Implement radd for MutableList

Summary: Add `__radd__` to handle cases like `[] + mutable_list`

Reviewed By: aristidisp

Differential Revision: D66812697

fbshipit-source-id: 5e8cef61913009df530dd7d459c53fa94c0029ed

third-party/thrift/src/thrift/lib/python/mutable_containers.pyi

@@ -147,6 +147,7 @@ class MutableList(MutableSequence[T]):
         self: MutableList[MutableMap[Any, Any]],
         other: Iterable[T | _ThriftMapWrapper],
     ) -> MutableList[T]: ...
+    def __radd__(self, other: Iterable[T]) -> MutableList[T]: ...
     def count(self, value: object) -> int: ...
     def index(
         self,

third-party/thrift/src/thrift/lib/python/mutable_containers.pyx

@@ -140,6 +140,12 @@ cdef class MutableList:
         lst.extend(other)
         return lst
 
+    def __radd__(self, other):
+        lst = MutableList(self._val_typeinfo, [])
+        lst.extend(other)
+        lst._list_data.extend(self._list_data)
+        return lst
+
     def __deepcopy__(self, memo):
         return MutableList(self._val_typeinfo, copy.deepcopy(self._list_data, memo))
 

third-party/thrift/src/thrift/lib/python/test/mutable_list_test.py

@@ -278,6 +278,27 @@ def test_add(self) -> None:
         self.assertIsInstance(result, MutableList)
         self.assertIsNot(result, mutable_list)
 
+    def test_radd(self) -> None:
+        mutable_list = _create_MutableList_i32([])
+
+        result_1 = [] + mutable_list
+        self.assertIsInstance(result_1, MutableList)
+        self.assertEqual([], result_1)
+
+        mutable_list.extend(range(100, 200))
+        self.assertEqual([], result_1)
+
+        result_2 = list(range(100)) + mutable_list
+        self.assertIsInstance(result_2, MutableList)
+        self.assertEqual(list(range(200)), result_2)
+
+        # Left hand side with wrong type raises `TypeError`
+        with self.assertRaisesRegex(
+            TypeError, "is not a <class 'int'>, is actually of type <class 'str'>"
+        ):
+            # pyre-ignore[58]: Intentional for test
+            _ = ["1", "2"] + mutable_list
+
     def test_count(self) -> None:
         mutable_list = _create_MutableList_i32([1, 2, 1, 1, 3, 2])