CMAKE_HIP_KNOWN_FEATURES
For the C++ language, we have: https://cmake.org/cmake/help/latest/prop_gbl/CMAKE_CXX_KNOWN_FEATURES.html
For the CUDA language, we have: https://cmake.org/cmake/help/latest/prop_gbl/CMAKE_CUDA_KNOWN_FEATURES.html
I am unable to find any equivalent for the HIP language.
It's not obvious to me if this is intentional or simply an oversight. I would have expected that HIP would support a very similar feature set to CUDA, as the languages are quite similar and C++ standard versions are very relevant to HIP in particular.
HIP already supports https://cmake.org/cmake/help/latest/prop_tgt/HIP_STANDARD.html so I imagine we'd just copy that list into the known features for the HIP language.
Edit: it's also possible this is merely a documentation oversight. I have not actually confirmed that this feature is missing for HIP.