Fix stdeb for python 3

[timonegk]

This is my attempt to fix #594. The following changes are done:

• replace dependency catkin-pkg with catkin-pkg-modules (> 0.2.9 can be dropped because catkin-pkg-modules was introduced with 0.3.0)
• Depends and Conflicts (i. e., the python 2 settings) were removed from stdeb.cfg because no further python 2 packages will be built.
• python3-osrf-pycommon was added as a deb dependency (I don't know why it was missing)

I tested the changes on five different systems:

• Debian 9 Stretch (python 3.5.3)
• Debian 10 Buster (python 3.7.3)
• Ubuntu 16.04 Xenial Xerus (python 3.5.2)
• Ubuntu 18.04 Bionic Beaver (python 3.6.9)
• Ubuntu 20.04 Focal Fossa (python 3.8.5)

Once all build dependencies were installed, I used the command python3 setup.py --command-packages=stdeb.command sdist_dsc --with-python2=False bdist_deb to create the deb file. It could be installed on all systems and catkin commands could be executed without error.
The mentioned systems cover all the systems in Suite, assuming that the non-LTS Ubuntu releases behave like either the predecessor or the successor.

Before the release with these changes, the trivial fix in osrf/osrf_pycommon#71 should be merged. Currently, python3-osrf-pycommon and python-osrf-pycommon don't conflict in all cases, resulting in annoying apt errors on installing python3-osrf-pycommon when python-osrf-pycommon was already installed.

Before the release, the version in setup.py an the changelog should obviously be updated.

[timonegk]

There is still a problem, we cannot require catkin-pkg-modules in setup.py because that will break catkin_tools on systems where no apt packages for ros are available (catkin-pkg-modules is not a pip package). Therefore we have to use catkin-pkg >= 0.3.0 in setup.py. This will now break on systems where only python3-catkin-pkg-modules is installed, because catikn-pkg is not available there. But python3-catkin-pkg can not be a requirement because it conflicts with ros. The best option might be to remove catkin-pkg(-modules) completely from setup.py – or find a way to depend on one of the two depending on pypi/deb installation...

[timonegk]

The cleanest solution (in my opinion) would be to create a pypi package catkin-pkg-modules that contains no code but depends on catkin-pkg, essentially a meta package or wrapper around catkin-pkg. Then, catkin-pkg-modules could be the dependency for deb and pypi/pip.

[timonegk]

Okay, I found another way, as ros_buildfarm is doing it.

[timonegk]

Sorry for the spam, now everything works with pip and with stdeb. Yay!

[timonegk]

As you found out, the build failure for ros-melodic-catkin is completely unrelated, this repository has no connection to ros-melodic-catkin.

[mikepurvis]

Looks sane to me; thanks for the thorough effort at testing this!

[timonegk]

I just added the changelog. Maybe you'll manage to take a look at it in the next few days.

[nuclearsandwich]

I don't think this line change is necessary. The separate Suite3 config field is only needed when the release suites differ between Python 2 and Python 3.

I'm pretty certain that stdeb defaults to unstable if no suites are configured although I haven't confirmed that. Leaving this line as it was while adding the No-Python2 field below should be sufficient to halt all further python2 releases of this package.

[timonegk]

Yes, you seem to be right. Thank you, I changed it back.