code: func (s *Snapshot) moduleManifest() modsdir.Manifest {
  	ret := make(modsdir.Manifest)
  
  	for k, modSnap := range s.Modules {
  		ret[k] = modsdir.Record{
  			Key:        k,
  			Dir:        modSnap.Dir,
  			SourceAddr: modSnap.SourceAddr,
  			Version:    modSnap.Version,
  		}
  	}
  
  	return ret
  }
docs: // moduleManifest constructs a module manifest based on the contents of
  // the receiving snapshot.