Fix deprecated resolver (#117)

In #57, the resolver was improved to handle dynamically created
descriptors and inconsistent types but silently broke resolving the
deprecated version of the protovalidate extension (introduced in
[protovalidate
v0.2.0](bufbuild/protovalidate@v0.1.15...v0.2.0)).
This patch dries up the resolver a bit and fixes the (albeit deprecated)
behavior.

Fixes #116

resolver/resolver.go

@@ -20,12 +20,13 @@ import (
 	"buf.build/gen/go/bufbuild/protovalidate/protocolbuffers/go/buf/validate"
 	"google.golang.org/protobuf/proto"
 	"google.golang.org/protobuf/reflect/protoreflect"
+	"google.golang.org/protobuf/reflect/protoregistry"
 	"google.golang.org/protobuf/runtime/protoimpl"
 )
 
 const (
-	newExtensionIndex      = "1159"
-	previousExtensionIndex = "51071"
+	newExtensionIndex      = "1159"  // protovalidate versions >= v0.2.0
+	previousExtensionIndex = "51071" // protovalidate versions < v0.2.0
 )
 
 // DefaultResolver resolves protovalidate constraints options from descriptors.
@@ -34,29 +35,31 @@ type DefaultResolver struct{}
 // ResolveMessageConstraints returns the MessageConstraints option set for the
 // MessageDescriptor.
 func (r DefaultResolver) ResolveMessageConstraints(desc protoreflect.MessageDescriptor) *validate.MessageConstraints {
-	constraints := resolveExt[protoreflect.MessageDescriptor, *validate.MessageConstraints](desc, validate.E_Message)
-	if constraints == nil {
-		constraints = resolveDeprecatedIndex[protoreflect.MessageDescriptor, *validate.MessageConstraints](desc, validate.E_Message)
-	}
-	return constraints
+	return resolveConstraints[validate.MessageConstraints](desc, validate.E_Message)
 }
 
 // ResolveOneofConstraints returns the OneofConstraints option set for the
 // OneofDescriptor.
 func (r DefaultResolver) ResolveOneofConstraints(desc protoreflect.OneofDescriptor) *validate.OneofConstraints {
-	constraints := resolveExt[protoreflect.OneofDescriptor, *validate.OneofConstraints](desc, validate.E_Oneof)
-	if constraints == nil {
-		constraints = resolveDeprecatedIndex[protoreflect.OneofDescriptor, *validate.OneofConstraints](desc, validate.E_Oneof)
-	}
-	return constraints
+	return resolveConstraints[validate.OneofConstraints](desc, validate.E_Oneof)
 }
 
 // ResolveFieldConstraints returns the FieldConstraints option set for the
 // FieldDescriptor.
 func (r DefaultResolver) ResolveFieldConstraints(desc protoreflect.FieldDescriptor) *validate.FieldConstraints {
-	constraints := resolveExt[protoreflect.FieldDescriptor, *validate.FieldConstraints](desc, validate.E_Field)
+	return resolveConstraints[validate.FieldConstraints](desc, validate.E_Field)
+}
+
+func resolveConstraints[C any, CP interface {
+	*C
+	proto.Message
+}](
+	desc protoreflect.Descriptor,
+	extType *protoimpl.ExtensionInfo,
+) (constraints CP) {
+	constraints = resolveExt[CP](desc.Options(), extType)
 	if constraints == nil {
-		constraints = resolveDeprecatedIndex[protoreflect.FieldDescriptor, *validate.FieldConstraints](desc, validate.E_Field)
+		constraints = resolveDeprecatedIndex[CP](desc.Options(), extType)
 	}
 	return constraints
 }
@@ -66,13 +69,14 @@ func (r DefaultResolver) ResolveFieldConstraints(desc protoreflect.FieldDescript
 // circumstances, particularly in dynamic or runtime contexts, the underlying
 // extension value's type may be a dynamicpb.Message. In this case, we fall back
 // through a proto.[Un]Marshal cycle to get it into the concrete type we expect.
-func resolveExt[D protoreflect.Descriptor, C proto.Message](
-	desc D,
+func resolveExt[C proto.Message](
+	options proto.Message,
 	extType protoreflect.ExtensionType,
 ) (constraints C) {
 	num := extType.TypeDescriptor().Number()
 	var msg proto.Message
-	proto.RangeExtensions(desc.Options(), func(typ protoreflect.ExtensionType, i interface{}) bool {
+
+	proto.RangeExtensions(options, func(typ protoreflect.ExtensionType, i interface{}) bool {
 		if num != typ.TypeDescriptor().Number() {
 			return true
 		}
@@ -93,16 +97,29 @@ func resolveExt[D protoreflect.Descriptor, C proto.Message](
 }
 
 // resolveDeprecatedIndex is a fallback for the deprecated extension index.
-func resolveDeprecatedIndex[D protoreflect.Descriptor, C proto.Message](
-	desc D,
+func resolveDeprecatedIndex[C proto.Message](
+	options proto.Message,
 	ext *protoimpl.ExtensionInfo,
 ) C {
-	return resolveExt[D, C](desc, &protoimpl.ExtensionInfo{
+	extInfo := &protoimpl.ExtensionInfo{
 		ExtendedType:  ext.ExtendedType,
 		ExtensionType: ext.ExtensionType,
 		Field:         51071,
 		Name:          ext.Name,
 		Tag:           strings.Replace(ext.Tag, newExtensionIndex, previousExtensionIndex, 1),
 		Filename:      ext.Filename,
-	})
+	}
+
+	// detect and handle if there are unknown options
+	if unknown := options.ProtoReflect().GetUnknown(); len(unknown) > 0 {
+		opts := options.ProtoReflect().Type().New()
+		resolver := &protoregistry.Types{}
+		if err := resolver.RegisterExtension(extInfo); err == nil {
+			if err = (&proto.UnmarshalOptions{Resolver: resolver}).Unmarshal(unknown, opts.Interface()); err == nil {
+				options = opts.Interface()
+			}
+		}
+	}
+
+	return resolveExt[C](options, extInfo)
 }