Re: [Question] Is extensions.partialClone defunct?

[Tao Klerks <tao@klerks.biz>]

Hi folks, my apologies if old thread reanimation is frowned upon, I
have not been able to find any indications that this is the case.

On Sat, Mar 14, 2020 at 6:43 AM Christian Couder
<christian.couder@gmail.com> wrote:
> On Fri, Mar 13, 2020 at 12:09 AM Jonathan Nieder <jrnieder@gmail.com> wrote:
> > [...]
> > >>> Hmm...besides giving the name of the promisor remote, the
> > >>> extensions.partialClone setting is there to prevent old versions of Git
> > >>> (that do not know this extension) from manipulating the repo.

I was going to start a new thread about just this topic today, but
learned to use the archives instead, for better or for worse...

> > I can start writing a proposed patch to send this evening or tomorrow.
> That would be very much appreciated! Thanks!

Was this change ever attempted? Git's current behavior (as of 2.31.1)
appears to still violate the semantics of
core.repositoryformatversion=1 as documented at
https://github.com/git/git/blob/master/Documentation/technical/repository-version.txt,
and this has been the case since git 2.24.
I assume the right fix at this point would be to do something like
auto-detecting promisor remotes and/or packfiles and adding the
extensions.partialClone config key automatically/transparently. The
main question seems to be *what value* the config key should hold, if
there are multiple promisor remotes?

> > >> Christian, what would your prefered way be to fix this?  Should
> > >> extensions.partialclone specify a particular "default" promisor
> > >> remote, or should we use a new repository extension for multiple
> > >> promisors?
> > [...]
> > > So I'd rather obsolete "extensions.partialClone = <remote>" and to
> > > find other ways.
> >
> > I *think* that means "new repository extension".
> > [...]
> > That suggests something like
> >
> >         [extensions]
> >                 multiplePromisors = true
> > [...]
> > > or maybe
> > > we could have another extension alltogether like
> > > "[extensions]\npromisorremotes=<bool>" and over time obsolete
> > > "extensions.partialClone" altogether. I prefer the later.
> >
> > I think we're going to have to continue to support
> > extensions.partialClone=<remote> for a long time anyway (breaking the
> > ability to work with existing repositories is expensive), so I'm
> > reasonably comfortable with multiplePromisors being a separate
> > extension.  Some faraway day, we can introduce
> > "repositoryFormatVersion = 2" that mandates support for these
> > extensions by default, allowing us to clean up and simplify.
>
> > This behavior has been around for a few releases so it would want to
> > cook until the 2.27 cycle.
>
> Yeah, and partial clone is experimental, so I think it's ok.
>

I'm a little confused by suggestions to create a *new* extension key
here. In principle, this would mean that existing repositories
created/updated by the newest git version would declare themselves to
be incompatible with git clients that don't understand this
entirely-new key, even though:
 * promisor packfiles are a reasonably longstanding thing now (several
years old),
 * they have officially/theoretically been associated with the
"partialClone" extension key throughout that time (at least in the
docs), and
 * partial clone is no longer considered "experimental" in any public doc,

The kind of sudden backwards-incompatibility implied by a new
"extensions.*" key seems... bad? (unless it's something that you
*newly* opt in to - which doesn't seem to be the case here)

Thanks,
Tao