[Xaml] Create value from positional argument text of markup extension (#8980)

The behavior introduced with this change conforms to the description of
[MS-XAML-2009] page 80 and 81.
fixes #6905

Xamarin.Forms.Build.Tasks/ExpandMarkupsVisitor.cs

@@ -143,11 +143,11 @@ namespace Xamarin.Forms.Build.Tasks
 				}
 				else
 				{
-					char next;
-					string piece;
-					while ((piece = GetNextPiece(serviceProvider, ref remaining, out next)) != null)
+					Property parsed;
+					do
 					{
-						var parsed = ParseProperty(piece, serviceProvider, ref remaining, next != '=');
+						parsed = ParseProperty(serviceProvider, ref remaining);
+
 						XmlName childname;
 
 						if (parsed.name == null)
@@ -177,6 +177,7 @@ namespace Xamarin.Forms.Build.Tasks
 							childnodes.Add((childname, childnode));
 						}
 					}
+					while (!parsed.last);
 				}
 
 				//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.

Xamarin.Forms.Xaml.UnitTests/MarkupExpressionParserTests.cs

@@ -12,6 +12,8 @@ namespace Xamarin.Forms.Xaml.UnitTests
 	{
 		IXamlTypeResolver typeResolver;
 
+		public static readonly string Foo = "Foo";
+
 		class MockElementNode : IElementNode, IValueNode, IXmlLineInfo
 		{
 			public bool HasLineInfo () { return false; }
@@ -93,11 +95,10 @@ namespace Xamarin.Forms.Xaml.UnitTests
 			Assert.AreEqual (Binding.SelfPath, ((Binding)binding).Path);
 		}
 
-		[Test]
-		public void BindingWithImplicitPath ()
+		[TestCase("{Binding Foo}")]
+		[TestCase("{Binding {x:Static local:MarkupExpressionParserTests.Foo}}")]
+		public void BindingWithImplicitPath (string bindingString)
 		{
-			var bindingString = "{Binding Foo}";
-
 			var binding = (new MarkupExtensionParser ()).ParseExpression (ref bindingString, new Internals.XamlServiceProvider (null, null) {
 				IXamlTypeResolver = typeResolver,
 			});
@@ -377,6 +378,8 @@ namespace Xamarin.Forms.Xaml.UnitTests
 
 		[TestCase("{Binding")]
 		[TestCase("{Binding 'Foo}")]
+		[TestCase("{Binding Foo, Converter={StaticResource Bar}")]
+		[TestCase("{Binding Foo, Converter={StaticResource Bar}?}")]
 		public void InvalidExpressions (string expression)
 		{
 			var serviceProvider = new Internals.XamlServiceProvider (null, null);

Xamarin.Forms.Xaml/ExpandMarkupsVisitor.cs

@@ -131,10 +131,9 @@ namespace Xamarin.Forms.Xaml
 					remaining = remaining.Substring(1);
 				}
 				else {
-					char next;
-					string piece;
-					while ((piece = GetNextPiece(serviceProvider, ref remaining, out next)) != null) {
-						var parsed = ParseProperty(piece, serviceProvider, ref remaining, next != '=');
+					Property parsed;
+					do {
+						parsed = ParseProperty(serviceProvider, ref remaining);
 						XmlName childname;
 
 						if (parsed.name == null) {
@@ -160,6 +159,7 @@ namespace Xamarin.Forms.Xaml
 							childnodes.Add((childname, childnode));
 						}
 					}
+					while (!parsed.last);
 				}
 
 

Xamarin.Forms.Xaml/MarkupExpressionParser.cs

@@ -40,6 +40,7 @@ namespace Xamarin.Forms.Xaml
 	{
 		protected struct Property
 		{
+			public bool last;
 			public string name;
 			public string strValue;
 			public object value;
@@ -119,50 +120,56 @@ namespace Xamarin.Forms.Xaml
 			return true;
 		}
 
-		protected Property ParseProperty(string prop, IServiceProvider serviceProvider, ref string remaining, bool isImplicit)
+		protected Property ParseProperty(IServiceProvider serviceProvider, ref string remaining)
 		{
 			char next;
 			object value = null;
 			string str_value;
+			string name;
 
-			if (isImplicit)
-			{
-				return new Property { name = null, strValue = prop, value = null };
-			}
 			remaining = remaining.TrimStart();
-			if (remaining.StartsWith("{", StringComparison.Ordinal))
-			{
-				value = ParseExpression(ref remaining, serviceProvider);
+			if (remaining[0] == '{')
+				return ParsePropertyExpression(null, serviceProvider, ref remaining);
+
+			str_value = GetNextPiece(serviceProvider, ref remaining, out next);
+			if (next == '=') {
 				remaining = remaining.TrimStart();
+				if (remaining[0] == '{')
+					return ParsePropertyExpression(str_value, serviceProvider, ref remaining);
 
-				if (remaining.Length > 0 && remaining[0] == ',')
-					remaining = remaining.Substring(1);
-				else if (remaining.Length > 0 && remaining[0] == '}')
-					remaining = remaining.Substring(1);
-
-				str_value = value as string;
+				name = str_value;
+				str_value = GetNextPiece(serviceProvider, ref remaining, out next);
 			}
 			else {
-				str_value = GetNextPiece(serviceProvider, ref remaining, out next);
-				if (str_value == null) {
-					throw new XamlParseException($"No value found for property '{prop}' in markup expression", serviceProvider);
-				}
+				name = null;
 			}
 
-			return new Property { name = prop, strValue = str_value, value = value };
+			return new Property { last = next == '}', name = name, strValue = str_value, value = value };
 		}
 
-		protected string GetNextPiece(IServiceProvider serviceProvider, ref string remaining, out char next)
+		private Property ParsePropertyExpression(string prop, IServiceProvider serviceProvider, ref string remaining)
+		{
+			bool last;
+			var value = ParseExpression(ref remaining, serviceProvider);
+			remaining = remaining.TrimStart();
+			if (remaining.Length <= 0)
+				throw new XamlParseException("Unexpected end of markup expression", serviceProvider);
+			if (remaining[0] == ',')
+				last = false;
+			else if (remaining[0] == '}')
+				last = true;
+			else
+				throw new XamlParseException("Unexpected character following value string", serviceProvider);
+
+			remaining = remaining.Substring(1);
+			return new Property { last = last, name = prop, strValue = value as string, value = value };
+		}
+
+		private string GetNextPiece(IServiceProvider serviceProvider, ref string remaining, out char next)
 		{
 			bool inString = false;
 			int end = 0;
 			char stringTerminator = '\0';
-			remaining = remaining.TrimStart();
-			if (remaining.Length == 0)
-			{
-				next = Char.MaxValue;
-				return null;
-			}
 
 			var piece = new StringBuilder();
 			// If we're inside a quoted string we append all chars to our piece until we hit the ending quote.
@@ -203,14 +210,8 @@ namespace Xamarin.Forms.Xaml
 			if (inString && end == remaining.Length)
 				throw new XamlParseException("Unterminated quoted string", serviceProvider);
 
-			if (end == remaining.Length && !remaining.EndsWith("}", StringComparison.Ordinal))
-				throw new XamlParseException("Expression did not end with '}'", serviceProvider);
-
 			if (end == 0)
-			{
-				next = Char.MaxValue;
-				return null;
-			}
+				throw new XamlParseException("Empty value string in markup expression", serviceProvider);
 
 			next = remaining[end];
 			remaining = remaining.Substring(end + 1);

Xamarin.Forms.Xaml/MarkupExtensionParser.cs

@@ -42,11 +42,12 @@ namespace Xamarin.Forms.Xaml
 			if (remaining == "}")
 				return markupExtension.ProvideValue(serviceProvider);
 
-			string piece;
-			while ((piece = GetNextPiece(serviceProvider, ref remaining, out char next)) != null) {
-				var value = ParseProperty(piece, serviceProvider, ref remaining, next != '=');
+			Property value;
+			do {
+				value = ParseProperty(serviceProvider, ref remaining);
 				SetPropertyValue(value.name, value.strValue, value.value, serviceProvider);
 			}
+			while (!value.last);
 
 			return markupExtension.ProvideValue(serviceProvider);
 		}