Bug: [Typescript] Failing to declare first parameter of guard breaks type inference in enqueueActions if another guard accepts dynamic parameters

[taraldr]

XState version

XState version 5

Description

Hi, love XState - just ported my teams typescript clients to XState, and came across this bug I think you might find interesting.

Parameter inference seems to break if you have:

1. A guard which fails to declare the first parameter - () vs (_)
2. Another guard which uses the second parameter - (_, params: { some: string )})
3. An action using enqueueActions

This results in a typescript error on the action along the lines of, indicating that parameter type inference broke.

Type '{ type: "guardWithParams"; params: unknown; }' is not assignable to type '{ type: "guardWithParams"; params: { some: string; }; }'.

Workaround is always declaring the first parameter of all guards, even if unused.

@Andarist

Expected result

No type error.

Actual result

Type error.

Reproduction

https://stackblitz.com/edit/vitejs-vite-iqaqw4d9?file=src%2Fmain.ts

Additional context

v5.16.0

[taraldr]

Also observing the same behaviour if you have:

1. An action which fails to declare the first parameter
2. Another action which uses the second parameter
3. A third action using enqueueActions

Repro: https://stackblitz.com/edit/vitejs-vite-kemb2g?file=src%2Fmain.ts&view=editor

[taraldr]

Fixed broken repro links.

[Tetheta]

Thank you so much for posting this @taraldr I thought I was going crazy.

Been poring over my code for the past few hours trying to figure out why on earth it was complaining about this. In my case I had an action using typed params, which would work alone. But as soon as I added in anything else (guards/actions/etc) it would error on all of them. Incredibly frustrating to try and debug as a brand new XState user.

I thought it had to do with my enqueue actions usage or needing to better type my actions, had no idea this was the cause till I decided to work backward from the broken guards instead and saw this issue.