From 08a3dd0da6c1c73e793f545bb0b3bb3665dc44be Mon Sep 17 00:00:00 2001
From: ManthanNimodiya <manthannimodiya989898@gmail.com>
Date: Fri, 19 Jun 2026 06:34:55 +0530
Subject: [PATCH] fix(dsl): prevent lexer panic on string ending in trailing
 backslash

---
 pkg/dsl/lexer/lexer.go      |  6 ++++++
 pkg/dsl/lexer/lexer_test.go | 16 ++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/pkg/dsl/lexer/lexer.go b/pkg/dsl/lexer/lexer.go
index 5a8b38fe4..c9927709e 100644
--- a/pkg/dsl/lexer/lexer.go
+++ b/pkg/dsl/lexer/lexer.go
@@ -212,6 +212,12 @@ func (l *Lexer) lexString() string {
 		if l.ch == '\\' {
 			str += l.input[position:l.position]
 			l.readChar() // Skip the backslash
+			if l.ch == 0 {
+				// Unterminated string: input ended right after a trailing
+				// backslash, so there's no character left to escape.
+				position = l.position
+				break
+			}
 			switch l.ch {
 			case 'n':
 				str += "\n"
diff --git a/pkg/dsl/lexer/lexer_test.go b/pkg/dsl/lexer/lexer_test.go
index 969054738..eef2f2212 100644
--- a/pkg/dsl/lexer/lexer_test.go
+++ b/pkg/dsl/lexer/lexer_test.go
@@ -1189,4 +1189,20 @@ rule test_rule(created_at time, started_at time) {
 		Expect(hasBoolean).Should(BeTrue())
 		Expect(hasComparison).Should(BeTrue())
 	})
+
+	It("Case 11 - Unterminated string ending in a trailing backslash should not panic", func() {
+		// Regression test: a string literal that ends right after a backslash
+		// (no character left to escape) used to overshoot the input bounds
+		// and panic with a slice-out-of-range error.
+		l := NewLexer("\"\\")
+
+		Expect(func() {
+			for {
+				tok := l.NextToken()
+				if tok.Type == token.EOF {
+					break
+				}
+			}
+		}).ShouldNot(Panic())
+	})
 })