Hono client typesafety for APIs with the expand or include pattern for relationships

[ashar-nadeem-lumi]

We're using Hono with Hono client for our REST API as well as data fetching layers. The setup looks something like this:

// server

export function jsonResponse<T extends object>(
    schema: z.Schema<T>,
    data: T,
    status: ContentfulStatusCode,
): TypedResponse<T> {
    return getContext().json(schema.parse(data), status) as unknown as TypedResponse<T>;
}

export type GetAdminsResponse = z.infer<typeof getAdminsResponseSchema>;
export const getAdminsResponseSchema = z.array(
    z.object({
        id: z.string().length(16),
        name: z.string().min(1),
        email: z.string().email(),
    }),
);

export const adminsRoute = new Hono()
    .get("/", authenticate, async (): Promise<TypedResponse<GetAdminsResponse>> => {
        const admins = await db.select().from(adminsTable);
        return jsonResponse(getAdminsResponseSchema, admins, 200);
    });

// client

export async function callApi<T, U extends number = StatusCode, F extends ResponseFormat = ResponseFormat>(
    fn: () => Promise<ClientResponse<T, U, F>>,
): Promise<T> {
    const resp = await fn();
    if (!resp.ok) {
        throw new Error(errorResponseBodySchema.parse(await resp.json()).message);
    }
    if (resp.headers.get("content-type")?.includes("application/json")) {
        return (await resp.json()) as T;
    }
    return resp as T;
}

const {
    data: admins,
    isLoading: isGetAdminsLoading,
    refetch: refetchAdmins,
} = useQuery({
    queryKey: ["admins"],
    queryFn: () => callApi(() => api.admins.$get()),
});

Now lets say I wanted to include a query param using zValidator, like expand. This param would take an array of relations of the admin entity that we want to expand, for example, ["businesses", "followers"].

Altering the query at the DB level is very easy, we'd just selectively join and add those to the select. Even ignoring zod for a second, how can we use generics to make Hono client know that if certain values are present in the expand query param, the return type of the endpoint changes?