Re: ORIG_HEAD after rebase is confusing

[Phillip Wood <phillip.wood123@gmail.com>]

Hi Caspar

On 22/10/2020 21:31, herr.kaste wrote:
> Reading the git rebase manual and some answer on stackoverflow I assumed
> `ORIG_HEAD` will point to the original HEAD, the tip of the branch *before*
> I started rebasing.  But it doesn't seem so.
> 
> For example, I have this:
> 
> 
>    $ git log --graph --all --oneline
>    * 9830f9f (master) X
>    | * fb7b6a6 (HEAD -> feature) D
>    | * 46b7a7a C
>    | * da5e4c7 B
>    | * 5c135da A
>    |/
>    * 6848823 Init
> 
>    $ git rebase master
>    Successfully rebased and updated refs/heads/feature.
> 
>    $ git rev-parse ORIG_HEAD
>    da5e4c7e9eb3b10c1efa08c534b9c9e4b92d9fd7
> 
>    $ git reflog
>    a647bd7 (HEAD -> feature) HEAD@{0}: rebase (finish): returning to
> refs/heads/feature
>    a647bd7 (HEAD -> feature) HEAD@{1}: rebase (pick): D
>    2f458e8 HEAD@{2}: rebase (pick): C
>    0aa2160 HEAD@{3}: rebase (pick): B
>    b957fc7 HEAD@{4}: rebase (pick): A
>    9830f9f (master) HEAD@{5}: rebase (start): checkout master
>    fb7b6a6 HEAD@{6}: checkout: moving from master to feature
>    9830f9f (master) HEAD@{7}: commit: X
>    6848823 HEAD@{8}: checkout: moving from feature to master
>    fb7b6a6 HEAD@{9}: commit: D
>    46b7a7a HEAD@{10}: commit: C
>    da5e4c7 HEAD@{11}: commit: B
>    5c135da HEAD@{12}: commit: A
>    6848823 HEAD@{13}: checkout: moving from master to feature
>    6848823 HEAD@{14}: commit (initial): Init
> 
> So `ORIG_HEAD` here points to the original B commit.  (I expected the D.)

It should be D, unless you ran `git reset` or `git rebase --skip` while 
you were rebasing as they also update ORIG_HEAD

> Honestly, this doesn't make much sense to me in that I don't know *why* it
> even chooses B which is a middle commit in the chain.  (And from reading the
> source `sequencer.c` I can't deduce it either.)
> 
>    $ git --version
>    git version 2.29.0.windows.1
> 
> What I actually wanted to do was `git reset --hard ORIG_HEAD` fwiw.  And for
> example `git diff HEAD..ORIG_HEAD` to check for unwanted changes after a merge
> conflict.

After you rebase you can user feature@{1} to get the head of feature 
before rebasing (until you make another commit on feature)

Best Wishes

Phillip

> Regards,
> Caspar Duregger
>