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

path.c

@@ -103,7 +103,8 @@ static void update_common_dir(struct strbuf *buf, int git_dir_len)
 	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

@@ -270,6 +270,7 @@ test_git_path GIT_COMMON_DIR=bar objects                  bar/objects
 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