docs: def get_source_contents(self, src_id):
          """Given a source ID this returns the embedded sourcecode if there
          is.  The sourcecode is returned as UTF-8 bytes for more efficient
          processing.
          """
          len_out = _ffi.new('unsigned int *')
          must_free = _ffi.new('int *')
          rv = rustcall(_lib.lsm_view_get_source_contents,
                        self._get_ptr(), src_id, len_out, must_free)
          if rv:
              try:
                  return _ffi.unpack(rv, len_out[0])
              finally:
                  if must_free[0]:
                      _lib.lsm_buffer_free(rv)