Re: [PATCH v5 20/20] rebase: rename the two primary rebase backends

On Thu, Mar 12, 2020 at 12:29:45PM -0700, Elijah Newren wrote:

First, note that this particular breakage would have occurred
regardless of the default setting, because the problem was that they
setting rebase.backend to an unrecognized value, not that we used a
different backend than they were used to.

If I understand correctly, it was also a setting that never worked in
any released version of Git. It was magic that was only ever in 'next'.

As annoying as it is to experience breakage, I'm not _too_ sympathetic
to this case, because that is part of the cost of running the bleeding
edge of 'next' or even 'master'. I.e., I think we have to make a cutoff
_somewhere_ to say "this is something that made it to the general
public, and therefore we can't break backwards compatibility" to keep
our sanity during development. And it seems like tagged releases are a
pretty good cutoff to me.

Though in this particular case, I don't mind too much just leaving "am"
as an alias for "apply" (it was actually the first thing I tried when
writing my earlier emails, but I'm probably not a representative user
there). Putting that in a release, though, may mean supporting it
forever. :)

   - We had multiple complaints this cycle about rebase.backend=apply
merging things incorrectly with the only workaround being to use the
merge backend[3,4]
   - The rebase-backend topic wasn't merged down to master until less
than a week before -rc0.  (For a variety of reasons.)  A big change
like this probably would have been better to merge down earlier in
some cycle.

It did feel a bit quick to me, hitting near the end of the cycle. We've
had the apply backend as the default for a decade, so even if there are
problems with it, they're known issues. So I don't think there's a
particular hurry. I'm not entirely convinced that cooking it longer
during the next cycle will turn up a lot of new data (I did find a few
issues, but the real test is the long-tail of weird use cases that we
won't see until an actual release). But it probably doesn't hurt much to
take it slow; it just delays a few bug-fixes (which people can still get
by setting a config option).

I guess like your email I'm going back and forth between the two
options. I think that means it probably doesn't matter _too_ much either
way.

-Peff