I know this is an old thread, but chiming in here - because _MSC_VER is defined when clang is building in msvc compatibility mode (via clang-cl), the addition of the changes in 957291343c16aa5d1ef3c54d024957f7316b110f to add `[[msvc::flatten]]` raises the diagnostic `-Wunknown-attributes` on clang-cl builds: #279
I know this is an old thread, but chiming in here - because _MSC_VER is defined when clang is building in msvc compatibility mode (via clang-cl), the addition of the changes in 957291343c16aa5d1ef3c54d024957f7316b110f to add `[[msvc::flatten]]` raises the diagnostic `-Wunknown-attributes` on clang-cl builds:
Originally posted by @remyjette in https://github.com/hanickadot/compile-time-regular-expressions/issues/172#issuecomment-1498048013