Re: [PATCH 11/27] unpack-trees: allow sparse directories

[Elijah Newren <newren@gmail.com>]

On Mon, Jan 25, 2021 at 9:42 AM Derrick Stolee via GitGitGadget
<gitgitgadget@gmail.com> wrote:
>
> From: Derrick Stolee <dstolee@microsoft.com>
>
> The index_pos_by_traverse_info() currently throws a BUG() when a
> directory entry exists exactly in the index. We need to consider that it
> is possible to have a directory in a sparse index as long as that entry
> is itself marked with the skip-worktree bit.
>
> The negation of the 'pos' variable must be conditioned to only when it
> starts as negative. This is identical behavior as before when the index
> is full.

The first sentence of this paragraph was really hard for me to parse.
Reading the code and then reading the sentence I could make sense of
it, but I struggled to do so the other way around.  Is there some way
to reword this?  Or is this just a reading comprehension issue on my
part?  (It might be...)

> The starts_with() condition matches because our name.buf terminates with
> a directory separator, just like our sparse directory entries.
>
> Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
> ---
>  unpack-trees.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/unpack-trees.c b/unpack-trees.c
> index 4dd99219073..b324eec2a5d 100644
> --- a/unpack-trees.c
> +++ b/unpack-trees.c
> @@ -746,9 +746,12 @@ static int index_pos_by_traverse_info(struct name_entry *names,
>         strbuf_make_traverse_path(&name, info, names->path, names->pathlen);
>         strbuf_addch(&name, '/');
>         pos = index_name_pos(o->src_index, name.buf, name.len);
> -       if (pos >= 0)
> -               BUG("This is a directory and should not exist in index");
> -       pos = -pos - 1;
> +       if (pos >= 0) {
> +               if (!o->src_index->sparse_index ||
> +                   !(o->src_index->cache[pos]->ce_flags & CE_SKIP_WORKTREE))
> +                       BUG("This is a directory and should not exist in index");
> +       } else
> +               pos = -pos - 1;
>         if (pos >= o->src_index->cache_nr ||
>             !starts_with(o->src_index->cache[pos]->name, name.buf) ||
>             (pos > 0 && starts_with(o->src_index->cache[pos-1]->name, name.buf)))
> --
> gitgitgadget

The patch looks pretty straightforward to me.