Re: [PATCH] sparse-checkout: avoid staging deletions of all files

> ...  Thus, instead of all the files appearing deleted in `git
> status` being known to git as a special artifact of not yet being on a
> branch, our recording of an empty index made it suddenly look to git as
> though it was definitely on a branch with ALL files staged for deletion!
> A subsequent checkout or switch then had to contend with the fact that
> it wasn't on an initial_checkout but had a bunch of staged deletions.

> Make sure that sparse-checkout changes nothing in the index other than
> the SKIP_WORKTREE bit; in particular, when the index is unborn we do not
> have any branch checked out so there is no sparsification or
> de-sparsification work to do.  Simply return from
> update_working_directory() early.

> Signed-off-by: Elijah Newren <newren@gmail.com>
> ---
>     sparse-checkout: avoid staging deletions of all files
>
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-801%2Fnewren%2Fsparse-checkout-and-unborn-index-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-801/newren/sparse-checkout-and-unborn-index-v1
> Pull-Request: https://github.com/git/git/pull/801
>
>  builtin/sparse-checkout.c          |  4 ++++
>  t/t1091-sparse-checkout-builtin.sh | 19 +++++++++++++++++++
>  2 files changed, 23 insertions(+)
>
> diff --git a/builtin/sparse-checkout.c b/builtin/sparse-checkout.c
> index 95d08824172..595463be68e 100644
> --- a/builtin/sparse-checkout.c
> +++ b/builtin/sparse-checkout.c
> @@ -99,6 +99,10 @@ static int update_working_directory(struct pattern_list *pl)
>  	struct lock_file lock_file = LOCK_INIT;
>  	struct repository *r = the_repository;
>  
> +	/* If no branch has been checked out, there are no updates to make. */
> +	if (is_index_unborn(r->index))
> +		return UPDATE_SPARSITY_SUCCESS;
> +
>  	memset(&o, 0, sizeof(o));
>  	o.verbose_update = isatty(2);
>  	o.update = 1;
> diff --git a/t/t1091-sparse-checkout-builtin.sh b/t/t1091-sparse-checkout-builtin.sh
> index 88cdde255cd..bc287e5c1fa 100755
> --- a/t/t1091-sparse-checkout-builtin.sh
> +++ b/t/t1091-sparse-checkout-builtin.sh
> @@ -100,6 +100,25 @@ test_expect_success 'clone --sparse' '
>  	check_files clone a
>  '
>  
> +test_expect_success 'interaction with clone --no-checkout (unborn index)' '
> +	git clone --no-checkout "file://$(pwd)/repo" clone_no_checkout &&
> +	git -C clone_no_checkout sparse-checkout init --cone &&
> +	git -C clone_no_checkout sparse-checkout set folder1 &&
> +	git -C clone_no_checkout sparse-checkout list >actual &&
> +	cat >expect <<-\EOF &&
> +	folder1
> +	EOF
> +	test_cmp expect actual &&
> +	ls clone_no_checkout >actual &&
> +	test_must_be_empty actual &&
> +	test_path_is_missing clone_no_checkout/.git/index &&
> +
> +	# No branch is checked out until we manually switch to one
> +	git -C clone_no_checkout switch master &&
> +	test_path_is_file clone_no_checkout/.git/index &&
> +	check_files clone_no_checkout a folder1
> +'
> +
>  test_expect_success 'set enables config' '
>  	git init empty-config &&
>  	(
>
> base-commit: 20514004ddf1a3528de8933bc32f284e175e1012