DYN-8088: DSCore.List.Flatten does not work in PythonNet3

DSPythonNet3/Encoders/ListEncodeDecoder.cs

@@ -28,18 +28,39 @@ public bool TryDecode<T>(PyObject pyObj, out T value)
                 return false;
             }
 
-            using (var pyList = PyList.AsList(pyObj))
+            if (typeof(T).IsGenericType)
             {
-                if (typeof(T).IsGenericType)
+                var genericDef = typeof(T).GetGenericTypeDefinition();
+                var elementType = typeof(T).GetGenericArguments().FirstOrDefault();
+
+                if (elementType != null && (genericDef == typeof(IEnumerable<>) || genericDef == typeof(List<>) || genericDef == typeof(IList<>)))
                 {
-                    value = pyList.ToList<T>();
+                    using var pyList = PyList.AsList(pyObj);
+                    var listType = typeof(List<>).MakeGenericType(elementType);
+                    var typedList = (IList)Activator.CreateInstance(listType)!;
+
+                    foreach (PyObject item in pyList)
+                    {
+                        using (item)
+                        {
+                            typedList.Add(ConvertGenericItem(item, elementType));
+                        }
+                    }
+
+                    value = (T)typedList;
+                    return true;
                 }
-                else
+
+                using (var pyList = PyList.AsList(pyObj))
                 {
-                    value = (T)pyList.ToList();
+                    value = pyList.ToList<T>();
                 }
                 return true;
             }
+
+            var converted = ConvertToArrayList(pyObj);
+            value = (T)converted;
+            return true;
         }
 
         public PyObject TryEncode(object value)
@@ -57,5 +78,105 @@ bool IPyObjectDecoder.CanDecode(PyType objectType, Type targetType)
             }
             return decodableTypes.IndexOf(targetType) >= 0;
         }
+
+        private static IList ConvertToArrayList(PyObject pyObj)
+        {
+            using var pyList = PyList.AsList(pyObj);
+            var result = new ArrayList();
+            foreach (PyObject item in pyList)
+            {
+                using (item)
+                {
+                    result.Add(ConvertItem(item));
+                }
+            }
+            return result;
+        }
+
+        private static object ConvertItem(PyObject item)
+        {
+            if (TryGetClrObject(item, out var clrObject))
+            {
+                return clrObject;
+            }
+
+            if (PyInt.IsIntType(item))
+            {
+                using var pyLong = PyInt.AsInt(item);
+                try { return pyLong.ToInt64(); }
+                catch (PythonException ex) when (ex.Message.StartsWith("int too big"))
+                {
+                    return pyLong.ToBigInteger();
+                }
+            }
+
+            if (PyFloat.IsFloatType(item))
+            {
+                using var pyFloat = PyFloat.AsFloat(item);
+                return pyFloat.ToDouble();
+            }
+
+            if (PyString.IsStringType(item))
+            {
+                return item.AsManagedObject(typeof(string));
+            }
+
+            if (PyList.IsListType(item) || PyTuple.IsTupleType(item))
+            {
+                return ConvertToArrayList(item);
+            }
+
+            return item.AsManagedObject(typeof(object));
+        }
+
+        private static bool TryGetClrObject(PyObject pyObj, out object clrObject)
+        {
+            try
+            {
+                clrObject = pyObj.GetManagedObject();
+                if (clrObject is PyObject || clrObject is null)
+                {
+                    clrObject = null;
+                    return false;
+                }
+                return true;
+            }
+            catch
+            {
+                clrObject = null;
+                return false;
+            }
+        }
+
+        private static object ConvertGenericItem(PyObject item, Type elementType)
+        {
+            if (elementType == typeof(object))
+            {
+                return ConvertItem(item);
+            }
+
+            if (TryGetClrObject(item, out var clrObject) && elementType.IsInstanceOfType(clrObject))
+            {
+                return clrObject;
+            }
+
+            if (PyList.IsListType(item) || PyTuple.IsTupleType(item))
+            {
+                // recursively decode nested generics
+                var listType = typeof(List<>).MakeGenericType(elementType);
+                var nestedList = (IList)Activator.CreateInstance(listType)!;
+                using var pyList = PyList.AsList(item);
+                foreach (PyObject child in pyList)
+                {
+                    using (child)
+                    {
+                        nestedList.Add(ConvertGenericItem(child, elementType));
+                    }
+                }
+                return nestedList;
+            }
+
+            return item.AsManagedObject(elementType);
+        }
     }
 }

pipeline.yml

@@ -1,4 +1,4 @@
-version: 1.4.5
+version: 1.4.6
 pipeline_os: windows
 create_pr_release_to_master: true