[X] avoid throwing in VisualDiagnostics (#7571)

this fixes a regression introduced in #7474

- fixes #7570

Xamarin.Forms.Xaml/ApplyPropertiesVisitor.cs

@@ -346,22 +346,28 @@ namespace Xamarin.Forms.Xaml
 
 			//If it's a BindableProberty, SetValue
 			if (xpe == null && TrySetValue(xamlelement, property, attached, value, lineInfo, serviceProvider, out xpe)) {
-				VisualDiagnostics.RegisterSourceInfo(value, null, ((IXmlLineInfo)node).LineNumber, ((IXmlLineInfo)node).LinePosition);
-				VisualDiagnostics.SendVisualTreeChanged(xamlelement, value);
+				if (!(node is ValueNode) && value != null && !value.GetType().GetTypeInfo().IsValueType && XamlFilePathAttribute.GetFilePathForObject(context.RootElement) is string path) {
+					VisualDiagnostics.RegisterSourceInfo(value, new Uri(path, UriKind.Relative), ((IXmlLineInfo)node).LineNumber, ((IXmlLineInfo)node).LinePosition);
+					VisualDiagnostics.SendVisualTreeChanged(xamlelement, value);
+				}
 				return;
 			}
 
 			//If we can assign that value to a normal property, let's do it
 			if (xpe == null && TrySetProperty(xamlelement, localName, value, lineInfo, serviceProvider, context, out xpe)) {
-				VisualDiagnostics.RegisterSourceInfo(value, null, ((IXmlLineInfo)node).LineNumber, ((IXmlLineInfo)node).LinePosition);
-				VisualDiagnostics.SendVisualTreeChanged(xamlelement, value);
+				if (!(node is ValueNode) && value != null && !value.GetType().GetTypeInfo().IsValueType && XamlFilePathAttribute.GetFilePathForObject(context.RootElement) is string path) {
+					VisualDiagnostics.RegisterSourceInfo(value, new Uri(path, UriKind.Relative), ((IXmlLineInfo)node).LineNumber, ((IXmlLineInfo)node).LinePosition);
+					VisualDiagnostics.SendVisualTreeChanged(xamlelement, value);
+				}
 				return;
 			}
 
 			//If it's an already initialized property, add to it
 			if (xpe == null && TryAddToProperty(xamlelement, propertyName, value, xKey, lineInfo, serviceProvider, context, out xpe)) {
-				VisualDiagnostics.RegisterSourceInfo(value, null, ((IXmlLineInfo)node).LineNumber, ((IXmlLineInfo)node).LinePosition);
-				VisualDiagnostics.SendVisualTreeChanged(xamlelement, value);
+				if (!(node is ValueNode) && value != null && !value.GetType().GetTypeInfo().IsValueType && XamlFilePathAttribute.GetFilePathForObject(context.RootElement) is string path) {
+					VisualDiagnostics.RegisterSourceInfo(value, new Uri(path, UriKind.Relative), ((IXmlLineInfo)node).LineNumber, ((IXmlLineInfo)node).LinePosition);
+					VisualDiagnostics.SendVisualTreeChanged(xamlelement, value);
+				}
 				return;
 			}
 

Xamarin.Forms.Xaml/Diagnostics/DebuggerHelper.cs

@@ -7,6 +7,10 @@ namespace Xamarin.Forms.Xaml.Diagnostics
 {
 	static class DebuggerHelper
 	{
+#if DEBUG
+		static DebuggerHelper() => _mockDebuggerIsAttached = true;
+#endif
+
 		internal static bool _mockDebuggerIsAttached;
 		public static bool DebuggerIsAttached => _mockDebuggerIsAttached || Debugger.IsAttached;
 	}

Xamarin.Forms.Xaml/Diagnostics/VisualDiagnostics.cs

@@ -12,7 +12,7 @@ namespace Xamarin.Forms.Xaml.Diagnostics
 		static ConditionalWeakTable<object, XamlSourceInfo> sourceInfos = new ConditionalWeakTable<object, XamlSourceInfo>();
 		internal static void RegisterSourceInfo(object target, Uri uri, int lineNumber, int linePosition)
 		{
-			if (DebuggerHelper.DebuggerIsAttached)
+			if (DebuggerHelper.DebuggerIsAttached && !sourceInfos.TryGetValue(target, out _))
 				sourceInfos.Add(target, new XamlSourceInfo(uri, lineNumber, linePosition));
 		}