[cmake] Set CMAKE_CXX_STANDARD explicitly in RootUseFile.cmake

Closes #6384,
---------

Co-authored-by: Jonas Rembser <jonas.rembser@cern.ch>

CMakeLists.txt

@@ -757,18 +757,24 @@ endif()
 cmake_host_system_information(RESULT PROCESSOR QUERY PROCESSOR_DESCRIPTION)
 
 message(STATUS "ROOT Configuration \n
-System          ${CMAKE_SYSTEM}
-Processor       ${PROCESSOR} (${CMAKE_SYSTEM_PROCESSOR})
-Build type      ${CMAKE_BUILD_TYPE}
-Install path    ${CMAKE_INSTALL_PREFIX}
-Compiler        ${CMAKE_CXX_COMPILER_ID} ${CMAKE_CXX_COMPILER_VERSION}
+System:            ${CMAKE_SYSTEM}
+ROOT Platform:     ${ROOT_PLATFORM}
+ROOT Architecture: ${ROOT_ARCHITECTURE}
+Processor:         ${PROCESSOR} (${CMAKE_SYSTEM_PROCESSOR})
+Build type:        ${CMAKE_BUILD_TYPE}
+Install path:      ${CMAKE_INSTALL_PREFIX}
+Compiler:          ${CMAKE_CXX_COMPILER_ID} ${CMAKE_CXX_COMPILER_VERSION}
+C++ standard:      ${CMAKE_CXX_STANDARD}
 Compiler flags:
-C               ${CMAKE_C_FLAGS} ${CMAKE_C_FLAGS_${_BUILD_TYPE_UPPER}}
-C++             ${CMAKE_CXX_FLAGS} ${CMAKE_CXX_FLAGS_${_BUILD_TYPE_UPPER}}
+ - C:                         ${CMAKE_C_FLAGS}
+ - C (built type specific):   ${CMAKE_C_FLAGS_${_BUILD_TYPE_UPPER}}
+ - C++:                       ${CMAKE_CXX_FLAGS}
+ - C++ (built type specific): ${CMAKE_CXX_FLAGS_${_BUILD_TYPE_UPPER}}
 Linker flags:
-Executable      ${CMAKE_EXE_LINKER_FLAGS}
-Module          ${CMAKE_MODULE_LINKER_FLAGS}
-Shared          ${CMAKE_SHARED_LINKER_FLAGS}\n")
+ - Executable:     ${CMAKE_EXE_LINKER_FLAGS}
+ - Module:         ${CMAKE_MODULE_LINKER_FLAGS}
+ - Shared:         ${CMAKE_SHARED_LINKER_FLAGS}\n")
+
 
 ROOT_SHOW_ENABLED_OPTIONS()
 

cmake/modules/CheckCompiler.cmake

@@ -176,9 +176,6 @@ if(NOT CMAKE_CXX_STANDARD MATCHES "17|20")
   message(FATAL_ERROR "Unsupported C++ standard: ${CMAKE_CXX_STANDARD}. Supported standards are: 17, 20.")
 endif()
 
-# needed by roottest, to be removed once roottest is fixed
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${CMAKE_CXX${CMAKE_CXX_STANDARD}_STANDARD_COMPILE_OPTION}")
-
 #---Check for libcxx option------------------------------------------------------------
 if(libcxx)
   CHECK_CXX_COMPILER_FLAG("-stdlib=libc++" HAS_LIBCXX11)
@@ -249,11 +246,3 @@ check_cxx_source_compiles(
 #endif
 int main() {}
 " GLIBCXX_USE_CXX11_ABI)
-
-#---Print the final compiler flags--------------------------------------------------------------------
-message(STATUS "ROOT Platform: ${ROOT_PLATFORM}")
-message(STATUS "ROOT Compiler: ${CMAKE_CXX_COMPILER_ID} ${CMAKE_CXX_COMPILER_VERSION}")
-message(STATUS "ROOT Processor: ${CMAKE_SYSTEM_PROCESSOR}")
-message(STATUS "ROOT Architecture: ${ROOT_ARCHITECTURE}")
-message(STATUS "Build Type: '${CMAKE_BUILD_TYPE}' (flags = '${CMAKE_CXX_FLAGS_${_BUILD_TYPE_UPPER}}')")
-message(STATUS "Compiler Flags: ${CMAKE_CXX_FLAGS} ${CMAKE_CXX_FLAGS_${_BUILD_TYPE_UPPER}}")

cmake/modules/RootConfiguration.cmake

@@ -613,6 +613,7 @@ string(REGEX REPLACE "(^|[ ]*)-W[^ ]*" "" __fflags "${CMAKE_Fortran_FLAGS}")
 string(REGEX MATCHALL "(-Wp,)?-(D|U)[^ ]*" __defs "${CMAKE_CXX_FLAGS}")
 set(ROOT_COMPILER_FLAG_HINTS "#
 set(ROOT_DEFINITIONS \"${__defs}\")
+set(ROOT_CXX_STANDARD ${CMAKE_CXX_STANDARD})
 set(ROOT_CXX_FLAGS \"${__cxxflags}\")
 set(ROOT_C_FLAGS \"${__cflags}\")
 set(ROOT_fortran_FLAGS \"${__fflags}\")
@@ -723,9 +724,11 @@ if(WIN32)
   # We cannot use the compiledata.sh script for windows
   configure_file(${CMAKE_SOURCE_DIR}/cmake/scripts/compiledata.win32.in ${CMAKE_BINARY_DIR}/ginclude/compiledata.h NEWLINE_STYLE UNIX)
 else()
+  # Needed by ACLIC, while in ROOT we are using everywhere C++ standard via CMake features that are requested to build target
+  set(CMAKE_CXX_ACLIC_FLAGS "${CMAKE_CXX_FLAGS} ${CMAKE_CXX${CMAKE_CXX_STANDARD}_STANDARD_COMPILE_OPTION}")
   execute_process(COMMAND ${CMAKE_SOURCE_DIR}/build/unix/compiledata.sh
     ${CMAKE_BINARY_DIR}/ginclude/compiledata.h "${CMAKE_CXX_COMPILER}"
-        "${CMAKE_CXX_FLAGS_RELEASE}" "${CMAKE_CXX_FLAGS_DEBUG}" "${CMAKE_CXX_FLAGS}"
+        "${CMAKE_CXX_FLAGS_RELEASE}" "${CMAKE_CXX_FLAGS_DEBUG}" "${CMAKE_CXX_ACLIC_FLAGS}"
         "${CMAKE_SHARED_LIBRARY_CREATE_CXX_FLAGS}" "${CMAKE_EXE_LINKER_FLAGS}" "so"
         "${libdir}" "-lCore" "-lRint" "${incdir}" "" "" "${ROOT_ARCHITECTURE}" "${ROOTBUILD}")
 endif()

cmake/modules/RootMacros.cmake

@@ -915,10 +915,6 @@ function(ROOT_LINKER_LIBRARY library)
     target_link_libraries(${library} PUBLIC ${ARG_LIBRARIES} ${ARG_DEPENDENCIES})
   endif()
 
-  if(DEFINED CMAKE_CXX_STANDARD)
-    target_compile_features(${library} INTERFACE cxx_std_${CMAKE_CXX_STANDARD})
-  endif()
-
   if(PROJECT_NAME STREQUAL "ROOT")
     if(NOT TARGET ROOT::${library})
       add_library(ROOT::${library} ALIAS ${library})

cmake/scripts/RootUseFile.cmake.in

@@ -12,3 +12,4 @@ add_definitions(${ROOT_DEFINITIONS})
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${ROOT_CXX_FLAGS}")
 set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${ROOT_C_FLAGS}")
 set(CMAKE_Fortran_FLAGS "${CMAKE_Fortran_FLAGS} ${ROOT_fortran_FLAGS}")
+set(CMAKE_CXX_STANDARD ${ROOT_CXX_STANDARD})

config/root-config.in

@@ -448,7 +448,7 @@ Usage: root-config [--prefix[=DIR]] [--exec-prefix[=DIR]] [--version]\
  [--noauxcflags] [--noauxlibs] [--noldflags] [--has-<feature>] [--arch]\
  [--platform] [--config] [--features] [--ncpu] [--git-revision]\
  [--python-version] [--python2-version] [--python3-version]\
- [--cc] [--cxx] [--f77] [--ld ] [--help]"
+ [--cxxstandard] [--cc] [--cxx] [--f77] [--ld ] [--help]"
 
 if test $# -eq 0; then
    echo "${usage}" 1>&2
@@ -573,6 +573,9 @@ while test $# -gt 0; do
     --python3-version)
       out="$out @python3vers@"
       ;;
+    --cxxstandard)
+      out="$out @CMAKE_CXX_STANDARD@"
+      ;;
     --cflags)
       ### Output the compiler flags
       if test "${incdir}" != "/usr/include"; then
@@ -849,6 +852,7 @@ while test $# -gt 0; do
       echo "  --python-version      Print the Python version used by ROOT"
       echo "  --python2-version     Print the Python2 version used by PyROOT"
       echo "  --python3-version     Print the Python3 version used by PyROOT"
+      echo "  --cxxstandard         Print the C++ standard used to compile ROOT"
       echo "  --ncpu                Print number of available (hyperthreaded) cores"
       echo "  --cc                  Print alternative C compiler specified when ROOT was built"
       echo "  --cxx                 Print alternative C++ compiler specified when ROOT was built"