[PATCH v2 4/9] mv: check if <destination> is a SKIP_WORKTREE_DIR

[Shaoxuan Yuan <shaoxuan.yuan02@gmail.com>]

Originally, <destination> is assumed to be in the working tree. If it is
not found as a directory, then it is determined to be either a regular file
path, or error out if used under the second form (move into a directory)
of 'git-mv'. Such behavior is not ideal, mainly because Git does not
look into the index for <destination>, which could potentially be a
SKIP_WORKTREE_DIR, which we need to determine for the later "moving from
in-cone to out-of-cone" patch.

Change the logic so that Git first check if <destination> is a directory
with all its contents sparsified (a SKIP_WORKTREE_DIR).

If <destination> is such a sparse directory, then we should modify the
index the same way as we would if this were a non-sparse directory. We
must be careful to ensure that the <destination> is marked with
SKIP_WORKTREE_DIR.

Also add a `dst_w_slash` to reuse the result from `add_slash()`, which
was everywhere and can be simplified.

Helped-by: Derrick Stolee <derrickstolee@github.com>
Helped-by: Victoria Dye <vdye@github.com>
Signed-off-by: Shaoxuan Yuan <shaoxuan.yuan02@gmail.com>
---
 builtin/mv.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/builtin/mv.c b/builtin/mv.c
index 0a999640c9..f213a92bf6 100644
--- a/builtin/mv.c
+++ b/builtin/mv.c
@@ -171,6 +171,7 @@ int cmd_mv(int argc, const char **argv, const char *prefix)
 		OPT_END(),
 	};
 	const char **source, **destination, **dest_path, **submodule_gitfile;
+	const char *dst_w_slash;
 	enum update_mode *modes;
 	struct stat st;
 	struct string_list src_for_dst = STRING_LIST_INIT_NODUP;
@@ -201,6 +202,7 @@ int cmd_mv(int argc, const char **argv, const char *prefix)
 	if (argc == 1 && is_directory(argv[0]) && !is_directory(argv[1]))
 		flags = 0;
 	dest_path = internal_prefix_pathspec(prefix, argv + argc, 1, flags);
+	dst_w_slash = add_slash(dest_path[0]);
 	submodule_gitfile = xcalloc(argc, sizeof(char *));
 
 	if (dest_path[0][0] == '\0')
@@ -208,12 +210,20 @@ int cmd_mv(int argc, const char **argv, const char *prefix)
 		destination = internal_prefix_pathspec(dest_path[0], argv, argc, DUP_BASENAME);
 	else if (!lstat(dest_path[0], &st) &&
 			S_ISDIR(st.st_mode)) {
-		dest_path[0] = add_slash(dest_path[0]);
-		destination = internal_prefix_pathspec(dest_path[0], argv, argc, DUP_BASENAME);
+		destination = internal_prefix_pathspec(dst_w_slash, argv, argc, DUP_BASENAME);
 	} else {
-		if (argc != 1)
+		if (!path_in_sparse_checkout(dst_w_slash, &the_index) &&
+		    empty_dir_has_sparse_contents(dst_w_slash)) {
+			destination = internal_prefix_pathspec(dst_w_slash, argv, argc, DUP_BASENAME);
+		} else if (argc != 1) {
 			die(_("destination '%s' is not a directory"), dest_path[0]);
-		destination = dest_path;
+		} else {
+			destination = dest_path;
+		}
+	}
+	if (dst_w_slash != dest_path[0]) {
+		free((char *)dst_w_slash);
+		dst_w_slash = NULL;
 	}
 
 	/* Checking */
-- 
2.37.0