[PATCH v5 06/30] refs.c: make update_ref_write update a strbuf on failure

@@ -3253,10 +3253,13 @@ static struct ref_lock *update_ref_lock(const char *refname,
 
 static int update_ref_write(const char *action, const char *refname,
 			    const unsigned char *sha1, struct ref_lock *lock,
-			    enum action_on_err onerr)
+			    struct strbuf *err, enum action_on_err onerr)
 {
 	if (write_ref_sha1(lock, sha1, action) < 0) {
 		const char *str = "Cannot update the ref '%s'.";
+		if (err)
+			strbuf_addf(err, str, refname);
+
 		switch (onerr) {
 		case UPDATE_REFS_MSG_ON_ERR: error(str, refname); break;
 		case UPDATE_REFS_DIE_ON_ERR: die(str, refname); break;

@@ -3382,7 +3385,7 @@ int update_ref(const char *action, const char *refname,
 	lock = update_ref_lock(refname, oldval, flags, NULL, onerr);
 	if (!lock)
 		return 1;
-	return update_ref_write(action, refname, sha1, lock, onerr);
+	return update_ref_write(action, refname, sha1, lock, NULL, onerr);
 }
 
 static int ref_update_compare(const void *r1, const void *r2)

@@ -3464,7 +3467,7 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 			ret = update_ref_write(msg,
 					       update->refname,
 					       update->new_sha1,
-					       update->lock, onerr);
+					       update->lock, err, onerr);
 			update->lock = NULL; /* freed by update_ref_write */
 			if (ret)
 				goto cleanup;