id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
36695	Model field validator with a generic parameter causes infinite recursion when making migrations	Michal Dabski		"Minimal code to reproduce (in `models.py`) in `Django==4.2.25`

{{{
from django.utils.deconstruct import deconstructible
from django.db import models

@deconstructible
class SchemaValidator:
    def __init__(self, expected_type: type):
        pass

    def __call__(self, *args, **kwargs):
        pass

class TestModel(models.Model):
    config: dict[str, float] = models.JSONField(validators=[SchemaValidator(dict[str, float])])

}}}

This triggers an error when running makemigrations:

{{{
$ ./manage.py makemigrations
C:\Users\Michal\src\mat-cms\.venv\Lib\site-packages\django_downloadview\__init__.py:4: UserWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html. The pkg_resources package is slated for removal as early as 2025-11-30. Refrain from using this package or pin to Setuptools<81.
  import pkg_resources
Migrations for 'audit_builder':
  meg_forms\audit_builder\migrations\0083_alter_testmodel_config.py
    - Alter field config on testmodel
Traceback (most recent call last):
  File ""C:\Users\Michal\src\mat-cms\.venv\Lib\site-packages\django\db\migrations\serializer.py"", line 214, in serialize
    item_string, item_imports = serializer_factory(item).serialize()
                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ""C:\Users\Michal\src\mat-cms\.venv\Lib\site-packages\django\db\migrations\serializer.py"", line 214, in serialize
    item_string, item_imports = serializer_factory(item).serialize()
                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ""C:\Users\Michal\src\mat-cms\.venv\Lib\site-packages\django\db\migrations\serializer.py"", line 214, in serialize
    item_string, item_imports = serializer_factory(item).serialize()
                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  [Previous line repeated 996 more times]
  File ""C:\Users\Michal\src\mat-cms\.venv\Lib\site-packages\django\db\migrations\serializer.py"", line 389, in serializer_factory
    if isinstance(value, type_):
       ^^^^^^^^^^^^^^^^^^^^^^^^
RecursionError: maximum recursion depth exceeded
}}}

Debugging locally shows that:
* removing generic parameters from the `dict` type passed to `SchemaValidator` does not trigger the error
* The loop happens in `django.db.migrations.serializer.IterableSerializer.serialize`, it keeps recursively invoking `serializer_factory(item).serialize()` with `item='*dict[str, float]'` (`GenericAlias`)"	Bug	new	Migrations	4.2	Normal			Michal Dabski	Unreviewed	0	0	0	0	0	0