Cannot type objects custom manager as ClassVar[ManagerClass]

[federicobond]

Bug report

What's wrong

I cannot explicitly type attribute as custom model manager when assigning to the model objects attribute.

from typing import ClassVar
from django.db import models

class A(models.Model):
    objects: ClassVar[models.Manager] = models.QuerySet.as_manager()

This returns:

models.py:7: error: Cannot override instance variable (previously declared on base class "Model") with class variable  [misc]
        objects: ClassVar[models.Manager] = models.QuerySet.as_manager()
        ^~~~~~~

How is that should be

It should type correctly.

System information

• OS: Linux
• python version: 3.11
• django version: 5.0.1
• mypy version: 1.8.0
• django-stubs version: latest
• django-stubs-ext version: latest

[federicobond]

Removing the type or typing as Any causes mypy to crash with:

Traceback (most recent call last):
  File "/usr/local/bin/mypy", line 8, in <module>
    sys.exit(console_entry())
             ^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/mypy/__main__.py", line 15, in console_entry
    main()
  File "/usr/local/lib/python3.11/site-packages/mypy/main.py", line 100, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/mypy/main.py", line 182, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/mypy/build.py", line 191, in build
    result = _build(
             ^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/mypy/build.py", line 265, in _build
    graph = dispatch(sources, manager, stdout)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/mypy/build.py", line 2943, in dispatch
    process_graph(graph, manager)
  File "/usr/local/lib/python3.11/site-packages/mypy/build.py", line 3341, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/usr/local/lib/python3.11/site-packages/mypy/build.py", line 3468, in process_stale_scc
    graph[id].write_cache()
  File "/usr/local/lib/python3.11/site-packages/mypy/build.py", line 2504, in write_cache
    new_interface_hash, self.meta = write_cache(
                                    ^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/mypy/build.py", line 1566, in write_cache
    data_str = json_dumps(data, manager.options.debug_cache)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/mypy/build.py", line 1511, in json_dumps
    return json.dumps(obj, sort_keys=True, separators=(",", ":"))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/json/__init__.py", line 238, in dumps
    **kw).encode(obj)
          ^^^^^^^^^^^
  File "/usr/local/lib/python3.11/json/encoder.py", line 200, in encode
    chunks = self.iterencode(o, _one_shot=True)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/json/encoder.py", line 258, in iterencode
    return _iterencode(o, 0)
           ^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/json/encoder.py", line 180, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type AnyType is not JSON serializable

[federicobond]

Interesting... looks like it does type correctly when I remove the explicit type and call it with --cache-dir=/dev/null, so it appears it could be an issue with TypeInfo metadata, as described here.

[flaeppe]

I've tried to but can't reproduce any error or problems with the provided snippet. I'm happy to reopen if you can provide a repro case.