[build] post-build fix of the assembly

XFCorePostProcessor.Tasks/FixXFCoreAssembly.cs

@@ -0,0 +1,64 @@
+using System;
+using Microsoft.Build.Utilities;
+using Mono.Cecil;
+using Mono.Cecil.Rocks;
+
+using Mono.Cecil.Cil;
+using Microsoft.Build.Framework;
+using System.IO;
+
+namespace XFCorePostProcessor.Tasks
+{
+	public class FixXFCoreAssembly : Task
+	{
+		[Required]
+		public string Assembly { get; set; }
+		public string ReferencePath { get; set; }
+
+		public override bool Execute()
+		{
+			Log.LogMessage("Generating backcompat code for #2835");
+
+			var resolver =  new AssemblyResolver();
+
+			if (!string.IsNullOrEmpty(ReferencePath)) {
+				var paths = ReferencePath.Replace("//", "/").Split(';');
+				foreach (var p in paths) {
+					var searchpath = Path.GetDirectoryName(p);
+					resolver.AddSearchDirectory(searchpath);
+				}
+			}
+
+			using (var assemblyDefinition = AssemblyDefinition.ReadAssembly(Assembly, new ReaderParameters { AssemblyResolver = resolver, ReadWrite = true, ReadSymbols = true })) {
+				var resourceLoader = assemblyDefinition.MainModule.GetType("Xamarin.Forms.Internals.ResourceLoader");
+				var module = assemblyDefinition.MainModule;
+				var methodDef = new MethodDefinition("get_ResourceProvider",
+													 MethodAttributes.Static | MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.HideBySig,
+													 module.ImportReference(module.ImportReference(typeof(Func<,>)).MakeGenericInstanceType(module.ImportReference(typeof(string)),
+														module.ImportReference(typeof(string)))));
+
+				var body = new MethodBody(methodDef);
+				var il = body.GetILProcessor();
+				il.Emit(OpCodes.Ldnull);
+				il.Emit(OpCodes.Ret);
+				methodDef.Body = body;
+				resourceLoader.Methods.Add(methodDef);
+
+				assemblyDefinition.Write(new WriterParameters {
+					WriteSymbols = true,
+				});
+			}
+			return true;
+		}
+	}
+
+	class AssemblyResolver : DefaultAssemblyResolver
+	{
+		public void AddAssembly(string p)
+		{
+			RegisterAssembly(AssemblyDefinition.ReadAssembly(p, new ReaderParameters {
+				AssemblyResolver = this
+			}));
+		}
+	}
+}

XFCorePostProcessor.Tasks/XFCorePostProcessor.Tasks.csproj

@@ -0,0 +1,15 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netstandard2.0</TargetFramework>
+		<CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Build" Version="15.7.179" />
+    <PackageReference Include="Microsoft.Build.Framework" Version="15.7.179" />
+    <PackageReference Include="Microsoft.Build.Utilities.Core" Version="15.7.179" />
+    <PackageReference Include="Microsoft.Build.Tasks.Core" Version="15.7.179" />
+    <PackageReference Include="Mono.Cecil" Version="0.10.0-beta7" />
+  </ItemGroup>
+</Project>

Xamarin.Forms.Core/Xamarin.Forms.Core.csproj

@@ -17,4 +17,8 @@
     <PackageReference Include="System.Dynamic.Runtime" Version="4.3.0" />
   </ItemGroup>
   <Import Project="..\Xamarin.Flex\Xamarin.Flex.projitems" Label="Shared" Condition="Exists('..\Xamarin.Flex\Xamarin.Flex.projitems')" />
+	<UsingTask TaskName="XFCorePostProcessor.Tasks.FixXFCoreAssembly" AssemblyFile="..\XFCorePostProcessor.Tasks\bin\Debug\netstandard2.0\XFCorePostProcessor.Tasks.dll" />
+	<Target AfterTargets="AfterCompile" Name="ShameHat">
+		<FixXFCoreAssembly Assembly="$(IntermediateOutputPath)$(TargetFileName)" ReferencePath="@(ReferencePath)" />
+	</Target>
 </Project>

Xamarin.Forms.Xaml.UnitTests/XFCorePostProcessorCodeInjected.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Reflection;
+using System.Linq;
+
+using NUnit.Framework;
+
+namespace Xamarin.Forms.Xaml.UnitTests
+{
+	[TestFixture]
+	public class XFCorePostProcessorCodeInjected
+	{
+		[Test]
+		public void InjectedCodeIsPresent()
+		{
+			var resLoader = typeof(Xamarin.Forms.Internals.ResourceLoader);
+			Assert.True(resLoader.GetMethods().Any(mi => mi.Name == "get_ResourceProvider" && mi.ReturnType == typeof(Func<string, string>)));
+			Assert.True(resLoader.GetMethods().Any(mi => mi.Name == "get_ResourceProvider" && mi.ReturnType == typeof(Func<AssemblyName, string, string>)));
+			Assert.True(resLoader.GetProperty("ResourceProvider") != null);
+			Assert.True(resLoader.GetProperty("ResourceProvider").GetMethod.ReturnType == typeof(Func<AssemblyName, string, string>));
+		}
+	}
+}

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

@@ -615,6 +615,7 @@
     <Compile Include="Issues\Gh2632.xaml.cs">
       <DependentUpon>Gh2632.xaml</DependentUpon>
     </Compile>
+    <Compile Include="XFCorePostProcessorCodeInjected.cs" />
   </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
   <Import Project="..\.nuspec\Xamarin.Forms.Debug.targets" Condition="'$(BuildingInsideVisualStudio)' == 'true' AND Exists('..\.nuspec\Xamarin.Forms.Build.Tasks.dll')" />

Xamarin.Forms.sln

@@ -174,6 +174,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Xamarin.Forms.Maps.Design",
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Xamarin.Forms.Xaml.Design", "Xamarin.Forms.Xaml.Design\Xamarin.Forms.Xaml.Design.csproj", "{65BC4888-CC59-428A-9B75-540CF1C09480}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "XFCorePostProcessor.Tasks", "XFCorePostProcessor.Tasks\XFCorePostProcessor.Tasks.csproj", "{5BBF4A3F-4AD1-47FD-B250-05EA793F939D}"
+EndProject
 Global
 	GlobalSection(SharedMSBuildProjectFiles) = preSolution
 		Xamarin.Forms.Controls.Issues\Xamarin.Forms.Controls.Issues.Shared\Xamarin.Forms.Controls.Issues.Shared.projitems*{0a39a74b-6f7a-4d41-84f2-b0ccdce899df}*SharedItemsImports = 4