Improved c++14/17 integration, follows more closely modern cmake

CMakeLists.txt

@@ -78,6 +78,7 @@ target_include_directories(xtensor-blas
     $<INSTALL_INTERFACE:include>)
 
 OPTION(CXXBLAS_DEBUG "print cxxblas debug information" OFF)
+OPTION(CPP17 "enables C++17" OFF)
 OPTION(XTENSOR_USE_FLENS_BLAS "use FLENS generic implementation instead of cblas" OFF)
 # Decide whether to use OpenBLAS or not.
 # The user might have the folder containing OpenBLASConfig.cmake file

benchmark/CMakeLists.txt

@@ -24,13 +24,6 @@ string(TOUPPER "${CMAKE_BUILD_TYPE}" U_CMAKE_BUILD_TYPE)
 
 if (CMAKE_CXX_COMPILER_ID MATCHES "Clang" OR CMAKE_CXX_COMPILER_ID MATCHES "GNU" OR CMAKE_CXX_COMPILER_ID MATCHES "Intel")
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -march=native -Wunused-parameter -Wextra -Wreorder")
-    CHECK_CXX_COMPILER_FLAG("-std=c++14" HAS_CPP14_FLAG)
-
-    if (HAS_CPP14_FLAG)
-        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14")
-    else()
-        message(FATAL_ERROR "Unsupported compiler -- xtensor requires C++14 support!")
-    endif()
 
     # Enable link time optimization and set the default symbol
     # visibility to hidden (very important to obtain small binaries)
@@ -124,6 +117,12 @@ set(XTENSOR_BENCHMARK
 set(XTENSOR_BENCHMARK_TARGET benchmark_xtensor)
 add_executable(${XTENSOR_BENCHMARK_TARGET} EXCLUDE_FROM_ALL ${XTENSOR_BENCHMARK} ${XTENSOR_HEADERS})
 target_link_libraries(${XTENSOR_BENCHMARK_TARGET} ${BLAS_LIBRARIES} ${LAPACK_LIBRARIES} ${GBENCHMARK_LIBRARIES})
+if(CPP17)
+    target_compile_features(${XTENSOR_BENCHMARK_TARGET} PUBLIC cxx_std_17)
+else()
+    target_compile_features(${XTENSOR_BENCHMARK_TARGET} PUBLIC cxx_std_14)
+endif()
+
 
 add_custom_target(xbenchmark
     COMMAND benchmark_xtensor

test/CMakeLists.txt

@@ -27,34 +27,6 @@ else()
     message(STATUS "Tests build type is ${CMAKE_BUILD_TYPE}")
 endif()
 
-include(CheckCXXCompilerFlag)
-
-string(TOUPPER "${CMAKE_BUILD_TYPE}" U_CMAKE_BUILD_TYPE)
-
-include(set_compiler_flag.cmake)
-
-if(CPP17)
-  # User requested C++17, but compiler might not oblige.
-  set_compiler_flag(
-    _cxx_std_flag CXX
-    "-std=c++17"  # this should work with GNU, Intel, PGI
-    "/std:c++17"  # this should work with MSVC
-  )
-  if(_cxx_std_flag)
-    message(STATUS "Building with C++17")
-  endif()
-else()
-  set_compiler_flag(
-    _cxx_std_flag CXX REQUIRED
-    "-std=c++14"  # this should work with GNU, Intel, PGI
-    "/std:c++14"  # this should work with MSVC
-  )
-  message(STATUS "Building with C++14")
-endif()
-
-if(NOT _cxx_std_flag)
-  message(FATAL_ERROR "xtensor-blas needs a C++14-compliant compiler.")
-endif()
 
 if(CMAKE_CXX_COMPILER_ID MATCHES "GNU" OR (CMAKE_CXX_COMPILER_ID MATCHES "Intel" AND NOT WIN32))
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${_cxx_std_flag} -march=native -Wunused-parameter -Wextra -Wreorder -Wconversion -Wsign-conversion")
@@ -153,6 +125,11 @@ if(DOWNLOAD_GTEST OR GTEST_SRC_DIR)
 endif()
 
 target_link_libraries(test_xtensor_blas ${BLAS_LIBRARIES} ${LAPACK_LIBRARIES} GTest::GTest GTest::Main ${CMAKE_THREAD_LIBS_INIT})
+if(CPP17)
+    target_compile_features(test_xtensor_blas PUBLIC cxx_std_17)
+else()
+    target_compile_features(test_xtensor_blas PUBLIC cxx_std_14)
+endif()
 
 add_custom_target(xtest COMMAND test_xtensor_blas DEPENDS test_xtensor_blas)
 add_test(NAME xtest COMMAND test_xtensor_blas)