Many thanks. I barely know what I'm doing with cmake.
@nwellnhof do you have any objections to any of these changes?

Looks good. I'm only curious about the claim that /TP is forced on all MSVC builds. All the tests pass, so this seems to be true. But why? Then we might also consider adding /TC when building with newer MSVC versions, although it's not strictly necessary.

@jgm my pleasure :)

@nwellnhof, yeah, that is very subtle, and an accident that I caused. In fbe364a I hoisted the shared configuration between the api_test and src directory. The variant that I used was from the api_test directory which was subtly different: it always set /TP unlike the src version which limited it to the older releases only. If that is truly a difference that should be preserved, Im happy to adjust the stack to do so. However, after that commit, /TP is passed whenever using MSVC. At that point, setting it for the older release becomes redundant (though CMake should unique the flags). I figure that less build configuration is better.

Ugh, add_compile_definitions apparently was introduced in 3.12. I'll move that to add_compile_options as a workaround.

However, after that commit, /TP is passed whenever using MSVC. At that point, setting it for the older release becomes redundant (though CMake should unique the flags). I figure that less build configuration is better.

Then I'd prefer to keep the version check which also serves as implicit documentation why the flag is needed.

I'd prefer to keep the version check which also serves as implicit documentation why the flag is needed.

Even better if a comment is added as explicit documentation.