Re: ancestor and descendant ~ clarification needed

From: Xue Fuqiao <xfq.free@gmail.com>
Date: Oct 23, 2015, 07:29 UTC
Message-ID: <CAAF+z6H+wwCOhPCU-_Uh-Odc=411N+G+d_iE_AKX+JxVMDtsMQ@mail.gmail.com>
In-Reply-To: <xmqqfv12r6vn.fsf@gitster.mtv.corp.google.com>

Hi Junio,

On Fri, Oct 23, 2015 at 4:22 AM, Junio C Hamano <gitster@pobox.com> wrote:

Show 14 quoted lines

> 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? I can send a more formal one using format-patch and send-email if needed.

diff --git a/Documentation/user-manual.txt b/Documentation/user-manual.txt
index 1b7987e..d68df13 100644
--- a/Documentation/user-manual.txt
+++ b/Documentation/user-manual.txt
@@ -1431,11 +1431,11 @@ differently.  Normally, a merge results in a
merge commit, with two
 parents, one pointing at each of the two lines of development that
 were merged.

-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.

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