[XamlC] throw XPE on missing resource key (#7073)

When a resource was missing a key (non-implicit resource), XamlC was throwing
an AssemblyResolutionException instead of a proper XamlParseException when the
type of the resource was in a different xmlns than the default Forms one.

All the other cases are fine (default xmlns, or non-compiled Xaml)

- fixes AB#946693

Xamarin.Forms.Build.Tasks/ModuleDefinitionExtensions.cs

@@ -192,6 +192,28 @@ namespace Xamarin.Forms.Build.Tasks
 			return module.ImportReference(methodRef.ResolveGenericParameters(type.MakeGenericInstanceType(classArguments), module));
 		}
 
+		public static MethodReference ImportMethodReference(this ModuleDefinition module,
+													 TypeReference type,
+													 string methodName,
+													 TypeReference[] parameterTypes = null,
+													 TypeReference[] classArguments = null,
+													 bool isStatic = false)
+		{
+			return module.ImportMethodReference(type,
+												methodName: methodName,
+												predicate: md => {
+													if (md.IsStatic != isStatic)
+														return false;
+													if (md.Parameters.Count != (parameterTypes?.Length ?? 0))
+														return false;
+													for (var i = 0; i < md.Parameters.Count; i++)
+														if (!TypeRefComparer.Default.Equals(md.Parameters[i].ParameterType, parameterTypes[i]))
+															return false;
+													return true;
+												},
+												classArguments: classArguments);
+		}
+
 		public static MethodReference ImportMethodReference(this ModuleDefinition module,
 															(string assemblyName, string clrNamespace, string typeName) type,
 															string methodName,

Xamarin.Forms.Build.Tasks/SetPropertiesVisitor.cs

@@ -1334,9 +1334,9 @@ namespace Xamarin.Forms.Build.Tasks
 			//is there a RD.Add() overrides that accepts this ?
 			var nodeTypeRef = context.Variables[node].VariableType;
 			var module = context.Body.Method.Module;
-			if (module.ImportMethodReference(("Xamarin.Forms.Core", "Xamarin.Forms", "ResourceDictionary"),
+			if (module.ImportMethodReference(module.GetTypeDefinition(("Xamarin.Forms.Core", "Xamarin.Forms", "ResourceDictionary")),
 											 methodName: "Add",
-											 parameterTypes: new[] { (nodeTypeRef.Scope.Name, nodeTypeRef.Namespace, nodeTypeRef.Name) }) != null)
+											 parameterTypes: new[] { (nodeTypeRef) }) != null)
 				return true;
 
 			throw new XamlParseException("resources in ResourceDictionary require a x:Key attribute", lineInfo);

Xamarin.Forms.Xaml.UnitTests/Issues/AB946693.xaml

@@ -0,0 +1,10 @@
+<?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.AB946693"
+        xmlns:local="clr-namespace:Xamarin.Forms.Xaml.UnitTests">
+    <ContentPage.Resources>
+        <local:Gh6192Template/>
+    </ContentPage.Resources>
+</ContentPage>

Xamarin.Forms.Xaml.UnitTests/Issues/AB946693.xaml.cs

@@ -0,0 +1,34 @@
+using System;
+using System.Collections.Generic;
+using NUnit.Framework;
+using Xamarin.Forms;
+using Xamarin.Forms.Core.UnitTests;
+
+namespace Xamarin.Forms.Xaml.UnitTests
+{
+	[XamlCompilation(XamlCompilationOptions.Skip)]
+	public partial class AB946693 : ContentPage
+	{
+		public AB946693() => InitializeComponent();
+		public AB946693(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 KeylessResourceThrowsMeaningfulException([Values(false, true)]bool useCompiledXaml)
+			{
+				if (useCompiledXaml)
+					Assert.Throws<XamlParseException>(() => MockCompiler.Compile(typeof(AB946693)));
+				else
+					Assert.Throws<XamlParseException>(() => new AB946693(useCompiledXaml));
+			}
+		}
+	}
+}