gate some tests behind C++17

Author: nmm0

CMakeLists.txt

@@ -148,7 +148,7 @@ if(MDSPAN_ENABLE_EXAMPLES)
 endif()
 
 if(MDSPAN_ENABLE_BENCHMARKS)
-  if(NOT MDSPAN_CXX_STANDARD STREQUAL "14" AND NOT MDSPAN_CXX_STANDARD STREQUAL "23")
+  if("cxx_std_17" IN_LIST CMAKE_CXX_COMPILE_FEATURES)
     add_subdirectory(benchmarks)
   else()
     MESSAGE(FATAL_ERROR "Benchmarks are not available in C++14 or C++23 mode. Turn MDSPAN_ENABLE_BENCHMARKS OFF or use C++17 or C++20.")

benchmarks/CMakeLists.txt

@@ -7,6 +7,7 @@ function(mdspan_add_benchmark EXENAME)
   )
   # Set flag to build with parenthesis enabled
   target_compile_definitions(${EXENAME} PRIVATE MDSPAN_USE_PAREN_OPERATOR=1)
+  target_compile_features(${EXENAME} PRIVATE cxx_std_17)
 endfunction()
 
 if(MDSPAN_USE_SYSTEM_BENCHMARK)
@@ -81,6 +82,7 @@ function(mdspan_add_openmp_benchmark EXENAME)
         $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/benchmarks>
       )
       target_compile_definitions(${EXENAME} PRIVATE MDSPAN_USE_PAREN_OPERATOR=1)
+      target_compile_features(${EXENAME} PRIVATE cxx_std_17)
     else()
       message(WARNING "Not adding target ${EXENAME} because OpenMP was not found")
     endif()

compilation_tests/CMakeLists.txt

@@ -21,8 +21,9 @@ if(NOT MDSPAN_ENABLE_CUDA)
   add_compilation_test(ctest_compressed_pair_layout)
 endif()
 add_compilation_test(ctest_constexpr_dereference)
-if(NOT CMAKE_CXX_STANDARD STREQUAL "14")
-add_compilation_test(ctest_constexpr_submdspan)
+if("cxx_std_17" IN_LIST CMAKE_CXX_COMPILE_FEATURES)
+  add_compilation_test(ctest_constexpr_submdspan)
+  target_compile_features(ctest_constexpr_submdspan PRIVATE cxx_std_17)
 endif()
 add_compilation_test(ctest_constexpr_layouts)
 add_compilation_test(ctest_namespace_std)