I guess the proper process here is that one starts with the code as it was before the contribution, with a ticket describing what needs to be done, and writes t

I guess the proper process here is that one starts with the code as it was before the contribution, with a ticket describing what needs to be done, and writes the missing code. Preferably this is done by a person who never saw the contributed code. Then you merge all future commits on top of this. If there are merge conflicts, it can be a lot of work for small (== no) gain, but it would put you in clear.