Adjust the standards for proto target to align with those of Protocol Buffers. by owent · Pull Request #3800 · open-telemetry/opentelemetry-cpp

owent · 2026-01-06T12:35:35Z

Changes

Please provide a brief description of the changes here.

For significant contributions please make sure you have completed the following items:

CHANGELOG.md updated for non-trivial changes
Unit tests have been added
Changes in public API reviewed

Analysis

The generated .pb.cc codes

inline constexpr EntityRef::Impl_::Impl_(
    ::_pbi::ConstantInitialized) noexcept
      : id_keys_{},
        description_keys_{},
        schema_url_(
            &::google::protobuf::internal::fixed_address_empty_string,
            ::_pbi::ConstantInitialized()),
        type_(
            &::google::protobuf::internal::fixed_address_empty_string,
            ::_pbi::ConstantInitialized()),
        _cached_size_{0} {}

port.h in protobuf:

// Take advantage of C++20 constexpr support in std::string.
class alignas(8) GlobalEmptyStringConstexpr {
 public:
  const std::string& get() const { return value_; }
  // Nothing to init, or destroy.
  std::string* Init() const { return nullptr; }

  template <typename T = std::string, bool = (T(), true)>
  static constexpr std::true_type HasConstexprDefaultConstructor(int) {
    return {};
  }
  static constexpr std::false_type HasConstexprDefaultConstructor(char) {
    return {};
  }

 private:
  std::string value_;
};

using GlobalEmptyString = std::conditional_t<
    GlobalEmptyStringConstexpr::HasConstexprDefaultConstructor(0),
    const GlobalEmptyStringConstexpr, GlobalEmptyStringDynamicInit>;

PROTOBUF_EXPORT extern GlobalEmptyString fixed_address_empty_string;

port.cc in protobuf

PROTOBUF_ATTRIBUTE_NO_DESTROY PROTOBUF_CONSTINIT
    PROTOBUF_ATTRIBUTE_INIT_PRIORITY1 GlobalEmptyString
        fixed_address_empty_string{};

If protobuf is built with C++17 but the generated .pb.cc files are built with C++20, protobuf exports GlobalEmptyStringDynamicInit fixed_address_empty_string; while .pb.cc expects GlobalEmptyStringConstexpr fixed_address_empty_string;, causing an unresolved external symbol.

On GCC/Clang, constexpr typically doesn’t require an extra symbol, so this mismatch doesn’t surface; MSVC’s behavior is right because constexpr is not a force rule, but it exposes the issue.

This didn’t happen before v30 because only the dynamic GlobalEmptyString existed. It was fixed in protobuf v32 by always using GlobalEmptyStringDynamicInit on MSVC, so the only affected case is MSVC with protobuf v31.

Copilot

Pull request overview

This PR adds CI validation to ensure OpenTelemetry C++ can be built with a different C++ standard than the protobuf dependency it uses, addressing issue #3799 where MSVC linking errors occurred when protobuf was compiled with C++17 but OpenTelemetry was built with C++20.

Key Changes:

Adds new cmake.different_std.test CI target for both Linux (GCC) and Windows (MSVC) platforms
Linux GCC test installs dependencies with C++17, then builds OpenTelemetry with C++23
Windows MSVC test validates similar scenario with C++20 for OpenTelemetry

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
ci/do_ci.sh	Adds new `cmake.different_std.test` target for Linux/GCC that builds with C++23 STL and enables OTLP file support
ci/do_ci.ps1	Adds new `cmake.different_std.test` target for Windows/MSVC that builds with C++20 STL, maintainer mode, and OTLP file support
.github/workflows/ci.yml	Adds two new CI jobs: one for GCC (installs protobuf with C++17, builds with C++23) and one for MSVC (tests different C++ standards)

.github/workflows/ci.yml

ci/do_ci.sh

ci/do_ci.ps1

.github/workflows/ci.yml

codecov · 2026-01-06T12:51:58Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.12%. Comparing base (508ec67) to head (d470150).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3800   +/-   ##
=======================================
  Coverage   90.12%   90.12%           
=======================================
  Files         227      227           
  Lines        7261     7261           
=======================================
  Hits         6543     6543           
  Misses        718      718

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

ThomsonTan · 2026-01-17T22:20:08Z

.github/workflows/ci.yml

    - name: run otprotocol test
      run: ./ci/do_ci.ps1 cmake.exporter.otprotocol.with_async_export.test

+  # Test case where protobuf is built with C++17 and OpenTelemetry with C++20 on MSVC will trigger a Internal compiler error


nit: remove this commented out test?

This test currently triggers an MSVC bug and causes an internal compiler error. Should we enable it once the MSVC compiler on GitHub runners is updated? I’m leaving it here so we can re-enable it quickly. It’s the only test that reproduces #3799; I can reproduce it locally with VS 2026, but that isn’t usable on gihutb right now. Alternatively, should we remove it and add it back later?

What is the ICE? Probably add TODO to track it?

Logs can be found at https://github.com/open-telemetry/opentelemetry-cpp/actions/runs/20818142168/job/59799024061

When building protobuf v31.1

libupb.vcxproj -> C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf-build\bin\Debug\libupbd.lib Building Custom Rule C:/Users/runneradmin/AppData/Local/Temp/otel-cpp-third-party-build/external/protobuf/src/protobuf/CMakeLists.txt any.cc any_lite.cc arena.cc arena_align.cc arenastring.cc arenaz_sampler.cc code_generator.cc code_generator_lite.cc plugin.pb.cc retention.cc cpp_features.pb.cc descriptor.cc C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf\src\google/protobuf/descriptor_visitor.h(108,1): fatal error C1001: Internal compiler error. [C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf-build\protoc-gen-upb.vcxproj] [C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\protobuf-build.vcxproj] (compiler file 'msc1.cpp', line 1589) To work around this problem, try simplifying or changing the program near the locations listed above. If possible please provide a repro here: https://developercommunity.visualstudio.com/ Please choose the Technical Support command on the Visual C++ Help menu, or open the Technical Support help file for more information C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf\src\google/protobuf/descriptor_visitor.h(108,1): message : the template instantiation context (the oldest one first) is [C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf-build\protoc-gen-upb.vcxproj] C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf\src\google\protobuf\descriptor.cc(8380,13): message : see reference to function template instantiation 'void google::protobuf::internal::VisitDescriptors<google::protobuf::DescriptorBuilder::CheckVisibilityRules::<lambda_eb886289529f14dfd0500371ca9c46d6>>(const google::protobuf::FileDescriptor &,const google::protobuf::FileDescriptorProto &,Visitor)' being compiled [C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf-build\protoc-gen-upb.vcxproj] with [ Visitor=google::protobuf::DescriptorBuilder::CheckVisibilityRules::<lambda_eb886289529f14dfd0500371ca9c46d6> ] C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf\src\google/protobuf/descriptor_visitor.h(167,58): message : see reference to function template instantiation 'void google::protobuf::internal::VisitImpl<google::protobuf::internal::VisitDescriptors::VisitorImpl>::Visit<const google::protobuf::FileDescriptorProto>(const google::protobuf::FileDescriptor &,const google::protobuf::FileDescriptorProto &)' being compiled [C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf-build\protoc-gen-upb.vcxproj] C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf\src\google/protobuf/descriptor_visitor.h(109,5): message : while compiling class template member function 'unknown-type google::protobuf::DescriptorBuilder::CheckVisibilityRules::<lambda_eb886289529f14dfd0500371ca9c46d6>::operator ()(const _T1 &,const _T2 &) const' [C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf-build\protoc-gen-upb.vcxproj] INTERNAL COMPILER ERROR in 'C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\bin\HostX64\x64\CL.exe' Please choose the Technical Support command on the Visual C++ Help menu, or open the Technical Support help file for more information Building Custom Rule C:/Users/runneradmin/AppData/Local/Temp/otel-cpp-third-party-build/external/protobuf/src/protobuf/CMakeLists.txt any.cc any_lite.cc arena.cc arena_align.cc arenastring.cc arenaz_sampler.cc code_generator.cc code_generator_lite.cc plugin.pb.cc retention.cc cpp_features.pb.cc descriptor.cc C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf\src\google/protobuf/descriptor_visitor.h(108,1): fatal error C1001: Internal compiler error. [C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf-build\protoc-gen-upbdefs.vcxproj] [C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\protobuf-build.vcxproj] (compiler file 'msc1.cpp', line 1589) To work around this problem, try simplifying or changing the program near the locations listed above. If possible please provide a repro here: https://developercommunity.visualstudio.com/ Please choose the Technical Support command on the Visual C++ Help menu, or open the Technical Support help file for more information C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf\src\google/protobuf/descriptor_visitor.h(108,1): message : the template instantiation context (the oldest one first) is [C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf-build\protoc-gen-upbdefs.vcxproj] C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf\src\google\protobuf\descriptor.cc(8380,13): message : see reference to function template instantiation 'void google::protobuf::internal::VisitDescriptors<google::protobuf::DescriptorBuilder::CheckVisibilityRules::<lambda_eb886289529f14dfd0500371ca9c46d6>>(const google::protobuf::FileDescriptor &,const google::protobuf::FileDescriptorProto &,Visitor)' being compiled [C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf-build\protoc-gen-upbdefs.vcxproj] with [ Visitor=google::protobuf::DescriptorBuilder::CheckVisibilityRules::<lambda_eb886289529f14dfd0500371ca9c46d6> ] C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf\src\google/protobuf/descriptor_visitor.h(167,58): message : see reference to function template instantiation 'void google::protobuf::internal::VisitImpl<google::protobuf::internal::VisitDescriptors::VisitorImpl>::Visit<const google::protobuf::FileDescriptorProto>(const google::protobuf::FileDescriptor &,const google::protobuf::FileDescriptorProto &)' being compiled [C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf-build\protoc-gen-upbdefs.vcxproj] C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf\src\google/protobuf/descriptor_visitor.h(109,5): message : while compiling class template member function 'unknown-type google::protobuf::DescriptorBuilder::CheckVisibilityRules::<lambda_eb886289529f14dfd0500371ca9c46d6>::operator ()(const _T1 &,const _T2 &) const' [C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\protobuf\src\protobuf-build\protoc-gen-upbdefs.vcxproj] INTERNAL COMPILER ERROR in 'C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\bin\HostX64\x64\CL.exe' Please choose the Technical Support command on the Visual C++ Help menu, or open the Technical Support help file for more information C:\Program Files\Microsoft Visual Studio\2022\Enterprise\MSBuild\Microsoft\VC\v170\Microsoft.CppCommon.targets(254,5): error MSB8066: Custom build for 'C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\CMakeFiles\b85673c8d2c887062bdd371d2afff3e1\protobuf-mkdir.rule;C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\CMakeFiles\b85673c8d2c887062bdd371d2afff3e1\protobuf-download.rule;C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\CMakeFiles\b85673c8d2c887062bdd371d2afff3e1\protobuf-update.rule;C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\CMakeFiles\b85673c8d2c887062bdd371d2afff3e1\protobuf-patch.rule;C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\CMakeFiles\b85673c8d2c887062bdd371d2afff3e1\protobuf-configure.rule;C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\CMakeFiles\b85673c8d2c887062bdd371d2afff3e1\protobuf-build.rule;C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\CMakeFiles\78a33ba8e4d1644ab3e8d5cd79f88cfd\protobuf-build.rule;D:\a\opentelemetry-cpp\opentelemetry-cpp\install\cmake\CMakeLists.txt' exited with code 1. [C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\protobuf-build.vcxproj] Performing install step for 'curl' MSBuild version 17.14.23+b0019275e for .NET Framework 1>Checking Build System Building Custom Rule C:/Users/runneradmin/AppData/Local/Temp/otel-cpp-third-party-build/external/curl/src/curl/lib/CMakeLists.txt libcurl_object.vcxproj -> C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\curl\src\curl-build\lib\libcurl_object.dir\Debug\libcurl_object.lib Building Custom Rule C:/Users/runneradmin/AppData/Local/Temp/otel-cpp-third-party-build/external/curl/src/curl/lib/CMakeLists.txt libcurl_shared.vcxproj -> C:\Users\runneradmin\AppData\Local\Temp\otel-cpp-third-party-build\external\curl\src\curl-build\lib\Debug\libcurl-d.dll Building Custom Rule C:/Users/runneradmin/AppData/Local/Temp/otel-cpp-third-party-build/external/curl/src/curl/CMakeLists.txt 1> -- Install configuration: "Debug"

I successfully built and tested Protobuf v31.1 on my system. It works well with the latest versions of both VS 2022 and VS 2026.
TODO comment is added and I squashed commits to clean up the history.

cmake/opentelemetry-proto.cmake

Fixes third_party_latest PATH install latest third party libs for windows Fixes copyright and parallel Fixes cmake args Restore windows version try to reproduce link error add --build-shared-libs "ON" Allow install_thirdparty to set BUILD_SHARED_LIBS Make the proto targets follow the CXX_STANDARD using by protobuf Fixes the compatibility for old version of protobuf with C++14 used Fixes DEFINED CMAKE_CXX_STANDARD checking Fixes compiling Fixes spelling Patch protobuf v31 only is enough Fixes cmake var Add TODO

dbarker · 2026-03-25T20:10:32Z

cmake/opentelemetry-proto.cmake

+       AND CMAKE_CXX_STANDARD GREATER_EQUAL 20
+       AND (Protobuf_VERSION_MAJOR EQUAL 31 OR Protobuf_VERSION MATCHES
+                                               "31\\..*"))
+      set(protobuf_lib_compile_features_cxx_std 17)


Do we need to consider users building protobuf and abseil-cpp with other c++ standards (c++14, 20, 23) and would they also experience similar ABI issues on other OSes?

This issue was introduced in protobuf v31 and has already been fixed in protobuf v32.
Protobuf v31 requires C++17, and the ABI remains compatible when it is built with C++20 or later.
GCC and Clang may inline the relevant code, which can hide the issue. While this is more of a workaround than a proper fix, it should not introduce additional problems.

dbarker · 2026-03-25T20:14:42Z

cmake/opentelemetry-proto.cmake

+      set(protobuf_lib_compile_features_cxx_std 17)
+      message(
+        STATUS
+          "protobuf::libprotobuf ${Protobuf_VERSION} detected and we force set CXX_STANDARD to 17 for .pb.cc files."


Would a simple option for the OTELCPP_PROTO_CXX_STANDARD address the original issue more generally?

# Default to what the rest of the project is using set(OTELCPP_PROTO_CXX_STANDARD "${CMAKE_CXX_STANDARD}" CACHE STRING "The C++ standard used to compile the imported Protobuf libraries") # Apply the user defined cxx standard to the proto target set_target_properties(opentelemetry_proto PROPERTIES CXX_STANDARD ${OTELCPP_PROTO_CXX_STANDARD})

According to the CMake documentation for LANG_STANDARD (https://cmake.org/cmake/help/latest/prop_tgt/LANG_STANDARD.html), the actual C++ standard used for compilation may be higher than the value specified by the CXX_STANDARD property.

Simply setting CXX_STANDARD does not work for our game server projects, so I changed implementation to patch the final compiling options.

lalitb · 2026-03-25T23:57:54Z

@owent Thanks for the PR. The PR look much broader than the bug it is trying to fix. The actual issue appears to be narrow: MSVC + protobuf v31 + building the generated .pb.cc files with a higher C++ standard than protobuf itself. That should be fixable with a small change in cmake/opentelemetry-proto.cmake plus a simple CXX_STANDARD override on the generated proto targets in cmake/tools.cmake. I would suggest to narrow down this PR to minimal fix with

narrow detection in cmake/opentelemetry-proto.cmake
set CXX_STANDARD directly on opentelemetry_proto / opentelemetry_proto_grpc
avoid the regex-based compile flag rewriting and unrelated warning flag changes

And then we can have a separate infra PR with install_thirdparty.ps1/sh related changes if required.

Copilot AI review requested due to automatic review settings January 6, 2026 12:35

owent requested a review from a team as a code owner January 6, 2026 12:35

Copilot started reviewing on behalf of owent January 6, 2026 12:36 View session

Copilot AI reviewed Jan 6, 2026

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owent force-pushed the proto_std_should_follow_pb branch 4 times, most recently from 3f725c7 to 7cab857 Compare January 10, 2026 17:00

owent changed the title ~~[WIP] Adjust the standards for proto target to align with those of Protocol Buffers.~~ Adjust the standards for proto target to align with those of Protocol Buffers. Jan 13, 2026

ThomsonTan reviewed Jan 17, 2026

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ThomsonTan reviewed Jan 26, 2026

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owent force-pushed the proto_std_should_follow_pb branch from 5426ace to 4e79eb3 Compare January 29, 2026 02:41

owent force-pushed the proto_std_should_follow_pb branch from ed30cbb to 6929949 Compare February 5, 2026 02:32

owent requested a review from ThomsonTan February 6, 2026 10:58

Merge branch 'main' into proto_std_should_follow_pb

4de6ef6

owent mentioned this pull request Mar 4, 2026

MSVC may link error when using protobuf built with C++17 but build otel-cpp with C++20 #3799

Open

ThomsonTan and others added 2 commits March 4, 2026 08:59

Merge branch 'main' into proto_std_should_follow_pb

04e2077

Merge branch 'main' into proto_std_should_follow_pb

39a82da

dbarker reviewed Mar 25, 2026

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Merge branch 'main' into proto_std_should_follow_pb

d470150

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