owner-err/double-mut.wo:14:19: error WO-E303: cannot borrow `it` as `mut` twice in the same call
  return swap(it, it)
                  ^
  owner-err/double-mut.wo:14:15: `it` first borrowed here
    return swap(it, it)
                ^

owner-err/double-mut.wo:18:29: error WO-E303: cannot borrow `bag.items[i]` as `mut` twice in the same call
  return swap(bag.items[i], bag.items[i])
                            ^
  owner-err/double-mut.wo:18:15: `bag.items[i]` first borrowed here
    return swap(bag.items[i], bag.items[i])
                ^