Add C# presence methods to proto3 oneof fields.

PiperOrigin-RevId: 514587333

Author: mkruskal-google

src/google/protobuf/compiler/csharp/csharp_helpers.h

@@ -140,28 +140,16 @@ inline bool IsWrapperType(const FieldDescriptor* descriptor) {
       descriptor->message_type()->file()->name() == "google/protobuf/wrappers.proto";
 }
 
-inline bool IsProto2(const FileDescriptor* descriptor) {
-  return descriptor->syntax() == FileDescriptor::SYNTAX_PROTO2;
-}
-
 inline bool SupportsPresenceApi(const FieldDescriptor* descriptor) {
   // Unlike most languages, we don't generate Has/Clear members for message
   // types, because they can always be set to null in C#. They're not really
   // needed for oneof fields in proto2 either, as everything can be done via
-  // oneof case, but we follow the convention from other languages. Proto3
-  // oneof fields never have Has/Clear members - but will also never have
-  // the explicit optional keyword either.
-  //
-  // None of the built-in helpers (descriptor->has_presence() etc) describe
-  // quite the behavior we want, so the rules are explicit below.
-
-  if (descriptor->is_repeated() ||
-      descriptor->type() == FieldDescriptor::TYPE_MESSAGE) {
+  // oneof case, but we follow the convention from other languages.
+  if (descriptor->type() == FieldDescriptor::TYPE_MESSAGE) {
     return false;
   }
-  // has_optional_keyword() has more complex rules for proto2, but that
-  // doesn't matter given the first part of this condition.
-  return IsProto2(descriptor->file()) || descriptor->has_optional_keyword();
+
+  return descriptor->has_presence();
 }
 
 inline bool RequiresPresenceBit(const FieldDescriptor* descriptor) {

src/google/protobuf/compiler/csharp/csharp_primitive_field.cc

@@ -67,18 +67,16 @@ PrimitiveFieldGenerator::~PrimitiveFieldGenerator() {
 }
 
 void PrimitiveFieldGenerator::GenerateMembers(io::Printer* printer) {
-  
   // Note: in multiple places, this code assumes that all fields
   // that support presence are either nullable, or use a presence field bit.
   // Fields which are oneof members are not generated here; they're generated in PrimitiveOneofFieldGenerator below.
   // Extensions are not generated here either.
 
-
-  // Proto2 allows different default values to be specified. These are retained
-  // via static fields. They don't particularly need to be, but we don't need
-  // to change that. In Proto3 the default value we don't generate these
-  // fields, just using the literal instead.
-  if (IsProto2(descriptor_->file())) {
+  // Explicit presence allows different default values to be specified. These
+  // are retained via static fields. They don't particularly need to be, but we
+  // don't need to change that. Under implicit presence we don't use static
+  // fields for default values and just use the literals instead.
+  if (descriptor_->has_presence()) {
     // Note: "private readonly static" isn't as idiomatic as
     // "private static readonly", but changing this now would create a lot of
     // churn in generated code with near-to-zero benefit.