From 749d32105462ab95380d4af3863d68b371341441 Mon Sep 17 00:00:00 2001
From: Duranka Kalpana <155367493+DuraCode2003@users.noreply.github.com>
Date: Wed, 24 Sep 2025 00:23:36 +0530
Subject: [PATCH] Fix NoSuchElementException in AbstractLexer.endMode()

- Add isEmpty() checks before modeStack.pop() and modeStack.peek()
- Prevents stack underflow during TOML parsing error recovery
- Handles malformed TOML files with invalid escape sequences gracefully

Fixes #44268
---
 .../io/ballerina/toml/internal/parser/AbstractLexer.java  | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/misc/toml-parser/src/main/java/io/ballerina/toml/internal/parser/AbstractLexer.java b/misc/toml-parser/src/main/java/io/ballerina/toml/internal/parser/AbstractLexer.java
index 0f2e0b5a2089..481af21868da 100644
--- a/misc/toml-parser/src/main/java/io/ballerina/toml/internal/parser/AbstractLexer.java
+++ b/misc/toml-parser/src/main/java/io/ballerina/toml/internal/parser/AbstractLexer.java
@@ -99,8 +99,12 @@ public void switchMode(ParserMode mode) {
      * End the current mode the mode of the lexer and fall back the previous mode.
      */
     public void endMode() {
-        this.modeStack.pop();
-        this.mode = this.modeStack.peek();
+        if (!this.modeStack.isEmpty()) {
+            this.modeStack.pop();
+            if (!this.modeStack.isEmpty()) {
+                this.mode = this.modeStack.peek();
+            }
+        }
     }
 
     private void resetDiagnosticList() {