RecursionError when using Literal types in GenericModel

[espdev]

Bug

If we are trying to use Literal types in GenericModel we are getting RecursionError: maximum recursion depth exceeded in comparison.

The minimal code example:

from typing import Literal, Dict, TypeVar, Generic
from pydantic.generics import GenericModel

Fields = Literal['foo', 'bar']

FieldType = TypeVar('FieldType')
ValueType = TypeVar('ValueType')

class GModel(GenericModel, Generic[FieldType, ValueType]):
    field: Dict[FieldType, ValueType]

GModelType = GModel[Fields, str]

The traceback:

Traceback (most recent call last):
  File "scratch_101.py", line 12, in <module>
    GModelType = GModel[Fields, str]
  File "virtualenvs\foobar-HGIuaRl7-py3.9\lib\site-packages\pydantic\generics.py", line 110, in __class_getitem__
    {param: None for param in iter_contained_typevars(typevars_map.values())}
  File "virtualenvs\foobar-HGIuaRl7-py3.9\lib\site-packages\pydantic\generics.py", line 110, in <dictcomp>
    {param: None for param in iter_contained_typevars(typevars_map.values())}
  File "virtualenvs\foobar-HGIuaRl7-py3.9\lib\site-packages\pydantic\generics.py", line 216, in iter_contained_typevars
    yield from iter_contained_typevars(var)
  File "virtualenvs\foobar-HGIuaRl7-py3.9\lib\site-packages\pydantic\generics.py", line 220, in iter_contained_typevars
    yield from iter_contained_typevars(arg)
  File "virtualenvs\foobar-HGIuaRl7-py3.9\lib\site-packages\pydantic\generics.py", line 216, in iter_contained_typevars
    yield from iter_contained_typevars(var)
  File "virtualenvs\foobar-HGIuaRl7-py3.9\lib\site-packages\pydantic\generics.py", line 216, in iter_contained_typevars
    yield from iter_contained_typevars(var)
  File "virtualenvs\foobar-HGIuaRl7-py3.9\lib\site-packages\pydantic\generics.py", line 216, in iter_contained_typevars
    yield from iter_contained_typevars(var)
  [Previous line repeated 982 more times]
  File "virtualenvs\foobar-HGIuaRl7-py3.9\lib\site-packages\pydantic\generics.py", line 214, in iter_contained_typevars
    elif isinstance(v, Iterable):
  File "C:\Programs\Python\Python39_x64\lib\typing.py", line 657, in __instancecheck__
    return self.__subclasscheck__(type(obj))
  File "C:\Programs\Python\Python39_x64\lib\typing.py", line 789, in __subclasscheck__
    return issubclass(cls, self.__origin__)
  File "C:\Programs\Python\Python39_x64\lib\abc.py", line 102, in __subclasscheck__
    return _abc_subclasscheck(cls, subclass)
RecursionError: maximum recursion depth exceeded in comparison

---

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

pydantic version: 1.8
        pydantic compiled: True
             install path: /home/esp/.cache/pypoetry/virtualenvs/foobar-n-Q38lsL-py3.9/lib/python3.9/site-packages/pydantic
           python version: 3.9.1 (default, Dec  8 2020, 02:26:20)  [GCC 9.3.0]
                 platform: Linux-4.4.0-19041-Microsoft-x86_64-with-glibc2.31
 optional deps. installed: ['typing-extensions']

[PrettyWood]

Hi @espdev thanks for reporting!
Does #2438 solve your issue?
I reckon we should update the change description of the fix 😬

EDIT: Just checked. It does :)

[espdev]

@PrettyWood Great! I am closing the issue because it has already been fixed in PR. Thanks!