def decode_source(source_bytes):
    """Decode bytes representing source code and return the string.
    Universal newline support is used in the decoding.
    """
    import _io
    import tokenize
    source_bytes_readline = _io.BytesIO(source_bytes).readline
    encoding = tokenize.detect_encoding(source_bytes_readline)
    newline_decoder = _io.IncrementalNewlineDecoder(None, True)
    return newline_decoder.decode(source_bytes.decode(encoding[0]))
