Re: Odd merge behaviour involving reverts

On Thu, 18 Dec 2008, Alan wrote:

I suspect we should warn about reverting merges. I'm surprised we don't already. Reverting a merge isn't "wrong", but it's a whole lot more subtle than reverting a regular commit.

Reverting a regular commit just effectively undoes what that commit did, and is fairly straightforward. But reverting a merge commit also undoes the _data_ that the commit changed, but it does absolutely nothing to the effects on _history_ that the merge had.

So the merge will still exist, and it will still be seen as joining the two branches together, and future merges will see that merge as the last shared state - and the revert that reverted the merge brought in will not affect that at all.

So a "revert" undoes the data changes, but it's very much _not_ an "undo" in the sense that it doesn't undo the effects of a commit on the repository history.

So if you think of "revert" as "undo", then you're going to always miss this part of reverts. Yes, it undoes the data, but no, it doesn't undo history.

			Linus