the right way to enable/disable Boost features in main CMake script?

[Bakul-Gaur]

Hi Orphis/boost-cmake experts,

I am trying to port an old build-system to CMake (I am not too experienced with CMake).
I just tried boost-cmake and hats-off to its developers.. great package!

My project depends on Boost::locale and I am having some trouble with static linking against ICU libs. I know there are dozens of forums talking about it and suggesting changing link-order, etc. but nothing has worked for me so far. FYI, I end-up with something like this:

/usr/bin/c++    -static CMakeFiles/test_boost.dir/main.cpp.o  -o test_boost  boost-cmake/libboost_locale.a boost-cmake/libboost_thread.a boost-cmake/libboost_chrono.a /usr/lib/x86_64-linux-gnu/librt.a -lpthread /usr/local/lib/libicudata.a /usr/local/lib/libicui18n.a /usr/local/lib/libicuuc.a -ldl
/usr/bin/ld: /usr/local/lib/libicuuc.a(putil.ao): in function `uprv_dl_open_70':
putil.cpp:(.text.uprv_dl_open_70+0x16): warning: Using 'dlopen' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
/usr/bin/ld: /usr/local/lib/libicuuc.a(udata.ao): in function `doLoadFromCommonData(signed char, char const*, char const*, char const*, char const*, char const*, char const*, char const*, signed char (*)(void*, char const*, char const*, UDataInfo const*), void*, UErrorCode*, UErrorCode*) [clone .constprop.0]':
udata.cpp:(.text._ZL20doLoadFromCommonDataaPKcS0_S0_S0_S0_S0_S0_PFaPvS0_S0_PK9UDataInfoES1_P10UErrorCodeS8_.constprop.0+0x3ca): undefined reference to `icudt70_dat'
/usr/bin/ld: udata.cpp:(.text._ZL20doLoadFromCommonDataaPKcS0_S0_S0_S0_S0_S0_PFaPvS0_S0_PK9UDataInfoES1_P10UErrorCodeS8_.constprop.0+0x4af): undefined reference to `icudt70_dat'

ICU lib has given me other troubles too, so I decided to disable it (and use the iconv lib instead) by doing:

set(BOOST_LOCALE_ENABLE_ICU_BACKEND OFF)
add_subdirectory(boost-cmake)
...

I know this is not the recommended way to override options in sub-projects. And of course it fails at configure:

-- Boost locale unsupported on platform: need either iconv or ICU.
-- Configuring done
CMake Error at CMakeLists.txt:11 (add_executable):
  Target "test_boost" links to target "Boost::locale" but the target was not
  found.  Perhaps a find_package() call is missing for an IMPORTED target, or
  an ALIAS target is missing?

I thought the option BOOST_LOCALE_ENABLE_ICONV_BACKEND in boost-cmake\libs\locale.cmake will take effect. But it doesn't. I have no idea of how to configure it right.

My questions is: what is the foreseen way to configure Boost with Orphis/boost-cmake? Can you please provide an example?

Here is my CMake script for a hello-world C++ program using Boost::locale:

cmake_minimum_required(VERSION 3.16)

project(test_boost)

# boost-cmake setup
# -----------------
find_library(RT_LIBRARY NAMES librt.a)
set(BOOST_LOCALE_ENABLE_ICU_BACKEND OFF)
add_subdirectory(boost-cmake)

# My hello-world binary
# ---------------------
add_executable(test_boost main.cpp)
target_link_libraries(test_boost
	PRIVATE
		Boost::boost
		Boost::locale
)
target_link_options(test_boost PRIVATE -static)

Other details about my setup:

• I am using WSL2 Ubuntu 20.04.3 LTS
• Orphis/boost-cmake branch master
• gcc 9.3.0
• cmake 3.16.3
• Boost 1.71.0 (default in Orphis/boost-cmake)

Thanks in advance!