[cpptools] Unknown C++ standard control flag: -std=c++23

[sweemer]

Brief Issue Summary

When compiling a CMake project with CMAKE_CXX_STANDARD=23 I see [cpptools] Unknown C++ standard control flag: -std=c++23 in the CMake/Build output.

CMake Tools Diagnostics

{
"os": "linux",
"vscodeVersion": "1.66.0",
"cmtVersion": "1.10.5",
"configurations": [
{
"folder": "/home/sweemer/QuantLib",
"cmakeVersion": "3.22.3",
"configured": true,
"generator": "Unix Makefiles",
"usesPresets": true,
"compilers": {
"CXX": "g++-11"
}
}
],
"cpptoolsIntegration": {
"isReady": true,
"hasCodeModel": true,
"activeBuildType": "Debug",
"buildTypesSeen": [
"Debug"
],
"requests": [],
"responses": [],
"partialMatches": [],
"targetCount": 51,
"executablesCount": 21,
"librariesCount": 2,
"targets": []
},
"settings": [
{
"communicationMode": "automatic",
"useCMakePresets": "auto",
"configureOnOpen": true
}
]
}

[bobbrow]

Thank you for reporting this. As I mentioned in the PR, we'll need to get the vscode-cpptools module and cpptools to support this before we can start sending it over. In the meantime, we could downgrade the standard level to c++20 when we encounter c++23 if this is currently blocking you.

[sweemer]

Thanks, this isn't blocking anything major for me at the moment.

But I'm curious - as I asked on the merge request, how does the cpptools or cmake extension know which version of Visual Studio is installed on the user's machine? As far as I understand, the value of /std:c++latest is different depending on which version is installed, so is it desirable to hardcode the mapping in src/cpptools.ts? Is there a way to dynamically resolve the standard number from /std:c++latest based on the version of Visual Studio installed?

[bobbrow]

From CMake Tools' perspective, we just tell cpptools what CMake told us. If a specific standard is requested, we send it, but otherwise we don't have to send it. cpptools owns the mappings, so we shouldn't do anything in cpptools.ts for this. Currently cpptools maps c++latest to c++20, but will be updated to use c++23 when they pick up the changes in the API. There is currently no mapping based on the version of the compiler sent. If that's something you'd like to see, I recommend opening a bug report for cpptools.

[Zingam]

I plan to switch to C++ 23 soon. Is this just an annoyance or a blocker?

Does this fix it:
microsoft/vscode-cpptools#9177
microsoft/vscode-cpptools#7506

[bobbrow]

I believe you will need 1.10.0 of cpptools (pre-release) which came out late last week. I think we already addressed the warnings in the CMake Tools pre-release (community contribution: #2476) but it requires the matching changes in cpptools.

[bobbrow]

It looks like our bookkeeping didn't mark this issue as fixed yet.