Remove PKT for mscorlib to allow PathAssemblyResolver to return most recent assembly version

src/Microsoft.DotNet.Wpf/src/PresentationBuildTasks/PresentationBuildTasks.csproj

@@ -98,6 +98,9 @@
     <Compile Include="$(WpfSharedDir)\System\Windows\Markup\ReflectionHelper.cs">
       <Link>Shared\System\Windows\Markup\ReflectionHelper.cs</Link>
     </Compile>
+    <Compile Include="$(WpfSharedDir)\System\Windows\Markup\RetargetablePathAssemblyResolver.cs">
+      <Link>Shared\System\Windows\Markup\RetargetablePathAssemblyResolver.cs</Link>
+    </Compile>
     <Compile Include="$(WpfSharedDir)\MS\Internal\Xaml\Parser\SpecialBracketCharacters.cs">
       <Link>Shared\MS\Internal\Xaml\Parser\SpecialBracketCharacters.cs</Link>
     </Compile>

src/Microsoft.DotNet.Wpf/src/Shared/System/Windows/Markup/ReflectionHelper.cs

@@ -62,7 +62,7 @@ namespace System.Xaml
             // System.Reflection.MetadataLoadContext Assembly cache 
             _cachedMetadataLoadContextAssemblies = new Dictionary<string, Assembly>(StringComparer.OrdinalIgnoreCase);
             _cachedMetadataLoadContextAssembliesByNameNoExtension = new Dictionary<string, Assembly>(StringComparer.OrdinalIgnoreCase);
-            _metadataLoadContext = new MetadataLoadContext(new PathAssemblyResolver(assemblyPaths), MscorlibReflectionAssemblyName);
+            _metadataLoadContext = new MetadataLoadContext(new RetargetablePathAssemblyResolver(assemblyPaths), MscorlibReflectionAssemblyName);
             _localAssemblyName = string.Empty;
         }
 

src/Microsoft.DotNet.Wpf/src/Shared/System/Windows/Markup/RetargetablePathAssemblyResolver.cs

@@ -0,0 +1,35 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Collections.Generic;
+using System.IO;
+using System.Reflection;
+
+namespace MS.Internal.Markup
+{
+    public class RetargetablePathAssemblyResolver : MetadataAssemblyResolver
+    {
+        private PathAssemblyResolver _pathAssemblyResolver; 
+
+        public RetargetablePathAssemblyResolver(IEnumerable<string> assemblyPaths)
+        {
+            _pathAssemblyResolver = new PathAssemblyResolver(assemblyPaths);
+        }
+
+        public override Assembly Resolve(MetadataLoadContext context, AssemblyName assemblyName)
+        {
+            // PathAssemblyResolver will resolve the target assembly to the highest 
+            // version of the target assembly available in the 'assemblyPaths' assembly
+            // list, only if the public key token for the target assembly is not set.
+            // Remove the public key token from 'mscorlib' to allow PathAssemblyResolver
+            // to resolve the most recent version of 'mscorlib'. 
+            if (assemblyName.Name.Equals(ReflectionHelper.MscorlibReflectionAssemblyName))
+            {
+                assemblyName.SetPublicKeyToken(null);
+            }
+
+            return _pathAssemblyResolver.Resolve(context, assemblyName);
+        }
+    }
+}