Fix #1251 three parameter equality operator

- Operators in generic classes do not attempt to generate as extension methods anymore
- Empty `...Extensions` classes are no longer generated
- `string` as a template argument is correctly cast
- `MarshalCharAsManagedChar` option also generates correct casts
- Suppress warning regarding returning struct field by ref
- Eliminate some tabs that snuck into the test C++ header

src/AST/TypeExtensions.cs

@@ -439,6 +439,22 @@
             return false;
         }
 
+        public static bool IsTemplate(this Type type)
+        {
+            if (type is TemplateParameterType or TemplateParameterSubstitutionType)
+                return true;
+
+            var ptr = type;
+            while (ptr is PointerType pType)
+            {
+                ptr = pType.Pointee;
+                if (ptr is TemplateParameterType or TemplateParameterSubstitutionType)
+                    return true;
+            }
+
+            return false;
+        }
+
         public static Module GetModule(this Type type)
         {
             Declaration declaration;

src/Generator/Generators/CSharp/CSharpMarshal.cs

@@ -601,7 +601,7 @@ namespace CppSharp.Generators.CSharp
                 if (Context.Context.Options.MarshalCharAsManagedChar &&
                     primitive == PrimitiveType.Char)
                 {
-                    Context.Return.Write($"({typePrinter.PrintNative(pointer)})");
+                    Context.Return.StringBuilder.Insert(0, $"({typePrinter.PrintNative(pointer)}) ");
                     if (isConst)
                         Context.Return.Write("&");
                     Context.Return.Write(param.Name);
@@ -643,8 +643,13 @@ namespace CppSharp.Generators.CSharp
                 }
                 else
                 {
-                    Context.Before.WriteLine("var {0} = {1}.{2};",
+                    Context.Before.Write($"var {arg} = ");
-                        arg, Context.Parameter.Name, Helpers.InstanceIdentifier);
+                    if (pointer.Pointee.IsTemplate())
+                        Context.Before.Write($"(({Context.Parameter.Type}) (object) {Context.Parameter.Name})");
+                    else
+                        Context.Before.WriteLine(Context.Parameter.Name);
+                    Context.Before.WriteLine($".{Helpers.InstanceIdentifier};");
+                    
                     Context.Return.Write($"new {typePrinter.IntPtrType}(&{arg})");
                 }
 
@@ -805,7 +810,12 @@ namespace CppSharp.Generators.CSharp
 
         private void MarshalValueClass()
         {
-            Context.Return.Write("{0}.{1}", Context.Parameter.Name, Helpers.InstanceIdentifier);
+            if (Context.Parameter.Type.IsTemplate())
+                Context.Return.Write($"(({Context.Parameter.Type}) (object) {Context.Parameter.Name})");
+            else
+                Context.Return.Write(Context.Parameter.Name);
+
+            Context.Return.Write($".{Helpers.InstanceIdentifier}");
         }
 
         public override bool VisitFieldDecl(Field field)

src/Generator/Generators/CSharp/CSharpSources.cs

@@ -85,6 +85,7 @@ namespace CppSharp.Generators.CSharp
             GenerateUsings();
 
             WriteLine("#pragma warning disable CS0109 // Member does not hide an inherited member; new keyword is not required");
+            WriteLine("#pragma warning disable CS9084 // Struct member returns 'this' or other instance members by reference");
             NewLine();
 
             if (!string.IsNullOrEmpty(Module.OutputNamespace))

src/Generator/Passes/SpecializationMethodsWithDependentPointersPass.cs

@@ -52,6 +52,7 @@ namespace CppSharp.Passes
             if (!methodsWithDependentPointers.Any())
                 return false;
 
+            var hasMethods = false;
             var classExtensions = new Class { Name = $"{@class.Name}Extensions", IsStatic = true };
             foreach (var specialization in @class.Specializations.Where(s => s.IsGenerated))
                 foreach (var method in methodsWithDependentPointers.Where(
@@ -59,9 +60,11 @@ namespace CppSharp.Passes
                 {
                     var specializedMethod = specialization.Methods.FirstOrDefault(
                         m => m.InstantiatedFrom == method);
-                    if (specializedMethod == null)
+                    if (specializedMethod == null || specializedMethod.IsOperator)
                         continue;
 
+                    hasMethods = true;
+
                     Method extensionMethod = GetExtensionMethodForDependentPointer(specializedMethod);
                     classExtensions.Methods.Add(extensionMethod);
                     extensionMethod.Namespace = classExtensions;
@@ -75,6 +78,10 @@ namespace CppSharp.Passes
                         extensionMethod.GenerationKind = GenerationKind.Generate;
                     }
                 }
+
+            if (!hasMethods)
+                return false;
+
             classExtensions.Namespace = @class.Namespace;
             classExtensions.OriginalClass = @class;
             extensions.Add(classExtensions);

src/Generator/Types/Std/Stdlib.CSharp.cs

@@ -329,7 +329,10 @@ namespace CppSharp.Types.Std
                 ctx.Return.Write($@"{qualifiedBasicString}Extensions.{
                     Helpers.InternalStruct}.{assign.Name}(new {
                     typePrinter.IntPtrType}(&{
-                    ctx.ReturnVarName}), {ctx.Parameter.Name})");
+                    ctx.ReturnVarName}), ");
+                if (ctx.Parameter.Type.IsTemplate())
+                    ctx.Return.Write("(string) (object) ");
+                ctx.Return.Write($"{ctx.Parameter.Name})");
                 ctx.ReturnVarName = string.Empty;
             }
             else
@@ -337,8 +340,13 @@ namespace CppSharp.Types.Std
                 var varBasicString = $"__basicString{ctx.ParameterIndex}";
                 ctx.Before.WriteLine($@"var {varBasicString} = new {
                     basicString.Visit(typePrinter)}();");
-                ctx.Before.WriteLine($@"{qualifiedBasicString}Extensions.{
+
-                    assign.Name}({varBasicString}, {ctx.Parameter.Name});");
+                ctx.Before.Write($@"{qualifiedBasicString}Extensions.{
+                    assign.Name}({varBasicString}, ");
+                if (ctx.Parameter.Type.IsTemplate())
+                    ctx.Before.Write("(string) (object) ");
+                ctx.Before.WriteLine($"{ctx.Parameter.Name});");
+
                 ctx.Return.Write($"{varBasicString}.{Helpers.InstanceIdentifier}");
                 ctx.Cleanup.WriteLine($@"{varBasicString}.Dispose({
                     (!Type.IsAddress() || ctx.Parameter?.IsIndirect == true ? "disposing: true, callNativeDtor:false" : string.Empty)});");

tests/dotnet/CSharp/CSharp.Tests.cs

@@ -2003,4 +2003,25 @@ public unsafe class CSharpTests
         Assert.AreEqual(2, unionTestA.A);
         Assert.AreEqual(2, unionTestB.B);
     }
+
+    [TestCase("hi")]
+    [TestCase(2u)]
+    public void TestOptional<T>(T value)
+    {
+        Assert.That(new CSharp.Optional<T>() != new CSharp.Optional<T>(value));
+        Assert.That(new CSharp.Optional<T>() != value);
+        Assert.That(new CSharp.Optional<T>() == new CSharp.Optional<T>());
+        Assert.That(new CSharp.Optional<T>(value) == new CSharp.Optional<T>(value));
+        Assert.That(new CSharp.Optional<T>(value) == value);
+    }
+
+    [Test]
+    public void TestOptionalIntPtr()
+    {
+        Assert.That(new CSharp.Optional<IntPtr>() != new CSharp.Optional<IntPtr>(IntPtr.MaxValue));
+        Assert.That(new CSharp.Optional<IntPtr>() != IntPtr.MaxValue);
+        Assert.That(new CSharp.Optional<IntPtr>() == new CSharp.Optional<IntPtr>());
+        Assert.That(new CSharp.Optional<IntPtr>(IntPtr.MaxValue) == new CSharp.Optional<IntPtr>(IntPtr.MaxValue));
+        Assert.That(new CSharp.Optional<IntPtr>(IntPtr.MaxValue) == IntPtr.MaxValue);
+    }
 }

tests/dotnet/CSharp/CSharp.h

@@ -1607,6 +1607,37 @@ DLL_API extern PointerTester* PointerToClass;
 union DLL_API UnionTester {
     float a;
     int b;
+    inline bool operator ==(const UnionTester& other) const {
+        return b == other.b;
+    }
 };
 
 int DLL_API ValueTypeOutParameter(CS_OUT UnionTester* testerA, CS_OUT UnionTester* testerB);
+
+template <class T>
+class Optional {
+public:
+    T m_value;
+    bool m_hasValue;
+
+    Optional() {
+        m_hasValue = false;
+    }
+
+    Optional(T value) {
+        m_value = std::move(value);
+        m_hasValue = true;
+    }
+
+    inline bool operator ==(const Optional<T>& rhs) const {
+        return (m_hasValue == rhs.m_hasValue && (!m_hasValue || m_value == rhs.m_value));
+    }
+
+    inline bool operator ==(const T& rhs) const {
+        return (m_hasValue && m_value == rhs);
+    }
+};
+
+// We just need a method that uses various instantiations of Optional.
+inline void DLL_API InstantiateOptionalTemplate(Optional<unsigned int>, Optional<std::string>,
+    Optional<TestComparison>, Optional<char*>, Optional<UnionTester>) { }