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It's probably not possible to make the same update to useActorRef for react and vue since the type is made optional by spreading options as the last function argument, but useActorRef has a third parameter observerOrListener, which does not allow to spread options to make them optional:

You can create [options?, observerOrListener?], make the first element required conditionally and spread the result. This way you will make the second argument conditionally required while keeping the third one optional

You can create [options?, observerOrListener?], make the first element required conditionally and spread the result. This way you will make the second argument conditionally required while keeping the third one optional

@Andarist not sure this works. I tried various implementations, but the issue is that making a parameter conditionally required requires to spread it, but spread is allowed only for the last parameter.

This below doesn’t work A rest element must be last in a destructuring pattern.ts(2462):

export function useActorRef<TLogic extends AnyActorLogic>(
  machine: TLogic,
  ...[...[options], observerOrListener]: [
    options: ConditionalRequired<
      [
        options?: ActorOptions<TLogic> & {
          [K in RequiredOptions<TLogic>]: unknown;
        }
      ],
      IsNotNever<RequiredOptions<TLogic>>
    >,
    observerOrListener?:
      | Observer<SnapshotFrom<TLogic>>
      | ((value: SnapshotFrom<TLogic>) => void)
  ]
): Actor<TLogic>

These two solutions below make the parameter always required:

export function useActorRef<TLogic extends AnyActorLogic>(
  machine: TLogic,
  ...[options, observerOrListener]: [
    options: ConditionalRequired<
      [
        options?: ActorOptions<TLogic> & {
          [K in RequiredOptions<TLogic>]: unknown;
        }
      ],
      IsNotNever<RequiredOptions<TLogic>>
    >,
    observerOrListener?:
      | Observer<SnapshotFrom<TLogic>>
      | ((value: SnapshotFrom<TLogic>) => void)
  ]
): Actor<TLogic>

export function useActorRef<TLogic extends AnyActorLogic>(
  machine: TLogic,
  ...[options, observerOrListener]: [
    ConditionalRequired<
      [
        options?: ActorOptions<TLogic> & {
          [K in RequiredOptions<TLogic>]: unknown;
        }
      ],
      IsNotNever<RequiredOptions<TLogic>>
    >['0'],
    observerOrListener?:
      | Observer<SnapshotFrom<TLogic>>
      | ((value: SnapshotFrom<TLogic>) => void)
  ]
): Actor<TLogic>

I also tried other options without much success. What do you think?

Those type helpers are not too readable anyway today so I wouldn't try to reuse them at all costs. At the very least something along those lines should work:

export function useActorRef<TLogic extends AnyActorLogic>(
  machine: TLogic,
  ...[options, observerOrListener]: IsNotNever<
    RequiredOptions<TLogic>
  > extends true
    ? [
        options: ActorOptions<TLogic> & {
          [K in RequiredOptions<TLogic>]: unknown;
        },
        observerOrListener?:
          | Observer<SnapshotFrom<TLogic>>
          | ((value: SnapshotFrom<TLogic>) => void),
      ]
    : [
        options?: ActorOptions<TLogic>,
        observerOrListener?:
          | Observer<SnapshotFrom<TLogic>>
          | ((value: SnapshotFrom<TLogic>) => void),
      ]
): Actor<TLogic>;

I don't mind some mild repetition.

@Andarist added type tests for required input and changeset. I marked this as a patch release, since I would consider this a bug fix. Let me know if this works.

LGTM - I just left one comment to address

My useMachine calls requires an empty object as a second parameter after this PR, even if there is no input required in any actors. Is that just the price I pay here?

@pckilgore please provide a repro case so we can take a look at your case

@pckilgore if your input is in the form { input: { value?: string; }} it will result required since only value is optional, whereas input is required to be defined

I was able to fix by updating xstate itself to 5.19 from 5.18. Yarn didn't give me any peer dependency warnings about the mismatch, which isn't what I would have expected?

Sorry to bother.

@pckilgore if your input is in the form { input: { value?: string; }} it will result required since only value is optional, whereas input is required to be defined

That would have still been odd, because I would have expected typescript to accept { input: {} } in that circumstance, not just {} as the second parameter. Appreciate the suggestion!

Yes, I would expect { input: {} } as well. Was it working with just {}? If so I wouldn’t be sure, definitely a repro is needed