Fix C# layouts for classes with nameless unions

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

src/AST/Class.cs

@@ -181,6 +181,8 @@ namespace CppSharp.AST
 
         public bool IsInterface => Type == ClassType.Interface;
 
+        public bool HasUnionFields { get; set; }
+
         public bool IsAbstractImpl
         {
             get { return Methods.Any(m => m.SynthKind == FunctionSynthKind.AbstractImplCall); }

src/Generator/Generators/CSharp/CSharpSources.cs

@@ -792,7 +792,7 @@ namespace CppSharp.Generators.CSharp
 
         private bool CanUseSequentialLayout(Class @class)
         {
-            if (@class.IsUnion)
+            if (@class.IsUnion || @class.HasUnionFields)
                 return false;
 
             foreach (var field in @class.Fields)

src/Generator/Passes/FlattenAnonymousTypesToFields.cs

@@ -31,6 +31,8 @@ namespace CppSharp.Passes
                 ReplaceField(@class, i, fieldType);
                 fieldType.Fields.Clear();
                 fieldType.ExplicitlyIgnore();
+                if (fieldType.IsUnion)
+                    @class.HasUnionFields = true;
             }
 
             if (@class.Layout == null)

tests/Common/Common.Tests.cs

@@ -389,6 +389,11 @@ public class CommonTests
         nestedPublic.J = 5;
         Assert.That(nestedPublic.L, Is.EqualTo(5));
         Assert.That(nestedPublic.G, Is.Not.EqualTo(0));
+        using (var nestedUnionWithNested = new NestedUnionWithNested())
+        {
+            nestedUnionWithNested.NestedField1 = 50;
+            Assert.That(nestedUnionWithNested.UnionField, Is.EqualTo(50));
+        }
     }
 
     [Test]

tests/Common/Common.h

@@ -1333,6 +1333,19 @@ public:
     static ReturnByValueWithReturnParam generate();
 };
 
+struct DLL_API NestedUnionWithNested
+{
+    union
+    {
+        struct
+        {
+            int nestedField1;
+            int nestedField2;
+        };
+        int unionField;
+    };
+};
+
 template<typename T> void TemplatedFunction(T type)
 {