StringMarshalling behavior override tests (#86963)

Adds tests to make sure MarshalAs and MarshalUsing override the default string marshalling behavior set by the interface-wide StringMarshalling. No changes were necessary in the generator.

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

@@ -22,6 +22,9 @@ public unsafe partial class StringMarshallingTests
         [LibraryImport(NativeExportsNE.NativeExportsNE_Binary, EntryPoint = "new_utf16_marshalling")]
         public static partial void* NewIUtf16Marshalling();
 
+        [LibraryImport(NativeExportsNE.NativeExportsNE_Binary, EntryPoint = "new_string_marshalling_override")]
+        public static partial void* NewStringMarshallingOverride();
+
         [GeneratedComClass]
         internal partial class Utf8MarshalledClass : IUTF8Marshalling
         {
@@ -107,5 +110,26 @@ public void RcwToCcw()
             customUtf16ComObject.SetString("Set from COM object");
             Assert.Equal(customUtf16.GetString(), customUtf16ComObject.GetString());
         }
+
+        [Fact]
+        public void MarshalAsAndMarshalUsingOverrideStringMarshalling()
+        {
+            var ptr = NewStringMarshallingOverride();
+            var cw = new StrategyBasedComWrappers();
+            var obj = cw.GetOrCreateObjectForComInstance((nint)ptr, CreateObjectFlags.None);
+            var stringMarshallingOverride = (IStringMarshallingOverride)obj;
+            Assert.Equal("Your string: MyUtf8String", stringMarshallingOverride.StringMarshallingUtf8("MyUtf8String"));
+            Assert.Equal("Your string: MyLPWStrString", stringMarshallingOverride.MarshalAsLPWString("MyLPWStrString"));
+            Assert.Equal("Your string: MyUtf16String", stringMarshallingOverride.MarshalUsingUtf16("MyUtf16String"));
+
+            // Make sure the shadowing methods generated for the derived interface also follow the rules
+            var stringMarshallingOverrideDerived = (IStringMarshallingOverrideDerived)obj;
+            Assert.Equal("Your string: MyUtf8String", stringMarshallingOverrideDerived.StringMarshallingUtf8("MyUtf8String"));
+            Assert.Equal("Your string: MyLPWStrString", stringMarshallingOverrideDerived.MarshalAsLPWString("MyLPWStrString"));
+            Assert.Equal("Your string: MyUtf16String", stringMarshallingOverrideDerived.MarshalUsingUtf16("MyUtf16String"));
+            Assert.Equal("Your string 2: MyUtf8String", stringMarshallingOverrideDerived.StringMarshallingUtf8_2("MyUtf8String"));
+            Assert.Equal("Your string 2: MyLPWStrString", stringMarshallingOverrideDerived.MarshalAsLPWString_2("MyLPWStrString"));
+            Assert.Equal("Your string 2: MyUtf16String", stringMarshallingOverrideDerived.MarshalUsingUtf16_2("MyUtf16String"));
+        }
     }
 }

src/libraries/System.Runtime.InteropServices/tests/TestAssets/NativeExports/ComInterfaceGenerator/StringMarshallingOverride.cs

@@ -0,0 +1,215 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using System.Runtime.InteropServices.Marshalling;
+using System.Text;
+using System.Threading.Tasks;
+using SharedTypes.ComInterfaces;
+using static System.Runtime.InteropServices.ComWrappers;
+
+namespace NativeExports.ComInterfaceGenerator
+{
+    public unsafe partial class StringMarshallingOverride
+    {
+        [UnmanagedCallersOnly(EntryPoint = "new_string_marshalling_override")]
+        public static void* CreateStringMarshallingOverrideObject()
+        {
+            MyComWrapper cw = new();
+            var myObject = new Implementation();
+            nint ptr = cw.GetOrCreateComInterfaceForObject(myObject, CreateComInterfaceFlags.None);
+            return (void*)ptr;
+        }
+
+        class MyComWrapper : ComWrappers
+        {
+            static void* _s_comInterfaceVTable = null;
+            static void* S_VTable
+            {
+                get
+                {
+                    if (_s_comInterfaceVTable != null)
+                        return _s_comInterfaceVTable;
+                    void** vtable = (void**)RuntimeHelpers.AllocateTypeAssociatedMemory(typeof(GetAndSetInt), sizeof(void*) * 6);
+                    GetIUnknownImpl(out var fpQueryInterface, out var fpAddReference, out var fpRelease);
+                    vtable[0] = (void*)fpQueryInterface;
+                    vtable[1] = (void*)fpAddReference;
+                    vtable[2] = (void*)fpRelease;
+                    vtable[3] = (delegate* unmanaged<void*, byte*, byte**, int>)&Implementation.ABI.StringMarshallingUtf8;
+                    vtable[4] = (delegate* unmanaged<void*, ushort*, ushort**, int>)&Implementation.ABI.MarshalAsLPWStr;
+                    vtable[5] = (delegate* unmanaged<void*, ushort*, ushort**, int>)&Implementation.ABI.MarshalUsingUtf16;
+                    _s_comInterfaceVTable = vtable;
+                    return _s_comInterfaceVTable;
+                }
+            }
+
+            static void* _s_derivedVTable = null;
+            static void* S_DerivedVTable
+            {
+                get
+                {
+                    if (_s_comInterfaceVTable != null)
+                        return _s_comInterfaceVTable;
+                    void** vtable = (void**)RuntimeHelpers.AllocateTypeAssociatedMemory(typeof(GetAndSetInt), sizeof(void*) * 9);
+                    GetIUnknownImpl(out var fpQueryInterface, out var fpAddReference, out var fpRelease);
+                    vtable[0] = (void*)fpQueryInterface;
+                    vtable[1] = (void*)fpAddReference;
+                    vtable[2] = (void*)fpRelease;
+                    vtable[3] = (delegate* unmanaged<void*, byte*, byte**, int>)&Implementation.ABI.StringMarshallingUtf8;
+                    vtable[4] = (delegate* unmanaged<void*, ushort*, ushort**, int>)&Implementation.ABI.MarshalAsLPWStr;
+                    vtable[5] = (delegate* unmanaged<void*, ushort*, ushort**, int>)&Implementation.ABI.MarshalUsingUtf16;
+                    vtable[6] = (delegate* unmanaged<void*, byte*, byte**, int>)&Implementation.ABI.StringMarshallingUtf8_2;
+                    vtable[7] = (delegate* unmanaged<void*, ushort*, ushort**, int>)&Implementation.ABI.MarshalAsLPWStr_2;
+                    vtable[8] = (delegate* unmanaged<void*, ushort*, ushort**, int>)&Implementation.ABI.MarshalUsingUtf16_2;
+                    _s_comInterfaceVTable = vtable;
+                    return _s_comInterfaceVTable;
+                }
+            }
+
+            protected override ComInterfaceEntry* ComputeVtables(object obj, CreateComInterfaceFlags flags, out int count)
+            {
+                if (obj is IStringMarshallingOverrideDerived)
+                {
+                    ComInterfaceEntry* comInterfaceEntry = (ComInterfaceEntry*)RuntimeHelpers.AllocateTypeAssociatedMemory(typeof(Implementation), sizeof(ComInterfaceEntry) * 2);
+                    comInterfaceEntry[0].IID = new Guid(IStringMarshallingOverrideDerived._guid);
+                    comInterfaceEntry[0].Vtable = (nint)S_DerivedVTable;
+                    comInterfaceEntry[1].IID = new Guid(IStringMarshallingOverride._guid);
+                    comInterfaceEntry[1].Vtable = (nint)S_VTable;
+                    count = 2;
+                    return comInterfaceEntry;
+                }
+                if (obj is IStringMarshallingOverride)
+                {
+                    ComInterfaceEntry* comInterfaceEntry = (ComInterfaceEntry*)RuntimeHelpers.AllocateTypeAssociatedMemory(typeof(Implementation), sizeof(ComInterfaceEntry));
+                    comInterfaceEntry->IID = new Guid(IStringMarshallingOverride._guid);
+                    comInterfaceEntry->Vtable = (nint)S_VTable;
+                    count = 1;
+                    return comInterfaceEntry;
+                }
+                count = 0;
+                return null;
+            }
+
+            protected override object? CreateObject(nint externalComObject, CreateObjectFlags flags) => throw new NotImplementedException();
+            protected override void ReleaseObjects(IEnumerable objects) => throw new NotImplementedException();
+        }
+
+        partial class Implementation : IStringMarshallingOverride, IStringMarshallingOverrideDerived
+        {
+            string _data = "Your string: ";
+            string IStringMarshallingOverride.StringMarshallingUtf8(string input) => _data + input;
+            string IStringMarshallingOverride.MarshalAsLPWString(string input) => _data + input;
+            string IStringMarshallingOverride.MarshalUsingUtf16(string input) => _data + input;
+
+            string _data2 = "Your string 2: ";
+            string IStringMarshallingOverrideDerived.StringMarshallingUtf8_2(string input) => _data2 + input;
+            string IStringMarshallingOverrideDerived.MarshalAsLPWString_2(string input) => _data2 + input;
+            string IStringMarshallingOverrideDerived.MarshalUsingUtf16_2(string input) => _data2 + input;
+
+            // Provides function pointers in the COM format to use in COM VTables
+            public static class ABI
+            {
+                [UnmanagedCallersOnly]
+                public static int StringMarshallingUtf8(void* @this, byte* input, byte** output)
+                {
+                    try
+                    {
+                        string inputStr = Utf8StringMarshaller.ConvertToManaged(input);
+                        string currValue = ComInterfaceDispatch.GetInstance<IStringMarshallingOverride>((ComInterfaceDispatch*)@this).StringMarshallingUtf8(inputStr);
+                        *output = Utf8StringMarshaller.ConvertToUnmanaged(currValue);
+                        return 0;
+                    }
+                    catch (Exception e)
+                    {
+                        return e.HResult;
+                    }
+                }
+
+                [UnmanagedCallersOnly]
+                public static int MarshalAsLPWStr(void* @this, ushort* input, ushort** output)
+                {
+                    try
+                    {
+                        string inputStr = Utf16StringMarshaller.ConvertToManaged(input);
+                        string currValue = ComInterfaceDispatch.GetInstance<IStringMarshallingOverride>((ComInterfaceDispatch*)@this).MarshalAsLPWString(inputStr);
+                        *output = Utf16StringMarshaller.ConvertToUnmanaged(currValue);
+                        return 0;
+                    }
+                    catch (Exception e)
+                    {
+                        return e.HResult;
+                    }
+                }
+
+                [UnmanagedCallersOnly]
+                public static int MarshalUsingUtf16(void* @this, ushort* input, ushort** output)
+                {
+                    try
+                    {
+                        string inputStr = Utf16StringMarshaller.ConvertToManaged(input);
+                        string currValue = ComInterfaceDispatch.GetInstance<IStringMarshallingOverride>((ComInterfaceDispatch*)@this).MarshalUsingUtf16(inputStr);
+                        *output = Utf16StringMarshaller.ConvertToUnmanaged(currValue);
+                        return 0;
+                    }
+                    catch (Exception e)
+                    {
+                        return e.HResult;
+                    }
+                }
+
+                [UnmanagedCallersOnly]
+                public static int StringMarshallingUtf8_2(void* @this, byte* input, byte** output)
+                {
+                    try
+                    {
+                        string inputStr = Utf8StringMarshaller.ConvertToManaged(input);
+                        string currValue = ComInterfaceDispatch.GetInstance<IStringMarshallingOverrideDerived>((ComInterfaceDispatch*)@this).StringMarshallingUtf8_2(inputStr);
+                        *output = Utf8StringMarshaller.ConvertToUnmanaged(currValue);
+                        return 0;
+                    }
+                    catch (Exception e)
+                    {
+                        return e.HResult;
+                    }
+                }
+
+                [UnmanagedCallersOnly]
+                public static int MarshalAsLPWStr_2(void* @this, ushort* input, ushort** output)
+                {
+                    try
+                    {
+                        string inputStr = Utf16StringMarshaller.ConvertToManaged(input);
+                        string currValue = ComInterfaceDispatch.GetInstance<IStringMarshallingOverrideDerived>((ComInterfaceDispatch*)@this).MarshalAsLPWString_2(inputStr);
+                        *output = Utf16StringMarshaller.ConvertToUnmanaged(currValue);
+                        return 0;
+                    }
+                    catch (Exception e)
+                    {
+                        return e.HResult;
+                    }
+                }
+
+                [UnmanagedCallersOnly]
+                public static int MarshalUsingUtf16_2(void* @this, ushort* input, ushort** output)
+                {
+                    try
+                    {
+                        string inputStr = Utf16StringMarshaller.ConvertToManaged(input);
+                        string currValue = ComInterfaceDispatch.GetInstance<IStringMarshallingOverrideDerived>((ComInterfaceDispatch*)@this).MarshalUsingUtf16_2(inputStr);
+                        *output = Utf16StringMarshaller.ConvertToUnmanaged(currValue);
+                        return 0;
+                    }
+                    catch (Exception e)
+                    {
+                        return e.HResult;
+                    }
+                }
+            }
+        }
+    }
+}

src/libraries/System.Runtime.InteropServices/tests/TestAssets/SharedTypes/ComInterfaces/IStringMarshallingOverride.cs

@@ -0,0 +1,27 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.InteropServices;
+using System.Runtime.InteropServices.Marshalling;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace SharedTypes.ComInterfaces
+{
+    [GeneratedComInterface(StringMarshalling = System.Runtime.InteropServices.StringMarshalling.Utf8)]
+    [Guid(_guid)]
+    internal partial interface IStringMarshallingOverride
+    {
+        public const string _guid = "5146B7DB-0588-469B-B8E5-B38090A2FC15";
+        string StringMarshallingUtf8(string input);
+
+        [return: MarshalAs(UnmanagedType.LPWStr)]
+        string MarshalAsLPWString([MarshalAs(UnmanagedType.LPWStr)] string input);
+
+        [return: MarshalUsing(typeof(Utf16StringMarshaller))]
+        string MarshalUsingUtf16([MarshalUsing(typeof(Utf16StringMarshaller))] string input);
+    }
+}

src/libraries/System.Runtime.InteropServices/tests/TestAssets/SharedTypes/ComInterfaces/IStringMarshallingOverrideDerived.cs

@@ -0,0 +1,27 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.InteropServices.Marshalling;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace SharedTypes.ComInterfaces
+{
+    [GeneratedComInterface(StringMarshalling = StringMarshalling.Utf8)]
+    [Guid(_guid)]
+    internal partial interface IStringMarshallingOverrideDerived : IStringMarshallingOverride
+    {
+        public new const string _guid = "3AFFE3FD-D11E-4195-8250-0C73321977A0";
+        string StringMarshallingUtf8_2(string input);
+
+        [return: MarshalAs(UnmanagedType.LPWStr)]
+        string MarshalAsLPWString_2([MarshalAs(UnmanagedType.LPWStr)] string input);
+
+        [return: MarshalUsing(typeof(Utf16StringMarshaller))]
+        string MarshalUsingUtf16_2([MarshalUsing(typeof(Utf16StringMarshaller))] string input);
+    }
+}