Rename ManagedVirtualMethodTable and adjust VTable indices (#83158)

src/libraries/System.Runtime.InteropServices/gen/ComInterfaceGenerator/ComInterfaceGenerator.cs

@@ -134,7 +134,7 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
                             var syntax = (MethodDeclarationSyntax)interfaceData.Syntax.FindNode(locationInAttributeSyntax.SourceSpan);
                             var method = (IMethodSymbol)member;
                             Diagnostic? diagnostic = GetDiagnosticIfInvalidMethodForGeneration(syntax, method);
-                            methods.Add((syntax, method, diagnostic is not null ? methodVtableOffset++ : 0, diagnostic));
+                            methods.Add((syntax, method, diagnostic is null ? methodVtableOffset++ : 0, diagnostic));
                         }
                     }
                 }
@@ -313,7 +313,7 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
 
                 private static void** m_vtable;
 
-                public static void* VirtualMethodTableManagedImplementation
+                public static void** ManagedVirtualMethodTable
                 {
                     get
                     {
@@ -555,7 +555,7 @@ private static InterfaceDeclarationSyntax GenerateImplementationVTable(Immutable
                                 ReturnStatement(LiteralExpression(SyntaxKind.NullLiteralExpression)))));
             }
 
-            // void** vtable = (void**)RuntimeHelpers.AllocateTypeAssociatedMemory(<interfaceType>, sizeof(void*) * <interfaceMethodStubs.Array.Length>);
+            // void** vtable = (void**)RuntimeHelpers.AllocateTypeAssociatedMemory(<interfaceType>, sizeof(void*) * <max(vtableIndex) + 1>);
             var vtableDeclarationStatement =
                 LocalDeclarationStatement(
                     VariableDeclaration(
@@ -575,7 +575,7 @@ private static InterfaceDeclarationSyntax GenerateImplementationVTable(Immutable
                                                 BinaryExpression(
                                                     SyntaxKind.MultiplyExpression,
                                                     SizeOfExpression(PointerType(PredefinedType(Token(SyntaxKind.VoidKeyword)))),
-                                                    LiteralExpression(SyntaxKind.NumericLiteralExpression, Literal(interfaceMethodStubs.Length)))))))))));
+                                                    LiteralExpression(SyntaxKind.NumericLiteralExpression, Literal(1 + interfaceMethodStubs.Max(x => x.VtableIndexData.Index))))))))))));
 
             var fillIUnknownSlots = Block()
                 .AddStatements(
@@ -680,7 +680,7 @@ private static ClassDeclarationSyntax GenerateInterfaceInformation(ComInterfaceC
                     FieldDeclaration(VariableDeclaration(VoidStarStarSyntax, SingletonSeparatedList(VariableDeclarator(vtableFieldName))))
                         .AddModifiers(Token(SyntaxKind.PrivateKeyword), Token(SyntaxKind.StaticKeyword)),
                     // public static void* VirtualMethodTableManagedImplementation => _vtable != null ? _vtable : (_vtable = InterfaceImplementation.CreateManagedVirtualMethodTable());
-                    PropertyDeclaration(PointerType(PredefinedType(Token(SyntaxKind.VoidKeyword))), "VirtualMethodTableManagedImplementation")
+                    PropertyDeclaration(VoidStarStarSyntax, "ManagedVirtualMethodTable")
                         .AddModifiers(Token(SyntaxKind.PublicKeyword), Token(SyntaxKind.StaticKeyword))
                         .WithExpressionBody(
                             ArrowExpressionClause(

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

@@ -6,8 +6,9 @@
 
 namespace System.Runtime.InteropServices.Marshalling
 {
-    public interface IIUnknownInterfaceType : IUnmanagedInterfaceType
+    public unsafe interface IIUnknownInterfaceType
     {
         public abstract static Guid Iid { get; }
+        public abstract static void** ManagedVirtualMethodTable { get; }
     }
 }

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

@@ -21,6 +21,6 @@ public IUnknownDerivedAttribute()
         public Type Implementation => typeof(TImpl);
 
         /// <inheritdoc />
-        public unsafe void* VirtualMethodTableManagedImplementation => T.VirtualMethodTableManagedImplementation;
+        public unsafe void* VirtualMethodTableManagedImplementation => T.ManagedVirtualMethodTable;
     }
 }