GH-48787: [C++] Upgrade s2n-tls to v1.6.4 and fix CMake 4.0 compatibility #48791

meher745 · 2026-01-08T17:52:41Z

Rationale for this change

Fixes the test-ubuntu-24.04-cpp-thread-sanitizer failure where s2n-tls builds were failing due to strict compiler warnings (documentation and integer precision) on newer Clang versions.

What changes are included in this PR?

Added -Wno-error specifically for the s2n target in cpp/cmake_modules/ThirdpartyToolchain.cmake. This allows the build to proceed despite intentional warnings in the s2n-tls project that Clang 18 now flags as errors.

Are these changes tested?

I am relying on the GitHub CI to verify that this suppression resolves the Ubuntu 24.04 compiler failures.

Are there any user-facing changes?

No. These changes only affect the C++ build system and third-party dependency management.

GitHub Issue: [CI][C++] test-ubuntu-24.04-cpp-thread-sanitizer fails to build s2n-tls #48787

github-actions · 2026-01-09T00:52:05Z

⚠️ GitHub issue #48787 has been automatically assigned in GitHub to PR creator.

kou · 2026-01-09T00:53:01Z

@github-actions crossbow submit test-ubuntu-24.04-cpp-thread-sanitizer

github-actions · 2026-01-09T00:53:07Z

⚠️ GitHub issue #48787 has been automatically assigned in GitHub to PR creator.

github-actions · 2026-01-09T00:55:11Z

Revision: 7ebcda0

Submitted crossbow builds: ursacomputing/crossbow @ actions-82a9f13dfd

Task	Status
test-ubuntu-24.04-cpp-thread-sanitizer

kou · 2026-01-09T01:23:43Z

Can we disable -Werror for bundled s2n-tls?

HyukjinKwon · 2026-01-09T01:36:43Z

I have some changes in #48797 could be applied here if that looks good!

meher745 · 2026-01-09T04:06:54Z

I have some changes in #48797 could be applied here if that looks good!

Thank you so much! @HyukjinKwon

kou · 2026-01-09T04:28:24Z

cpp/CMakeLists.txt

+# Allow older bundled dependencies to build with CMake 4.0+
+set(CMAKE_POLICY_VERSION_MINIMUM 3.5)


Do we need this?

While building on my local system, I was getting this error. So I thought it would be better to comply with this requirement.

Just my two cents. I would rather make this PR minimized to fix the issue, and separately file an issue for this and make a PR :-).

Yes. We should not mix separated problems as much as possible.

Let's revert this change from this PR, open a separated issue and let's discuss it there.

FYI: We already have similar code:

arrow/cpp/cmake_modules/ThirdpartyToolchain.cmake

Lines 1023 to 1026 in b126c6e

# We set CMAKE_POLICY_VERSION_MINIMUM temporarily due to failures with CMake 4

# We should remove it once we have updated the dependencies:

# https://github.com/apache/arrow/issues/45985

set(CMAKE_POLICY_VERSION_MINIMUM 3.5)

kou · 2026-01-09T04:28:40Z

@github-actions crossbow submit test-ubuntu-24.04-cpp-thread-sanitizer

github-actions · 2026-01-09T04:30:47Z

Revision: 5852bc1

Submitted crossbow builds: ursacomputing/crossbow @ actions-d8e1dd6f27

Task	Status
test-ubuntu-24.04-cpp-thread-sanitizer

meher745 · 2026-01-09T05:42:35Z

I have reverted the extra changes as requested. This PR now only contains the -Wno-error suppression.

I will open a separate PR shortly for the CMake 4.0 compatibility fix. Thank you once again!

HyukjinKwon · 2026-01-09T05:45:33Z

The change LGTM! BTW seems like there was testing deletion that mistakenly happened

Might need to restore 👍

meher745 · 2026-01-09T06:00:11Z

The change LGTM! BTW seems like there was testing deletion that mistakenly happened
Might need to restore 👍

Done! Thank you!

kou · 2026-01-09T06:20:57Z

@github-actions crossbow submit test-ubuntu-24.04-cpp-thread-sanitizer

kou · 2026-01-09T06:21:04Z

Could you update the PR description?

github-actions · 2026-01-09T06:23:25Z

Revision: 92b2cd0

Submitted crossbow builds: ursacomputing/crossbow @ actions-0a32f5ea59

Task	Status
test-ubuntu-24.04-cpp-thread-sanitizer

kou · 2026-01-09T06:23:29Z

I will open a separate PR shortly for the CMake 4.0 compatibility fix.

Could you open an issue before this? It's for "openness" of the Apache way.
See also: https://theapacheway.com/open/

And could you add a "take" comment to #48787 to assign the issue to you?

raulcd · 2026-01-09T14:23:57Z

@github-actions crossbow submit -g cpp

raulcd · 2026-01-09T14:24:47Z

The Python / AMD64 Conda Python 3.10 Sphinx & Numpydoc failure is unrelated and has been fixed on main now.

github-actions · 2026-01-09T14:26:36Z

Revision: 92b2cd0

Submitted crossbow builds: ursacomputing/crossbow @ actions-5488c7cb94

Task	Status
example-cpp-minimal-build-static
example-cpp-minimal-build-static-system-dependency
example-cpp-tutorial
test-build-cpp-fuzz
test-conda-cpp
test-conda-cpp-valgrind
test-cuda-cpp-ubuntu-22.04-cuda-11.7.1
test-cuda-cpp-ubuntu-24.04-cuda-13.0.2
test-debian-12-cpp-amd64
test-debian-12-cpp-i386
test-debian-experimental-cpp-gcc-15
test-fedora-42-cpp
test-ubuntu-22.04-cpp
test-ubuntu-22.04-cpp-20
test-ubuntu-22.04-cpp-bundled
test-ubuntu-22.04-cpp-emscripten
test-ubuntu-22.04-cpp-no-threading
test-ubuntu-24.04-cpp
test-ubuntu-24.04-cpp-bundled-offline
test-ubuntu-24.04-cpp-gcc-13-bundled
test-ubuntu-24.04-cpp-gcc-14
test-ubuntu-24.04-cpp-minimal-with-formats
test-ubuntu-24.04-cpp-thread-sanitizer

raulcd

LGTM

raulcd · 2026-01-09T14:52:54Z

cpp/cmake_modules/ThirdpartyToolchain.cmake

+        # Disable -Werror for s2n-tls: it has Clang 18 warnings that it intentionally allows.
+        # See: https://github.com/aws/s2n-tls/issues/5696
+        if(TARGET s2n)
+          target_compile_options(s2n PRIVATE -Wno-error)


Sounds reasonable to me, do we want to be more explicit as we do with substrait flags for example?

set(SUBSTRAIT_SUPPRESSED_FLAGS) if(MSVC) # Protobuf generated files trigger some spurious warnings on MSVC. # Implicit conversion from uint64_t to uint32_t: list(APPEND SUBSTRAIT_SUPPRESSED_FLAGS "/wd4244") # Missing dll-interface: list(APPEND SUBSTRAIT_SUPPRESSED_FLAGS "/wd4251") else() # GH-44954: silence [[deprecated]] declarations in protobuf-generated code list(APPEND SUBSTRAIT_SUPPRESSED_FLAGS "-Wno-deprecated") if(CMAKE_CXX_COMPILER_ID STREQUAL "AppleClang" OR CMAKE_CXX_COMPILER_ID STREQUAL "Clang") # Protobuf generated files trigger some errors on CLANG TSAN builds list(APPEND SUBSTRAIT_SUPPRESSED_FLAGS "-Wno-error=shorten-64-to-32") endif() endif()

Thinking on something like:

if(TARGET s2n) set(S2N_SUPPRESSED_FLAGS) if(CMAKE_CXX_COMPILER_ID STREQUAL "AppleClang" OR CMAKE_CXX_COMPILER_ID STREQUAL "Clang") # Disable specific warnings for s2n-tls: it has Clang 18 warnings that it intentionally allows. # See: https://github.com/aws/s2n-tls/issues/5696 list(APPEND S2N_SUPPRESSED_FLAGS "-Wno-error=documentation") list(APPEND S2N_SUPPRESSED_FLAGS "-Wno-error=documentation-deprecated-sync") list(APPEND S2N_SUPPRESSED_FLAGS "-Wno-error=shorten-64-to-32") endif() if(S2N_SUPPRESSED_FLAGS) target_compile_options(s2n PRIVATE ${S2N_SUPPRESSED_FLAGS}) endif() endif()

@kou @HyukjinKwon what are your thoughts?

Also maybe only add the flags for Clang compiler?

build: upgrade s2n-tls and fix CMake 4.0 compatibility

7ebcda0

github-actions bot added Component: C++ awaiting review Awaiting review labels Jan 8, 2026

kou changed the title ~~MINOR: [Cpp] Upgrade s2n-tls to v1.6.4 and fix CMake 4.0 compatibility~~ GH-48787: [C++] Upgrade s2n-tls to v1.6.4 and fix CMake 4.0 compatibility Jan 9, 2026

build: disable -Werror for s2n-tls as recommended

5852bc1

kou reviewed Jan 9, 2026

View reviewed changes

github-actions bot added awaiting changes Awaiting changes and removed awaiting review Awaiting review labels Jan 9, 2026

build: disable -Werror for s2n-tls to fix Ubuntu 24.04 CI

0b3cc89

github-actions bot added awaiting change review Awaiting change review and removed awaiting changes Awaiting changes labels Jan 9, 2026

chore: restore testing submodule to match upstream

92b2cd0

raulcd reviewed Jan 9, 2026

View reviewed changes

github-actions bot added awaiting changes Awaiting changes and removed awaiting change review Awaiting change review labels Jan 9, 2026

		# Allow older bundled dependencies to build with CMake 4.0+
		set(CMAKE_POLICY_VERSION_MINIMUM 3.5)

	# We set CMAKE_POLICY_VERSION_MINIMUM temporarily due to failures with CMake 4
	# We should remove it once we have updated the dependencies:
	# https://github.com/apache/arrow/issues/45985
	set(CMAKE_POLICY_VERSION_MINIMUM 3.5)

GH-48787: [C++] Upgrade s2n-tls to v1.6.4 and fix CMake 4.0 compatibility #48791

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GH-48787: [C++] Upgrade s2n-tls to v1.6.4 and fix CMake 4.0 compatibility #48791

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meher745 commented Jan 8, 2026 •

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