Forward code generation for function pointers from type aliases (#170)

src/cs/examples/helloworld/helloworld-app/Generated/AssemblyAttributes.g.cs

@@ -1,6 +1,6 @@
 // <auto-generated>
-//  This code was generated by the following tool on 2025-01-03 14:36:43 GMT-05:00:
-//      https://github.com/bottlenoselabs/c2cs (v2025-01-03 14:36:43 GMT-05:00)
+//  This code was generated by the following tool on 2025-01-04 10:45:12 GMT-05:00:
+//      https://github.com/bottlenoselabs/c2cs (v2025-01-04 10:45:12 GMT-05:00)
 //
 //  Changes to this file may cause incorrect behavior and will be lost if the code is regenerated.
 // </auto-generated>

src/cs/examples/helloworld/helloworld-app/Generated/Runtime.g.cs

@@ -1,5 +1,5 @@
 // <auto-generated>
-//  This code was generated by the following tool on 2025-01-03 14:36:43 GMT-05:00:
+//  This code was generated by the following tool on 2025-01-04 10:45:12 GMT-05:00:
 //      https://github.com/bottlenoselabs/c2cs (v0.0.0.0)
 //
 //  Changes to this file may cause incorrect behavior and will be lost if the code is regenerated.

src/cs/examples/helloworld/helloworld-app/Generated/SourceGenerators/Microsoft.Interop.LibraryImportGenerator/Microsoft.Interop.LibraryImportGenerator/LibraryImports.g.cs

@@ -11,8 +11,16 @@ namespace helloworld
 {
     public static unsafe partial class my_c_library
     {
-        [global::System.Runtime.InteropServices.DllImportAttribute("my_c_library", EntryPoint = "hw_invoke_callback", ExactSpelling = true)]
-        public static extern partial void hw_invoke_callback(global::helloworld.my_c_library.FnPtr_CString_Void f, global::Interop.Runtime.CString s);
+        [global::System.Runtime.InteropServices.DllImportAttribute("my_c_library", EntryPoint = "hw_invoke_callback1", ExactSpelling = true)]
+        public static extern partial void hw_invoke_callback1(global::helloworld.my_c_library.hw_callback f, global::Interop.Runtime.CString s);
+    }
+}
+namespace helloworld
+{
+    public static unsafe partial class my_c_library
+    {
+        [global::System.Runtime.InteropServices.DllImportAttribute("my_c_library", EntryPoint = "hw_invoke_callback2", ExactSpelling = true)]
+        public static extern partial void hw_invoke_callback2(global::helloworld.my_c_library.FnPtr_CString_Void f, global::Interop.Runtime.CString s);
     }
 }
 namespace helloworld

src/cs/examples/helloworld/helloworld-app/Generated/my_c_library.g.cs

@@ -1,5 +1,5 @@
 // <auto-generated>
-//  This code was generated by the following tool on 2025-01-03 14:36:43 GMT-05:00:
+//  This code was generated by the following tool on 2025-01-04 10:45:12 GMT-05:00:
 //      https://github.com/bottlenoselabs/c2cs (v0.0.0.0)
 //
 //  Changes to this file may cause incorrect behavior and will be lost if the code is regenerated.
@@ -29,9 +29,13 @@ public static unsafe partial class my_c_library
     [UnmanagedCallConv(CallConvs = new[] { typeof(CallConvCdecl) })]
     public static partial void hw_hello_world();
 
-    [LibraryImport(LibraryName, EntryPoint = "hw_invoke_callback")]
+    [LibraryImport(LibraryName, EntryPoint = "hw_invoke_callback1")]
     [UnmanagedCallConv(CallConvs = new[] { typeof(CallConvCdecl) })]
-    public static partial void hw_invoke_callback(FnPtr_CString_Void f, CString s);
+    public static partial void hw_invoke_callback1(hw_callback f, CString s);
+
+    [LibraryImport(LibraryName, EntryPoint = "hw_invoke_callback2")]
+    [UnmanagedCallConv(CallConvs = new[] { typeof(CallConvCdecl) })]
+    public static partial void hw_invoke_callback2(FnPtr_CString_Void f, CString s);
 
     [LibraryImport(LibraryName, EntryPoint = "hw_pass_enum")]
     [UnmanagedCallConv(CallConvs = new[] { typeof(CallConvCdecl) })]
@@ -62,6 +66,17 @@ public enum hw_my_enum_week_day : int
         _HW_MY_ENUM_WEEK_DAY_FORCE_U32 = 2147483647
     }
 
+    [StructLayout(LayoutKind.Sequential)]
+    public partial struct hw_callback
+    {
+        public delegate* unmanaged<CString, void> Pointer;
+
+        public hw_callback(delegate* unmanaged<CString, void> pointer)
+        {
+            Pointer = pointer;
+        }
+    }
+
     [StructLayout(LayoutKind.Sequential)]
     public partial struct FnPtr_CString_Void
     {

src/cs/examples/helloworld/helloworld-app/Program.cs

@@ -48,13 +48,16 @@ private static unsafe void Main()
         //      - It uses the same naming as `System.Func<>`. The last type on the name is always the return type. In this case 'void`.
         //  Only available in C# 9 (.NET 5+). See https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/unsafe-code#function-pointers
         //  Additionally function pointers need to use the `address-of` operator (&) to a C# static function marked with the UnmanagedCallersOnly attribute. See https://learn.microsoft.com/en-us/dotnet/api/system.runtime.interopservices.unmanagedcallersonlyattribute?view=net-9.0
-        var functionPointer = new FnPtr_CString_Void(&Callback);
+        var functionPointer = new hw_callback(&Callback);
 #else
         var functionPointer = new FnPtr_CString_Void(Callback);
 #endif
 
-        using var cStringCallback = (CString)"Hello from callback!";
-        hw_invoke_callback(functionPointer, cStringCallback);
+        using var cStringCallback1 = (CString)"Hello from callback!";
+        hw_invoke_callback1(functionPointer, cStringCallback1);
+
+        // using var cStringCallback2 = (CString)"Hello again from callback!";
+        // hw_invoke_callback2(functionPointer, cStringCallback2);
     }
 
 #if NET5_0_OR_GREATER

src/cs/examples/helloworld/helloworld-bindgen/my_c_library/include/my_c_library.h

@@ -24,8 +24,11 @@ typedef enum hw_my_enum_week_day {
     _HW_MY_ENUM_WEEK_DAY_FORCE_U32 = 0x7FFFFFFF
 } hw_my_enum_week_day;
 
+typedef void (*hw_callback)(const char* s);
+
 MY_C_LIBRARY_API_DECL void hw_hello_world(void);
-MY_C_LIBRARY_API_DECL void hw_invoke_callback(void f(const char*), const char* s);
+MY_C_LIBRARY_API_DECL void hw_invoke_callback1(hw_callback f, const char* s);
+MY_C_LIBRARY_API_DECL void hw_invoke_callback2(void f(const char*), const char* s);
 MY_C_LIBRARY_API_DECL void hw_pass_string(const char* s);
 MY_C_LIBRARY_API_DECL void hw_pass_integers_by_value(uint16_t a, int32_t b, uint64_t c);
 MY_C_LIBRARY_API_DECL void hw_pass_integers_by_reference(const uint16_t* a, const int32_t* b, const uint64_t* c);

src/cs/examples/helloworld/helloworld-bindgen/my_c_library/src/my_c_library.c

@@ -8,7 +8,17 @@ void hw_hello_world(void)
     printf("Hello world from C!\n");
 }
 
-void hw_invoke_callback(void f(const char*), const char* s)
+void hw_invoke_callback1(hw_callback f, const char* s)
+{
+    if (f == 0)
+    {
+        return;
+    }
+
+    f(s);
+}
+
+void hw_invoke_callback2(void f(const char*), const char* s)
 {
     if (f == 0)
     {

src/cs/production/c2cs.Tool/GenerateCSharpCode/CodeGenerator.cs

@@ -9,6 +9,10 @@
 using C2CS.GenerateCSharpCode.Generators;
 using c2ffi.Data;
 using c2ffi.Data.Nodes;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.FindSymbols;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
 
@@ -58,9 +62,11 @@ public CodeProject GenerateCodeProject(CFfiCrossPlatform ffi, DiagnosticsSink di
             AddDocumentInteropRuntime(options, documents);
             AddDocumentAssemblyAttributes(options, documents);
 
+            var newDocuments = PostProcessDocuments(documents.ToImmutableArray());
+
             return new CodeProject
             {
-                Documents = documents.ToImmutable()
+                Documents = [..newDocuments]
             };
         }
 #pragma warning disable CA1031
@@ -72,12 +78,78 @@ public CodeProject GenerateCodeProject(CFfiCrossPlatform ffi, DiagnosticsSink di
         }
     }
 
+    private static ImmutableArray<CodeProjectDocument> PostProcessDocuments(
+        ImmutableArray<CodeProjectDocument> documents)
+    {
+        using var workspace = new AdhocWorkspace();
+        var project = workspace.CurrentSolution.AddProject(
+                "TemporaryProject", "TemporaryAssembly", LanguageNames.CSharp)
+            .AddMetadataReferences([
+                MetadataReference.CreateFromFile(typeof(object).Assembly.Location)
+            ]);
+        foreach (var document in documents)
+        {
+            project = project.AddDocument(document.FileName, document.Code).Project;
+        }
+
+        var newDocuments = new List<CodeProjectDocument>();
+        var compilation = project.GetCompilationAsync().Result!;
+        foreach (var syntaxTree in compilation.SyntaxTrees)
+        {
+            var code = PostProcessDocumentSyntaxTree(syntaxTree, compilation, project.Solution);
+            var newDocument = new CodeProjectDocument
+            {
+                Code = code,
+                FileName = syntaxTree.FilePath
+            };
+            newDocuments.Add(newDocument);
+        }
+
+        return [..newDocuments];
+    }
+
+    private static string PostProcessDocumentSyntaxTree(
+        SyntaxTree syntaxTree,
+        Compilation compilation,
+        Solution solution)
+    {
+        var root = syntaxTree.GetRoot();
+        var semanticModel = compilation.GetSemanticModel(syntaxTree);
+
+        var functionPointerStructWrappers = root.DescendantNodes()
+            .OfType<StructDeclarationSyntax>()
+            .Where(x =>
+                x.Identifier.Text.StartsWith("FnPtr_", StringComparison.InvariantCultureIgnoreCase))
+            .ToImmutableArray();
+        if (functionPointerStructWrappers.IsDefaultOrEmpty)
+        {
+            return root.SyntaxTree.ToString();
+        }
+
+        var newRoot = root;
+        foreach (var functionPointerStructWrapper in functionPointerStructWrappers)
+        {
+            var symbol = semanticModel.GetDeclaredSymbol(functionPointerStructWrapper)!;
+            var references = SymbolFinder
+                .FindReferencesAsync(symbol, solution).Result
+                .ToImmutableArray();
+
+            var referencesCount = references.Sum(x => x.Locations.Count());
+            if (referencesCount == 0)
+            {
+                newRoot = newRoot.RemoveNode(functionPointerStructWrapper, SyntaxRemoveOptions.KeepNoTrivia)!;
+            }
+        }
+
+        return newRoot.SyntaxTree.ToString();
+    }
+
     private void AddDocumentPInvoke(
         CodeGeneratorDocumentOptions options,
         ImmutableArray<CodeProjectDocument>.Builder documents,
         CFfiCrossPlatform ffi)
     {
-        var context = new CodeGeneratorContext(_input, _nodeCodeGenerators);
+        var context = new CodeGeneratorContext(_input, ffi, _nodeCodeGenerators);
         var document = _codeGeneratorDocumentPInvoke.Generate(options, context, ffi);
         documents.Add(document);
 

src/cs/production/c2cs.Tool/GenerateCSharpCode/CodeGeneratorContext.cs

@@ -6,6 +6,7 @@
 using System.Collections.Immutable;
 using bottlenoselabs.Common.Tools;
 using C2CS.GenerateCSharpCode.Generators;
+using c2ffi.Data;
 using c2ffi.Data.Nodes;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
@@ -23,26 +24,26 @@ public sealed class CodeGeneratorContext
 
     public InputSanitized Input { get; }
 
+    public CFfiCrossPlatform Ffi { get; }
+
     public NameMapper NameMapper => _nameMapper;
 
     public CodeGeneratorContext(
         InputSanitized input,
+        CFfiCrossPlatform ffi,
         ImmutableDictionary<Type, BaseGenerator> nodeCodeGenerators)
     {
         Input = input;
+        Ffi = ffi;
         _nameMapper = new NameMapper(this);
         _nodeCodeGenerators = nodeCodeGenerators;
     }
 
-    internal TMemberDeclarationSyntax? ProcessCNode<TNode, TMemberDeclarationSyntax>(TNode node)
+    public TMemberDeclarationSyntax? ProcessCNode<TNode, TMemberDeclarationSyntax>(TNode node)
         where TNode : CNode
         where TMemberDeclarationSyntax : MemberDeclarationSyntax
     {
-        var type = typeof(TNode);
-        if (!_nodeCodeGenerators.TryGetValue(type, out var codeGenerator))
-        {
-            throw new ToolException($"A code generator '{nameof(BaseGenerator)}' does not exist for the type '{type.FullName ?? type.Name}'.");
-        }
+        var codeGenerator = GetCodeGenerator<TNode>();
 
         var nameCSharp = _nameMapper.GetNodeNameCSharp(node);
         var isAlreadyAdded = !_existingNamesCSharp.Add(nameCSharp);
@@ -51,7 +52,12 @@ public CodeGeneratorContext(
             return null;
         }
 
-        var code = codeGenerator.GenerateCode(nameCSharp, this, node);
+        var code = codeGenerator.GenerateCode(this, nameCSharp, node);
+        if (string.IsNullOrEmpty(code))
+        {
+            return null;
+        }
+
         var memberDeclarationSyntax = SyntaxFactory.ParseMemberDeclaration(code.Trim())!;
         if (memberDeclarationSyntax is not TMemberDeclarationSyntax typedMemberDeclarationSyntax)
         {
@@ -64,4 +70,17 @@ public CodeGeneratorContext(
 
         return memberDeclarationSyntaxWithTrivia;
     }
+
+    public BaseGenerator<TNode> GetCodeGenerator<TNode>()
+        where TNode : CNode
+    {
+        var type = typeof(TNode);
+        if (!_nodeCodeGenerators.TryGetValue(type, out var codeGenerator))
+        {
+            throw new ToolException(
+                $"A code generator does not exist for the C node '{type.Name}'.");
+        }
+
+        return (BaseGenerator<TNode>)codeGenerator;
+    }
 }

src/cs/production/c2cs.Tool/GenerateCSharpCode/Generators/BaseGenerator.cs

@@ -10,7 +10,7 @@ public abstract class BaseGenerator(ILogger<BaseGenerator> logger)
 {
     protected readonly ILogger<BaseGenerator> Logger = logger;
 
-    protected internal abstract string GenerateCode(
+    protected abstract string? GenerateCode(
         string nameCSharp,
         CodeGeneratorContext context,
         object obj);
@@ -20,15 +20,15 @@ public abstract class BaseGenerator<TNode>(ILogger<BaseGenerator<TNode>> logger)
     : BaseGenerator(logger)
     where TNode : CNode
 {
-    protected internal override string GenerateCode(
+    public abstract string? GenerateCode(CodeGeneratorContext context, string nameCSharp, TNode node);
+
+    protected override string? GenerateCode(
         string nameCSharp,
         CodeGeneratorContext context,
         object obj)
     {
         var node = (TNode)obj;
-        var code = GenerateCode(nameCSharp, context, node);
+        var code = GenerateCode(context, nameCSharp, node);
         return code;
     }
-
-    protected abstract string GenerateCode(string nameCSharp, CodeGeneratorContext context, TNode node);
 }

src/cs/production/c2cs.Tool/GenerateCSharpCode/Generators/GeneratorAliasType.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Bottlenose Labs Inc. (https://github.com/bottlenoselabs). All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the Git repository root directory for full license information.
 
+using c2ffi.Data;
 using c2ffi.Data.Nodes;
 using JetBrains.Annotations;
 using Microsoft.Extensions.Logging;
@@ -11,13 +12,21 @@ namespace C2CS.GenerateCSharpCode.Generators;
 public class GeneratorAliasType(ILogger<GeneratorAliasType> logger)
     : BaseGenerator<CTypeAlias>(logger)
 {
-    protected override string GenerateCode(
-        string nameCSharp, CodeGeneratorContext context, CTypeAlias node)
+    public override string? GenerateCode(CodeGeneratorContext context, string nameCSharp, CTypeAlias node)
     {
         var underlyingTypeNameCSharp = context.NameMapper.GetTypeNameCSharp(node.UnderlyingType);
         var sizeOf = node.UnderlyingType.SizeOf;
         var alignOf = node.UnderlyingType.AlignOf;
 
+        if (node.UnderlyingType.NodeKind == CNodeKind.FunctionPointer)
+        {
+            var functionPointer = context.Ffi.FunctionPointers[node.UnderlyingType.Name];
+            var functionPointerCodeGenerator = context.GetCodeGenerator<CFunctionPointer>();
+            var functionPointerCode = functionPointerCodeGenerator.GenerateCode(
+                context, nameCSharp, functionPointer);
+            return functionPointerCode;
+        }
+
         var code = $$"""
                      [StructLayout(LayoutKind.Explicit, Size = {{sizeOf}}, Pack = {{alignOf}})]
                      public partial struct {{nameCSharp}}

src/cs/production/c2cs.Tool/GenerateCSharpCode/Generators/GeneratorEnum.cs

@@ -13,10 +13,7 @@ namespace C2CS.GenerateCSharpCode.Generators;
 public class GeneratorEnum(ILogger<GeneratorEnum> logger)
     : BaseGenerator<CEnum>(logger)
 {
-    protected override string GenerateCode(
-        string nameCSharp,
-        CodeGeneratorContext context,
-        CEnum node)
+    public override string? GenerateCode(CodeGeneratorContext context, string nameCSharp, CEnum node)
     {
         var integerTypeNameCSharp = node.SizeOf switch
         {

src/cs/production/c2cs.Tool/GenerateCSharpCode/Generators/GeneratorFunction.cs

@@ -15,10 +15,7 @@ namespace C2CS.GenerateCSharpCode.Generators;
 public class GeneratorFunction(ILogger<GeneratorFunction> logger)
     : BaseGenerator<CFunction>(logger)
 {
-    protected override string GenerateCode(
-        string nameCSharp,
-        CodeGeneratorContext context,
-        CFunction function)
+    public override string? GenerateCode(CodeGeneratorContext context, string nameCSharp, CFunction function)
     {
         var returnTypeNameCSharp = context.NameMapper.GetTypeNameCSharp(function.ReturnType);
         var parametersStringCSharp = string.Join(',', function.Parameters.Select(