XamlLoader should not ignore x:TypeArguments on root node (#5804)

Xamarin.Forms.Xaml.UnitTests/DesignTimeLoaderTests.cs

@@ -607,7 +607,6 @@ namespace Xamarin.Forms.Xaml.UnitTests
 			string clrNamespace = null;
 			string typeName = null;
 
-
 			XamlLoader.FallbackTypeResolver = (fallbackTypeInfos, type) =>
 			{
 				assemblyName = fallbackTypeInfos?[1].AssemblyName;
@@ -682,6 +681,24 @@ namespace Xamarin.Forms.Xaml.UnitTests
 			Assert.DoesNotThrow(() => XamlLoader.Create(xaml, true));
 			Assert.That(exceptions.Count, Is.GreaterThanOrEqualTo(1));
 		}
+
+		[Test]
+		public void MissingGenericRootTypeProvidesCorrectTypeName()
+		{
+			var xaml = @"
+					<local:GenericContentPage xmlns=""http://xamarin.com/schemas/2014/forms""
+						xmlns:x=""http://schemas.microsoft.com/winfx/2009/xaml""
+						xmlns:local=""clr-namespace:MissingNamespace""
+						x:TypeArguments=""x:Object"" />";
+
+			XamlLoader.FallbackTypeResolver = (p, type) =>
+			{
+				Assert.That(p.Select(i => i.TypeName), Has.Some.EqualTo("GenericContentPage`1"));
+				return typeof(ContentPage);
+			};
+
+			Assert.DoesNotThrow(() => XamlLoader.Create(xaml, true));
+		}
 	}
 
 	public class InstantiateThrows

Xamarin.Forms.Xaml/XamlLoader.cs

@@ -119,7 +119,8 @@ namespace Xamarin.Forms.Xaml
 						continue;
 					}
 
-					var rootnode = new RuntimeRootNode(new XmlType(reader.NamespaceURI, reader.Name, null), null, (IXmlNamespaceResolver)reader);
+					var typeArguments = XamlParser.GetTypeArguments(reader);
+					var rootnode = new RuntimeRootNode(new XmlType(reader.NamespaceURI, reader.Name, typeArguments), null, (IXmlNamespaceResolver)reader);
 					XamlParser.ParseXaml(rootnode, reader);
 					var visitorContext = new HydrationContext {
 						ExceptionHandler = exceptionHandler,

Xamarin.Forms.Xaml/XamlParser.cs

@@ -155,10 +155,7 @@ namespace Xamarin.Forms.Xaml
 
 						var attributes = ParseXamlAttributes(reader, out xmlns);
 						var prefixes = PrefixesToIgnore(xmlns);
-
-						IList<XmlType> typeArguments = null;
-						if (attributes.Any(kvp => kvp.Key == XmlName.xTypeArguments))
-							typeArguments = ((ValueNode)attributes.First(kvp => kvp.Key == XmlName.xTypeArguments).Value).Value as IList<XmlType>;
+						var typeArguments = GetTypeArguments(attributes);
 
 						node = new ElementNode(new XmlType(elementNsUri, elementName, typeArguments), elementNsUri,
 							reader as IXmlNamespaceResolver, elementXmlInfo.LineNumber, elementXmlInfo.LinePosition);
@@ -185,6 +182,15 @@ namespace Xamarin.Forms.Xaml
 			throw new XamlParseException("Closing PropertyElement expected", (IXmlLineInfo)reader);
 		}
 
+		internal static IList<XmlType> GetTypeArguments(XmlReader reader) => GetTypeArguments(ParseXamlAttributes(reader, out _));
+
+		static IList<XmlType> GetTypeArguments(IList<KeyValuePair<XmlName, INode>> attributes)
+		{
+			return attributes.Any(kvp => kvp.Key == XmlName.xTypeArguments)
+				? ((ValueNode)attributes.First(kvp => kvp.Key == XmlName.xTypeArguments).Value).Value as IList<XmlType>
+				: null;
+		}
+
 		static IList<KeyValuePair<XmlName, INode>> ParseXamlAttributes(XmlReader reader, out IList<KeyValuePair<string,string>> xmlns)
 		{
 			Debug.Assert(reader.NodeType == XmlNodeType.Element);