Re: [PATCH] pull: abort if --ff-only is given and fast-forwarding is impossible

[Elijah Newren <newren@gmail.com>]

On Mon, Jul 12, 2021 at 10:08 AM Junio C Hamano <gitster@pobox.com> wrote:
>
> Phillip Wood <phillip.wood123@gmail.com> writes:
>
> > Thanks for revising this patch, I like this approach much better. I do
> > however have some concerns about the interaction of pull.ff with the
> > rebase config and command line options. I'd naively expect the
> > following behavior (where rebase can fast-forward if possible)
> >
> >   pull.ff  pull.rebase  commandline  action
> >    only     not false                rebase
> >    only     not false   --no-rebase  fast-forward only
> >     *       not false    --ff-only   fast-forward only
> >    only     not false    --ff        merge --ff
> >    only     not false    --no-ff     merge --no-ff
> >    only       false                  fast-forward only
> >    only       false      --rebase    rebase
> >    only       false      --ff        merge --ff
> >    only       false      --no-ff     merge --no-ff
>
> Do you mean by "not false" something other than "true"?  Are you
> trying to capture what should happen when these configuration
> options are unspecified as well (and your "not false" is "either set
> to true or unspecified")?  I ask because the first row does not make
> any sense to me.  It seems to say
>
>     "If pull.ff is set to 'only', pull.rebase is not set to 'false',
>     and the command line does not say anything, we will rebase".

I think Phillip is trying to answer what to do when pull.ff and
pull.rebase conflict.  If I read his "not false" means "is set to
something other than false", then I agree with his table, but I think
he missed covering some cases.

I think his table says that pull.rebase=false cannot conflict with
pull.ff settings, but any other value for pull.rebase can.  That makes
sense to me.

I'd similarly say that pull.ff=true cannot conflict with any
pull.rebase settings...but that both pull.ff=only AND pull.ff=false
conflict with pull.rebase={true,merges}.

My opinion would be:
  * conflicting command line flags results in the last one winning.
  * --no-rebase makes pull.ff determine the action.
  * --ff makes pull.rebase determine the action.
  * any other command line flag (-r|--rebase|--no-ff|--ff-only)
overrides both pull.ff and pull.rebase
  * If no command line option is given, and pull.ff and pull.rebase
conflict, then error out.

I believe my recommendation above is consistent with every entry in
Phillip's table except the first line (where I suggest erroring out
instead).