About cmake variable HIGHFIVE_PARALLEL_HDF5 and documentation

[pkestene]

Hello,

If I'm not mistaken cmake variable HIGHFIVE_PARALLEL_HDF5 is only used in unit testing. So setting this variable is only required if one wants to build the unit tests that require parallel hdf5.

I noticed that current documentation at https://bluebrain.github.io/HighFive/index.html in section "Dependencies" mentions that this variable should be set to have parallel hdf5 feature, while the top-level README.md is ok. I believe the documentation is just slightly outdated ?

Another point:
in unit test, if the user sets HIGHFIVE_PARALLEL_HDF5=ON but forgot to set HDF5_PREFER_PARALLEL, on a system where both serial and parallel version are available (e.g. on my ubuntu 22.04), the serial HDF5 will be detected, and the unit tests will fail to compile.
I suggest the following simple modification in tests/unit/CMakeLists.txt

if(HIGHFIVE_PARALLEL_HDF5 AND HDF5_IS_PARALLEL)
...
endif()
# instead of
if(HIGHFIVE_PARALLEL_HDF5)
...
endif()

to make sure the unit tests that require parallel hdf5 are only built when HDF5 is actually parallel.

Maybe the top-level CMakeLists.txt should check the case where HIGHFIVE_PARALLEL_HDF5=ON and HDF5_IS_PARALLEL=OFF and sends a FATAL_ERROR message: "You requested building parallel unit tests, but your HDF5 library is not parallel. Make sure to use HDF5_PREFER_PARALLEL=ON and a parallel HDF5 is available on your host system."

[1uc]

We're currently preparing v3.0.0. One of the important changes is the CMake code. The documentation is documentation for the last release, i.e. 2.9.0. While the README is part of the master branch and therefore is true for v3.0.0.

The CMake for 2.x has issues. I think some are related to HIGHFIVE_PARALLEL_*.

The CMake for 3.x doesn't use HIGHFIVE_PARALLEL_HDF5 (technically not true, but the fix is ready). Controlling the HDF5 flavour is done using the HDF5 variables, e.g.

cmake -DHDF5_PREFER_PARALLEL=On ...

HighFive will then either build parallel tests if pHDF5 is available or not if it isn't.

[pkestene]

ok, I saw the PR that fixes the problem.