docs: def _metahash(self):
          """Include genrule cmd in the metahash."""
          if self._cached_metahash:
              return self._cached_metahash
          mhash = base.BaseBuilder._metahash(self)
          log.debug('[%s]: Metahash input: cmd="%s"', self.address, self.cmd)
          mhash.update(self.cmd)
          self._cached_metahash = mhash
          return mhash