sha1_file: let for_each_file_in_obj_subdir() handle subdir names

The function for_each_file_in_obj_subdir() takes a object subdirectory
number and expects the name of the same subdirectory to be included in
the path strbuf.  Avoid this redundancy by letting the function append
the hexadecimal subdirectory name itself.  This makes it a bit easier
and safer to use the function -- it becomes impossible to specify
different subdirectories in subdir_nr and path.

Suggested-by: Jeff King <peff@peff.net>
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sha1_file.c

@@ -3742,15 +3742,22 @@ int for_each_file_in_obj_subdir(int subdir_nr,
 				each_loose_subdir_fn subdir_cb,
 				void *data)
 {
-	size_t baselen = path->len;
-	DIR *dir = opendir(path->buf);
+	size_t origlen, baselen;
+	DIR *dir;
 	struct dirent *de;
 	int r = 0;
 
+	origlen = path->len;
+	strbuf_complete(path, '/');
+	strbuf_addf(path, "%02x", subdir_nr);
+	baselen = path->len;
+
+	dir = opendir(path->buf);
 	if (!dir) {
-		if (errno == ENOENT)
-			return 0;
-		return error_errno("unable to open %s", path->buf);
+		if (errno != ENOENT)
+			r = error_errno("unable to open %s", path->buf);
+		strbuf_setlen(path, origlen);
+		return r;
 	}
 
 	while ((de = readdir(dir))) {
@@ -3788,6 +3795,8 @@ int for_each_file_in_obj_subdir(int subdir_nr,
 	if (!r && subdir_cb)
 		r = subdir_cb(subdir_nr, path->buf, data);
 
+	strbuf_setlen(path, origlen);
+
 	return r;
 }
 
@@ -3797,15 +3806,12 @@ int for_each_loose_file_in_objdir_buf(struct strbuf *path,
 			    each_loose_subdir_fn subdir_cb,
 			    void *data)
 {
-	size_t baselen = path->len;
 	int r = 0;
 	int i;
 
 	for (i = 0; i < 256; i++) {
-		strbuf_addf(path, "/%02x", i);
 		r = for_each_file_in_obj_subdir(i, path, obj_cb, cruft_cb,
 						subdir_cb, data);
-		strbuf_setlen(path, baselen);
 		if (r)
 			break;
 	}

sha1_name.c

@@ -109,7 +109,6 @@ static void find_short_object_filename(struct disambiguate_state *ds)
 
 		if (!alt->loose_objects_subdir_seen[subdir_nr]) {
 			struct strbuf *buf = alt_scratch_buf(alt);
-			strbuf_addf(buf, "%02x/", subdir_nr);
 			for_each_file_in_obj_subdir(subdir_nr, buf,
 						    append_loose_object,
 						    NULL, NULL,