Switch to DownCastToGenerated to fix linking issues

Author: vitalybuka

port/protobuf.h

@@ -24,6 +24,29 @@
 #include "google/protobuf/util/message_differencer.h"
 #include "google/protobuf/wire_format.h"
 
+#include "google/protobuf/port_def.inc"  // MUST be last header included
+#if PROTOBUF_VERSION < 4025000
+
+namespace google {
+namespace protobuf {
+
+template <typename T>
+const T* DownCastToGenerated(const Message* message) {
+  return static_cast<const T*>(message);
+}
+
+template <typename T>
+T* DownCastToGenerated(Message* message) {
+  const Message* message_const = message;
+  return const_cast<T*>(DownCastToGenerated<T>(message_const));
+}
+
+}  // namespace protobuf
+}  // namespace google
+#endif  // PROTOBUF_VERSION
+#include "google/protobuf/port_undef.inc"
+
+
 namespace protobuf_mutator {
 
 namespace protobuf = google::protobuf;

src/libfuzzer/libfuzzer_macro.h

@@ -119,7 +119,7 @@ struct PostProcessorRegistration {
     RegisterPostProcessor(
         Proto::descriptor(),
         [callback](protobuf::Message* message, unsigned int seed) {
-          callback(static_cast<Proto*>(message), seed);
+          callback(protobuf::DownCastToGenerated<Proto>(message), seed);
         });
   }
 };

src/mutator.cc

@@ -381,13 +381,13 @@ std::unique_ptr<Message> UnpackAny(const Any& any) {
 
 const Any* CastToAny(const Message* message) {
   return Any::GetDescriptor() == message->GetDescriptor()
-             ? static_cast<const Any*>(message)
+             ? protobuf::DownCastToGenerated<Any>(message)
              : nullptr;
 }
 
 Any* CastToAny(Message* message) {
   return Any::GetDescriptor() == message->GetDescriptor()
-             ? static_cast<Any*>(message)
+             ? protobuf::DownCastToGenerated<Any>(message)
              : nullptr;
 }
 

src/mutator_test.cc

@@ -29,6 +29,7 @@
 
 namespace protobuf_mutator {
 
+using protobuf::DownCastToGenerated;
 using protobuf::util::MessageDifferencer;
 using testing::TestWithParam;
 using testing::ValuesIn;
@@ -622,7 +623,7 @@ TYPED_TEST(MutatorTypedTest, RegisterPostProcessor) {
         TestFixture::Message::descriptor(),
         [=](protobuf::Message* message, unsigned int seed) {
           auto test_message =
-              static_cast<typename TestFixture::Message*>(message);
+              DownCastToGenerated<typename TestFixture::Message>(message);
           if (seed % 2) test_message->set_optional_string(v);
         });
   }