Apply [StructLayout(CharSet.Unicode)] to structs that contain the char type

src/Microsoft.Windows.CsWin32/FastSyntaxFactory.cs

@@ -274,7 +274,7 @@ internal static SyntaxList<TNode> SingletonList<TNode>(TNode node)
 
         internal static AttributeArgumentListSyntax AttributeArgumentList(SeparatedSyntaxList<AttributeArgumentSyntax> arguments = default) => SyntaxFactory.AttributeArgumentList(Token(SyntaxKind.OpenParenToken), arguments, Token(SyntaxKind.CloseParenToken));
 
-        internal static AttributeListSyntax AttributeList() => SyntaxFactory.AttributeList(Token(SyntaxKind.OpenBracketToken), null, SeparatedList<AttributeSyntax>(), Token(SyntaxKind.CloseBracketToken));
+        internal static AttributeListSyntax AttributeList() => SyntaxFactory.AttributeList(Token(SyntaxKind.OpenBracketToken), null, SeparatedList<AttributeSyntax>(), TokenWithLineFeed(SyntaxKind.CloseBracketToken));
 
         internal static SyntaxList<TNode> List<TNode>()
             where TNode : SyntaxNode => SyntaxFactory.List<TNode>();

src/Microsoft.Windows.CsWin32/Generator.cs

@@ -1844,7 +1844,7 @@ private static string GetClassNameForModule(string moduleName) =>
 
         private static AttributeSyntax FieldOffset(int offset) => FieldOffsetAttributeSyntax.AddArgumentListArguments(AttributeArgument(LiteralExpression(SyntaxKind.NumericLiteralExpression, Literal(offset))));
 
-        private static AttributeSyntax StructLayout(TypeAttributes typeAttributes, TypeLayout layout)
+        private static AttributeSyntax StructLayout(TypeAttributes typeAttributes, TypeLayout layout = default, CharSet charSet = CharSet.Ansi)
         {
             LayoutKind layoutKind = (typeAttributes & TypeAttributes.ExplicitLayout) == TypeAttributes.ExplicitLayout ? LayoutKind.Explicit : LayoutKind.Sequential;
             var structLayoutAttribute = Attribute(IdentifierName("StructLayout")).AddArgumentListArguments(
@@ -1867,6 +1867,13 @@ private static AttributeSyntax StructLayout(TypeAttributes typeAttributes, TypeL
                         .WithNameEquals(NameEquals(nameof(StructLayoutAttribute.Size))));
             }
 
+            if (charSet != CharSet.Ansi)
+            {
+                structLayoutAttribute = structLayoutAttribute.AddArgumentListArguments(
+                    AttributeArgument(MemberAccessExpression(SyntaxKind.SimpleMemberAccessExpression, IdentifierName(nameof(CharSet)), IdentifierName(Enum.GetName(typeof(CharSet), charSet)!)))
+                    .WithNameEquals(NameEquals(IdentifierName(nameof(StructLayoutAttribute.CharSet)))));
+            }
+
             return structLayoutAttribute;
         }
 
@@ -3231,6 +3238,7 @@ private StructDeclarationSyntax DeclareStruct(TypeDefinition typeDef)
             IdentifierNameSyntax name = IdentifierName(this.Reader.GetString(typeDef.Name));
             TypeSyntaxSettings typeSettings = this.fieldTypeSettings;
 
+            bool hasUtf16CharField = false;
             var members = new List<MemberDeclarationSyntax>();
             SyntaxList<MemberDeclarationSyntax> additionalMembers = default;
             foreach (FieldDefinitionHandle fieldDefHandle in typeDef.GetFields())
@@ -3269,6 +3277,7 @@ private StructDeclarationSyntax DeclareStruct(TypeDefinition typeDef)
                     {
                         CustomAttributeHandleCollection fieldAttributes = fieldDef.GetCustomAttributes();
                         TypeHandleInfo fieldTypeInfo = fieldDef.DecodeSignature(SignatureHandleProvider.Instance, null);
+                        hasUtf16CharField |= fieldTypeInfo is PrimitiveTypeHandleInfo { PrimitiveTypeCode: PrimitiveTypeCode.Char };
                         TypeSyntaxAndMarshaling fieldTypeSyntax = fieldTypeInfo.ToTypeSyntax(typeSettings, fieldAttributes);
                         var fieldInfo = this.ReinterpretFieldType(fieldDef, fieldTypeSyntax.Type, fieldAttributes);
                         additionalMembers = additionalMembers.AddRange(fieldInfo.AdditionalMembers);
@@ -3309,9 +3318,10 @@ private StructDeclarationSyntax DeclareStruct(TypeDefinition typeDef)
                 .WithModifiers(TokenList(TokenWithSpace(this.Visibility), TokenWithSpace(SyntaxKind.PartialKeyword)));
 
             TypeLayout layout = typeDef.GetLayout();
-            if (!layout.IsDefault || (typeDef.Attributes & TypeAttributes.ExplicitLayout) == TypeAttributes.ExplicitLayout)
+            CharSet charSet = hasUtf16CharField ? CharSet.Unicode : CharSet.Ansi;
+            if (!layout.IsDefault || (typeDef.Attributes & TypeAttributes.ExplicitLayout) == TypeAttributes.ExplicitLayout || charSet != CharSet.Ansi)
             {
-                result = result.AddAttributeLists(AttributeList().AddAttributes(StructLayout(typeDef.Attributes, layout)));
+                result = result.AddAttributeLists(AttributeList().AddAttributes(StructLayout(typeDef.Attributes, layout, charSet)));
             }
 
             if (this.FindGuidFromAttribute(typeDef) is Guid guid)
@@ -4830,6 +4840,10 @@ private ParameterSyntax CreateParameter(TypeHandleInfo parameterInfo, Parameter
                 }
 
                 fixedLengthStruct = fixedLengthStruct.AddMembers(conversionDecl);
+
+                // Make sure .NET marshals these `char` arrays as UTF-16.
+                fixedLengthStruct = fixedLengthStruct
+                    .AddAttributeLists(AttributeList().AddAttributes(StructLayout(TypeAttributes.SequentialLayout, charSet: CharSet.Unicode)));
             }
 
             IdentifierNameSyntax indexParamName = IdentifierName("index");

test/GenerationSandbox.Tests/BasicTests.cs

@@ -10,6 +10,9 @@
 using Windows.Win32.Foundation;
 using Windows.Win32.Graphics.DirectShow;
 using Windows.Win32.Storage.FileSystem;
+using Windows.Win32.System.Console;
+using Windows.Win32.System.ErrorReporting;
+using Windows.Win32.System.SystemServices;
 using Windows.Win32.UI.DisplayDevices;
 using Xunit;
 using Xunit.Abstractions;
@@ -413,4 +416,17 @@ public unsafe void GetProcAddress_String()
         ticks = getTickCountPtr();
         Assert.NotEqual(0u, ticks);
     }
+
+    [Fact]
+    public void StructCharFieldsMarshaledAsUtf16()
+    {
+        Assert.Equal(128 * sizeof(char), Marshal.SizeOf<WER_REPORT_INFORMATION.__char_128>());
+        Assert.Equal(sizeof(char), Marshal.SizeOf<KEY_EVENT_RECORD._uChar_e__Union>());
+    }
+
+    [Fact]
+    public void CHAR_MarshaledAsUtf8()
+    {
+        Assert.Equal(1, Marshal.SizeOf<CHAR>());
+    }
 }

test/GenerationSandbox.Tests/NativeMethods.txt

@@ -1,4 +1,5 @@
 BOOL
+CHAR
 CreateFile
 DISPLAYCONFIG_VIDEO_SIGNAL_INFO
 EnumWindows
@@ -8,9 +9,11 @@ GetWindowText
 GetWindowTextLength
 HDC_UserSize
 IEnumDebugPropertyInfo
+KEY_EVENT_RECORD
 LoadLibrary
 MainAVIHeader
 NTSTATUS
 RM_PROCESS_INFO
+WER_REPORT_INFORMATION
 wglGetProcAddress
 WPARAM