protos: remove need for customname on ID fields

Credit to Aaron Lehmann for the implementation from SwarmKit.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

cmd/protoc-gen-gogoctrd/customnameid.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"strings"
+
+	"github.com/gogo/protobuf/gogoproto"
+	"github.com/gogo/protobuf/proto"
+	"github.com/gogo/protobuf/protoc-gen-gogo/descriptor"
+	"github.com/gogo/protobuf/protoc-gen-gogo/generator"
+	"github.com/gogo/protobuf/vanity"
+)
+
+// CustomNameID preprocess the field, and set the [(gogoproto.customname) = "..."]
+// if necessary, in order to avoid setting `gogoproto.customname` manually.
+// The automatically assigned name should conform to Golang convention.
+func CustomNameID(file *descriptor.FileDescriptorProto) {
+
+	f := func(field *descriptor.FieldDescriptorProto) {
+		// Skip if [(gogoproto.customname) = "..."] has already been set.
+		if gogoproto.IsCustomName(field) {
+			return
+		}
+		// Skip if embedded
+		if gogoproto.IsEmbed(field) {
+			return
+		}
+		if field.OneofIndex != nil {
+			return
+		}
+		fieldName := generator.CamelCase(*field.Name)
+		switch {
+		case *field.Name == "id":
+			// id -> ID
+			fieldName = "ID"
+		case strings.HasPrefix(*field.Name, "id_"):
+			// id_some -> IDSome
+			fieldName = "ID" + fieldName[2:]
+		case strings.HasSuffix(*field.Name, "_id"):
+			// some_id -> SomeID
+			fieldName = fieldName[:len(fieldName)-2] + "ID"
+		case strings.HasSuffix(*field.Name, "_ids"):
+			// some_ids -> SomeIDs
+			fieldName = fieldName[:len(fieldName)-3] + "IDs"
+		default:
+			return
+		}
+		if field.Options == nil {
+			field.Options = &descriptor.FieldOptions{}
+		}
+		if err := proto.SetExtension(field.Options, gogoproto.E_Customname, &fieldName); err != nil {
+			panic(err)
+		}
+	}
+
+	// Iterate through all fields in file
+	vanity.ForEachFieldExcludingExtensions(file.MessageType, f)
+}

cmd/protoc-gen-gogoctrd/main.go

@@ -17,6 +17,7 @@ func main() {
 		vanity.TurnOnStringerAll,
 		vanity.TurnOnUnmarshalerAll,
 		vanity.TurnOnSizerAll,
+		CustomNameID,
 	} {
 		vanity.ForEachFile(files, opt)
 	}