A problem with VC++ and vcpkg due to setting C++ standard as public compile option for Folly::folly target

[eao197]

There is a line in FollyCompilerMSVC.cmake that adds /std: compiler option for Folly::folly target:

folly/CMake/FollyCompilerMSVC.cmake

Line 122 in 7f69f88

/std:${MSVC_LANGUAGE_VERSION} # Build in the requested version of C++

This line causes a problem with I'm trying to use Folly with VC++ via vcpkg. There is the output from the compiler:

FAILED: CMakeFiles/folly_case.dir/main.cpp.obj
C:\PROGRA~1\MIB055~1\2022\COMMUN~1\VC\Tools\MSVC\1440~1.338\bin\Hostx64\x64\cl.exe 
  /nologo /TP -DBOOST_ATOMIC_NO_LIB -DBOOST_ATOMIC_STATIC_LINK -DBOOST_CHRONO_NO_LIB
  -DBOOST_CHRONO_STATIC_LINK -DBOOST_CONFIG_SUPPRESS_OUTDATED_MESSAGE -DBOOST_CONTAINER_NO_LIB
  -DBOOST_CONTAINER_STATIC_LINK -DBOOST_CONTEXT_EXPORT="" -DBOOST_CONTEXT_NO_LIB=""
  -DBOOST_CONTEXT_STATIC_LINK="" -DBOOST_DATE_TIME_NO_LIB -DBOOST_DATE_TIME_STATIC_LINK
  -DBOOST_FILESYSTEM_NO_LIB -DBOOST_FILESYSTEM_STATIC_LINK=1 -DBOOST_PROGRAM_OPTIONS_NO_LIB
  -DBOOST_PROGRAM_OPTIONS_STATIC_LINK -DBOOST_THREAD_NO_LIB -DBOOST_THREAD_STATIC_LINK
  -DBOOST_THREAD_USE_LIB -DGFLAGS_IS_A_DLL=0 -DGLOG_NO_ABBREVIATED_SEVERITIES -DGLOG_USE_GFLAGS
  -DGLOG_USE_GLOG_EXPORT -DNOMINMAX -DWIN32_LEAN_AND_MEAN -D_CRT_NONSTDC_NO_WARNINGS
  -D_CRT_SECURE_NO_WARNINGS -D_ENABLE_EXTENDED_ALIGNED_STORAGE -D_SCL_SECURE_NO_WARNINGS
  -D_STL_EXTRA_DISABLED_WARNINGS="4774 4987"
  -external:IC:\home\eao197\sandboxes\folly_vcpkg_msvc_cpp20\cmake_build_release\vcpkg_installed\x64-windows-static\include
  -external:W0 /DWIN32 /D_WINDOWS /EHsc /O2 /Ob2 /DNDEBUG
  -std:c++20
  -MT /EHs /GF /Zc:referenceBinding /Zc:rvalueCast /Zc:implicitNoexcept /Zc:strictStrings /Zc:threadSafeInit /Zc:throwingNew
  /permissive-
  /std:c++17
  /wd4191 /wd4291 /wd4309 /wd4310 /wd4366 /wd4587 /wd4592 /wd4628 /wd4723 /wd4724 /wd4868 /wd4996
  /wd4068 /wd4091 /wd4146 /wd4800 /wd4018 /wd4365 /wd4388 /wd4389 /wd4100 /wd4459 /wd4505 /wd4701
  /wd4702 /wd4061 /wd4127 /wd4200 /wd4201 /wd4296 /wd4316 /wd4324 /wd4355 /wd4371 /wd4435 /wd4514
  /wd4548 /wd4571 /wd4574 /wd4582 /wd4583 /wd4619 /wd4623 /wd4625 /wd4626 /wd4643 /wd4647 /wd4668
  /wd4706 /wd4710 /wd4711 /wd4714 /wd4820 /wd5026 /wd5027 /wd5031 /wd5045 /we4099 /we4129 /we4566
  /utf-8 /Zc:__cplusplus /showIncludes /FoCMakeFiles\folly_case.dir\main.cpp.obj /FdCMakeFiles\folly_case.dir\ /FS
  -c C:\home\eao197\sandboxes\folly_vcpkg_msvc_cpp20\main.cpp
cl : Command line warning D9025 : overriding '/std:c++20' with '/std:c++17'
C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.40.33807\include\concepts(12): warning STL4038: The contents of <concepts> are available only with C++20 or later.
C:\home\eao197\sandboxes\folly_vcpkg_msvc_cpp20\main.cpp(5): error C2039: 'movable': is not a member of 'std'

The /std:c++17 inherited from Folly::folly overrides /std:c++20 from my project and prevents compilation in C++20 mode.

There is a demo project that show this case: https://github.com/eao197/folly_vcpkg_msvc_cpp20

It seems that there is no need to add /std:${MSVC_LANGUAGE_VERSION} as a PUBLIC compile option for the target Folly::folly, it has to be PRIVATE option in terms of CMake's target_compile_options.