allow to subclass queryset without loss of typing

mypy_django_plugin/transformers/meta.py

@@ -5,7 +5,7 @@ from mypy.types import Type as MypyType
 from mypy.types import TypeOfAny
 
 from mypy_django_plugin.django.context import DjangoContext
-from mypy_django_plugin.lib import fullnames, helpers
+from mypy_django_plugin.lib import helpers
 
 
 def _get_field_instance(ctx: MethodContext, field_fullname: str) -> MypyType:
@@ -20,21 +20,25 @@ def return_proper_field_type_from_get_field(ctx: MethodContext, django_context:
     # Options instance
     assert isinstance(ctx.type, Instance)
 
+    # bail if list of generic params is empty
+    if len(ctx.type.args) == 0:
+        return ctx.default_return_type
+
     model_type = ctx.type.args[0]
     if not isinstance(model_type, Instance):
-        return _get_field_instance(ctx, fullnames.FIELD_FULLNAME)
+        return ctx.default_return_type
 
     model_cls = django_context.get_model_class_by_fullname(model_type.type.fullname())
     if model_cls is None:
-        return _get_field_instance(ctx, fullnames.FIELD_FULLNAME)
+        return ctx.default_return_type
 
     field_name_expr = helpers.get_call_argument_by_name(ctx, 'field_name')
     if field_name_expr is None:
-        return _get_field_instance(ctx, fullnames.FIELD_FULLNAME)
+        return ctx.default_return_type
 
     field_name = helpers.resolve_string_attribute_value(field_name_expr, ctx, django_context)
     if field_name is None:
-        return _get_field_instance(ctx, fullnames.FIELD_FULLNAME)
+        return ctx.default_return_type
 
     try:
         field = model_cls._meta.get_field(field_name)

mypy_django_plugin/transformers/querysets.py

@@ -3,6 +3,7 @@ from typing import List, Optional, Sequence, Type, Union, cast
 
 from django.core.exceptions import FieldError
 from django.db.models.base import Model
+from django.db.models.fields.related import RelatedField
 from mypy.newsemanal.typeanal import TypeAnalyser
 from mypy.nodes import Expression, NameExpr, TypeInfo
 from mypy.plugin import AnalyzeTypeContext, FunctionContext, MethodContext
@@ -10,11 +11,19 @@ from mypy.types import AnyType, Instance
 from mypy.types import Type as MypyType
 from mypy.types import TypeOfAny
 
-from django.db.models.fields.related import RelatedField
 from mypy_django_plugin.django.context import DjangoContext
 from mypy_django_plugin.lib import fullnames, helpers
 
 
+def _extract_model_type_from_queryset(queryset_type: Instance) -> Optional[Instance]:
+    for base_type in [queryset_type, *queryset_type.type.bases]:
+        if (len(base_type.args)
+                and isinstance(base_type.args[0], Instance)
+                and base_type.args[0].type.has_base(fullnames.MODEL_CLASS_FULLNAME)):
+            return base_type.args[0]
+    return None
+
+
 def determine_proper_manager_type(ctx: FunctionContext) -> MypyType:
     default_return_type = ctx.default_return_type
     assert isinstance(default_return_type, Instance)
@@ -98,11 +107,10 @@ def extract_proper_type_queryset_values_list(ctx: MethodContext, django_context:
     assert isinstance(ctx.type, Instance)
     assert isinstance(ctx.default_return_type, Instance)
 
-    # bail if queryset of Any or other non-instances
-    if not isinstance(ctx.type.args[0], Instance):
+    model_type = _extract_model_type_from_queryset(ctx.type)
+    if model_type is None:
         return AnyType(TypeOfAny.from_omitted_generics)
 
-    model_type = ctx.type.args[0]
     model_cls = django_context.get_model_class_by_fullname(model_type.type.fullname())
     if model_cls is None:
         return ctx.default_return_type
@@ -148,11 +156,10 @@ def extract_proper_type_queryset_values(ctx: MethodContext, django_context: Djan
     assert isinstance(ctx.type, Instance)
     assert isinstance(ctx.default_return_type, Instance)
 
-    # if queryset of non-instance type
-    if not isinstance(ctx.type.args[0], Instance):
+    model_type = _extract_model_type_from_queryset(ctx.type)
+    if model_type is None:
         return AnyType(TypeOfAny.from_omitted_generics)
 
-    model_type = ctx.type.args[0]
     model_cls = django_context.get_model_class_by_fullname(model_type.type.fullname())
     if model_cls is None:
         return ctx.default_return_type

test-data/typecheck/managers/querysets/test_values_list.yml

@@ -205,3 +205,21 @@
                     pass
                 class Blog(models.Model):
                     publisher = models.ForeignKey(to=Publisher, on_delete=models.CASCADE)
+
+-   case: subclass_of_queryset_has_proper_typings_on_methods
+    main: |
+        from myapp.models import TransactionQuerySet
+        reveal_type(TransactionQuerySet())  # N: Revealed type is 'myapp.models.TransactionQuerySet'
+        reveal_type(TransactionQuerySet().values())  # N: Revealed type is 'django.db.models.query.QuerySet[myapp.models.Transaction, TypedDict({'id': builtins.int, 'total': builtins.int})]'
+        reveal_type(TransactionQuerySet().values_list())  # N: Revealed type is 'django.db.models.query.QuerySet[myapp.models.Transaction, Tuple[builtins.int, builtins.int]]'
+    installed_apps:
+        - myapp
+    files:
+        -   path: myapp/__init__.py
+        -   path: myapp/models.py
+            content: |
+                from django.db import models
+                class TransactionQuerySet(models.QuerySet['Transaction']):
+                    pass
+                class Transaction(models.Model):
+                    total = models.IntegerField()