FindPETSc tests fail with missing include <mpi.h>

[fsimonis]

FindPETSc does not respect MPI include paths and therefore fails to compile the tests on systems with scoped mpi installs such as OpenMPI on Ubuntu 16.04 (/usr/include/openmpi/mpi.h)

It should include MPI_INCLUDE_DIRS, or similar here.

cmake-modules/FindPETSc.cmake

Line 292 in 91f9617

set (petsc_includes_minimal ${PETSC_INCLUDE_CONF} ${PETSC_INCLUDE_DIR})

A possible solution is to adapt FindPETSc to call FindMPI internally.

[jedbrown]

FindMPI.cmake is an unreliable convoluted mess and even some CMake developers discourage using it. I recommend using CC=/path/to/mpicc.

[fsimonis]

Are you referring to the version prior to the rewrite that came with 3.10 or in general?

[jedbrown]

@fsimonis My experience is prior to that merge, but we're currently using cmake_policy(VERSION 3.3) and I think it's more hardship than it's worth to require people to upgrade CMake to gratuitously use a module that has amassed a decade of ill-will for creating inconsistencies where the less-typing method (CC=) has been more reliable.

[fsimonis]

@jedbrown Fair enough.

The error message is misleading though as the tests fail due to the missing include and not a faulty PETSc install. The root of the problem is only visible by inspecting the error logs.
I suggest adding a trivial check to make sure the compiler can find the header:

#include <mpi.h>
int main() { return 0; }

[jedbrown]

Patch welcome.