From: Michael Montalbo <mmontalbo@gmail.com>
Date: Fri, 29 May 2026 00:55:35 GMT
Subject: Re: [PATCH v2 3/4] diff: add long-running diff process via diff.<driver>.process
Message-ID: <CAC2QwmLa24iaUz5G0rnt-kxE5_o+4WdS2eYA_JyC_GfPhLUW6g@mail.gmail.com>
In-Reply-To: <xmqqjysqnbxu.fsf@gitster.g>

On Mon, May 25, 2026 at 7:26 PM Junio C Hamano <gitster@pobox.com> wrote:
>
> "Michael Montalbo via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
> > Zero hunks with status=success means the tool considers the
> > files equivalent.  Git skips diff output for that file.
>
> Is "zero hunk" a common word or some random string you invented?  If
> the latter, which is I am assuming it to be, you should define what
> it means at/before the first use.  Here in the proposed log message,
> and ...
>
> >
> > Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
> > ---
> >  Documentation/config/diff.adoc   |   8 +
> >  Documentation/gitattributes.adoc |  40 ++++
> >  Makefile                         |   1 +
> >  diff-process.c                   | 206 +++++++++++++++++++
> >  diff-process.h                   |  28 +++
> >  diff.c                           |  23 +++
> >  t/.gitattributes                 |   1 +
> >  t/t4080-diff-process.sh          | 338 +++++++++++++++++++++++++++++++
> >  8 files changed, 645 insertions(+)
> >  create mode 100644 diff-process.c
> >  create mode 100644 diff-process.h
> >  create mode 100755 t/t4080-diff-process.sh
> >
> > diff --git a/Documentation/config/diff.adoc b/Documentation/config/diff.adoc
> > index 1135a62a0a..4ab5f60df6 100644
> > --- a/Documentation/config/diff.adoc
> > +++ b/Documentation/config/diff.adoc
> > @@ -218,6 +218,14 @@ endif::git-diff[]
> >       Set this option to `true` to make the diff driver cache the text
> >       conversion outputs.  See linkgit:gitattributes[5] for details.
> >
> > +`diff.<driver>.process`::
> > +     The command to run as a long-running diff process.
> > +     The tool communicates via the pkt-line protocol and returns
> > +     hunks that are fed into Git's diff and blame pipelines.
> > +     If the tool returns zero hunks, the file is treated as
> > +     unchanged for both diff output and blame attribution.
> > +     See linkgit:gitattributes[5] for details.
>
> ... also here.
>
> I do not know if you mean "the tool returns no hunks" (there is no
> "hunk <old_start> <old_count> <new_start> <new_count>" line passed
> from the tool over the protocol) or "the tool returns zero-hunk"
> (there is a special "zero-hunk" message to signal this particular
> condition sent over the protocol), and this description does not
> quite help disambiguating between the two.
>
> If the former, then avoid "zero hunks" as it sounds like a noun with
> special meaning.  Yes, we can say "tool returns one hunk", "tool
> returns 31 hunks", etc., so "tool returns zero hunks" may logically
> be correct, but "when the tool returns no hunks with status=success"
> is much less confusing, I think.

Yes, "zero hunks" was my own invention and I see why it's confusing. Will
update the messaging to use "no hunks" instead and do a broader sweep of
the documentation to clarify the protocol and expected tool behavior.