`tools/class_loader` produces broken `class_loader.pc`

[moooeeeep]

When I build tools/class_loader, the installed class_loader.pc seems to be broken.

Probably this is a cmake issue. It seems to configure the dependencies as a semicolon-separated string, instead of space-separated string. On Ubuntu 20.04 it additionally writes the cmake target aliases instead of the actual libraries.

Output on Ubuntu 18.04:

prefix=/path/to/ws/install/tools/class_loader
exec_prefix=/path/to/ws/install/tools/class_loader
libdir=${prefix}/lib
includedir=${prefix}/include

Name: class_loader
Description: "Package for loading plugins at runtime"
Version: 
Requires: console_bridge 
Libs: -L${libdir} -lclass_loader /usr/lib/x86_64-linux-gnu/libboost_thread.so;/usr/lib/x86_64-linux-gnu/libboost_system.so;/usr/lib/x86_64-linux-gnu/libboost_chrono.so;/usr/lib/x86_64-linux-gnu/libboost_date_time.so;/usr/lib/x86_64-linux-gnu/libboost_atomic.so;/usr/lib/x86_64-linux-gnu/libpthread.so;/path/to/ws/install/base/logging/lib/libbase-logging.so;/usr/lib/libPocoFoundation.so;dl
Cflags: -I${includedir} 

Output on Ubuntu 20.04:

prefix=/path/to/ws/install/tools/class_loader
exec_prefix=/path/to/ws/install/tools/class_loader
libdir=${prefix}/lib
includedir=${prefix}/include

Name: class_loader
Description: "Package for loading plugins at runtime"
Version: 
Requires: console_bridge 
Libs: -L${libdir} -lclass_loader Boost::thread;Boost::system;/path/to/ws/install/base/console_bridge/lib/libconsole_bridge.so;/path/to/ws/install/base/logging/lib/libbase-logging.so;/usr/lib/x86_64-linux-gnu/libPocoFoundation.so;dl
Cflags: -I${includedir} 

Expected output (or similar):

prefix=/path/to/ws/install/tools/class_loader
exec_prefix=/path/to/ws/install/tools/class_loader
libdir=${prefix}/lib
includedir=${prefix}/include

Name: class_loader
Description: "Package for loading plugins at runtime"
Version: 
Requires: console_bridge 
Libs: -L${libdir} -lclass_loader /usr/lib/x86_64-linux-gnu/libboost_thread.so /usr/lib/x86_64-linux-gnu/libboost_system.so /usr/lib/x86_64-linux-gnu/libboost_chrono.so /usr/lib/x86_64-linux-gnu/libboost_date_time.so /usr/lib/x86_64-linux-gnu/libboost_atomic.so /usr/lib/x86_64-linux-gnu/libpthread.so /path/to/ws/install/base/console_bridge/lib/libconsole_bridge.so /path/to/ws/install/base/logging/lib/libbase-logging.so /usr/lib/x86_64-linux-gnu/libPocoFoundation.so dl
Cflags: -I${includedir}

For comparison, the version installed by my ROS distribution:

prefix=/opt/ros/melodic

Name: class_loader
Description: Description of class_loader
Version: 0.4.1
Cflags: -I${prefix}/include -I/usr/include
Libs: -L${prefix}/lib -lclass_loader /usr/lib/x86_64-linux-gnu/libboost_thread.so /usr/lib/x86_64-linux-gnu/libboost_system.so /usr/lib/x86_64-linux-gnu/libboost_chrono.so /usr/lib/x86_64-linux-gnu/libboost_date_time.so /usr/lib/x86_64-linux-gnu/libboost_atomic.so /usr/lib/x86_64-linux-gnu/libpthread.so /usr/lib/libPocoFoundation.so -ldl /usr/lib/x86_64-linux-gnu/libconsole_bridge.so.0.4
Requires: 

[skasperski]

I think i should be fixed after this PR: ros/class_loader#187

[moooeeeep]

It doesn't seem to work like that. At least when I try this, it will still write the PKGCONFIG_LIBS separated by semicolons. Also, I think you would need to add -l if you specify the libs this way?

The aliases from Boost_LIBRARIES will not appear then though. But I'm not sure if I like that the exact libraries are spelled out there again.

[moooeeeep]

I have played around with the config myself, and this would be my suggestion: moooeeeep/class_loader@4adbad2

It seems to work even without forwarding all those dependencies to client code.

We might run into problems, when someone wants to link this statically, right? Related:

• https://people.freedesktop.org/~dbn/pkg-config-guide.html
• https://wiki.mageia.org/en/Overlinking_issues_in_packaging
• https://stackoverflow.com/questions/3971703/how-to-use-c-boost-library-with-pkg-config

Related: generate a space separated string from the list: string(REPLACE ";" " " OUTPUT_VAR "${INPUT_VAR}")

Perspectively it may be a good idea to keep track with recent changes on the ROS2 branches.