[XSG] Handle NaN values in ThicknessConverter

src/Controls/src/SourceGen/TypeConverters/ThicknessConverter.cs

@@ -26,36 +26,79 @@ public string Convert(string value, BaseNode node, ITypeSymbol toType, IndentedT
 				switch (thickness.Length)
 				{
 					case 2:
-						if (double.TryParse(thickness[0], NumberStyles.Number, CultureInfo.InvariantCulture, out double h)
-							&& double.TryParse(thickness[1], NumberStyles.Number, CultureInfo.InvariantCulture, out double v))
+						if (TryParseDouble(thickness[0], out double h)
+							&& TryParseDouble(thickness[1], out double v))
 						{
 							var thicknessType = context.Compilation.GetTypeByMetadataName("Microsoft.Maui.Thickness")!;
-							return $"new {thicknessType.ToFQDisplayString()}({FormatInvariant(h)}, {FormatInvariant(v)})";
+							return $"new {thicknessType.ToFQDisplayString()}({FormatDouble(h)}, {FormatDouble(v)})";
 						}
 						break;
 					case 4:
-						if (double.TryParse(thickness[0], NumberStyles.Number, CultureInfo.InvariantCulture, out double l)
-							&& double.TryParse(thickness[1], NumberStyles.Number, CultureInfo.InvariantCulture, out double t)
-							&& double.TryParse(thickness[2], NumberStyles.Number, CultureInfo.InvariantCulture, out double r)
-							&& double.TryParse(thickness[3], NumberStyles.Number, CultureInfo.InvariantCulture, out double b))
+						if (TryParseDouble(thickness[0], out double l)
+							&& TryParseDouble(thickness[1], out double t)
+							&& TryParseDouble(thickness[2], out double r)
+							&& TryParseDouble(thickness[3], out double b))
 						{
 							var thicknessType = context.Compilation.GetTypeByMetadataName("Microsoft.Maui.Thickness")!;
-							return $"new {thicknessType.ToFQDisplayString()}({FormatInvariant(l)}, {FormatInvariant(t)}, {FormatInvariant(r)}, {FormatInvariant(b)})";
+							return $"new {thicknessType.ToFQDisplayString()}({FormatDouble(l)}, {FormatDouble(t)}, {FormatDouble(r)}, {FormatDouble(b)})";
 						}
 						break;
 				}
 			}
 			else
 			{ //single uniform thickness
-				if (double.TryParse(value, NumberStyles.Number, CultureInfo.InvariantCulture, out double l))
+				if (TryParseDouble(value, out double l))
 				{
 					var thicknessType = context.Compilation.GetTypeByMetadataName("Microsoft.Maui.Thickness")!;
-					return $"new {thicknessType.ToFQDisplayString()}({FormatInvariant(l)})";
+					return $"new {thicknessType.ToFQDisplayString()}({FormatDouble(l)})";
 				}
 			}
 		}
 
 		context.ReportConversionFailed(xmlLineInfo, value, Descriptors.ThicknessConversionFailed);
 		return "default";
 	}
+
+	/// <summary>
+	/// Tries to parse a double value, including special values like NaN, Infinity, -Infinity.
+	/// </summary>
+	static bool TryParseDouble(string value, out double result)
+	{
+		value = value.Trim();
+
+		// Handle special values that NumberStyles.Number doesn't parse
+		if (value.Equals("NaN", System.StringComparison.OrdinalIgnoreCase))
+		{
+			result = double.NaN;
+			return true;
+		}
+		if (value.Equals("Infinity", System.StringComparison.OrdinalIgnoreCase) ||
+			value.Equals("+Infinity", System.StringComparison.OrdinalIgnoreCase))
+		{
+			result = double.PositiveInfinity;
+			return true;
+		}
+		if (value.Equals("-Infinity", System.StringComparison.OrdinalIgnoreCase))
+		{
+			result = double.NegativeInfinity;
+			return true;
+		}
+
+		return double.TryParse(value, NumberStyles.Number, CultureInfo.InvariantCulture, out result);
+	}
+
+	/// <summary>
+	/// Formats a double value for C# code generation, handling special values.
+	/// </summary>
+	static string FormatDouble(double value)
+	{
+		if (double.IsNaN(value))
+			return "double.NaN";
+		if (double.IsPositiveInfinity(value))
+			return "double.PositiveInfinity";
+		if (double.IsNegativeInfinity(value))
+			return "double.NegativeInfinity";
+
+		return FormatInvariant(value);
+	}
 }

src/Controls/tests/Xaml.UnitTests/Issues/Maui33871.xaml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+			 xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+			 x:Class="Microsoft.Maui.Controls.Xaml.UnitTests.Maui33871">
+	<!-- Test: Thickness type converter should handle NaN values -->
+	<Button x:Name="nanButton" Text="NaN Padding" Padding="NaN"/>
+</ContentPage>

src/Controls/tests/Xaml.UnitTests/Issues/Maui33871.xaml.cs

@@ -0,0 +1,30 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+using Xunit;
+
+namespace Microsoft.Maui.Controls.Xaml.UnitTests;
+
+public partial class Maui33871 : ContentPage
+{
+	public Maui33871() => InitializeComponent();
+
+	[Collection("Issue")]
+	public class Tests
+	{
+		[Theory]
+		[XamlInflatorData]
+		internal void ThicknessConverterHandlesNaN(XamlInflator inflator)
+		{
+			// This test reproduces issue #33871:
+			// XSG fails to parse Padding="NaN" which creates a Thickness with all NaN values.
+			// This is used by Button to indicate "use platform default padding".
+			var page = new Maui33871(inflator);
+
+			Assert.NotNull(page);
+			Assert.NotNull(page.nanButton);
+
+			// Verify the padding was parsed correctly as NaN
+			Assert.True(page.nanButton.Padding.IsNaN);
+		}
+	}
+}