Adds support for proto3opt

Attempts to detect optional fields by using
`field.Oneof.Desc.IsSynthetic()` and relies on nil checking pointers for
the marshall and unmarshalling

features/json/message-marshal.go

@@ -143,13 +143,13 @@ nextField:
 
 		// If this is the first field in a oneof, write the if statement that checks for nil
 		// and start the switch statement for the oneof type.
-		if field.Oneof != nil && field == field.Oneof.Fields[0] {
+		if field.Oneof != nil && field == field.Oneof.Fields[0] && !field.Oneof.Desc.IsSynthetic() {
 			// NOTE: we don't support field masks here (yet).
 			g.P("if x.", field.Oneof.GoName, " != nil {")
 			g.P("switch ov := x.", field.Oneof.GoName, ".(type) {")
 		}
 
-		if field.Oneof != nil {
+		if field.Oneof != nil && !field.Oneof.Desc.IsSynthetic() {
 			// If we're in a oneof, check if this is the field that's set in the oneof.
 			g.P("case *", field.GoIdent.GoName, ":")
 			messageOrOneofIdent = "ov"
@@ -192,6 +192,12 @@ nextField:
 		switch field.Desc.Kind() {
 		default:
 			// Scalar types can be written by the library.
+			if field.Oneof != nil && field.Oneof.Desc.IsSynthetic() {
+				g.P("s.Write", g.libNameForField(field), "(*", messageOrOneofIdent, ".", fieldGoName, ")")
+			} else {
+				g.P("s.Write", g.libNameForField(field), "(", messageOrOneofIdent, ".", fieldGoName, ")")
+			}
+		case protoreflect.BytesKind:
 			g.P("s.Write", g.libNameForField(field), "(", messageOrOneofIdent, ".", fieldGoName, ")")
 		case protoreflect.EnumKind:
 			// If the field is of type enum, and the enum has a marshaler, use that.
@@ -207,12 +213,12 @@ nextField:
 		}
 
 		// If we're not in a oneof, end the "if not zero".
-		if field.Oneof == nil {
+		if field.Oneof == nil || field.Oneof.Desc.IsSynthetic() {
 			g.P("}") // end if x.{field.GoName} != zero value {
 		}
 
 		// If this is the last field in the oneof, close the switch and if statements.
-		if field.Oneof != nil && field == field.Oneof.Fields[len(field.Oneof.Fields)-1] {
+		if field.Oneof != nil && field == field.Oneof.Fields[len(field.Oneof.Fields)-1] && !field.Oneof.Desc.IsSynthetic() {
 			g.P("}") // end switch v := x.{field.Oneof.GoName}.(type) {
 			g.P("}") // end if x.{field.Oneof.GoName} != nil {
 		}

features/json/message-unmarshal.go

@@ -162,7 +162,7 @@ nextField:
 		messageOrOneofIdent := "x"
 
 		// If this field is in a oneof, allocate a new oneof value wrapper.
-		if field.Oneof != nil {
+		if field.Oneof != nil && !field.Oneof.Desc.IsSynthetic() {
 			g.P("ov := &", field.GoIdent.GoName, "{}")
 			g.P("x.", field.Oneof.GoName, " = ov")
 			messageOrOneofIdent = "ov"
@@ -190,6 +190,13 @@ nextField:
 		switch field.Desc.Kind() {
 		default:
 			// Scalar types can be read by the library.
+			if field.Oneof != nil && field.Oneof.Desc.IsSynthetic() {
+				g.P("t := s.Read", g.libNameForField(field), "()")
+				g.P(messageOrOneofIdent, ".", fieldGoName, " = &t")
+			} else {
+				g.P(messageOrOneofIdent, ".", fieldGoName, " = s.Read", g.libNameForField(field), "()")
+			}
+		case protoreflect.BytesKind:
 			g.P(messageOrOneofIdent, ".", fieldGoName, " = s.Read", g.libNameForField(field), "()")
 		case protoreflect.EnumKind:
 			// If the field is of type enum, and the enum has an unmarshaler, call the unmarshaler.

features/json/message.go

@@ -6,7 +6,6 @@ package json
 
 import (
 	"fmt"
-	"slices"
 
 	"github.com/aperturerobotics/protobuf-go-lite/compiler/protogen"
 	"google.golang.org/protobuf/reflect/protoreflect"
@@ -28,26 +27,17 @@ func (g *jsonGenerator) genMessage(message *protogen.Message) {
 		return
 	}
 
-	// Check if the message has any optional fields and skip generation if so.
-	anyOptional := slices.ContainsFunc(message.Fields, func(f *protogen.Field) bool {
-		return f.Desc.HasOptionalKeyword()
-	})
+	g.genMessageMarshaler(message)
+	g.genStdMessageMarshaler(message)
 
-	if !anyOptional {
-		g.genMessageMarshaler(message)
-		g.genStdMessageMarshaler(message)
-
-		g.genMessageUnmarshaler(message)
-		g.genStdMessageUnmarshaler(message)
-	} else {
-		// We do not support marshaling this field, skip the entire message.
-		g.P("// NOTE: protobuf-go-lite json only supports proto3 and not proto3opt (optional fields).")
-		g.P()
-	}
+	g.genMessageUnmarshaler(message)
+	g.genStdMessageUnmarshaler(message)
 }
 
 func fieldIsNullable(field *protogen.Field) bool {
-	// In the supported subset of syntax (proto3 and not proto3opt) we only use pointers for messages.
+	if field.Oneof != nil && field.Oneof.Desc.IsSynthetic() {
+		return true
+	}
 	nullable := field.Desc.Kind() == protoreflect.MessageKind
 	return nullable
 }