Re: [PATCH v2] unpack_trees: fix breakage when o->src_index != o->dst_index

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

Elijah Newren <newren@gmail.com> writes:

>  unpack-trees.c | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/unpack-trees.c b/unpack-trees.c
> index e73745051e..08f6cab82e 100644
> --- a/unpack-trees.c
> +++ b/unpack-trees.c
> @@ -1284,9 +1284,20 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
>  	o->result.timestamp.sec = o->src_index->timestamp.sec;
>  	o->result.timestamp.nsec = o->src_index->timestamp.nsec;
>  	o->result.version = o->src_index->version;
> -	o->result.split_index = o->src_index->split_index;
> -	if (o->result.split_index)
> +	if (!o->src_index->split_index) {
> +		o->result.split_index = NULL;
> +	} else if (o->src_index == o->dst_index) {
> +		/*
> +		 * o->dst_index (and thus o->src_index) will be discarded
> +		 * and overwritten with o->result at the end of this function,
> +		 * so just use src_index's split_index to avoid having to
> +		 * create a new one.
> +		 */
> +		o->result.split_index = o->src_index->split_index;
>  		o->result.split_index->refcount++;
> +	} else {
> +		o->result.split_index = init_split_index(&o->result);
> +	}
>  	hashcpy(o->result.sha1, o->src_index->sha1);
>  	o->merge_size = len;
>  	mark_all_ce_unused(o->src_index);
> @@ -1412,7 +1423,7 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
>  						  WRITE_TREE_SILENT |
>  						  WRITE_TREE_REPAIR);
>  		}
> -		move_index_extensions(&o->result, o->dst_index);
> +		move_index_extensions(&o->result, o->src_index);

Can src_index be NULL here?  I am getting segfaults everywhere,
starting from t0000-basic that populates the index by reading one
tree object via read-tree.

>  		discard_index(o->dst_index);
>  		*o->dst_index = o->result;
>  	} else {