Support C++23

[long-recruit2]

• I've read Brief overview section and do understand basic concepts. [Yes|]
• I've read F.A.Q. section and haven't found an answer to my question. [Yes]
• I've read Code of Conduct, I promise to be polite and will do my best at being constructive. [Yes]

---

When we set CXX_standards as 23, hunter raise this error
[hunter ** INTERNAL **] CXX standard 23 not known
I wonder expected CXX_standard is set in below, we should just add 23?
hunter/cmake/modules/hunter_get_lang_standard_flag.cmake

function(hunter_get_lang_standard_flag LANG OUTPUT)
  # https://github.com/Kitware/CMake/blob/9d48d3f61b25400a191f12ea92b8e5496ab47a8f/Source/cmLocalGenerator.cxx#L1766-L1782
  set(CXX_standards 20 17 14 11 98)
  set(C_standards 11 99 90)

it has a comment pointing to a specific version of CMake but not sure where the version is from.

[NeroBurner]

I want to fix this before releasing v0.26.0. Probably a good idea to support C++23 and C++26?

[NeroBurner]

I don't find the linked code in the current CMake master

  static std::map<std::string, std::vector<std::string>> langStdMap;
  if (langStdMap.empty()) {
    // Maintain sorted order, most recent first.
    langStdMap["CXX"].emplace_back("20");
    langStdMap["CXX"].emplace_back("17");
    langStdMap["CXX"].emplace_back("14");
    langStdMap["CXX"].emplace_back("11");
    langStdMap["CXX"].emplace_back("98");

    langStdMap["C"].emplace_back("11");
    langStdMap["C"].emplace_back("99");
    langStdMap["C"].emplace_back("90");

    langStdMap["CUDA"].emplace_back("14");
    langStdMap["CUDA"].emplace_back("11");
    langStdMap["CUDA"].emplace_back("98");
  }

Maybe we can remove the handling in Hunter as well?

---

edit: codeblock removed in Kitware/CMake@56cf509

Currently the list is found in https://github.com/Kitware/CMake/blob/v4.0.1/Source/cmStandardLevelResolver.cxx#L491-L517

std::unordered_map<std::string,
                   StandardLevelComputer> const StandardComputerMapping = {
  { "C",
    StandardLevelComputer{
      "C", std::vector<int>{ 90, 99, 11, 17, 23 },
      std::vector<std::string>{ "90", "99", "11", "17", "23" } } },
  { "CXX",
    StandardLevelComputer{
      "CXX", std::vector<int>{ 98, 11, 14, 17, 20, 23, 26 },
      std::vector<std::string>{ "98", "11", "14", "17", "20", "23", "26" } } },
  { "CUDA",
    StandardLevelComputer{
      "CUDA", std::vector<int>{ 03, 11, 14, 17, 20, 23, 26 },
      std::vector<std::string>{ "03", "11", "14", "17", "20", "23", "26" } } },
  { "OBJC",
    StandardLevelComputer{
      "OBJC", std::vector<int>{ 90, 99, 11, 17, 23 },
      std::vector<std::string>{ "90", "99", "11", "17", "23" } } },
  { "OBJCXX",
    StandardLevelComputer{
      "OBJCXX", std::vector<int>{ 98, 11, 14, 17, 20, 23, 26 },
      std::vector<std::string>{ "98", "11", "14", "17", "20", "23", "26" } } },
  { "HIP",
    StandardLevelComputer{
      "HIP", std::vector<int>{ 98, 11, 14, 17, 20, 23, 26 },
      std::vector<std::string>{ "98", "11", "14", "17", "20", "23", "26" } } }
};

edit2: use tag link instead of commit permalink for StandardLevelComputerMapping