Re: [PATCH 9/9] update-index: reduce scope of index expansion in do_reupdate

[Elijah Newren <newren@gmail.com>]

On Tue, Jan 4, 2022 at 9:37 AM Victoria Dye via GitGitGadget
<gitgitgadget@gmail.com> wrote:
>
> From: Victoria Dye <vdye@github.com>
>
> Expand the full index (and redo reupdate operation) only if a sparse
> directory in the index differs from HEAD.

This was a bit hard to parse and follow for me.  Perhaps:

Avoid pre-emptively expanding to a full index in update-index's do_reupdate().
However, if a sparse directory in the index differs from HEAD, we will need to
then expand the index and restart the operation.

> Only the index entries that differ
> between the index and HEAD are updated when performing `git update-index
> --again`, so unmodified sparse directories are safely skipped. The index
> does need to be expanded when sparse directories contain changes, though,
> because `update_one(...)` will not operate on sparse directory index
> entries.
>
> Because the index should only be expanded if a sparse directory is modified,
> add a test ensuring the index is not expanded when differences only exist
> within the sparse cone.
>
> Signed-off-by: Victoria Dye <vdye@github.com>
> ---
>  builtin/update-index.c                   | 14 +++++++++++---
>  t/t1092-sparse-checkout-compatibility.sh |  5 ++++-
>  2 files changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/builtin/update-index.c b/builtin/update-index.c
> index 605cc693bbd..52ecc714d99 100644
> --- a/builtin/update-index.c
> +++ b/builtin/update-index.c
> @@ -606,7 +606,7 @@ static struct cache_entry *read_one_ent(const char *which,
>                         error("%s: not in %s branch.", path, which);
>                 return NULL;
>         }
> -       if (mode == S_IFDIR) {
> +       if (!the_index.sparse_index && mode == S_IFDIR) {
>                 if (which)
>                         error("%s: not a blob in %s branch.", path, which);
>                 return NULL;
> @@ -743,8 +743,6 @@ static int do_reupdate(int ac, const char **av,
>                  */
>                 has_head = 0;
>   redo:
> -       /* TODO: audit for interaction with sparse-index. */
> -       ensure_full_index(&the_index);
>         for (pos = 0; pos < active_nr; pos++) {
>                 const struct cache_entry *ce = active_cache[pos];
>                 struct cache_entry *old = NULL;
> @@ -761,6 +759,16 @@ static int do_reupdate(int ac, const char **av,
>                         discard_cache_entry(old);
>                         continue; /* unchanged */
>                 }
> +
> +               /* At this point, we know the contents of the sparse directory are
> +                * modified with respect to HEAD, so we expand the index and restart
> +                * to process each path individually
> +                */
> +               if (S_ISSPARSEDIR(ce->ce_mode)) {
> +                       ensure_full_index(&the_index);
> +                       goto redo;
> +               }
> +
>                 /* Be careful.  The working tree may not have the
>                  * path anymore, in which case, under 'allow_remove',
>                  * or worse yet 'allow_replace', active_nr may decrease.
> diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
> index bc0741c970d..0863c9747c4 100755
> --- a/t/t1092-sparse-checkout-compatibility.sh
> +++ b/t/t1092-sparse-checkout-compatibility.sh
> @@ -1225,7 +1225,10 @@ test_expect_success 'sparse index is not expanded: update-index' '
>
>         ensure_not_expanded update-index --add README.md &&
>         ensure_not_expanded update-index a &&
> -       ensure_not_expanded update-index --remove deep/a
> +       ensure_not_expanded update-index --remove deep/a &&
> +
> +       ensure_not_expanded reset --soft update-deep &&
> +       ensure_not_expanded update-index --add --remove --again
>  '
>
>  # NEEDSWORK: a sparse-checkout behaves differently from a full checkout
> --
> gitgitgadget

I think the rest makes sense.  Thanks for working on these!