anchor.diff:    if (redirectDartdocPages.containsKey(docFilePath.package)) {
       return redirectResponse(redirectDartdocPages[docFilePath.package]);
     }
  -  if (docFilePath.version == null) {
  -    final version = await dartdocBackend.getLatestVersion(docFilePath.package);
  -    if (version == null) {
  -      return redirectToSearch(docFilePath.package);
  -    } else {
  -      return redirectResponse(pkgDocUrl(docFilePath.package, version: version));
  -    }
  +  final effectiveVersion = await _effectiveVersion(docFilePath);
  +  if (effectiveVersion == null) {
  +    return redirectToSearch(docFilePath.package);
     }
     if (docFilePath.path == null) {
       return redirectResponse('${request.requestedUri}/');
  
positive.code:   final String requestMethod = request.method?.toUpperCase();
    if (requestMethod == 'GET') {
      final entry = await dartdocBackend.getLatestEntry(
          docFilePath.package, docFilePath.version, true);
      if (entry == null) {
        return notFoundHandler(request);
      }
  
negative.code:   }
  
    final String version = uri.pathSegments[2];
    if (version.isEmpty) {
      return new DocFilePath(package, null, null);
    }
    if (segmentCount == 3) {
  