update cmake

example/CMakeLists.txt

@@ -1,27 +1,16 @@
 include(CheckCXXCompilerFlag)
 
 if((CMAKE_CXX_COMPILER_ID MATCHES "GNU") OR (CMAKE_CXX_COMPILER_ID MATCHES "Clang"))
-    check_cxx_compiler_flag(-std=c++17 HAS_CPP17_FLAG)
-    if(!HAS_CPP17_FLAG)
-        MESSAGE(FATAL_ERROR "The compiler ${CMAKE_CXX_COMPILER} has no C++17 support.")
-    endif()
-
-    set(CMAKE_VERBOSE_MAKEFILE ON)
-    set(OPTIONS -Wall -Wextra -pedantic-errors -Werror -std=c++17)
+    set(OPTIONS -Wall -Wextra -pedantic-errors -Werror)
 elseif(CMAKE_CXX_COMPILER_ID MATCHES "MSVC")
-    check_cxx_compiler_flag(/std:c++17 HAS_CPP17_FLAG)
-    if(!HAS_CPP17_FLAG)
-        MESSAGE(FATAL_ERROR "The compiler ${CMAKE_CXX_COMPILER} has no C++17 support.")
-    endif()
-
-    set(OPTIONS /W4 /WX /std:c++17)
+    set(OPTIONS /W4 /WX)
     if(HAS_PERMISSIVE_FLAG)
         set(OPTIONS ${OPTIONS} /permissive-)
     endif()
 endif()
 
-add_executable(example
-                    example.cpp
-                    ${CMAKE_SOURCE_DIR}/include/${CMAKE_PROJECT_NAME}.hpp)
+add_executable(example example.cpp)
+set_target_properties(example PROPERTIES CXX_EXTENSIONS OFF)
+target_compile_features(example PRIVATE cxx_std_17)
 target_compile_options(example PRIVATE ${OPTIONS})
 target_link_libraries(example PRIVATE ${CMAKE_PROJECT_NAME})

test/CMakeLists.txt

@@ -9,14 +9,12 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "MSVC")
         set(OPTIONS ${OPTIONS} /permissive-)
     endif()
 
-    check_cxx_compiler_flag(/std:c++17 HAS_CPP17_FLAG)
     check_cxx_compiler_flag(/std:c++20 HAS_CPP20_FLAG)
     check_cxx_compiler_flag(/std:c++latest HAS_CPPLATEST_FLAG)
 elseif(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
     set(CMAKE_VERBOSE_MAKEFILE ON)
     set(OPTIONS -Wall -Wextra -pedantic-errors -Werror)
 
-    check_cxx_compiler_flag(-std=c++17 HAS_CPP17_FLAG)
     check_cxx_compiler_flag(-std=c++20 HAS_CPP20_FLAG)
 endif()
 
@@ -25,6 +23,7 @@ function(make_test target std)
     target_compile_options(${target} PRIVATE ${OPTIONS})
     target_include_directories(${target} PRIVATE 3rdparty/Catch2)
     target_link_libraries(${target} PRIVATE ${CMAKE_PROJECT_NAME})
+    set_target_properties(${target} PROPERTIES CXX_EXTENSIONS OFF)
     if(std)
         if(CMAKE_CXX_COMPILER_ID MATCHES "MSVC")
             target_compile_options(${target} PRIVATE /std:${std})
@@ -35,8 +34,10 @@ function(make_test target std)
     add_test(NAME ${target} COMMAND ${target})
 endfunction()
 
-if(HAS_CPP17_FLAG)
-    make_test(${CMAKE_PROJECT_NAME}-cpp17.t c++17)
+make_test(${CMAKE_PROJECT_NAME}-cpp17.t c++17)
+
+if(HAS_CPP20_FLAG)
+    make_test(${CMAKE_PROJECT_NAME}-cpp20.t c++20)
 endif()
 
 if(HAS_CPPLATEST_FLAG)