FindXROOTD adds libraries to link against irrespective of xrootd version used

[andresailer]

Dear ROOT devs,

These lines in the FindXROOTD

root/cmake/modules/FindXROOTD.cmake

Lines 137 to 149 in 323c214

	# libXrdClient (old client; will be dropped at some point)
	find_library(XROOTD_XrdClient_LIBRARY
	NAMES XrdClient
	HINTS ${searchpath}
	PATH_SUFFIXES lib)
	if (XROOTD_XrdClient_LIBRARY)
	list(APPEND XROOTD_LIBRARIES ${XROOTD_XrdClient_LIBRARY})
	else ()
	set(XROOTD_NOOLDCLNT TRUE)
	if(NOT XROOTD_FIND_QUIETLY)
	message(STATUS " libXrdClient not found: use built-in")
	endif ()
	endif ()

make some root libraries, e.g., libNetxNG.so, link against old versions of xrootd if they are found on the system, even though one wants to build against the new version of xrootd.
We for SPI run into this problem when building on a machine which just happens to have this installed, and we cannot control the packages.

e.g. this is printed during configure:

-- Found Xrootd version num: 5.3.1 (setting -DROOTXRDVERS=500030001)
--
--              libXrdMain not found: xproofd will be a wrapper around xrootd
--              include_dirs: /data/sftnight/build/workspace/lcg_release_pipeline/install/xrootd/5.3.1/aarch64-centos7-gcc8-opt/include/xrootd;/data/sftnight/build/workspace/lcg_release_pipeline/install/xrootd/5.3.1/aarch64-centos7-gcc8-opt/include/xrootd/private
--              libraries: /data/sftnight/build/workspace/lcg_release_pipeline/install/xrootd/5.3.1/aarch64-centos7-gcc8-opt/lib64/libXrdUtils.so;/usr/lib64/libXrdClient.so;/data/sftnight/build/workspace/lcg_release_pipeline/install/xrootd/5.3.1/aarch64-centos7-gcc8-opt/lib64/libXrdCl.so

This then causes problem when our ROOT is used on some other machine.
So at the moment we just patch these lines out. If you could consider dropping them, or some check based on xrootd version?

Thanks,
Andre

[bellenot]

Can't you simply use the -Dbuiltin_xrootd=ON option?

[andresailer]

No, we don't want to use the builtin xrootd.

[bellenot]

And I suppose adding the XROOTD you want in CMAKE_PREFIX_PATH doesn't help either? So should we introduce a way of specifying which version and/or which location XROOTD is taken from? Does XROOTD provide a standard way of finding it with CMake?

[andresailer]

The problem is that find_library just looks in the system library location finds the library and makes ROOT link against it. So something like if version < 5 around this find_library call would probably already solve the issue.

I.e., from the opening post this finds xrootd version 5.3.1 from where we put it, but then just adds /usr/lib64/libXrdClient.so into the mix

--              libraries: /data/sftnight/build/workspace/lcg_release_pipeline/install/xrootd/5.3.1/aarch64-centos7-gcc8-opt/lib64/libXrdUtils.so;/usr/lib64/libXrdClient.so;/data/sftnight/build/workspace/lcg_release_pipeline/install/xrootd/5.3.1/aarch64-centos7-gcc8-opt/lib64/libXrdCl.so

[bellenot]

OK, then I'll need to set-up a VM and investigate...

[bellenot]

I think we should rely on XRootDConfig.cmake, but I'll have to see the implications

[guitargeek]

Re-opened because the XRootDConfig.cmake from xrootd upstream didn't work after all, see:
#14170