useMutation adds undefined to TResult of MutateFunction type

Describe the bug

useMutation changes the return type of provided promise by adding undefined to it.

To Reproduce

const apiCall = () => new Promise<string>(resolve => resolve());

const useExample = async () => {
	const [mutateCall] = useMutation(apiCall);
	const response = await apiCall(); // string
	const mutateR = await mutateCall(); // string | undefined
};

Wrapping a function in useMutation adds a undefined to it’s returned promise

Expected behavior

The provided function’s return type should not be changed.

Desktop (please complete the following information):

• Version: 23

Additional context

I don’t see any reason why this would be required. Together with #1077 this is making migration to this library pretty unnecessarily painful by imposing this opinionated types.

[tannerlinsley]

I think the PR above fixes this issue. v3 will be awesome!

[boschni]

What about providing two mutate functions? One for callbacks and for promises?

Callback version:

const { mutate } = useMutation(apiMutate)

mutate({
  onSuccess: result => {
    console.log(result)
  },
  onError: error => {
    console.error(error)
  },
});

Promise version:

const { mutateAsync } = useMutation(apiMutate)

try {
  const result = await mutateAsync()
  console.log(result)
} catch (error) {
  console.error(error)
}

Then mutate would return nothing, mutateAsync would return a promise and throwOnError can be removed.