Mutation function arguments type correction

[Lisenish]

I wanted to do a PR but decided to discuss before that.

I think we have a mistake with types of mutation function here:
https://github.com/tannerlinsley/react-query/blob/master/src/core/types.ts#L264
https://github.com/tannerlinsley/react-query/blob/master/src/core/types.ts#L273

I suppose it should be ...variables: TVariables instead of just variables: TVariable because now if you have several arguments in mutation function there is no way to type them all in a clean way.

E.g. I want to provide types for two argumentsTVariables = [string, number], but now if I do so it will lead to a situation where I have to call mutation function in that way mutation(['someStr', 42]) and I want it to be mutation('someStr', 42)

[TkDodo]

I don't think this would work. As you have pointed out with your second link, there is an overloaded function that has the config as the last parameter. You can only have varargs at the end of a parameter list, so, to take your example:

mutation('someStr', 42, { onSuccess })

wouldn't really work I think. TypeScript also yields the following error if I try to do that in a playground

A rest parameter must be last in a parameter list.(1014)

[Lisenish]

@TkDodo Actually it's a different type and not an overload but anyway, you were right I missed config object for the second type during my testing.

But thanks to TS 4.0 variadic tuples I think we can make it work, take a look at your fixed example

[TkDodo]

oh that is really nice :)

[stefanprobst]

will this be fixed in v3?