Add BStrStringMarshaller to source generator

src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems

@@ -867,6 +867,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\MarshalDirectiveException.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\Marshalling\AnsiStringMarshaller.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\Marshalling\ArrayMarshaller.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\Marshalling\BStrStringMarshaller.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\Marshalling\CustomTypeMarshallerAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\Marshalling\CustomTypeMarshallerDirection.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\Marshalling\CustomTypeMarshallerFeatures.cs" />

src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs

@@ -0,0 +1,122 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Diagnostics;
+using System.Runtime.CompilerServices;
+using System.Text;
+
+namespace System.Runtime.InteropServices.Marshalling
+{
+    /// <summary>
+    /// Marshaller for BSTR strings
+    /// </summary>
+    [CLSCompliant(false)]
+    [CustomTypeMarshaller(typeof(string), BufferSize = 0x200,
+        Features = CustomTypeMarshallerFeatures.UnmanagedResources | CustomTypeMarshallerFeatures.TwoStageMarshalling | CustomTypeMarshallerFeatures.CallerAllocatedBuffer)]
+    public unsafe ref struct BStrStringMarshaller
+    {
+        private ushort* _ptrToFirstChar;
+        private bool _allocated;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="BStrStringMarshaller"/>.
+        /// </summary>
+        /// <param name="str">The string to marshal.</param>
+        public BStrStringMarshaller(string? str)
+            : this(str, default)
+        { }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="BStrStringMarshaller"/>.
+        /// </summary>
+        /// <param name="str">The string to marshal.</param>
+        /// <param name="buffer">Buffer that may be used for marshalling.</param>
+        /// <remarks>
+        /// The <paramref name="buffer"/> must not be movable - that is, it should not be
+        /// on the managed heap or it should be pinned.
+        /// <seealso cref="CustomTypeMarshallerFeatures.CallerAllocatedBuffer"/>
+        /// </remarks>
+        public BStrStringMarshaller(string? str, Span<ushort> buffer)
+        {
+            _allocated = false;
+
+            if (str is null)
+            {
+                _ptrToFirstChar = null;
+                return;
+            }
+
+            int lengthInBytes = checked(sizeof(char) * str.Length);
+
+            // A caller provided buffer must be at least (lengthInBytes + 6) bytes
+            // in order to be constructed manually. The 6 extra bytes are 4 for byte length and 2 for wide null.
+            int manualBstrNeeds = checked(lengthInBytes + 6);
+            if (manualBstrNeeds > buffer.Length)
+            {
+                // Use precise byte count when the provided stack-allocated buffer is not sufficient
+                _ptrToFirstChar = (ushort*)Marshal.AllocBSTRByteLen((uint)lengthInBytes);
+                _allocated = true;
+            }
+            else
+            {
+                // Set length and update buffer target
+                byte* pBuffer = (byte*)Unsafe.AsPointer(ref MemoryMarshal.GetReference(buffer));
+                *((uint*)pBuffer) = (uint)lengthInBytes;
+                _ptrToFirstChar = (ushort*)(pBuffer + sizeof(uint));
+            }
+
+            // Confirm the size is properly set for the allocated BSTR.
+            Debug.Assert(lengthInBytes == Marshal.SysStringByteLen((IntPtr)_ptrToFirstChar));
+
+            // Copy characters from the managed string
+            str.CopyTo(new Span<char>(_ptrToFirstChar, str.Length));
+            _ptrToFirstChar[str.Length] = '\0'; // null-terminate
+        }
+
+        /// <summary>
+        /// Returns the native value representing the string.
+        /// </summary>
+        /// <remarks>
+        /// <seealso cref="CustomTypeMarshallerFeatures.TwoStageMarshalling"/>
+        /// </remarks>
+        public ushort* ToNativeValue() => _ptrToFirstChar;
+
+        /// <summary>
+        /// Sets the native value representing the string.
+        /// </summary>
+        /// <param name="value">The native value.</param>
+        /// <remarks>
+        /// <seealso cref="CustomTypeMarshallerFeatures.TwoStageMarshalling"/>
+        /// </remarks>
+        public void FromNativeValue(ushort* value)
+        {
+            _ptrToFirstChar = value;
+            _allocated = true;
+        }
+
+        /// <summary>
+        /// Returns the managed string.
+        /// </summary>
+        /// <remarks>
+        /// <seealso cref="CustomTypeMarshallerDirection.Out"/>
+        /// </remarks>
+        public string? ToManaged()
+        {
+            if (_ptrToFirstChar is null)
+                return null;
+            return Marshal.PtrToStringBSTR((IntPtr)_ptrToFirstChar);
+        }
+
+        /// <summary>
+        /// Frees native resources.
+        /// </summary>
+        /// <remarks>
+        /// <seealso cref="CustomTypeMarshallerFeatures.UnmanagedResources"/>
+        /// </remarks>
+        public void FreeNative()
+        {
+            if (_allocated)
+                Marshal.FreeBSTR((IntPtr)_ptrToFirstChar);
+        }
+    }
+}

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/MarshallingAttributeInfo.cs

@@ -12,7 +12,6 @@
 
 namespace Microsoft.Interop
 {
-
     /// <summary>
     /// Type used to pass on default marshalling details.
     /// </summary>
@@ -73,7 +72,6 @@ public enum CharEncoding
         Undefined,
         Utf8,
         Utf16,
-        Ansi,
         Custom
     }
 
@@ -762,7 +760,13 @@ private bool TryCreateTypeBasedMarshallingInfo(
                 }
                 else
                 {
-                    marshallingInfo = CreateStringMarshallingInfo(type, _defaultInfo.CharEncoding);
+                    marshallingInfo = _defaultInfo.CharEncoding switch
+                    {
+                        CharEncoding.Utf16 => CreateStringMarshallingInfo(type, TypeNames.Utf16StringMarshaller),
+                        CharEncoding.Utf8 => CreateStringMarshallingInfo(type, TypeNames.Utf8StringMarshaller),
+                        _ => throw new InvalidOperationException()
+                    };
+
                     return true;
                 }
 
@@ -843,30 +847,25 @@ private MarshallingInfo CreateStringMarshallingInfo(
             ITypeSymbol type,
             UnmanagedType unmanagedType)
         {
-            CharEncoding charEncoding = unmanagedType switch
+            string? marshallerName = unmanagedType switch
             {
-                UnmanagedType.LPStr => CharEncoding.Ansi,
-                UnmanagedType.LPTStr or UnmanagedType.LPWStr => CharEncoding.Utf16,
-                MarshalAsInfo.UnmanagedType_LPUTF8Str => CharEncoding.Utf8,
-                _ => CharEncoding.Undefined
+                UnmanagedType.BStr => TypeNames.BStrStringMarshaller,
+                UnmanagedType.LPStr => TypeNames.AnsiStringMarshaller,
+                UnmanagedType.LPTStr or UnmanagedType.LPWStr => TypeNames.Utf16StringMarshaller,
+                MarshalAsInfo.UnmanagedType_LPUTF8Str => TypeNames.Utf8StringMarshaller,
+                _ => null
             };
-            if (charEncoding == CharEncoding.Undefined)
+
+            if (marshallerName is null)
                 return new MarshalAsInfo(unmanagedType, _defaultInfo.CharEncoding);
 
-            return CreateStringMarshallingInfo(type, charEncoding);
+            return CreateStringMarshallingInfo(type, marshallerName);
         }
 
         private MarshallingInfo CreateStringMarshallingInfo(
             ITypeSymbol type,
-            CharEncoding charEncoding)
+            string marshallerName)
         {
-            string? marshallerName = charEncoding switch
-            {
-                CharEncoding.Ansi => TypeNames.AnsiStringMarshaller,
-                CharEncoding.Utf16 => TypeNames.Utf16StringMarshaller,
-                CharEncoding.Utf8 => TypeNames.Utf8StringMarshaller,
-                _ => throw new InvalidOperationException()
-            };
             INamedTypeSymbol? stringMarshaller = _compilation.GetTypeByMetadataName(marshallerName);
             if (stringMarshaller is null)
                 return new MissingSupportMarshallingInfo();
@@ -877,9 +876,9 @@ private MarshallingInfo CreateStringMarshallingInfo(
             return CreateNativeMarshallingInfoForValue(
                 type,
                 stringMarshaller,
-                default,
+                null,
                 customTypeMarshallerData.Value,
-                allowPinningManagedType: charEncoding == CharEncoding.Utf16,
+                allowPinningManagedType: marshallerName is TypeNames.Utf16StringMarshaller,
                 useDefaultMarshalling: false);
         }
 

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/TypeNames.cs

@@ -18,6 +18,7 @@ public static class TypeNames
         public const string CustomTypeMarshallerAttributeGenericPlaceholder = "System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerAttribute.GenericPlaceholder";
 
         public const string AnsiStringMarshaller = "System.Runtime.InteropServices.Marshalling.AnsiStringMarshaller";
+        public const string BStrStringMarshaller = "System.Runtime.InteropServices.Marshalling.BStrStringMarshaller";
         public const string Utf16StringMarshaller = "System.Runtime.InteropServices.Marshalling.Utf16StringMarshaller";
         public const string Utf8StringMarshaller = "System.Runtime.InteropServices.Marshalling.Utf8StringMarshaller";
 

src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs

@@ -2078,6 +2078,20 @@ public void FromNativeValue(byte* value) { }
         public string? ToManaged() { throw null; }
         public void FreeNative() { }
     }
+    [System.CLSCompliant(false)]
+    [System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerAttribute(typeof(string), BufferSize = 0x200,
+        Features = System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerFeatures.UnmanagedResources
+            | System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerFeatures.CallerAllocatedBuffer
+            | System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerFeatures.TwoStageMarshalling )]
+    public unsafe ref struct BStrStringMarshaller
+    {
+        public BStrStringMarshaller(string? str) { }
+        public BStrStringMarshaller(string? str, System.Span<ushort> buffer) { }
+        public ushort* ToNativeValue() { throw null; }
+        public void FromNativeValue(ushort* value) { }
+        public string? ToManaged() { throw null; }
+        public void FreeNative() { }
+    }
     [System.CLSCompliantAttribute(false)]
     [System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerAttribute(typeof(System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerAttribute.GenericPlaceholder[]),
         System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerKind.LinearCollection, BufferSize = 0x200,

src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/StringTests.cs

@@ -23,6 +23,7 @@ private class EntryPoints
 
             private const string UShortSuffix = "_ushort";
             private const string ByteSuffix = "_byte";
+            private const string BStrSuffix = "_bstr";
 
             public class Byte
             {
@@ -41,6 +42,15 @@ public class UShort
                 public const string ReverseInplace = EntryPoints.ReverseInplace + UShortSuffix;
                 public const string ReverseReplace = EntryPoints.ReverseReplace + UShortSuffix;
             }
+
+            public class BStr
+            {
+                public const string ReturnLength = EntryPoints.ReturnLength + BStrSuffix;
+                public const string ReverseReturn = EntryPoints.ReverseReturn + BStrSuffix;
+                public const string ReverseOut = EntryPoints.ReverseOut + BStrSuffix;
+                public const string ReverseInplace = EntryPoints.ReverseInplace + BStrSuffix;
+                public const string ReverseReplace = EntryPoints.ReverseReplace + BStrSuffix;
+            }
         }
 
         public partial class Utf16
@@ -185,6 +195,31 @@ public partial class LPStr
             public static partial void Reverse_Replace_Ref([MarshalAs(UnmanagedType.LPStr)] ref string s);
         }
 
+        public partial class BStr
+        {
+            [LibraryImport(NativeExportsNE_Binary, EntryPoint = EntryPoints.BStr.ReturnLength)]
+            public static partial int ReturnLength([MarshalAs(UnmanagedType.BStr)] string s);
+
+            [LibraryImport(NativeExportsNE_Binary, EntryPoint = EntryPoints.BStr.ReturnLength, StringMarshalling = StringMarshalling.Utf16)]
+            public static partial int ReturnLength_IgnoreStringMarshalling([MarshalAs(UnmanagedType.BStr)] string s);
+
+            [LibraryImport(NativeExportsNE_Binary, EntryPoint = EntryPoints.BStr.ReverseReturn)]
+            [return: MarshalAs(UnmanagedType.BStr)]
+            public static partial string Reverse_Return([MarshalAs(UnmanagedType.BStr)] string s);
+
+            [LibraryImport(NativeExportsNE_Binary, EntryPoint = EntryPoints.BStr.ReverseOut)]
+            public static partial void Reverse_Out([MarshalAs(UnmanagedType.BStr)] string s, [MarshalAs(UnmanagedType.BStr)] out string ret);
+
+            [LibraryImport(NativeExportsNE_Binary, EntryPoint = EntryPoints.BStr.ReverseInplace)]
+            public static partial void Reverse_Ref([MarshalAs(UnmanagedType.BStr)] ref string s);
+
+            [LibraryImport(NativeExportsNE_Binary, EntryPoint = EntryPoints.BStr.ReverseInplace)]
+            public static partial void Reverse_In([MarshalAs(UnmanagedType.BStr)] in string s);
+
+            [LibraryImport(NativeExportsNE_Binary, EntryPoint = EntryPoints.BStr.ReverseReplace)]
+            public static partial void Reverse_Replace_Ref([MarshalAs(UnmanagedType.BStr)] ref string s);
+        }
+
         public partial class StringMarshallingCustomType
         {
             public partial class Utf16
@@ -418,6 +453,48 @@ public void AnsiStringByRef(string value)
             Assert.Equal(expected, refValue);
         }
 
+        [Theory]
+        [MemberData(nameof(UnicodeStrings))]
+        public void BStrStringMarshalledAsExpected(string value)
+        {
+            int expectedLen = value != null ? value.Length : -1;
+
+            Assert.Equal(expectedLen, NativeExportsNE.BStr.ReturnLength(value));
+            Assert.Equal(expectedLen, NativeExportsNE.BStr.ReturnLength_IgnoreStringMarshalling(value));
+        }
+
+        [Theory]
+        [MemberData(nameof(UnicodeStrings))]
+        public void BStrStringReturn(string value)
+        {
+            string expected = ReverseChars(value);
+
+            Assert.Equal(expected, NativeExportsNE.BStr.Reverse_Return(value));
+
+            string ret;
+            NativeExportsNE.BStr.Reverse_Out(value, out ret);
+            Assert.Equal(expected, ret);
+        }
+
+        [Theory]
+        [MemberData(nameof(UnicodeStrings))]
+        public void BStrStringByRef(string value)
+        {
+            string refValue = value;
+            string expected = ReverseChars(value);
+
+            NativeExportsNE.BStr.Reverse_In(in refValue);
+            Assert.Equal(value, refValue); // Should not be updated when using 'in'
+
+            refValue = value;
+            NativeExportsNE.BStr.Reverse_Ref(ref refValue);
+            Assert.Equal(expected, refValue);
+
+            refValue = value;
+            NativeExportsNE.BStr.Reverse_Replace_Ref(ref refValue);
+            Assert.Equal(expected, refValue);
+        }
+
         [Theory]
         [MemberData(nameof(UnicodeStrings))]
         public void StringMarshallingCustomType_MarshalledAsExpected(string value)

src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/Compiles.cs

@@ -108,9 +108,11 @@ public static IEnumerable<object[]> CodeSnippetsToCompile()
             yield return new[] { CodeSnippets.MarshalAsParametersAndModifiers<string>(UnmanagedType.LPTStr) };
             yield return new[] { CodeSnippets.MarshalAsParametersAndModifiers<string>(UnmanagedType.LPUTF8Str) };
             yield return new[] { CodeSnippets.MarshalAsParametersAndModifiers<string>(UnmanagedType.LPStr) };
+            yield return new[] { CodeSnippets.MarshalAsParametersAndModifiers<string>(UnmanagedType.BStr) };
             yield return new[] { CodeSnippets.MarshalAsArrayParameterWithNestedMarshalInfo<string>(UnmanagedType.LPWStr) };
             yield return new[] { CodeSnippets.MarshalAsArrayParameterWithNestedMarshalInfo<string>(UnmanagedType.LPUTF8Str) };
             yield return new[] { CodeSnippets.MarshalAsArrayParameterWithNestedMarshalInfo<string>(UnmanagedType.LPStr) };
+            yield return new[] { CodeSnippets.MarshalAsArrayParameterWithNestedMarshalInfo<string>(UnmanagedType.BStr) };
 
             // [In, Out] attributes
             // By value non-blittable array