Xaml empty service provider (#736)

* [Xaml] AcceptEmptyServiceProvider

* [XamlC] AcceptEmptyServiceProvider

* docs

Xamarin.Forms.Build.Tasks/SetPropertiesVisitor.cs

@@ -279,6 +279,7 @@ namespace Xamarin.Forms.Build.Tasks
 			else if (vardefref.VariableDefinition.VariableType.ImplementsGenericInterface("Xamarin.Forms.Xaml.IMarkupExtension`1",
 				out markupExtension, out genericArguments))
 			{
+				var acceptEmptyServiceProvider = vardefref.VariableDefinition.VariableType.GetCustomAttribute(module.ImportReference(typeof(AcceptEmptyServiceProviderAttribute))) != null;
 				if (vardefref.VariableDefinition.VariableType.FullName == "Xamarin.Forms.Xaml.BindingExtension")
 					foreach (var instruction in CompileBindingPath(node, context, vardefref.VariableDefinition))
 						yield return instruction;
@@ -291,6 +292,9 @@ namespace Xamarin.Forms.Build.Tasks
 
 				vardefref.VariableDefinition = new VariableDefinition(module.ImportReference(genericArguments.First()));
 				yield return Instruction.Create(OpCodes.Ldloc, context.Variables[node]);
+				if (acceptEmptyServiceProvider)
+					yield return Instruction.Create(OpCodes.Ldnull);
+				else
 					foreach (var instruction in node.PushServiceProvider(context, bpRef, propertyRef, propertyDeclaringTypeRef))
 						yield return instruction;
 				yield return Instruction.Create(OpCodes.Callvirt, provideValue);
@@ -298,12 +302,16 @@ namespace Xamarin.Forms.Build.Tasks
 			}
 			else if (context.Variables[node].VariableType.ImplementsInterface(module.ImportReference(typeof (IMarkupExtension))))
 			{
+				var acceptEmptyServiceProvider = context.Variables[node].VariableType.GetCustomAttribute(module.ImportReference(typeof(AcceptEmptyServiceProviderAttribute))) != null;
 				var markExt = module.ImportReference(typeof (IMarkupExtension)).Resolve();
 				var provideValueInfo = markExt.Methods.First(md => md.Name == "ProvideValue");
 				var provideValue = module.ImportReference(provideValueInfo);
 
 				vardefref.VariableDefinition = new VariableDefinition(module.TypeSystem.Object);
 				yield return Instruction.Create(OpCodes.Ldloc, context.Variables[node]);
+				if (acceptEmptyServiceProvider)
+					yield return Instruction.Create(OpCodes.Ldnull);
+				else
 					foreach (var instruction in node.PushServiceProvider(context, bpRef, propertyRef, propertyDeclaringTypeRef))
 						yield return instruction;
 				yield return Instruction.Create(OpCodes.Callvirt, provideValue);
@@ -311,6 +319,7 @@ namespace Xamarin.Forms.Build.Tasks
 			}
 			else if (context.Variables[node].VariableType.ImplementsInterface(module.ImportReference(typeof (IValueProvider))))
 			{
+				var acceptEmptyServiceProvider = context.Variables[node].VariableType.GetCustomAttribute(module.ImportReference(typeof(AcceptEmptyServiceProviderAttribute))) != null;
 				var valueProviderType = context.Variables[node].VariableType;
 				//If the IValueProvider has a ProvideCompiledAttribute that can be resolved, shortcut this
 				var compiledValueProviderName = valueProviderType?.GetCustomAttribute(module.ImportReference(typeof(ProvideCompiledAttribute)))?.ConstructorArguments?[0].Value as string;
@@ -334,6 +343,9 @@ namespace Xamarin.Forms.Build.Tasks
 
 				vardefref.VariableDefinition = new VariableDefinition(module.TypeSystem.Object);
 				yield return Instruction.Create(OpCodes.Ldloc, context.Variables[node]);
+				if (acceptEmptyServiceProvider)
+					yield return Instruction.Create(OpCodes.Ldnull);
+				else
 					foreach (var instruction in node.PushServiceProvider(context, bpRef, propertyRef, propertyDeclaringTypeRef))
 						yield return instruction;
 				yield return Instruction.Create(OpCodes.Callvirt, provideValue);

Xamarin.Forms.Core/IMarkupExtension.cs

@@ -11,4 +11,9 @@ namespace Xamarin.Forms.Xaml
 	{
 		object ProvideValue(IServiceProvider serviceProvider);
 	}
+
+	[AttributeUsage(AttributeTargets.Class, Inherited = false)]
+	public sealed class AcceptEmptyServiceProviderAttribute : Attribute
+	{
+	}
 }

Xamarin.Forms.Xaml.UnitTests/AcceptEmptyServiceProvider.xaml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
+	xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+	xmlns:local="clr-namespace:Xamarin.Forms.Xaml.UnitTests"
+	x:Class="Xamarin.Forms.Xaml.UnitTests.AcceptEmptyServiceProvider" ServiceProvider="{local:Foo}">
+</ContentPage>

Xamarin.Forms.Xaml.UnitTests/AcceptEmptyServiceProvider.xaml.cs

@@ -0,0 +1,61 @@
+using System;
+using System.Collections.Generic;
+using NUnit.Framework;
+using Xamarin.Forms;
+using Xamarin.Forms.Core.UnitTests;
+
+namespace Xamarin.Forms.Xaml.UnitTests
+{
+	[AcceptEmptyServiceProvider]
+	public class FooExtension : IMarkupExtension<IServiceProvider>
+	{
+		public IServiceProvider ProvideValue(IServiceProvider serviceProvider)
+		{
+			return serviceProvider;
+		}
+
+		object IMarkupExtension.ProvideValue(IServiceProvider serviceProvider)
+		{
+			return (this as IMarkupExtension<IServiceProvider>).ProvideValue(serviceProvider);
+		}
+	}
+
+	public partial class AcceptEmptyServiceProvider : ContentPage
+	{
+		public AcceptEmptyServiceProvider()
+		{
+			InitializeComponent();
+		}
+
+		public AcceptEmptyServiceProvider(bool useCompiledXaml)
+		{
+			//this stub will be replaced at compile time
+		}
+
+		public IServiceProvider ServiceProvider { get; set; }
+
+		[TestFixture]
+		class Tests
+		{
+			[SetUp]
+			public void Setup()
+			{
+				Device.PlatformServices = new MockPlatformServices();
+			}
+
+			[TearDown]
+			public void TearDown()
+			{
+				Device.PlatformServices = null;
+			}
+
+			[TestCase(true)]
+			[TestCase(false)]
+			public void ServiceProviderIsNullOnAttributedExtensions(bool useCompiledXaml)
+			{
+				var p = new AcceptEmptyServiceProvider(useCompiledXaml);
+				Assert.IsNull(p.ServiceProvider);
+			}
+		}
+	}
+}

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

@@ -441,6 +441,10 @@
     </Compile>
     <Compile Include="Issues\Bz44216.xaml.cs">
       <DependentUpon>Bz44216.xaml</DependentUpon>
+      <DependentUpon>AcceptEmptyServiceProvider.xaml</DependentUpon>
+    </Compile>
+    <Compile Include="AcceptEmptyServiceProvider.xaml.cs">
+      <DependentUpon>AcceptEmptyServiceProvider.xaml</DependentUpon>
     </Compile>
   </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
@@ -805,6 +809,9 @@
     <EmbeddedResource Include="Issues\Bz44216.xaml">
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
     </EmbeddedResource>
+    <EmbeddedResource Include="AcceptEmptyServiceProvider.xaml">
+      <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
+    </EmbeddedResource>
   </ItemGroup>
   <ItemGroup>
     <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />

Xamarin.Forms.Xaml/ApplyPropertiesVisitor.cs

@@ -91,12 +91,12 @@ namespace Xamarin.Forms.Xaml
 			var valueProvider = value as IValueProvider;
 
 			if (markupExtension != null) {
-				var serviceProvider = new XamlServiceProvider(node, Context);
+				var serviceProvider = value.GetType().GetTypeInfo().GetCustomAttribute<AcceptEmptyServiceProviderAttribute>() == null ? new XamlServiceProvider(node, Context) : null;
 				value = markupExtension.ProvideValue(serviceProvider);
 			}
 
 			if (valueProvider != null) {
-				var serviceProvider = new XamlServiceProvider(node, Context);
+				var serviceProvider = value.GetType().GetTypeInfo().GetCustomAttribute<AcceptEmptyServiceProviderAttribute>() == null ? new XamlServiceProvider(node, Context) : null;
 				value = valueProvider.ProvideValue(serviceProvider);
 			}
 

docs/Xamarin.Forms.Core/Xamarin.Forms.Xaml/AcceptEmptyServiceProviderAttribute.xml

@@ -0,0 +1,36 @@
+<Type Name="AcceptEmptyServiceProviderAttribute" FullName="Xamarin.Forms.Xaml.AcceptEmptyServiceProviderAttribute">
+  <TypeSignature Language="C#" Value="public sealed class AcceptEmptyServiceProviderAttribute : Attribute" />
+  <TypeSignature Language="ILAsm" Value=".class public auto ansi sealed beforefieldinit AcceptEmptyServiceProviderAttribute extends System.Attribute" />
+  <AssemblyInfo>
+    <AssemblyName>Xamarin.Forms.Core</AssemblyName>
+    <AssemblyVersion>2.0.0.0</AssemblyVersion>
+  </AssemblyInfo>
+  <Base>
+    <BaseTypeName>System.Attribute</BaseTypeName>
+  </Base>
+  <Interfaces />
+  <Attributes>
+    <Attribute>
+      <AttributeName>System.AttributeUsage(System.AttributeTargets.Class, Inherited=false)</AttributeName>
+    </Attribute>
+  </Attributes>
+  <Docs>
+    <summary>To be added.</summary>
+    <remarks>To be added.</remarks>
+  </Docs>
+  <Members>
+    <Member MemberName=".ctor">
+      <MemberSignature Language="C#" Value="public AcceptEmptyServiceProviderAttribute ();" />
+      <MemberSignature Language="ILAsm" Value=".method public hidebysig specialname rtspecialname instance void .ctor() cil managed" />
+      <MemberType>Constructor</MemberType>
+      <AssemblyInfo>
+        <AssemblyVersion>2.0.0.0</AssemblyVersion>
+      </AssemblyInfo>
+      <Parameters />
+      <Docs>
+        <summary>To be added.</summary>
+        <remarks>To be added.</remarks>
+      </Docs>
+    </Member>
+  </Members>
+</Type>

docs/Xamarin.Forms.Core/index.xml

@@ -494,6 +494,7 @@
       <Type Name="ToolbarPlacement" Kind="Enumeration" />
     </Namespace>
     <Namespace Name="Xamarin.Forms.Xaml">
+      <Type Name="AcceptEmptyServiceProviderAttribute" Kind="Class" />
       <Type Name="IMarkupExtension" Kind="Interface" />
       <Type Name="IMarkupExtension`1" DisplayName="IMarkupExtension&lt;T&gt;" Kind="Interface" />
       <Type Name="IProvideValueTarget" Kind="Interface" />