code: func (x *Index) HasLegacySHA1() (ok bool, err error) {
  	if x.corpus != nil {
  		return x.corpus.hasLegacySHA1, err
  	}
  	it := x.queryPrefix(keyWholeToFileRef, "sha1-")
  	defer closeIterator(it, &err)
  	for it.Next() {
  		return true, err
  	}
  	return false, err
  }
docs: // HasLegacySHA1 reports whether the index has legacy SHA-1 blobs.