Re: [PATCH v2 02/14] pull: improve default warning

From: Felipe Contreras <felipe.contreras@gmail.com>
Date: Dec 15, 2020, 02:36 UTC
Message-ID: <5fd8213598c33_d7c4820837@natae.notmuch>
In-Reply-To: <xmqqzh2g9e0r.fsf@gitster.c.googlers.com>

Junio C Hamano wrote:

Show 11 quoted lines

> Felipe Contreras <felipe.contreras@gmail.com> writes:
> 
> >> We do not have to or implement both, but either should give us the
> >> "when pull sees a non-ff history, it should stop without merging or
> >> rebasing, and the user won't be given the advice on how to choose
> >> between merge and rebase" behaviour, I would think.
> >
> > Right, so both should error out.
> 
> One of them, not both; the one we choose to implement would make it
> fail, I would think.

If only one of them fail, then it's impossible to tell the user:

  If you want to try the new behavior, type this command:

    git config $something

We have to go straight for the error, with no deprecation period.

Show 5 quoted lines

> > And what should these do?
> >
> >   git -c pull.rebase=no -c pull.ff=only pull --merge
> 
> There is no --merge, so let's reread with s/--merge/--no-rebase/;

Back in 2013 everyone found it easier to speak in terms of --merge, even you, BTW, who was the first one to send a patch with --merge [1], after Linus suggested it [2].

Show 17 quoted lines

> the command line would be saying "I only want to fast-forward, or I
> want the command to fail".  The advice code should not trigger
> (i.e. we gave an explicit preference to merge and not to rebase, so
> rebase_unspecified would be false), but the configured preference
> that says "we take only fast-forward merges" will still be in effect.
> If the history is fast-forward, the merge backend will happily
> advance our history.  If not, the merge backend will happily fail
> the pull.
> 
> If you want to countermand the configured preference from the
> command line and allow a merge to be done when non-ff history is
> given, what you'd need to override is not --merge/--no-rebase.  The
> configuration pull.rebase=no already says you do not want rebase and
> you want merge).  You want to override --ff-only, so I'd expect
> "pull --ff" (or "pull --no-ff") to be how you override your
> configured preference and merge in a non-ff history, either by fast
> forwarding or creating an extra merge commit.

Precisely, so you can't tell the user:

  If you want to try the new behavior, type this command:

    git config pull.ff only

Because, after the user gets the error:

  Not a fast-forward, either merge or rebase.

She cannot do:

  git pull --merge

Which is the best idiom to specify she wants a merge.

The command will still fail, even after the user has specified she wants the new mode, and that she wants to merge in this perticular case.

Show 5 quoted lines

> >   git -c advice.pullnonff=false pull --merge
> 
> Again with s/--merge/--no-rebase/; but that is showing the
> preference not to rebase and to merge from the command line, so
> shouldn't it just go ahead and merge without any advice?

Yes, but *before* we make this the default, what configuration get us there today?

Show 8 quoted lines

> > I'm going to answer because I think it's obvious what you would expect:
> > if you pass --merge, both should succeed.
> >
> > Except they won't, because "git pull --ff-only --merge" fails.
> >
> > Correct?
> 
> See above.

That's a "correct". There's no configuration today that gives us both:

 1. fail: git -c $config pull
 2. pass: git -c $config pull --merge

Like this does:

 1. fail: git -c pull.mode=fast-forward pull
 2. pass: git -c pull.mode=fast-forward pull --merge

Cheers.

[1] https://lore.kernel.org/git/7v4ncjs5az.fsf_-_@alter.siamese.dyndns.org/ [2] https://lore.kernel.org/git/CA+55aFz2Uvq4vmyjJPao5tS-uuVvKm6mbP7Uz8sdq1VMxMGJCw@mail.gmail.com/

-- 
Felipe Contreras