[petsc-dev] Sean is going to love this

[Barry Smith]

 Pretty much

> On Dec 23, 2014, at 6:45 PM, Sean Farley <sean.michael.farley at gmail.com> wrote:
> 
> 
> Barry Smith writes:
> 
>>> On Dec 23, 2014, at 6:11 PM, Sean Farley <sean.michael.farley at gmail.com> wrote:
>>> 
>>> 
>>> Barry Smith writes:
>>> 
>>>>  Sean,
>>>> 
>>>>   Say I am writing a PETSc package (for any generic packaging system) that will use the MPICH compilers package and the BLAS/LAPACK package (and say, the hdf5 package). How do I indicate to PETSc's configure the information for MPICH, BLAS/LAPACK, and hdf5 so they will be correct for users when they link and run their applications? That is, I don't want to randomly list some hdf5 on the system but is it enough to just list the exact location of the hdf5 I know the package manager will install hdf5 to?
>>> 
>>> That is a hard problem. Jed and others will chime in on this problem,
>>> but this is why some packages have a binary / script that outputs its
>>> compiler / linker flags. For example, netcdf has nc-config:
>>> 
>>> $ nc-config --has-hdf5
>>> yes
>>> 
>>> $ nc-config --libs
>>> -L/opt/local/lib -lnetcdf
>>> 
>>> There is also pkg-config:
>>> 
>>> $ pkg-config --libs libpng
>>> -L/opt/local/lib -lpng16
>>> 
>>> Ideally, package managers should provide this information. Currently,
>>> they do not. For PETSc, this would mean something akin to 'petscmpiexec'
>>> and / or supplying this information to pkg-config (this actually should
>>> be fairly easy).
>>> 
>>> An end-user would then use pkg-config or a PETSc-provided script for
>>> compiling and linking,
>>> 
>>> $ pkg-config --libs petsc
>>> -L/opt/local/lib -lnetcdf -lpetsc -L/opt/local/lib/mpich-mp -lmpi -lpmpi
>> 
>>  Yeah in theory we do this.
>> 
>>  But this actually doesn't answer my question; I'm also asking about the situation when the package system (like brew) is compiling the package on the users machine.  Say I need the -I info for hdf5 to pass to PETSc's configure. If the user has selected a nonstandard location for installs with brew(not /usr/local) how do I know what directory to pass with the -I ? Somehow the package system has to provide the information for me to use in calling configure.
> 
> Ah, sorry, then I misunderstood. This is definitely dependent on the
> package manager system. In MacPorts, this is just listing the libraries
> directory:
> 
> configure.args-append --with-hdf5-dir=${prefix}
> 
> The requirement (of most?) package managers to have a locked-down prefix
> (e.g. /opt/local) is that installing something outside of the package
> would break the above code.
> 
> In some package managers (MacPorts is an example), CPPFLAGS are set to
> ${prefix}/include and LDFLAGS are set to ${prefix}/lib. To prevent
> over-linking and help deter incorrect linking, there is a trace mode
> that sandboxes the whole process so that only dependencies are
> explicitly allowed.
> 
> Is that what you were asking?