$dllexport_decl$ is missing in generated .pb.cc

[owent]

What version of protobuf and what language are you using?
Version: v21/v23
Language: C++

What operating system (Linux, Windows, ...) and version?

Windows,Linux

What runtime / compiler are you using (e.g., python version or gcc version)

GCC 13, GCC 4.8, MSVC 19.36

What did you do?

1. Using --cpp_out=dllexport_decl=XXX_API:<OUTPUT DIR>.
2. Set the visibility to hidden.
3. Build generated .pb.cc as shared libraries.
4. See error

What did you expect to see

Linking success.

What did you see instead?

Unresolved reference to PACKAGE::_MESSAGE_default_instance_.

Anything else we should know about your project / environment

$dllexport_decl$ is missing for default instance in generated .pb.cc.

[deannagarcia]

Can you provide some more details here? What version of C++ are you using? What's the full command you are running? And can you copy over error logs?

[fowles]

They sent a PR that I am already reviewing, so no need for details

[owent]

Can you provide some more details here? What version of C++ are you using? What's the full command you are running? And can you copy over error logs?

For the usage in our project.

1. We write a message in proto file , for example message DBattleAffix {...} in affix.proto
2. Generate affix.pb.h and affix.pb.cc with protoc --cpp_out=dllexport_decl=TGF_BATTLE_PROTOCOL_API:$SOURCE_DIR and build them as a dll and define TGF_BATTLE_PROTOCOL_API=__declspec(dllexport).(Unreal Engine plugin on Windows)
3. In another dll(another Unreal Engine plugin on Windows), we use the generated header file above (affix.pb.h) and define TGF_BATTLE_PROTOCOL_API=__declspec(dllimport) .
4. When linking, it shows TGFBattleUtility.lib(BattleAffixAlgorithm.obj): Error LNK2001: unresolved external symbol "struct tgf::DBattleAffixDefaultTypeInternal tgf::_DBattleAffix_default_instance_" (?_DBattleAffix_default_instance_@tgf@@3UDBattleAffixDefaultTypeInternal@1@A)

I think there is similar problems when we build these .pb.cc files with -fvisibility=hidden and define TGF_BATTLE_PROTOCOL_API=__attribute__((visibility("default"))) , but I didn't test it yet.