TanStack
Overly restrictive typing for mutation callbacks (`onSuccess` etc) 2
Describe the bug
Right now types are defined as void | Promise<unknown>. This restricts returning and discarding values.
() => void type allows returning anything from the function, but void | whatever allows only "Nothing or whatever".
This means that a simple pattern of
{ onSuccess: () => toast("Message") }
Doesn't work if toast returns anything (usually the toast id for future manipulation).
Your minimal, reproducible example
https://www.typescriptlang.org/play?#code/C4TwDgpgBA8gdgZQK4GMUQM4YIxQLxQAUAlPgHxQBuA9gJYAmAUCtXBsFAGZJwrYBcsRKnRZcBEuSgBvRlCgAnCMCQK4UAOQAJCABtd1DYwC+jRqEhDkaTBgBM+IqTwUaDKAB8oABQXUAtrQYEAA8PADWcNQA7nBkzKzsXDwodoLw1qL2jpIuMnKKyqrq2noGRsZAA
react-query version
4.0.10
TypeScript version
4.7.3
Additional context
The problem is minor and easily enough bypassed by either marking the callback as async or avoiding the shorthand syntax that returns implicitly.
Still, I think making the return type unknown entirely would be better ergonomics.
Also, found a similar issue here: https://github.com/TanStack/query/issues/2166
I agree making the return type unknown would be better, I could get to work on it.
Sure, though that's technically no different than just unknown.
Honestly, it feels like a Typescript bug, but I'm not ready to champion a cause with Typescript. And they might think it's a feature.