CMake: Set CXX language level via target_compile_features()

See: https://gitlab.kitware.com/cmake/cmake/-/issues/18446
See: https://cmake.org/cmake/help/latest/manual/cmake-compile-features.7.html#requiring-language-standards

README.md

@@ -124,9 +124,6 @@ After the `find_package(FairMQ)` call the following CMake variables are defined:
 | `${FairMQ_LIBDIR}` | the installation lib directory |
 | `${FairMQ_DATADIR}` | the installation data directory (`../share/fairmq`) |
 | `${FairMQ_CMAKEMODDIR}` | the installation directory of shipped CMake find modules |
-| `${FairMQ_CXX_STANDARD_REQUIRED}` | the value of `CMAKE_CXX_STANDARD_REQUIRED` at build-time |
-| `${FairMQ_CXX_STANDARD}` | the value of `CMAKE_CXX_STANDARD` at build-time |
-| `${FairMQ_CXX_EXTENSIONS}` | the values of `CMAKE_CXX_EXTENSIONS` at build-time |
 | `${FairMQ_BUILD_TYPE}` | the value of `CMAKE_BUILD_TYPE` at build-time |
 | `${FairMQ_CXX_FLAGS}` | the values of `CMAKE_CXX_FLAGS` and `CMAKE_CXX_FLAGS_${CMAKE_BUILD_TYPE}` at build-time |
 

cmake/FairMQConfig.cmake.in

@@ -1,5 +1,5 @@
 ################################################################################
-#    Copyright (C) 2018 GSI Helmholtzzentrum fuer Schwerionenforschung GmbH    #
+# Copyright (C) 2018-2021 GSI Helmholtzzentrum fuer Schwerionenforschung GmbH  #
 #                                                                              #
 #              This software is distributed under the terms of the             #
 #              GNU Lesser General Public Licence (LGPL) version 3,             #
@@ -20,9 +20,6 @@ set(@PROJECT_NAME@_LIBDIR @PACKAGE_CMAKE_INSTALL_PREFIX@/@PROJECT_INSTALL_LIBDIR
 set(@PROJECT_NAME@_DATADIR @PACKAGE_CMAKE_INSTALL_PREFIX@/@PROJECT_INSTALL_DATADIR@)
 set(@PROJECT_NAME@_CMAKEMODDIR @PACKAGE_CMAKE_INSTALL_PREFIX@/@PROJECT_INSTALL_CMAKEMODDIR@)
 
-set(@PROJECT_NAME@_CXX_STANDARD_REQUIRED @CMAKE_CXX_STANDARD_REQUIRED@)
-set(@PROJECT_NAME@_CXX_STANDARD @CMAKE_CXX_STANDARD@)
-set(@PROJECT_NAME@_CXX_EXTENSIONS @CMAKE_CXX_EXTENSIONS@)
 set(@PROJECT_NAME@_VERSION_HOTFIX @PROJECT_VERSION_HOTFIX@)
 set(@PROJECT_NAME@_BUILD_TYPE @CMAKE_BUILD_TYPE@)
 set(@PROJECT_NAME@_BUILD_TYPE_UPPER @PROJECT_BUILD_TYPE_UPPER@)

cmake/FairMQLib.cmake

@@ -75,10 +75,7 @@ macro(set_fairmq_defaults)
   set(PROJECT_MIN_CXX_STANDARD 17)
 
   # Handle C++ standard level
-  set(CMAKE_CXX_STANDARD_REQUIRED ON)
+  if(CMAKE_CXX_STANDARD AND CMAKE_CXX_STANDARD VERSION_LESS PROJECT_MIN_CXX_STANDARD)
-  if(NOT CMAKE_CXX_STANDARD)
-    set(CMAKE_CXX_STANDARD ${PROJECT_MIN_CXX_STANDARD})
-  elseif(${CMAKE_CXX_STANDARD} LESS ${PROJECT_MIN_CXX_STANDARD})
     message(FATAL_ERROR "A minimum CMAKE_CXX_STANDARD of ${PROJECT_MIN_CXX_STANDARD} is required.")
   endif()
   set(CMAKE_CXX_EXTENSIONS OFF)

fairmq/CMakeLists.txt

@@ -47,6 +47,7 @@ if(BUILD_FAIRMQ OR BUILD_SDK)
     ${TOOLS_SOURCE_FILES}
     ${TOOLS_PUBLIC_HEADER_FILES}
   )
+  target_compile_features(${target} PUBLIC cxx_std_17)
   target_compile_definitions(${target} PUBLIC BOOST_ERROR_CODE_HEADER_ONLY)
   # workaround https://github.com/boostorg/asio/commit/43874d5497414c67655d901e48c939ef01337edb
   if(    Boost_VERSION VERSION_LESS 1.69
@@ -106,6 +107,7 @@ if(BUILD_FAIRMQ OR BUILD_SDK)
     ${FSM_SOURCE_FILES}
     ${FSM_PUBLIC_HEADER_FILES}
   )
+  target_compile_features(${target} PUBLIC cxx_std_17)
   target_compile_definitions(${target} PUBLIC BOOST_ERROR_CODE_HEADER_ONLY)
   target_include_directories(${target}
     PUBLIC
@@ -263,6 +265,7 @@ if(BUILD_FAIRMQ)
     ${FAIRMQ_PUBLIC_HEADER_FILES} # for IDE integration
     ${FAIRMQ_PRIVATE_HEADER_FILES} # for IDE integration
   )
+  target_compile_features(${target} PUBLIC cxx_std_17)
   set_target_properties(${target} PROPERTIES LABELS coverage)
 
 
@@ -350,6 +353,7 @@ if(BUILD_FAIRMQ)
   target_link_libraries(fairmq-splitter FairMQ)
 
   add_executable(fairmq-shmmonitor shmem/Monitor.cxx shmem/Monitor.h shmem/runMonitor.cxx)
+  target_compile_features(fairmq-shmmonitor PUBLIC cxx_std_17)
   target_compile_definitions(fairmq-shmmonitor PUBLIC BOOST_ERROR_CODE_HEADER_ONLY)
   if(FAIRMQ_DEBUG_MODE)
     target_compile_definitions(fairmq-shmmonitor PUBLIC FAIRMQ_DEBUG_MODE)

fairmq/plugins/DDS/CMakeLists.txt

@@ -8,6 +8,7 @@
 
 set(plugin FairMQPlugin_dds)
 add_library(${plugin} SHARED ${CMAKE_CURRENT_SOURCE_DIR}/DDS.cxx ${CMAKE_CURRENT_SOURCE_DIR}/DDS.h)
+target_compile_features(${plugin} PUBLIC cxx_std_17)
 target_link_libraries(${plugin} PUBLIC FairMQ StateMachine DDS::dds_intercom_lib DDS::dds_protocol_lib Boost::boost PRIVATE Commands)
 target_include_directories(${plugin} PRIVATE ${CMAKE_CURRENT_BINARY_DIR})
 set_target_properties(${plugin} PROPERTIES CXX_VISIBILITY_PRESET hidden)

fairmq/plugins/PMIx/CMakeLists.txt

@@ -13,6 +13,7 @@ add_library(${plugin} SHARED
   ${CMAKE_CURRENT_SOURCE_DIR}/PMIxCommands.h
   ${CMAKE_CURRENT_SOURCE_DIR}/PMIx.hpp
 )
+target_compile_features(${plugin} PUBLIC cxx_std_17)
 target_link_libraries(${plugin} PUBLIC FairMQ PMIx::libpmix PRIVATE Commands)
 target_include_directories(${plugin} PRIVATE ${CMAKE_CURRENT_BINARY_DIR})
 set_target_properties(${plugin} PROPERTIES

fairmq/sdk/CMakeLists.txt

@@ -45,6 +45,7 @@ add_library(${target}
   ${SDK_PUBLIC_HEADER_FILES} # for IDE integration
   ${SDK_PRIVATE_HEADER_FILES} # for IDE integration
 )
+target_compile_features(${target} PUBLIC cxx_std_17)
 set_target_properties(${target} PROPERTIES LABELS coverage)
 target_include_directories(${target}
   PUBLIC