Protobuf ld undefined symbol ~InternalMetadata() - c++

Question

I'm hitting an issue with some fairly basic Protobuf files in a library of mine. This is built as a static library successfully but then when compiling tests (Catch2) and linking to the same protobuf library I'm getting the below undefined symbol:-
[build] Starting build
[proc] Executing command: /usr/local/bin/cmake --build /Volumes/TB3-1/git/skunkworks/herald-for-cpp/build --config Debug --target herald-tests --
[build] [1/1 100% :: 0.182] Linking CXX executable herald-tests/herald-tests
[build] FAILED: herald-tests/herald-tests
[build] : && /usr/bin/clang++ -g -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.3.sdk -Wl,-search_paths_first -Wl,-headerpad_max_install_names herald-tests/CMakeFiles/herald-tests.dir/test-templates.cpp.o herald-tests/CMakeFiles/herald-tests.dir/test-util.cpp.o herald-tests/CMakeFiles/herald-tests.dir/mesh-tests.cpp.o herald-tests/CMakeFiles/herald-tests.dir/main.cpp.o -o herald-tests/herald-tests herald/libherald.a /usr/local/lib/libprotobuf.a /usr/local/opt/openssl#3/lib/libcrypto.a && :
[build] Undefined symbols for architecture x86_64:
[build] "google::protobuf::internal::InternalMetadata::~InternalMetadata()", referenced from:
[build] google::protobuf::MessageLite::~MessageLite() in libherald.a(modem.pb.cc.o)
[build] google::protobuf::MessageLite::~MessageLite() in libherald.a(mesh.pb.cc.o)
[build] google::protobuf::MessageLite::~MessageLite() in libherald.a(models.pb.cc.o)
[build] ld: symbol(s) not found for architecture x86_64
[build] clang: error: linker command failed with exit code 1 (use -v to see invocation)
[build] ninja: build stopped: subcommand failed.
[build] Build finished with exit code 1
The super interesting thing is it even complains about the missing symbol from the ~MessageLite call when I force SPEED instead of LITE_RUNTIME. Doesn't seem to matter whether I link the library and programme to the dylib or the static lib on my mac, whether the full library or the lite library. Tried both SPEED and LITE_RUNTIME in my proto files with exactly the same result.
I've been struggling with this a while. Any ideas greatly appreciated.
Note: My library's target platform ranges from a container on a server to an embedded hardware device. These particular tests are compiled local (Mac OS X x86_64 Intel Mac in my case currently).

Answer 1

This issue was tracked here and ought to be fixed in the recently released Protobuf 3.21.3.
The library builds that ship with package managers are usually built with NDEBUG defined (-DNDEBUG to the compiler, #define NDEBUG in the code). Usually this just turns off checking assert() macros, but Protobuf keys on this symbol to turn on and off its own internal debugging. It turns out that in release mode the InternalMetadata destructor was always inlined and (with -fvisibility-inlines-hidden in the compiler options) never produced a symbol to link against, while in debug mode it was not always inlined and needed to be linked against.
So trying to build user code that didn't define NDEBUG for the Protobuf headers would result in code that needed to link against that destructor, which wouldn't be in the release Protobuf packaged libraries.
The workaround is to use -DNDEBUG in your application, or to build a debug build of Protobuf to link against, or to use a Protobuf new enough (3.21.3+) or old enough (I think <=3.19) to not have this particular problem.
The only remaining mystery is why the whole Internet noticed this bug in the past few days, when it's been there for much longer.