func protobufTagToField()

in cmd/go-to-protobuf/protobuf/generator.go [549:619]
57 lines of code
12 McCabe index (conditional complexity)

func protobufTagToField(tag string, field *protoField, m types.Member, t *types.Type, localPackage types.Name) error {
	if len(tag) == 0 || tag == "-" {
		return nil
	}

	// protobuf:"bytes,3,opt,name=Id,customtype=github.com/gogo/protobuf/test.Uuid"
	parts := strings.Split(tag, ",")
	if len(parts) < 3 {
		return fmt.Errorf("member %q of %q malformed 'protobuf' tag, not enough segments\n", m.Name, t.Name)
	}
	protoTag, err := strconv.Atoi(parts[1])
	if err != nil {
		return fmt.Errorf("member %q of %q malformed 'protobuf' tag, field ID is %q which is not an integer: %v\n", m.Name, t.Name, parts[1], err)
	}
	field.Tag = protoTag

	// In general there is doesn't make sense to parse the protobuf tags to get the type,
	// as all auto-generated once will have wire type "bytes", "varint" or "fixed64".
	// However, sometimes we explicitly set them to have a custom serialization, e.g.:
	//   type Time struct {
	//     time.Time `protobuf:"Timestamp,1,req,name=time"`
	//   }
	// to force the generator to use a given type (that we manually wrote serialization &
	// deserialization methods for).
	switch parts[0] {
	case "varint", "fixed32", "fixed64", "bytes", "group":
	default:
		var name types.Name
		if last := strings.LastIndex(parts[0], "."); last != -1 {
			prefix := parts[0][:last]
			name = types.Name{
				Name:    parts[0][last+1:],
				Package: prefix,
				Path:    strings.Replace(prefix, ".", "/", -1),
			}
		} else {
			name = types.Name{
				Name:    parts[0],
				Package: localPackage.Package,
				Path:    localPackage.Path,
			}
		}
		field.Type = &types.Type{
			Name: name,
			Kind: types.Protobuf,
		}
	}

	protoExtra := make(map[string]string)
	for i, extra := range parts[3:] {
		parts := strings.SplitN(extra, "=", 2)
		if len(parts) != 2 {
			return fmt.Errorf("member %q of %q malformed 'protobuf' tag, tag %d should be key=value, got %q\n", m.Name, t.Name, i+4, extra)
		}
		switch parts[0] {
		case "name":
			protoExtra[parts[0]] = parts[1]
		case "casttype", "castkey", "castvalue":
			parts[0] = fmt.Sprintf("(gogoproto.%s)", parts[0])
			protoExtra[parts[0]] = strconv.Quote(parts[1])
		}
	}

	field.Extras = protoExtra
	if name, ok := protoExtra["name"]; ok {
		field.Name = name
		delete(protoExtra, "name")
	}

	return nil
}