git-reflog: add option --updateref to write the last reflog sha1 into…

… the ref

Certain sanity checks on the reflog assume that the sha1 of the top reflog
entry will be equal to the sha1 stored in the ref.

When reflog entries are deleted, this assumption may not hold. This patch
adds a new option to git-reflog which causes the subcommands "expire" and
"delete" to update the ref with the sha1 of the top-most reflog entry.

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-reflog.c

@@ -15,7 +15,7 @@
 static const char reflog_expire_usage[] =
 "git-reflog (show|expire) [--verbose] [--dry-run] [--stale-fix] [--expire=<time>] [--expire-unreachable=<time>] [--all] <refs>...";
 static const char reflog_delete_usage[] =
-"git-reflog delete [--verbose] [--dry-run] [--rewrite] <refs>...";
+"git-reflog delete [--verbose] [--dry-run] [--rewrite] [--updateref] <refs>...";
 
 static unsigned long default_reflog_expire;
 static unsigned long default_reflog_expire_unreachable;
@@ -25,6 +25,7 @@ struct cmd_reflog_expire_cb {
 	int dry_run;
 	int stalefix;
 	int rewrite;
+	int updateref;
 	int verbose;
 	unsigned long expire_total;
 	unsigned long expire_unreachable;
@@ -292,10 +293,20 @@ static int expire_reflog(const char *ref, const unsigned char *sha1, int unused,
 			status |= error("%s: %s", strerror(errno),
 					newlog_path);
 			unlink(newlog_path);
+		} else if (cmd->updateref &&
+			(write_in_full(lock->lock_fd,
+				sha1_to_hex(cb.last_kept_sha1), 40) != 40 ||
+			 write_in_full(lock->lock_fd, "\n", 1) != 1 ||
+			 close_ref(lock) < 0)) {
+			status |= error("Couldn't write %s",
+				lock->lk->filename);
+			unlink(newlog_path);
 		} else if (rename(newlog_path, log_file)) {
 			status |= error("cannot rename %s to %s",
 					newlog_path, log_file);
 			unlink(newlog_path);
+		} else if (cmd->updateref && commit_ref(lock)) {
+			status |= error("Couldn't set %s", lock->ref_name);
 		}
 	}
 	free(newlog_path);
@@ -372,6 +383,8 @@ static int cmd_reflog_expire(int argc, const char **argv, const char *prefix)
 			cb.stalefix = 1;
 		else if (!strcmp(arg, "--rewrite"))
 			cb.rewrite = 1;
+		else if (!strcmp(arg, "--updateref"))
+			cb.updateref = 1;
 		else if (!strcmp(arg, "--all"))
 			do_all = 1;
 		else if (!strcmp(arg, "--verbose"))
@@ -443,6 +456,8 @@ static int cmd_reflog_delete(int argc, const char **argv, const char *prefix)
 			cb.dry_run = 1;
 		else if (!strcmp(arg, "--rewrite"))
 			cb.rewrite = 1;
+		else if (!strcmp(arg, "--updateref"))
+			cb.updateref = 1;
 		else if (!strcmp(arg, "--verbose"))
 			cb.verbose = 1;
 		else if (!strcmp(arg, "--")) {