REGR: mypyc 0.971 seems to not handle keyword-only arguments when unpickling (and shallow copying)

[twoertwein]

Bug Report

The following worked with 0.961: object's whose __init__ has a keyword-only argument can no longer be unpickled.

To Reproduce

test.py

from typing import Any

class Test:
    def __init__(self, *, x: Any) -> None:
        ...

save_load.py

import pickle
from test import Test

test = Test(x=1)

with open("test.pickle", mode="w+b") as file:
    pickle.dump(test, file)
with open("test.pickle", mode="r+b") as file:
    pickle.load(file)

$ mypyc test.py
$ python save_load.py 
Traceback (most recent call last):
  File "save_load.py", line 9, in <module>
    pickle.load(file)
TypeError: __init__() missing required keyword-only argument 'x'

Expected Behavior
No TypeError

Actual Behavior
TypeError

Your Environment

• Mypy version used: 0.971
• Python version used: 3.10.4
• Operating system and version: Fedora Silverblue

[twoertwein]

slightly smaller reproducer:

test.py:

class Test:
    def __init__(self, *, x: int) -> None:
        ...

$ mypyc test.py
$ python -c "from test import Test; from copy import copy; copy(Test(x=1))"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib64/python3.10/copy.py", line 102, in copy
    return _reconstruct(x, None, *rv)
  File "/usr/lib64/python3.10/copy.py", line 265, in _reconstruct
    y = func(*args)
  File "/usr/lib64/python3.10/copyreg.py", line 101, in __newobj__
    return cls.__new__(cls, *args)
TypeError: __init__() missing required keyword-only argument 'x'

[hauntsaninja]

Sounds like this might be https://github.com/python/mypy/pull/12600/files#r873178396

[hauntsaninja]

Looks like mypyc docs isn't up to date cc @JukkaL mypyc/mypyc#920

[hauntsaninja]

If you make me an RTD admin (like you did for mypy), I can get the docs working again

[twoertwein]

Thank you @hauntsaninja, using this decorator leads to a new issue without pickle/copy (and without keyword-only arguments):

from mypy_extensions import mypyc_attr

@mypyc_attr(serializable=True)
class Test:
    def __init__(self, x: int) -> None:
        self.x = x

    def test(self) -> int:
        return self.x

$ mypyc test.py
$ python -c "from test import Test; Test(x=1).test()"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "test.py", line 11, in test
    return self.x
AttributeError: attribute 'Test' of 'x' undefined

[ingambe]

Is there any news regarding this issue?