Re: [PATCH 04/10] unpack-trees API: don't have clear_unpack_trees_porcelain() reset

[Elijah Newren <newren@gmail.com>]

On Sun, Oct 3, 2021 at 5:46 PM Ævar Arnfjörð Bjarmason <avarab@gmail.com> wrote:
>
> Change the clear_unpack_trees_porcelain() to be like a *_release()
> function, not a *_reset() (in strbuf.c terms). Let's move the only API
> user that relied on the latter to doing its own
> unpack_trees_options_init(). See the commit that introduced
> unpack_trees_options_init() for details on the control flow involved
> here.
>
> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
> ---
>  merge-recursive.c | 1 +
>  unpack-trees.c    | 1 -
>  2 files changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/merge-recursive.c b/merge-recursive.c
> index d24a4903f1d..a77f66b006c 100644
> --- a/merge-recursive.c
> +++ b/merge-recursive.c
> @@ -442,6 +442,7 @@ static void unpack_trees_finish(struct merge_options *opt)
>  {
>         discard_index(&opt->priv->orig_index);
>         clear_unpack_trees_porcelain(&opt->priv->unpack_opts);
> +       unpack_trees_options_init(&opt->priv->unpack_opts);

This is wrong.  It suggests that unpack_opts is used after
unpack_trees_finish() (other than an outer merge first calling
unpack_trees_start() again), which can only serve to greatly confuse
future readers.  Drop this hunk.

>  }
>
>  static int save_files_dirs(const struct object_id *oid,
> diff --git a/unpack-trees.c b/unpack-trees.c
> index 94767d3f96f..e7365322e82 100644
> --- a/unpack-trees.c
> +++ b/unpack-trees.c
> @@ -197,7 +197,6 @@ void clear_unpack_trees_porcelain(struct unpack_trees_options *opts)
>  {
>         strvec_clear(&opts->msgs_to_free);
>         dir_clear(&opts->dir);
> -       memset(opts->msgs, 0, sizeof(opts->msgs));

This seems like a very dangerous change.  You want to leave opts->msgs
pointing at freed memory?