Re: [PATCH] git-rebase--merge: don't include absent parent as a base

[Junio C Hamano <gitster@pobox.com>]

Ben Woosley <Ben.Woosley@gmail.com> writes:

> From: Ben Woosley <ben.woosley@gmail.com>
>
> Absent this fix, attempts to rebase an orphan branch with --strategy recursive
> will fail with:
>
>     $ git rebase ORPHAN_TARGET_BASE -s recursive
>     First, rewinding head to replay your work on top of it...
>     fatal: Could not parse object 'ORPHAN_ROOT_SHA^'
>     Unknown exit code (128) from command: git-merge-recursive ORPHAN_ROOT_SHA^ -- HEAD ORPHAN_ROOT_SHA
>
> To fix, this will only include the rebase root's parent as a base if it exists,
> so that in cases of rebasing an orphan branch, it is a simple two-way merge.
>
> Note the default rebase behavior does not fail:
>
>     $ git rebase ORPHAN_TARGET_BASE
>     First, rewinding head to replay your work on top of it...
>     Applying: ORPHAN_ROOT_COMMIT_MSG
>     Using index info to reconstruct a base tree...
>
> Signed-off-by: Ben Woosley <ben.woosley@gmail.com>
> ---
>  git-rebase--merge.sh    | 4 +++-
>  t/t3402-rebase-merge.sh | 9 +++++++++
>  2 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/git-rebase--merge.sh b/git-rebase--merge.sh
> index 2cc2a6d..8d43db9 100644
> --- a/git-rebase--merge.sh
> +++ b/git-rebase--merge.sh
> @@ -67,7 +67,9 @@ 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"'
> +	# If cmt doesn't have a parent, don't include it as a base
> +	base=$(git rev-parse --verify --quiet $cmt^)
> +	eval 'git-merge-$strategy' $strategy_opts $base ' -- "$hd" "$cmt"'

Makes sense to me.  It is not clear if such a merge without common
ancestor is all that useful, but as it is mechanically possible,
I do not see a reason to forbid it.

>  	rv=$?
>  	case "$rv" in
>  	0)
> diff --git a/t/t3402-rebase-merge.sh b/t/t3402-rebase-merge.sh
> index 8f64505..488945e 100755
> --- a/t/t3402-rebase-merge.sh
> +++ b/t/t3402-rebase-merge.sh
> @@ -85,6 +85,15 @@ test_expect_success 'rebase -Xtheirs' '
>  	! grep 11 original
>  '
>  
> +test_expect_success 'rebase -Xtheirs from orphan' '
> +	git checkout --orphan orphan-conflicting master~2 &&
> +	echo "AB $T" >> original &&
> +	git commit -morphan-conflicting original &&
> +	git rebase -Xtheirs master &&
> +	grep AB original &&
> +	! grep 11 original
> +'
> +
>  test_expect_success 'merge and rebase should match' '
>  	git diff-tree -r test-rebase test-merge >difference &&
>  	if test -s difference
>
> --
> https://github.com/git/git/pull/228