find_package cannot find Boost

[Mohammadabd]

I have built osrm-backend successfully on my mac machine, but when CMake example I get multiple warning related to boost such as

Target "osrm-example" links to target "Boost::regex" but the target was not found.  Perhaps a find_package() call is missing for an IMPORTED target, or an ALIAS target is missing?

and then when running build it throws error and fails

ld: library not found for -lBoost::regex

How to get around this issue? I have boost already installed. Thanks

ls /usr/local/Cellar/boost/
1.72.0

[Mohammadabd]

FIX:
in ./example/CMakeLists.txt add
find_package(Boost 1.52.0 COMPONENTS filesystem system thread iostreams chrono date_time regex REQUIRED)

[mjjbell]

This is happening because FindBoost changed (I think in cmake v3.11) to use Imported Targets for library component variables, rather than file paths to the Boost libraries.

cmake uses these targets when linking (e.g. target_link_library) and knows how to correctly substitute the values. However, the OSRM pkg-config file that we generate doesn't do this, and ends up writing the actual target symbols, hence the errors trying to link Boost::<component>

The example works when OSRM is built with older versions of cmake (CI is using 3.7.2) as you get the old behaviour of writing file paths to libosrm.pc.

To fix this for newer cmake versions, I think we need to add a file(GENERATE... step to the pkg-config creation, which has the information needed to make the imported target substitutions, as suggested here: https://cmake.org/pipermail/cmake/2018-December/068812.html