libReg.a fails to link to Boost in Ubuntu 20.04

[paskino]

In SyneRBI/SIRF-SuperBuild#649 it seems there is a linker error for libReg.a

Apparently boost linking is taken care of by

SIRF/src/Registration/cReg/CMakeLists.txt

Lines 76 to 87 in 6c0b1fe

	# Add boost library dependencies
	if((CMAKE_VERSION VERSION_LESS 3.5.0) OR (NOT _Boost_IMPORTED_TARGETS))
	# This is harder than it should be on older CMake versions to be able to cope with
	# spaces in filenames.
	foreach(C SYSTEM FILESYSTEM)
	target_link_libraries(Reg PUBLIC optimized "${Boost_${C}_LIBRARY_RELEASE}")
	target_link_libraries(Reg PUBLIC debug "${Boost_${C}_LIBRARY_DEBUG}")
	endforeach()
	else()
	# Nice and simple for recent CMake (which knows about your Boost version)
	target_link_libraries(Reg PUBLIC Boost::system Boost::filesystem)
	endif()

The current if statement has been merged in long ago, before we used CMake 3.5.

Given that now we require CMake 3.9 I believe the if is not useful, probably harmful. I suggest to remove them in the 3 places where this is done.

[KrisThielemans]

_Boost_IMPORTED_TARGETS. is set by CMake https://github.com/Kitware/CMake/blob/9d439dfd1b7f8599905e687005dd8dc69921f4d2/Modules/FindBoost.cmake#L1391
I would guess that it never happens for us as our Boost and CMake version combination should always give them, (see here so you could get rid of the if I believe. You can check in which branch of the if it goes.

However, I think the problem is with filesystem. I see 2 possibly causes:

• we don't install boost/filesystem library
• we have incorrect dependencies. I think this is probably the case, see boost linking problems on Travis OSX #429

[paskino]

We do install libboost-filesystem-dev

It is arguably a problem with the Boost version? I don't think so because I'm building with USE_SYSTEM_Boost=ON so there shouldn't be another Boost around?

Ubuntu 18.04 should have 1.65, but in some messages during the build I could see 1.36 (STIR's CMake output during config) and 1.48, which buffles me.

[KrisThielemans]

We do install libboost-filesystem-dev

great

We do install libboost-filesystem-dev

It is arguably a problem with the Boost version? I don't think so because I'm building with USE_SYSTEM_Boost=ON so there shouldn't be another Boost around?

Ubuntu 18.04 should have 1.65, but in some messages during the build I could see 1.36 (STIR's CMake output during config) and 1.48,

We require 1.36, which is probably what you see. Maybe STIR requires 1.48. not sure. Of course, I think we likely need more recent boost...

Not sure what's going on. I guess you'' find out if we really use the boost::filesystem et al. targets. If we do, I guess you want to do a make VERBOSE=ON after the first failure.

[KrisThielemans]

I wonder now if this is because the Boost version was more recent than the CMake version (as discussed in SyneRBI/SIRF-SuperBuild#667). Which CMake and Boost version was this using?

[paskino]

@KrisThielemans is this still relevant?
AFAIK, the SuperBuild builds on Ubuntu 20.04 both on GHA and docker?

[KrisThielemans]

AFAIK, the SuperBuild builds on Ubuntu 20.04 both on GHA and docker?

yes. In fact, GHA is on ubuntu-latest I believe, which could be 22.04 by now.

I first thought we could merge db4479d via a PR to simplify our files, but I now think that this code could cover the case where CMake is older than Boost (in which case FindBOOST.cmake gives up and doesn't define the targets I think). I'm not 100% sure, but unless you want to investigate that, it might be easiest to just leave it in.

Of course, I have no idea what happened when you had this problem, so there might be some problem lurking somewhere, but finding out is going to be tough.

Summary : I'm fine with closing this issue.