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[Bug] Build fails with protobuf 36.1 under -Werror=unused-result #623
Description
Search before asking
- I searched in the issues and found nothing similar.
Version
pulsar-client-cpp 4.2.0 on Arch Linux (x86_64), GCC 16.2.1, protobuf 36.1, abseil-cpp 20260817.0. The same calls are present on main at f71d7e9 (source inspection; in lib/Commands.cc they are at lines 130, 239, 251, 936 and 979).
Minimal reproduce step
With protobuf 36.1 and the other dependencies installed:
cmake -S . -B build -DBUILD_TESTS=ON -DCMAKE_CXX_FLAGS=-O2
cmake --build build
The library compilation fails before the test target is built.
What did you expect to see?
The library builds.
What did you see instead?
Diagnostics collected from 4.2.0 with the one-line MessageTest fix proposed in #622 applied, using cmake --build build -- -k (Unix Makefiles generator). The library call sites were unchanged; line numbers below are from 4.2.0.
lib/Commands.cc:129:25: error: ignoring return value of 'bool google::protobuf::MessageLite::SerializeToArray(void*, int) const', declared with attribute 'nodiscard' [-Werror=unused-result]
lib/Commands.cc:238:25: error: ignoring return value of 'bool google::protobuf::MessageLite::SerializeToArray(void*, int) const', declared with attribute 'nodiscard' [-Werror=unused-result]
lib/Commands.cc:250:30: error: ignoring return value of 'bool google::protobuf::MessageLite::SerializeToArray(void*, int) const', declared with attribute 'nodiscard' [-Werror=unused-result]
lib/Commands.cc:880:30: error: ignoring return value of 'bool google::protobuf::MessageLite::SerializeToArray(void*, int) const', declared with attribute 'nodiscard' [-Werror=unused-result]
lib/Commands.cc:923:28: error: ignoring return value of 'bool google::protobuf::MessageLite::ParseFromArray(const void*, int)', declared with attribute 'nodiscard' [-Werror=unused-result]
lib/MessageId.cc:87:29: error: ignoring return value of 'bool google::protobuf::MessageLite::SerializeToString(std::string*) const', declared with attribute 'nodiscard' [-Werror=unused-result]
lib/ProtobufNativeSchema.cc:49:39: error: ignoring return value of 'bool google::protobuf::MessageLite::SerializeToArray(void*, int) const', declared with attribute 'nodiscard' [-Werror=unused-result]
With -Wno-error=unused-result, the build also reports the same warnings in tests/ProtobufNativeSchemaTest.cc:114 (SerializeToArray) and :123 (ParseFromArray).
Anything else?
In protobuf 36.1, these methods are annotated [[nodiscard]] (message_lite.h, port_def.inc). The project's -Werror setting turns the unused-result diagnostics at the listed call sites into build errors. The listed call sites do not check the returned success value. Adding -Wno-error=unused-result downgrades these diagnostics to warnings; it does not resolve the separate MessageTest strncpy build failure tracked in #621.
Are you willing to submit a PR?
- I'm willing to submit a PR!
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