LAMMPS_jll doesn't have MPI support

[Joroks]

@vchuravy I've noticed that the LAMMPS binaries we provide don't have MPI enabled.
This can be tested with API.lammps_config_has_mpi_support()

Should we enable MPI support or is there a reason why this is disabled?

[vchuravy]

I don't know why the API call doesn't say that we don't have MPI support. But the Yggdrasil build ought to have it: https://github.com/JuliaPackaging/Yggdrasil/blob/3c457abd9bb07c3a769dc5f617b97cf4d1ba5ad5/L/LAMMPS/build_tarballs.jl#L80

We have a minimal test for MPI support here

LAMMPS.jl/test/runtests.jl

Line 296 in e92fbc8

@test success(pipeline(`$(MPI.mpiexec()) -n 2 $(Base.julia_cmd()) mpitest.jl`, stderr=stderr, stdout=stdout))

[vchuravy]

Probably https://github.com/JuliaPackaging/Yggdrasil/blob/3c457abd9bb07c3a769dc5f617b97cf4d1ba5ad5/L/LAMMPS/build_tarballs.jl#L42 needs to be BUILD_MPI

[Joroks]

The test passes even if our LAMMPS binary doesn't have MPI support as it then uses MPI STUBS to pretend to have MPI. In the end the test just starts two independent lammps instances that can't communicate with each other.

maybe we should add

@test LAMMPS.API.lammps_config_has_mpi_support() != 0

to our tests