From: Yann Dirson <ydirson@altern.org>
Date: Thu, 16 Jul 2009 22:23:56 GMT
Subject: Re: [PATCH 2/2] Improve doc for format-patch threading options.
Message-ID: <20090716222356.GD5762@nan92-1-81-57-214-146.fbx.proxad.net>
In-Reply-To: <200907061049.30084.markus.heidelberg@web.de>

On Mon, Jul 06, 2009 at 10:49:29AM +0200, Markus Heidelberg wrote:
> Yann Dirson, 06.07.2009:
> > +++ b/Documentation/git-format-patch.txt
> > @@ -132,9 +133,15 @@ The optional <style> argument can be either `shallow` or `deep`.
> >  'shallow' threading makes every mail a reply to the head of the
> >  series, where the head is chosen from the cover letter, the
> >  `\--in-reply-to`, and the first patch mail, in this order.  'deep'
> > -threading makes every mail a reply to the previous one.  If not
> > -specified, defaults to the 'format.thread' configuration, or `shallow`
> > -if that is not set.
> > +threading makes every mail a reply to the previous one.
> > ++
> > +The default is --no-thread, unless the 'format.thread' configuration
> > +is set.  If --thread is specified without a style, it defaults to the
> > +style specified by 'format.thread' if any, or else `shallow`.
> > ++
> > +Beware that the default for 'git send-email' is to do deep threading
> > +if the emails to be sent have no Message-Id header, which is what
> > +happens when then are generated by 'git format-patch --no-thread'.
> 
> Oh, due to the typo I mentioned in my previous mail, I forgot to really
> comment.
> 
> The last paragraph is misleading. git-send-email always adds headers for
> deep threading by default, regardless of any existing Message-Id
> headers.
> The current wording makes one believe, git-send-email respects existing
> headers if the patches are created with 'git format-patch --thread'.
> But that it isn't aware of them is exactly what you want to explain
> here.

Indeed I realize that I did not grasp correctly how things are
supposed to fit together.  Reading the code and experimenting, I see
that:

- as you say, send-email completely ignores any pre-existing
In-Reply-To and References header (it does keep the Message-Id's,
though)

- send-email simply adds its own In-Reply-To and References headers.
That IMHO does not make any sense, and the behaviour of such a thing
is likely to vary among MUAs (if it even does not violate the
standards, which I did not check)

- even when --no-thread is specified, and format-patch was run with
--no-thread as well, it still adds In-Reply-To and References headers,
and I must say I do not see what in the code causes this behaviour.

Looks like we should clarify things first, and possibly fix things,
before we can start to document them - or did I miss some point that
would seem obvious to others ?