Add helper APIs for variable-length inline arrays

src/Microsoft.Windows.CsWin32/FastSyntaxFactory.cs

@@ -102,6 +102,8 @@ internal static ForStatementSyntax ForStatement(VariableDeclarationSyntax? decla
 
     internal static VariableDeclarationSyntax VariableDeclaration(TypeSyntax type) => SyntaxFactory.VariableDeclaration(type.WithTrailingTrivia(TriviaList(Space)));
 
+    internal static SizeOfExpressionSyntax SizeOfExpression(TypeSyntax type) => SyntaxFactory.SizeOfExpression(Token(SyntaxKind.SizeOfKeyword), Token(SyntaxKind.OpenParenToken), type, Token(SyntaxKind.CloseParenToken));
+
     internal static MemberAccessExpressionSyntax MemberAccessExpression(SyntaxKind kind, ExpressionSyntax expression, SimpleNameSyntax name) => SyntaxFactory.MemberAccessExpression(kind, expression, Token(GetMemberAccessExpressionOperatorTokenKind(kind)), name);
 
     internal static ConditionalAccessExpressionSyntax ConditionalAccessExpression(ExpressionSyntax expression, SimpleNameSyntax name) => SyntaxFactory.ConditionalAccessExpression(expression, Token(SyntaxKind.QuestionToken), MemberBindingExpression(name));

src/Microsoft.Windows.CsWin32/Generator.Features.cs

@@ -8,6 +8,7 @@ public partial class Generator
     private readonly bool canUseSpan;
     private readonly bool canCallCreateSpan;
     private readonly bool canUseUnsafeAsRef;
+    private readonly bool canUseUnsafeAdd;
     private readonly bool canUseUnsafeNullRef;
     private readonly bool canUseUnmanagedCallersOnlyAttribute;
     private readonly bool canUseSetLastPInvokeError;

src/Microsoft.Windows.CsWin32/Generator.Struct.cs

@@ -28,11 +28,14 @@ private StructDeclarationSyntax DeclareStruct(TypeDefinitionHandle typeDefHandle
 
         // If the last field has the [FlexibleArray] attribute, we must disable marshaling since the struct
         // is only ever valid when accessed via a pointer since the struct acts as a header of an arbitrarily-sized array.
+        FieldDefinitionHandle flexibleArrayFieldHandle = default;
+        MethodDeclarationSyntax? sizeOfMethod = null;
         if (typeDef.GetFields().LastOrDefault() is FieldDefinitionHandle { IsNil: false } lastFieldHandle)
         {
             FieldDefinition lastField = this.Reader.GetFieldDefinition(lastFieldHandle);
             if (MetadataUtilities.FindAttribute(this.Reader, lastField.GetCustomAttributes(), InteropDecorationNamespace, FlexibleArrayAttribute) is not null)
             {
+                flexibleArrayFieldHandle = lastFieldHandle;
                 context = context with { AllowMarshaling = false };
             }
         }
@@ -80,6 +83,37 @@ private StructDeclarationSyntax DeclareStruct(TypeDefinitionHandle typeDefHandle
                                 .WithArgumentList(BracketedArgumentList(SingletonSeparatedList(Argument(size)))))
                         .AddModifiers(TokenWithSpace(this.Visibility), TokenWithSpace(SyntaxKind.UnsafeKeyword), Token(SyntaxKind.FixedKeyword));
                 }
+                else if (fieldDefHandle == flexibleArrayFieldHandle)
+                {
+                    CustomAttributeHandleCollection fieldAttributes = fieldDef.GetCustomAttributes();
+                    var fieldTypeInfo = (ArrayTypeHandleInfo)fieldDef.DecodeSignature(SignatureHandleProvider.Instance, null);
+                    TypeSyntax fieldType = fieldTypeInfo.ElementType.ToTypeSyntax(typeSettings, GeneratingElement.StructMember, fieldAttributes).Type;
+
+                    if (fieldType is PointerTypeSyntax or FunctionPointerTypeSyntax)
+                    {
+                        // These types are not allowed as generic type arguments (https://github.com/dotnet/runtime/issues/13627)
+                        // so we have to generate a special nested struct dedicated to this type instead of using the generic type.
+                        StructDeclarationSyntax helperStruct = this.DeclareVariableLengthInlineArrayHelper(context, fieldType);
+                        additionalMembers = additionalMembers.Add(helperStruct);
+
+                        field = FieldDeclaration(
+                            VariableDeclaration(IdentifierName(helperStruct.Identifier.ValueText)))
+                            .AddDeclarationVariables(fieldDeclarator)
+                            .AddModifiers(TokenWithSpace(this.Visibility));
+                    }
+                    else
+                    {
+                        this.RequestVariableLengthInlineArrayHelper(context);
+                        field = FieldDeclaration(
+                            VariableDeclaration(
+                                GenericName($"global::Windows.Win32.VariableLengthInlineArray")
+                                .WithTypeArgumentList(TypeArgumentList().AddArguments(fieldType))))
+                            .AddDeclarationVariables(fieldDeclarator)
+                            .AddModifiers(TokenWithSpace(this.Visibility));
+                    }
+
+                    sizeOfMethod = this.DeclareSizeOfMethod(name, fieldType, typeSettings);
+                }
                 else
                 {
                     CustomAttributeHandleCollection fieldAttributes = fieldDef.GetCustomAttributes();
@@ -334,6 +368,12 @@ private StructDeclarationSyntax DeclareStruct(TypeDefinitionHandle typeDefHandle
             }
         }
 
+        // Add a SizeOf method, if there is a FlexibleArray field.
+        if (sizeOfMethod is not null)
+        {
+            members.Add(sizeOfMethod);
+        }
+
         // Add the additional members, taking care to not introduce redundant declarations.
         members.AddRange(additionalMembers.Where(c => c is not StructDeclarationSyntax cs || !members.OfType<StructDeclarationSyntax>().Any(m => m.Identifier.ValueText == cs.Identifier.ValueText)));
 
@@ -370,6 +410,95 @@ private StructDeclarationSyntax DeclareStruct(TypeDefinitionHandle typeDefHandle
         return result;
     }
 
+    private StructDeclarationSyntax DeclareVariableLengthInlineArrayHelper(Context context, TypeSyntax fieldType)
+    {
+        IdentifierNameSyntax firstElementFieldName = IdentifierName("e0");
+        List<MemberDeclarationSyntax> members = new();
+
+        // internal unsafe T e0;
+        members.Add(FieldDeclaration(VariableDeclaration(fieldType).AddVariables(VariableDeclarator(firstElementFieldName.Identifier)))
+            .AddModifiers(TokenWithSpace(this.Visibility), TokenWithSpace(SyntaxKind.UnsafeKeyword)));
+
+        if (this.canUseUnsafeAdd)
+        {
+            ////[MethodImpl(MethodImplOptions.AggressiveInlining)]
+            ////get { fixed (int** p = &e0) return *(p + index); }
+            IdentifierNameSyntax pLocal = IdentifierName("p");
+            AccessorDeclarationSyntax getter = AccessorDeclaration(SyntaxKind.GetAccessorDeclaration)
+                .WithBody(Block().AddStatements(
+                    FixedStatement(
+                        VariableDeclaration(PointerType(fieldType)).AddVariables(
+                            VariableDeclarator(pLocal.Identifier).WithInitializer(EqualsValueClause(PrefixUnaryExpression(SyntaxKind.AddressOfExpression, firstElementFieldName)))),
+                        ReturnStatement(PrefixUnaryExpression(SyntaxKind.PointerIndirectionExpression, ParenthesizedExpression(BinaryExpression(SyntaxKind.AddExpression, pLocal, IdentifierName("index"))))))))
+                .AddAttributeLists(AttributeList().AddAttributes(MethodImpl(MethodImplOptions.AggressiveInlining)));
+
+            ////[MethodImpl(MethodImplOptions.AggressiveInlining)]
+            ////set { fixed (int** p = &e0) *(p + index) = value; }
+            AccessorDeclarationSyntax setter = AccessorDeclaration(SyntaxKind.SetAccessorDeclaration)
+                .WithBody(Block().AddStatements(
+                    FixedStatement(
+                        VariableDeclaration(PointerType(fieldType)).AddVariables(
+                            VariableDeclarator(pLocal.Identifier).WithInitializer(EqualsValueClause(PrefixUnaryExpression(SyntaxKind.AddressOfExpression, firstElementFieldName)))),
+                        ExpressionStatement(AssignmentExpression(
+                            SyntaxKind.SimpleAssignmentExpression,
+                            PrefixUnaryExpression(SyntaxKind.PointerIndirectionExpression, ParenthesizedExpression(BinaryExpression(SyntaxKind.AddExpression, pLocal, IdentifierName("index")))),
+                            IdentifierName("value"))))))
+                .AddAttributeLists(AttributeList().AddAttributes(MethodImpl(MethodImplOptions.AggressiveInlining)));
+
+            ////internal unsafe T this[int index]
+            members.Add(IndexerDeclaration(fieldType.WithTrailingTrivia(Space))
+                .AddModifiers(TokenWithSpace(this.Visibility), TokenWithSpace(SyntaxKind.UnsafeKeyword))
+                .AddParameterListParameters(Parameter(Identifier("index")).WithType(PredefinedType(TokenWithSpace(SyntaxKind.IntKeyword))))
+                .AddAccessorListAccessors(getter, setter));
+        }
+
+        // internal partial struct VariableLengthInlineArrayHelper
+        return StructDeclaration(Identifier("VariableLengthInlineArrayHelper"))
+            .AddModifiers(TokenWithSpace(this.Visibility), TokenWithSpace(SyntaxKind.PartialKeyword))
+            .AddMembers(members.ToArray());
+    }
+
+    private MethodDeclarationSyntax DeclareSizeOfMethod(TypeSyntax structType, TypeSyntax elementType, TypeSyntaxSettings typeSettings)
+    {
+        PredefinedTypeSyntax intType = PredefinedType(TokenWithSpace(SyntaxKind.IntKeyword));
+        IdentifierNameSyntax countName = IdentifierName("count");
+        IdentifierNameSyntax localName = IdentifierName("v");
+        List<StatementSyntax> statements = new();
+
+        // int v = sizeof(OUTER_STRUCT);
+        statements.Add(LocalDeclarationStatement(VariableDeclaration(intType).AddVariables(
+            VariableDeclarator(localName.Identifier).WithInitializer(EqualsValueClause(SizeOfExpression(structType))))));
+
+        // if (count > 1)
+        //   v += checked((count - 1) * sizeof(ELEMENT_TYPE));
+        // else if (count < 0)
+        //   throw new ArgumentOutOfRangeException(nameof(count));
+        statements.Add(IfStatement(
+            BinaryExpression(SyntaxKind.GreaterThanExpression, countName, LiteralExpression(SyntaxKind.NumericLiteralExpression, Literal(1))),
+            ExpressionStatement(AssignmentExpression(
+                SyntaxKind.AddAssignmentExpression,
+                localName,
+                CheckedExpression(BinaryExpression(
+                    SyntaxKind.MultiplyExpression,
+                    ParenthesizedExpression(BinaryExpression(SyntaxKind.SubtractExpression, countName, LiteralExpression(SyntaxKind.NumericLiteralExpression, Literal(1)))),
+                    SizeOfExpression(elementType))))),
+            ElseClause(IfStatement(
+                BinaryExpression(SyntaxKind.LessThanExpression, countName, LiteralExpression(SyntaxKind.NumericLiteralExpression, Literal(0))),
+                ThrowStatement(ObjectCreationExpression(IdentifierName(nameof(ArgumentOutOfRangeException))))).WithCloseParenToken(TokenWithLineFeed(SyntaxKind.CloseParenToken)))).WithCloseParenToken(TokenWithLineFeed(SyntaxKind.CloseParenToken)));
+
+        // return v;
+        statements.Add(ReturnStatement(localName));
+
+        // internal static unsafe int SizeOf(int count)
+        MethodDeclarationSyntax sizeOfMethod = MethodDeclaration(intType, Identifier("SizeOf"))
+            .AddParameterListParameters(Parameter(countName.Identifier).WithType(intType))
+            .WithBody(Block().AddStatements(statements.ToArray()))
+            .AddModifiers(TokenWithSpace(this.Visibility), TokenWithSpace(SyntaxKind.StaticKeyword), TokenWithSpace(SyntaxKind.UnsafeKeyword))
+            .WithLeadingTrivia(ParseLeadingTrivia("/// <summary>Computes the amount of memory that must be allocated to store this struct, including the specified number of elements in the variable length inline array at the end.</summary>\n"));
+
+        return sizeOfMethod;
+    }
+
     private (TypeSyntax FieldType, SyntaxList<MemberDeclarationSyntax> AdditionalMembers, AttributeSyntax? MarshalAsAttribute) ReinterpretFieldType(FieldDefinition fieldDef, TypeSyntax originalType, CustomAttributeHandleCollection customAttributes, Context context)
     {
         TypeSyntaxSettings typeSettings = context.Filter(this.fieldTypeSettings);
@@ -397,4 +526,23 @@ private StructDeclarationSyntax DeclareStruct(TypeDefinitionHandle typeDefHandle
 
         return (originalType, default(SyntaxList<MemberDeclarationSyntax>), marshalAs);
     }
+
+    private void RequestVariableLengthInlineArrayHelper(Context context)
+    {
+        if (this.IsWin32Sdk)
+        {
+            if (!this.IsTypeAlreadyFullyDeclared($"{this.Namespace}.{this.variableLengthInlineArrayStruct.Identifier.ValueText}"))
+            {
+                this.DeclareUnscopedRefAttributeIfNecessary();
+                this.volatileCode.GenerateSpecialType("VariableLengthInlineArray", () => this.volatileCode.AddSpecialType("VariableLengthInlineArray", this.variableLengthInlineArrayStruct));
+            }
+        }
+        else if (this.SuperGenerator is not null && this.SuperGenerator.TryGetGenerator("Windows.Win32", out Generator? generator))
+        {
+            generator.volatileCode.GenerationTransaction(delegate
+            {
+                generator.RequestVariableLengthInlineArrayHelper(context);
+            });
+        }
+    }
 }

src/Microsoft.Windows.CsWin32/Generator.cs

@@ -22,6 +22,7 @@ public partial class Generator : IGenerator, IDisposable
     private readonly TypeSyntaxSettings errorMessageTypeSettings;
 
     private readonly ClassDeclarationSyntax comHelperClass;
+    private readonly StructDeclarationSyntax variableLengthInlineArrayStruct;
 
     private readonly Dictionary<string, IReadOnlyList<ISymbol>> findTypeSymbolIfAlreadyAvailableCache = new(StringComparer.Ordinal);
     private readonly Rental<MetadataReader> metadataReader;
@@ -86,7 +87,8 @@ public Generator(string metadataLibraryPath, Docs? docs, GeneratorOptions option
 
         this.canUseSpan = this.compilation?.GetTypeByMetadataName(typeof(Span<>).FullName) is not null;
         this.canCallCreateSpan = this.compilation?.GetTypeByMetadataName(typeof(MemoryMarshal).FullName)?.GetMembers("CreateSpan").Any() is true;
-        this.canUseUnsafeAsRef = this.compilation?.GetTypeByMetadataName(typeof(Unsafe).FullName)?.GetMembers("AsRef").Any() is true;
+        this.canUseUnsafeAsRef = this.compilation?.GetTypeByMetadataName(typeof(Unsafe).FullName)?.GetMembers("Add").Any() is true;
+        this.canUseUnsafeAdd = this.compilation?.GetTypeByMetadataName(typeof(Unsafe).FullName)?.GetMembers("AsRef").Any() is true;
         this.canUseUnsafeNullRef = this.compilation?.GetTypeByMetadataName(typeof(Unsafe).FullName)?.GetMembers("NullRef").Any() is true;
         this.canUseUnmanagedCallersOnlyAttribute = this.compilation?.GetTypeByMetadataName("System.Runtime.InteropServices.UnmanagedCallersOnlyAttribute") is not null;
         this.canUseSetLastPInvokeError = this.compilation?.GetTypeByMetadataName("System.Runtime.InteropServices.Marshal")?.GetMembers("GetLastSystemError").IsEmpty is false;
@@ -110,6 +112,7 @@ public Generator(string metadataLibraryPath, Docs? docs, GeneratorOptions option
             AddSymbolIf(this.canUseSpan, "canUseSpan");
             AddSymbolIf(this.canCallCreateSpan, "canCallCreateSpan");
             AddSymbolIf(this.canUseUnsafeAsRef, "canUseUnsafeAsRef");
+            AddSymbolIf(this.canUseUnsafeAdd, "canUseUnsafeAdd");
             AddSymbolIf(this.canUseUnsafeNullRef, "canUseUnsafeNullRef");
             AddSymbolIf(compilation?.GetTypeByMetadataName("System.Drawing.Point") is not null, "canUseSystemDrawing");
             AddSymbolIf(this.IsFeatureAvailable(Feature.InterfaceStaticMembers), "canUseInterfaceStaticMembers");
@@ -149,6 +152,7 @@ void AddSymbolIf(bool condition, string symbol)
         this.methodsAndConstantsClassName = IdentifierName(options.ClassName);
 
         FetchTemplate("ComHelpers", this, out this.comHelperClass);
+        FetchTemplate("VariableLengthInlineArray`1", this, out this.variableLengthInlineArrayStruct);
     }
 
     internal enum GeneratingElement

src/Microsoft.Windows.CsWin32/templates/VariableLengthInlineArray`1.cs

@@ -0,0 +1,33 @@
+internal struct VariableLengthInlineArray<T>
+	where T : unmanaged
+{
+	internal T e0;
+
+#if canUseUnsafeAdd
+	internal ref T this[int index]
+	{
+		[UnscopedRef]
+		[MethodImpl(MethodImplOptions.AggressiveInlining)]
+		get => ref Unsafe.Add(ref this.e0, index);
+	}
+#endif
+
+#if canUseSpan
+	[UnscopedRef]
+	[MethodImpl(MethodImplOptions.AggressiveInlining)]
+	internal Span<T> AsSpan(int length)
+	{
+#if canCallCreateSpan
+		return MemoryMarshal.CreateSpan(ref this.e0, length);
+#else
+		unsafe
+		{
+			fixed (void* p = &this.e0)
+			{
+				return new Span<T>(p, length);
+			}
+		}
+#endif
+	}
+#endif
+}

test/GenerationSandbox.Tests/FlexibleArrayTests.cs

@@ -0,0 +1,37 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System.Runtime.InteropServices;
+using Windows.Win32.System.Ole;
+
+public class FlexibleArrayTests
+{
+    [Fact]
+    public unsafe void FlexibleArraySizing()
+    {
+        const int count = 3;
+        PAGESET* pPageSet = (PAGESET*)Marshal.AllocHGlobal(PAGESET.SizeOf(count));
+        try
+        {
+            pPageSet->rgPages[0].nFromPage = 0;
+
+            Span<PAGERANGE> pageRange = pPageSet->rgPages.AsSpan(count);
+            for (int i = 0; i < count; i++)
+            {
+                pageRange[i].nFromPage = i * 2;
+                pageRange[i].nToPage = (i * 2) + 1;
+            }
+        }
+        finally
+        {
+            Marshal.FreeHGlobal((IntPtr)pPageSet);
+        }
+    }
+
+    [Fact]
+    public void SizeOf_Minimum1Element()
+    {
+        Assert.Equal(PAGESET.SizeOf(1), PAGESET.SizeOf(0));
+        Assert.Equal(Marshal.SizeOf<PAGERANGE>(), PAGESET.SizeOf(2) - PAGESET.SizeOf(1));
+    }
+}

test/GenerationSandbox.Tests/NativeMethods.txt

@@ -30,6 +30,7 @@ MAKELRESULT
 MAKEWPARAM
 MAX_PATH
 NTSTATUS
+PAGESET
 PathParseIconLocation
 PROCESS_BASIC_INFORMATION
 PZZSTR

test/Microsoft.Windows.CsWin32.Tests/StructTests.cs

@@ -244,6 +244,22 @@ public void StructConstantsAreGeneratedAsConstants()
         Assert.NotEmpty(type.Members.OfType<FieldDeclarationSyntax>().Where(f => f.Modifiers.Any(SyntaxKind.ConstKeyword)));
     }
 
+    [Theory]
+    [MemberData(nameof(TFMData))]
+    public void FlexibleArrayMember(string tfm)
+    {
+        this.compilation = this.starterCompilations[tfm];
+        this.GenerateApi("BITMAPINFO");
+        var type = (StructDeclarationSyntax)Assert.Single(this.FindGeneratedType("BITMAPINFO"));
+        FieldDeclarationSyntax flexArrayField = Assert.Single(type.Members.OfType<FieldDeclarationSyntax>(), m => m.Declaration.Variables.Any(v => v.Identifier.ValueText == "bmiColors"));
+        var fieldType = Assert.IsType<GenericNameSyntax>(Assert.IsType<QualifiedNameSyntax>(flexArrayField.Declaration.Type).Right);
+        Assert.Equal("VariableLengthInlineArray", fieldType.Identifier.ValueText);
+        Assert.Equal("RGBQUAD", Assert.IsType<QualifiedNameSyntax>(Assert.Single(fieldType.TypeArgumentList.Arguments)).Right.Identifier.ValueText);
+
+        // Verify that the SizeOf method was generated.
+        Assert.Single(this.FindGeneratedMethod("SizeOf"));
+    }
+
     [Theory]
     [CombinatorialData]
     public void InterestingStructs(