Re: [PATCH v1] rebase -m: Use empty tree base for parentless commits

From: Junio C Hamano <gitster@pobox.com>
Date: Oct 9, 2014, 19:05 UTC
Message-ID: <xmqq1tqh6p3y.fsf@gitster.dls.corp.google.com>
In-Reply-To: <bf0e177fbaac91f8c55526729e580fade9f0f395.1412879523.git.bafain@gmail.com>

Fabian Ruch <bafain@gmail.com> writes:

Show 16 quoted lines

> diff --git a/git-rebase--merge.sh b/git-rebase--merge.sh
> index d3fb67d..3f754ae 100644
> --- a/git-rebase--merge.sh
> +++ b/git-rebase--merge.sh
> @@ -67,7 +67,13 @@ call_merge () {
>  		GIT_MERGE_VERBOSITY=1 && export GIT_MERGE_VERBOSITY
>  	fi
>  	test -z "$strategy" && strategy=recursive
> -	eval 'git-merge-$strategy' $strategy_opts '"$cmt^" -- "$hd" "$cmt"'
> +	base=$(git rev-list --parents -1 $cmt | cut -d ' ' -s -f 2 -)
> +	if test -z "$base"
> +	then
> +		# the empty tree sha1
> +		base=4b825dc642cb6eb9a060e54bf8d69288fbee4904
> +	fi
> +	eval 'git-merge-$strategy' $strategy_opts '"$base" -- "$hd" "$cmt"'

This looks wrong.

The interface to "git-merge-$strategy" is designed in such a way that each strategy should be capable of taking _no_ base at all.

See how unquoted $common is given to git-merge-$strategy in contrib/examples/git-merge.sh, i.e.

    eval 'git-merge-$strategy '"$xopt"' $common -- "$head_arg" "$@"'

where common comes from

	common=$(git merge-base ...)

which would be empty when you are looking at disjoint histories.

Also rev-list piped to cut is too ugly to live in our codebase X-<.

Wouldn't it be sufficient to do something like this instead?

	eval 'git-merge-$strategy' $strategy_opts \
        	$(git rev-parse --quiet --verify "$cmt^") -- "$hd" "$cmt"