Building with static dependencies breaks CMake exports

[ricrogz]

Recently, I had to build and link RDKit & dependencies into another project as static libs. The other project used CMake, so I tried to import RDKit's exports to configure the project, and found a problem that broke the build of the other project:

When we use external builds of maeparser and coordgen, RDKit's mechanism to build static libraries is breaking the export target. Looking into rdkit-targets.cmake (generated under rdkit/build/CMakeFiles/Export/lib/cmake/rdkit), it contains the following (I added line breaks after each semicolon, to make it more readable):

set_target_properties(RDKit::Depictor_static PROPERTIES
  INTERFACE_LINK_LIBRARIES "RDKit::RDGeometryLib_static;
RDKit::RDGeneral_static;
RDKit::MolAlign_static;
/tmp/deps/coordgen-install/lib/libcoordgen.a_static;
/tmp/deps/maeparser-install/lib/libmaeparser.a_static;
Boost::system;
Boost::iostreams;
Boost::system;
Boost::iostreams;
RDKit::SubstructMatch_static;
RDKit::GraphMol_static;
RDKit::RDGeneral_static;
RDKit::rdkit_base"
)

[...]

set_target_properties(RDKit::FileParsers_static PROPERTIES
  INTERFACE_LINK_LIBRARIES "RDKit::RDGeometryLib_static;
RDKit::RDGeneral_static;
RDKit::Depictor_static;
RDKit::SmilesParse_static;
RDKit::GraphMol_static;
/tmp/deps/maeparser-install/lib/libmaeparser.a_static;
Boost::system;
Boost::iostreams;
Boost::system;
Boost::iostreams;
/usr/lib/x86_64-linux-gnu/libz.so;
RDKit::rdkit_base"
)

The problem here is that neither /tmp/deps/coordgen-install/lib/libcoordgen.a_static nor /tmp/deps/maeparser-install/lib/libmaeparser.a_static exist: the actual lib filenames (libcoordgen.a and libmaeparser.a) have been added a "_static" suffix). So, importing this CMake targets file will cause the parent project to fail building, since we won't be able to link against these libraries.

I know where this comes from, and I think I can improve/fix it, so I'll post a PR soon.

Also, there's a second issue, which is that having explicit file names in the CMake export target prevents it from being relocatable, but that's a different issue (the exports will work, as long as the explicitly mentioned dependencies aren't moved).