builtin/fsck: add git refs verify child process

At now, we have already implemented the ref consistency checks for both
"files-backend" and "packed-backend". Although we would check some
redundant things, it won't cause trouble. So, let's integrate it into
the "git-fsck(1)" command to get feedback from the users. And also by
calling "git refs verify" in "git-fsck(1)", we make sure that the new
added checks don't break.

Introduce a new function "fsck_refs" that initializes and runs a child
process to execute the "git refs verify" command. In order to provide
the user interface create a progress which makes the total task be 1.
It's hard to know how many loose refs we will check now. We might
improve this later.

And we run this function in the first execution sequence of
"git-fsck(1)" because we don't want the existing code of "git-fsck(1)"
which implicitly checks the consistency of refs to die the program.

Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fsck.c

@@ -902,6 +902,32 @@ static int check_pack_rev_indexes(struct repository *r, int show_progress)
 	return res;
 }
 
+static void fsck_refs(void)
+{
+	struct child_process refs_verify = CHILD_PROCESS_INIT;
+	struct progress *progress = NULL;
+
+	if (show_progress)
+		progress = start_progress(_("Checking ref database"), 1);
+
+	if (verbose)
+		fprintf_ln(stderr, _("Checking ref database"));
+
+	child_process_init(&refs_verify);
+	refs_verify.git_cmd = 1;
+	strvec_pushl(&refs_verify.args, "refs", "verify", NULL);
+	if (verbose)
+		strvec_push(&refs_verify.args, "--verbose");
+	if (check_strict)
+		strvec_push(&refs_verify.args, "--strict");
+
+	if (run_command(&refs_verify))
+		errors_found |= ERROR_REFS;
+
+	display_progress(progress, 1);
+	stop_progress(&progress);
+}
+
 static char const * const fsck_usage[] = {
 	N_("git fsck [--tags] [--root] [--unreachable] [--cache] [--no-reflogs]\n"
 	   "         [--[no-]full] [--strict] [--verbose] [--lost-found]\n"
@@ -967,6 +993,8 @@ int cmd_fsck(int argc,
 	git_config(git_fsck_config, &fsck_obj_options);
 	prepare_repo_settings(the_repository);
 
+	fsck_refs();
+
 	if (connectivity_only) {
 		for_each_loose_object(mark_loose_for_connectivity, NULL, 0);
 		for_each_packed_object(the_repository,