Re: ancestor and descendant ~ clarification needed

From: Junio C Hamano <gitster@pobox.com>
Date: Oct 23, 2015, 16:56 UTC
Message-ID: <xmqqsi51plpz.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <CAAF+z6H+wwCOhPCU-_Uh-Odc=411N+G+d_iE_AKX+JxVMDtsMQ@mail.gmail.com>

Xue Fuqiao <xfq.free@gmail.com> writes:

Show 21 quoted lines

> Hi Junio,
>
> On Fri, Oct 23, 2015 at 4:22 AM, Junio C Hamano <gitster@pobox.com> wrote:
>
>> Yeah, that is the other way around.
>>
>>  (1) If the current branch is a descendant of the other--so every
>>      commit present in the other branch is already contained in the
>>      current branch--then merging the other branch into the current
>>      branch is a no-op "Already up-to-date!".
>>
>>  (2) If the current branch is an ancestor of the other--so every
>>      commit present in the current branch is already contained in
>>      the other branch--then merging the other branch into the
>>      current branch can be fast-forwarded, by moving the tip of the
>>      current branch to point at the commit at the tip of the other
>>      branch, and by default Git does so, instead of creating an
>>      unnecessary merge.
>
> I see.  Thank you.  What do you think about the following minor patch
> for user-manual.txt?

While the updated text is more correct than the original, I do not know if that is sufficient, or we would also want to mention the "Already up-to-date!" case here while at it.

Show 11 quoted lines

> -However, if the current branch is a descendant of the other--so every
> -commit present in the one is already contained in the other--then Git
> -just performs a "fast-forward"; the head of the current branch is moved
> -forward to point at the head of the merged-in branch, without any new
> -commits being created.
> +However, if the current branch is an ancestor of the other--so every commit
> +present in the current branch is already contained in the other
> branch--then Git
> +just performs a "fast-forward"; the head of the current branch is moved forward
> +to point at the head of the merged-in branch, without any new commits being
> +created.