Self-referenced ClassVar causes TypeError: issubclass() arg 1 must be a class (in 1.9.0, worked in 1.8.2)

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I added a descriptive title to this issue
I have searched (google, github) for similar issues and couldn't find anything -> Issue TypeError: issubclass() arg 1 must be a class #545 is similar, but this case is a regression in 1.9.
I have read and followed the docs and still think this is a bug

Bug

Output of python -c "import pydantic.utils; print(pydantic.utils.version_info())":

pydantic version: 1.9.0
pydantic compiled: True
install path: C:\Program Files\Python39\Lib\site-packages\pydantic
python version: 3.9.0 (tags/v3.9.0:9cf6752, Oct  5 2020, 15:34:40) [MSC v.1927 64 bit (AMD64)]
platform: Windows-10-10.0.19041-SP0
optional deps. installed: ['email-validator', 'typing-extensions']

Also occurs on Linux with Python 3.9.9.

from __future__ import annotations
import pydantic
import typing

class WithClassVar(pydantic.BaseModel):
    Instances : typing.ClassVar[dict[str,WithClassVar]] = {} # fails with issubclass() arg 1 must be a class; arg  1 is typing.ClassVar object 
    # Instances : typing.ClassVar[dict[str,'WithClassVar']] = {} # works
    # instance : dict[str,WithClassVar] = {} # no classvar - works

...

I believe this case is specific to a ClassVar referencing itself. The argument passed to issubclass is not a class, but an instance of typing.ClassVar.

Call stack:

__subclasscheck__ (c:\Program Files\Python39\Lib\typing.py:789)
pydantic.fields.ModelField._type_analysis (c:\Program Files\Python39\Lib\site-packages\pydantic\fields.py:638)
pydantic.fields.ModelField.prepare (c:\Program Files\Python39\Lib\site-packages\pydantic\fields.py:534)
pydantic.typing.update_field_forward_refs (c:\Program Files\Python39\Lib\site-packages\pydantic\typing.py:451)
pydantic.typing.update_model_forward_refs (c:\Program Files\Python39\Lib\site-packages\pydantic\typing.py:480)
pydantic.main.BaseModel.__try_update_forward_refs__ (c:\Program Files\Python39\Lib\site-packages\pydantic\main.py:773)
pydantic.main.ModelMetaclass.__new__ (c:\Program Files\Python39\Lib\site-packages\pydantic\main.py:292)
<module> (.... \pydantic_bug.py:5)

I get the same error with the following variant:

from __future__ import annotations
import pydantic
import typing

class WithClassVar(pydantic.BaseModel):
    Instance : typing.ClassVar['WithClassVar']

However, if I remove the first line (importing annotations), the example seems to work.

The following class definition passes initial muster

from __future__ import annotations
import pydantic
import typing

class WithClassVar(pydantic.BaseModel):
    Instance : typing.ClassVar[WithClassVarAlias]

WithClassVarAlias = WithClassVar

... but if I try to construct an instance, I get a problem:

print(WithClassVar())

leads to

pydantic.error_wrappers.ValidationError: 1 validation error for WithClassVar
Instance
  field required (type=value_error.missing)

guard against ClassVar in fields, fix #3679

guard against ClassVar in fields (#4064)

Fetch upstream

guard against ClassVar in fields (#4064)

fix ClassVars, better fix for #3679

fix ClassVars, better fix for #3679 (#4077)

guard against ClassVar in fields (pydantic#4064)

fix ClassVars, better fix for pydantic#3679 (pydantic#4077)

Unfortunately, this stopped working again on 1.10.2 with Python 3.11:

             pydantic version: 1.10.2
            pydantic compiled: True
                 install path: C:\Projects\DDH\.venv\Lib\site-packages\pydantic
               python version: 3.11.0 (main, Oct 24 2022, 18:26:48) [MSC v.1933 64 bit (AMD64)]
                     platform: Windows-10-10.0.19044-SP0
     optional deps. installed: ['email-validator', 'typing-extensions']

Now, it doesn't work even when quoted, this "workaround" was ok before:

from __future__ import annotations
import pydantic
import typing

class WithClassVar(pydantic.BaseModel):
    Instances : typing.ClassVar[dict[str,WithClassVar]] = {} # fails with issubclass() arg 1 must be a class; arg  1 is typing.ClassVar object 
    # Instances : typing.ClassVar[dict[str,'WithClassVar']] = {} # worked in 1.9, stopped working in 1.10.2
    # instance : dict[str,WithClassVar] = {} # no classvar - works

Workaround for pydantic/pydantic#3679 (comment)

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Self-referenced ClassVar causes TypeError: issubclass() arg 1 must be a class (in 1.9.0, worked in 1.8.2) #3679

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Self-referenced ClassVar causes TypeError: issubclass() arg 1 must be a class (in 1.9.0, worked in 1.8.2) #3679

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ajkaijanaho commented on Jan 18, 2022

mcgfeller commented on Dec 5, 2022

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