/**
 * Function used to assert a given code path is unreachable
 */
export function unreachable(): never
/**
 * Function used to assert a given code path is unreachable.
 * Very useful for ensuring switches are exhaustive:
 *
 * ```ts
 * switch (a.type) {
 *   case Types.A:
 *   case Types.B:
 *     break
 *   default:
 *     unreachable(a) // will cause a build error if there was
 *                    // a Types.C that was not checked
 * }
 * ```
 *
 * @param value Value to be asserted as unreachable
 */
// NOTE: Uses separate overloads, _not_ `value?: never`, to not allow `undefined` to be passed

export function unreachable(value: never): never
export function unreachable(value?: never): never {
  throw new Error(
    arguments.length === 0
      ? 'unreachable'
      : `unreachable (${JSON.stringify(value)})`,
  )
}