const Schema = z
  .union([WithB, WithoutB])
  .and(z.union([WithC, WithoutC]))
  .and(z.union([WithD, WithoutD]));

const Schema = z
  .union([WithB, WithoutB])
  .and(z.union([WithC, WithoutC]))
  .and(z.union([WithD, WithoutD]));

const BaseReservation = z.object({
  reservationId: z.number(),
  reservedBy: z.string(),
  haveRoom: z.coerce.boolean().default(false),
});

const WithRoom = z.object({
  haveRoom: z.literal(true),
  roomNumber: z.number(),
});

const Reservation = z.union([BaseReservation, WithRoom]);

console.log(
  Reservation.parse({ reservationId: 1, reservedBy: "Joe"})
);

const BaseReservation = z.object({
  reservationId: z.number(),
  reservedBy: z.string(),
  haveRoom: z.coerce.boolean().default(false),
});

const WithRoom = z.object({
  haveRoom: z.literal(true),
  roomNumber: z.number(),
});

const Reservation = z.union([BaseReservation, WithRoom]);

console.log(
  Reservation.parse({ reservationId: 1, reservedBy: "Joe"})
);