Including both glog and gflags as cmake subdirectories

[growly]

I haven't found a definitive answer so I'm asking here: does glog support being included as subdirectory in a subsuming cmake project, next to gflags? I'd like my CMakeLists.txt to be as simple as:

add_subdirectory(gflags)
add_subdirectory(glog)

but no dice (find_package fails). I've tried playing with the WITH_GFLAGS, HAVE_LIB_GFLAGS, gflags_FOUND, gflags_NAMESPACE, gflags_INSTALL, etc, variables to trick glog into finding the right installation. @Mizux mentioned that this works when glog is an ExternalProject in #198 - is that the only known/blessed way?

Thanks!

[growly]

I just found @sergiud's comment in #251 that suggests again that only ExternalProject is supported, but that was in 2017. Is that still the case?

[growly]

Ok, if gflags_DIR is set correctly then I get the same error as in #381 regardless of whether I use ExternalProject_Add or add_subdirectory. Based on @sergiud's comments in #381 this is a gflags problem.

So is there any known workaround for getting glog and gflags to co-exist in-tree?

edit: this bug in gflags is still waiting gflags/gflags#279

[sergiud]

Unfortunately, I don't see any way to work around this gflags issue in glog.

[Mizux]

an other way is to hack locally (i.e. by applying a git patch) to your dependency (glog here) so before glog perform a find_package(gflag) you add a check if gflag is present:

so you can modify

glog/CMakeLists.txt

Lines 62 to 69 in 0a2e593

	if (WITH_GFLAGS)
	find_package (gflags 2.2.0)
	if (gflags_FOUND)
	set (HAVE_LIB_GFLAGS 1)
	determine_gflags_namespace (gflags_NAMESPACE)
	endif (gflags_FOUND)
	endif (WITH_GFLAGS)

into something like:

if (WITH_GFLAGS)
  if(NOT TARGET gflag::gflag)
    find_package (gflags 2.2.0)

    if (gflags_FOUND)
      set (HAVE_LIB_GFLAGS 1)
      determine_gflags_namespace (gflags_NAMESPACE)
    endif (gflags_FOUND)
  else()
  set(gflags_NAMESPACE gflags) 
  endif()
endif (WITH_GFLAGS)

note: not tested, and blind supposition of the purpose of determine_gflags_namespace(...)

note: In CMake having find_package(Foo) working seamlessly when using add_subdirectory, ExternalProject or FetchContent is still an open issue.
see: https://gitlab.kitware.com/cmake/cmake/-/issues/17735

I would say CMake has always been targeted to unix system/distro way where you install your deps first then you 'find_package()' them so having super build/monolithic project is more or less outside of the kitware scope IMHO
Still I would be happy to see some Kitware/Modern CMake recommendation/good practice to make a library "super build" compatible (for ascendants and descendants deps).

[growly]

thanks!

[eAzure]

@growly Have you found a solution now? thank you!

[growly]

I gave up trying to include gflags and glog as subdirectories with my source, I now rely on a system-wide install and find_package. The project CMakeLists is here. I was hoping to make installation and dependency control a little simpler by doing it the subdirectory way, but this will have to do.

[eAzure]

I gave up trying to include gflags and glog as subdirectories with my source, I now rely on a system-wide install and find_package. The project CMakeLists is here. I was hoping to make installation and dependency control a little simpler by doing it the subdirectory way, but this will have to do.

I think I have to change to your way, thank you！