From a24e9a933ff71ff6287d03bb7c0d60e1b1633c48 Mon Sep 17 00:00:00 2001
From: Michael Petter <petter@cs.tum.edu>
Date: Thu, 25 Mar 2021 11:46:30 +0100
Subject: [PATCH] added an error for duplicate labels

---
 src/cup/parser.cup | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/cup/parser.cup b/src/cup/parser.cup
index e805de3..ba5bb1c 100644
--- a/src/cup/parser.cup
+++ b/src/cup/parser.cup
@@ -124,7 +124,9 @@ action code {:
       if (rhs_pos >= MAX_RHS)
 	throw new Exception("Internal Error: Productions limited to " + 
 			     MAX_RHS + " symbols and actions"); 
-
+	  for (int i=0;i<rhs_pos;i++)
+	  	if (part.label()!=null && part.label().equals(rhs_parts[i].label()))
+		  this.parser.report_error("Label '"+part.label()+"' for symbol #"+rhs_pos+" already used for symbol #"+i+"; compilation will fail",parser.stack.peek());
       rhs_parts[rhs_pos] = part;
       rhs_pos++;
     }
-- 
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