Re: [PATCH v3 3/4] format-patch: introduce --base=auto option

From: Junio C Hamano <gitster@pobox.com>
Date: Apr 1, 2016, 16:06 UTC
Message-ID: <xmqqlh4xjoub.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <20160401135207.GB2915@yexl-desktop>

Ye Xiaolong <xiaolong.ye@intel.com> writes:

Show 11 quoted lines

> On Thu, Mar 31, 2016 at 10:43:48AM -0700, Junio C Hamano wrote:
>>Xiaolong Ye <xiaolong.ye@intel.com> writes:
>>
>>> Introduce --base=auto to record the base commit info automatically, the base_commit
>>> will be the merge base of tip commit of the upstream branch and revision-range
>>> specified in cmdline.
>>
>>This line is probably a bit too long.
>
> How about simplifying it to "the base_commit is the merge base of upstream and
> specified revision-range."?

What I meant was not that profound. I just wanted you to wrap your lines a bit shorter so that quoting in the discussion thread like this would not make the result overlong to fit on a 80-column terminal ;-)

Show 11 quoted lines

>>> +			base = base_list->item;
>>> +			free_commit_list(base_list);
>>
>>What should happen when there are multiple merge bases?  The code
>>picks one at random and ignores the remainder, if I am reading this
>>correctly.
>
> If there is more than one merge base, commits in base_list should
> be sorted by date, if I am understanding it correctly, so
> base_list->item should be the lastest merge base commit, it should
> be enough for us to used as base commit.

By definition, when there are multiple merge bases, there is no latest one among them.

When the history involves criss-cross merges, there can be more than one 'best' common ancestor for two commits. For example, with this topology (note that X is not a commit; it merely denotes crossing of two lines):

       ---1---o---A
      /    \ /
  ---O      X
      \    / \
       ---2---o---o---B

both '1' and '2' are merge-bases of 'A' and 'B'. And the timestamps on one (be it committer or author timestamp) being later than those of the other do not make it any more suitable than the other one.