[Win] Labels will now wrap when inside horizontally infinite layouts (#639)

* Add repro for 42559

* [Win] Override GetDesiredSize for LabelRenderer

* [Win] Invalidate size on font/align change

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Bugzilla42599.cs

@@ -0,0 +1,67 @@
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+using System.Linq;
+using System;
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Bugzilla, 42599, "LineBreakMode does not work on UWP", PlatformAffected.WinRT)]
+	public class Bugzilla42599 : TestContentPage
+	{
+		protected override void Init()
+		{
+			var scrollView = new ScrollView();
+			var layout = new StackLayout();
+
+			foreach (var lineBreakMode in Enum.GetValues(typeof(LineBreakMode)).Cast<LineBreakMode>())
+			{
+				layout.Children.Add(GetLayout(lineBreakMode));
+			}
+			scrollView.Content = layout;
+			Content = scrollView;
+		}
+
+		static StackLayout GetLayout(LineBreakMode lineBreakMode)
+		{
+			var text = "";
+
+			switch (lineBreakMode)
+			{
+				default:
+				case LineBreakMode.NoWrap:
+					text = "This is a long sentence that should NOT wrap. If this sentence has wrapped, then this test has failed.";
+					break;
+				case LineBreakMode.WordWrap:
+					text = "This is a long sentence that should word wrap. If this sentence has NOT wrapped, then this test has failed.";
+					break;
+				case LineBreakMode.CharacterWrap:
+					text = "This is a long sentence that should character wrap. If this sentence has NOT wrapped, then this test has failed.";
+					break;
+				case LineBreakMode.HeadTruncation:
+					text = "This is a long sentence that should truncate at the beginning. If this sentence has NOT truncated, then this test has failed.";
+					break;
+				case LineBreakMode.TailTruncation:
+					text = "This is a long sentence that should truncate at the end. If this sentence has NOT truncated, then this test has failed.";
+					break;
+				case LineBreakMode.MiddleTruncation:
+					text = "This is a long sentence that should truncate at the middle. If this sentence has NOT truncated, then this test has failed.";
+					break;
+			}
+
+			var label = new Label
+			{
+				LineBreakMode = lineBreakMode,
+				Text = text,
+			};
+
+			var layout = new StackLayout
+			{
+				Children = { label },
+				Orientation = StackOrientation.Horizontal
+			};
+
+			return layout;
+		}
+	}
+}

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems

@@ -251,6 +251,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla28650.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla37431.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla44777.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Bugzilla42599.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla51503.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla51505.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla52533.cs" />

Xamarin.Forms.Platform.WinRT/LabelRenderer.cs

@@ -35,6 +35,8 @@ namespace Xamarin.Forms.Platform.WinRT
 	{
 		bool _fontApplied;
 		bool _isInitiallyDefault;
+		SizeRequest _perfectSize;
+		bool _perfectSizeValid;
 
 		protected override Windows.Foundation.Size ArrangeOverride(Windows.Foundation.Size finalSize)
 		{
@@ -61,6 +63,29 @@ namespace Xamarin.Forms.Platform.WinRT
 			return finalSize;
 		}
 
+		public override SizeRequest GetDesiredSize(double widthConstraint, double heightConstraint)
+		{
+			if (!_perfectSizeValid)
+			{
+				_perfectSize = base.GetDesiredSize(double.PositiveInfinity, double.PositiveInfinity);
+				_perfectSize.Minimum = new Size(Math.Min(10, _perfectSize.Request.Width), _perfectSize.Request.Height);
+				_perfectSizeValid = true;
+			}
+
+			if (widthConstraint >= _perfectSize.Request.Width && heightConstraint >= _perfectSize.Request.Height)
+				return _perfectSize;
+
+			var result = base.GetDesiredSize(widthConstraint, heightConstraint);
+			result.Minimum = new Size(Math.Min(10, result.Request.Width), result.Request.Height);
+			if (Element.LineBreakMode != LineBreakMode.NoWrap)
+			{
+				if (result.Request.Width > widthConstraint || Element.LineBreakMode == LineBreakMode.WordWrap || Element.LineBreakMode == LineBreakMode.CharacterWrap)
+					result.Request = new Size(Math.Max(result.Minimum.Width, widthConstraint), result.Request.Height);
+			}
+
+			return result;
+		}
+
 		protected override void OnElementChanged(ElementChangedEventArgs<Label> e)
 		{
 			base.OnElementChanged(e);
@@ -100,6 +125,8 @@ namespace Xamarin.Forms.Platform.WinRT
 
 		void UpdateAlign(TextBlock textBlock)
 		{
+			_perfectSizeValid = false;
+
 			if (textBlock == null)
 				return;
 
@@ -129,6 +156,8 @@ namespace Xamarin.Forms.Platform.WinRT
 
 		void UpdateFont(TextBlock textBlock)
 		{
+			_perfectSizeValid = false;
+
 			if (textBlock == null)
 				return;
 
@@ -146,6 +175,8 @@ namespace Xamarin.Forms.Platform.WinRT
 
 		void UpdateLineBreakMode(TextBlock textBlock)
 		{
+			_perfectSizeValid = false;
+
 			if (textBlock == null)
 				return;
 
@@ -164,6 +195,7 @@ namespace Xamarin.Forms.Platform.WinRT
 					textBlock.TextWrapping = TextWrapping.Wrap;
 					break;
 				case LineBreakMode.HeadTruncation:
+					// TODO: This truncates at the end.
 					textBlock.TextTrimming = TextTrimming.WordEllipsis;
 					textBlock.TextWrapping = TextWrapping.NoWrap;
 					break;
@@ -172,6 +204,7 @@ namespace Xamarin.Forms.Platform.WinRT
 					textBlock.TextWrapping = TextWrapping.NoWrap;
 					break;
 				case LineBreakMode.MiddleTruncation:
+					// TODO: This truncates at the end.
 					textBlock.TextTrimming = TextTrimming.WordEllipsis;
 					textBlock.TextWrapping = TextWrapping.NoWrap;
 					break;
@@ -182,6 +215,8 @@ namespace Xamarin.Forms.Platform.WinRT
 
 		void UpdateText(TextBlock textBlock)
 		{
+			_perfectSizeValid = false;
+
 			if (textBlock == null)
 				return;