Should this part also be changed:

find_path(HWY_INCLUDE_DIR
  NAMES hwy/highway.h
  HINTS ${PC_HWY_INCLUDEDIR} ${PC_HWY_INCLUDE_DIRS}
)

Should this part also be changed:

find_path(HWY_INCLUDE_DIR
  NAMES hwy/highway.h
  HINTS ${PC_HWY_INCLUDEDIR} ${PC_HWY_INCLUDE_DIRS}
)

good point, added a mitigation for that

Will test this later today.

You should also do this:

if(NOT HWY_VERSION_MAJOR STREQUAL "" AND NOT HWY_VERSION_MINOR STREQUAL "" AND NOT HWY_VERSION_PATCH STREQUAL "")
  set(HWY_VERSION "${HWY_VERSION_MAJOR}.${HWY_VERSION_MINOR}.${HWY_VERSION_PATCH}")
endif()

Otherwise the value will be overwritten from the other header file. But when I use base-foo.h and and highway-foo it will then not set HWY_VERSION and continue without any errors. That can be fixed with:

if (HWY_INCLUDE_DIR AND NOT HWY_VERSION)
  set(HWY_VERSION "")

You should also do this:

if(NOT HWY_VERSION_MAJOR STREQUAL "" AND NOT HWY_VERSION_MINOR STREQUAL "" AND NOT HWY_VERSION_PATCH STREQUAL "")
  set(HWY_VERSION "${HWY_VERSION_MAJOR}.${HWY_VERSION_MINOR}.${HWY_VERSION_PATCH}")
endif()

Make sense. I guess we could instead also break out of the foreach after setting this the first time

Otherwise the value will be overwritten from the other header file. But when I use base-foo.h and and highway-foo it will then not set HWY_VERSION and continue without any errors. That can be fixed with:

if (HWY_INCLUDE_DIR AND NOT HWY_VERSION)
  set(HWY_VERSION "")

I added this.
Thanks @dlemstra !

Maybe a bit OCD but if (NOT looks better.

and yes I know I send it to you like this 😁