Re: git clone of empty repositories doesn't preserve hash

From: Jeff King <peff@peff.net>
Date: Apr 5, 2023, 20:01 UTC
Message-ID: <20230405200153.GA525125@coredump.intra.peff.net>
In-Reply-To: <d04c430e-b609-b0a1-fd0f-0f3734d5c3b1@zombino.com>

On Wed, Apr 05, 2023 at 09:47:55PM +0200, Adam Majer wrote:

Show 10 quoted lines

> On 4/5/23 21:04, Junio C Hamano wrote:
> > Does such a clone copy the name of the primary branch from the
> > remote repository to the newly created repository?
> 
> Yes it does.
> 
> # git init -b maestro --object-format=sha256 a
> # git clone a b
> # cat b/.git/HEAD
> ref: refs/heads/maestro

Yeah, we send a special capability line in that case. If you do:

  GIT_TRACE_PACKET=1 git clone a b

you can see that upload-pack indicates that ls-refs understands the "unborn" capability:

  packet:  upload-pack> version 2
  packet:  upload-pack> agent=git/2.40.0.824.g7b678b1f643
  packet:  upload-pack> ls-refs=unborn
  packet:  upload-pack> fetch=shallow wait-for-done
  packet:  upload-pack> server-option
  packet:  upload-pack> object-format=sha256
  packet:  upload-pack> object-info
  packet:  upload-pack> 0000

And then clone asks for it say "yes, I also understand unborn":

  packet:        clone> command=ls-refs
  packet:        clone> agent=git/2.40.0.824.g7b678b1f643
  packet:        clone> object-format=sha256
  packet:        clone> 0001
  packet:        clone> peel
  packet:        clone> symrefs
  packet:        clone> unborn
  packet:        clone> ref-prefix HEAD
  packet:        clone> ref-prefix refs/heads/
  packet:        clone> ref-prefix refs/tags/
  packet:        clone> 0000

And then upload-pack can send us the extra information:

  packet:  upload-pack> unborn HEAD symref-target:refs/heads/maestro
  packet:  upload-pack> 0000

I think we'd need to do something similar here for object-format.

-Peff