[fix] Prevent crash on slice decorator for 'six' decorated function (#2738)

Closes #2721

Author: Pierre-Sassoulas

ChangeLog

@@ -41,6 +41,11 @@ Release date: TBA
 
  Closes #2734
 
+* Fix a crash when parsing a slice called in a decorator on a function that is also decorated with
+ a known ``six`` decorator.
+
+ Closes #2721
+
 What's New in astroid 3.3.10?
 =============================
 Release date: 2025-05-10

astroid/brain/brain_six.py

@@ -182,7 +182,11 @@ def transform_six_add_metaclass(node): # pylint: disable=inconsistent-return-st
  func = next(decorator.func.infer())
  except (InferenceError, StopIteration):
  continue
- if func.qname() == SIX_ADD_METACLASS and decorator.args:
+ if (
+ isinstance(func, (nodes.FunctionDef, nodes.ClassDef))
+ and func.qname() == SIX_ADD_METACLASS
+ and decorator.args
+ ):
  metaclass = decorator.args[0]
  node._metaclass = metaclass
  return node

tests/test_regrtest.py

@@ -504,3 +504,19 @@ def test_regression_no_crash_during_build() -> None:
  node: nodes.Attribute = extract_node("__()")
  assert node.args == []
  assert node.as_string() == "__()"
+
+
+def test_regression_no_crash_on_called_slice() -> None:
+ """Regression test for issue #2721."""
+ node: nodes.Attribute = extract_node(
+ textwrap.dedent(
+ """
+ s = slice(-2)
+ @s()
+ @six.add_metaclass()
+ class a: ...
+ """
+ )
+ )
+ assert isinstance(node, nodes.ClassDef)
+ assert node.name == "a"