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

[Jeff King <peff@peff.net>]

On Thu, Jul 16, 2020 at 12:01:09AM -0700, Junio C Hamano wrote:

> > To avoid mistakes, continue to forbid repository format upgrades in v0
> > repositories with an unrecognized extension.  This way, a v0 user
> > using a misspelled extension field gets a chance to correct the
> > mistake before updating to the less forgiving v1 format.
> 
> This needs to be managed carefully.  When the next extension is
> added to the codebase, that extension may be "known" to Git, but I
> do not think it is a good idea to honor it in v0 repository, or
> allow upgrading v0 repository to v1 with such an extension that
> weren't "known" to Git.  For example, a topic in flight adds
> objectformat extension and I do not think it should be honored in v0
> repository.
> 
> Having said that, the approach is OK for now at the tip of tonight's
> master, but the point is "known" vs "unknown" must be fixed right
> with some means.  E.g. tell people to throw the "new" extensions to
> the list of "unknown extensions" in check_repo_format() when they
> add new ones, or something.

Yeah, I agree with this line of reasoning. I'd prefer to see it
addressed now, so that we don't have to remember to do anything later.
I.e., for this patch to put the existing known extensions into the
"good" list for v0, locking it into place forever, and leaving the
objectformat topic with nothing particular it needs to do.

But in the name of -rc1 expediency, I'm also OK moving forward with this
for now.

-Peff