Junio C Hamano wrote:
> Matthias Baumgarten <matthias.baumgarten@xxxxxxxxxx> writes:
>
> >>> pull.ff pull.rebase commandline action
> >>> ...
> >>> * * --ff-only fast-forward only[1]
> >>> ...
> > What about
> >
> > * !false --ff-only ???
>
> This is covered by an earlier entry ("*" stands for "any value"), I
> think; it should fast-forward or fail. The reasoning goes like
> this:
>
> The user configures pull.rebase to some kind of rebase; it could be
> just true (the traditional flattening rebase), or the one that
> preserves the shape of the history, or even the interactive one.
> With the configuration, what the user declares is:
>
> I may have my own development on top of the result of my last
> integration with the upstream I did when I ran "git pull" the
> last time, and when the upstream has more commits, the way I
> want my local work to integrate with their work is to replay my
> work on top of theirs (as opposed to "merging their work into my
> history").
>
> But by passing "--ff-only" from the command line, the user tells us
> this:
>
> This time only, I want fast-forward update and nothing else. I
> do not remember doing any of my own development on top of their
> history, and I expect that this update from the upstream would
> fast-forward. If that is not the case, please error out, as I
> need to inspect the situation further and I do not want to see
> conflicts in unexpected commits I thought I did not have.
No, this is what you think the user would be telling us, but that's not
what the user is *actually* telling us right now.
git -c pull.ff=only pull --rebase
What the user is actually telling us right now is that while he normally
would expect a fast-forward, in this case he would like a rebase.
Today this is the equivalent of:
git -c pull.rebase=true pull --ff-only
If you change this interpretation, it would break the symmetry between
configurations and command line arguments.
> So the "action" would be
>
> - If their history is a descendant of ours, that means that on top
> of their history previously observed by us, we haven't added any
> development of our own. We just move to the tip of their history
> and we are done.
>
> This is not so surprising anyway. If we are doing any kind of
> rebasing, what happens is to start from the tip of their history
> and then commits from our own development are replayed on top of
> that. When their history is a descendant of ours, we end up
> doing just fast-forward, as there is nothing to replay on top.
But --ff-only is not for rebases, the documentation is very clear:
Specifies how a merge is handled when the merged-in history is
already a descendant of the current history. `--ff` is the
default unless merging an annotated (and possibly signed) tag
that is not stored in its natural place in the `refs/tags/`
hierarchy, in which case `--no-ff` is assumed.
With `--ff-only`, resolve the merge as a fast-forward when possible.
When not possible, refuse to merge and exit with a non-zero status.
> - Otherwise, because the user expects the command to fail if their
> history is not a descendant of ours, we fail.
>
> And "fast-forward only" in Elijah's table is a concise way to say
> that.
Yes, but it's taking us in the wrong direction by ignoring how the users
actually use --ff-only today, what the documentation actually says,
breaking the symmetry of configurations and arguments, and making
everything less intuitive.
On the other hand if --ff-only was mapped to pull.mode=fast-forward
instead, everything is clear:
git -c pull.mode=fast-forward pull --rebase
git -c pull.mode=rebase pull --ff-only
I don't even need to explain what these do.
--
Felipe Contreras
