Re: Pick the right default and stop warn on `git pull`

From: Felipe Contreras <felipe.contreras@gmail.com>
To: Jeff King <peff@peff.net>
Cc: "Junio C Hamano" <gitster@pobox.com>,
	"Theodore Y. Ts'o" <tytso@mit.edu>,
	"Alex Henrie" <alexhenrie24@gmail.com>,
	"Vít Ondruch" <vondruch@redhat.com>,
	"Git mailing list" <git@vger.kernel.org>
Subject: Re: Pick the right default and stop warn on `git pull`
Date: Mon, 23 Nov 2020 21:41:05 -0600	[thread overview]
Message-ID: <CAMP44s08mEyYqbjOeTeS46CngrbQMqP2=cMr1dtRLLk_BLAq3w@mail.gmail.com> (raw)
In-Reply-To: <X7xw0xb9UnGKbS8m@coredump.intra.peff.net>

On Mon, Nov 23, 2020 at 8:32 PM Jeff King <peff@peff.net> wrote:
> On Mon, Nov 23, 2020 at 06:18:40PM -0800, Junio C Hamano wrote:

> > So an obvious thing we could do, if pull.mode is too much of a
> > change, is to make "pull --rebase" codepath honor pull.ff as well,
> > perhaps?  I.e. those who set pull.ff=only are saying that "please
> > stop me when I have any local change---I want to be notified if my
> > pull on this branch results in anything but a fast-forward from the
> > upstream".
> >
> > And then making an unconfigured pull.ff to default to pull.ff=only
> > may give a proper failure whether you merge or rebase.  I dunno.
>
> Yeah, I would be perfectly happy with that (and it's in fact what I
> _thought_ was happening before today's discussion).
>
> I do wonder if anybody has set:
>
>   pull.rebase=true
>   pull.ff=only
>
> which would then refuse to rebase at all, and whether they would be
> annoyed. I am scratching my head over why one would do that, though. It
> is meaningful only if you usually rebase, but when you say "--no-rebase"
> you want to make sure you do not create a merge commit. Which seems
> weird.

I think you are losing track of the goal.

The goal is that *eventually*:

1. No warning is issued
2. No configuration is needed
3. The default behavior is sane.

The whole point of "pull.rebase=ff-only" (aka. "pull.mode=ff-only")
was to make it the *default*.

If you make "pull.ff=only" the default, *and* you make "git pull
--rebase" respect that, then "git pull --rebase" will fail by default
(unless it's a fast-forward).

What we really need is something like:

1. git pull # fail by default unless it's a fast-forward
2. git pull --merge # force a merge (unless it's a fast-forward,
depending on pull.ff)
3. git pull --rebase # force a rebase (unless it's a fast-forward,
depending on pull.ff)

Therefore, what we really want is "git pull --rebase" *ignore*
"pull.ff=only" (a possible default) or ignore "pull.rebase=ff-only"
(also another possible default).

It would be possible to do something like:

  if (!opt_rebase && (!opt_ff || !strcmp(opt_ff, "--ff-only")))
    turn_default_behavior = 1;

But then how would we distinguish between "git pull", and "git pull
--no-rebase" (aka. "git pull --merge" / "pull.rebase=false")?

This is just too much unnecessary complication There's no need to
entertain a dozen possible heuristics to avoid "pull.mode", none of
which avoid breaking existing behavior.

Let's just accept we need push.mode, and then we can have everything:
default, ff-only, merge, rebase.

Cheers.

-- 
Felipe Contreras