PhutilInvisibleSyntaxHighlighter.php

<?php

final class PhutilInvisibleSyntaxHighlighter extends Phobject {

  private $config = array();

  public function setConfig($key, $value) {
    $this->config[$key] = $value;
    return $this;
  }

  public function getHighlightFuture($source) {
    $keys      = array_map('chr', range(0x0, 0x1F));
    $vals      = array_map(
      array($this, 'decimalToHtmlEntityDecoded'), range(0x2400, 0x241F));

    $invisible = array_combine($keys, $vals);

    $result = array();
    foreach (str_split($source) as $character) {
      if (isset($invisible[$character])) {
        $result[] = phutil_tag(
          'span',
          array('class' => 'invisible'),
          $invisible[$character]);

        if ($character === "\n") {
          $result[] = $character;
        }
      } else {
        $result[] = $character;
      }
    }

    $result = phutil_implode_html('', $result);
    return new ImmediateFuture($result);
  }

  private function decimalToHtmlEntityDecoded($dec) {
    return html_entity_decode("&#{$dec};");
  }

}