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[ci] Add special build with Clang and libc++ on Linux #23647

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d2b6b7e
[ci] Add special build with Clang and libc++ on Linux
guitargeek Oct 3, 2026
62f9b4f
[cling] Look up headers of the C++ standard library ROOT is built with
guitargeek Oct 7, 2026
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38 changes: 38 additions & 0 deletions .github/workflows/root-ci-config/buildconfig/fedora44-clang_libcxx.txt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,38 @@
# Build ROOT with Clang and libc++ instead of GNU libstdc++ on Linux.
# The Fedora 44 image provides clang and libcxx/libcxxabi-devel packages.
CMAKE_C_COMPILER=clang
CMAKE_CXX_COMPILER=clang++
CMAKE_GENERATOR=Ninja
CMAKE_CXX_STANDARD=20
soversion=ON
libcxx=ON
davix=OFF
tpython=OFF
minuit2_omp=OFF
# All C++ dependencies must be built with the same toolchain: the ones
# shipped by the distribution are compiled with libstdc++ and are ABI
# incompatible with a libc++ ROOT build.
builtin_civetweb=ON
builtin_fftw3=ON
builtin_freetype=ON
builtin_ftgl=ON
builtin_gif=ON
builtin_gl2ps=ON
builtin_gtest=ON
builtin_gsl=ON
builtin_jpeg=ON
builtin_lz4=ON
builtin_lzma=ON
builtin_nlohmann=ON
builtin_pcre=ON
builtin_png=ON
builtin_tbb=ON
builtin_tiff=ON
builtin_unuran=ON
builtin_vdt=ON
builtin_xrootd=ON
builtin_xxhash=ON
builtin_zlib=ON
builtin_zstd=ON
test_distrdf_dask=OFF
test_distrdf_pyspark=OFF
5 changes: 5 additions & 0 deletions .github/workflows/root-ci.yml
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Expand Up @@ -120,7 +120,7 @@
matrix:
# Specify platform + optional build option overrides
# Build options: https://root.cern/install/build_from_source/#all-build-options
platform: [mac26, mac27, mac-beta]

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label "mac27" is unknown. available labels are "windows-latest", "windows-latest-8-cores", "windows-2025", "windows-2025-vs2026", "windows-2022", "windows-11-arm", "ubuntu-slim", "ubuntu-latest", "ubuntu-latest-4-cores", "ubuntu-latest-8-cores", "ubuntu-latest-16-cores", "ubuntu-24.04", "ubuntu-24.04-arm", "ubuntu-22.04", "ubuntu-22.04-arm", "macos-latest", "macos-latest-xlarge", "macos-latest-large", "macos-26-intel", "macos-26-xlarge", "macos-26-large", "macos-26", "macos-15-intel", "macos-15-xlarge", "macos-15-large", "macos-15", "macos-14-xlarge", "macos-14-large", "macos-14", "self-hosted", "x64", "arm", "arm64", "linux", "macos", "windows", "mac14", "mac15", "mac26", "mac-beta", "cpu", "latest", "preview". if it is a custom label for self-hosted runner, set list of labels in actionlint.yaml config file
arch: [ARM64]
include:
- platform: mac15
Expand All @@ -132,7 +132,7 @@
- self-hosted
- ${{ matrix.platform }}

name: |

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property "overrides" is not defined in object type {arch: string; is_special: bool; platform: string}
${{ matrix.platform }} ${{ matrix.arch }}
${{ (github.event_name != 'schedule' && github.event_name != 'workflow_dispatch' && join( matrix.overrides, ', ' )) || '' }}

Expand All @@ -151,8 +151,8 @@
if: github.event_name == 'pull_request'
env:
GITHUB_PR_ORIGIN: ${{ github.event.pull_request.head.repo.clone_url }}
OVERRIDES: ${{ join( matrix.overrides, ' ') }}

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property "overrides" is not defined in object type {arch: string; is_special: bool; platform: string}
run: |

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GitHub Actions / lint-action-files 

"github.event.pull_request.head.ref" is potentially untrusted. avoid using it directly in inline scripts. instead, pass it through an environment variable. see https://docs.github.com/en/actions/reference/security/secure-use#good-practices-for-mitigating-script-injection-attacks for more details
[ -d "${VIRTUAL_ENV_DIR}" ] && source ${VIRTUAL_ENV_DIR}/bin/activate
echo "Python is now $(which python3) $(python3 --version)"
src/.github/workflows/root-ci-config/build_root.py \
Expand Down Expand Up @@ -430,6 +430,11 @@
is_special: true
property: "clang Ninja builtins auto-registration off"
overrides: ["CMAKE_CXX_STANDARD=20"]
# Fedora 44 with Clang and libc++ instead of GNU libstdc++
- image: fedora44
platform_config: fedora44-clang_libcxx
is_special: true
property: "clang Ninja libc++"
# Asan build
- image: alma10
platform_config: alma10-asan
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12 changes: 10 additions & 2 deletions interpreter/cling/lib/Interpreter/CMakeLists.txt
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Expand Up @@ -264,11 +264,19 @@ if (UNIX)
endif()
endif()

# If CMAKE_CXX_FLAGS selects the C++ standard library (e.g. -stdlib=libc++
# with a clang that defaults to libstdc++), cling has to look up the headers
# of that library, not the ones of the compiler default.
string(REGEX MATCH "-stdlib=[^ ]+" cling_cxx_stdlib "${CMAKE_CXX_FLAGS}")
if (cling_cxx_stdlib AND CLING_CXX_RLTV)
set(CLING_CXX_RLTV "${CLING_CXX_RLTV} ${cling_cxx_stdlib}")
endif()

if(NOT CLING_CXX_HEADERS)
if (CLING_CXX_PATH)
execute_process(COMMAND ${CLING_CXX_PATH} ${CLING_CXX_PATH_ARGS} -xc++ -E -v /dev/null
execute_process(COMMAND ${CLING_CXX_PATH} ${CLING_CXX_PATH_ARGS} ${cling_cxx_stdlib} -xc++ -E -v /dev/null
OUTPUT_QUIET ERROR_VARIABLE CLING_CXX_HEADERS)
set(CLING_CXX_PATH "${CLING_CXX_PATH} ${CLING_CXX_PATH_ARGS}")
set(CLING_CXX_PATH "${CLING_CXX_PATH} ${CLING_CXX_PATH_ARGS} ${cling_cxx_stdlib}")
else()
# convert CMAKE_CXX_FLAGS to a list for execute_process
string(REPLACE "-fdiagnostics-color=always" "" cling_tmp_arg_list ${CMAKE_CXX_FLAGS})
Expand Down
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