CMake build

[jchristopherson]

Hello,

I've added CMake support for the build of this library. I've included support for testing (CTest), installation, and building the example file. Hopefully this is helpful!

Regards,
Jason

[zoziha]

@jchristopherson, thank you for adding CMake support for fftpack, looks good to me!
Do we need to add CI support for CMake?

[jchristopherson]

Good point! I will add it!

[jchristopherson]

The CMake process seems to be working but I am unsure why the fpm builds or doc-deployment builds are failing.

[certik]

@jchristopherson thanks for this. I agree having a nice cmake build system is needed if you cannot or do not want to use fpm.

The only downside is that we now have to maintain two buildsystems, fpm and cmake. At the CI as well as manually, and debug bugs and when we add or change files we need to now test both.

I still think the best way forward is to teach fpm to just generate this cmake build system for you, see fortran-lang/fpm#69.

@jchristopherson would you have time to collaborate on this? The only involved part is dependencies handling, which we do not have for fftpack, and so we simply give an error message in the cmake backend in fpm if there is a dependency (for now).

[certik]

Let's add this cmake backend to fpm, see my comment.

[jchristopherson]

Hi @certik , that completely makes sense, and I do agree with your comments. I'd also be willing to help collaborate on the cmake backend for fpm; however, I am not familiar with the code base at this point - it'll take me a bit of time to get up to speed. Regardless, I can assist - just not in a timely manner.

[zoziha]

The CMake process seems to be working but I am unsure why the fpm builds or doc-deployment builds are failing.

@jchristopherson, it seems that the CI environment has changed, causing ford and fpm to fail. Don't worry, this has nothing to do with this PR, we can fix the CI environment in a PR thereafter.

Everything looks good, thanks.

[milancurcic]

While I agree that a CMake backend for fpm is a good long-term solution, it may be a long time before that's implemented. I don't think the maintenance burden here would be high--source files have not changed in almost a year, and as I understand it, fftpack is stable. @jchristopherson, would you be interested in helping maintain the CMake build for fftpack? If so, I think this PR should be merged, and we can remove the CMake build when fpm is ready.

[jchristopherson]

@milancurcic I sure can maintain the CMake build for fftpack.

[certik]

@jchristopherson if you are willing to maintain the backend to ensure everything works at the CI and can help update it if things move, then I think we can merge this, until fpm itself can "maintain such cmake backends".

@milancurcic regarding fpm, this is becoming an urgent feature, that will save time overall. The longer we wait, the more work it becomes for the whole community to create and maintain these multiple build systems.

[certik]

Approving conditionally that @jchristopherson will maintain this build system in fftpack.

[milancurcic]

Great, thanks, I think we all agree. I'll let a maintainer merge when ready.

[zoziha]

Thanks for supporting CMake for fftpack @jchristopherson , I will merge this PR.

[jchristopherson]

Sounds good.