[petsc-dev] Install location for MPIUNI mpi.h

[Satish Balay]

On Wed, 25 Apr 2018, Jed Brown wrote:

> It is currently installed to include/petsc/mpiuni/mpi.h and petscsys.h
> includes it as <mpi.h>, which means that users of MPIUNI need to put
> -I/prefix/include/petsc/mpiuni in their command lines.  Matt and I agree
> that this is bad.  We disagree on the solution.

Well in this context MPIUNI behaves like any other externalpackage.

> He wants to install it to /prefix/include/mpi.h as though the user had
> written --download-mpich.  This would conflict if a user later installs
> a real MPI to that location.

We already have this conflict when switching between mpich and openmpi [so this issue would extend to mpiuni]

> 
> I would rather that petscsys.h include <petsc/mpiuni/mpi.h> because it
> can't be used without PETSc and nobody who ever wrote #include <mpi.h>
> in their own code will be happy if they get MPIUNI.

The reason for using supporting '#include <mpi.h>' - is so that user
codes that might use '#include <mpi.h>' would also work with mpiuni
build of petsc.

Yeah - tradeoffs for each choice - so we settled on the current one -
with petsc-makefile usage as the primary supported mode for users.

This issue does not come up for such users. And non-petsc-makefile
users were to grab all the flags from petsc makefiles and use them
anyway.

This issue is primarily comes up for users who expect the following to
work [which never worked portably]

gcc -Ipath_to_petsc_include -Lpath_to_petsc_lib -lpetsc


Satish