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

On Mon, Jul 12, 2021 at 12:55 PM Junio C Hamano [off-list ref] wrote:

Alex Henrie [off-list ref] writes:

quoted

Sorry, I misspoke. I was thinking of the case where fast-forwarding is
impossible.

When we cannot fast-forward (i.e. we have our own development that
is not in the tip of their history),

 --ff-only would cause the operation fail
 --ff would become no-op (as it merely allows fast-forwarding)
 --no-ff would become no-op (as it merely forbids fast-forwarding)

and the latter two case, we'd either merge or rebase (with possibly
specified mode like --preserve-merges).  I thought the current
documentation is already fairly clear on this point?

git pull's --no-ff is documented to "create a merge commit in all
cases", and thus as worded, seems incompatible with rebasing to me.
Treating --no-ff as a no-op when we cannot fast-forward (i.e. allowing
rebasing to happen) could be seen as a backwards incompatible change
at this point.

Having --ff be compatible with rebasing works because the end result
will be the same as described in the existing documentation.

quoted

If fast-forwarding is possible, --ff-only already effectively
implies --no-rebase, and we might want to make that explicit in
the documentation.

When we fast-forward (i.e. their history is descendant from ours,
and the user did not give --no-ff), it does not matter if it is done
using the merge backend, the rebase backend, or by the "git pull"
wrapper. The end user does not care.  The end result is that the tip
of the branch now points at the tip of the history we pulled from
the other side and that is all what matters.

So, from that point of view, I do not think we want to say rebase or
merge or anything else for such a case in the documentation.

All three of --ff, --no-ff, and --ff-only come from
Documentation/merge-options.txt and are shared between git-merge and
git-pull.  The description of each of those items mentions "merges" or
"merging" at least once in every sentence.