Build error when using g++ 9.3 and associated std lib

[RajivKurian]

What version of gRPC and what language are you using?

GRPC master, commit 0da56bc

What operating system (Linux, Windows,...) and version?

Ubuntu 20.04

What runtime / compiler are you using (e.g. python version or version of gcc)

g++ 9.30, libstdc++.so.6

What did you do?

Try to build a hello world server/client example in my project using bazel.
I import grpc in my bazel workspace as follows:
I use the absl version that I found used in grpc deps.

http_archive(
    name = "com_google_absl",
    sha256 = "dcf71b9cba8dc0ca9940c4b316a0c796be8fab42b070bb6b7cab62b48f0e66c4",
    strip_prefix = "abseil-cpp-20211102.0",
    urls = [
        "https://storage.googleapis.com/grpc-bazel-mirror/github.com/abseil/abseil-cpp/archive/20211102.0.tar.gz",
        "https://github.com/abseil/abseil-cpp/archive/20211102.0.tar.gz",
    ],
)

http_archive(
    name = "com_github_grpc_grpc",
    strip_prefix = "grpc-0da56bcc0e42a9e288d7511ed8426b9831ffbfb5",
    urls = [
        "https://github.com/grpc/grpc/archive/0da56bcc0e42a9e288d7511ed8426b9831ffbfb5.tar.gz",
    ],
)

load("@com_github_grpc_grpc//bazel:grpc_deps.bzl", "grpc_deps")
grpc_deps()
load("@com_github_grpc_grpc//bazel:grpc_extra_deps.bzl", "grpc_extra_deps")
grpc_extra_deps()

I compile a copy of https://github.com/grpc/grpc/blob/master/examples/cpp/helloworld/greeter_server.cc by issuing
bazel build //grpc_example:greeter_server

What did you expect to see?

A successful compilation

What did you see instead?

A compile error like this:

In file included from external/com_github_grpc_grpc/src/core/ext/filters/client_channel/resolver/xds/xds_resolver.cc:28:
In file included from external/com_github_grpc_grpc/src/core/ext/filters/client_channel/config_selector.h:30:
In file included from external/com_github_grpc_grpc/src/core/lib/channel/channel_stack.h:62:
In file included from external/com_github_grpc_grpc/src/core/lib/resource_quota/arena.h:42:
In file included from external/com_github_grpc_grpc/src/core/lib/resource_quota/memory_quota.h:33:
In file included from external/com_github_grpc_grpc/src/core/lib/promise/activity.h:33:
In file included from external/com_google_absl/absl/types/variant.h:50:
/my_conda_envs/conda/envs/d9695e4b93d2/bin/../lib/gcc/x86_64-conda-linux-gnu/9.3.0/../../../../x86_64-conda-linux-gnu/include/c++/9.3.0/variant:609:6: error: no matching conversion for functional-style cast from 'const std::basic_string<char>' to 'variant<std::basic_string<char>, std::vector<grpc_core::XdsRouteConfigResource::Route::RouteAction::ClusterWeight>, std::basic_string<char>>'
                        = variant<_Types...>(__rhs_mem);

I am using gcc 9.3 and libstdc++.so.6 from conda. I notice that this problem goes away if I update gcc and libstdc++ to higher versions but sadly that is not an option in my environment. Is there anything I can do to make this problem go away without updating gcc? I am already on one of the latest commits on grpc. Is there a downgrade I could perhaps do to make this problem go away?

Anything else we should know about your project / environment?

[RajivKurian]

I also noticed that the problem goes away if I use downgrade to commit 1c159689ceda2c408f7f9d97d96a264c9521b806 which corresponds to v1.45.1(1c15968)

[markdroth]

Looks like a possible portability issue. Esun, can you please take a look?

[veblush]

I briefly tried to reproduce this on Ubuntu 20 with gcc 9 but it worked as followings;

docker run -it --rm ubuntu:20.04
apt update
apt install build-essential git
# install bazel
curl -fsSL https://bazel.build/bazel-release.pub.gpg | gpg --dearmor > bazel.gpg
mv bazel.gpg /etc/apt/trusted.gpg.d/
echo "deb [arch=amd64] https://storage.googleapis.com/bazel-apt stable jdk1.8" | tee /etc/apt/sources.list.d/bazel.list
apt update && apt install bazel
# get grpc
cd /tmp
git clone https://github.com/grpc/grpc
cd grpc
# build an example
export CC=gcc
export CXX=g++
bazel build examples/cpp/helloworld:greeter_server

If you can give us repro, it would be helpful to address it.

[RajivKurian]

Hi @veblush, we are using conda to get our gcc toolchain including libstdc++. I can give it a shot in terms of reproducing it with that toolchain. I wonder if the conda libstdc++ is slightly different as surprising as that would be.

[veblush]

I guess #30118 fixed ths issue.