Re: [PATCH] sequencer: honor --empty when a fixup!/squash! empties its target

[Yuxuan Chen <i@yuxuan.ch>]

From: Yuxuan Chen <i@yuxuan.ch>

Hi Phillip,

I'm Yuxuan, and I work with Farid at Meta. Thank you for reviewing this patch.
It addresses a workflow problem for us, and we appreciate your feedback.

Regarding

> Using an empty commit has a marker has the advantage that applying it cannot
> create conflicts, so you only have to deal with the conflicts caused by the
> commit being dropped, not the by fixup not applying cleanly.

I am concerned, however, that representing a `drop!` commit as an empty marker
would be semantically unsound. We expect `rebase --autosquash` to drop the
target commit, but until that rebase happens, the repository is not in a state
where we consider the target commit dropped: the target's changes are still
present, and the empty marker changes nothing. Therefore, I think a `drop!`
commit should contain the inverse of the patch we intend to drop. That way,
the repository state reflects the intended removal even before autosquash
rewrites the history.

I recognize that applying the inverse patch may cause conflicts. However,
this is not a new problem; `git revert` has the same issue when the inverse
patch does not apply cleanly. Such conflicts reflect the actual difficulty of
undoing the change at that point in the history.

Thanks,
Yuxuan