[X] Allow tracking the assignment of StaticResource (#6868)

This allows advanced tracking of SR for debugging purposes. It doesn't affects
apps running without the debugger.

See also https://docs.microsoft.com/en-us/dotnet/api/system.windows.diagnostics.resourcedictionarydiagnostics

Xamarin.Forms.Core/ResourceDictionary.cs

@@ -260,19 +260,25 @@ namespace Xamarin.Forms
 		}
 
 		public bool TryGetValue(string key, out object value)
+			=> TryGetValueAndSource(key, out value, out _);
+
+		internal bool TryGetValueAndSource(string key, out object value, out ResourceDictionary source)
 		{
+			source = this;
 			return _innerDictionary.TryGetValue(key, out value)
-				|| (_mergedInstance != null && _mergedInstance.TryGetValue(key, out value))
-				|| (MergedDictionaries != null && TryGetMergedDictionaryValue(key, out value));
+				|| (_mergedInstance != null && _mergedInstance.TryGetValueAndSource(key, out value, out source))
+				|| (MergedDictionaries != null && TryGetMergedDictionaryValue(key, out value, out source));
 		}
 
-		bool TryGetMergedDictionaryValue(string key, out object value)
+		bool TryGetMergedDictionaryValue(string key, out object value, out ResourceDictionary source)
 		{
 			foreach (var dictionary in MergedDictionaries.Reverse())
-				if (dictionary.TryGetValue(key, out value))
+				if (dictionary.TryGetValue(key, out value)) {
+					source = dictionary;
 					return true;
+				}
 
-			value = null;
+			value = null; source = null;
 			return false;
 		}
 

Xamarin.Forms.Xaml/Diagnostics/ResourceDictionaryDiagnostics.cs

@@ -0,0 +1,10 @@
+using System;
+namespace Xamarin.Forms.Xaml.Diagnostics
+{
+	internal static class ResourceDictionaryDiagnostics
+	{
+		internal static void OnStaticResourceResolved(ResourceDictionary resourceDictionary, string key, object targetObject, object targetProperty)
+			=> StaticResourceResolved?.Invoke(resourceDictionary, new StaticResourceResolvedEventArgs(resourceDictionary, key, targetObject, targetProperty));
+		public static event EventHandler<StaticResourceResolvedEventArgs> StaticResourceResolved;
+	}
+}

Xamarin.Forms.Xaml/Diagnostics/StaticResourceResolvedEventArgs.cs

@@ -0,0 +1,19 @@
+using System;
+namespace Xamarin.Forms.Xaml.Diagnostics
+{
+	internal class StaticResourceResolvedEventArgs : EventArgs
+	{
+		internal StaticResourceResolvedEventArgs(ResourceDictionary resourceDictionary, string key, object targetObject, object targetProperty)
+		{
+			ResourceDictionary = resourceDictionary;
+			Key = key;
+			TargetObject = targetObject;
+			TargetProperty = targetProperty;
+		}
+
+		public ResourceDictionary ResourceDictionary { get; }
+		public string Key { get; }
+		public object TargetObject { get; }
+		public object TargetProperty { get; }
+	}
+}

Xamarin.Forms.Xaml/MarkupExtensions/StaticResourceExtension.cs

@@ -3,14 +3,16 @@ using System.Reflection;
 using System.Xml;
 using System.Linq;
 using Xamarin.Forms.Internals;
+using System.Collections.Generic;
 
 namespace Xamarin.Forms.Xaml
 {
 	[ContentProperty(nameof(Key))]
 	public sealed class StaticResourceExtension : IMarkupExtension
 	{
-		public string Key { get; set; }
+		internal static bool _mockDebuggerIsAttached; //for unit testing
 
+		public string Key { get; set; }
 		public object ProvideValue(IServiceProvider serviceProvider)
 		{
 			if (serviceProvider == null)
@@ -21,64 +23,86 @@ namespace Xamarin.Forms.Xaml
 				throw new ArgumentException();
 
 			var xmlLineInfo = serviceProvider.GetService(typeof(IXmlLineInfoProvider)) is IXmlLineInfoProvider xmlLineInfoProvider ? xmlLineInfoProvider.XmlLineInfo : null;
-			object resource = null;
 
-			foreach (var p in valueProvider.ParentObjects) {
-				var resDict = p is IResourcesProvider irp && irp.IsResourcesCreated ? irp.Resources : p as ResourceDictionary;
-				if (resDict == null)
-					continue;
-				if (resDict.TryGetValue(Key, out resource))
-					break;
-			}
-			resource = resource ?? GetApplicationLevelResource(Key, xmlLineInfo);
+			if (   !TryGetResource(Key, valueProvider.ParentObjects, out var resource, out var resourceDictionary)
+				&& !TryGetApplicationLevelResource(Key, out resource, out resourceDictionary))
+				throw new XamlParseException($"StaticResource not found for key {Key}", xmlLineInfo);
 
-			var bp = valueProvider.TargetProperty as BindableProperty;
-			var pi = valueProvider.TargetProperty as PropertyInfo;
+			if (System.Diagnostics.Debugger.IsAttached || _mockDebuggerIsAttached)
+				Diagnostics.ResourceDictionaryDiagnostics.OnStaticResourceResolved(resourceDictionary, Key, valueProvider.TargetObject, valueProvider.TargetProperty);
+
+			return CastTo(resource, valueProvider.TargetProperty);
+		}
+
+		//used by X.HR.F
+		internal static object CastTo(object value, object targetProperty)
+		{
+			var bp = targetProperty as BindableProperty;
+			var pi = targetProperty as PropertyInfo;
 			var propertyType = bp?.ReturnType ?? pi?.PropertyType;
-			if (propertyType == null) {
-				if (resource.GetType().GetTypeInfo().IsGenericType && (resource.GetType().GetGenericTypeDefinition() == typeof(OnPlatform<>) || resource.GetType().GetGenericTypeDefinition() == typeof(OnIdiom<>))) {
+			if (propertyType == null)
+			{
+				if (value.GetType().GetTypeInfo().IsGenericType && (value.GetType().GetGenericTypeDefinition() == typeof(OnPlatform<>) || value.GetType().GetGenericTypeDefinition() == typeof(OnIdiom<>)))
+				{
 					// This is only there to support our backward compat story with pre 2.3.3 compiled Xaml project who was not providing TargetProperty
-					var method = resource.GetType().GetRuntimeMethod("op_Implicit", new[] { resource.GetType() });
-					resource = method.Invoke(null, new[] { resource });
+					var method = value.GetType().GetRuntimeMethod("op_Implicit", new[] { value.GetType() });
+					value = method.Invoke(null, new[] { value });
 				}
-				return resource;
+				return value;
 			}
-			if (propertyType.IsAssignableFrom(resource.GetType()))
-				return resource;
-			var implicit_op =  resource.GetType().GetImplicitConversionOperator(fromType: resource.GetType(), toType: propertyType)
-							?? propertyType.GetImplicitConversionOperator(fromType: resource.GetType(), toType: propertyType);
+			if (propertyType.IsAssignableFrom(value.GetType()))
+				return value;
+			var implicit_op = value.GetType().GetImplicitConversionOperator(fromType: value.GetType(), toType: propertyType)
+							?? propertyType.GetImplicitConversionOperator(fromType: value.GetType(), toType: propertyType);
 			if (implicit_op != null)
-				return implicit_op.Invoke(resource, new [] { resource });
+				return implicit_op.Invoke(value, new[] { value });
 
 			//Special case for https://bugzilla.xamarin.com/show_bug.cgi?id=59818
 			//On OnPlatform, check for an opImplicit from the targetType
-			if (   Device.Flags != null
+			if (Device.Flags != null
 				&& Device.Flags.Contains("xamlDoubleImplicitOpHack")
-				&& resource.GetType().GetTypeInfo().IsGenericType
-				&& (resource.GetType().GetGenericTypeDefinition() == typeof(OnPlatform<>))) {
-				var tType = resource.GetType().GenericTypeArguments[0];
+				&& value.GetType().GetTypeInfo().IsGenericType
+				&& (value.GetType().GetGenericTypeDefinition() == typeof(OnPlatform<>)))
+			{
+				var tType = value.GetType().GenericTypeArguments[0];
 				var opImplicit = tType.GetImplicitConversionOperator(fromType: tType, toType: propertyType)
 								?? propertyType.GetImplicitConversionOperator(fromType: tType, toType: propertyType);
 
-				if (opImplicit != null) {
+				if (opImplicit != null)
+				{
 					//convert the OnPlatform<T> to T
-					var opPlatformImplicitConversionOperator = resource.GetType().GetImplicitConversionOperator(fromType: resource.GetType(), toType: tType);
-					resource = opPlatformImplicitConversionOperator.Invoke(null, new[] { resource });
+					var opPlatformImplicitConversionOperator = value.GetType().GetImplicitConversionOperator(fromType: value.GetType(), toType: tType);
+					value = opPlatformImplicitConversionOperator.Invoke(null, new[] { value });
 
 					//and convert to toType
-					resource = opImplicit.Invoke(null, new[] { resource });
-					return resource;
+					value = opImplicit.Invoke(null, new[] { value });
+					return value;
 				}
 			}
 
-			return resource;
+			return value;
 		}
 
-		internal object GetApplicationLevelResource(string key, IXmlLineInfo xmlLineInfo)
+		bool TryGetResource(string key, IEnumerable<object> parentObjects, out object resource, out ResourceDictionary resourceDictionary)
 		{
-			if (Application.Current == null || !((IResourcesProvider)Application.Current).IsResourcesCreated || !Application.Current.Resources.TryGetValue(Key, out object resource))
-				throw new XamlParseException($"StaticResource not found for key {Key}", xmlLineInfo);
-			return resource;
+			resource = null;
+			resourceDictionary = null;
+
+			foreach (var p in parentObjects) {
+				var resDict = p is IResourcesProvider irp && irp.IsResourcesCreated ? irp.Resources : p as ResourceDictionary;
+				if (resDict == null)
+					continue;
+				if (resDict.TryGetValueAndSource(Key, out resource, out resourceDictionary))
+					return true;
+			}
+			return false;
+		}
+
+		bool TryGetApplicationLevelResource(string key, out object resource, out ResourceDictionary resourceDictionary)
+		{
+			resource = null;
+			resourceDictionary = null;
+			return Application.Current != null && ((IResourcesProvider)Application.Current).IsResourcesCreated && Application.Current.Resources.TryGetValueAndSource (key, out resource, out resourceDictionary);
 		}
 	}
 }

Xamarin.Forms.Xaml/Properties/AssemblyInfo.cs

@@ -8,6 +8,7 @@ using Xamarin.Forms.Internals;
 [assembly: InternalsVisibleTo("Xamarin.Forms.Xaml.Design")]
 [assembly: InternalsVisibleTo("Xamarin.Forms.Loader")]// Xamarin.Forms.Loader.dll Xamarin.Forms.Xaml.XamlLoader.Load(object, string), kzu@microsoft.com
 [assembly: InternalsVisibleTo("Xamarin.HotReload.Forms")]
+[assembly: InternalsVisibleTo("Xamarin.HotReload.UnitTests")]
 [assembly: Preserve]
 
 [assembly: XmlnsDefinition("http://xamarin.com/schemas/2014/forms", "Xamarin.Forms.Xaml")]

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

@@ -10,4 +10,7 @@
     <ProjectReference Include="..\Xamarin.Forms.Core\Xamarin.Forms.Core.csproj">
     </ProjectReference>
   </ItemGroup>
+  <ItemGroup>
+    <Folder Include="Diagnostics\" />
+  </ItemGroup>
 </Project>