// line starts at 1
svoid printLineWithContext(S text, int line) {
  print();
  L<S> lines = lines(text);
  for (int i = max(1, line-5); i <= min(l(lines), line+5); i++)
    print((i == line ? "* " : "  ") + "LINE " + i + ": " + lines.get(i-1));
  print();
}

Began life as a copy of #1015769