DPC++ Feature Testing

[ax3l]

Hi,

it would be great for us if DPC++ and general SYCL extension features can be detected via macro and/or other feature tests in codes.

Currently, out of the list in here https://spec.oneapi.com/versions/latest/elements/dpcpp/source/index.html it seems that only SYCL_INTEL_unnamed_kernel_lambda has a feature test macro (__SYCL_INTEL_UNNAMED_LAMBDA__), but I might be missing something.

This would help us downstream developers to test proposed SYCL features with simple fallback paths for various SYCL compilers.

Refs.:

• ISO C++ feature tests: https://en.cppreference.com/w/cpp/feature_test
• full list: https://spec.oneapi.com/versions/latest/elements/dpcpp/source/index.html
• unnamed lambda example: https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/UnnamedKernelLambda/SYCL_INTEL_unnamed_kernel_lambda.asciidoc

[bader]

@ax3l, thanks for the feedback.
We discussed this topic here: #806 and @AlexeySachkov prepared a PR with the detailed proposal: #1793.
Please, let us know if it doesn't fit your needs.

[ax3l]

Thanks a lot @bader, I will close this as duplicate and contributed additional thoughts in both the issue and PR :)