clickhouse-cpp/2.5.1 Conan package fails to build with GCC 11

Summary

After the recent ConanCenter update of the clickhouse-cpp/2.5.1 recipe (as shown on the ConanCenter page, last updated 2025‑11‑17), building clickhouse-cpp/2.5.1 from source via Conan fails with GCC 11 and C++20.

The main error is:

* use of std::memory_order::memory_order_relaxed instead of std::memory_order_relaxed in types.cpp

Additionally, there is another build failure due to a deprecated enum‑enum bitwise operation being treated as an error (-Werror).

Downgrading to clickhouse-cpp/2.5.0 makes the issue disappear, so this seems to be a regression in the 2.5.1 Conan recipe / sources.

———

Environment

* OS: Linux x86_64
* Compiler: GCC 11
* C++ standard: gnu20 (profile compiler.cppstd=gnu20)
* Conan client: 2.x (using conancenter remote)
* Package: clickhouse-cpp/2.5.1 from ConanCenter
* Consumer project uses:
* [conanfile.py]() with self.requires("clickhouse-cpp/2.5.1")
* Profile sets compiler.libcxx=libstdc++11, build_type=Release

———

Conan profile (relevant parts)

\[settings\]
arch=x86_64
build_type=Release
compiler=gcc
compiler.version=11
compiler.cppstd=gnu20
compiler.libcxx=libstdc++11
os=Linux

———

Steps to reproduce

1. Create a minimal [conanfile.py]():

from conan import ConanFile

class TestClickhouseCpp(ConanFile):
settings = "os", "compiler", "build_type", "arch"
generators = "CMakeDeps", "CMakeToolchain"

```
def requirements(self):
self.requires("clickhouse-cpp/2.5.1")
```
2. Run:

conan install . --output-folder=build/conan_files --build=missing
3. Let Conan download and build clickhouse-cpp/2.5.1 from ConanCenter.

———

Actual behavior

The build fails in the clickhouse-cpp sources.

Key errors (paths are Conan’s build folder):

/home//.conan2/p/b/click6c1a182889a69/b/src/clickhouse/types/types.cpp: In member function ‘uint64_t clickhouse::Type::GetTypeUniqueId() const’: /home//.conan2/p/b/click6c1a182889a69/b/src/clickhouse/types/types.cpp:164:57: error: ‘memory_order_relaxed’ is not a member of ‘std::memory_order’ 164 | if (type_unique_id\_.load(std::memory_order::memory_order_relaxed) == 0) { | ^\~\~\~\~\~\~\~\~\~\~\~\~\~\~\~\~\~\~\~ /home//.conan2/p/b/click6c1a182889a69/b/src/clickhouse/types/types.cpp:166:112: error: ‘memory_order_relaxed’ is not a member of ‘std::memory_order’ 166 | type_unique_id\_.store(CityHash64WithSeed(name.c_str(), name.size(), code\_), std::memory_order::memory_order_relaxed); | ^\~\~\~\~\~\~\~\~\~\~\~\~\~\~\~\~\~\~\~

From the same build, another error:

/home//.conan2/p/b/click6c1a182889a69/b/src/clickhouse/columns/lowcardinality.cpp: In member function ‘virtual void clickhouse::ColumnLowCardinality::SaveBody(clickhouse::OutputStream\*)’: /home//.conan2/p/b/click6c1a182889a69/b/src/clickhouse/columns/lowcardinality.cpp:344:88: error: bitwise operation between different enumeration types ‘{anonymous}::IndexType’ and ‘{anonymous}::IndexFlag’ is deprecated \[-Werror=deprecated-enum- enum-conversion\] 344 | const uint64_t index_serialization_type = indexTypeFromIndexColumn(\*index_column\_) | IndexFlag::HasAdditionalKeysBit; | \~\~\~\~\~\~\~\~\~~~^~~ cc1plus: all warnings being treated as errors make\[2\]: \*\*\* \[clickhouse/CMakeFiles/clickhouse-cpp-lib.dir/columns/lowcardinality.cpp.o\] Error 1

Full CMake/Make invocation is driven by Conan; the key point is that warnings are treated as errors and the deprecated enum‑enum bitwise OR becomes a hard error.

———

Expected behavior

* clickhouse-cpp/2.5.1 builds successfully with GCC 11 and C++20 (and typical -Werror settings) via ConanCenter.
* No misuse of std::memory_order.

———

Analysis

1. Invalid use of std::memory_order

In src/clickhouse/types/types.cpp the code currently uses:

if (type_unique_id\_.load(std::memory_order::memory_order_relaxed) == 0) {
const auto name = GetName();
type_unique_id\_.store(
CityHash64WithSeed(name.c_str(), name.size(), code\_),
std::memory_order::memory_order_relaxed
);
}

But in standard C++ (since C++11):
* std::memory_order is the enum type.
* Enumerators are std::memory_order_relaxed, std::memory_order_acquire, etc., in namespace std, not as nested names inside the enum.

The correct usage should be:

if (type_unique_id\_.load(std::memory_order_relaxed) == 0) {
const auto name = GetName();
type_unique_id\_.store(
CityHash64WithSeed(name.c_str(), name.size(), code\_),
std::memory_order_relaxed
);
}

With this change, GCC 11 accepts the code.
2. Deprecated enum bitwise OR with -Werror

In src/clickhouse/columns/lowcardinality.cpp:

const uint64_t index_serialization_type =
indexTypeFromIndexColumn(\*index_column\_) | IndexFlag::HasAdditionalKeysBit;

indexTypeFromIndexColumn returns an IndexType, and IndexFlag is a different enum. GCC 11 (with C++20 and current warning settings) warns:

> bitwise operation between different enumeration types … is deprecated

Because warnings are treated as errors, this stops the build. One way to avoid this is to explicitly cast to an integer type before the bitwise operation, for example:

const uint64_t index_serialization_type =
static_cast(indexTypeFromIndexColumn(\*index_column\_)) |
static_cast(IndexFlag::HasAdditionalKeysBit);

———

Workaround

As a temporary workaround on the consumer side, downgrading to clickhouse-cpp/2.5.0 in [conanfile.py]():

self.requires("clickhouse-cpp/2.5.0")

allows conan install ... to complete successfully in the same environment.

———

Request

* Please fix the std::memory_order::memory_order_relaxed usage to std::memory_order_relaxed in types.cpp.
* Please also consider adjusting the enum bitwise operation in lowcardinality.cpp (or relaxing the relevant warning) so that the library builds cleanly with modern compilers and -Werror.