Explicitly map @(Reference) to @(PackageReference) for Microsoft.Internal.Extensions.Refs

Author: dougbu

eng/targets/ResolveReferences.targets

@@ -210,6 +210,24 @@
            Text="Could not resolve this reference. Could not locate the package or project for "%(Reference.Identity)". Did you update baselines and dependencies lists? See docs/ReferenceResolution.md for more details." />
   </Target>
 
+  <PropertyGroup>
+    <_CompileTfmUsingReferenceAssemblies>false</_CompileTfmUsingReferenceAssemblies>
+    <_CompileTfmUsingReferenceAssemblies
+        Condition=" '$(CompileUsingReferenceAssemblies)' != false AND '$(TargetFramework)' == '$(DefaultNetCoreTargetFramework)' ">true</_CompileTfmUsingReferenceAssemblies>
+  </PropertyGroup>
+  <!--
+    If we have a ref/ assembly from Extensions for a package, use that when compiling. The build-only reference to
+    Microsoft.Internal.Extensions.Refs ensures package is installed and $(MicrosoftInternalExtensionsRefsPath) is set.
+  -->
+  <ItemGroup
+      Condition=" $(_CompileTfmUsingReferenceAssemblies) OR ('$(IsTargetingPackBuilding)' != 'false' AND '$(MSBuildProjectName)' == 'Microsoft.AspNetCore.App.Ref') ">
+    <PackageReference Include="Microsoft.Internal.Extensions.Refs"
+        Version="$(MicrosoftInternalExtensionsRefsPackageVersion)"
+        IsImplicitlyDefined="true"
+        IncludeAssets="Build"
+        PrivateAssets="All" />
+  </ItemGroup>
+
   <!-- These targets are used to generate the map of assembly name to project files. See also the /t:GenerateProjectList target in build/repo.targets. -->
   <Target Name="GetReferencesProvided" Returns="@(ProvidesReference)">
     <ItemGroup>

src/Framework/ref/Microsoft.AspNetCore.App.Ref.csproj

@@ -59,7 +59,6 @@ This package is an internal implementation of the .NET Core SDK and is not meant
   <ItemGroup>
     <!-- Note: do not add _TransitiveExternalAspNetCoreAppReference to this list. This is intentionally not listed as a direct package reference. -->
     <Reference Include="@(AspNetCoreAppReference);@(AspNetCoreAppReferenceAndPackage);@(ExternalAspNetCoreAppReference)" />
-    <Reference Include="Microsoft.Internal.Extensions.Refs" Version="$(MicrosoftInternalExtensionsRefsPackageVersion)" IncludeAssets="Build" />
     <!-- Enforce build order. Targeting pack needs to bundle information about the runtime. -->
     <ProjectReference Include="..\src\Microsoft.AspNetCore.App.Runtime.csproj">
       <ReferenceOutputAssembly>false</ReferenceOutputAssembly>