F821 false positive for __class__ in lambda expression in class definition #20562
Description
Summary
undefined-name (F821) has a false positive for __class__ in a lambda expression within a class definition. Example:
$ cat >f821.py <<'# EOF'
class C:
f = lambda self: __class__
print(C().f().__name__)
# EOF
$ python f821.py
C
$ ruff --isolated check f821.py --select F821 --output-format concise -q
f821.py:2:22: F821 Undefined name `__class__`Version
ruff 0.13.1 (706be0a 2025-09-18)