Generate valid C# for pure functions returning or taking dependent pointers

Signed-off-by: Dimitar Dobrev <dpldobrev@protonmail.com>

src/Generator/Generators/CSharp/CSharpSources.cs

@@ -1676,7 +1676,7 @@ namespace CppSharp.Generators.CSharp
             NewLine();
 
             // Generate a delegate type for each method.
-            foreach (var method in wrappedEntries.Select(e => e.Method))
+            foreach (var method in wrappedEntries.Select(e => e.Method).Where(m => !m.Ignore))
                 GenerateVTableMethodDelegates(containingClass, method.Namespace.IsDependent ?
                    (Method) method.InstantiatedFrom : method);
 
@@ -1701,7 +1701,7 @@ namespace CppSharp.Generators.CSharp
                 WriteLine($"static VTableLoader()");
                 {
                     WriteOpenBraceAndIndent();
-                    foreach (var entry in wrappedEntries.Distinct())
+                    foreach (var entry in wrappedEntries.Distinct().Where(e => !e.Method.Ignore))
                     {
                         var name = GetVTableMethodDelegateName(entry.Method);
                         WriteLine($"{name + "Instance"} += {name}Hook;");
@@ -1709,9 +1709,12 @@ namespace CppSharp.Generators.CSharp
                     for (var i = 0; i < wrappedEntries.Count; ++i)
                     {
                         var entry = wrappedEntries[i];
+                        if (!entry.Method.Ignore)
+                        {
                             var name = GetVTableMethodDelegateName(entry.Method);
                             WriteLine($"Thunks[{i}] = Marshal.GetFunctionPointerForDelegate({name + "Instance"});");
                         }
+                    }
                     UnindentAndWriteCloseBrace();
                 }
                 NewLine();

src/Generator/Passes/GenerateAbstractImplementationsPass.cs

@@ -1,6 +1,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using CppSharp.AST;
+using CppSharp.AST.Extensions;
 
 namespace CppSharp.Passes
 {
@@ -72,6 +73,12 @@ namespace CppSharp.Passes
                     };
                 impl.OverriddenMethods.Clear();
                 impl.OverriddenMethods.Add(abstractMethod);
+                if (abstractMethod.OriginalReturnType.Type.IsDependentPointer() ||
+                    abstractMethod.Parameters.Any(p => p.Type.IsDependentPointer()))
+                {
+                    // this is an extension but marks the class as an abstract impl
+                    impl.ExplicitlyIgnore();
+                }
                 internalImpl.Methods.Add(impl);
             }
 

src/Generator/Passes/SpecializationMethodsWithDependentPointersPass.cs

@@ -118,6 +118,11 @@ namespace CppSharp.Passes
             extensionMethod.OriginalFunction = specializedMethod;
             extensionMethod.Kind = CXXMethodKind.Normal;
             extensionMethod.IsStatic = true;
+            if (extensionMethod.IsPure)
+            {
+                extensionMethod.IsPure = false;
+                extensionMethod.SynthKind = FunctionSynthKind.AbstractImplCall;
+            }
 
             var qualReturnType = extensionMethod.OriginalReturnType;
             RemoveTemplateSubstitution(ref qualReturnType);

tests/CSharp/CSharp.Tests.cs

@@ -1328,6 +1328,18 @@ public unsafe class CSharpTests
         }
     }
 
+    [Test]
+    public void TestAbstractImplTemplate()
+    {
+        using (var returnsPointer = new DependentValueFields<int>())
+        {
+            using (var value = returnsPointer.AbstractReturnPointer)
+            {
+                Assert.That(new IntPtr(value.AbstractReturnPointer()), Is.EqualTo(IntPtr.Zero));
+            }
+        }
+    }
+
     [Test]
     public void TestSpecializationForSecondaryBase()
     {

tests/CSharp/CSharpTemplates.h

@@ -36,6 +36,50 @@ class DLL_API Ignored
 {
 };
 
+template <typename T>
+class HasAbstractReturnPointer
+{
+public:
+    HasAbstractReturnPointer();
+    ~HasAbstractReturnPointer();
+    virtual const T* abstractReturnPointer() = 0;
+};
+
+template <typename T>
+HasAbstractReturnPointer<T>::HasAbstractReturnPointer()
+{
+}
+
+template <typename T>
+HasAbstractReturnPointer<T>::~HasAbstractReturnPointer()
+{
+}
+
+template <typename T>
+class ImplReturnPointer : public HasAbstractReturnPointer<T>
+{
+public:
+    ImplReturnPointer();
+    ~ImplReturnPointer();
+    virtual const T* abstractReturnPointer() override;
+};
+
+template <typename T>
+ImplReturnPointer<T>::ImplReturnPointer()
+{
+}
+
+template <typename T>
+ImplReturnPointer<T>::~ImplReturnPointer()
+{
+}
+
+template <typename T>
+const T* ImplReturnPointer<T>::abstractReturnPointer()
+{
+    return 0;
+}
+
 template <typename T>
 class IndependentFields : public T1
 {
@@ -176,6 +220,7 @@ public:
     const T* returnTakeDependentPointer(const T* p);
     const T* propertyReturnDependentPointer();
     void hasDefaultDependentParam(T* ptr, const T& refT = T());
+    HasAbstractReturnPointer<T>* getAbstractReturnPointer();
     typedef void (*DependentFunctionPointer)(T);
     DependentFunctionPointer dependentFunctionPointerField;
 private:
@@ -235,6 +280,12 @@ void DependentValueFields<T>::hasDefaultDependentParam(T* ptr, const T& refT)
 {
 }
 
+template <typename T>
+HasAbstractReturnPointer<T>* DependentValueFields<T>::getAbstractReturnPointer()
+{
+    return new ImplReturnPointer<T>();
+}
+
 template <typename T>
 DependentValueFields<T>& DependentValueFields<T>::returnInjectedClass()
 {