From 9ba6e5283efd2fe454d3bc92eca960b3ebd91294 Mon Sep 17 00:00:00 2001
From: Serguey Parkhomovsky <sergueyparkhomovsky@gmail.com>
Date: Mon, 30 Nov 2015 19:27:32 -0500
Subject: [PATCH] Error on unbalanced parentheses in rules section.

---
 src/scan.l | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/scan.l b/src/scan.l
index 1a0dc8d..bc316be 100644
--- a/src/scan.l
+++ b/src/scan.l
@@ -738,7 +738,13 @@ nmstr[yyleng - 2 - end_is_ws] = '\0';  /* chop trailing brace */
                     return '(';
                 }
     "("         sf_push(); return '(';
-    ")"         sf_pop(); return ')';
+    ")"         {
+                    if (_sf_top_ix > 0) {
+                        sf_pop();
+                        return ')';
+                    } else
+                        synerr(_("unbalanced parenthesis"));
+                }
 
 	[/|*+?.(){}]	return (unsigned char) yytext[0];
 	.		RETURNCHAR;
-- 
2.40.0