Re: help for git format-patch lost diffstat

> On Sun, Apr 24, 2022 at 9:00 AM FanJun Kong <bh1scw@gmail.com> wrote:
> > First, I created two commits to a demo project.
> >
> > when I use command:
> > git format-patch --cover-letter -1
> > [...]
> > FanJun Kong (1):
> >   First commit.
> >    1.c | 4 ++++
> >    1 file changed, 4 insertions(+)
> >
> > ok, you can see the cover letter has diffstat, just above "--".
> >
> > git format-patch --cover-letter -2
> > [...]
> > FanJun Kong (2):
> >   First commit.
> >   Second commit.
> >
> > Comparing with last command, I just want to get 2 patches,
> > but this time the diffstat is missing.
> >
> > I am not sure if this is a bug or I miss some options.
> 
> This is expected behavior according to this code in
> make_cover_letter() in builtin/log.c:
> 
>     /* We can only do diffstat with a unique reference point */
>     if (origin)
>         show_diffstat(rev, origin, head);
> 
> The problem is that when you format both patches of a two-commit
> repository, `origin` is NULL because there is no commit preceding the
> initial commit; the initial commit is the root of the history. Thus,
> there is nothing prior to the first patch against which to create a
> diffstat.
> 

> I have not investigated, but it may be possible to teach
> show_diffstat() how to generate a diffstat against the "emptiness"
> preceding the initial commit, but nobody has done so yet. Perhaps this
> would be a good project for someone interested in contributing to the
> project (or perhaps not -- as mentioned, I haven't investigated how
> hard this would be).