[release/6.0-preview4][wasm] Fix Blazor AOT builds inside Visual Studio (#52078)v6.0.0-preview.4.21253.7

* [wasm] Build tasks for net472 also (#51959)

* [wasm] Fix loading WebAssembly tasks in VS

- In case of `WasmAppBuilder.dll`, we were packaging only the task assembly, and
  `System.Reflection.MetadataLoadContext` for net472, same as net6.0 .

- But for net472, VS fails with errors like:

```
C:\Program Files\dotnet\packs\Microsoft.NET.Runtime.WebAssembly.Sdk\6.0.0-preview.4.21222.10\Sdk\WasmApp.targets(424,4): Error MSB4018: The "PInvokeTableGenerator" task failed unexpectedly.
System.IO.FileNotFoundException: Could not load file or assembly 'System.Reflection.Metadata, Version=1.4.5.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.
File name: 'System.Reflection.Metadata, Version=1.4.5.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'
   at System.Reflection.MetadataLoadContext.LoadFromStreamCore(Stream peStream)
   at System.Reflection.MetadataLoadContext.LoadFromAssemblyPath(String assemblyPath)
   at System.Reflection.PathAssemblyResolver.Resolve(MetadataLoadContext context, AssemblyName assemblyName)
   at System.Reflection.MetadataLoadContext.TryFindAssemblyByCallingResolveHandler(RoAssemblyName refName)
   at System.Reflection.MetadataLoadContext.ResolveToAssemblyOrExceptionAssembly(RoAssemblyName refName)
   at System.Reflection.MetadataLoadContext.TryResolveAssembly(RoAssemblyName refName, Exception& e)
   at System.Reflection.MetadataLoadContext.TryGetCoreAssembly(String coreAssemblyName, Exception& e)
   at System.Reflection.TypeLoading.CoreTypes..ctor(MetadataLoadContext loader, String coreAssemblyName)
   at System.Reflection.MetadataLoadContext..ctor(MetadataAssemblyResolver resolver, String coreAssemblyName)
   at PInvokeTableGenerator.GenPInvokeTable(String[] pinvokeModules, String[] assemblies) in /Users/radical/dev/r2/src/tasks/WasmAppBuilder/PInvokeTableGenerator.cs:line 42
   at PInvokeTableGenerator.Execute() in /Users/radical/dev/r2/src/tasks/WasmAppBuilder/PInvokeTableGenerator.cs:line 28
   at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute()
   at Microsoft.Build.BackEnd.TaskBuilder.<ExecuteInstantiatedTask>d__26.MoveNext()
```

- So, bundle all the dependent assemblies from the publish folder

* Address review feedback

* Update src/tasks/AotCompilerTask/MonoAOTCompiler.csproj

Co-authored-by: Daniel Plaisted <dsplaisted@gmail.com>

* Update src/tasks/AotCompilerTask/MonoAOTCompiler.csproj

Co-authored-by: Daniel Plaisted <dsplaisted@gmail.com>

* Update src/tasks/WasmAppBuilder/WasmAppBuilder.csproj

Co-authored-by: Daniel Plaisted <dsplaisted@gmail.com>

* Update src/tasks/WasmAppBuilder/WasmAppBuilder.csproj

Co-authored-by: Daniel Plaisted <dsplaisted@gmail.com>

* Apply suggestions from code review

Co-authored-by: Daniel Plaisted <dsplaisted@gmail.com>

* Use a property for net472

Co-authored-by: Ankit Jain <radical@gmail.com>
Co-authored-by: Daniel Plaisted <dsplaisted@gmail.com>

9 files changed, 78 insertions, 26 deletions

diff --git a/src/mono/nuget/Microsoft.NET.Runtime.MonoAOTCompiler.Task/Sdk/Sdk.props b/src/mono/nuget/Microsoft.NET.Runtime.MonoAOTCompiler.Task/Sdk/Sdk.props
index adcad9f50e1..a94224b1858 100644
--- a/src/mono/nuget/Microsoft.NET.Runtime.MonoAOTCompiler.Task/Sdk/Sdk.props
+++ b/src/mono/nuget/Microsoft.NET.Runtime.MonoAOTCompiler.Task/Sdk/Sdk.props
@@ -1,6 +1,7 @@
 <Project>
   <PropertyGroup>
-    <MonoAOTCompilerTasksAssemblyPath>$(MSBuildThisFileDirectory)..\tasks\MonoAOTCompiler.dll</MonoAOTCompilerTasksAssemblyPath>
+    <MonoAOTCompilerTasksAssemblyPath Condition="'$(MSBuildRuntimeType)' == 'Core'">$(MSBuildThisFileDirectory)..\tasks\net6.0\MonoAOTCompiler.dll</MonoAOTCompilerTasksAssemblyPath>
+    <MonoAOTCompilerTasksAssemblyPath Condition="'$(MSBuildRuntimeType)' != 'Core'">$(MSBuildThisFileDirectory)..\tasks\net472\MonoAOTCompiler.dll</MonoAOTCompilerTasksAssemblyPath>
   </PropertyGroup>
   <UsingTask TaskName="MonoAOTCompiler" AssemblyFile="$(MonoAOTCompilerTasksAssemblyPath)" />
 </Project>
diff --git a/src/mono/nuget/Microsoft.NET.Runtime.WebAssembly.Sdk/Sdk/Sdk.targets b/src/mono/nuget/Microsoft.NET.Runtime.WebAssembly.Sdk/Sdk/Sdk.targets
index 9bd74455ac6..2c2959c87e5 100644
--- a/src/mono/nuget/Microsoft.NET.Runtime.WebAssembly.Sdk/Sdk/Sdk.targets
+++ b/src/mono/nuget/Microsoft.NET.Runtime.WebAssembly.Sdk/Sdk/Sdk.targets
@@ -1,8 +1,11 @@
 <Project>
   <!-- Property overrides -->
   <PropertyGroup>
-    <WasmAppBuilderTasksAssemblyPath>$(MSBuildThisFileDirectory)..\tasks\WasmAppBuilder.dll</WasmAppBuilderTasksAssemblyPath>
-    <WasmBuildTasksAssemblyPath>$(MSBuildThisFileDirectory)..\tasks\WasmBuildTasks.dll</WasmBuildTasksAssemblyPath>
+    <_TasksDir Condition="'$(MSBuildRuntimeType)' == 'Core'">$(MSBuildThisFileDirectory)..\tasks\net6.0\</_TasksDir>
+    <_TasksDir Condition="'$(MSBuildRuntimeType)' != 'Core'">$(MSBuildThisFileDirectory)..\tasks\net472\</_TasksDir>
+
+    <WasmAppBuilderTasksAssemblyPath>$(_TasksDir)WasmAppBuilder.dll</WasmAppBuilderTasksAssemblyPath>
+    <WasmBuildTasksAssemblyPath>$(_TasksDir)WasmBuildTasks.dll</WasmBuildTasksAssemblyPath>
   </PropertyGroup>
 
   <Import Project="$(MSBuildThisFileDirectory)\WasmApp.props" />
diff --git a/src/tasks/AotCompilerTask/MonoAOTCompiler.cs b/src/tasks/AotCompilerTask/MonoAOTCompiler.cs
index 108b550725a..51acec5216c 100644
--- a/src/tasks/AotCompilerTask/MonoAOTCompiler.cs
+++ b/src/tasks/AotCompilerTask/MonoAOTCompiler.cs
@@ -185,7 +185,7 @@ public class MonoAOTCompiler : Microsoft.Build.Utilities.Task
 
         if (!Enum.TryParse(Mode, true, out parsedAotMode))
         {
-            Log.LogError($"Unknown Mode value: {Mode}. '{nameof(Mode)}' must be one of: {string.Join(',', Enum.GetNames(typeof(MonoAotMode)))}");
+            Log.LogError($"Unknown Mode value: {Mode}. '{nameof(Mode)}' must be one of: {string.Join(",", Enum.GetNames(typeof(MonoAotMode)))}");
             return false;
         }
 
@@ -217,7 +217,7 @@ public class MonoAOTCompiler : Microsoft.Build.Utilities.Task
 
         string? monoPaths = null;
         if (AdditionalAssemblySearchPaths != null)
-            monoPaths = string.Join(Path.PathSeparator, AdditionalAssemblySearchPaths);
+            monoPaths = string.Join(Path.PathSeparator.ToString(), AdditionalAssemblySearchPaths);
 
         if (DisableParallelAot)
         {
@@ -252,13 +252,13 @@ public class MonoAOTCompiler : Microsoft.Build.Utilities.Task
         var a = assemblyItem.GetMetadata("AotArguments");
         if (a != null)
         {
-             aotArgs.AddRange(a.Split(";", StringSplitOptions.RemoveEmptyEntries));
+             aotArgs.AddRange(a.Split(new char[]{ ';' }, StringSplitOptions.RemoveEmptyEntries));
         }
 
         var p = assemblyItem.GetMetadata("ProcessArguments");
         if (p != null)
         {
-            processArgs.AddRange(p.Split(";", StringSplitOptions.RemoveEmptyEntries));
+            processArgs.AddRange(p.Split(new char[]{ ';' }, StringSplitOptions.RemoveEmptyEntries));
         }
 
         Log.LogMessage(MessageImportance.Low, $"[AOT] {assembly}");
diff --git a/src/tasks/AotCompilerTask/MonoAOTCompiler.csproj b/src/tasks/AotCompilerTask/MonoAOTCompiler.csproj
index 419a364377d..c9bf35cf473 100644
--- a/src/tasks/AotCompilerTask/MonoAOTCompiler.csproj
+++ b/src/tasks/AotCompilerTask/MonoAOTCompiler.csproj
@@ -1,11 +1,14 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFramework>$(NetCoreAppToolCurrent)</TargetFramework>
+    <TargetFrameworks>$(NetCoreAppToolCurrent);$(TargetFrameworkForNETFramework)</TargetFrameworks>
     <OutputType>Library</OutputType>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
     <EnableDefaultCompileItems>false</EnableDefaultCompileItems>
     <Nullable>enable</Nullable>
     <NoWarn>$(NoWarn),CA1050</NoWarn>
+
+    <!-- Ignore nullable warnings on net4* -->
+    <NoWarn Condition="$([MSBuild]::GetTargetFrameworkIdentifier('$(TargetFramework)')) == '.NETFramework'">$(NoWarn),CS8604,CS8602</NoWarn>
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.Build" Version="$(RefOnlyMicrosoftBuildVersion)" />
@@ -16,6 +19,7 @@
   <ItemGroup>
     <Compile Include="MonoAOTCompiler.cs" />
     <Compile Include="..\Common\Utils.cs" />
+    <Compile Include="$(RepoRoot)src\libraries\System.Private.CoreLib/src/System/Diagnostics/CodeAnalysis/NullableAttributes.cs" Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework'" />
   </ItemGroup>
   <ItemGroup>
     <Content Include="MonoAOTCompiler.props">
@@ -26,7 +30,10 @@
   <!-- GetFilesToPackage assists to place `MonoAOTCompiler.dll` in a NuGet package in Microsoft.NET.Runtime.MonoAOTCompiler.Task.pkgproj for external use -->
   <Target Name="GetFilesToPackage" Returns="@(FilesToPackage)">
     <ItemGroup>
-      <FilesToPackage Include="$(OutputPath)$(AssemblyName).dll" TargetPath="tasks" />
+      <_PublishFramework Remove="@(_PublishFramework)" />
+      <_PublishFramework Include="$(TargetFrameworks)" />
+
+      <FilesToPackage Include="$(OutputPath)%(_PublishFramework.Identity)\$(AssemblyName).dll" TargetPath="tasks\%(_PublishFramework.Identity)" />
     </ItemGroup>
   </Target>
 </Project>
diff --git a/src/tasks/Common/IsExternalInit.cs b/src/tasks/Common/IsExternalInit.cs
new file mode 100644
index 00000000000..d7be6913103
--- /dev/null
+++ b/src/tasks/Common/IsExternalInit.cs
@@ -0,0 +1,7 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Runtime.CompilerServices
+{
+    internal sealed class IsExternalInit { }
+}
diff --git a/src/tasks/Common/Utils.cs b/src/tasks/Common/Utils.cs
index b7c1fd6d91e..78738d59be2 100644
--- a/src/tasks/Common/Utils.cs
+++ b/src/tasks/Common/Utils.cs
@@ -102,6 +102,7 @@ internal static class Utils
         return outputBuilder.ToString().Trim('\r', '\n');
     }
 
+#if NETCOREAPP
     public static void DirectoryCopy(string sourceDir, string destDir, Func<string, bool> predicate)
     {
         string[] files = Directory.GetFiles(sourceDir, "*", SearchOption.AllDirectories);
@@ -118,6 +119,7 @@ internal static class Utils
             File.Copy(file, Path.Combine(destDir, relativePath), true);
         }
     }
+#endif
 
     public static TaskLoggingHelper? Logger { get; set; }
 
diff --git a/src/tasks/Directory.Build.props b/src/tasks/Directory.Build.props
new file mode 100644
index 00000000000..7ed8a459d2f
--- /dev/null
+++ b/src/tasks/Directory.Build.props
@@ -0,0 +1,7 @@
+<Project>
+  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.props, '$(MSBuildThisFileDirectory)..'))" />
+
+  <PropertyGroup>
+    <TargetFrameworkForNETFramework>net472</TargetFrameworkForNETFramework>
+  </PropertyGroup>
+</Project>
diff --git a/src/tasks/WasmAppBuilder/WasmAppBuilder.cs b/src/tasks/WasmAppBuilder/WasmAppBuilder.cs
index d1cf986b3cc..9ef7679c292 100644
--- a/src/tasks/WasmAppBuilder/WasmAppBuilder.cs
+++ b/src/tasks/WasmAppBuilder/WasmAppBuilder.cs
@@ -144,18 +144,18 @@ public class WasmAppBuilder : Task
         var config = new WasmAppConfig ();
 
         // Create app
-        var asmRootPath = Path.Join(AppDir, config.AssemblyRoot);
+        var asmRootPath = Path.Combine(AppDir, config.AssemblyRoot);
         Directory.CreateDirectory(AppDir!);
         Directory.CreateDirectory(asmRootPath);
         foreach (var assembly in _assemblies)
         {
-            FileCopyChecked(assembly, Path.Join(asmRootPath, Path.GetFileName(assembly)), "Assemblies");
+            FileCopyChecked(assembly, Path.Combine(asmRootPath, Path.GetFileName(assembly)), "Assemblies");
             if (DebugLevel != 0)
             {
                 var pdb = assembly;
                 pdb = Path.ChangeExtension(pdb, ".pdb");
                 if (File.Exists(pdb))
-                    FileCopyChecked(pdb, Path.Join(asmRootPath, Path.GetFileName(pdb)), "Assemblies");
+                    FileCopyChecked(pdb, Path.Combine(asmRootPath, Path.GetFileName(pdb)), "Assemblies");
             }
         }
 
@@ -165,10 +165,10 @@ public class WasmAppBuilder : Task
             if (!FileCopyChecked(item.ItemSpec, dest, "NativeAssets"))
                 return false;
         }
-        FileCopyChecked(MainJS!, Path.Join(AppDir, "runtime.js"), string.Empty);
+        FileCopyChecked(MainJS!, Path.Combine(AppDir, "runtime.js"), string.Empty);
 
         var html = @"<html><body><script type=""text/javascript"" src=""runtime.js""></script></body></html>";
-        File.WriteAllText(Path.Join(AppDir, "index.html"), html);
+        File.WriteAllText(Path.Combine(AppDir, "index.html"), html);
 
         foreach (var assembly in _assemblies)
         {
@@ -190,16 +190,16 @@ public class WasmAppBuilder : Task
                 string culture = assembly.GetMetadata("CultureName") ?? string.Empty;
                 string fullPath = assembly.GetMetadata("Identity");
                 string name = Path.GetFileName(fullPath);
-                string directory = Path.Join(AppDir, config.AssemblyRoot, culture);
+                string directory = Path.Combine(AppDir, config.AssemblyRoot, culture);
                 Directory.CreateDirectory(directory);
-                FileCopyChecked(fullPath, Path.Join(directory, name), "SatelliteAssemblies");
+                FileCopyChecked(fullPath, Path.Combine(directory, name), "SatelliteAssemblies");
                 config.Assets.Add(new SatelliteAssemblyEntry(name, culture));
             }
         }
 
         if (FilesToIncludeInFileSystem != null)
         {
-            string supportFilesDir = Path.Join(AppDir, "supportFiles");
+            string supportFilesDir = Path.Combine(AppDir, "supportFiles");
             Directory.CreateDirectory(supportFilesDir);
 
             var i = 0;
@@ -216,7 +216,7 @@ public class WasmAppBuilder : Task
 
                 var generatedFileName = $"{i++}_{Path.GetFileName(item.ItemSpec)}";
 
-                FileCopyChecked(item.ItemSpec, Path.Join(supportFilesDir, generatedFileName), "FilesToIncludeInFileSystem");
+                FileCopyChecked(item.ItemSpec, Path.Combine(supportFilesDir, generatedFileName), "FilesToIncludeInFileSystem");
 
                 var asset = new VfsEntry ($"supportFiles/{generatedFileName}") {
                     VirtualPath = targetPath
@@ -246,7 +246,7 @@ public class WasmAppBuilder : Task
             config.Extra[name] = valueObject;
         }
 
-        string monoConfigPath = Path.Join(AppDir, "mono-config.js");
+        string monoConfigPath = Path.Combine(AppDir, "mono-config.js");
         using (var sw = File.CreateText(monoConfigPath))
         {
             var json = JsonSerializer.Serialize (config, new JsonSerializerOptions { WriteIndented = true });
@@ -284,9 +284,9 @@ public class WasmAppBuilder : Task
             return true;
 
         // Try parsing as a quoted string
-        if (rawValue!.Length > 1 && rawValue![0] == '"' && rawValue![^1] == '"')
+        if (rawValue!.Length > 1 && rawValue![0] == '"' && rawValue![rawValue!.Length - 1] == '"')
         {
-            valueObject = rawValue![1..^1];
+            valueObject = rawValue!.Substring(1, rawValue!.Length - 2);
             return true;
         }
 
diff --git a/src/tasks/WasmAppBuilder/WasmAppBuilder.csproj b/src/tasks/WasmAppBuilder/WasmAppBuilder.csproj
index 0846c59795d..e7641b3ab1a 100644
--- a/src/tasks/WasmAppBuilder/WasmAppBuilder.csproj
+++ b/src/tasks/WasmAppBuilder/WasmAppBuilder.csproj
@@ -1,9 +1,18 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFramework>$(NetCoreAppToolCurrent)</TargetFramework>
+    <TargetFrameworks>$(NetCoreAppToolCurrent);$(TargetFrameworkForNETFramework)</TargetFrameworks>
     <Nullable>enable</Nullable>
     <NoWarn>$(NoWarn),CA1050</NoWarn>
+
+    <!-- Ignore nullable warnings on net4* -->
+    <NoWarn Condition="$([MSBuild]::GetTargetFrameworkIdentifier('$(TargetFramework)')) == '.NETFramework'">$(NoWarn),CS8604,CS8602</NoWarn>
   </PropertyGroup>
+
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework'">
+    <Compile Include="..\Common\IsExternalInit.cs" />
+    <Compile Include="$(RepoRoot)src\libraries\System.Private.CoreLib/src/System/Diagnostics/CodeAnalysis/NullableAttributes.cs" />
+  </ItemGroup>
+
   <ItemGroup>
     <PackageReference Include="Microsoft.Build" Version="$(RefOnlyMicrosoftBuildVersion)" />
     <PackageReference Include="Microsoft.Build.Framework" Version="$(RefOnlyMicrosoftBuildFrameworkVersion)" />
@@ -13,13 +22,29 @@
   </ItemGroup>
 
   <Target Name="PublishBuilder"
-          AfterTargets="Build"
-          DependsOnTargets="Publish" />
+          AfterTargets="Build">
+
+    <!-- needed for publishing with multi-targeting. We are publishing essentially to get the SR.MetadataLoadContext.dll :/ -->
+    <ItemGroup>
+      <_PublishFramework Include="$(TargetFrameworks)" />
+    </ItemGroup>
+    <MSBuild Projects="$(MSBuildProjectFile)" Targets="Publish" Properties="TargetFramework=%(_PublishFramework.Identity)" />
+  </Target>
 
   <Target Name="GetFilesToPackage" Returns="@(FilesToPackage)">
     <ItemGroup>
-      <FilesToPackage Include="$(OutputPath)$(MSBuildProjectName)*" TargetPath="tasks" />
-      <FilesToPackage Include="$(PublishDir)System.Reflection.MetadataLoadContext.dll" TargetPath="tasks" />
+      <_PublishFramework Remove="@(_PublishFramework)" />
+      <_PublishFramework Include="$(TargetFrameworks)" />
+
+      <!-- non-net4* -->
+      <FilesToPackage Include="$(OutputPath)$(NetCoreAppToolCurrent)\$(MSBuildProjectName)*"
+                      TargetPath="tasks\$(NetCoreAppToolCurrent)" />
+      <FilesToPackage Include="$(OutputPath)$(NetCoreAppToolCurrent)\publish\System.Reflection.MetadataLoadContext.dll"
+                      TargetPath="tasks\$(NetCoreAppToolCurrent)" />
+
+      <!-- for net472 we need all the dependent assemblies too, so copy from the publish folder -->
+      <FilesToPackage Include="$(OutputPath)$(TargetFrameworkForNETFramework)\publish\*"
+                      TargetPath="tasks\$(TargetFrameworkForNETFramework)" />
     </ItemGroup>
   </Target>