[PATCH] setup: return correct prefix if worktree is '/'

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

The same old problem reappears after setup code is reworked. We tend
to assume there is at least one path component in a path and forget
that path can be simply '/'.

Reported-by: Matthijs Kooijman <matthijs@stdin.nl>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 cache.h |    2 ++
 path.c  |   35 +++++++++++++++++++++++++++++++++++
 setup.c |    5 ++---
 3 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/cache.h b/cache.h
index f765cf5..f579807 100644
--- a/cache.h
+++ b/cache.h
@@ -741,6 +741,8 @@ int longest_ancestor_length(const char *path, const char *prefix_list);
 char *strip_path_suffix(const char *path, const char *suffix);
 int daemon_avoid_alias(const char *path);
 int offset_1st_component(const char *path);
+int is_subdir_or_same(const char *subdir, const char *dir);
+const char *skip_dir(const char *dir, int skip);
 
 /* Read and unpack a sha1 file into memory, write memory to a sha1 file */
 extern int sha1_object_info(const unsigned char *, unsigned long *);
diff --git a/path.c b/path.c
index 4d73cc9..9f77aea 100644
--- a/path.c
+++ b/path.c
@@ -662,3 +662,38 @@ int offset_1st_component(const char *path)
 		return 2 + is_dir_sep(path[2]);
 	return is_dir_sep(path[0]);
 }
+
+/* return 1 if subdir is either dir or inside dir */
+int is_subdir_or_same(const char *subdir, const char *dir)
+{
+	if (!*subdir || !*dir)
+		die("BUG: how can I compare a dir to empty?");
+
+	while (*dir && *subdir && *dir == *subdir) {
+		dir++;
+		subdir++;
+	}
+
+	/* help/me vs hell/yeah */
+	if (*dir && *subdir)
+		return 0;
+
+	if (!*subdir)
+		return !*dir;	/* same dir */
+
+	/* foo/bar vs foo/ */
+	if (is_dir_sep(dir[-1]))
+		return is_dir_sep(subdir[-1]);
+
+	/* foo/bar vs foo */
+	return is_dir_sep(*subdir);
+}
+
+/* skip 'skip' chars and the trailing separator if any */
+const char *skip_dir(const char *dir, int skip)
+{
+	dir += skip;
+	if (is_dir_sep(*dir))
+		dir++;
+	return dir;
+}
diff --git a/setup.c b/setup.c
index 03cd84f..79f8ea7 100644
--- a/setup.c
+++ b/setup.c
@@ -390,15 +390,14 @@ static const char *setup_explicit_git_dir(const char *gitdirenv,
 		return NULL;
 	}
 
-	if (!prefixcmp(cwd, worktree) &&
-	    cwd[strlen(worktree)] == '/') { /* cwd inside worktree */
+	if (is_subdir_or_same(cwd, worktree)) {	/* cwd inside worktree? */
 		set_git_dir(real_path(gitdirenv));
 		if (chdir(worktree))
 			die_errno("Could not chdir to '%s'", worktree);
 		cwd[len++] = '/';
 		cwd[len] = '\0';
 		free(gitfile);
-		return cwd + strlen(worktree) + 1;
+		return skip_dir(cwd, strlen(worktree));
 	}
 
 	/* cwd outside worktree */
-- 
1.7.4.74.g639db