Reverts "[Xaml] require escaping curly braces (#4723)" and "[X] only require escaping if starts with '{' (#5169)" (#5424)

* Revert "[X] only require escaping if starts with '{' (#5169)"

This reverts commit cd73391c3a.

* Revert "[Xaml] require escaping curly braces (#4723)"

This reverts commit 6753ace40e.

* Make sure parsing doesn't fail when there *are* curly braces now

Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/EmptyViewGalleries/EmptyViewTemplateGallery.xaml

@@ -20,7 +20,7 @@
 						<StackLayout> 
 							<Label FontAttributes="Bold" FontSize="18" Margin="10,25,10,10"
 									HorizontalOptions="Fill" HorizontalTextAlignment="Center" 
-									Text="{Binding Filter, StringFormat='{}Your filter term of {0} did not match any records'}"></Label>
+									Text="{Binding Filter, StringFormat='Your filter term of {0} did not match any records'}"></Label>
 						</StackLayout>
 					</DataTemplate>
 				</CollectionView.EmptyViewTemplate>

Xamarin.Forms.Xaml.UnitTests/Issues/Gh2756.xaml

@@ -1,10 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<ContentPage
-        xmlns="http://xamarin.com/schemas/2014/forms"
-        xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
-        x:Class="Xamarin.Forms.Xaml.UnitTests.Gh2756">
-    <StackLayout>
-        <Label Text="{Binding Color.R, StringFormat='R = {0:F2}'}"/> <!-- should parse -->
-        <Label Text="{Binding Path=StartTime, StringFormat='{0:yy-MM-dd}'}"/> <!-- should throw -->
-    </StackLayout>
-</ContentPage>

Xamarin.Forms.Xaml.UnitTests/Issues/Gh2756.xaml.cs

@@ -1,34 +0,0 @@
-using NUnit.Framework;
-
-using Xamarin.Forms.Core.UnitTests;
-
-using Xamarin.Forms;
-
-namespace Xamarin.Forms.Xaml.UnitTests
-{
-	[XamlCompilation(XamlCompilationOptions.Skip)]
-	public partial class Gh2756 : ContentPage
-	{
-		public Gh2756() => InitializeComponent();
-		public Gh2756(bool useCompiledXaml)
-		{
-			//this stub will be replaced at compile time
-		}
-
-		[TestFixture]
-		class Tests
-		{
-			[SetUp] public void Setup() => Device.PlatformServices = new MockPlatformServices();
-			[TearDown] public void TearDown() => Device.PlatformServices = null;
-
-			[Test]
-			public void UnescapedBraces([Values(false, true)]bool useCompiledXaml)
-			{
-				if (useCompiledXaml)
-					Assert.Throws(new XamlParseExceptionConstraint(8, 16), () => MockCompiler.Compile(typeof(Gh2756)));
-				else
-					Assert.Throws(new XamlParseExceptionConstraint(8, 16), () => new Gh2756(useCompiledXaml));
-			}
-		}
-	}
-}

Xamarin.Forms.Xaml.UnitTests/Issues/Issue1438.xaml

@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="UTF-8"?>
+<?xml version="1.0" encoding="UTF-8"?>
 <ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
 			 xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
 			 x:Class="Xamarin.Forms.Xaml.UnitTests.Issue1438">

Xamarin.Forms.Xaml.UnitTests/Issues/Issue1549.cs

@@ -82,7 +82,7 @@ xmlns=""http://xamarin.com/schemas/2014/forms""
 <local:SeverityColorConverter x:Key=""SeverityColorConverter"" />
 </ResourceDictionary>
 </ContentPage.Resources>
-				<Label Text=""{Binding value, StringFormat='{}{0}'}"" 
+				<Label Text=""{Binding value, StringFormat='{0}'}"" 
 					WidthRequest=""50"" 
 					TextColor=""Black""
 					x:Name=""label""
@@ -97,6 +97,35 @@ xmlns=""http://xamarin.com/schemas/2014/forms""
 			Assert.AreEqual (1, SeverityColorConverter.count);
 		}
 
+		[Test]
+		public void ConverterIsInvoked_Escaped()
+		{
+			var xaml = @"
+<ContentPage 							
+xmlns=""http://xamarin.com/schemas/2014/forms"" 
+							xmlns:x=""http://schemas.microsoft.com/winfx/2009/xaml""
+							xmlns:local=""clr-namespace:Xamarin.Forms.Xaml.UnitTests;assembly=Xamarin.Forms.Xaml.UnitTests"">
+
+<ContentPage.Resources>
+<ResourceDictionary>
+<local:SeverityColorConverter x:Key=""SeverityColorConverter"" />
+</ResourceDictionary>
+</ContentPage.Resources>
+				<Label Text=""{Binding value, StringFormat='{}{0}'}"" 
+					WidthRequest=""50"" 
+					TextColor=""Black""
+					x:Name=""label""
+					BackgroundColor=""{Binding Severity, Converter={StaticResource SeverityColorConverter}}""
+					XAlign=""Center"" YAlign=""Center""/>
+</ContentPage>";
+
+			var layout = new ContentPage().LoadFromXaml(xaml);
+			layout.BindingContext = new { Value = "Foo", Severity = "Bar" };
+			var label = layout.FindByName<Label>("label");
+			Assert.AreEqual(Color.Blue, label.BackgroundColor);
+			Assert.AreEqual(1, SeverityColorConverter.count);
+		}
+
 		[Test]
 		public void ResourcesInNonXFBaseClassesAreFound ()
 		{

Xamarin.Forms.Xaml.UnitTests/MarkupExpressionParserTests.cs

@@ -248,25 +248,17 @@ namespace Xamarin.Forms.Xaml.UnitTests
 		}
 
 		[Test]
-		public void NonStartingBracesDoNotNeedToBeEscaped()
+		public void BindingStringFormatWithoutEscaping ()
 		{
-			var bindingString = "{Binding Foo, StringFormat='Hello {0}'}";
+			var bindingString = "{Binding Foo, StringFormat='{0,20}'}";
 
-			Assert.DoesNotThrow(() => new MarkupExtensionParser().ParseExpression(ref bindingString, new Internals.XamlServiceProvider(null, null)
-			{
+			var binding = (new MarkupExtensionParser ()).ParseExpression (ref bindingString, new Internals.XamlServiceProvider (null, null) {
 				IXamlTypeResolver = typeResolver,
-			}));
-		}
+			});
 
-		[Test]
-		public void BracesNeedsToBeEscaped2()
-		{
-			var bindingString = "{Binding Foo, StringFormat='{0}'}";
-
-			Assert.Throws<XamlParseException>(() => new MarkupExtensionParser().ParseExpression(ref bindingString, new Internals.XamlServiceProvider(null, null)
-			{
-				IXamlTypeResolver = typeResolver,
-			}));
+			Assert.That (binding, Is.InstanceOf<Binding> ());
+			Assert.AreEqual ("Foo", ((Binding)binding).Path);
+			Assert.AreEqual ("{0,20}", ((Binding)binding).StringFormat);
 		}
 
 		[Test]

Xamarin.Forms.Xaml/MarkupExpressionParser.cs

@@ -46,10 +46,7 @@ namespace Xamarin.Forms.Xaml
 				return expression.Substring(2);
 
 			if (expression[expression.Length - 1] != '}')
-			{
-				var lineInfo = (serviceProvider.GetService(typeof(IXmlLineInfoProvider)) as IXmlLineInfoProvider != null) ? (serviceProvider.GetService(typeof(IXmlLineInfoProvider)) as IXmlLineInfoProvider).XmlLineInfo : new XmlLineInfo();
-				throw new XamlParseException("Expression must end with '}'", lineInfo);
-			}
+				throw new Exception("Expression must end with '}'");
 
 			int len;
 			string match;
@@ -117,6 +114,7 @@ namespace Xamarin.Forms.Xaml
 
 		protected void HandleProperty(string prop, IServiceProvider serviceProvider, ref string remaining, bool isImplicit)
 		{
+			char next;
 			object value = null;
 			string str_value;
 
@@ -139,13 +137,7 @@ namespace Xamarin.Forms.Xaml
 				str_value = value as string;
 			}
 			else
-				str_value = GetNextPiece(ref remaining, out var next);
-
-			if (str_value != null && !str_value.StartsWith("{}", StringComparison.Ordinal) && str_value.Length > 2 && str_value.StartsWith("{", StringComparison.Ordinal))
-			{
-				var lineInfo = (serviceProvider.GetService(typeof(IXmlLineInfoProvider)) as IXmlLineInfoProvider != null) ? (serviceProvider.GetService(typeof(IXmlLineInfoProvider)) as IXmlLineInfoProvider).XmlLineInfo : new XmlLineInfo();
-				throw new XamlParseException("Strings starting with `{` needs to be escaped. Start the string with `{}`", lineInfo);
-			}
+				str_value = GetNextPiece(ref remaining, out next);
 
 			SetPropertyValue(prop, str_value, value, serviceProvider);
 		}

Xamarin.Forms.Xaml/MarkupExtensionParser.cs

@@ -5,31 +5,27 @@ namespace Xamarin.Forms.Xaml
 {
 	internal sealed class MarkupExtensionParser : MarkupExpressionParser, IExpressionParser<object>
 	{
-		IMarkupExtension _markupExtension;
+		IMarkupExtension markupExtension;
 
 		public object Parse(string match, ref string remaining, IServiceProvider serviceProvider)
 		{
 			var typeResolver = serviceProvider.GetService(typeof (IXamlTypeResolver)) as IXamlTypeResolver;
-			switch (match) {
-			case "Binding":
-				_markupExtension = new BindingExtension();
-				break;
-			case "TemplateBinding":
-				_markupExtension = new TemplateBindingExtension();
-				break;
-			case "StaticResource":
-				_markupExtension = new StaticResourceExtension();
-				break;
-			case "OnPlatform":
-				_markupExtension = new OnPlatformExtension();
-				break;
-			case "OnIdiom":
-				_markupExtension = new OnIdiomExtension();
-				break;
-			case "DataTemplate":
-				_markupExtension = new DataTemplateExtension();
-				break;
-			default:
+
+			//shortcut for Binding and StaticResource, to avoid too many reflection calls.
+			if (match == "Binding")
+				markupExtension = new BindingExtension();
+			else if (match == "TemplateBinding")
+				markupExtension = new TemplateBindingExtension();
+			else if (match == "StaticResource")
+				markupExtension = new StaticResourceExtension();
+			else if (match == "OnPlatform")
+				markupExtension = new OnPlatformExtension();
+			else if (match == "OnIdiom")
+				markupExtension = new OnIdiomExtension();
+			else if (match == "DataTemplate")
+				markupExtension = new DataTemplateExtension();
+			else
+			{
 				if (typeResolver == null)
 					return null;
 				Type type;
@@ -37,21 +33,20 @@ namespace Xamarin.Forms.Xaml
 				//The order of lookup is to look for the Extension-suffixed class name first and then look for the class name without the Extension suffix.
 				if (!typeResolver.TryResolve(match + "Extension", out type) && !typeResolver.TryResolve(match, out type))
 					throw new XamlParseException($"MarkupExtension not found for {match}", serviceProvider);
-				_markupExtension = Activator.CreateInstance(type) as IMarkupExtension;
-				break;
+				markupExtension = Activator.CreateInstance(type) as IMarkupExtension;
 			}
 
-			if (_markupExtension == null)
+			if (markupExtension == null)
 				throw new XamlParseException($"Missing public default constructor for MarkupExtension {match}", serviceProvider);
 
 			if (remaining == "}")
-				return _markupExtension.ProvideValue(serviceProvider);
+				return markupExtension.ProvideValue(serviceProvider);
 
 			string piece;
 			while ((piece = GetNextPiece(ref remaining, out char next)) != null)
 				HandleProperty(piece, serviceProvider, ref remaining, next != '=');
 
-			return _markupExtension.ProvideValue(serviceProvider);
+			return markupExtension.ProvideValue(serviceProvider);
 		}
 
 		protected override void SetPropertyValue(string prop, string strValue, object value, IServiceProvider serviceProvider)
@@ -59,7 +54,7 @@ namespace Xamarin.Forms.Xaml
 			MethodInfo setter;
 			if (prop == null) {
 				//implicit property
-				var t = _markupExtension.GetType();
+				var t = markupExtension.GetType();
 				prop = ApplyPropertiesVisitor.GetContentPropertyName(t.GetTypeInfo());
 				if (prop == null)
 					return;
@@ -72,26 +67,26 @@ namespace Xamarin.Forms.Xaml
 			}
 			else {
 				try {
-					setter = _markupExtension.GetType().GetRuntimeProperty(prop).SetMethod;
+					setter = markupExtension.GetType().GetRuntimeProperty(prop).SetMethod;
 				}
 				catch (AmbiguousMatchException e) {
-					throw new XamlParseException($"Multiple properties with name  '{_markupExtension.GetType()}.{prop}' found.", serviceProvider, innerException: e);
+					throw new XamlParseException($"Multiple properties with name  '{markupExtension.GetType()}.{prop}' found.", serviceProvider, innerException: e);
 				}
 
 			}
 			if (value == null && strValue != null) {
 				try {
-					value = strValue.ConvertTo(_markupExtension.GetType().GetRuntimeProperty(prop).PropertyType,
+					value = strValue.ConvertTo(markupExtension.GetType().GetRuntimeProperty(prop).PropertyType,
 						(Func<TypeConverter>)null, serviceProvider, out Exception converterException);
 					if (converterException != null)
 						throw converterException;
 				}
 				catch (AmbiguousMatchException e) {
-					throw new XamlParseException($"Multiple properties with name  '{_markupExtension.GetType()}.{prop}' found.", serviceProvider, innerException: e);
+					throw new XamlParseException($"Multiple properties with name  '{markupExtension.GetType()}.{prop}' found.", serviceProvider, innerException: e);
 				}
 			}
 
-			setter.Invoke(_markupExtension, new[] { value });
+			setter.Invoke(markupExtension, new[] { value });
 		}
 	}
-}
+}