empy merge works on empty repo without --allow-empty

[tkalir]

while working on #7824 I noticed that it is possible, if main is empty, to:
create branch a from main
create branch b from main
make an empty commit to a
merge a to b without --allow-empty

It doesn't seem very important but for consistency I believe it should require --allow-empty or --force. It does require these flags if main is not empty.

If I understand correctly, it can be solved by adding a check in graveler\commited\manager.go:Merge if source metaRangeId == destination metaRangeId and require the flags in this case.

I can create a PR if you think it should be changed.

[arielshaqed]

What does Git do in this case? When there is no clear preference, we should generally follow Git.

[tkalir]

Good point. I checked and git does allow such a merge (without additional flags), whether main is empty or not. lakefs already doesn't follow git in that it requires --force when main is not empty.
So the question is whether it's better to be consistent with git in the case that main is empty, or being consistent with lakefs's behavior when it's not.

[arielshaqed]

@ozkatz has a rule for lakeFS,

If there's no simple answer that's clearly correct, do what Git does.

The reasoning is that Git had been around for many more years, has more users, and if a user has any preconception about what should happen -it's probably been influenced by Git.

Given that it's not clearly wrong, let's do what Git does here.