src/common/util.js/getAlignmentSize
function getAlignmentSize(value, tabWidth, startIndex = 0) {
  let size = 0;
  for (let i = startIndex; i < value.length; ++i) {
    if (value[i] === "\t") {
      // Tabs behave in a way that they are aligned to the nearest
      // multiple of tabWidth:
      // 0 -> 4, 1 -> 4, 2 -> 4, 3 -> 4
      // 4 -> 8, 5 -> 8, 6 -> 8, 7 -> 8 ...
      size = size + tabWidth - (size % tabWidth);
    } else {
      size++;
    }
  }

  return size;
}