[release/9.0-staging] Fix obtaining type handles of IDynamicInterface…

…CastableImplementation (#109909)

Fixes #109496.

We try to optimize away type handles (MethodTables) of types that are only needed due to metadata. Trying to grab type handle of such type throws. This fixes it by unconditionally generating type handles of IDynamicInterfaceCastableImplementation.

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/TypeMetadataNode.cs

@@ -130,6 +130,18 @@ public static void GetMetadataDependencies(ref DependencyList dependencies, Node
                 default:
                     Debug.Assert(type.IsDefType);
 
+                    // We generally postpone creating MethodTables until absolutely needed.
+                    // IDynamicInterfaceCastableImplementation is special in the sense that just obtaining a System.Type
+                    // (by e.g. browsing custom attribute metadata) gives the user enough to pass this to runtime APIs
+                    // that need a MethodTable. We don't have a legitimate type handle without the MethodTable. Other
+                    // kinds of APIs that expect a MethodTable have enough dataflow annotation to trigger warnings.
+                    // There's no dataflow annotations on the IDynamicInterfaceCastable.GetInterfaceImplementation API.
+                    if (type.IsInterface && ((MetadataType)type).IsDynamicInterfaceCastableImplementation())
+                    {
+                        dependencies ??= new DependencyList();
+                        dependencies.Add(nodeFactory.ReflectedType(type), "Reflected IDynamicInterfaceCastableImplementation");
+                    }
+
                     TypeDesc typeDefinition = type.GetTypeDefinition();
                     if (typeDefinition != type)
                     {

src/tests/nativeaot/SmokeTests/UnitTests/Interfaces.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Text;
 using System.Collections.Generic;
+using System.Reflection;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Diagnostics.CodeAnalysis;
@@ -60,6 +61,7 @@ public static int Run()
         TestDefaultDynamicStaticNonGeneric.Run();
         TestDefaultDynamicStaticGeneric.Run();
         TestDynamicStaticGenericVirtualMethods.Run();
+        TestRuntime109496Regression.Run();
 
         return Pass;
     }
@@ -1780,4 +1782,57 @@ public static void Run()
             Console.WriteLine(s_entry.Enter1<SimpleCallStruct<object>>("One"));
         }
     }
+
+    class TestRuntime109496Regression
+    {
+        class CastableThing : IDynamicInterfaceCastable
+        {
+            RuntimeTypeHandle IDynamicInterfaceCastable.GetInterfaceImplementation(RuntimeTypeHandle interfaceType)
+                => Type.GetTypeFromHandle(interfaceType).GetCustomAttribute<TypeAttribute>().TheType.TypeHandle;
+            bool IDynamicInterfaceCastable.IsInterfaceImplemented(RuntimeTypeHandle interfaceType, bool throwIfNotImplemented)
+                => Type.GetTypeFromHandle(interfaceType).IsDefined(typeof(TypeAttribute));
+        }
+
+        [Type(typeof(IMyInterfaceImpl))]
+        interface IMyInterface
+        {
+            int Method();
+        }
+
+        [DynamicInterfaceCastableImplementation]
+        interface IMyInterfaceImpl : IMyInterface
+        {
+            int IMyInterface.Method() => 42;
+        }
+
+        [Type(typeof(IMyGenericInterfaceImpl<int>))]
+        interface IMyGenericInterface
+        {
+            int Method();
+        }
+
+        [DynamicInterfaceCastableImplementation]
+        interface IMyGenericInterfaceImpl<T> : IMyGenericInterface
+        {
+            int IMyGenericInterface.Method() => typeof(T).Name.Length;
+        }
+
+        class TypeAttribute : Attribute
+        {
+            public Type TheType { get; }
+
+            public TypeAttribute(Type t) => TheType = t;
+        }
+
+        public static void Run()
+        {
+            object o = new CastableThing();
+
+            if (((IMyInterface)o).Method() != 42)
+                throw new Exception();
+
+            if (((IMyGenericInterface)o).Method() != 5)
+                throw new Exception();
+        }
+    }
 }