Schema generation with GenericModel and multiple enums is broken since 1.8.0

[pboehm]

Checks

• I added a descriptive title to this issue
• I have searched (google, github) for similar issues and couldn't find anything
• I have read and followed the docs and still think this is a bug

Bug

Since pydantic 1.8.0 schema generation with GenericModel and multiple Enum fields using this GenericModel fails with a KeyError. I have tried the fix in #2536 but this seems to be another corner case that has to be fixed.

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

             pydantic version: 1.8.1
            pydantic compiled: True
                 install path: /Users/philipp/.pyenv/versions/3.7.10/envs/pydantic_schema_error@3.7.10/lib/python3.7/site-packages/pydantic
               python version: 3.7.10 (default, Mar  4 2021, 21:37:12)  [Clang 12.0.0 (clang-1200.0.32.29)]
                     platform: Darwin-20.3.0-x86_64-i386-64bit
     optional deps. installed: ['typing-extensions']

from enum import Enum
from typing import TypeVar, Generic, Optional
from pydantic import BaseModel
from pydantic.generics import GenericModel

ConfigValueT = TypeVar("ConfigValueT")


class ConfigOption(GenericModel, Generic[ConfigValueT]):
    value: ConfigValueT
    value_source: str


class EnumA(str, Enum):
    a = "a"
    aa = "aa"


class EnumB(str, Enum):
    b = "b"
    bb = "bb"


class TestModel(BaseModel):
    option_a: ConfigOption[EnumA]
    option_b: ConfigOption[EnumB]  # it also works with only `option_a` but not with multiple


print(TestModel.schema_json())  # This works until 1.7.3 but crashes on 1.8+

This results in a KeyError:

Traceback (most recent call last):
  File "test.py", line 29, in <module>
    print(TestModel.schema_json())  # This works until 1.7.3 but crashes on 1.8+
  File "pydantic/main.py", line 715, in pydantic.main.BaseModel.schema_json
  File "pydantic/main.py", line 704, in pydantic.main.BaseModel.schema
  File "pydantic/schema.py", line 167, in pydantic.schema.model_schema
  File "pydantic/schema.py", line 548, in pydantic.schema.model_process_schema
  File "pydantic/schema.py", line 589, in pydantic.schema.model_type_schema
  File "pydantic/schema.py", line 241, in pydantic.schema.field_schema
  File "pydantic/schema.py", line 495, in pydantic.schema.field_type_schema
  File "pydantic/schema.py", line 839, in pydantic.schema.field_singleton_schema
KeyError: <class '__main__.ConfigOption[str]'>

Thank you for your work on this amazing library!

[PrettyWood]

Hi @pboehm!
Thank you for reporting with a clear example AND for checking open fixes like #2536. Always nice to spare some time 🙏
You're absolutely right and the fix has in fact nothing to do with schema generation per se. I opened a fix I'll see if fastapi tests are ok