Build failure

[outpaddling]

I'm working on updating the google-cloud-cpp FreeBSD port, and hit the build issue below. It also occurs under FreeBSD 14.2 with clang18.

# uname -a
FreeBSD barracuda.acadix.biz 14.3-RELEASE-p2 FreeBSD 14.3-RELEASE-p2 GENERIC amd64

# clang --version
FreeBSD clang version 19.1.7 (https://github.com/llvm/llvm-project.git llvmorg-19.1.7-0-gcd708029e0b2)
Target: x86_64-unknown-freebsd14.3
Thread model: posix
InstalledDir: /usr/bin

# pkg info|grep -E 'opentelemetry|grpc|abseil'
abseil-20250127.1              Abseil Common Libraries (C++)
grpc-1.74.0,2                  HTTP/2-based RPC framework
opentelemetry-cpp-1.20.0       OpenTelemetry C++ client

# git describe --tags
v2.41.0-9-gc06d686e32

[ 50% 744/1457] /usr/bin/c++ -DGOOGLE_CLOUD_CPP_HAVE_OPENSSL -DOPENTELEMETRY_ABI_VERSION_NO=1 -DPROTOBUF_USE_DLLS -Dgoogle_cloud_cpp_opentelemetry_EXPORTS -I/usr/ports/wip/google-cloud-cpp/work/google-cloud-cpp-2.41.0-9-gc06d686e32 -isystem /usr/local/include -isystem /usr/ports/wip/google-cloud-cpp/work/.build -isystem /usr/ports/wip/google-cloud-cpp/work/.build/external/googleapis -isystem /usr/ports/wip/google-cloud-cpp/work/.build/google/cloud/monitoring -isystem /usr/ports/wip/google-cloud-cpp/work/.build/google/cloud/trace -O2 -pipe  -fstack-protector-strong -fno-strict-aliasing   -std=c++17 -O2 -pipe  -fstack-protector-strong -fno-strict-aliasing   -std=c++17  -DNDEBUG -fPIC -Wall -Wextra -Wconversion -Wno-sign-conversion -fno-exceptions -pthread -Wno-float-conversion -Wno-implicit-float-conversion -Wno-implicit-int-float-conversion -Wno-unknown-warning-option -DNOMINMAX -MD -MT google/cloud/opentelemetry/CMakeFiles/google_cloud_cpp_opentelemetry.dir/internal/monitored_resource.cc.o -MF google/cloud/opentelemetry/CMakeFiles/google_cloud_cpp_opentelemetry.dir/internal/monitored_resource.cc.o.d -o google/cloud/opentelemetry/CMakeFiles/google_cloud_cpp_opentelemetry.dir/internal/monitored_resource.cc.o -c /usr/ports/wip/google-cloud-cpp/work/google-cloud-cpp-2.41.0-9-gc06d686e32/google/cloud/opentelemetry/internal/monitored_resource.cc
FAILED: google/cloud/opentelemetry/CMakeFiles/google_cloud_cpp_opentelemetry.dir/internal/monitored_resource.cc.o 
/usr/bin/c++ -DGOOGLE_CLOUD_CPP_HAVE_OPENSSL -DOPENTELEMETRY_ABI_VERSION_NO=1 -DPROTOBUF_USE_DLLS -Dgoogle_cloud_cpp_opentelemetry_EXPORTS -I/usr/ports/wip/google-cloud-cpp/work/google-cloud-cpp-2.41.0-9-gc06d686e32 -isystem /usr/local/include -isystem /usr/ports/wip/google-cloud-cpp/work/.build -isystem /usr/ports/wip/google-cloud-cpp/work/.build/external/googleapis -isystem /usr/ports/wip/google-cloud-cpp/work/.build/google/cloud/monitoring -isystem /usr/ports/wip/google-cloud-cpp/work/.build/google/cloud/trace -O2 -pipe  -fstack-protector-strong -fno-strict-aliasing   -std=c++17 -O2 -pipe  -fstack-protector-strong -fno-strict-aliasing   -std=c++17  -DNDEBUG -fPIC -Wall -Wextra -Wconversion -Wno-sign-conversion -fno-exceptions -pthread -Wno-float-conversion -Wno-implicit-float-conversion -Wno-implicit-int-float-conversion -Wno-unknown-warning-option -DNOMINMAX -MD -MT google/cloud/opentelemetry/CMakeFiles/google_cloud_cpp_opentelemetry.dir/internal/monitored_resource.cc.o -MF google/cloud/opentelemetry/CMakeFiles/google_cloud_cpp_opentelemetry.dir/internal/monitored_resource.cc.o.d -o google/cloud/opentelemetry/CMakeFiles/google_cloud_cpp_opentelemetry.dir/internal/monitored_resource.cc.o -c /usr/ports/wip/google-cloud-cpp/work/google-cloud-cpp-2.41.0-9-gc06d686e32/google/cloud/opentelemetry/internal/monitored_resource.cc
/usr/ports/wip/google-cloud-cpp/work/google-cloud-cpp-2.41.0-9-gc06d686e32/google/cloud/opentelemetry/internal/monitored_resource.cc:225:10: error: no matching function for call to 'visit'
  225 |   return absl::visit(AsStringVisitor{}, attribute);
      |          ^~~~~~~~~~~
/usr/include/c++/v1/variant:1573:1: note: candidate template ignored: substitution failure [with _Visitor = AsStringVisitor, _Vs = <const opentelemetry::sdk::common::OwnedAttributeValue &>]: no matching function for call to '__as_variant'
 1153 | visit(_Visitor&& __visitor, _Vs&&... __vs) {
      | ^
1 error generated.

[outpaddling]

FYI, I get the exact same error when building with GCC 13.

[outpaddling]

2.40.0 is the first release to exhibit this issue. 2.39.0 builds successfully.

Update: This appears to be only because opentelemetry is disabled by default in 2.39.0 and earlier. When I enable it using

-DGOOGLE_CLOUD_CPP_ENABLE="storage,opentelemetry"

I get the same error as 2.40.x.

[scotthart]

Looks like there's some differing definitions of variant and visit between abseil and opentelemetry, with the possibilities being std::variant, absl::variant, and opentelemetry's nostd::variant.

[outpaddling]

You think it might just be a matter of clarifying the namespace in the scope(s) where the errors are happening?

[outpaddling]

Following your clue and using trial and error, I came up with the following patch set that produces a successful build, though I have no idea if there are runtime differences between these conflicting implementations that we need to worry about. These patches work with opentelemetry-cpp 1.20.0, but 1.21.0 requires additional patches that aren't so simple.

--- google/cloud/opentelemetry/internal/monitored_resource.cc.orig      2025-09-05 00:42:39 UTC
+++ google/cloud/opentelemetry/internal/monitored_resource.cc
@@ -222,7 +222,7 @@ std::string AsString(
 
 std::string AsString(
     opentelemetry::sdk::common::OwnedAttributeValue const& attribute) {
-  return absl::visit(AsStringVisitor{}, attribute);
+  return opentelemetry::nostd::visit(AsStringVisitor{}, attribute);
 }
 
 MonitoredResource ToMonitoredResource(
--- google/cloud/opentelemetry/internal/recordable.cc.orig      2025-09-05 00:43:49 UTC
+++ google/cloud/opentelemetry/internal/recordable.cc
@@ -207,7 +207,7 @@ void AddAttributeImpl(
     std::size_t limit) {
   auto* proto = ProtoOrDrop(attributes, key, limit);
   if (proto) {
-    absl::visit(AttributeVisitor{*proto}, value);
+    opentelemetry::nostd::visit(AttributeVisitor{*proto}, value);
   } else {
     attributes.set_dropped_attributes_count(
         attributes.dropped_attributes_count() + 1);
--- google/cloud/opentelemetry/internal/time_series.cc.orig     2025-09-05 00:45:42 UTC
+++ google/cloud/opentelemetry/internal/time_series.cc
@@ -41,10 +41,10 @@ google::monitoring::v3::TypedValue ToValue(
 google::monitoring::v3::TypedValue ToValue(
     opentelemetry::sdk::metrics::ValueType value) {
   google::monitoring::v3::TypedValue proto;
-  if (absl::holds_alternative<double>(value)) {
-    proto.set_double_value(absl::get<double>(value));
+  if (opentelemetry::nostd::holds_alternative<double>(value)) {
+    proto.set_double_value(opentelemetry::nostd::get<double>(value));
   } else {
-    proto.set_int64_value(absl::get<std::int64_t>(value));
+    proto.set_int64_value(opentelemetry::nostd::get<std::int64_t>(value));
   }
   return proto;
 }
@@ -63,9 +63,9 @@ double AsDouble(opentelemetry::sdk::metrics::ValueType
 }
 
 double AsDouble(opentelemetry::sdk::metrics::ValueType const& v) {
-  return absl::holds_alternative<double>(v)
-             ? absl::get<double>(v)
-             : static_cast<double>(absl::get<std::int64_t>(v));
+  return opentelemetry::nostd::holds_alternative<double>(v)
+             ? opentelemetry::nostd::get<double>(v)
+             : static_cast<double>(opentelemetry::nostd::get<std::int64_t>(v));
 }
 
 std::vector<google::monitoring::v3::CreateTimeSeriesRequest> ToRequestsHelper(
@@ -118,7 +118,7 @@ void ToTimeSeriesHelper(
             return absl::nullopt;
           }
         };
-        auto ts = absl::visit(Visitor{metric_data}, pda.point_data);
+        auto ts = opentelemetry::nostd::visit(Visitor{metric_data}, pda.point_data);
         if (!ts) continue;
         ts->set_unit(metric_data.instrument_descriptor.unit_);
         ts_collector_fn(metric_data, pda, *std::move(ts));

[anlexN]

@google-cloud-cpp team.

Today, I also in trouble for this build issue.

To be honest, have you successfully build this package: https://github.com/googleapis/google-cloud-cpp/tree/v2.42.0/google/cloud/opentelemetry?

I need this package very much. I am very painful now.

Hello everyone, can you give me this package that you successfully build?

@outpaddling @scotthart @google-cloud-cpp team

[outpaddling]

For FreeBSD, I have working google-cloud-cpp-2.42.0 and opentelemetry-1.2.0 work-in-progress ports:

https://github.com/outpaddling/freebsd-ports-wip

That's what I'll be using until this issue is resolved and we can upgrade to the latest.

[anlexN]

For FreeBSD, I have working google-cloud-cpp-2.42.0 and opentelemetry-1.2.0 work-in-progress ports:

https://github.com/outpaddling/freebsd-ports-wip

That's what I'll be using until this issue is resolved and we can upgrade to the latest.

@outpaddling opentelemetry-1.2.0, 1.2.0 is very old version. are you sure you don't type error?

I use debian os, how to use your freebsd-ports-wip? freebsd use glibc?

[outpaddling]

That's the latest version that will work with google-cloud-cpp-2.4.2 + minimal patching.

[anlexN]

That's the latest version that will work with google-cloud-cpp-2.4.2 + minimal patching.

I use debian os, how to use your freebsd-ports-wip? freebsd use glibc?

@outpaddling execuse me.

[outpaddling]

It will only serve as an example for some other package manager, like Debian packages, vcpkg, etc. FreeBSD ports only works on FreeBSD and Dragonfly BSD AFAIK.

[anlexN]

After review all google-cloud-cpp and opentelemetry-cpp source codes, I find that:

1. google-cloud-cpp namespace use opentelemetry-cpp namespace, opentelemetry-cpp namespace use google-cloud-cpp namespace. opentelemetry-cpp namespace's depth is very deep and long. This sacrifice coding happy. This make package version lock-in
2. why must C++ namespace? Can we transform C++ namespace's codes to code in the folders?

[wangjiezhe]

Here is my patch to compile google-cloud-cpp 1.42.0 with opentelemetry-cpp-1.20.0 and pass the tests on gentoo.

https://github.com/wangjiezhe/gentoo-local/tree/main/net-libs/google-cloud-cpp/files

similar with outpaddling's patch, with more changes.