Why debug packages don't include sources?

Question

I was expecting that after installing the package libgtk-3-0-dbg I would get DDD to show the source code when stepping into gtk+, however I had to download the source package myself (from here) and move it to the proper /build directory :(

Answer 1

-dbg packages aren't automatic - the package maintainer needs to define the package, and pass the appropriate parameters to the package building tools to ensure the package has any content.

By convention, but not by actual policy, the -dbg package is populated with data which would otherwise be removed by a call to GNU strip, i.e. debugging symbols which are stripped by default (again, by convention, but not policy). Or some language-specific equivalent in the case of non-ELF libraries (e.g. .mdb files for .NET libraries).

The convention doesn't call for -dbg packages to include source (since we already have a mechanism for including those and making them available, i.e. apt-get source pkgname).

Ubuntu has a mechanism for automatic creation of "Debug debs", or .ddeb files, which are functionally the same as -dbg packages but are created automatically by build servers (i.e. an unmodified package with no -dbg package, compiled on Ubuntu's servers, will get a .ddeb automatically) - but, again, because there is a mechanism in place for making source available, .ddebs do not include source as they don't need to.