fix(fieldmask): traverse repeated fields with wildcard in validation

fieldmask/validate.go

@@ -22,12 +22,24 @@ func Validate(fm *fieldmaskpb.FieldMask, m proto.Message) error {
 	md0 := m.ProtoReflect().Descriptor()
 	for _, path := range fm.GetPaths() {
 		md := md0
+		var fd protoreflect.FieldDescriptor
 		if !rangeFields(path, func(field string) bool {
 			// Search the field within the message.
 			if md == nil {
 				return false // not within a message
 			}
-			fd := md.Fields().ByName(protoreflect.Name(field))
+			// Parent message is a repeated field.
+			// Targeting sub-fields is allowed with the use of wildcard
+			// https://google.aip.dev/161#wildcards
+			if fd != nil && fd.IsList() {
+				if field == WildcardPath {
+					fd = nil
+					return true
+				}
+
+				return false
+			}
+			fd = md.Fields().ByName(protoreflect.Name(field))
 			// The real field name of a group is the message name.
 			if fd == nil {
 				gd := md.Fields().ByName(protoreflect.Name(strings.ToLower(field)))

fieldmask/validate_test.go

@@ -3,6 +3,7 @@ package fieldmask
 import (
 	"testing"
 
+	freightv1 "go.einride.tech/aip/proto/gen/einride/example/freight/v1"
 	"google.golang.org/genproto/googleapis/example/library/v1"
 	"google.golang.org/protobuf/proto"
 	"google.golang.org/protobuf/types/known/fieldmaskpb"
@@ -71,6 +72,23 @@ func TestValidate(t *testing.T) {
 			message:       &library.CreateBookRequest{},
 			errorContains: "invalid field path: book.foo",
 		},
+
+		{
+			name: "invalid nested in repeated field",
+			fieldMask: &fieldmaskpb.FieldMask{
+				Paths: []string{"shipment.line_items.title"},
+			},
+			message:       &freightv1.CreateShipmentRequest{},
+			errorContains: "invalid field path: shipment.line_items.title",
+		},
+
+		{
+			name: "valid nested in repeated field",
+			fieldMask: &fieldmaskpb.FieldMask{
+				Paths: []string{"shipment.line_items.*.title"},
+			},
+			message: &freightv1.CreateShipmentRequest{},
+		},
 	} {
 		tt := tt
 		t.Run(tt.name, func(t *testing.T) {