code: func (f *file) Hash() []byte {
  	if f.hash == nil {
  		h := fnv.New64a()
  		h.Write([]byte(f.contents)) // it nevers returns an error.
  		f.hash = h.Sum(nil)
  	}
  
  	return f.hash
  }
docs: // The hash of a file is just its contents.
  // Empty files will have the fnv64 basis offset as its hash.