Re: [PATCH 2/3] stash: avoid feeding directories to update-index

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Elijah,

On Wed, 8 Sep 2021, Elijah Newren via GitGitGadget wrote:

> From: Elijah Newren <newren@gmail.com>
>
> When a file is removed from the cache, but there is a file of the same
> name present in the working directory, we would normally treat that file
> in the working directory as untracked.  However, in the case of stash,
> doing that would prevent a simple 'git stash push', because the untracked
> file would be in the way of restoring the deleted file.
>
> git stash, however, blindly assumes that whatever is in the working
> directory for a deleted file is wanted and passes that path along to
> update-index.  That causes problems when the working directory contains
> a directory with the same name as the deleted file.  Add some code for
> this special case that will avoid passing directory names to
> update-index.
>
> Signed-off-by: Elijah Newren <newren@gmail.com>
> ---
>  builtin/stash.c  | 9 +++++++++
>  t/t3903-stash.sh | 2 +-
>  2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/builtin/stash.c b/builtin/stash.c
> index 8f42360ca91..b85cf9d267e 100644
> --- a/builtin/stash.c
> +++ b/builtin/stash.c
> @@ -313,6 +313,12 @@ static int reset_head(void)
>  	return run_command(&cp);
>  }
>
> +static int is_path_a_directory(const char *path)
> +{
> +	struct stat st;
> +	return (!lstat(path, &st) && S_ISDIR(st.st_mode));
> +}

Git's API is unnecessarily confusing (because grown organically), so it is
easy to get confused by that `is_directory()` function that is declared in
`cache.h` and defined in `abspath.c`:

	/*
	 * Do not use this for inspecting *tracked* content.  When path is a
	 * symlink to a directory, we do not want to say it is a directory when
	 * dealing with tracked content in the working tree.
	 */
	int is_directory(const char *path)
	{
		struct stat st;
		return (!stat(path, &st) && S_ISDIR(st.st_mode));
	}

The difference I see is that you use an `lstat()`, which is kind of
important here.

Maybe you could add a paragraph pointing out that we cannot use
`is_directory()` here because it would follow symbolic links, which we
need to avoid here?

> +
>  static void add_diff_to_buf(struct diff_queue_struct *q,
>  			    struct diff_options *options,
>  			    void *data)
> @@ -320,6 +326,9 @@ static void add_diff_to_buf(struct diff_queue_struct *q,
>  	int i;
>
>  	for (i = 0; i < q->nr; i++) {
> +		if (is_path_a_directory(q->queue[i]->one->path))
> +			continue;
> +
>  		strbuf_addstr(data, q->queue[i]->one->path);
>
>  		/* NUL-terminate: will be fed to update-index -z */
> diff --git a/t/t3903-stash.sh b/t/t3903-stash.sh
> index 0727a494aa4..fc74918ccc0 100755
> --- a/t/t3903-stash.sh
> +++ b/t/t3903-stash.sh
> @@ -1307,7 +1307,7 @@ test_expect_success 'stash -c stash.useBuiltin=false warning ' '
>  	test_must_be_empty err
>  '
>
> -test_expect_failure 'git stash succeeds despite directory/file change' '
> +test_expect_success 'git stash succeeds despite directory/file change' '

Excellent!

Thanks,
Dscho

>  	test_create_repo directory_file_switch_v1 &&
>  	(
>  		cd directory_file_switch_v1 &&
> --
> gitgitgadget
>
>