Moving @rhaschke 's documentation and proposal here for further debate.

@rhaschke :

In contrast to the merge-strategy suggested in #26 (comment), I propose the following for the future:

git clone https://github.com/ros-planning/moveit2
cd moveit2
git fetch https://github.com/ros-planning/moveit master  # fetch MoveIt 1 branch
git merge FETCH_HEAD  # and merge into MoveIt 2 head

If approved, such a sync PR should be "merged" manually using fast-forward. github's web interface doesn't provide such an option!
Using github's merge commit, will create another, superfluous commit and squashing or rebasing doesn't make sense at all.
However, looks like @davetcoleman has forbidden to push to the MoveIt 2 repo from cmdline. This is a typical use case, where interaction from cmdline is desirable 😉

When there are no merge conflicts, the following procedure using github's web interface will work too:

git clone https://github.com/ros-planning/moveit2
cd moveit2
git fetch https://github.com/ros-planning/moveit master  # fetch MoveIt 1 branch
git checkout -b melodic-sync FETCH_HEAD  # check it out as branch melodic-sync
git push origin melodic-sync  # push to file a PR

Subsequently, file a PR for the created melodic-sync branch and merge using a standard merge-commit.