Do not install plugins in CMAKE_INSTALL_LIBDIR

[jmcarcell]

BEGINRELEASENOTES

• Cmake: Do not install plugins in CMAKE_INSTALL_LIBDIR, but always in lib

ENDRELEASENOTES

CMAKE_INSTALL_LIBDIR can change between cmake versions for the same OS and since everything is hardcoded to use lib it is unexpected that the plugins are installed somewhere else. In practice it happens that CMAKE_INSTALL_LIBDIR is set almost always (but not always, sometimes it is set to lib64, see https://cmake.org/cmake/help/v3.30/module/GNUInstallDirs.html) to lib. This is something that can be of course solved from the packaging point of view, but I think it would be a good practice to either set everything to CMAKE_INSTALL_LIBDIR (which could change) or everything to lib (this PR).

Given that the inclusion of both non-plugins libraries and plugins libraries in LD_LIBRARY_PATH to make DD4hep work fine having everything in the same directory I think is a good idea. Otherwise another variable could be added if someone wanted to install the plugins in a different location.

[github-actions]

Test Results

   10 files     10 suites   4h 24m 51s ⏱️
  365 tests   362 ✅ 0 💤 3 ❌
1 166 runs  1 157 ✅ 0 💤 9 ❌

For more details on these failures, see this check.

Results for commit 8f56cda.

♻️ This comment has been updated with latest results.

[andresailer]

I think you need to stop replacing CMAKE_INSTALL_LIBDIR with lib and instead fix the places which lib64 shows up, or set CMAKE_INSTALL_LIBDIR to lib, because CMAKE_INSTALL_LIBDIR was put in place for a reason.

[andresailer]

Not like this.

[andresailer]

We are not setting CMAKE_INSTALL_LIBDIR in dd4hep itself? We are not using GNUInstallDirs.
So this issue comes from some other package? That package should fix itself?

cf. this PR 3343988

[jmcarcell]

Indeed it shouldn't be changed here. Something weird is happening after updating to cmake 3.30.2 on Alma 9, it seems CMAKE_INSTALL_LIBDIR was being set for DD4hep even when I ran manually the cmake command (which doesn't have CMAKE_INSTALL_LIBDIR), to be investigated...