From 8fe22dc3eeb6718216565472b74f66992134e135 Mon Sep 17 00:00:00 2001
From: Compunet <117437050+dme-compunet@users.noreply.github.com>
Date: Thu, 9 Jan 2025 15:28:17 +0200
Subject: [PATCH] Fix TextLayout overflow (#17914)

* Update TextLayout only if finalSize is different from _constraint

* Added comment
---
 .../Presenters/TextPresenter.cs                | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/src/Avalonia.Controls/Presenters/TextPresenter.cs b/src/Avalonia.Controls/Presenters/TextPresenter.cs
index 622727ccbe..e0cb22607d 100644
--- a/src/Avalonia.Controls/Presenters/TextPresenter.cs
+++ b/src/Avalonia.Controls/Presenters/TextPresenter.cs
@@ -634,6 +634,8 @@ namespace Avalonia.Controls.Presenters
 
         protected override Size ArrangeOverride(Size finalSize)
         {
+            var finalWidth = finalSize.Width;
+
             var textWidth = Math.Ceiling(TextLayout.OverhangLeading + TextLayout.WidthIncludingTrailingWhitespace + TextLayout.OverhangTrailing);
 
             if (finalSize.Width < textWidth)
@@ -641,15 +643,17 @@ namespace Avalonia.Controls.Presenters
                 finalSize = finalSize.WithWidth(textWidth);
             }
 
-            if (MathUtilities.AreClose(_constraint.Width, finalSize.Width))
+            // Check if the '_constraint' has changed since the last measure,
+            // if so recalculate the TextLayout according to the new size
+            // NOTE: It is important to check this against the actual final size
+            // (excluding the trailing whitespace) to avoid TextLayout overflow.
+            if (MathUtilities.AreClose(_constraint.Width, finalWidth) == false)
             {
-                return finalSize;
-            }
-
-            _constraint = new Size(Math.Ceiling(finalSize.Width), double.PositiveInfinity);
+                _constraint = new Size(Math.Ceiling(finalWidth), double.PositiveInfinity);
 
-            _textLayout?.Dispose();
-            _textLayout = null;
+                _textLayout?.Dispose();
+                _textLayout = null;
+            }
 
             return finalSize;
         }