Plugin regression with mypy 0.99x: FieldDoesNotExist

[intgr]

mypy_django_plugin causes a mypy internal error when running typecheck_tests.py on Django 3.2 source with mypy 0.991. Does not occur with Django 4.0.

See typecheck failures in PR #1260.

I have not yet had the time to investigate this. Any help would be welcome.

  File "/home/runner/work/django-stubs/django-stubs/mypy_django_plugin/transformers/fields.py", line 117, in set_descriptor_types_for_field_callback
  File "/home/runner/work/django-stubs/django-stubs/mypy_django_plugin/transformers/fields.py", line 215, in transform_into_proper_return_type
  File "/home/runner/work/django-stubs/django-stubs/mypy_django_plugin/transformers/fields.py", line 41, in _get_current_field_from_assignment
  File "/opt/hostedtoolcache/Python/3.8.14/x64/lib/python3.8/site-packages/django/db/models/options.py", line 610, in get_field
  File "mypy/checkexpr.py", line 1004, in apply_function_plugin
  File "mypy/checkexpr.py", line 1181, in check_call_expr_with_callee_type
  File "mypy/checkexpr.py", line 1264, in check_call
  File "mypy/checkexpr.py", line 1466, in check_callable_call
  File "mypy/checkexpr.py", line 410, in visit_call_expr
  File "mypy/checkexpr.py", line 4665, in accept
  File "mypy/checkexpr.py", line 530, in visit_call_expr_inner
  File "mypy/nodes.py", line 1841, in accept
/home/runner/work/django-stubs/django-stubs/django-source/tests/model_fields/models.py:176: error: INTERNAL ERROR -- Please try using mypy master on GitHub:
FieldDoesNotExist: RenamedField has no field named 'modelname'

[intgr]

Please let me know if this issue affects any real codebase as well. Currently it has only been observed in our CI.

Possible work-around: downgrade to mypy 0.982.

[flaeppe]

From my digging:

RenamedField is declared in Django's test suite like:

class RenamedField(models.Model):
    modelname = models.IntegerField(name="fieldname", choices=((1, 'One'),))

It should be noted that name= isn't a documented argument/feature and it seems that it renames the instance(?) attribute on the model. As such, you'd access the field value like: RenamedField().fieldname. If you do RenamedField().modelname you get a FieldDoesNotExist in your face.

I'm only guessing, but perhaps it could be useful to avoid shadowing? e.g.

class X(models.Model):
    _type = models.IntegerField(name="type")

In any case, the plugin doesn't support the name= argument and we could try to catch FieldDoesNotExist around .get_field(...) here:

django-stubs/mypy_django_plugin/transformers/fields.py

Lines 34 to 42 in 7d50e5b

	if field_name is None:
	return None
	model_cls = django_context.get_model_class_by_fullname(outer_model_info.fullname)
	if model_cls is None:
	return None
	current_field = model_cls._meta.get_field(field_name)
	return current_field

[flaeppe]

I'm suspecting that should be good enough until there would be any support for name= (if at all). Since we check

if field_name is None:
    return None

a couple of lines before. As such, field_name is seen to appear on the class definition (if not None)

[flaeppe]

See my fix in #1329