Fix the regressed C# marshalling of char*

Fixes https://github.com/mono/CppSharp/issues/1258.

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

src/Generator/Generators/CSharp/CSharpMarshal.cs

@@ -566,10 +566,16 @@ namespace CppSharp.Generators.CSharp
                     return true;
                 }
 
+                bool isConst = quals.IsConst || pointer.QualifiedPointee.Qualifiers.IsConst ||
+                     pointer.GetFinalQualifiedPointee().Qualifiers.IsConst;
+
                 if (Context.Context.Options.MarshalCharAsManagedChar &&
                     primitive == PrimitiveType.Char)
                 {
-                    Context.Return.Write($"({typePrinter.PrintNative(pointer)}) &{param.Name}");
+                    Context.Return.Write($"({typePrinter.PrintNative(pointer)})");
+                    if (isConst)
+                        Context.Return.Write("&");
+                    Context.Return.Write(param.Name);
                     return true;
                 }
 
@@ -577,13 +583,8 @@ namespace CppSharp.Generators.CSharp
 
                 if (Context.Parameter.IsIndirect)
                     Context.ArgumentPrefix.Write("&");
-
-                bool isVoid = primitive == PrimitiveType.Void &&
-                    pointee.IsAddress() && pointer.IsReference() &&
-                    (quals.IsConst || pointer.QualifiedPointee.Qualifiers.IsConst ||
-                     pointer.GetFinalQualifiedPointee().Qualifiers.IsConst);
-                if (pointer.Pointee.Desugar(false) is TemplateParameterSubstitutionType ||
-                    isVoid)
+                bool isVoid = primitive == PrimitiveType.Void && pointer.IsReference() && isConst;
+                if (pointer.Pointee.Desugar(false) is TemplateParameterSubstitutionType || isVoid)
                 {
                     var local = Generator.GeneratedIdentifier($@"{
                         param.Name}{Context.ParameterIndex}");

tests/CSharp/CSharp.Tests.cs

@@ -110,6 +110,13 @@ public unsafe class CSharpTests : GeneratorTestFixture
         Assert.That(*CSharp.CSharp.TakeConstCharRef(z), Is.EqualTo(z));
     }
 
+    [Test]
+    public void TestTakeCharPointer()
+    {
+        char c = 'c';
+        Assert.That(*CSharp.CSharp.TakeCharPointer(&c), Is.EqualTo(c));
+    }
+
     [Test]
     public void TestIndexer()
     {

tests/CSharp/CSharp.cpp

@@ -1645,6 +1645,11 @@ char* returnCharPointer()
     return 0;
 }
 
+char* takeCharPointer(char* c)
+{
+    return c;
+}
+
 char* takeConstCharRef(const char& c)
 {
     return const_cast<char*>(&c);

tests/CSharp/CSharp.h

@@ -1362,6 +1362,7 @@ public:
 
 DLL_API void va_listFunction(va_list v);
 DLL_API char* returnCharPointer();
+DLL_API char* takeCharPointer(char* c);
 DLL_API char* takeConstCharRef(const char& c);
 DLL_API const char*& takeConstCharStarRef(const char*& c);
 DLL_API const void*& rValueReferenceToPointer(void*&& v);