[CMake] Qhull is a private dependency

[nim65s]

Hi,

This revert f5bb137 and remove the need for 5beff60.

On systems where Qhull is not installed, Qhull is build from the submodule. Then, if we leak the dependency to the CMake exports of hpp-fcl, all projects depending on hpp-fcl will require a system installation of Qhull, which was not available in the first place. In such cases, configuration will fail, because hpp-fcl won't be considered complete without qhull:

CMake Warning at /usr/share/cmake-3.16/Modules/CMakeFindDependencyMacro.cmake:47 (find_package):
By not providing "FindQhull.cmake" in CMAKE_MODULE_PATH this project has
asked CMake to find a package configuration file provided by "Qhull", but
CMake did not find one.

Could not find a package configuration file provided by "Qhull" with any of
the following names:

QhullConfig.cmake
qhull-config.cmake

Add the installation prefix of "Qhull" to CMAKE_PREFIX_PATH or set
"Qhull_DIR" to a directory containing one of the above files.  If "Qhull"
provides a separate development package or SDK, be sure it has been
installed.
Call Stack (most recent call first):
/opt/openrobots/lib/cmake/hpp-fcl/hpp-fclConfig.cmake:152 (find_dependency)
cmake/package-config.cmake:97 (find_package)
CMakeLists.txt:34 (ADD_PROJECT_DEPENDENCY)


CMake Warning at cmake/package-config.cmake:97 (find_package):
Found package configuration file:

/opt/openrobots/lib/cmake/hpp-fcl/hpp-fclConfig.cmake

but it set hpp-fcl_FOUND to FALSE so package "hpp-fcl" is considered to be
NOT FOUND.  Reason given by package:

hpp-fcl could not be found because dependency Qhull could not be found.

Call Stack (most recent call first):
CMakeLists.txt:34 (ADD_PROJECT_DEPENDENCY)

As hpp-fcl links to Qhull are private (https://github.com/humanoid-path-planner/hpp-fcl/blob/v1.7.8/src/CMakeLists.txt#L189-L198), I think we should not expose this dependency to packages depending on hpp-fcl.

[jmirabel]

Thanks.
Any news on releasing qhull in robotpkg ?

[nim65s]

It is already available in most major distributions. CMake is not finding it because it is an outdated version on 20.04 (2015.2) without CMake exports ; but on Arch with 2020.2, CMake exports are available and it is correctly found.

I don't remember if we already talk about this, but we can:

1. do nothing and wait for debian/ubuntu to upgrade it ; meanwhile people needing it in hpp-fcl will build it
2. add some CMake logic to find correctly 2015.2
3. add a more recent version in robotpkg

I'm not sure 3 is the best way. What do you think ?

[jmirabel]

I wasn't aware of this. Then, don't add it in robotpkg.

The issue some years ago was that some libs were not in the binary package.

Is this qhull.cmake useful for option 2 ?

[nim65s]

Looks a bit dusty, but this is surely a good basis