cloudpickle fails to pickle NewType in main module by value on Python 3.10 and newer

[hauntsaninja]

In a.py:

import cloudpickle
from typing import Any, NewType
RunDict = NewType("RunDict", dict[str, Any])
with open("tmp.pickle", "wb") as f:
    f.write(cloudpickle.dumps(RunDict))

In b.py

import cloudpickle
with open("tmp.pickle", "rb") as f:
    value = cloudpickle.load(f)
print(value)

λ python3.9 a.py
λ python3.9 b.py
<function NewType.<locals>.new_type at 0x1004580d0>
λ python3.10 a.py
λ python3.10 b.py
Traceback (most recent call last):
  File "/Users/shantanu/devoai/openai/b.py", line 3, in <module>
    value = cloudpickle.load(f)
AttributeError: Can't get attribute 'RunDict' on <module '__main__' from '/Users/shantanu/devoai/openai/b.py'>

[ogrisel]

Thanks for the report. I confirm I can reproduce with Python 3.11 (I haven't tried Python 3.12).

I suspect we might need something like the _typevar_reduce custom reducer. Feel free to open a PR if you wish.