static <A> S treeViewToString_withoutHijackPrint(final TreeView<A> t, fO... _) {
  new LS out;
  treeViewToString_withoutHijackPrint_impl(t, 0, out, _);
  ret lines(out);
}

static <A> void treeViewToString_withoutHijackPrint_impl(TreeView<A> t, int indent, LS out, O... _) {
  if (t == null) ret;
  O stringifier = optPar stringifier(_);
  out.add(spaces(indent) + callStringifier(stringifier, t));
  for (TreeView<A> c : unnull(t.children()))
    treeViewToString_withoutHijackPrint_impl(c, indent+2, out, _);
}

Began life as a copy of #1021921