code: func Source(filename string, src []byte) ([]byte, error) {
  	module, err := ast.ParseModule(filename, string(src))
  	if err != nil {
  		return nil, err
  	}
  	formatted, err := Ast(module)
  	if err != nil {
  		return nil, fmt.Errorf("%s: %v", filename, err)
  	}
  	return formatted, nil
  }
docs: // Source formats a Rego source file. The bytes provided must describe a complete
  // Rego module. If they don't, Source will return an error resulting from the attempt
  // to parse the bytes.