<?php

final class WarningCustomField extends DifferentialCustomField {

  public function getFieldKey() {
    return 'mycompany:mycustomfield';
  }

  public function shouldAppearInPropertyView() {
    // This is required or the field won't be loaded on the detail page.
    return true;
  }

  public function renderPropertyViewValue(array $handles) {
    // This prevents it from actually rendering a property.
    return null;
  }

  public function getWarningsForRevisionHeader(array $handles) {
    $revision = $this->getObject();
    
    // Do some magic here to figure out if the branch the revision will land
    // onto is bad.
    $is_bad = some_magic($revision);
    
    $warnings = array();
    
    if ($is_bad) {
      $warnings[] = pht(
        'IMPORTANT! The branch this revision is targeting has a broken '.
        'build!');
    }
    
    return $warnings;
  }

}