Add _fields attribute to ast

Lib/test/test_ast.py

@@ -275,8 +275,6 @@ class AST_Tests(unittest.TestCase):
                 self._assertTrueorder(value, parent_pos)
         self.assertEqual(ast_node._fields, ast_node.__match_args__)
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_AST_objects(self):
         x = ast.AST()
         self.assertEqual(x._fields, ())

vm/src/stdlib/ast.rs

@@ -24,8 +24,9 @@ use rustpython_parser::parser;
 #[pymodule]
 mod _ast {
     use crate::{
-        builtins::PyStrRef, function::FuncArgs, AsObject, PyObjectRef, PyPayload, PyResult,
-        VirtualMachine,
+        builtins::{PyStrRef, PyTupleRef},
+        function::FuncArgs,
+        AsObject, Context, PyObjectRef, PyPayload, PyResult, VirtualMachine,
     };
     #[pyattr]
     #[pyclass(module = "_ast", name = "AST")]
@@ -65,6 +66,11 @@ mod _ast {
             }
             Ok(())
         }
+
+        #[pyattr(name = "_fields")]
+        fn fields(ctx: &Context) -> PyTupleRef {
+            ctx.empty_tuple.clone()
+        }
     }
 
     #[pyattr(name = "PyCF_ONLY_AST")]