setup: allow check_repository_format to read repository format

In some cases, we will want to not only check the repository format, but
extract the information that we've gained.  To do so, allow
check_repository_format to take a pointer to struct repository_format.
Allow passing NULL for this argument if we're not interested in the
information, and pass NULL for all existing callers.  A future patch
will make use of this information.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/init-db.c

@@ -378,7 +378,7 @@ int init_db(const char *git_dir, const char *real_git_dir,
 	 * config file, so this will not fail.  What we are catching
 	 * is an attempt to reinitialize new repository with an old tool.
 	 */
-	check_repository_format();
+	check_repository_format(NULL);
 
 	reinit = create_default_files(template_dir, original_git_dir);
 

cache.h

@@ -1086,8 +1086,10 @@ int verify_repository_format(const struct repository_format *format,
  * and die if it is a version we don't understand. Generally one would
  * set_git_dir() before calling this, and use it only for "are we in a valid
  * repo?".
+ *
+ * If successful and fmt is not NULL, fill fmt with data.
  */
-void check_repository_format(void);
+void check_repository_format(struct repository_format *fmt);
 
 #define MTIME_CHANGED	0x0001
 #define CTIME_CHANGED	0x0002

path.c

@@ -851,7 +851,7 @@ const char *enter_repo(const char *path, int strict)
 
 	if (is_git_directory(".")) {
 		set_git_dir(".");
-		check_repository_format();
+		check_repository_format(NULL);
 		return path;
 	}
 

setup.c

@@ -1253,10 +1253,12 @@ int git_config_perm(const char *var, const char *value)
 	return -(i & 0666);
 }
 
-void check_repository_format(void)
+void check_repository_format(struct repository_format *fmt)
 {
 	struct repository_format repo_fmt = REPOSITORY_FORMAT_INIT;
-	check_repository_format_gently(get_git_dir(), &repo_fmt, NULL);
+	if (!fmt)
+		fmt = &repo_fmt;
+	check_repository_format_gently(get_git_dir(), fmt, NULL);
 	startup_info->have_repository = 1;
 	clear_repository_format(&repo_fmt);
 }