Some of you may already know, but just following this official documentation cannot build private ros2 packages because it cannot resolve dependencies of private packages. The following image is the result of running bloom-generate rosdebian in h6x_internship_gazebo package. Even if you continue this, bloom-generate cannot resolve this dependency problem. This seems to be because bloom-generate tries to resolve dependencies with rosdep, and rosdep tries to find the dependencies with the name of the debian package (not the name of ros2 package).
To solve this problem, this ros2_deb_builder makes a correspondence table of ros2 packages and debian packages and makes rosdep to import it. This is done in update-rosdep.bash. This script creates /etc/ros/rosdep/sources.list.d/50-my-packages.list and it references my_rosdep.yaml, which contains the correspondence table.
However, just importing the correspondence table cannot solve the problem yet. Debian packages have to be installed before referencing them. But most of the time your private package would reference your another private package, so you have to build, generate deb file, and install it in order from the lowest dependency. If the buid and install are done from the lowest dependency, bloom-generate can resolve rosdep keys because the dependencies (as debian packages) are always installed before referencing them.
But how can we know the order of dependencies? This sounds a bit complicated, but fortunately, colcon command can solve this problem.
colcon list -tn lists the names of packages in the topological ordering, and this is what we need to follow to build packages. generate-deb.bash uses this list to build.
After building debian packages, the name of the package changes. If the name of your ros2 package is h6x_internship_gazeo, then the name of debian package will be ros-galactic-h6x-internship-gazebo.
This rule may not be perfect, but it seems like the name changes as:
ros-{ros2-version-name}prefix is added"_"becomes"-"- Upper case becomes lower case
Version number of debian package is important, because apt-get upgrade command ugrades the packages of which newer version is available.
Actually, setting version number of deiban package is simple. The version number in package.xml of your ros2 package is used to create debian package.