typing.Counter is not supported

[vhsw]

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: 1.7
            pydantic compiled: True
                 install path: /home/user/app/.venv/lib/python3.8/site-packages/pydantic
               python version: 3.8.6 (default, Sep 25 2020, 09:36:53)  [GCC 10.2.0]
                     platform: Linux-5.9.0-1-amd64-x86_64-with-glibc2.29
     optional deps. installed: ['typing-extensions']

Minimal example:

from typing import Counter
from pydantic import BaseModel
class ProcessedDoc(BaseModel):
    named_entities: Counter[str]

Result:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "pydantic/main.py", line 262, in pydantic.main.ModelMetaclass.__new__
  File "pydantic/fields.py", line 315, in pydantic.fields.ModelField.infer
  File "pydantic/fields.py", line 284, in pydantic.fields.ModelField.__init__
  File "pydantic/fields.py", line 356, in pydantic.fields.ModelField.prepare
  File "pydantic/fields.py", line 492, in pydantic.fields.ModelField._type_analysis
IndexError: tuple index out of range

[samuelcolvin]

this is not a bug but a feature request.