Trying to compile a ROS 2 Eloquent package depending on a pure cmake package using colcon [closed]

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Hello there,

I have been fighting for some time with CMakeLists trying to compile a ROS 2 Eloquent package (bar) depending on a pure cmake package (foo) using colcon but I get the following error:

<...>/bar.hpp:5:10: fatal error: foo/foo.hpp: No such file or directory #include "foo/foo.hpp"

I've made a minimal repo showing my problem here: https://github.com/MarcTestier/ros2_c....

The install folder of the cmake package (foo) seems somewhat normal though, its folder tree looks like this:

install/foo/  
├── include  
│   └── foo  
│       ├── foo.hpp  
│       └── foo_export.h  
├── lib  
│   └── libfoo.so  
└── share  
    ├── colcon-core  
    │   └── packages  
    │       └── foo  
    └── foo  
        ├── cmake  
        │   ├── fooConfig.cmake  
        │   ├── fooConfigVersion.cmake  
        │   ├── fooTargets-noconfig.cmake  
        │   └── fooTargets.cmake  
        ├── hook  
        │   ├── cmake_prefix_path.dsv  
        │   ├── cmake_prefix_path.ps1  
        │   ├── cmake_prefix_path.sh  
        │   ├── ld_library_path_lib.dsv  
        │   ├── ld_library_path_lib.ps1  
        │   ├── ld_library_path_lib.sh  
        │   ├── pkg_config_path.dsv  
        │   ├── pkg_config_path.ps1  
        │   ├── pkg_config_path.sh  
        │   ├── pkg_config_path_multiarch.dsv  
        │   ├── pkg_config_path_multiarch.ps1  
        │   └── pkg_config_path_multiarch.sh  
        ├── package.bash  
        ├── package.dsv  
        ├── package.ps1  
        ├── package.sh  
        └── package.zsh

It seems like the ROS 2 package (bar) has trouble finding the cmake package (foo) library and headers but find_package(foo) works.

I found an ugly solution (available in the repo here) which consists of 2 steps:

1.Manually add the include directory

get_filename_component(INSTALL_DIR ${CMAKE_INSTALL_PREFIX} DIRECTORY)
include_directories(${INSTALL_DIR}/foo/include/)

If I only perform step 1, I can find the header files but I get an error: /usr/bin/ld: cannot find -lfoo which I guess means that even though I do the following:

target_link_libraries(Bar foo)

Bar still can't properly find the foo library.

2.If on top of the first step I link directly against the .so file:

target_link_libraries(Bar "${INSTALL_DIR}/foo/lib/libfoo.so")

Now the packages can compile but the solution seems a bit ugly.

I'm out of idea and I can't tell if the problem comes from a pure cmake problem, colcon moving/linking stuff around or anything else so any suggestions are welcomed, thanks.