Merge branch 'msvc-cuda-cccl' into rc173 (MSVC: conforming preprocessor for CUDA sources, as CCCL requires)

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01D1G8gJVAy6gp1K5Dz3NE5C

CMakeLists.txt

@@ -28,8 +28,17 @@ SET(CMAKE_CXX_STANDARD_REQUIRED True)
 # Catch2 compiles itself with CATCH_CONFIG_DISABLE_EXCEPTIONS. Adding it here, before any
 # FetchContent, reaches every C++ target whatever CMAKE_CXX_FLAGS holds. CUDA gets it from its own
 # default CMAKE_CUDA_FLAGS, which nothing overrides.
+#
+# CUDA's CCCL headers (cub, thrust, libcu++) stop with an #error under MSVC's traditional
+# preprocessor, which miscompiles their macros. nvcc preprocesses and compiles host code with cl.exe,
+# so the standard-conforming preprocessor is switched on for .cu sources here, reaching every CUDA
+# target, fetched ones included (VS 2019 16.5 or newer). ffbidx already sets the same for its own
+# CUB-using kernel, which is why the other CUDA targets never needed it. C++ sources keep the
+# default: none includes a CCCL header, and the switch would change the preprocessing of Qt, the
+# Windows SDK and every fetched dependency with nothing to gain.
 IF (MSVC)
     ADD_COMPILE_OPTIONS($<$<COMPILE_LANGUAGE:CXX>:/EHsc>)
+    ADD_COMPILE_OPTIONS($<$<COMPILE_LANGUAGE:CUDA>:-Xcompiler=/Zc:preprocessor>)
 ENDIF()
 
 SET(JFJOCH_WRITER_ONLY           OFF CACHE BOOL "Compile HDF5 writer only")