code: func schemaFromMessage(desc *descriptor.FileDescriptorSet, messageName string) (schema bigquery.Schema, description string, err error) {
  	conv := schemaConverter{
  		desc:           desc,
  		sourceCodeInfo: make(map[*descriptor.FileDescriptorProto]sourceCodeInfoMap, len(desc.File)),
  	}
  	for _, f := range desc.File {
  		conv.sourceCodeInfo[f], err = descutil.IndexSourceCodeInfo(f)
  		if err != nil {
  			return nil, "", errors.Annotate(err, "failed to index source code info in file %q", f.GetName()).Err()
  		}
  	}
  	return conv.schema(messageName)
  }
docs: // schemaFromMessage loads a message by name from .proto files in dir
  // and converts the message to a bigquery schema.