This is the PIFR code that deals with applying the patch and then getting what files were changed by it.

Problems with patch p detection

  public function apply($patch) {
    return pifr_client_review::exec("patch -p1 -i $patch");
  }

  public function get_changed_files($patch) {
    $contents = file_get_contents($patch);
    // This regex looks through the patch file for lines of the format
    // +++ b/install.php
    // and removes the '+++ b/' from them, returning the filenames that have
    // had content added.
    preg_match_all('%^[\+-]{3}\s+[^/]\/(.*?)\s%m', $contents, $matches, PREG_SET_ORDER);

    $files = array();
    foreach ($matches as $match) {
      if ($match[1] != '/dev/null') {
        $files[] = $match[1];
      }
    }
    return array_unique($files);
  }

It seems to me like the regex is going to be fragile if we make it work for -p1 and -p0.