Pydantic unable to generate schema() when one of the fields is of type Type

[Koratun]

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

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

             pydantic version: 1.9.0
            pydantic compiled: True
                 install path: C:\Users\...\.venv\Lib\site-packages\pydantic
               python version: 3.9.6 (tags/v3.9.6:db3ff76, Jun 28 2021, 15:26:21) [MSC v.1929 64 bit (AMD64)]
                     platform: Windows-10-10.0.22000-SP0
     optional deps. installed: ['typing-extensions']

from pydantic import BaseModel
from typing import Type

class TypeTest(BaseModel):
  t: Type[BaseModel]

print(TypeTest.schema())

Stack Trace:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "pydantic\main.py", line 647, in pydantic.main.BaseModel.schema
  File "pydantic\schema.py", line 185, in pydantic.schema.model_schema
  File "pydantic\schema.py", line 617, in pydantic.schema.model_process_schema
  File "pydantic\schema.py", line 658, in pydantic.schema.model_type_schema
  File "pydantic\schema.py", line 258, in pydantic.schema.field_schema
  File "pydantic\schema.py", line 563, in pydantic.schema.field_type_schema
  File "pydantic\schema.py", line 922, in pydantic.schema.field_singleton_schema
  File "C:\Users\...\AppData\Local\Programs\Python\Python39\lib\abc.py", line 123, in __subclasscheck__
    return _abc_subclasscheck(cls, subclass)
TypeError: issubclass() arg 1 must be a class

Instantiating the TypeTest with various types works and raises Validation errors as appropriate.

>>> TypeTest(t=BaseModel)
TypeTest(t=<class 'pydantic.main.BaseModel'>)
>>> TypeTest(t=TypeTest)  
TypeTest(t=<class '__main__.TypeTest'>)
>>> TypeTest(t=int)      
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "pydantic\main.py", line 331, in pydantic.main.BaseModel.__init__
pydantic.error_wrappers.ValidationError: 1 validation error for TypeTest
t
  subclass of BaseModel expected (type=type_error.subclass; expected_class=BaseModel)

[samuelcolvin]

Is this specific to Type[BaseModel] or would it happen with Tuple[AnyClass]?

PR welcome to fix this, shouldn't be too hard to ignore or use something general for these fields.

[ofercaspi]

Looks like a duplicate of #3390