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Date:   Mon, 9 Jul 2018 22:38:09 +0200 (DST)
From:   Johannes Schindelin <Johannes.Schindelin@gmx.de>
X-X-Sender: virtualbox@gitforwindows.org
To:     Stefan Beller <sbeller@google.com>
cc:     gitgitgadget@gmail.com, git <git@vger.kernel.org>,
        Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH v3 17/20] range-diff: add a man page
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Hi Stefan,

On Mon, 9 Jul 2018, Stefan Beller wrote:

> On Mon, Jul 9, 2018 at 1:00 PM Johannes Schindelin
> <Johannes.Schindelin@gmx.de> wrote:
> >
> > On Mon, 9 Jul 2018, Stefan Beller wrote:
> >
> > > On Tue, Jul 3, 2018 at 4:26 AM Johannes Schindelin via GitGitGadget
> > > <gitgitgadget@gmail.com> wrote:
> > >
> > > > +'git range-diff' [--color=[<when>]] [--no-color] [<diff-options>]
> > > > +       [--dual-color] [--creation-factor=<factor>]
> > > > +       ( <range1> <range2> | <rev1>...<rev2> | <base> <rev1> <rev2> )
> > > > +
> > > > +DESCRIPTION
> > > > +-----------
> > > > +
> > > > +This command shows the differences between two versions of a patch
> > > > +series, or more generally, two commit ranges (ignoring merges).
> > >
> > > Does it completely ignore merges or does it die("not supported"), how is
> > > the user expected to cope with the accidental merge in the given range?
> >
> > It ignores merges. It does not reject them. It simply ignores them and
> > won't talk about them as a consequence.
> >
> > Could you suggest an improved way to say that?
> 
> Well that is what the patch said already; I was just dense in reading.
> I just tested it, and the commit with more than one parent itself is
> ignored (not showing up in the output), but the commits that are merged
> in are still considered.

So a more accurate wording would be "ignoring merge commits" rather than
"ignoring merges".

Makes sense?

> So giving range1 as f7761a5a065..0a5677f6f68 with
> 
>   0a5677f6f68 (Merge branch 'js/branch-diff' into pu, 2018-07-06)
>   f7761a5a065 (Merge branch 'jk/fsck-gitmodules-gently' into jch, 2018-07-06)
> 
> still produces cool output and with --word-diff it is even more amazing, as it
> just tells me a large part was s/branch-diff/range-diff/ :-)

I never thought about using `--word-diff` with `range-diff`.

Sadly, for me it gives rather stupid output, e.g.

4:  6927c11a311 ! 4:  ebf3fea2517 range-diff: make --dual-color the default mode
    @@ -14,6 +14,15 @@
    diff --git a/Documentation/git-range-diff.txt b/Documentation/git-range-diff.txt
    --- a/Documentation/git-range-diff.txt
    +++ b/Documentation/git-range-diff.txt
    {+@@+}
    {+ --------+}
    {+ [verse]+}
    {+ 'git range-diff' [--color=[<when>]] [--no-color] [<diff-options>]+}
    {+- [--dual-color] [--creation-factor=<factor>]+}
    {++ [--no-dual-color] [--creation-factor=<factor>]+}
    {+  ( <range1> <range2> | <rev1>...<rev2> | <base> <rev1> <rev2> )+}
    {+ +}
    {+ DESCRIPTION+}
    @@

     OPTIONS

> > > > +Algorithm
> > > > +---------
> > > > +
> > > > +The general idea is this: we generate a cost matrix between the commits
> > > > +in both commit ranges, then solve the least-cost assignment.
> > >
> > > Can you say more about the generation of the cost matrix?
> > > I assume that it counts the number of lines added/deleted to make
> > > one patch into the other patch.
> >
> > I think that is correct.
> >
> > *reading the patch*
> >
> > Actually, no, I was wrong. For the cost matrix, the *length* of the diff
> > *of the diffs* is computed. Think of it as
> >
> >         git diff --no-index <(git diff A^!) <(git diff B^!) | wc -l
> 
> So the matching is based only on diffs, but the output still takes
> the commit messages into account. So when diffing my series to the
> series that Junio applies, (merely adding his sign off,) would be a
> "cost of 0" in this context, but I still have output.

Exactly.

> > > Another spot to look at is further metadata, such as author and
> > > author-date, which are kept the same in a rebase workflow.
> >
> > I encourage you to offer that as an add-on patch series. Because what you
> > suggest is not necessary for my use cases, so I'd rather not spend time on
> > it.
> 
> Makes sense. When I stumble about this yet theoretical problem to
> materialize in practice I will send a patch. In my mind this is not
> another use case, but just an improved matching, with the matching that
> this series provides being good enough for now.

Sure.

Ciao,
Dscho