Re: [PATCH 2/2] repository: allow repository format upgrade with extensions

From: Jeff King <peff@peff.net>
Date: Jul 17, 2020, 15:27 UTC
Message-ID: <20200717152744.GB1224964@coredump.intra.peff.net>
In-Reply-To: <xmqqh7u7f29h.fsf@gitster.c.googlers.com>

On Thu, Jul 16, 2020 at 04:50:34PM -0700, Junio C Hamano wrote:

Show 18 quoted lines

> > - improving the behavior when an extension not supported in v0 is
> >   encountered in a v0 repository.  For extensions that are supported
> >   in v1 and not v0, we should presumably error out so the user can
> >   repair the repository, and we can put the "noop" extension in that
> >   category for the sake of easy testing.  We can also include a check
> >   in "git fsck" for repositories that request the undefined behavior
> >   of v0 repositories with non-v0 extensions, for faster diagnosis.
> >
> >   What about unrecognized extensions that are potentially extensions
> >   yet to be defined?  Should these be silently ignored to match the
> >   historical behavior, or should we error out even in repository
> >   format v0?  I lean toward the latter; we'll need to be cautious,
> >   though, e.g. by making this a separate patch so we can easily tweak
> >   it if this ends up being disruptive in some unanticipated way.
> 
> I disagree with your first paragraph.  Those that weren't honored by
> mistake back in v0 days, in addition to those that aren't known to us
> even now, should just be silently ignored, not causing an error.

That's very much the opposite of my patch. As we add new extensions, those "unknowns" will start to die().

I remain unconvinced that there are a bunch of unknown extension.* config options hanging around in the wild, but maybe I'm being naive. It seems to me more likely that users will be helped by warning about extensions that _should_ have had v1 set than that they will be harmed because they put random crap in their extensions.* config. But maybe you know of a specific example?

Anyway, if we move to "v1" as the default for "git init" anyway, then the number of people being helped would become much smaller.

Show 8 quoted lines

> > My preference would be to move forward in 2.28 with the first two
> > patches in that topic branch (i.e., *not* the third yet), since they
> > don't produce any user facing behavior that would create danger for
> > users or clash with this plan.
> 
> Yup, I agree.  I'd give another name to the third commit and then
> rewind jn/v0-with-extensions-fix by one to prevent mistakes from
> happening.  Thanks.

OK. I was confused to see it still at the tip in the latest What's Cooking, but I think we're just crossing emails. :)

-Peff