Generate valid C# with explicit external specializations

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

src/Generator/Generators/CSharp/CSharpTypePrinter.cs

@@ -537,11 +537,11 @@ namespace CppSharp.Generators.CSharp
             var names = new Stack<string>();
 
             Declaration ctx;
-            var specialization = decl as ClassTemplateSpecialization;
+            if (decl is ClassTemplateSpecialization specialization)
-            if (specialization != null && ContextKind == TypePrinterContextKind.Native)
             {
                 ctx = specialization.TemplatedDecl.TemplatedClass.Namespace;
-                if (specialization.OriginalNamespace is Class &&
+                if (ContextKind == TypePrinterContextKind.Native &&
+                    specialization.OriginalNamespace is Class &&
                     !(specialization.OriginalNamespace is ClassTemplateSpecialization))
                 {
                     names.Push(string.Format("{0}_{1}", decl.OriginalNamespace.Name, decl.Name));

tests/NamespacesBase/NamespacesBase.h

@@ -76,7 +76,7 @@ void TemplateClass<T>::setField(const T& value)
 }
 
 template <typename T>
-class DLL_API TemplateWithIndependentFields
+class TemplateWithIndependentFields
 {
 public:
     void useDependentPointer(const T* t);

tests/NamespacesDerived/NamespacesDerived.Tests.cs

@@ -13,6 +13,8 @@ public class NamespaceDerivedTests
     public void TestCodeGeneration()
     {
         using (new DerivedFromSecondaryBaseInDependency()) { }
+        using (var der2 = new Derived2())
+        using (der2.ExplicitExternalSpecialization) { }
     }
 
     [Test]

tests/NamespacesDerived/NamespacesDerived.cpp

@@ -70,6 +70,11 @@ TemplateClass<int> Derived2::getTemplate()
     return t;
 }
 
+TemplateWithIndependentFields<int> Derived2::getExplicitExternalSpecialization()
+{
+    return TemplateWithIndependentFields<int>();
+}
+
 Abstract* Derived2::getAbstract()
 {
     return 0;

tests/NamespacesDerived/NamespacesDerived.h

@@ -45,6 +45,11 @@ class Base3
 
 template <typename T> class TemplateClass;
 
+template<>
+class DLL_API TemplateWithIndependentFields<int>
+{
+};
+
 class DLL_API Derived2 : public Base3
 {
 public:
@@ -60,6 +65,7 @@ public:
     void defaultEnumValueFromDependency(OverlappingNamespace::ColorsEnum c = OverlappingNamespace::ColorsEnum::black);
 
     TemplateClass<int> getTemplate();
+    TemplateWithIndependentFields<int> getExplicitExternalSpecialization();
     Abstract* getAbstract();
 private:
     TemplateClass<int> t;