Check support for C++17 in a platform-agnostic manner

test/CMakeLists.txt

@@ -4,12 +4,25 @@ enable_testing()
 
 include(CheckCXXSourceCompiles)
 
+#  report an updated value for recent C++ language standards support. By
+#  default, Visual Studio always returns the value "199711L" for the
+#  __cplusplus preprocessor macro.
+if(MSVC)
+  string(APPEND CMAKE_CXX_FLAGS " /Zc:__cplusplus")
+endif()
+
 set(OLD_CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS}")
-set(CMAKE_REQUIRED_FLAGS -std=c++17)
+if(MSVC)
+    set(CMAKE_REQUIRED_FLAGS /std:c++17)
+else()
+    set(CMAKE_REQUIRED_FLAGS -std=c++17)
+endif()
+
 check_cxx_source_compiles("
 #include <string_view>
 #include <type_traits>
 int main() { return std::is_same_v<std::string_view, int>; }" CAN_COMPILE_17)
+
 set(CMAKE_REQUIRED_FLAGS "${OLD_CMAKE_REQUIRED_FLAGS}")
 
 if (EXISTS ${CMAKE_BINARY_DIR}/conan_paths.cmake)
@@ -22,7 +35,7 @@ find_package(Catch2 REQUIRED)
 if (CAN_COMPILE_17)
     add_executable(wise_enum_test test_main.cpp cxx17.cpp)
     target_compile_features(wise_enum_test PRIVATE cxx_std_17)
-    target_include_directories(wise_enum_test PRIVATE ..)
+    target_include_directories(wise_enum_test PRIVATE ${CMAKE_CURRENT_LIST_DIR}/..)
 else ()
     add_executable(wise_enum_test test_main.cpp)
 endif ()
@@ -31,7 +44,7 @@ target_link_libraries(wise_enum_test PRIVATE Catch2::Catch2)
 add_executable(wise_enum_test14 test_main.cpp cxx14.cpp)
 target_compile_features(wise_enum_test14 PRIVATE cxx_std_14)
 target_link_libraries(wise_enum_test14 PRIVATE Catch2::Catch2)
-target_include_directories(wise_enum_test14 PRIVATE ..)
+target_include_directories(wise_enum_test14 PRIVATE ${CMAKE_CURRENT_LIST_DIR}/..)
 
 add_test(NAME wise_enum.unit_tests COMMAND wise_enum_test)
 add_test(NAME wise_enum.unit_tests14 COMMAND wise_enum_test14)