Re: [PATCH v2 0/6] teach branch-specific options for format-patch

From: Denton Liu <liu.denton@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: "Git Mailing List" <git@vger.kernel.org>,
	"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Subject: Re: [PATCH v2 0/6] teach branch-specific options for format-patch
Date: Fri, 17 May 2019 03:25:15 -0400	[thread overview]
Message-ID: <20190517072515.GA22326@archbookpro.localdomain> (raw)
In-Reply-To: <xmqqk1ep3ejv.fsf@gitster-ct.c.googlers.com>

Hi Junio,

On Fri, May 17, 2019 at 01:12:04PM +0900, Junio C Hamano wrote:
> Denton Liu <liu.denton@gmail.com> writes:
> 
> > diff --git a/Documentation/config/format.txt b/Documentation/config/format.txt
> > index dc77941c48..d387451573 100644
> > --- a/Documentation/config/format.txt
> > +++ b/Documentation/config/format.txt
> > @@ -28,14 +28,22 @@ format.headers::
> >  
> >  format.to::
> >  format.cc::
> > +format.<branch-name>.to::
> > +format.<branch-name>.cc::
> >  	Additional recipients to include in a patch to be submitted
> > -	by mail.  See the --to and --cc options in
> > -	linkgit:git-format-patch[1].
> > +	by mail.  For the <branch-name> options, the recipients are only
> > +	included if patches are generated for the given <branch-name>.
> > +	See the --to and --cc options in linkgit:git-format-patch[1].
> 
> An obvious question that somebody else may raise is:
> 
>     What makes the branch name that special?  What guarantees that
>     it would stay to be the *only* thing that affects the choice of
>     these variables?
> 
> An obvious answer to that is "nothing---we are painting ourselves in
> a corner we cannot easily get out of with this design".
> 
> If we want to drive format-patch differently depending on the
> combination of the worktree location *and* the branch the patches
> are generated from, we can do something like:
> 
> 	[includeif "gitdir:/path/to/worktree/1"] path = one.inc
> 	[includeif "gitdir:/path/to/worktree/2"] path = two.inc
> 
> and then have one.inc/two.inc have customized definition of these
> format.<branch>.{to,cc,...} variables.
> 
> But at that point, Ævar's "wouldn't this fit better with includeif"
> suggestion becomes more and more appropriate.  Once we invent the
> way to combine the conditions for includeIf, it would benefit not
> just this set of variables but all others that will follow in the
> future.

Hmm, I'm starting to like Ævar's idea more the more I think about it.

> 
> Having said that, as long as we are fine with the plan to deprecate
> and remove these three-level variables this patch introdues in the
> future, I think it is OK to have them as a temporary stop-gap
> measure.
> 
> > +format.<branch-name>.coverSubject::
> > +	When format-patch generates a cover letter for the given
> > +	<branch-name>, use the specified subject for the cover letter
> > +	instead of the generic template.
> 
> I still think it is a mistake that this has to be given separately
> and possibly redundantly from the branch description.

I forgot about incorporating this. Since we don't need a branch-specific
coverSubject anymore, we can push everything into a includeif since now
format.<name>.coverSubject doesn't really need to exist.

I'm going to repurpose --cover-subject format.coverSubject to be a
boolean option which'll mean "process the description and if you can
extract a subject out of it, put it on the cover letter". This way, we
can maintain backwards compatability in case users have some specific
use-case.

Unless you'd like this processing to be the default behaviour? I'm
impartial either way.

> 
> > +static const char *branch_specific_config[] = {
> > +	"branch",
> > +	"format",
> > +	NULL
> > +};
> 
> Yuck.  This will break a workflow where a fixed branch with a known
> configuration is deleted and recreated over and over again
> (e.g. think of "for-linus" branches used for request-pull in each
> merge window).

I suppose when we implement `onBranch`, you'd prefer `git branch -d` to
also not discard those sections.

> 
> >  static void delete_branch_config(const char *branchname)
> >  {
> >  	struct strbuf buf = STRBUF_INIT;
> > -	strbuf_addf(&buf, "branch.%s", branchname);
> > -	if (git_config_rename_section(buf.buf, NULL) < 0)
> > -		warning(_("Update of config-file failed"));
> > +	int i;
> > +	for (i = 0; branch_specific_config[i]; i++) {
> > +		strbuf_addf(&buf, "%s.%s", branch_specific_config[i], branchname);
> > +		if (git_config_rename_section(buf.buf, NULL) < 0)
> > +			warning(_("Update of config-file failed"));
> > +		strbuf_reset(&buf);
> > +	}
> 
> This will hardcode the unwarranted limitation that the second level
> of the format.*.var hierarchy MUST be branch names and nothing else,
> won't it?  
> 

I was expecting it to only be branch names but now let's take a
different approach.

Consider patches 3-6 dropped. I'd like to queue 1-2, though, since
they're just cleanup patches.

Also, expect a onBranch patchset some time in the future (not the near
future, school is busy).

Thanks for your feedback, Junio.