BOOST_ROOT not respected at link stage after cmake config - c++

Question

Apologies for a lengthy title.
I am struggling linking boost with cmake due to existence of boost libraries in /usr/lib64 directory. My boost is compiled in a different place and I am pointing cmake with BOOST_ROOT. Aware of potential problems I am setting a minimal version and Boost_NO_SYSTEM_PATH. Configure stage works fine, but when linking I get an error:
test.cpp:(.text._ZN5boost15program_options25basic_command_line_parserIcEC2EiPKPKc[_ZN5boost15program_options25basic_command_line_parserIcEC5EiPKPKc]+0xa8): undefined reference to `boost::program_options::detail::cmdline::cmdline(std::vector<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>
>, std::allocator<std::__cxx11::basic_string<char,std::char_traits<char>, std::allocator<char> > > > const&)'
This is clearly a problem of picking up the wrong library and I can see with make VERBOSE=2 that the g++ line doesn't respect my previously found boost setting in BOOST_ROOT
g++ CMakeFiles/test.dir/test.cpp.o -o test -rdynamic -lboost_program_options-mt
But I would expect something along these lines:
g++ ... -L/path/to/my/own/boost/lib -lboost_program_options-mt
As a "debug" step I print out a message in cmake with Boost_LIBRARY_DIRS and I can see /path/to/my/own/boost/lib. When I "manually" add the -L flag the linking works, which is how I know that the system libs are still interfering. Also, my *LIBRARY_PATH are pointing only at /path/to/my/own/boost/lib.
Perhaps, it's not unlikely that this is a bug of FindBoost module, but I am finding it hard to believe. It seems to me that there's still something major in cmake I do not understand? Why is the -L flag not generated in this instance or a link to a specific file? Please advise.
Here is my CMakeLists.txt
cmake_minimum_required(VERSION 2.8)
set(Boost_NO_SYSTEM_PATHS ON)
find_package(Boost 1.67.0 REQUIRED COMPONENTS program_options)
include_directories(${Boost_INCLUDE_DIR})
add_executable(test test.cpp)
target_link_libraries(test LINK_PUBLIC ${Boost_PROGRAM_OPTIONS_LIBRARY})
And my program:
#include <iostream>
#include <string>
#include <boost/program_options.hpp>
namespace po=boost::program_options;
int main( int argc, char* argv[])
{
po::options_description options_description;
po::positional_options_description positional_options_description;
po::variables_map variables_map;
options_description.add_options()
("help,h", "print usage message");
po::store(po::command_line_parser(argc, argv).options(
options_description).positional(positional_options_description).run(),
variables_map);
return 0;
}
Other relevant output
I am using message to pull out varables from cmake config step after find_package:
${Boost_INCLUDE_DIR} /path/to/my/own/boost/include
${Boost_LIBRARY_DIRS} /path/to/my/own/boost/lib
${Boost_LIBRARIES} /path/to/my/own/boost/lib/libboost_program_options-mt.so
${Boost_PROGRAM_OPTIONS_LIBRARY} /path/to/my/own/boost/lib/libboost_program_options-mt.so

Answer 1

I don't know which CMake version you are using but did you try using Boost imported target instead of the old-fashioned CMake variable:
i.e.
replace:
target_link_libraries(test LINK_PUBLIC ${Boost_PROGRAM_OPTIONS_LIBRARY})
by
target_link_libraries(test LINK_PUBLIC Boost::program_options)

Answer 2

After calling in on cmake-developer mailing list and finally leaving a post on cmake gitlab issues I realised that the problem was not so much my cmake version, but rather my cmake_minimum_required which I inherited from an older project.
I was setting:
cmake_minium_required(VERSION 2.8)
After updating it to 3.12 that I got the correct behaviour:
/path/to/g++ -rdynamic CMakeFiles/test.dir/test.cpp.o -o test -lboost_program_options-mt
Reading cmake_minimum_required docs I understood that "command implicitly invokes" cmake_policy. I believe the latter wasn't playing well with FindBoost from my 3.12 `cmake.
I am not sure if this post is useful to SO, but I have certainly learnt my cmake lesson here.