COMObject invoke through reflection (dotnet#106677)

A regression was introduced by implementing
IDynamicInterfaceCastable on __ComObject. This means
that the order of checks is now important. Made the
order consistent in all places and added a test for
this particular case.

src/coreclr/vm/methodtable.cpp

@@ -481,6 +481,22 @@ PTR_MethodTable InterfaceInfo_t::GetApproxMethodTable(Module * pContainingModule
     MethodTable *pServerMT = (*pServer)->GetMethodTable();
     PREFIX_ASSUME(pServerMT != NULL);
 
+#ifdef FEATURE_COMINTEROP
+    if (pServerMT->IsComObjectType() && !pItfMD->HasMethodInstantiation())
+    {
+        // interop needs an exact MethodDesc
+        pItfMD = MethodDesc::FindOrCreateAssociatedMethodDesc(
+            pItfMD,
+            ownerType.GetMethodTable(),
+            FALSE,              // forceBoxedEntryPoint
+            Instantiation(),    // methodInst
+            FALSE,              // allowInstParam
+            TRUE);              // forceRemotableMethod
+
+        RETURN(pServerMT->GetMethodDescForComInterfaceMethod(pItfMD, false));
+    }
+#endif // !FEATURE_COMINTEROP
+
     // For IDynamicInterfaceCastable, instead of trying to find method implementation in the real object type
     // we call GetInterfaceImplementation on the object and call GetMethodDescForInterfaceMethod
     // with whatever type it returns.
@@ -501,22 +517,6 @@ PTR_MethodTable InterfaceInfo_t::GetApproxMethodTable(Module * pContainingModule
         RETURN(implTypeHandle.GetMethodTable()->GetMethodDescForInterfaceMethod(ownerType, pItfMD, TRUE /* throwOnConflict */));
     }
 
-#ifdef FEATURE_COMINTEROP
-    if (pServerMT->IsComObjectType() && !pItfMD->HasMethodInstantiation())
-    {
-        // interop needs an exact MethodDesc
-        pItfMD = MethodDesc::FindOrCreateAssociatedMethodDesc(
-            pItfMD,
-            ownerType.GetMethodTable(),
-            FALSE,              // forceBoxedEntryPoint
-            Instantiation(),    // methodInst
-            FALSE,              // allowInstParam
-            TRUE);              // forceRemotableMethod
-
-        RETURN(pServerMT->GetMethodDescForComInterfaceMethod(pItfMD, false));
-    }
-#endif // !FEATURE_COMINTEROP
-
     // Handle pure COM+ types.
     RETURN (pServerMT->GetMethodDescForInterfaceMethod(ownerType, pItfMD, TRUE /* throwOnConflict */));
 }

src/tests/Interop/COM/NETClients/Primitives/CallViaReflectionTests.cs

@@ -0,0 +1,33 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace NetClient
+{
+    using System;
+    using System.Reflection;
+    using Xunit;
+
+    class CallViaReflectionTests
+    {
+        private readonly Server.Contract.Servers.NumericTesting server;
+
+        public CallViaReflectionTests()
+        {
+            this.server = (Server.Contract.Servers.NumericTesting)new Server.Contract.Servers.NumericTestingClass();
+        }
+
+        public void Run()
+        {
+            Console.WriteLine(nameof(CallViaReflectionTests));
+            this.InvokeInstanceMethod();
+        }
+
+        private void InvokeInstanceMethod()
+        {
+            MethodInfo minfo = typeof(Server.Contract.INumericTesting).GetMethod("Add_Int")!;
+            object[] parameters = new object[2] { 10, 20 };
+            int sum = (int)minfo.Invoke(this.server, parameters);
+            Assert.Equal(30, sum);
+        }
+    }
+}

src/tests/Interop/COM/NETClients/Primitives/NETClientPrimitives.csproj

@@ -7,6 +7,7 @@
   <ItemGroup>
     <Compile Include="Program.cs" />
     <Compile Include="ArrayTests.cs" />
+    <Compile Include="CallViaReflectionTests.cs" />
     <Compile Include="ErrorTests.cs" />
     <Compile Include="NumericTests.cs" />
     <Compile Include="StringTests.cs" />

src/tests/Interop/COM/NETClients/Primitives/Program.cs

@@ -40,6 +40,7 @@ private static void RunTests()
             new StringTests().Run();
             new ErrorTests().Run();
             new ColorTests().Run();
+            new CallViaReflectionTests().Run();
         }
     }
 }