UnboundLocalError for `new_scope`

[treykeown]

Description

The issue here https://github.com/jcrist/msgspec/blob/4d4a02e62ee7b9ccc5dadaa2b0d1336279561bb4/msgspec/_utils.py#L88 If the else on line 75 is taken, but neither of the two inner if statements are true, new_scope is unset.

Traceback from msgspec:

    return msgspec.msgpack.decode(encoded, type=cls._decode_type)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/.../.venv/lib/python3.12/site-packages/msgspec/_utils.py", line 113, in get_class_annotations
    mro, typevar_mappings = _get_class_mro_and_typevar_mappings(obj)
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/.../.venv/lib/python3.12/site-packages/msgspec/_utils.py", line 90, in _get_class_mro_and_typevar_mappings
    inner(obj, {})
  File "/Users/.../.venv/lib/python3.12/site-packages/msgspec/_utils.py", line 88, in inner
    inner(b, ...)
  File "/Users/.../.venv/lib/python3.12/site-packages/msgspec/_utils.py", line 88, in inner
    inner(b, new_scope)
  File "/Users/.../.venv/lib/python3.12/site-packages/msgspec/_utils.py", line 88, in inner
    inner(b, new_scope)
             ^^^^^^^^^
UnboundLocalError: cannot access local variable 'new_scope' where it is not associated with a value

I'll work on creating a minimal example.

[treykeown]

import msgspec
from typing import Generic, TypeVar

T = TypeVar('T')
T_int = TypeVar('T_int', bound=int)

class Base(msgspec.Struct, Generic[T], tag=True):
    """..."""

class Subclass(Base[int]):
    """..."""

class Bug(Subclass, Base[T_int], Generic[T_int]):
    """..."""

if __name__ == "__main__":
    enc = msgspec.msgpack.encode(Bug())
    dec = msgspec.msgpack.decode(enc, type=list[Bug])
    print(dec)

Traceback (most recent call last):
  File "/Users/.../scratch.py", line 21, in <module>
    dec = msgspec.msgpack.decode(enc, type=list[Bug])
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/.../.venv/lib/python3.12/site-packages/msgspec/_utils.py", line 113, in get_class_annotations
    mro, typevar_mappings = _get_class_mro_and_typevar_mappings(obj)
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/.../.venv/lib/python3.12/site-packages/msgspec/_utils.py", line 90, in _get_class_mro_and_typevar_mappings
    inner(obj, {})
  File "/Users/.../.venv/lib/python3.12/site-packages/msgspec/_utils.py", line 88, in inner
    inner(b, new_scope)
  File "/Users/.../.venv/lib/python3.12/site-packages/msgspec/_utils.py", line 88, in inner
    inner(b, new_scope)
             ^^^^^^^^^
UnboundLocalError: cannot access local variable 'new_scope' where it is not associated with a value

[treykeown]

I've since fixed how my classes are structured, but this is still an issue any time a generic class appears both in a parent class and in a child class.

[jcrist]

Thanks for the excellent reproducible issue, this should be fixed by #626.