Add test for TypeIdentifierAttribute

src/libraries/Common/tests/TestUtilities/System/PlatformDetection.cs

@@ -184,6 +184,7 @@ private static bool GetLinqExpressionsBuiltWithIsInterpretingOnly()
 
         public static bool IsInvokingStaticConstructorsSupported => !IsNativeAot;
         public static bool IsInvokingFinalizersSupported => !IsNativeAot;
+        public static bool IsTypeEquivalenceSupported => !IsNativeAot && !IsMonoRuntime && IsWindows;
 
         public static bool IsMetadataUpdateSupported => !IsNativeAot;
 

src/libraries/System.Reflection/tests/GetTypeTests.cs

@@ -279,6 +279,24 @@ public void GetType_InvalidAssemblyName()
             Assert.Null(Type.GetType("ExtraComma, , System.Runtime"));
             Assert.Throws<FileLoadException>(() => Type.GetType("System.Object, System.Runtime, Version=x.y"));
         }
+
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsTypeEquivalenceSupported))]
+        public void TestTypeIdentifierAttribute()
+        {
+            string typeName = $"{typeof(EquivalentValueType).FullName},{typeof(TestAssembly.ClassToInvoke).Assembly.GetName().Name}";
+            Type otherEquivalentValueType = Type.GetType(typeName);
+            Assert.True(otherEquivalentValueType.IsEquivalentTo(typeof(EquivalentValueType)));
+
+            var mi = typeof(MyNamespace1.ClassForTypeIdentifier).GetMethod("MyMethod");
+
+            // Sanity check.
+            object[] args = new object[1] { Activator.CreateInstance(typeof(EquivalentValueType)) };
+            Assert.Equal(42, mi.Invoke(null, args));
+
+            // Ensure we can invoke with an arg type that is duplicated in another assembly but having [TypeIdentifier].
+            args = new object[1] { Activator.CreateInstance(otherEquivalentValueType) };
+            Assert.Equal(42, mi.Invoke(null, args));
+        }
     }
 
     namespace MyNamespace1
@@ -323,6 +341,11 @@ namespace MyNamEspace3
         {
             public class Foo { }
         }
+
+        public class ClassForTypeIdentifier
+        {
+            public static int MyMethod(EquivalentValueType v) => 42;
+        }
     }
 
     public class MyClass1 { }

src/libraries/System.Reflection/tests/System.Reflection.Tests.csproj

@@ -42,6 +42,8 @@
     <Compile Include="ExceptionTests.cs" />
     <Compile Include="PointerTests.cs" />
     <Compile Include="TypeTests.Constraints.cs" />
+    <Compile Include="TestAssembly\EquivalentValueType.cs"
+             Link="EquivalentValueType.cs" />
   </ItemGroup>
   <ItemGroup>
     <EmbeddedResource Include="Resources\EmbeddedImage.png">

src/libraries/System.Reflection/tests/TestAssembly/EquivalentValueType.cs

@@ -0,0 +1,10 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Runtime.InteropServices;
+
+[TypeIdentifier("MyScope", "MyTypeId")]
+public struct EquivalentValueType
+{
+    public int A;
+}

src/libraries/System.Reflection/tests/TestAssembly/TestAssembly.csproj

@@ -5,6 +5,7 @@
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="ClassToInvoke.cs" />
+    <Compile Include="EquivalentValueType.cs" />    
     <Compile Include="TestAssembly.cs" />
   </ItemGroup>
-</Project>
+</Project>