Include GNUInstallDirs to set CMAKE_INSTALL_LIBDIR for MacOS builds

[jmcarcell]

The issue is that when building on MacOS, the installation rpath is always set to @loader_path/.. which causes the lookup to look in <install-prefix>/lib/.. and this doesn't work. The default path is related to CMAKE_INSTALL_LIBDIR, so by including GNUInstallDirs CMAKE_INSTALL_LIBDIR gets set to lib and then the rpath becomes @loader_path/../lib which works.

Before

$ otool -l libMarlin.dylib | grep -A2 RPATH
...
          cmd LC_RPATH
      cmdsize 32
         path @loader_path/../ (offset 12)

After

$ otool -l libgear.dylib | grep -A2 RPATH
...
          cmd LC_RPATH
      cmdsize 32
         path @loader_path/../lib (offset 12)

BEGINRELEASENOTES

• Include GNUInstallDirs to set CMAKE_INSTALL_LIBDIR so that the default rpath is correct in MacOS and can be used in downstream projects, like in k4MarlinWrapper

ENDRELEASENOTES

I tried adding Key4hepConfig.cmake but that didn't change anything. I wonder if passing libraries by full paths instead of cmake targets is the cause since I haven't seen this issue for other packages.

With iLCSoft/GEAR#14 I was able to build k4MarlinWrapper on MacOS.

[tmadlener]

Does this change anything for linux builds?

[jmcarcell]

The files are installed to the same places. I only saw that for rpaths before there was this path:

$ORIGIN/../lib64

and now it is

$ORIGIN/../lib

I think this should be harmless since libraries are installed to lib so since we currently have the path with lib64 with libs installed in lib it's probably not doing anything.

[tmadlener]

Thanks for checking. If the installation is unchanged and working, this can go in.

[tmadlener]

new tag as well?

[jmcarcell]

Yes please. I'm not sure if everything will be OK but at least we'll have tags for a buildable stack on MacOS (on the LCG stacks)

[tmadlener]

Done: https://github.com/iLCSoft/Marlin/releases/tag/v01-19-04
Also for GEAR: https://github.com/iLCSoft/GEAR/releases/tag/v01-09-04

[jmcarcell]

Thanks! 😃