Subject: Re: [PATCH 2/5] apply: read in the index in --intent-to-add mode

From: Junio C Hamano <[email-masked]>
Date: Mon, 30 Jun 2025 11:47:46 -0700

"Raymond E. Pasco" <[email-masked]> writes:

> There are three main modes of operation for apply: applying only to the
> worktree, applying to the worktree and index (--index), and applying
> only to the index (--cached).
>
> The --intent-to-add flag modifies the first of these modes, applying
> only to the worktree, in a way which touches the index, because
> intents to add are special index entries. However, it has not ever
> worked correctly in any but the most trivial (empty repository)
> cases, because the index was never read in (in apply, this is done
> in read_apply_cache()) before writing to it.

As the inventor of "add -N", I think what "apply -N" does may be
wrong (only judging from the above description; it's been a while
since I really read the code in apply.c).  It does not make any
sense to write a new index that has only the ITA entries.

> If we merely gate read_apply_cache() behind update_index, then it will
> not be read when state->apply is false, even if it must be checked.
> Therefore, we instead read the index if it will be either checked or
> updated, because reading the index is a prerequisite to either.

Makes sense.

> Reported-by: Ryan Hodges <[email-masked]>
> Original-patch-by: Johannes Altmanninger <[email-masked]>
> Signed-off-by: Raymond E. Pasco <[email-masked]>
> ---
>  apply.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/apply.c b/apply.c
> index e7856ae6b3..1757d34618 100644
> --- a/apply.c
> +++ b/apply.c
> @@ -4837,7 +4837,7 @@ static int apply_patch(struct apply_state *state,
>  					       LOCK_DIE_ON_ERROR);
>  	}
>  
> -	if (state->check_index && read_apply_cache(state) < 0) {
> +	if ((state->check_index || state->update_index) && read_apply_cache(state) < 0) {
>  		error(_("unable to read index file"));
>  		res = -128;
>  		goto end;