[git] Completely cancel a rebase

I performed a rebase like this:

git rebase --onto master new_background_processing export_background_processing

That didn't do what I wanted it to, so I performed a reset:

git reset --hard HEAD@{1}

I got my branch back to the state it was, but I received this message when I type git status:

# You are currently rebasing branch 'export_background_processing' on 'e378641'.

How do I cancel that rebase completely? Not sure what that means per se.

In the case of a past rebase that you did not properly aborted, you now (Git 2.12, Q1 2017) have git rebase --quit

See commit 9512177 (12 Nov 2016) by Nguy?n Thái Ng?c Duy (pclouds). ^{(Merged by Junio C Hamano -- gitster -- in commit 06cd5a1, 19 Dec 2016)}

rebase: add --quit to cleanup rebase, leave everything else untouched

There are occasions when you decide to abort an in-progress rebase and move on to do something else but you forget to do "git rebase --abort" first. Or the rebase has been in progress for so long you forgot about it. By the time you realize that (e.g. by starting another rebase) it's already too late to retrace your steps. The solution is normally

rm -r .git/<some rebase dir>

and continue with your life.
But there could be two different directories for <some rebase dir> (and it obviously requires some knowledge of how rebase works), and the ".git" part could be much longer if you are not at top-dir, or in a linked worktree. And "rm -r" is very dangerous to do in .git, a mistake in there could destroy object database or other important data.

Provide "git rebase --quit" for this use case, mimicking a precedent that is "git cherry-pick --quit".

Before Git 2.27 (Q2 2020), The stash entry created by "git merge --autostash" to keep the initial dirty state were discarded by mistake upon "git rebase --quit", which has been corrected.

See commit 9b2df3e (28 Apr 2020) by Denton Liu (Denton-L).
^{(Merged by Junio C Hamano -- gitster -- in commit 3afdeef, 29 Apr 2020)}

rebase: save autostash entry into stash reflog on --quit

^{Signed-off-by: Denton Liu}

In a03b55530a ("merge: teach --autostash option", 2020-04-07, Git v2.27.0 -- merge listed in batch #5), the --autostash option was introduced for git merge.

(See "Can “git pull” automatically stash and pop pending changes?")

Notably, when git merge --quit is run with an autostash entry present, it is saved into the stash reflog.

This is contrasted with the current behaviour of git rebase --quit where the autostash entry is simply just dropped out of existence.

Adopt the behaviour of git merge --quit in git rebase --quit and save the autostash entry into the stash reflog instead of just deleting it.

If you are "Rebasing", "Already started rebase" which you want to cancel, just comment (#) all commits listed in rebase editor.

As a result you will get a command line message

Nothing to do

You are lucky that you didn't complete the rebase, so you can still do git rebase --abort. If you had completed the rebase (it rewrites history), things would have been much more complex. Consider tagging the tips of branches before doing potentially damaging operations (particularly history rewriting), that way you can rewind if something blows up.