git_path(): keep "info/sparse-checkout" per work-tree

Currently git_path("info/sparse-checkout") resolves to
$GIT_COMMON_DIR/info/sparse-checkout in multiple worktree mode. It
makes more sense for the sparse checkout patterns to be per worktree,
so you can have multiple checkouts with different parts of the tree.

With this, "git checkout --to <new>" on a sparse checkout will create
<new> as a full checkout. Which is expected, it's how a new checkout
is made. The user can reshape the worktree afterwards.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

path.c

diff --git a/path.c b/path.c
index cd8e2d6..35d498e 100644
--- a/path.c
+++ b/path.c
@@ -103,7 +103,8 @@
 	char *base = buf->buf + git_dir_len;
 	const char **p;
 
-	if (is_dir_file(base, "logs", "HEAD"))
+	if (is_dir_file(base, "logs", "HEAD") ||
+	    is_dir_file(base, "info", "sparse-checkout"))
 		return;	/* keep this in $GIT_DIR */
 	for (p = common_list; *p; p++) {
 		const char *path = *p;

t/t0060-path-utils.sh

diff --git a/t/t0060-path-utils.sh b/t/t0060-path-utils.sh
index f5d6f80..93605f4 100755
--- a/t/t0060-path-utils.sh
+++ b/t/t0060-path-utils.sh
@@ -270,6 +270,7 @@
 test_git_path GIT_COMMON_DIR=bar objects/bar              bar/objects/bar
 test_git_path GIT_COMMON_DIR=bar info/exclude             bar/info/exclude
 test_git_path GIT_COMMON_DIR=bar info/grafts              bar/info/grafts
+test_git_path GIT_COMMON_DIR=bar info/sparse-checkout     .git/info/sparse-checkout
 test_git_path GIT_COMMON_DIR=bar remotes/bar              bar/remotes/bar
 test_git_path GIT_COMMON_DIR=bar branches/bar             bar/branches/bar
 test_git_path GIT_COMMON_DIR=bar logs/refs/heads/master   bar/logs/refs/heads/master