From 14118ef7cd57f515b61e504dffa251b7f9201ca0 Mon Sep 17 00:00:00 2001
From: Dong Bin <14807942+rabbitism@users.noreply.github.com>
Date: Tue, 21 Jul 2026 17:15:15 +0800
Subject: [PATCH] Fix line break enumerator infinite loop (#21808)

* Add failing test: LineBreakEnumerator infinite loop on empty string

* Return false immediately for empty string in LineBreakEnumerator

Empty text has no content and should not produce any line break
opportunities. Short-circuit in MoveNext before entering the
read/rule loop, while keeping the PeekAt EndOfText fix as a
defensive safeguard.
---
 .../Media/TextFormatting/Unicode/LineBreakEnumerator.cs   | 5 +++++
 .../Media/TextFormatting/LineBreakEnumeratorTests.cs      | 8 ++++++++
 2 files changed, 13 insertions(+)

diff --git a/src/Avalonia.Base/Media/TextFormatting/Unicode/LineBreakEnumerator.cs b/src/Avalonia.Base/Media/TextFormatting/Unicode/LineBreakEnumerator.cs
index 576f0ad872..2198a18cd3 100644
--- a/src/Avalonia.Base/Media/TextFormatting/Unicode/LineBreakEnumerator.cs
+++ b/src/Avalonia.Base/Media/TextFormatting/Unicode/LineBreakEnumerator.cs
@@ -24,6 +24,11 @@ namespace Avalonia.Media.TextFormatting.Unicode
         {
             lineBreak = default;
 
+            if (_text.IsEmpty)
+            {
+                return false;
+            }
+
             if (_state.Current.EndOfText)
             {
                 return false;
diff --git a/tests/Avalonia.Base.UnitTests/Media/TextFormatting/LineBreakEnumeratorTests.cs b/tests/Avalonia.Base.UnitTests/Media/TextFormatting/LineBreakEnumeratorTests.cs
index 59ddf6932e..56d346fc59 100644
--- a/tests/Avalonia.Base.UnitTests/Media/TextFormatting/LineBreakEnumeratorTests.cs
+++ b/tests/Avalonia.Base.UnitTests/Media/TextFormatting/LineBreakEnumeratorTests.cs
@@ -19,6 +19,14 @@ namespace Avalonia.Base.UnitTests.Media.TextFormatting
             _outputHelper = outputHelper;
         }
 
+        [Fact]
+        public void ShouldHandleEmptyString()
+        {
+            var lineBreaker = new LineBreakEnumerator(string.Empty);
+
+            Assert.False(lineBreaker.MoveNext(out _));
+        }
+
         [Fact]
         public void BasicLatinTest()
         {