Add methods for providing virtual method table length.

src/libraries/System.Runtime.InteropServices/tests/Ancillary.Interop/IUnmanagedVirtualMethodTableProvider.cs

@@ -37,6 +37,12 @@ public sealed VirtualMethodTableInfo GetVirtualMethodTableInfoForKey<TUnmanagedI
             return GetVirtualMethodTableInfoForKey(TUnmanagedInterfaceType.TypeKey);
         }
 
+        public static int GetVirtualMethodTableLength<TUnmanagedInterfaceType>()
+            where TUnmanagedInterfaceType : IUnmanagedInterfaceType<TUnmanagedInterfaceType, T>
+        {
+            return TUnmanagedInterfaceType.VirtualMethodTableLength;
+        }
+
         public static void* GetVirtualMethodTableManagedImplementation<TUnmanagedInterfaceType>()
             where TUnmanagedInterfaceType : IUnmanagedInterfaceType<TUnmanagedInterfaceType, T>
         {
@@ -60,6 +66,8 @@ public unsafe interface IUnmanagedInterfaceType<TInterface, TKey>
         where TInterface : IUnmanagedInterfaceType<TInterface, TKey>
         where TKey : IEquatable<TKey>
     {
+        public static abstract int VirtualMethodTableLength { get; }
+
         public static abstract void* VirtualMethodTableManagedImplementation { get; }
 
         public static abstract void* GetUnmanagedWrapperForObject(TInterface obj);

src/libraries/System.Runtime.InteropServices/tests/ComInterfaceGenerator.Tests/ImplicitThisTests.cs

@@ -17,16 +17,18 @@ internal partial class ImplicitThis
 
             internal partial interface INativeObject : IUnmanagedInterfaceType<INativeObject, NoCasting>
             {
+                static int IUnmanagedInterfaceType<INativeObject, NoCasting>.VirtualMethodTableLength => 2;
+
                 static NoCasting IUnmanagedInterfaceType<INativeObject, NoCasting>.TypeKey => default;
 
-                private static void** s_vtable = (void**)RuntimeHelpers.AllocateTypeAssociatedMemory(typeof(INativeObject), sizeof(void*) * 2);
+                private static void** s_vtable = (void**)RuntimeHelpers.AllocateTypeAssociatedMemory(typeof(INativeObject), sizeof(void*) * IUnmanagedVirtualMethodTableProvider<NoCasting>.GetVirtualMethodTableLength<INativeObject>());
                 static void* IUnmanagedInterfaceType<INativeObject, NoCasting>.VirtualMethodTableManagedImplementation
                 {
                     get
                     {
                         if (s_vtable[0] == null)
                         {
-                            Native.PopulateUnmanagedVirtualMethodTable(new Span<IntPtr>(s_vtable, 2));
+                            Native.PopulateUnmanagedVirtualMethodTable(new Span<IntPtr>(s_vtable, IUnmanagedVirtualMethodTableProvider<NoCasting>.GetVirtualMethodTableLength<INativeObject>()));
                         }
                         return s_vtable;
                     }

src/libraries/System.Runtime.InteropServices/tests/ComInterfaceGenerator.Tests/NoImplicitThisTests.cs

@@ -16,6 +16,7 @@ internal partial class NoImplicitThis
 
             internal partial interface IStaticMethodTable : IUnmanagedInterfaceType<IStaticMethodTable, NoCasting>
             {
+                static int IUnmanagedInterfaceType<IStaticMethodTable, NoCasting>.VirtualMethodTableLength => 2;
                 static void* IUnmanagedInterfaceType<IStaticMethodTable, NoCasting>.VirtualMethodTableManagedImplementation => null;
 
                 static void* IUnmanagedInterfaceType<IStaticMethodTable, NoCasting>.GetUnmanagedWrapperForObject(IStaticMethodTable obj) => null;
@@ -40,7 +41,8 @@ public StaticMethodTable(void* vtableStart)
                     _vtableStart = vtableStart;
                 }
 
-                public VirtualMethodTableInfo GetVirtualMethodTableInfoForKey(NoCasting typeKey) => new VirtualMethodTableInfo(IntPtr.Zero, new ReadOnlySpan<IntPtr>(_vtableStart, 2));
+                public VirtualMethodTableInfo GetVirtualMethodTableInfoForKey(NoCasting typeKey) =>
+                    new VirtualMethodTableInfo(IntPtr.Zero, new ReadOnlySpan<IntPtr>(_vtableStart, IUnmanagedVirtualMethodTableProvider<NoCasting>.GetVirtualMethodTableLength<IStaticMethodTable>()));
             }
 
             [CustomMarshaller(typeof(StaticMethodTable), MarshalMode.ManagedToUnmanagedOut, typeof(StaticMethodTableMarshaller))]

src/libraries/System.Runtime.InteropServices/tests/ComInterfaceGenerator.Tests/VTableGCHandlePair.cs

@@ -16,7 +16,7 @@ public static unsafe class VTableGCHandlePair<TUnmanagedInterface, TKey>
     {
         public static void* Allocate(TUnmanagedInterface obj)
         {
-            void** unmanaged = (void**)NativeMemory.Alloc((nuint)sizeof(void*) * 2);
+            void** unmanaged = (void**)NativeMemory.Alloc((nuint)sizeof(void*) * (nuint)IUnmanagedVirtualMethodTableProvider<TKey>.GetVirtualMethodTableLength<TUnmanagedInterface>());
             unmanaged[0] = TUnmanagedInterface.VirtualMethodTableManagedImplementation;
             unmanaged[1] = (void*)GCHandle.ToIntPtr(GCHandle.Alloc(obj));
             return unmanaged;

src/libraries/System.Runtime.InteropServices/tests/ComInterfaceGenerator.Unit.Tests/CodeSnippets.cs

@@ -18,6 +18,7 @@ partial interface INativeAPI
             """;
 
         public const string INativeAPI_NoCasting_IUnmanagedInterfaceTypeMethodImpl = """
+                static int IUnmanagedInterfaceType<INativeAPI, NoCasting>.VirtualMethodTableLength => 1;
                 static unsafe void* IUnmanagedInterfaceType<INativeAPI, NoCasting>.VirtualMethodTableManagedImplementation => null;
                 static unsafe void* IUnmanagedInterfaceType<INativeAPI, NoCasting>.GetUnmanagedWrapperForObject(INativeAPI obj) => null;
                 static unsafe INativeAPI IUnmanagedInterfaceType<INativeAPI, NoCasting>.GetObjectForUnmanagedWrapper(void* ptr) => null;

src/libraries/System.Runtime.InteropServices/tests/ComInterfaceGenerator.Unit.Tests/IVirtualMethodIndexSignatureProvider.cs

@@ -27,6 +27,7 @@ partial interface INativeAPI
             """;
 
         public const string INativeAPI_NoCasting_IUnmanagedInterfaceTypeMethodImpl = """
+                static int IUnmanagedInterfaceType<INativeAPI, NoCasting>.VirtualMethodTableLength => 1;
                 static unsafe void* IUnmanagedInterfaceType<INativeAPI, NoCasting>.VirtualMethodTableManagedImplementation => null;
                 static unsafe void* IUnmanagedInterfaceType<INativeAPI, NoCasting>.GetUnmanagedWrapperForObject(INativeAPI obj) => null;
                 static unsafe INativeAPI IUnmanagedInterfaceType<INativeAPI, NoCasting>.GetObjectForUnmanagedWrapper(void* ptr) => null;