[eru]

Bors doesn't force you to rebase. Forcing the rebase is super annoying in projects with more than a few developers (I've worked on one that did).

What bors does is essentially the same thing, but automated: after all the tests have run on your MR branch, and people have approved your changes, bors does a speculative merge into master, and runs the tests on that merge commit.

If the tests pass, bors declares that very same commit to be the new master.

The effect is the same as the Gitlab option you mention, but the busy work is done by the bot.