fix #368: respect synthetic oneof in marshaller

encoding/protobq/marshal.go

@@ -80,10 +80,14 @@ func (o MarshalOptions) marshalMessage(msg protoreflect.Message) (map[string]big
 	if o.Schema.UseOneofFields {
 		for i := 0; i < msg.Descriptor().Oneofs().Len(); i++ {
 			oneofDescriptor := msg.Descriptor().Oneofs().Get(i)
+			if oneofDescriptor.IsSynthetic() {
+				continue
+			}
 			oneofField := msg.WhichOneof(oneofDescriptor)
-			if oneofField != nil {
-				result[string(oneofDescriptor.Name())] = string(oneofField.Name())
+			if oneofField == nil {
+				continue
 			}
+			result[string(oneofDescriptor.Name())] = string(oneofField.Name())
 		}
 	}
 	return result, nil

encoding/protobq/marshal_test.go

@@ -335,6 +335,40 @@ func TestMarshalOptions_Marshal(t *testing.T) {
 			opt:      MarshalOptions{Schema: SchemaOptions{UseOneofFields: true}},
 			expected: map[string]bigquery.Value{},
 		},
+
+		{
+			name: "optional oneof and optional message",
+			msg: &examplev1.ExampleOptional{
+				OptMessage_2: &examplev1.ExampleOptMessage{
+					StringValue: "opt_message_string_value",
+				},
+				OptOneofMessage_3: &examplev1.ExampleOptOneof{
+					OneofFields_1: &examplev1.ExampleOptOneof_OneofMessage_2{
+						OneofMessage_2: &examplev1.ExampleOptOneof_Message{
+							StringValue: "opt_one_of_message_string_value",
+						},
+					},
+				},
+			},
+			opt: MarshalOptions{Schema: SchemaOptions{UseOneofFields: true}},
+			expected: map[string]bigquery.Value{
+				"opt_message_2": map[string]bigquery.Value{"string_value": string("opt_message_string_value")},
+				"opt_oneof_message_3": map[string]bigquery.Value{
+					"oneof_fields_1":  string("oneof_message_2"),
+					"oneof_message_2": map[string]bigquery.Value{"string_value": string("opt_one_of_message_string_value")},
+				},
+			},
+		},
+
+		{
+			name: "optional empty oneof and optional empty message",
+			msg: &examplev1.ExampleOptional{
+				OptMessage_2:      nil,
+				OptOneofMessage_3: nil,
+			},
+			opt:      MarshalOptions{Schema: SchemaOptions{UseOneofFields: true}},
+			expected: map[string]bigquery.Value{},
+		},
 	} {
 		tt := tt
 		t.Run(tt.name, func(t *testing.T) {

encoding/protobq/schema_test.go

@@ -394,10 +394,32 @@ func TestSchemaOptions_InferSchema(t *testing.T) {
 			msg: &examplev1.ExampleOptional{},
 			expected: bigquery.Schema{
 				{
-					Name:     "opt",
+					Name:     "opt_double_1",
 					Type:     bigquery.FloatFieldType,
 					Required: false,
 				},
+				{
+					Name:   "opt_message_2",
+					Type:   "RECORD",
+					Schema: bigquery.Schema{{Name: "string_value", Type: bigquery.StringFieldType}},
+				},
+				{
+					Name:     "opt_oneof_message_3",
+					Type:     bigquery.RecordFieldType,
+					Required: false,
+					Schema: bigquery.Schema{
+						{
+							Name:   "oneof_message_2",
+							Type:   bigquery.RecordFieldType,
+							Schema: bigquery.Schema{{Name: "string_value", Type: bigquery.StringFieldType}},
+						},
+						{
+							Name:        "oneof_fields_1",
+							Description: "One of: oneof_empty_message_1, oneof_message_2.",
+							Type:        bigquery.StringFieldType,
+						},
+					},
+				},
 			},
 		},
 	} {

internal/examples/proto/einride/bigquery/example/v1/example_optional.proto

@@ -3,5 +3,22 @@ syntax = "proto3";
 package einride.bigquery.example.v1;
 
 message ExampleOptional {
-  optional double opt = 1;
+  optional double opt_double_1 = 1;
+  optional ExampleOptMessage opt_message_2 = 2;
+  optional ExampleOptOneof opt_oneof_message_3 = 3;
+}
+
+message ExampleOptMessage {
+  string string_value = 1;
+}
+
+message ExampleOptOneof {
+  oneof oneof_fields_1 {
+    EmptyMessage oneof_empty_message_1 = 1;
+    Message oneof_message_2 = 2;
+  }
+  message EmptyMessage {}
+  message Message {
+    string string_value = 1;
+  }
 }