Optional mutation type for the parameter of select in MutationStateOptions

[mohamedhamza12]

Hey, I'm currently working with gRPC endpoints using grpc-web and @tanstack/react-query. Because of this, if a mutation fails the type of error it returns is RpcError. I'm using useMutationState to return a an array of mutations but passing select to its options to return the error of each mutation always expects the error to be of type Error. My suggestion is passing an extra optional generic type parameter to useMutationState representing the mutation type, so something similar to the following:

type MutationStateOptions<TResult = MutationState, TMutation = Mutation> = {
    filters?: MutationFilters;
    select?: (mutation: TMutation) => TResult;
};
declare function useMutationState<TResult = MutationState, TMutation = Mutation>(options?: MutationStateOptions<TResult, TMutation>, queryClient?: QueryClient): Array<TResult>;

This would enable me to use the hook as follows:

  const mutationState = useMutationState<RpcError | null, Mutation<unknown, RpcError>>({
    select(mutation) {
      return mutation.state.error;
    },
  });

[TkDodo]

if you want to narrow error states, it has to be either globally with module augmentation or by doing runtime type narrowing (which is preferred)

[mohamedhamza12]

Well yes, that makes sense in my specific use case. More generally though, wouldn't it be good to be able to specify what the type of each mutation is specifically? For example, if you would want to change the type of other generic type parameters, not just the error type particularly