Re: pull.rebase config vs. --ff-only on command line

From: Felipe Contreras <felipe.contreras@gmail.com>
Date: Jul 19, 2021, 17:43 UTC
Message-ID: <60f5b9a9e29d8_13f2e22084b@natae.notmuch>
In-Reply-To: <fa757764-db25-849d-d8d5-e28908059f6b@aixigo.com>

Matthias Baumgarten wrote:

Show 49 quoted lines

> On 7/16/21 8:00 PM, Felipe Contreras wrote:
> > Matthias Baumgarten wrote:
> >> On 7/16/21 6:44 PM, Felipe Contreras wrote:
> >>> Elijah Newren wrote:
> >>>> On Fri, Jul 16, 2021 at 7:52 AM Matthias Baumgarten
> >>>> <matthias.baumgarten@aixigo.com> wrote:
> >>>>> this is my first time contacting you guys and girls so I hope this mail
> >>>>> achieves the expected standard. I've discovered the following behaviour
> >>>>> of git:
> >>>>>
> >>>>> If pull.rebase is configured to true and git pull --ff-only is executed
> >>>>> it seems like the config wins, i.e. issuing "Successfully rebased and
> >>>>> updated refs/heads/...", which is not what I would expect. I always
> >>>>> believed that command line options would overwrite configured options.
> >>>>>
> >>>>> Is my assumption that command line options always win wrong or is this a
> >>>>> bug?
> >>>>
> >>>> It's a bug.
> >>>
> >>> No it isn't.
> >>>
> >>> Elijah is elevating to fact his opinion of what --ff-only should be
> >>> changed to.
> >>>
> >>> But it has not been changed. Today --ff-only is meant only for the merge
> >>> mode of `git pull`, and like other merge-only options (e.g. --ff,
> >>> --no-ff, and --squash) it's ignored in the rebase mode.
> >>
> >> Shouldn't every explicitly given merge option (like --ff-only) overwrite
> >> any configured option that would not even result in a merge, i.e.
> >> forcing a merge and thus forcing ff-only?
> > 
> > Perhaps. Other developers have suggested that before.
> > 
> > The problem is that everyone wants to make --ff-only the default, and
> > then we start to get into a tricky situation, because what should these
> > do:
> > 
> >    git -c pull.ff=only pull
> >    git -c pull.ff=only pull --merge
> >    git -c pull.ff=only pull --rebase
> 
> If my assumption were true, and every explicit (cli given) option would 
> overwrite implicitly given ones (i.e. configured options), wouldn't
> 
>   * git -c pull.ff=only pull, do a fast-forward (or merge)
>   * git -c pull.ff=only pull --merge, force a merge commit
>   * git -c pull.ff=only pull --rebase, force rebase

The documentation says --ff-only is meant for merges, therefore these three should be valid and do the same:

  git pull --ff-only # --merge is the default
  git pull --merge --ff-only
  git pull --ff-only --merge

In order for your assumption above to be correct, the semantics of --ff-only have to be changed (along with the documentation), but people are *already* relying on the current semantics:

  [pull]
    ff = only
    rebase = true

I made a poll on reddit [1], and 19% (so far) said they do use both configurations, and they know what `git pull --no-rebase` would do.

In other words: they would expect `git pull` to do a rebase, but `git pull --merge` to do a fast-forward merge.

Changing the semantics of --ff-only would break behavior they rely on, unless we break symmetry from --ff-only and pull.ff=only which would be very hard to explain the documentation.

However, if --ff-only wasn't mapped to pull.ff=only, but pull.mode=fast-forward, then we can have both: the configurations people rely on today wouldn't be broken, and your expectation that `git pull --ff-only` overrides pull.mode=rebase would be met.

It's the perfect solution.

> > One of these will always fail, when it shouldn't
> Would this even apply under the above assumption?

[I think you meant to paste this]

Under your assumption it wouldn't fail, but other behavior users rely on today would be broken.

> > I proposed a solution for that, but is has been ignored.
> I'm sorry!

It's not me the one that suffers (I don't even use `git pull`), it's the users that have been negatively affected for more than ten years.

[1] https://www.reddit.com/r/git/comments/omcngl/do_you_use_both_pullff_and_pullrebase/

-- 
Felipe Contreras