Desugar a type to test whether or not it is a tag declaration.

src/AST/TypeExtensions.cs

@@ -114,7 +114,7 @@
 
         public static bool IsTagDecl<T>(this Type t, out T decl) where T : Declaration
         {
-            var tag = t as TagType;
+            var tag = t.Desugar() as TagType;
             
             if (tag == null)
             {

tests/Basic/Basic.h

@@ -302,3 +302,13 @@ struct EmptyNamedNestedEnum
 {
     enum { Value = 10 };
 };
+
+
+typedef struct SomeStruct
+{
+}
+SomeStruct;
+
+class SomeClassExtendingTheStruct : public SomeStruct
+{
+};