[XamlC] Find the real VisualState parent (#2036)

`VisualStateGroupList` can be implicit, and it looks like tht wasn't
tested. This adds a test, and a fix.

 - fixes #2034

Xamarin.Forms.Build.Tasks/CompiledConverters/BindablePropertyConverter.cs

@@ -1,5 +1,6 @@
 using System.Collections.Generic;
 using System.Linq;
+using System.Xml;
 using Mono.Cecil;
 using Mono.Cecil.Cil;
 
@@ -32,27 +33,23 @@ namespace Xamarin.Forms.Core.XamlC
 			var parts = value.Split('.');
 			if (parts.Length == 1) {
 				var parent = node.Parent?.Parent as IElementNode ?? (node.Parent?.Parent as IListNode)?.Parent as IElementNode;
-
-				if ((node.Parent as ElementNode)?.XmlType.NamespaceUri == XamlParser.XFUri &&
-				    ((node.Parent as ElementNode)?.XmlType.Name == "Setter" || (node.Parent as ElementNode)?.XmlType.Name == "PropertyCondition")) {
+				if (   (node.Parent as ElementNode)?.XmlType.NamespaceUri == XamlParser.XFUri
+				    && (   (node.Parent as ElementNode)?.XmlType.Name == nameof(Setter)
+				        || (node.Parent as ElementNode)?.XmlType.Name == nameof(PropertyCondition))) {
 					if (parent.XmlType.NamespaceUri == XamlParser.XFUri &&
-						(parent.XmlType.Name == "Trigger" || parent.XmlType.Name == "DataTrigger" || parent.XmlType.Name == "MultiTrigger" || parent.XmlType.Name == "Style")) {
+					    (   parent.XmlType.Name == nameof(Trigger)
+					     || parent.XmlType.Name == nameof(DataTrigger)
+					     || parent.XmlType.Name == nameof(MultiTrigger)
+					     || parent.XmlType.Name == nameof(Style))) {
 						var ttnode = (parent as ElementNode).Properties [new XmlName("", "TargetType")];
 						if (ttnode is ValueNode)
 							typeName = (ttnode as ValueNode).Value as string;
 						else if (ttnode is IElementNode)
 							typeName = ((ttnode as IElementNode).CollectionItems.FirstOrDefault() as ValueNode)?.Value as string ?? ((ttnode as IElementNode).Properties [new XmlName("", "TypeName")] as ValueNode)?.Value as string;
-					} else if (parent.XmlType.NamespaceUri == XamlParser.XFUri && parent.XmlType.Name == "VisualState") {
-						var current = parent.Parent.Parent.Parent as IElementNode;
-						if (current.XmlType.NamespaceUri == XamlParser.XFUri && current.XmlType.Name == "Setter") {
-							// Parent will be a Style, and the type will be that Style's TargetType
-							typeName =
-								((current?.Parent as IElementNode)?.Properties[new XmlName("", "TargetType")] as ValueNode)?.Value as string;
-						} else {
-							typeName = current.XmlType.Name;
-						}
+					} else if (parent.XmlType.NamespaceUri == XamlParser.XFUri && parent.XmlType.Name == nameof(VisualState)) {
+						typeName = FindTypeNameForVisualState(parent, node);
 					}
-				} else if ((node.Parent as ElementNode)?.XmlType.NamespaceUri == XamlParser.XFUri && (node.Parent as ElementNode)?.XmlType.Name == "Trigger")
+				} else if ((node.Parent as ElementNode)?.XmlType.NamespaceUri == XamlParser.XFUri && (node.Parent as ElementNode)?.XmlType.Name == nameof(Trigger))
 					typeName = ((node.Parent as ElementNode).Properties [new XmlName("", "TargetType")] as ValueNode).Value as string;
 				propertyName = parts [0];
 			} else if (parts.Length == 2) {
@@ -73,6 +70,29 @@ namespace Xamarin.Forms.Core.XamlC
 			return bpRef;
 		}
 
+		static string FindTypeNameForVisualState(IElementNode parent, IXmlLineInfo lineInfo)
+		{
+			//1. parent is VisualState, don't check that
+
+			//2. check that the VS is in a VSG
+			if (!(parent.Parent is IElementNode target) || target.XmlType.NamespaceUri != XamlParser.XFUri || target.XmlType.Name != nameof(VisualStateGroup))
+				throw new XamlParseException($"Expected {nameof(VisualStateGroup)} but found {parent.Parent}", lineInfo);
+
+			//3. if the VSG is in a VSGL, skip that as it could be implicit
+			if (   target.Parent is ListNode
+				|| (  (target.Parent as IElementNode)?.XmlType.NamespaceUri == XamlParser.XFUri
+				   && (target.Parent as IElementNode)?.XmlType.Name == nameof(VisualStateGroupList)))
+				target = target.Parent.Parent as IElementNode;
+			else
+				target = target.Parent as IElementNode;
+
+			//4. target is now a Setter in a Style, or a VE
+			if (target.XmlType.NamespaceUri == XamlParser.XFUri && target.XmlType.Name == nameof(Setter))
+				return ((target?.Parent as IElementNode)?.Properties[new XmlName("", "TargetType")] as ValueNode)?.Value as string;
+			else
+				return target.XmlType.Name;
+		}
+
 		public static FieldReference GetBindablePropertyFieldReference(TypeReference typeRef, string propertyName, ModuleDefinition module)
 		{
 			TypeReference declaringTypeReference;

Xamarin.Forms.Xaml.UnitTests/Issues/Gh2034.xaml

@@ -0,0 +1,21 @@
+<?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.Gh2034">
+    <FlexLayout StyleClass="login-form">
+        <Label >
+            <VisualStateManager.VisualStateGroups>
+                    <VisualStateGroupList>
+                        <VisualStateGroup x:Name="StrengthStates">
+                                
+                            <VisualState x:Name="VeryWeak">
+                                <VisualState.Setters>
+                                    <Setter Property="Text" Value="foo"/>
+                                </VisualState.Setters>
+                            </VisualState>
+                        </VisualStateGroup>
+                </VisualStateGroupList>
+            </VisualStateManager.VisualStateGroups>
+        </Label>
+    </FlexLayout>
+</ContentPage>

Xamarin.Forms.Xaml.UnitTests/Issues/Gh2034.xaml.cs

@@ -0,0 +1,33 @@
+using System;
+using System.Collections.Generic;
+using NUnit.Framework;
+using Xamarin.Forms;
+
+namespace Xamarin.Forms.Xaml.UnitTests
+{
+	[XamlCompilation(XamlCompilationOptions.Skip)]
+	public partial class Gh2034 : ContentPage
+	{
+		public Gh2034()
+		{
+			InitializeComponent();
+		}
+		public Gh2034(bool useCompiledXaml)
+		{
+			//this stub will be replaced at compile time
+		}
+
+		[TestFixture]
+		class Tests
+		{
+			[TestCase(true)]
+			public void Compiles(bool useCompiledXaml)
+			{
+				if (!useCompiledXaml)
+					return;
+				MockCompiler.Compile(typeof(Gh2034));
+				Assert.Pass();
+			}
+		}
+	}
+}

Xamarin.Forms.Xaml.UnitTests/Xamarin.Forms.Xaml.UnitTests.csproj

@@ -579,6 +579,9 @@
     <Compile Include="Issues\Gh1978.xaml.cs">
       <DependentUpon>Gh1978.xaml</DependentUpon>
     </Compile>
+    <Compile Include="Issues\Gh2034.xaml.cs">
+      <DependentUpon>Gh2034.xaml</DependentUpon>
+    </Compile>
   </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
   <Import Project="..\.nuspec\Xamarin.Forms.Debug.targets" />
@@ -1036,6 +1039,10 @@
       <SubType>Designer</SubType>
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
     </EmbeddedResource>
+    <EmbeddedResource Include="Issues\Gh2034.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
+    </EmbeddedResource>
   </ItemGroup>
   <ItemGroup>
     <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />