Switched the C# generator from manual conversion between strings and pointers to the built-in string marshallers.

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

src/Generator/Generators/CSharp/CSharpMarshal.cs

@@ -13,7 +13,8 @@ namespace CppSharp.Generators.CSharp
         Unknown,
         NativeField,
         GenericDelegate,
-        DefaultExpression
+        DefaultExpression,
+        VTableReturnValue
     }
 
     public class CSharpMarshalContext : MarshalContext
@@ -160,7 +161,8 @@ namespace CppSharp.Generators.CSharp
             var pointee = pointer.Pointee.Desugar();
             bool marshalPointeeAsString = CSharpTypePrinter.IsConstCharString(pointee) && isRefParam;
 
-            if (CSharpTypePrinter.IsConstCharString(pointer) || marshalPointeeAsString)
+            if ((CSharpTypePrinter.IsConstCharString(pointer) && !MarshalsParameter) ||
+                marshalPointeeAsString)
             {
                 Context.Return.Write(MarshalStringToManaged(Context.ReturnVarName,
                     pointer.GetFinalPointee().Desugar() as BuiltinType));
@@ -505,9 +507,7 @@ namespace CppSharp.Generators.CSharp
             var isRefParam = param != null && (param.IsInOut || param.IsOut);
 
             var pointee = pointer.Pointee.Desugar();
-            bool marshalPointeeAsString = CSharpTypePrinter.IsConstCharString(pointee) && isRefParam;
+            if (CSharpTypePrinter.IsConstCharString(pointee) && isRefParam)
-
-            if (CSharpTypePrinter.IsConstCharString(pointer) || marshalPointeeAsString)
             {
                 if (param.IsOut)
                 {
@@ -555,9 +555,11 @@ namespace CppSharp.Generators.CSharp
                 return true;
             }
 
+            var marshalAsString = CSharpTypePrinter.IsConstCharString(pointer);
             var finalPointee = pointer.GetFinalPointee();
             PrimitiveType primitive;
-            if (finalPointee.IsPrimitiveType(out primitive) || finalPointee.IsEnumType())
+            if (finalPointee.IsPrimitiveType(out primitive) || finalPointee.IsEnumType() ||
+                marshalAsString)
             {
                 // From MSDN: "note that a ref or out parameter is classified as a moveable
                 // variable". This means we must create a local variable to hold the result
@@ -576,13 +578,19 @@ namespace CppSharp.Generators.CSharp
                 }
                 else
                 {
-                    if (Context.Driver.Options.MarshalCharAsManagedChar && primitive == PrimitiveType.Char)
+                    if (!marshalAsString &&
+                        Context.Driver.Options.MarshalCharAsManagedChar &&
+                        primitive == PrimitiveType.Char)
                     {
-                        var typePrinter = new CSharpTypePrinter(Context.Driver);
                         typePrinter.PushContext(CSharpTypePrinterContextKind.Native);
                         Context.Return.Write(string.Format("({0}) ", pointer.Visit(typePrinter)));
+                        typePrinter.PopContext();
                     }
-                    Context.Return.Write(Context.Parameter.Name);
+                    if (marshalAsString && (Context.Kind == CSharpMarshalKind.NativeField ||
+                        Context.Kind == CSharpMarshalKind.VTableReturnValue))
+                        Context.Return.Write(MarshalStringToUnmanaged(Context.Parameter.Name));
+                    else
+                        Context.Return.Write(Context.Parameter.Name);
                 }
 
                 return true;

src/Generator/Generators/CSharp/CSharpSources.cs

@@ -670,8 +670,7 @@ namespace CppSharp.Generators.CSharp
         {
             TypePrinter.PushContext(CSharpTypePrinterContextKind.Native);
 
-            var retParam = new Parameter { QualifiedType = function.ReturnType };
+            retType = function.ReturnType.CSharpType(TypePrinter);
-            retType = retParam.CSharpType(TypePrinter);
 
             var @params = function.GatherInternalParams(Driver.Options.IsItaniumLikeAbi).Select(p =>
                 string.Format("{0} {1}", p.CSharpType(TypePrinter), p.Name)).ToList();
@@ -962,7 +961,8 @@ namespace CppSharp.Generators.CSharp
                 if (marshal.Context.Return.StringBuilder.Length > 0)
                 {
                     WriteLine("{0} = {1}{2};", ctx.ReturnVarName,
-                        field.Type.IsPointer() && field.Type.GetFinalPointee().IsPrimitiveType() ?
+                        field.Type.IsPointer() && field.Type.GetFinalPointee().IsPrimitiveType() &&
+                        !CSharpTypePrinter.IsConstCharString(field.Type) ?
                             string.Format("({0}) ", CSharpTypePrinter.IntPtrType) :
                             string.Empty,
                         marshal.Context.Return);
@@ -1659,7 +1659,8 @@ namespace CppSharp.Generators.CSharp
                 {
                     ArgName = Helpers.ReturnIdentifier,
                     Parameter = param,
-                    Function = method
+                    Function = method,
+                    Kind = CSharpMarshalKind.VTableReturnValue
                 };
 
                 var marshal = new CSharpMarshalManagedToNativePrinter(ctx);

src/Generator/Generators/CSharp/CSharpTypePrinter.cs

@@ -6,6 +6,7 @@ using CppSharp.Types;
 using Type = CppSharp.AST.Type;
 using ParserTargetInfo = CppSharp.Parser.ParserTargetInfo;
 using System.Linq;
+using System.Text;
 
 namespace CppSharp.Generators.CSharp
 {
@@ -265,7 +266,19 @@ namespace CppSharp.Generators.CSharp
             var isManagedContext = ContextKind == CSharpTypePrinterContextKind.Managed;
 
             if (allowStrings && IsConstCharString(pointer))
-                return isManagedContext ? "string" : IntPtrType;
+            {
+                if (isManagedContext || MarshalKind == CSharpMarshalKind.GenericDelegate)
+                    return "string";
+                if (Context.Parameter == null || Context.Parameter.Name == Helpers.ReturnIdentifier)
+                    return IntPtrType;
+                if (driver.Options.Encoding == Encoding.ASCII)
+                    return string.Format("[MarshalAs(UnmanagedType.LPStr)] string");
+                if (driver.Options.Encoding == Encoding.Unicode ||
+                    driver.Options.Encoding == Encoding.BigEndianUnicode)
+                    return string.Format("[MarshalAs(UnmanagedType.LPWStr)] string");
+                throw new NotSupportedException(string.Format("{0} is not supported yet.",
+                    driver.Options.Encoding.EncodingName));
+            }
 
             var desugared = pointee.Desugar();
 
@@ -288,6 +301,9 @@ namespace CppSharp.Generators.CSharp
                 if (pointee.IsPrimitiveType(PrimitiveType.Void))
                     return IntPtrType;
 
+                if (IsConstCharString(pointee) && isRefParam)
+                    return IntPtrType + "*";
+
                 // Do not allow strings inside primitive arrays case, else we'll get invalid types
                 // like string* for const char **.
                 allowStrings = isRefParam;
@@ -300,9 +316,6 @@ namespace CppSharp.Generators.CSharp
             Enumeration @enum;
             if (desugared.TryGetEnum(out @enum))
             {
-                if (MarshalKind == CSharpMarshalKind.GenericDelegate && isManagedContext)
-                    return IntPtrType;
-
                 // Skip one indirection if passed by reference
                 var param = Context.Parameter;
                 if (isManagedContext && param != null && (param.IsOut || param.IsInOut)

tests/CSharp/CSharp.Tests.cs

@@ -555,6 +555,29 @@ public unsafe class CSharpTests : GeneratorTestFixture
         }
     }
 
+    [Test]
+    public void TestOverrideVirtualWithString()
+    {
+        using (var overrideVirtualWithString = new OverrideVirtualWithString())
+        {
+            Assert.That(overrideVirtualWithString.CallsVirtualToReturnString("test"), Is.EqualTo("test_test"));
+            Assert.IsFalse(overrideVirtualWithString.CallsVirtualToReturnBool(true));
+        }
+    }
+
+    private class OverrideVirtualWithString : HasVirtualTakesReturnsProblematicTypes
+    {
+        public override string VirtualTakesAndReturnsString(string c)
+        {
+            return "test_test";
+        }
+
+        public override bool VirtualTakesAndReturnsBool(bool b)
+        {
+            return !base.VirtualTakesAndReturnsBool(b);
+        }
+    }
+
     private class GetEnumFromNativePointer : UsesPointerToEnumInParamOfVirtual
     {
         public override Flags HasPointerToEnumInParam(Flags pointerToEnum)

tests/CSharp/CSharp.cpp

@@ -1036,3 +1036,31 @@ bool VirtualDtorAddedInDerived::dtorCalled = false;
 void NamespaceB::B::Function(CS_OUT NamespaceA::A &a)
 {
 }
+
+HasVirtualTakesReturnsProblematicTypes::HasVirtualTakesReturnsProblematicTypes()
+{
+}
+
+HasVirtualTakesReturnsProblematicTypes::~HasVirtualTakesReturnsProblematicTypes()
+{
+}
+
+const char* HasVirtualTakesReturnsProblematicTypes::virtualTakesAndReturnsString(const char* c)
+{
+    return c;
+}
+
+const char* HasVirtualTakesReturnsProblematicTypes::callsVirtualToReturnString(const char* c)
+{
+    return virtualTakesAndReturnsString(c);
+}
+
+bool HasVirtualTakesReturnsProblematicTypes::virtualTakesAndReturnsBool(bool b)
+{
+    return b;
+}
+
+bool HasVirtualTakesReturnsProblematicTypes::callsVirtualToReturnBool(bool b)
+{
+    return virtualTakesAndReturnsBool(b);
+}

tests/CSharp/CSharp.h

@@ -969,3 +969,14 @@ private:
 };
 
 class ForwardInOtherUnitButSameModule;
+
+class DLL_API HasVirtualTakesReturnsProblematicTypes
+{
+public:
+    HasVirtualTakesReturnsProblematicTypes();
+    ~HasVirtualTakesReturnsProblematicTypes();
+    virtual const char* virtualTakesAndReturnsString(const char* c);
+    const char* callsVirtualToReturnString(const char* c);
+    virtual bool virtualTakesAndReturnsBool(bool b);
+    bool callsVirtualToReturnBool(bool b);
+};