[lilyball]

As I understand it, in Git Flow, the result of the merge into main should be identical to the tree that was in develop, meaning there's no difference, it's just a matter of maintaining the appropriate history.

Under normal conditions this should be trivially true. Develop forked off from main, no commits on main, therefore the merge back into main has no changes on the first-parent side and is equal to the second parent. The two ways to screw this up are:

1. You did a hotfix release and didn't merge the hotfix back into develop properly, or

2. You made changes on a release branch and forgot to merge that back into develop.

In both cases, the fact that the results of merging develop into main produced a different tree than what was in develop (or rather, in the current release branch) should be a signal that you screwed up somewhere.

Having said all that, I'm willing to bet that 98% of places that do Git Flow don't actually have any checks to ensure that the tree on main is identical to the tree on the release branch. And this is because the model is actually rather complex, most people don't understand Git properly, and the accessible documentation about Git Flow doesn't even bother to mention the possibility that the merge into main could produce a different tree.