Re: [PATCH 2/3] git add: make -p/-i aware of sparse index

>
> From: Derrick Stolee <stolee@gmail.com>
>
> It is slow to expand a sparse index in-memory due to parsing of trees.
> We aim to minimize that performance cost when possible. 'git add -p'
> uses 'git apply' child processes to modify the index, but still there
> are some expansions that occur.

> It turns out that control flows out of cmd_add() in the interactive
> cases before the lines that confirm that the builtin is integrated with
> the sparse index. We need to move that earlier to ensure it prevents a
> full index expansion on read.
>
> Add more test cases that confirm that these interactive add options work
> with the sparse index. One interesting aspect here is that the '-i'
> option avoids expanding the sparse index when a sparse directory exists
> on disk while the '-p' option does hit the ensure_full_index() method.
> This leaves some room for improvement, but this case should be atypical
> as users should remain within their sparse-checkout.

> Signed-off-by: Derrick Stolee <stolee@gmail.com>
> ---
>  builtin/add.c                            |  7 +--
>  t/t1092-sparse-checkout-compatibility.sh | 56 ++++++++++++++++++++++++
>  2 files changed, 60 insertions(+), 3 deletions(-)
>
> diff --git a/builtin/add.c b/builtin/add.c
> index 747511b68bc3..7c292ffdc6c2 100644
> --- a/builtin/add.c
> +++ b/builtin/add.c
> @@ -390,6 +390,10 @@ int cmd_add(int argc,
>
>         argc = parse_options(argc, argv, prefix, builtin_add_options,
>                           builtin_add_usage, PARSE_OPT_KEEP_ARGV0);
> +
> +       prepare_repo_settings(repo);
> +       repo->settings.command_requires_full_index = 0;
> +
>         if (patch_interactive)
>                 add_interactive = 1;
>         if (add_interactive) {
> @@ -426,9 +430,6 @@ int cmd_add(int argc,
>         add_new_files = !take_worktree_changes && !refresh_only && !add_renormalize;
>         require_pathspec = !(take_worktree_changes || (0 < addremove_explicit));
>
> -       prepare_repo_settings(repo);
> -       repo->settings.command_requires_full_index = 0;
> -
>         repo_hold_locked_index(repo, &lock_file, LOCK_DIE_ON_ERROR);
>
>         /*
> diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
> index ab8bd371eff3..0dc5dd27184d 100755
> --- a/t/t1092-sparse-checkout-compatibility.sh
> +++ b/t/t1092-sparse-checkout-compatibility.sh
> @@ -384,6 +384,38 @@ test_expect_success 'add, commit, checkout' '
>         test_all_match git checkout -
>  '
>
> +test_expect_success 'git add -p' '
> +       init_repos &&
> +
> +       write_script edit-contents <<-\EOF &&
> +       echo text >>$1
> +       EOF
> +
> +       # Does not expand when edits are within sparse checkout.
> +       run_on_all ../edit-contents deep/a &&
> +       run_on_all ../edit-contents deep/deeper1/a &&
> +
> +       test_write_lines y n >in &&
> +       run_on_all git add -p <in &&
> +       test_all_match git status --porcelain=v2 &&
> +       test_all_match git reset &&
> +
> +       test_write_lines u 1 "" q >in &&
> +       run_on_all git add -i <in &&
> +       test_all_match git status --porcelain=v2 &&
> +       test_all_match git reset --hard &&
> +
> +       run_on_sparse mkdir -p folder1 &&
> +       run_on_all ../edit-contents folder1/a &&
> +       test_write_lines y n y >in &&
> +       run_on_all git add -p <in &&
> +       test_sparse_match git status --porcelain=v2 &&
> +       test_sparse_match git reset &&
> +       test_write_lines u 2 3 "" q >in &&
> +       run_on_all git add -i <in &&
> +       test_sparse_match git status --porcelain=v2
> +'
> +
>  test_expect_success 'deep changes during checkout' '
>         init_repos &&
>
> @@ -2391,6 +2423,30 @@ test_expect_success 'sparse-index is not expanded: git apply' '
>         ensure_not_expanded apply --cached ../patch-outside
>  '
>
> +test_expect_success 'sparse-index is not expanded: git add -p' '
> +       init_repos &&
> +
> +       # Does not expand when edits are within sparse checkout.
> +       echo "new content" >sparse-index/deep/a &&
> +       echo "new content" >sparse-index/deep/deeper1/a &&
> +       test_write_lines y n >in &&
> +       ensure_not_expanded add -p <in &&
> +       git -C sparse-index reset &&
> +       ensure_not_expanded add -i <in &&
> +
> +       mkdir -p sparse-index/folder1 &&
> +       echo "new content" >sparse-index/folder1/a &&
> +
> +       # -p does expand when edits are outside sparse checkout.
> +       test_write_lines y n y >in &&
> +       ensure_expanded add -p <in &&
> +
> +       # but -i does not expand.
> +       git -C sparse-index reset &&
> +       test_write_lines u 2 3 "" q >in &&
> +       ensure_not_expanded add -i <in