Add Libs.private

[fsimonis]

This PR:

• Keeps track of dependencies building a list of libraries
• Adds the field Libs.private to the configured .pc file.

TODO

• Verify that MPI work like this

Closes #313

[MakisH]

I built preCICE as a static library using -DBUILD_SHARED_LIBS=OFF.

Then I tried to build the C++ (and C) solver dummies, which failed with an error for finding Eigen, MPI, and NumPy:

-- Configuring done
CMake Error at CMakeLists.txt:6 (add_executable):
  Target "solverdummy" links to target "Eigen3::Eigen" but the target was not
  found.  Perhaps a find_package() call is missing for an IMPORTED target, or
  an ALIAS target is missing?


CMake Error at CMakeLists.txt:6 (add_executable):
  Target "solverdummy" links to target "MPI::MPI_CXX" but the target was not
  found.  Perhaps a find_package() call is missing for an IMPORTED target, or
  an ALIAS target is missing?


CMake Error at CMakeLists.txt:6 (add_executable):
  Target "solverdummy" links to target "NumPy::NumPy" but the target was not
  found.  Perhaps a find_package() call is missing for an IMPORTED target, or
  an ALIAS target is missing?

This seems to be a different issue (@fsimonis). I then tried to build the OpenFOAM adapter with preCICE as a static library, by using the --static option in pkg-config --silence-errors --libs --static libprecice.

Since the OpenFOAM adapter is a shared library, I got an error regarding relocation, which I solved by rebuilding preCICE with:

 CMAKE_CXX_FLAGS = -fPIC

Maybe we should integrate this by default.

The current issue, as @fsimonis expected, is for MPI during linking:

undefined symbol: _ZN3MPI8Datatype4FreeEv       (/home/makish/OpenFOAM/makish-5.0/platforms/linux64GccDPInt32Opt/lib/libpreciceAdapterFunctionObject.so)
undefined symbol: _ZN3MPI3Win4FreeEv    (/home/makish/OpenFOAM/makish-5.0/platforms/linux64GccDPInt32Opt/lib/libpreciceAdapterFunctionObject.so)
undefined symbol: ompi_mpi_cxx_op_intercept     (/home/makish/OpenFOAM/makish-5.0/platforms/linux64GccDPInt32Opt/lib/libpreciceAdapterFunctionObject.so)
undefined symbol: _ZN3MPI4CommC2Ev      (/home/makish/OpenFOAM/makish-5.0/platforms/linux64GccDPInt32Opt/lib/libpreciceAdapterFunctionObject.so)

[MakisH]

OpenMPI also provides a pkg-config module:

$ pkg-config --libs --static mpi
-L/usr/lib/openmpi/lib -Wl,-rpath -Wl,/usr/lib/openmpi/lib -Wl,--enable-new-dtags -lmpi -ldl -libverbs -lutil -lm

[MakisH]

I assume that we also need Requires.private. However, I tried adding Requires.private: mpi to the used libprecice.pc file and I still get the same error.

Here are the flags & paths that pkg-config returns on my system:

$ pkg-config --cflags libprecice 
-pthread -I/home/makish/inst/include -I/usr/lib/openmpi/include -I/usr/lib/openmpi/include/openmpi -I/usr/lib/openmpi/include/openmpi/opal/mca/event/libevent2021/libevent -I/usr/lib/openmpi/include/openmpi/opal/mca/event/libevent2021/libevent/include

$ pkg-config --libs --static libprecice 
-L/home/makish/inst/lib -L/usr/lib/openmpi/lib -lprecice -lboost_filesystem -lboost_log -lboost_log_setup -lboost_program_options -lboost_system -lboost_thread -lboost_unit_test_framework -lboost_date_time -lboost_regex -lboost_chrono -lboost_atomic -ldl -lxml2 -lpetsc -lpython2.7 -Wl,-rpath -Wl,/usr/lib/openmpi/lib -Wl,--enable-new-dtags -lmpi -ldl -libverbs -lutil -lm

[MakisH]

We are currently confused about why this is happening but we don't consider it a high priority. We decided to postpone it.

[fsimonis]

This is not worth the hassle until we have a real reason to do provide this.
Until then, maybe CMake has a generator for find package files ...