MacOS build failure: printer/google/protobuf/io/printer.h:94:55: error: unused parameter 'semantic' [-Werror,-Wunused-parameter]

[jtattermusch]

I'm building on MacOS as part of the grpc bazel build. I'm getting this error:

In file included from src/compiler/cpp_generator.cc:19:
In file included from ./src/compiler/cpp_generator.h:30:
In file included from ./src/compiler/config.h:24:
In file included from ./src/compiler/config_protobuf.h:33:
bazel-out/host/bin/external/com_google_protobuf/src/google/protobuf/io/_virtual_includes/printer/google/protobuf/io/printer.h:94:55: error: unused parameter 'semantic' [-Werror,-Wunused-parameter]
                             absl::optional<Semantic> semantic) {
                                                      ^
1 error generated.
Error in child process '/usr/bin/xcrun'. 1
ERROR: /Volumes/BuildData/tmpfs/altsrc/github/grpc/src/proto/grpc/testing/BUILD:177:19 Middleman _middlemen/_S_Ssrc_Sproto_Sgrpc_Stesting_Ctest_Uproto-BazelCppSemantics_build_arch_darwin-opt failed: (Aborted): wrapped_clang_pp failed: error executing command

https://source.cloud.google.com/results/invocations/7bed9dcc-9f09-410f-a4cd-443267f9af94/log

Canonical bazel command:
bazel --max_idle_secs=10800 --noshutdown_on_low_sys_mem --connect_timeout_secs=30 --output_user_root=/var/tmp/_bazel_kbuilder --output_base=/private/var/tmp/_bazel_kbuilder/56f0bf568ea4b00a9aa3000e432900f1 --failure_detail_out=/private/var/tmp/_bazel_kbuilder/56f0bf568ea4b00a9aa3000e432900f1/failure_detail.rawproto --expand_configs_in_place --idle_server_tasks --write_command_log --nowatchfs --nofatal_event_bus_exceptions --nowindows_enable_symlinks --client_debug=false --host_jvm_args=-Djava.net.preferIPv6Addresses=true --host_jvm_args=-Dbazel.DigestFunction=SHA256 --ignore_all_rc_files test --enable_platform_specific_config --cxxopt=-std=c++14 --host_cxxopt=-std=c++14 --jvmopt=-Djava.net.preferIPv6Addresses --copt=-DGRPC_BAZEL_BUILD --host_copt=-DGRPC_BAZEL_BUILD --action_env=GRPC_BAZEL_RUNTIME=1 --define=use_fast_cpp_protos=true --invocation_id=7bed9dcc-9f09-410f-a4cd-443267f9af94 --workspace_status_command=tools/remote_build/workspace_status_kokoro.sh --remote_instance_name=projects/grpc-testing/instances/default_instance --auth_enabled=true --remote_cache=grpcs://remotebuildexecution.googleapis.com --bes_backend=grpcs://buildeventservice.googleapis.com --bes_timeout=600s --bes_results_url=https://source.cloud.google.com/results/invocations/ --project_id=grpc-testing --test_tag_filters=-no_mac --build_tag_filters=-no_mac --define=use_strict_warning=true --dynamic_mode=off --verbose_failures=true --test_output=errors --test_env=GRPC_VERBOSITY=debug --google_credentials=/tmpfs/src/gfile/GrpcTesting-d0eeee2db331.json --remote_upload_local_results=true --remote_default_exec_properties=grpc_cache_silo_key1=83d8e488-1ca9-40fd-929e-d37d13529c99 --remote_default_exec_properties=grpc_cache_silo_key2=20221213-1155monterey-MacService --config=opt --compilation_mode=opt --copt=-Wframe-larger-than=16384 -- //test/...

I'm building on MacOS monterey (standard kokoro worker)

[jtattermusch]

@deannagarcia @mkruskal-google this is one of the issues that block grpc's upgrade to 22.x

[jtattermusch]

Indeed, the parameter semantic seems unused, so it's not surprising that it triggers and error via "-Werror,-Wunused-parameter"

protobuf/src/google/protobuf/io/printer.h

Line 94 in 58ecf38

absl::optional<Semantic> semantic) {

[fowles]

We don't support compiling with arbitrary warning flags. It is simply not sustainable as some warnings are mutually contradictory.

[jtattermusch]

Got that, but given that gRPC's upgrade to protobuf 22.x has been dragging on for quite a while now and there are still several other issues to resolve with the upgrade, IMHO fixing this one warning would make our lives much easier.
gRPC actually enables the unused-parameter warning in quite a few builds and the draft PR to upgrade us to protobuf 22.x is already way too complex and makes many other necessary adjustment.

So if we fix this warning (seems trivial to fix) and backport it to 22.x branch, it would help us prevent bloating the upgrade PR even more and allow us to focus on real problems with the upgrade instead. WDYT?

[fowles]

We will accept a patch and cherry pix for this, but it can break again without any notice.

[deannagarcia]

What do we mean by "fix" here? I think the fix the protobuf team wants is for this warning to be explicitly excluded in this file: https://github.com/protocolbuffers/protobuf/blob/main/src/google/protobuf/port_def.inc. Would that work for grpc?

[jtattermusch]

I think whatever makes the "unused parameter" errors go away works

This is one of our builds that uses strict warnings (and has the broadest scope among all of them I htink). You can run the build on glinux at https://github.com/jtattermusch/grpc/tree/repro_protobuf_12313

bazel build --define=use_strict_warning=true -- \
  :all \
  //src/core/... \
  //src/compiler/... \
  //test/... \
  //examples/... \
  -//examples/android/binder/...

It should reproduce the error as mentioned above.

[jtattermusch]

Simplified repro is bazel build --keep_going --define=use_strict_warning=true //src/compiler:grpc_cpp_plugin