[wasm] Restore net472 multi-targeting for WasmAppBuilder; fix Type.IsFunctionPointer compile break

src/tasks/WasmAppBuilder/WasmAppBuilder.csproj

@@ -1,13 +1,20 @@
 <Project Sdk="Microsoft.NET.Sdk">
-
   <PropertyGroup>
-    <TargetFramework>$(NetCoreAppToolCurrent)</TargetFramework>
-    <NoWarn>$(NoWarn),CA1050,CA1850</NoWarn>
+    <TargetFrameworks>$(NetCoreAppToolCurrent);$(NetFrameworkToolCurrent)</TargetFrameworks>
+    <Nullable>enable</Nullable>
+    <!-- Ignore nullable warnings on net4* -->
+    <NoWarn Condition="$([MSBuild]::GetTargetFrameworkIdentifier('$(TargetFramework)')) == '.NETFramework'">$(NoWarn),CA1050,CS8604,CS8602</NoWarn>
+    <NoWarn Condition="$([MSBuild]::GetTargetFrameworkIdentifier('$(TargetFramework)')) != '.NETFramework'">$(NoWarn),CA1050,CA1850</NoWarn>
     <EnableSingleFileAnalyzer>false</EnableSingleFileAnalyzer>
     <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </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 Condition="'$(RuntimeFlavor)' == 'CoreCLR'">
     <Compile Remove="mono/*.cs" />
   </ItemGroup>
@@ -31,17 +38,25 @@
 
     <!-- Reference Microsoft.Build.Tasks.Core directly to avoid bringing in it's package closure.
          This assembly is provided by MSBuild.  -->
-    <PackageDownloadAndReference Include="Microsoft.Build.Tasks.Core" Version="$(MicrosoftBuildTasksCoreVersion)" Folder="ref/net8.0" />
+    <PackageDownloadAndReference Include="Microsoft.Build.Tasks.Core" Version="$(MicrosoftBuildTasksCoreVersion)" Folder="ref/net472" Condition="$([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)', 'net472'))" />
+    <PackageDownloadAndReference Include="Microsoft.Build.Tasks.Core" Version="$(MicrosoftBuildTasksCoreVersion)" Folder="ref/net8.0" Condition="$([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)', 'net8.0'))" />
   </ItemGroup>
 
   <Target Name="GetFilesToPackage" Returns="@(FilesToPackage)">
     <ItemGroup>
-      <FilesToPackage Include="$(OutputPath)$(MSBuildProjectName)*" TargetPath="tasks\$(NetCoreAppToolCurrent)" />
-      <FilesToPackage Include="$(OutputPath)Microsoft.NET.WebAssembly.Webcil.dll" TargetPath="tasks\$(NetCoreAppToolCurrent)" />
+      <!-- .NETCoreApp -->
+      <FilesToPackage Include="$(OutputPath)$(NetCoreAppToolCurrent)\$(MSBuildProjectName)*"
+                      TargetPath="tasks\$(NetCoreAppToolCurrent)" />
+      <FilesToPackage Include="$(OutputPath)$(NetCoreAppToolCurrent)\Microsoft.NET.WebAssembly.Webcil.dll"
+                      TargetPath="tasks\$(NetCoreAppToolCurrent)" />
+
+      <!-- For .NETFramework we need all the dependent assemblies too, so copy from the publish folder -->
+      <FilesToPackage Include="$(OutputPath)$(NetFrameworkToolCurrent)\*"
+                      TargetPath="tasks\$(NetFrameworkToolCurrent)" />
     </ItemGroup>
   </Target>
 
-  <UsingTask TaskName="ManagedToNativeGenerator" Runtime="NET" TaskFactory="TaskHostFactory" AssemblyFile="$(TargetPath)" />
+  <UsingTask TaskName="ManagedToNativeGenerator" TaskFactory="TaskHostFactory" AssemblyFile="$(OutputPath)$(NetCoreAppToolCurrent)\WasmAppBuilder.dll" />
   <Target Name="RunGenerator" DependsOnTargets="Build" Condition="'$(AssembliesScanPath)' != ''">
       <ItemGroup>
         <WasmPInvokeAssembly Include="$(AssembliesScanPath)*.dll" />

src/tasks/WasmAppBuilder/coreclr/PInvokeTableGenerator.cs

@@ -267,7 +267,7 @@ private static string PickCTypeNameForUnknownType(Type t)
         if (!t.IsValueType)
             return "void *";
         // Pass pointers and function pointers by-value
-        else if (t.IsPointer || t.IsFunctionPointer)
+        else if (t.IsPointer || IsFunctionPointer(t))
             return "void *";
         else if (t.IsPrimitive)
             throw new NotImplementedException("No native type mapping for type " + t);
@@ -504,6 +504,12 @@ private string ThunkMapEntryLine(PInvokeCallback cb, LogAdapter Log)
 
     private static readonly Dictionary<Type, bool> _blittableCache = new();
 
+    public static bool IsFunctionPointer(Type type)
+    {
+        object? bIsFunctionPointer = type.GetType().GetProperty("IsFunctionPointer")?.GetValue(type);
+        return (bIsFunctionPointer is bool b) && b;
+    }
+
     public static bool IsBlittable(Type type, LogAdapter log)
     {
         // We maintain a cache of results in order to only produce log messages the first time
@@ -523,7 +529,7 @@ static bool IsBlittableUncached(Type type, LogAdapter log)
             if (type.IsPrimitive || type.IsByRef || type.IsPointer || type.IsEnum)
                 return true;
 
-            if (type.IsFunctionPointer)
+            if (IsFunctionPointer(type))
                 return true;
 
             // HACK: SkiaSharp has pinvokes that rely on this

src/tasks/WasmAppBuilder/coreclr/SignatureMapper.cs

@@ -63,7 +63,7 @@ internal static class SignatureMapper
         }
         else if (t.IsPointer)
             c = 'i';
-        else if (t.IsFunctionPointer)
+        else if (PInvokeTableGenerator.IsFunctionPointer(t))
             c = 'i';
         else if (t.IsValueType)
         {