threads / bug / 57092

bug?: ORIG_HEAD incorrect after reset during git-rebase -i

Subject: bug?: ORIG_HEAD incorrect after reset during git-rebase -i

## tl;dr

7 messages between Dec 16, 2021 and Jan 7, 2023.

replies: 6people: 3as markdown or json

Erik Cervin Edin· Dec 16, 2021, 14:30 UTC · lore
Steps to reproduce:
1. git-rebase -i
2. edit XYZ
3. git-reset HEAD~
4. git-commit -C ORIG_HEAD -a
5. git-rebase --continue
6. git-show ORIG_HEAD

Expected behavior: ORIG_HEAD should point at the previous HEAD of the rebased branch

Actual behavior: ORIG_HEAD points to XYZ

My understanding from reading https://stackoverflow.com/a/64949884 is that this is incorrect behavior.

Perhaps this is as intended but I would at least personally prefer that ORIG_HEAD would point to the previous HEAD of the rebased branch.

Seen in: git version 2.31.1.windows.1

Possibly related to e100bea481 - rebase -i: stop overwriting ORIG_HEAD buffer

Phillip Wood· Dec 16, 2021, 16:27 UTC · re: Erik Cervin Edin · lore

Re: bug?: ORIG_HEAD incorrect after reset during git-rebase -i

Hi Erik
On 16/12/2021 14:30, Erik Cervin Edin wrote:
> Steps to reproduce:
> 1. git-rebase -i
> 2. edit XYZ
> 3. git-reset HEAD~

"git reset" will update ORIG_HEAD to the current HEAD before resetting so here ORIG_HEAD gets updated to point to XYZ

Show 15 quoted lines
> 4. git-commit -C ORIG_HEAD -a
> 5. git-rebase --continue
> 6. git-show ORIG_HEAD
> 
> Expected behavior:
> ORIG_HEAD should point at the previous HEAD of the rebased branch
> 
> Actual behavior:
> ORIG_HEAD points to XYZ
> 
> My understanding from reading https://stackoverflow.com/a/64949884 is
> that this is incorrect behavior.
> 
> Perhaps this is as intended but I would at least personally prefer
> that ORIG_HEAD would point to the previous HEAD of the rebased branch.

You can use the reflog to get the previous HEAD of the rebased branch after rebasing. Immediately after the rebase branch-name@{1} will point to the pre-rebase HEAD.

Best Wishes
Phillip
Show 5 quoted lines
> Seen in:
> git version 2.31.1.windows.1
> 
> Possibly related to
> e100bea481 - rebase -i: stop overwriting ORIG_HEAD buffer
Erik Cervin Edin· Dec 16, 2021, 16:44 UTC · re: Phillip Wood · lore

Re: bug?: ORIG_HEAD incorrect after reset during git-rebase -i

Hi Phillip,

Yes, I know. It's just that I was under the impression ORIG_HEAD was to be reverted to .git/rebase-merge/orig-head at the finish of the rebase. Personally, it's the behavior I would expect.

Thanks for the tips.

Regards, Erik

On Thu, Dec 16, 2021 at 5:27 PM Phillip Wood <phillip.wood@talktalk.net> wrote:
Show 43 quoted lines
>
> Hi Erik
>
> On 16/12/2021 14:30, Erik Cervin Edin wrote:
> > Steps to reproduce:
> > 1. git-rebase -i
> > 2. edit XYZ
> > 3. git-reset HEAD~
>
> "git reset" will update ORIG_HEAD to the current HEAD before resetting
> so here ORIG_HEAD gets updated to point to XYZ
>
> > 4. git-commit -C ORIG_HEAD -a
> > 5. git-rebase --continue
> > 6. git-show ORIG_HEAD
> >
> > Expected behavior:
> > ORIG_HEAD should point at the previous HEAD of the rebased branch
> >
> > Actual behavior:
> > ORIG_HEAD points to XYZ
> >
> > My understanding from reading https://stackoverflow.com/a/64949884 is
> > that this is incorrect behavior.
> >
> > Perhaps this is as intended but I would at least personally prefer
> > that ORIG_HEAD would point to the previous HEAD of the rebased branch.
>
> You can use the reflog to get the previous HEAD of the rebased branch
> after rebasing. Immediately after the rebase branch-name@{1} will point
> to the pre-rebase HEAD.
>
> Best Wishes
>
> Phillip
>
>
> > Seen in:
> > git version 2.31.1.windows.1
> >
> > Possibly related to
> > e100bea481 - rebase -i: stop overwriting ORIG_HEAD buffer
>
-- 
Erik Cervin-Edin
Erik.CervinEd.in
Philippe Blain· Jan 5, 2023, 00:11 UTC · re: Erik Cervin Edin · lore

Re: bug?: ORIG_HEAD incorrect after reset during git-rebase -i

Hi Phillip and Erik,
Le 2021-12-16 à 11:44, Erik Cervin Edin a écrit :
Show 8 quoted lines
> Hi Phillip,
> 
> Yes, I know.
> It's just that I was under the impression ORIG_HEAD was to be reverted
> to .git/rebase-merge/orig-head at the finish of the rebase.
> Personally, it's the behavior I would expect.
> 
> Thanks for the tips.

I just hit the same bug (I think it qualifies as one). In fact git-rebase(1) explicitely mentions that ORIG_HEAD is set to the branch tip before the rebase starts:

$ git grep -C2 ORIG_HEAD Documentation/git-rebase.txt Documentation/git-rebase.txt-36-The current branch is reset to `<upstream>` or `<newbase>` if the Documentation/git-rebase.txt-37-`--onto` option was supplied. This has the exact same effect as Documentation/git-rebase.txt:38:50:`git reset --hard <upstream>` (or `<newbase>`). `ORIG_HEAD` is set Documentation/git-rebase.txt-39-to point at the tip of the branch before the reset. Documentation/git-rebase.txt-40-

Here is my runnable reproducer. It is slightly more complicated than Erik's, since I split the second commit in two, but this is not necessary to trigger the bug; just running 'git reset HEAD^' as Erik wrote is enough.

```bash #!/bin/bash rm -rf repro git init repro ( cd repro # Create 3 commits cat << EOF >test hello every one EOF git add test git commit -m initial cat << EOF >test hello

add new lines
every
and also here

one EOF git commit -am second cat << EOF >test hello

add new lines
every
and also here
one

still more changes EOF git commit -am third # Rebase to split the second commit GIT_SEQUENCE_EDITOR="sed -ie '1 s/^p /e /'" git rebase -i HEAD~2 git reset HEAD^ cat << EOF >test hello

add new lines

every one EOF git ci -am "second 1/2" cat <<EOF >test hello

add new lines
every
and also here

one EOF git ci -am "second 2/2" # Finish rebase and demonstrate bug git rebase --continue echo --- echo "@{1} is :" git log -1 @{1} echo "ORIG_HEAD is :" git log -1 ORIG_HEAD

) ```

Cheers,
Philippe.
Phillip Wood· Jan 6, 2023, 14:29 UTC · re: Philippe Blain · lore

Re: bug?: ORIG_HEAD incorrect after reset during git-rebase -i

Hi Philippe & Erik
On 05/01/2023 00:11, Philippe Blain wrote:
Show 14 quoted lines
> Hi Phillip and Erik,
> 
> Le 2021-12-16 à 11:44, Erik Cervin Edin a écrit :
>> Hi Phillip,
>>
>> Yes, I know.
>> It's just that I was under the impression ORIG_HEAD was to be reverted
>> to .git/rebase-merge/orig-head at the finish of the rebase.
>> Personally, it's the behavior I would expect.
>>
>> Thanks for the tips.
> 
> I just hit the same bug (I think it qualifies as one). In fact git-rebase(1) explicitely mentions
> that ORIG_HEAD is set to the branch tip before the rebase starts:

Strictly speaking that is what we do so we're documentation the implemented behavior. What's not clear from the documentation is that if the user run 'git reset' while rebasing then ORIG_HEAD will be overwritten. We could update ORIG_HEAD at the end of the rebase as you suggested but I wouldn't be surprised if some else complains that ORIG_HEAD no longer points to the commit that the reset while running rebase. I also wonder if users would expect 'git rebase --continue' to update ORIG_HEAD to point to the pre-rebase HEAD so it is consistent each time rebase stops. Basically I think the situation is confusing and I don't have a clear idea as to how to make it better. If someone submits a patch to try and clean things up I'll happily look at it but unless I'm hit by a bright idea as to how to fix it I probably wont work on it myself.

Best Wishes
Phillip
Show 89 quoted lines
> $ git grep -C2 ORIG_HEAD Documentation/git-rebase.txt
> Documentation/git-rebase.txt-36-The current branch is reset to `<upstream>` or `<newbase>` if the
> Documentation/git-rebase.txt-37-`--onto` option was supplied.  This has the exact same effect as
> Documentation/git-rebase.txt:38:50:`git reset --hard <upstream>` (or `<newbase>`). `ORIG_HEAD` is set
> Documentation/git-rebase.txt-39-to point at the tip of the branch before the reset.
> Documentation/git-rebase.txt-40-
> 
> Here is my runnable reproducer. It is slightly more complicated than Erik's, since
> I split the second commit in two, but this is not necessary to trigger the bug; just
> running 'git reset HEAD^' as Erik wrote is enough.
> 
> ```bash
> #!/bin/bash
> rm -rf repro
> git init repro
> (
> cd repro
> # Create 3 commits
> cat << EOF >test
> hello
> every
> one
> EOF
> git add test
> git commit -m initial
> cat << EOF >test
> hello
> 
> add new lines
> 
> every
> 
> and also here
> 
> one
> EOF
> git commit -am second
> cat << EOF >test
> hello
> 
> add new lines
> 
> every
> 
> and also here
> 
> one
> 
> still more changes
> EOF
> git commit -am third
> # Rebase to split the second commit
> GIT_SEQUENCE_EDITOR="sed -ie '1 s/^p /e /'" git rebase -i HEAD~2
> git reset HEAD^
> cat << EOF >test
> hello
> 
> add new lines
> 
> every
> one
> EOF
> git ci -am "second 1/2"
> cat <<EOF >test
> hello
> 
> add new lines
> 
> every
> 
> and also here
> 
> one
> EOF
> git ci -am "second 2/2"
> # Finish rebase and demonstrate bug
> git rebase --continue
> echo ---
> echo "@{1} is :"
> git log -1 @{1}
> echo "ORIG_HEAD is :"
> git log -1 ORIG_HEAD
> 
> )
> ```
> 
> Cheers,
> 
> Philippe.
Philippe Blain· Jan 7, 2023, 17:06 UTC · re: Phillip Wood · lore

Re: bug?: ORIG_HEAD incorrect after reset during git-rebase -i

Hi Phillip,
Le 2023-01-06 à 09:29, Phillip Wood a écrit :
Show 22 quoted lines
> Hi Philippe & Erik
> 
> On 05/01/2023 00:11, Philippe Blain wrote:
>> Hi Phillip and Erik,
>>
>> Le 2021-12-16 à 11:44, Erik Cervin Edin a écrit :
>>> Hi Phillip,
>>>
>>> Yes, I know.
>>> It's just that I was under the impression ORIG_HEAD was to be reverted
>>> to .git/rebase-merge/orig-head at the finish of the rebase.
>>> Personally, it's the behavior I would expect.
>>>
>>> Thanks for the tips.
>>
>> I just hit the same bug (I think it qualifies as one). In fact git-rebase(1) explicitely mentions
>> that ORIG_HEAD is set to the branch tip before the rebase starts:
> 
> Strictly speaking that is what we do so we're documentation the
> implemented behavior. What's not clear from the documentation is that
> if the user run 'git reset' while rebasing then ORIG_HEAD will be
> overwritten. 
Yes, I agree. I think we could highlight it in the doc.
Show 10 quoted lines
> We could update ORIG_HEAD at the end of the rebase as
> you suggested but I wouldn't be surprised if some else complains that
> ORIG_HEAD no longer points to the commit that the reset while running
> rebase. I also wonder if users would expect 'git rebase --continue'
> to update ORIG_HEAD to point to the pre-rebase HEAD so it is
> consistent each time rebase stops. Basically I think the situation is
> confusing and I don't have a clear idea as to how to make it better.
> If someone submits a patch to try and clean things up I'll happily
> look at it but unless I'm hit by a bright idea as to how to fix it I
> probably wont work on it myself.

Thanks for your thoughts. I think you make good points, it's true that some people might be relying on the current behaviour.

I'll try to send a few updates to the doc to make this hopefully clearer.

Cheers, Philippe.

Philippe Blain· Jan 7, 2023, 19:50 UTC · re: Philippe Blain · lore

Re: bug?: ORIG_HEAD incorrect after reset during git-rebase -i

Le 2023-01-07 à 12:06, Philippe Blain a écrit :
> 
> Hi Phillip,
> 
> I'll try to send a few updates to the doc to make this hopefully clearer.
See https://lore.kernel.org/git/pull.1456.git.1673120359.gitgitgadget@gmail.com/T/#t

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