Fix crash when filtering on implicit pk field on abstract model

mypy_django_plugin/django/context.py

@@ -384,6 +384,10 @@ def resolve_lookup_into_field(
 
     def resolve_lookup_expected_type(self, ctx: MethodContext, model_cls: Type[Model], lookup: str) -> MypyType:
         query = Query(model_cls)
+        if lookup == "pk" or lookup.startswith("pk__") and query.get_meta().pk is None:
+            # Primary key lookup when no primary key field is found, model is presumably
+            # abstract and we can't say anything about 'pk'.
+            return AnyType(TypeOfAny.implementation_artifact)
         try:
             lookup_parts, field_parts, is_expression = query.solve_lookup_type(lookup)
             if is_expression:

tests/typecheck/models/test_abstract.yml

@@ -0,0 +1,9 @@
+- case: test_filter_on_abstract_user_pk
+  main: |
+    from django.contrib.auth.models import AbstractUser
+    AbstractUser.objects.get(pk=1)
+    AbstractUser.objects.get(pk__in=[1])
+    reveal_type(AbstractUser().pk)  # N: Revealed type is "Any"
+    AbstractUser.objects.get(pkey=1)  # ER: Cannot resolve keyword 'pkey' into field..*
+  installed_apps:
+    - django.contrib.auth