Re: [RFC PATCH] `log --merge` also for rebase/cherry pick/revert

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

Hi Michael

On 12/01/2024 15:03, Michael Lohmann wrote:
> Hi Phillip,
> 
> On 12. Jan 2024, at 12:01, phillip.wood123@gmail.com wrote:
>> I should start by saying that I didn't know "git log --merge" existed before
>> I saw this message
> I also just found it and it looked very useful...
> 
>> so please correct me if I've misunderstood what this patch is doing. If I
>> understand correctly it shows the commits from each side of the merge and is
>> equivalent to
>>
>>     git log HEAD MERGE_HEAD ^$(git merge-base HEAD MERGE_HEAD)
>>
>> When a commit is cherry-picked the merge base used is CHERRY_PICK_HEAD^ [*]
>> so I'm not sure what
>>
>>     git log HEAD CHERRY_PICK_HEAD ^$(git merge-base HEAD CHERRY_PICK_HEAD)
> 
> Almost, but not quite: "git log —merge" only shows the commits touching the
> conflict, so it would be equivalent to (I think):
> 
>     git log HEAD CHERRY_PICK_HEAD ^$(git merge-base HEAD CHERRY_PICK_HEAD) -- $(git diff --name-only --diff-filter=U --relative)
> 
> (or replace CHERRY_PICK with one of the other actions)

Thanks for clarifying that.

>> Indeed there HEAD and CHERRY_PICK_HEAD may not share a common ancestor.
> 
> True - but same for MERGE_HEAD ("git merge --allow-unrelated-histories"). I
> have to confess I did not check how it would behave under those circumstances.
> It could either error, or (more helpful) show the log touching the file until
> the root commit.

What I was trying to get at was that with "git merge" "git log --merge" 
will show commits that are part of the merge. With "git cherry-pick" 
that's not the case because we're selecting the commits to show using 
the merge base of HEAD and CHERRY_PICK_HEAD while cherry-pick uses 
CHERRY_PICK_HEAD^ as the base of the merge. I think Junio explains why 
it is still useful to show those commits in [1] i.e. they help the user 
understand the conflicts even though they are not part of the merge. It 
might be worth expanding the commit message to explain that.

Best Wishes

Phillip

[1] https://lore.kernel.org/git/xmqqil3y9rvm.fsf@gitster.g/