[BUILD] Opentelemetry C++20 extension causes Envoy build issue

[shiponcs]

Title: [BUILD] Opentelemetry C++20 extension causes Envoy build issue

Description:
Envoy build failed because of Opentelemetry C++20 requirement.

$ bazel build envoy
ERROR: /source/source/extensions/tracers/opentelemetry/BUILD:14:19: Compiling source/extensions/tracers/opentelemetry/config.cc failed: (Exit 1): clang-14 failed: error executing command (from target //source/extensions/tracers/opentelemetry:config) /opt/llvm/bin/clang-14 -U_FORTIFY_SOURCE -fstack-protector -Wall -Wthread-safety -Wself-assign -Wunused-but-set-parameter -Wno-free-nonheap-object -fcolor-diagnostics -fno-omit-frame-pointer ... (remaining 239 arguments skipped)

Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
In file included from source/extensions/tracers/opentelemetry/config.cc:8:
In file included from ./source/extensions/tracers/opentelemetry/opentelemetry_tracer_impl.h:17:
In file included from bazel-out/k8-fastbuild/bin/external/io_opentelemetry_cpp/api/_virtual_includes/api/opentelemetry/logs/provider.h:10:
In file included from bazel-out/k8-fastbuild/bin/external/io_opentelemetry_cpp/api/_virtual_includes/api/opentelemetry/logs/noop.h:11:
In file included from bazel-out/k8-fastbuild/bin/external/io_opentelemetry_cpp/api/_virtual_includes/api/opentelemetry/logs/event_logger.h:7:
bazel-out/k8-fastbuild/bin/external/io_opentelemetry_cpp/api/_virtual_includes/api/opentelemetry/logs/logger.h:261:5: error: use of the 'likely' attribute is a C++20 extension [-Werror,-Wc++20-attribute-extensions]
    OPENTELEMETRY_LIKELY_IF(Enabled(severity) == false) { return false; }
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
bazel-out/k8-fastbuild/bin/external/io_opentelemetry_cpp/api/_virtual_includes/api/opentelemetry/common/macros.h:12:11: note: expanded from macro 'OPENTELEMETRY_LIKELY_IF'
        [[likely]]
        ~~^~~~~~~~
In file included from source/extensions/tracers/opentelemetry/config.cc:8:
In file included from ./source/extensions/tracers/opentelemetry/opentelemetry_tracer_impl.h:17:
In file included from bazel-out/k8-fastbuild/bin/external/io_opentelemetry_cpp/api/_virtual_includes/api/opentelemetry/logs/provider.h:10:
In file included from bazel-out/k8-fastbuild/bin/external/io_opentelemetry_cpp/api/_virtual_includes/api/opentelemetry/logs/noop.h:11:
In file included from bazel-out/k8-fastbuild/bin/external/io_opentelemetry_cpp/api/_virtual_includes/api/opentelemetry/logs/event_logger.h:7:
bazel-out/k8-fastbuild/bin/external/io_opentelemetry_cpp/api/_virtual_includes/api/opentelemetry/logs/logger.h:267:5: error: use of the 'likely' attribute is a C++20 extension [-Werror,-Wc++20-attribute-extensions]
    OPENTELEMETRY_LIKELY_IF(Enabled(severity) == false) { return false; }
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
bazel-out/k8-fastbuild/bin/external/io_opentelemetry_cpp/api/_virtual_includes/api/opentelemetry/common/macros.h:12:11: note: expanded from macro 'OPENTELEMETRY_LIKELY_IF'
        [[likely]]
        ~~^~~~~~~~
2 errors generated.
Target //source/exe:envoy-static failed to build
Use --verbose_failures to see the command lines of failed build steps.
INFO: Elapsed time: 2625.963s, Critical Path: 76.06s
INFO: 14619 processes: 6232 internal, 1 local, 8385 processwrapper-sandbox, 1 worker.
FAILED: Build did NOT complete successfully

[marcalff]

Please clarify:

• which compiler is used, including the exact compiler version
• which --std=c++ standard version is used (C++11/14/17/20/23)

The relevant opentelemetry-cpp code is:

#if !defined(OPENTELEMETRY_LIKELY_IF) && defined(__cplusplus)
// GCC 9 has likely attribute but do not support declare it at the beginning of statement
#  if defined(__has_cpp_attribute) && (defined(__clang__) || !defined(__GNUC__) || __GNUC__ > 9)
#    if __has_cpp_attribute(likely)
#      define OPENTELEMETRY_LIKELY_IF(...) \
        if (__VA_ARGS__)                   \
        [[likely]]

#    endif
#  endif
#endif
#if !defined(OPENTELEMETRY_LIKELY_IF) && (defined(__clang__) || defined(__GNUC__))
#  define OPENTELEMETRY_LIKELY_IF(...) if (__builtin_expect(!!(__VA_ARGS__), true))
#endif
#ifndef OPENTELEMETRY_LIKELY_IF
#  define OPENTELEMETRY_LIKELY_IF(...) if (__VA_ARGS__)
#endif

In other words, opentelemetry-cpp will use [[likely]] if the compiler supports it.

Building with [-Werror,-Wc++20-attribute-extensions] is likely the cause of the build break here.

[owent]

Just wondering why envoy do not allow -Wc++20-attribute-extensions here? Is it necessary for otel-cpp to close this warning for some specify compilers here?

[shiponcs]

@marcalff

I am building envoy-contrib with this option --config=rbe-toolchain-clang-libc++.

I have tried building -Wno-c++20-attribute-extensions that failed also.

[marcalff]

I am building envoy-contrib with this option --config=rbe-toolchain-clang-libc++.

Ok, but this does not tell us anything about the compiler version, and the C++ standard used.

[shiponcs]

I am building envoy-contrib with this option --config=rbe-toolchain-clang-libc++.

Ok, but this does not tell us anything about the compiler version, and the C++ standard used.

You're right. I have to ask Envoy team about this.

[shiponcs]

FYI, Envoy has recently switched to C++ 20. So, we can build without hitting any error. envoyproxy/envoy#32660 (comment)

[github-actions]

This issue was marked as stale due to lack of activity.

[marcalff]

@shiponcs

I see this issue got reopened.

PR #2580 should resolve the issue with C++20, what are the remaining problems at this point ?