Transparent fnptr structs

sources/ClangSharp.PInvokeGenerator/Abstractions/TransparentStructDesc.cs

@@ -0,0 +1,13 @@
+// Copyright (c) .NET Foundation and Contributors. All Rights Reserved. Licensed under the MIT License (MIT). See License.md in the repository root for more information.
+
+namespace ClangSharp.Abstractions;
+
+internal struct TransparentStructDesc
+{
+    public string ParentName { get; set; }
+    public string Name { get; set; }
+    public string? NativeName { get; set; }
+    public string Type { get; set; }
+    public string? NativeType { get; set; }
+    public PInvokeGeneratorTransparentStructKind Kind { get; set; }
+}

sources/ClangSharp.PInvokeGenerator/CSharp/CSharpOutputBuilder.cs

@@ -299,7 +299,7 @@ private void AddVtblIndexAttribute(long vtblIndex, string? prefix = null, string
         }
     }
 
-    private void AddNativeTypeNameAttribute(string nativeTypeName, string? prefix = null, string? postfix = null, string? attributePrefix = null)
+    public void AddNativeTypeNameAttribute(string nativeTypeName, string? prefix = null, string? postfix = null, string? attributePrefix = null)
     {
         foreach (var entry in _generator.Config.NativeTypeNamesToStrip)
         {

sources/ClangSharp.PInvokeGenerator/PInvokeGenerator.VisitDecl.cs

@@ -717,7 +717,7 @@ private void VisitFunctionDecl(FunctionDecl functionDecl)
                 {
                     outputBuilder.Write("Base");
                 }
-                
+
                 outputBuilder.Write('.');
                 outputBuilder.Write(name);
                 outputBuilder.Write('(');
@@ -3194,22 +3194,44 @@ private void VisitTypedefDecl(TypedefDecl typedefDecl, bool onlyHandleRemappings
 
         void ForFunctionProtoType(TypedefDecl typedefDecl, FunctionProtoType functionProtoType, Type? parentType, bool onlyHandleRemappings)
         {
-            if (!_config.ExcludeFnptrCodegen || onlyHandleRemappings)
+            var hasOutput = _config.GenerateFnPtrWrapper || _config.ExcludeFnptrCodegen;
+            if (!hasOutput || onlyHandleRemappings)
             {
                 return;
             }
 
             var name = GetRemappedCursorName(typedefDecl);
             var escapedName = EscapeName(name);
 
-            var callingConventionName = GetCallingConvention(typedefDecl, context: null, typedefDecl.TypeForDecl);
+            StartUsingOutputBuilder(name);
+            Debug.Assert(_outputBuilder is not null);
 
-            var returnType = functionProtoType.ReturnType;
-            var returnTypeName = GetRemappedTypeName(typedefDecl, context: null, returnType, out var nativeTypeName);
+            if (_config.GenerateFnPtrWrapper)
+            {
+                var type = GetTypeName(typedefDecl, null, typedefDecl.TypeForDecl, true, false, out var nativeName);
+                _ = GetTypeName(typedefDecl, null, typedefDecl.UnderlyingType, true, false, out var nativeType);
 
-            StartUsingOutputBuilder(name);
+                if (IsNativeTypeNameEquivalent(nativeName, name))
+                {
+                    nativeName = null;
+                }
+
+                var desc = new TransparentStructDesc() {
+                    ParentName = name,
+                    Name = escapedName,
+                    NativeName = nativeName,
+                    Type = type,
+                    NativeType = nativeType,
+                    Kind = PInvokeGeneratorTransparentStructKind.FnPtr
+                };
+                GenerateTransparentStruct(desc);
+            }
+            else
             {
-                Debug.Assert(_outputBuilder is not null);
+                var callingConventionName = GetCallingConvention(typedefDecl, context: null, typedefDecl.TypeForDecl);
+
+                var returnType = functionProtoType.ReturnType;
+                var returnTypeName = GetRemappedTypeName(typedefDecl, context: null, returnType, out var nativeTypeName);
 
                 var desc = new FunctionOrDelegateDesc {
                     AccessSpecifier = GetAccessSpecifier(typedefDecl, matchStar: true),