ament_package() should set reasonable defaults on CPACK_* variables

[stewpend0us]

I can't think of a good reason not to set some reasonable defaults on CPACK_* variables from within ament_package().

• Best case users can just call include(CPack) and now they can produce "packages" (installers)
• Worst case they and over-write and/or fill out the rest of their CPACK_* variables before calling include(CPack)
• I'm guessing this would have no effect on the majority of users but may encourage people to move toward using CPack (which is a fantastic tool!)

[traversaro]

Which reasonable defaults you have in mind? As CPACK_* variables already have a bunch of reasonable defaults (see https://cmake.org/cmake/help/latest/module/CPack.html), if any was missing perhaps it could make more sense to add these defaults upstream in CMake/CPack, or there is some information that ament_package has that is not available in a regular non-ament CMake package?

[stewpend0us]

I guess the lowest hanging fruit would be the variables taken from package.xml. (I assume) ament parses the package.xml and puts the results in ament_cmake_core/package.cmake at a minimum the Version and Maintainer should be set to the CPACK versions I would think?

The bigger one though is the dependencies. For my own purposes I use the EXEC_DEPENDS out of package.cmake, pass those through rosdep resolve, and put the results (importantly including the errors) as the CPACK*_PACKAGE_DEPENDS. I include the errors because (in my case) the errors are simply my own packages that I depend on. They're not known by rosdep but that doesn't matter. When I do this for all of my packages apt will take care of the rest.

If these things were all done by ament then creating a package for most of my stuff would be as easy as adding an include(CPack) to the bottom of my CMakeLists.txt