Properly handled nulls passed to C++ refs by throwing an exception.

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

src/Generator/Generators/CLI/CLIMarshal.cs

@@ -679,14 +679,28 @@ namespace CppSharp.Generators.CLI
 
         private void MarshalRefClass(Class @class)
         {
-            TypeMap typeMap = null;
+            TypeMap typeMap;
             if (Context.Driver.TypeDatabase.FindTypeMap(@class, out typeMap) && typeMap.DoesMarshalling)
             {
                 typeMap.CLIMarshalToNative(Context);
                 return;
             }
 
-            if (!Context.Parameter.Type.Desugar().SkipPointerRefs().IsPointer())
+            var type = Context.Parameter.Type.Desugar();
+            var method = Context.Function as Method;
+            if (type.IsReference() && (method == null ||
+                // redundant for comparison operators, they are handled in a special way
+                (method.OperatorKind != CXXOperatorKind.EqualEqual &&
+                method.OperatorKind != CXXOperatorKind.ExclaimEqual)))
+            {
+                Context.SupportBefore.WriteLine("if (ReferenceEquals({0}, nullptr))", Context.Parameter.Name);
+                Context.SupportBefore.WriteLineIndent(
+                    "throw gcnew ::System::ArgumentNullException(\"{0}\", " +
+                    "\"{0} cannot be null because it is a C++ reference (&).\");",
+                    Context.Parameter.Name);
+            }
+
+            if (!type.SkipPointerRefs().IsPointer())
             {
                 Context.Return.Write("*");
 
@@ -694,7 +708,6 @@ namespace CppSharp.Generators.CLI
                     VarPrefix.Write("&");
             }
 
-            var method = Context.Function as Method;
             if (method != null
                 && method.Conversion == MethodConversionKind.FunctionToInstanceMethod
                 && Context.ParameterIndex == 0)

src/Generator/Generators/CSharp/CSharpMarshal.cs

@@ -654,12 +654,31 @@ namespace CppSharp.Generators.CSharp
                 if (type.TryGetClass(out decl) && decl.IsValueType)
                     Context.Return.Write("{0}.{1}", param, Helpers.InstanceIdentifier);
                 else
+                {
+                    if (type.IsPointer())
+                    {
                         Context.Return.Write("{0}{1}.{2}",
                             method != null && method.OperatorKind == CXXOperatorKind.EqualEqual
                                 ? string.Empty
                                 : string.Format("ReferenceEquals({0}, null) ? global::System.IntPtr.Zero : ", param),
-                        param,
-                        Helpers.InstanceIdentifier, type);
+                            param, Helpers.InstanceIdentifier, type);
+                    }
+                    else
+                    {
+                        if (method == null ||
+                            // redundant for comparison operators, they are handled in a special way
+                            (method.OperatorKind != CXXOperatorKind.EqualEqual &&
+                            method.OperatorKind != CXXOperatorKind.ExclaimEqual))
+                        {
+                            Context.SupportBefore.WriteLine("if (ReferenceEquals({0}, null))", param);
+                            Context.SupportBefore.WriteLineIndent(
+                                "throw new global::System.ArgumentNullException(\"{0}\", " +
+                                "\"{0} cannot be null because it is a C++ reference (&).\");",
+                                param);
+                        }
+                        Context.Return.Write("{0}.{1}", param, Helpers.InstanceIdentifier);
+                    }
+                }
                 return;
             }
 

tests/CSharp/CSharp.Tests.cs

@@ -103,18 +103,25 @@ public class CSharpTests : GeneratorTestFixture
         Assert.That(proprietor.Value, Is.EqualTo(20));
         proprietor.Prop = 50;
         Assert.That(proprietor.Prop, Is.EqualTo(50));
-        var p = new P((IQux) null) { Value = 20 };
+        using (var qux = new Qux())
+        {
+            using (var p = new P((IQux) qux) { Value = 20 })
+            {
                 Assert.That(p.Value, Is.EqualTo(30));
                 p.Prop = 50;
                 Assert.That(p.Prop, Is.EqualTo(150));
 
-        ComplexType complexType = new ComplexType();
+                using (var complexType = new ComplexType())
+                {
                     p.ComplexType = complexType;
                     Assert.That(p.ComplexType.Check(), Is.EqualTo(5));
+                }
 
                 Assert.That(p.Test, Is.True);
                 Assert.That(p.IsBool, Is.False);
             }
+        }
+    }
 
     [Test]
     public void TestAttributes()

tests/Common/Common.Tests.cs

@@ -590,6 +590,15 @@ public class CommonTests : GeneratorTestFixture
         Assert.That(Foo.charArray, Is.EqualTo("abc"));
     }
 
+    [Test]
+    public void TestPassingNullToRef()
+    {
+        using (var foo = new Foo())
+        {
+            Assert.Catch<ArgumentNullException>(() => foo.TakesRef(null));
+        }
+    }
+
     private class CustomDerivedFromVirtual : AbstractWithVirtualDtor
     {
         public override void @abstract()

tests/Common/Common.cpp

@@ -23,6 +23,11 @@ void Foo::TakesTypedefedPtr(FooPtr date)
 {
 }
 
+int Foo::TakesRef(const Foo &other)
+{
+    return other.A;
+}
+
 bool Foo::operator ==(const Foo& other) const
 {
     return A == other.A && B == other.B;

tests/Common/Common.h

@@ -59,6 +59,7 @@ public:
     typedef Foo* FooPtr;
 
     void TakesTypedefedPtr(FooPtr date);
+    int TakesRef(const Foo& other);
 
     bool operator ==(const Foo& other) const;
 };