Fix type errors on other models' managers when using objects = models.Manager() in Model. (#34)

* Fix bug where models with a class variable using a manager defined would interfere with other managers.

- Fill in the type argument for that particular instance of the manager, rather than modifying the bases of the Manager type.
- Instantiate a new Instance from determine_proper_manager_type so The code doesn't crash under mypy-mypyc.

* Use helpers.reparametrize_instance per review comment.

* Updated ignored errors in Django test for get_objects_or_404.

- For some reason, `Manager[nothing]` is now removed from expected types.
  However, I think this makes sense anyway, as Manager is a subclass of QuerySet.

mypy_django_plugin/main.py

@@ -64,13 +64,20 @@ def determine_proper_manager_type(ctx: FunctionContext) -> Type:
     if not isinstance(ret, Instance):
         return ret
 
+    has_manager_base = False
     for i, base in enumerate(ret.type.bases):
         if base.type.fullname() in {helpers.MANAGER_CLASS_FULLNAME,
                                     helpers.RELATED_MANAGER_CLASS_FULLNAME,
                                     helpers.BASE_MANAGER_CLASS_FULLNAME}:
-            ret.type.bases[i] = Instance(base.type, [Instance(outer_model_info, [])])
-            return ret
-    return ret
+            has_manager_base = True
+            break
+
+    if has_manager_base:
+        # Fill in the manager's type argument from the outer model
+        new_type_args = [Instance(outer_model_info, [])]
+        return helpers.reparametrize_instance(ret, new_type_args)
+    else:
+        return ret
 
 
 def return_user_model_hook(ctx: FunctionContext) -> Type:

scripts/typecheck_tests.py

@@ -199,9 +199,9 @@ IGNORED_ERRORS = {
     ],
     'get_object_or_404': [
         'Argument 1 to "get_object_or_404" has incompatible type "str"; '
-        + 'expected "Union[Type[<nothing>], Manager[<nothing>], QuerySet[<nothing>]]"',
+        + 'expected "Union[Type[<nothing>], QuerySet[<nothing>]]"',
         'Argument 1 to "get_list_or_404" has incompatible type "List[Type[Article]]"; '
-        + 'expected "Union[Type[<nothing>], Manager[<nothing>], QuerySet[<nothing>]]"',
+        + 'expected "Union[Type[<nothing>], QuerySet[<nothing>]]"',
         'CustomClass'
     ],
     'get_or_create': [

test-data/typecheck/managers.test

@@ -136,4 +136,66 @@ class AbstractBase2(models.Model):
 
 class Child(AbstractBase1, AbstractBase2):
     pass
+[out]
+
+[CASE managers_from_unrelated_models_dont_interfere]
+
+from django.db import models
+
+# Normal scenario where one model has a manager with an annotation of the same type as the model
+class UnrelatedModel(models.Model):
+    objects = models.Manager[UnrelatedModel]()
+
+class MyModel(models.Model):
+    pass
+
+reveal_type(UnrelatedModel.objects) # E: Revealed type is 'django.db.models.manager.Manager[main.UnrelatedModel]'
+reveal_type(UnrelatedModel.objects.first()) # E: Revealed type is 'Union[main.UnrelatedModel*, None]'
+
+reveal_type(MyModel.objects) # E: Revealed type is 'django.db.models.manager.Manager[main.MyModel]'
+reveal_type(MyModel.objects.first()) # E: Revealed type is 'Union[main.MyModel*, None]'
+
+# Possible to specify objects without explicit annotation of models.Manager()
+class UnrelatedModel2(models.Model):
+    objects = models.Manager()
+
+class MyModel2(models.Model):
+    pass
+
+reveal_type(UnrelatedModel2.objects) # E: Revealed type is 'django.db.models.manager.Manager[main.UnrelatedModel2]'
+reveal_type(UnrelatedModel2.objects.first()) # E: Revealed type is 'Union[main.UnrelatedModel2*, None]'
+
+reveal_type(MyModel2.objects) # E: Revealed type is 'django.db.models.manager.Manager[main.MyModel2]'
+reveal_type(MyModel2.objects.first()) # E: Revealed type is 'Union[main.MyModel2*, None]'
+
+
+# Inheritance works
+class ParentOfMyModel3(models.Model):
+    objects = models.Manager()
+
+class MyModel3(ParentOfMyModel3):
+    pass
+
+
+reveal_type(ParentOfMyModel3.objects) # E: Revealed type is 'django.db.models.manager.Manager[main.ParentOfMyModel3]'
+reveal_type(ParentOfMyModel3.objects.first()) # E: Revealed type is 'Union[main.ParentOfMyModel3*, None]'
+
+reveal_type(MyModel3.objects) # E: Revealed type is 'django.db.models.manager.Manager[main.MyModel3]'
+reveal_type(MyModel3.objects.first()) # E: Revealed type is 'Union[main.MyModel3*, None]'
+
+
+# Inheritance works with explicit objects in child
+class ParentOfMyModel4(models.Model):
+    objects = models.Manager()
+
+class MyModel4(ParentOfMyModel4):
+    objects = models.Manager[MyModel4]()
+
+reveal_type(ParentOfMyModel4.objects) # E: Revealed type is 'django.db.models.manager.Manager[main.ParentOfMyModel4]'
+reveal_type(ParentOfMyModel4.objects.first()) # E: Revealed type is 'Union[main.ParentOfMyModel4*, None]'
+
+reveal_type(MyModel4.objects) # E: Revealed type is 'django.db.models.manager.Manager[main.MyModel4]'
+reveal_type(MyModel4.objects.first()) # E: Revealed type is 'Union[main.MyModel4*, None]'
+
+
 [out]