Fix ref pack after merge

Author: John Luo

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

@@ -117,6 +117,12 @@ This package is an internal implementation of the .NET Core SDK and is not meant
       <Output TaskParameter="JoinResult" ItemName="_ReferencedExtensionsRefAssemblies" />
     </JoinItems>
 
+    <!-- _DuplicatedExtensionsRefAssemblies represents ref assemblies that are present in Microsoft.Internal.Extensions.Refs package and also are built in this repo. -->
+    <!-- This should be temporary while we migrate sources since there should be no duplication when sources are deleted from extensions. -->
+    <JoinItems Left="@(_ReferencedExtensionsRefAssemblies)" Right="@(_ResolvedProjectReferencePaths)" LeftKey="Filename" RightKey="Filename" ItemSpecToUse="Left">
+      <Output TaskParameter="JoinResult" ItemName="_DuplicatedExtensionsRefAssemblies" />
+    </JoinItems>
+
     <JoinItems Left="@(_ReferencedExtensionsRefAssemblies)" Right="@(ExternalAspNetCoreAppReference)" LeftKey="Filename" RightKey="Identity" ItemSpecToUse="Left">
       <Output TaskParameter="JoinResult" ItemName="_SelectedExtensionsRefs" />
     </JoinItems>
@@ -126,12 +132,15 @@ This package is an internal implementation of the .NET Core SDK and is not meant
     </JoinItems>
 
     <ItemGroup>
+      <!-- Do not exclude the ref assemblies that we built in this repo if it's also included in Microsoft.Internal.Extensions.Refs -->
+      <_ReferencedExtensionsRefAssembliesToExclude Include="@(_ReferencedExtensionsRefAssemblies)" Exclude="@(_DuplicatedExtensionsRefAssemblies)" />
+
       <!-- Exclude transitive external dependencies that are not directly referenced by projects in AspNetCore or Extensions -->
       <AspNetCoreReferenceAssemblyPath
           Include="@(ReferencePathWithRefAssemblies)"
           Condition="'%(ReferencePathWithRefAssemblies.IsReferenceAssembly)' == 'true'"
           Exclude="
-            @(_ReferencedExtensionsRefAssemblies);
+            @(_ReferencedExtensionsRefAssembliesToExclude);
             @(ReferencePathWithRefAssemblies->WithMetadataValue('NuGetPackageId', 'Microsoft.NETCore.App.Ref'));
             @(ReferencePathWithRefAssemblies->WithMetadataValue('NuGetPackageId', 'System.Security.Cryptography.Pkcs'));
             @(ReferencePathWithRefAssemblies->WithMetadataValue('NuGetPackageId', 'System.Drawing.Common'));