Jeff King [off-list ref] writes:
If we could reliably tell the difference between those two cases, it
might be worth doing the up-front check. But I'm not sure we can do that
without declaring that people in the ff-only case should be using a
different workflow (e.g., fetch + "reset --hard").
Yup, it _might_ be nicer but I tend to think probably it is not
worth the potential trouble.
Thanks.