Re: git clone (ssh://) skips detached HEAD

From: Jeff King <peff@peff.net>
Date: Jun 1, 2011, 22:05 UTC
Message-ID: <20110601220518.GA32681@sigill.intra.peff.net>
In-Reply-To: <BANLkTi=xK+hmvGTLnKREScABU=7v_SKqPQ@mail.gmail.com>

On Thu, Jun 02, 2011 at 03:30:37AM +0600, Dmitry Ivankov wrote:

> For some reason git doesn't try to fetch detached HEAD object if it's
> not needed by needed heads.

The reason is that the default refspec on clone is:

  $ git config remote.origin.fetch
  +refs/heads/*:refs/remotes/origin/*

And HEAD is not under refs/heads/.

So you can do:

  git init test2 && cd test2
  git fetch ../test HEAD

if you want. So I don't think it's a bug that we don't fetch it, but...

Show 15 quoted lines

> Steps to reproduce:
> git init test && cd test
> touch 1 && git add 1 && git commit -m 123
> touch 2 && git add 2 && git commit -m 345
> git reset --hard HEAD^
> git checkout HEAD@{1}
> 
> cd ../
> git clone ssh://127.0.0.1/`pwd`/test test2
> remote: Counting objects: 3, done.
> remote: Total 3 (delta 0), reused 0 (delta 0)
> Receiving objects: 100% (3/3), done.
> error: Trying to write ref HEAD with nonexistant object
> 91dbc2403853783f637744c31036f94a66084286
> fatal: Cannot update the ref 'HEAD'.

This is quite bad behavior. In addition to the ugly error messages, it actually aborts the clone. So it is impossible to clone a repo with a detached HEAD that is not otherwise referenced.

We basically have two choices:

  1. Fetch objects for HEAD on clone.

  2. Don't checkout a detached HEAD if we don't have the object (or
     possibly, don't checkout a detached HEAD at all; we already do
     something similar for the case of a HEAD that points to a bogus
     branch).

I think (2) is more consistent with the refspec we set up, but (1) is probably more convenient to users (and better matches the case where the remote is on a detached HEAD that _does_ point to something we have).

> HEAD seems to be treated in a special way in various places, so
> haven't found any easy patch to fix this.

I think it should just be a matter of adding HEAD to the list of things we fetch, although we don't actually want to write it to a ref. I'll take a look.

> And by the way, clone --no-hardlinks test test2 still goes to is_local
> codepath and avoids the bug.

Yeah. --no-hardlinks still avoids the git-transport; it just copies instead of hardlinking. I saw you used ssh://localhost above to do your test. You can also use file://$PWD/test to accomplish the same thing without having to run an ssh daemon.

-Peff