Build: CMake 4.x compatibility, selectable C++ standard, GCC 16 / Clang 22 CI

.github/workflows/ci.yml

@@ -8,31 +8,58 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
       matrix:
         include:
-          # GCC 12
-          - cc: gcc-12
+          # GCC 12 (default standard)
+          - os: ubuntu-24.04
+            cc: gcc-12
             cxx: g++-12
             f77: gfortran-12
             packages: gcc-12 g++-12 gfortran-12
-          # GCC 14
-          - cc: gcc-14
+          # GCC 14 (C++14)
+          - os: ubuntu-24.04
+            cc: gcc-14
             cxx: g++-14
             f77: gfortran-14
             packages: gcc-14 g++-14 gfortran-14
-          # Clang 18
-          - cc: clang-18
+            cxx_std: 14
+          # GCC 16 (C++17)
+          - os: ubuntu-26.04
+            cc: gcc-16
+            cxx: g++-16
+            f77: gfortran-16
+            packages: gcc-16 g++-16 gfortran-16
+            cxx_std: 17
+          # GCC 16 (C++20)
+          - os: ubuntu-26.04
+            cc: gcc-16
+            cxx: g++-16
+            f77: gfortran-16
+            packages: gcc-16 g++-16 gfortran-16
+            cxx_std: 20
+          # Clang 18 (C++14)
+          - os: ubuntu-24.04
+            cc: clang-18
             cxx: clang++-18
             f77: gfortran-14
             packages: gfortran-14 clang-18
+            cxx_std: 14
+          # Clang 22 (C++20)
+          - os: ubuntu-26.04
+            cc: clang-22
+            cxx: clang++-22
+            f77: gfortran-15
+            packages: gfortran-15 clang-22
+            cxx_std: 20
 
     env:
       CC: ${{ matrix.cc }}
       CXX: ${{ matrix.cxx }}
       FC: ${{ matrix.f77 }}
+      UCX_TLS: tcp,self,sm
 
     steps:
       - uses: actions/checkout@v4
@@ -45,7 +72,7 @@ jobs:
       - name: Set up ccache
         uses: hendrikmuhs/ccache-action@v1
         with:
-          key: ${{ matrix.cc }}
+          key: ${{ matrix.os }}-${{ matrix.cc }}-cxx${{ matrix.cxx_std }}
 
       - name: Configure ccache symlinks
         run: |
@@ -73,7 +100,11 @@ jobs:
         run: |
           ccache -s
           mkdir build && cd build
-          cmake -DEL_TESTS=ON -DEL_EXAMPLES=ON -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=~/Install .. || \
+          STD_FLAG=""
+          if [ -n "${{ matrix.cxx_std }}" ]; then
+            STD_FLAG="-DCMAKE_CXX_STANDARD=${{ matrix.cxx_std }}"
+          fi
+          cmake $STD_FLAG -DEL_TESTS=ON -DEL_EXAMPLES=ON -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=~/Install .. || \
             (cat CMakeFiles/CMakeError.log; exit 1)
           make -j$(nproc)
           make install

CMakeLists.txt

@@ -385,10 +385,33 @@ endif()
 # --------------
 include(detect/Fortran)
 
-# Detect C++11
-# ------------
+# Select the C++ standard
+# -----------------------
+# Default to C++14; override with -DCMAKE_CXX_STANDARD=17 (or 20). This must
+# precede detect/CXX so that its feature checks compile at the selected
+# standard (CMP0067).
+if(NOT DEFINED CMAKE_CXX_STANDARD)
+  set(CMAKE_CXX_STANDARD 14)
+endif()
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+# CMAKE_CXX_STANDARD only affects this build, so also append the flag to
+# CXX_FLAGS, which is what gets exported to downstream consumers via
+# Elemental_COMPILE_FLAGS and ElVars' EL_COMPILE_FLAGS.
+# GNU needs extended mode (-std=gnu++XX) for libquadmath literals.
+if(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
+  set(CMAKE_CXX_EXTENSIONS ON)
+  set(CXX_FLAGS
+    "${CXX_FLAGS} ${CMAKE_CXX${CMAKE_CXX_STANDARD}_EXTENSION_COMPILE_OPTION}")
+else()
+  set(CMAKE_CXX_EXTENSIONS OFF)
+  set(CXX_FLAGS
+    "${CXX_FLAGS} ${CMAKE_CXX${CMAKE_CXX_STANDARD}_STANDARD_COMPILE_OPTION}")
+endif()
+message(STATUS "Building with C++${CMAKE_CXX_STANDARD}")
+
+# Detect C++ features
+# -------------------
 include(detect/CXX)
-set(CXX_FLAGS "${CXX_FLAGS} ${CXX14_COMPILER_FLAGS}")
 
 # Detect MPI
 # ----------

cmake/detect/CXX.cmake

@@ -6,12 +6,10 @@
 #  which can be found in the LICENSE file in the root directory, or at
 #  http://opensource.org/licenses/BSD-2-Clause
 #
-include(FindCXXFeatures)
 include(CheckCXXSourceCompiles)
 
-message(STATUS "CXX11_COMPILER_FLAGS=${CXX11_COMPILER_FLAGS}")
-message(STATUS "CXX14_COMPILER_FLAGS=${CXX14_COMPILER_FLAGS}")
-set(CMAKE_REQUIRED_FLAGS ${CXX14_COMPILER_FLAGS})
+# NOTE: the checks below compile at ${CMAKE_CXX_STANDARD}, which CMake
+#       propagates into try_compile() via CMP0067.
 
 # TODO(poulson): Test for C++14 features such as [[deprecated]]
 
@@ -131,5 +129,4 @@ set(PRETTY_FUNCTION_CODE
      }")
 check_cxx_source_compiles("${PRETTY_FUNCTION_CODE}" EL_HAVE_PRETTY_FUNCTION)
 
-unset(CMAKE_REQUIRED_FLAGS)
 unset(CMAKE_REQUIRED_DEFINITIONS)

cmake/external_projects/ElMath/BLIS_LAPACK.cmake

@@ -103,6 +103,7 @@ elseif(EL_HAVE_F90_INTERFACE AND
     TMP_DIR    ${LAPACK_BINARY_DIR}/tmp
     UPDATE_COMMAND ""
     CMAKE_ARGS 
+      -D CMAKE_POLICY_VERSION_MINIMUM=3.5
       -D CMAKE_C_COMPILER=${CMAKE_C_COMPILER}
       -D CMAKE_Fortran_COMPILER=${CMAKE_Fortran_COMPILER}
       -D CMAKE_C_FLAGS=${CMAKE_C_FLAGS}

cmake/external_projects/ElMath/METIS.cmake

@@ -49,6 +49,7 @@ elseif(NOT EL_PREVENT_METIS_DOWNLOAD)
     TMP_DIR    ${METIS_BINARY_DIR}/tmp
     UPDATE_COMMAND "" 
     CMAKE_ARGS 
+      -D CMAKE_POLICY_VERSION_MINIMUM=3.5
       -D PCRE=${METIS_PCRE}
       -D GKREGEX=${METIS_GKREGEX}
       -D CMAKE_C_COMPILER=${CMAKE_C_COMPILER}

cmake/external_projects/ElMath/ParMETIS.cmake

@@ -74,6 +74,7 @@ elseif(NOT EL_PREVENT_PARMETIS_DOWNLOAD)
     UPDATE_COMMAND ""
     LIST_SEPARATOR ^^
     CMAKE_ARGS
+      -D CMAKE_POLICY_VERSION_MINIMUM=3.5
       -D PCRE=${METIS_PCRE}
       -D GKREGEX=${METIS_GKREGEX}
       -D CMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}

cmake/external_projects/ElMath/ScaLAPACK.cmake

@@ -279,6 +279,7 @@ elseif(EL_HAVE_F90_INTERFACE AND EL_HAVE_MPI_FORTRAN AND
     UPDATE_COMMAND ""
     LIST_SEPARATOR ^^
     CMAKE_ARGS 
+      -D CMAKE_POLICY_VERSION_MINIMUM=3.5
       -D CMAKE_C_COMPILER=${CMAKE_C_COMPILER}
       -D CMAKE_Fortran_COMPILER=${CMAKE_Fortran_COMPILER}
       -D CMAKE_C_FLAGS=${CMAKE_C_FLAGS}