code: public static ImmutableList<File> loadPossiblyCompressedFileList(File fileList)
        throws IOException {
      final CharSource source;
      if (fileList.getName().endsWith(".gz") || fileList.getName().endsWith(".tgz")) {
        source = GZIPByteSource.fromCompressed(fileList).asCharSource(Charsets.UTF_8);
      } else {
        source = Files.asCharSource(fileList, Charsets.UTF_8);
      }
      return loadFileList(source);
    }
docs: Like {@link #loadFileList(java.io.File)}, except if the file name ends in ".gz" or ".tgz" it is
  treated as GZIP compressed. This is often convenient for loading e.g. document lists which
  benefit from being compressed for large corpora.