Re: [PATCH 6/6] diff-merges: let -m imply -p

[Alex Henrie <alexhenrie24@gmail.com>]

On Tue, May 11, 2021 at 12:46 PM Sergey Organov <sorganov@gmail.com> wrote:
>
> Alex Henrie <alexhenrie24@gmail.com> writes:
>
> > On Tue, May 11, 2021 at 8:03 AM Sergey Organov <sorganov@gmail.com> wrote:
> >>
> >> Junio C Hamano <gitster@pobox.com> writes:
> >>
> >> > Junio C Hamano <gitster@pobox.com> writes:
> >>
> >> [...]
> >>
> >> > If we enable "some kind of diff" for "-m", I actually think that by
> >> > default "git log -m" should be turned into "log --cc".  As you told
> >> > Alex in your response, "log -m -p" is a quite unpleasant format to
> >> > read---it is there only because it was the only thing we had before
> >> > we invented "-c/--cc".
> >>
> >> Please, no! --cc has unfortunate feature of outputting exactly nothing
> >> for a lot of merge commits, causing even more confusion than historical
> >> "-m -p" format.
> >>
> >> The best default for -m output is --diff-merges=first-parent. Everybody
> >> is familiar with it, and it's useful.
> >>
> >> > But that might be outside the scope of this series.  I dunno, but if
> >> > there is no other constraints (like backward compatibility issues),
> >> > I have a moderately strong preference to use "--cc" over "-m -p"
> >> > from the get go for unconfigured people, rather than forcing
> >> > everybody to configure
> >>
> >> I rather have strong preference for --diff-merges=first-parent. --cc is
> >> only suitable for Git experts, and they know how to get what they want
> >> anyway. Yep, by using --cc. Why spare yet another short option for that?
> >>
> >> Overall, let's rather make -m give diff to the first parent by default.
> >> Simple. Useful. Not confusing.
> >
> > Honestly --diff-merges=separate is fine. Two weeks ago, when I started
> > this discussion, I was trying to use `git log -m` and `git show -m` to
> > find which merge commit introduced a particular change. Extremely
> > verbose diff output would have been great for that, the confusing part
> > was just that `git show -m` produced diff output and `git log -m` did
> > not.
>
> This is not a case in favor of "separate" over "first-parent" as the
> default for "-m", right?
>
> "Which merge commit introduced particular change" is exactly what
> --diff-merges=1 achieves, so "--diff-merges=separate" was not in fact
> needed, as I see it. Moreover, it could have produced wrong positives.
> Looks like --diff-merges=1 is a better fit.

I didn't know which branch the change came from. If the change came
from the first branch, it would not have appeared under the merge
commit with --diff-merges=first-parent. But the change would
definitely appear with --diff-merges=separate, which enabled me to
identify the merge commit that included it. So yes, this is a case in
favor of "separate" over "first-parent", but it's probably not a
common enough scenario to demand keeping "separate" for -m.

On Tue, May 11, 2021 at 12:31 PM Elijah Newren <newren@gmail.com> wrote:
>
> Interesting.  I have a strong preference for --diff-merges=remerge
> (yeah, I know it's not upstream, but it's been ready to submit for
> months, but just backed up behind the other ort changes.  Sorry, I
> can't push those through any faster).  I've had others using it for
> about 9 months now.

--diff-merges=remerge is the default I would expect when no options
have been configured or passed on the command line (although it would
not have helped in the scenario I described above). I look forward to
using it!

-Alex