[BUG]: FindParMETIS.cmake has flawed behaviour

[chrisrichardson]

Summarize the issue

When building with cmake, the search path for parmetis includes PARMETIS_ROOT/lib, but if PARMETIS_ROOT is not set, then it will search in /lib. For some installations, (as I have found), there may be a copy of libparmetis.so in /lib.

e.g. when I build with spack on this specific machine, it links against both the parmetis in spack, and the one in /lib, causing MPI issues.

How to reproduce the bug

Build dolfinx using spack on a machine with parmetis installed in /lib.

Minimal Example (Python)

N/A

Output (Python)

N/A

Version

main branch

DOLFINx git commit

No response

Installation

No response

Additional information

No response

[chrisrichardson]

I am not sure how to clean up the cmake file to prevent this from happening, currently has: HINTS ${PARMETIS_ROOT}/lib $ENV{PARMETIS_ROOT}/lib ${PETSC_INCLUDE_DIRS}

but if PARMETIS_ROOT is not set, (or in ENV) then will revert to /lib

[garth-wells]

I've cleaned up the CMake. One of the issues is that we were often using undefined variables, e.g. using PARMETIS_ROOT even when it's not set. This is now fixed, and CI will now fail if we use undefined variables in CMake.