math_c99 and friends when using CMake

[philippremy]

Maybe I am missing something, but building Boost.Math (or Boost in general) with CMake causes the components of math_c99 and friends to be missing. I don't see the libraries in CMakeLists.txt. Is that intended?

When I build with b2 the libraries are build and the CMake components are available...

EDIT:

(Re-)Adding support for these libraries in CMake appears to be quite trivial. I could provide a PR for that if required and wanted.

[mborland]

Is this something you actually need? It was never added because I couldn't imagine someone using CMake also needed this backwards compatibility.

[philippremy]

Well, no, at least not personally...

But apparently some vcpkg stuff relies/relied on math_c99 to be available (I have no idea why): microsoft/vcpkg#38728

If you asked me, I would put some documentation somewhere which indicates that the CMake build behaves a little differently than b2. Or is that common sense in the Boost world? I honestly don't know 😅.
Or we put the compiled libraries behind a special switch in CMake (something like BOOST_MATH_ENABLE_LEGACY)...

[jzmaddock]

We should find a way to include this as a target in the CMake file, I wouldn't even make it conditional on a macro as it's not deprecated, just not used much, so a separate target, or maybe even a separate CMake file? My apologies, but my ignorance of all things CMake is showing ;)

[mborland]

We should find a way to include this as a target in the CMake file, I wouldn't even make it conditional on a macro as it's not deprecated, just not used much, so a separate target, or maybe even a separate CMake file? My apologies, but my ignorance of all things CMake is showing ;)

The easiest way would be to take the .patch file out of the Vcpkg build which adds this support. I don't think I agree with building them by default. I expect that suddenly going from a header only library to a compiled library will cause issues downstream. Vcpkg requires a macro to build these legacy bits.

[jzmaddock]

The easiest way would be to take the .patch file out of the Vcpkg build which adds this support. I don't think I agree with building them by default. I expect that suddenly going from a header only library to a compiled library will cause issues downstream. Vcpkg requires a macro to build these legacy bits.

They would be separate targets (there are 6 of them and none are called "boost_math"), as I said I know nothing about CMake, but I would not expect any target depending on "boost_math" to cause them to build in that case? If you're installing Boost.Math via CMake, then they really should be built anyway IMO, just as they are via b2.

[philippremy]

The easiest way would be to take the .patch file out of the Vcpkg build which adds this support. I don't think I agree with building them by default. I expect that suddenly going from a header only library to a compiled library will cause issues downstream. Vcpkg requires a macro to build these legacy bits.

They would be separate targets (there are 6 of them and none are called "boost_math"), as I said I know nothing about CMake, but I would not expect any target depending on "boost_math" to cause them to build in that case? If you're installing Boost.Math via CMake, then they really should be built anyway IMO, just as they are via b2.

I agree. Imo that would not change the header-only math library. That can be used without modifications, just as before. But if someone (for whatever reason) requires the legacy modules and can't use b2, they would still be available...

The point is: Using b2 on macOS is somewhat painful. Currently, bootstrap.sh does not work with a Homebrew LLVM/Clang, because it links to the wrong C++ standard library (that obviously is an issue in itself, see Homebrew/homebrew-core#235411). That can be fixed by simply adding a -L<LLVM_LIB_PATH> to LDFLAGS. But bootstrap.sh does not allow any custom CXXFLAGS or LDFLAGS. So I would need my project's users to uninstall LLVM completely if they want to build Boost with the legacy libraries :(. In CMake, I could just pass the additional flags and if I recall correctly, that wasn't even required there (maybe CMake already passes the correct search paths).

[mborland]

Boost is in the middle of release cycle, but once things are ready for the next version I will make these changes.

[philippremy]

Thank you :). That helps me out a lot!