[Bug 223678] devel/cmake: find_package(OpenMP) doesn't find the openmp package

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=223678

--- Comment #12 from Christian Pfeiffer <cpfeiffer at live.de> ---
@adriaan I had a look through the cmake ports description and noticed you
generally replace `/usr/local` with $LOCALBASE using sed and applied some
patches.

>From what I explained above, it's in both CMake's and FreeBSD's best interest
to keep the number of patches and adaptions needed as small as somehow
possible. For one, upstream does nightly testing with *unpatched* CMake trunks,
and that includes FreeBSD test machines. Secondly, some packages require
FreeBSD specific adaptations going beyond just replacing `/usr/local` with
$LOCALBASE, e.g. FindMPI needs to consider all subdirectories for
`/usr/local/mpi` and that's something just introduced with 3.10 now.

I think the `/usr/local` hard coding is an issue that needs addressing in CMake
itself instead of patching it downstream. One of the reasons is that by simply
replacing `/usr/local` using sed, you'll get strange results for
cross-compilation builds using a `CMAKE_SYSROOT` where it should be
`/usr/local`. For OpenBSD this issue is as a matter of fact addressed upstream,
see here:
https://gitlab.kitware.com/cmake/cmake/blob/master/Modules/Platform/OpenBSD.cmake#L28-37
The exact same approach could be used for FreeBSD.

Given the other path replacements, I think the approach used in the OpenBSD
platform file would address all of these, but it needs a bit of testing. I can
cook up a patch upstream and we can see if that already works out?

Regarding the patches: The wxWidgets, wxWindows and ImageMagick ones could be
merged upstream as is.

The FindSDL one should be done with care, if you install SDL manually in an
isolated prefix environment, system CMake would then always include the system
path - this breaks cross compilation environments for instance. The superior
choice would be to use `find_path` to determine the header path in order to not
break 

I'm not quite certain what the FindQt4 one is trying to achieve, but it will
overwrite user-set variables and also break cross compilation scenarios due to
`CMAKE_SYSROOT` not being searched anymore. If there's a scenario where this is
needed, that sounds like a bug in the module.

In general, given CMake's set goals, you should consider any downstream bug for
CMake an upstream bug as well. FreeBSD is a platform that CMake strives to
support fully and needed downstream adjustments are therefore a bug.

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