Re: fatal: bad revision 'HEAD'

From: Junio C Hamano <gitster@pobox.com>
Date: Aug 12, 2009, 07:37 UTC
Message-ID: <7v7hx98otz.fsf@alter.siamese.dyndns.org>
In-Reply-To: <20090812032740.GA26089@coredump.intra.peff.net>

Jeff King <peff@peff.net> writes:

> I was able to replicate your problem, but only if I set
> branch.master.rebase to "true" in my user-wide git config (i.e.,
> ~/.gitconfig). It looks like "git pull" is not capable of handling a
> rebase when you have no commits yet.

It does sound sick to store such a setting in $HOME/.gitconfig file, when the variable is clearly per-repository. As you wrote, you can easily trigger it with an explicit --rebase, but again, it is insane to ask "rebase" when you clearly do not have anything.

But just like we twisted the definition of merge to mean "merging something into nothing yields that something", we could twist the definition of rebase to mean "rebasing nothing on top of something result in that something". It sort of makes sense in a twisted way.

Show 19 quoted lines

> diff --git a/git-pull.sh b/git-pull.sh
> index 0f24182..427b5c6 100755
> --- a/git-pull.sh
> +++ b/git-pull.sh
> @@ -119,9 +119,15 @@ error_on_no_merge_candidates () {
>  }
>  
>  test true = "$rebase" && {
> +	if git rev-parse -q --verify HEAD >/dev/null; then
> +		parent_tree=HEAD
> +	else # empty tree
> +		parent_tree=4b825dc642cb6eb9a060e54bf8d69288fbee4904
> +	fi
> +
>  	git update-index --ignore-submodules --refresh &&
>  	git diff-files --ignore-submodules --quiet &&
> -	git diff-index --ignore-submodules --cached --quiet HEAD -- ||
> +	git diff-index --ignore-submodules --cached --quiet $parent_tree -- ||
>  	die "refusing to pull with rebase: your working tree is not up-to-date"

Two comments.

 * Is "rev-parse -q --verify" a safe test to guarantee that HEAD is
   unborn?  Shouldn't we be checking with "symbolic-ref" or something?

 * In such an "unborn branch" case, by definition, a non-empty index won't
   be based on whatever we are pulling down from the remote.  So how about
   doing something like the following instead?

	if on unborn branch
	then
		if test -f "$GIT_DIR/index"
                then
			die "refusing to update; you have a non-empty index"
		fi
	else
		... existing tests against HEAD ...
	fi