davidkpiano]

Thanks @andrewgordstewart! Can you create a quick changeset? Just run yarn changeset in the root xstate directory (this will be a patch change).