fix as manager IndexError: tuple index out of range (#1785)

mypy_django_plugin/transformers/managers.py

@@ -124,7 +124,7 @@ def _process_dynamic_method(
             ret_type = Instance(queryset_info, [manager_instance.args[0], manager_instance.args[0]])
         variables = []
     args_types = method_type.arg_types[1:]
-    if _has_compatible_type_vars(base_that_has_method):
+    if _has_compatible_type_vars(base_that_has_method) and manager_instance.args:
         ret_type = _replace_type_var(
             ret_type, base_that_has_method.defn.type_vars[0].fullname, manager_instance.args[0]
         )

tests/typecheck/managers/querysets/test_from_queryset.yml

@@ -70,6 +70,43 @@
                 NewManager = BaseManager.from_queryset(ModelQuerySet)
                 class MyModel(models.Model):
                     objects = NewManager()
+
+-   case: bug_1785
+    main: |
+        from myapp.models import NewManager
+        reveal_type(NewManager().example())  # N: Revealed type is "_CTE`1"
+    installed_apps:
+        - myapp
+    files:
+        -   path: myapp/__init__.py
+        -   path: myapp/querysets.py
+            content: |
+                from typing import TypeVar, TYPE_CHECKING
+
+                from django.db import models
+                from django.db.models.manager import BaseManager
+                if TYPE_CHECKING:
+                    from .models import MyModel
+
+                _CTE = TypeVar("_CTE", bound=models.Model)
+
+                class _MyModelQuerySet(models.QuerySet[_CTE]):
+
+                    def example(self) -> _CTE: ...
+
+                class MyModelQuerySet(_MyModelQuerySet["MyModel"]): ...
+
+        - path: myapp/models.py
+          content: |
+            from django.db import models
+            from django.db.models.manager import BaseManager
+            from .querysets import MyModelQuerySet
+
+            class TypedManager(BaseManager[models.Model]): ...
+
+            NewManager = TypedManager.from_queryset(MyModelQuerySet)
+            class MyModel(models.Model):
+                objects = NewManager()
 -   case: handles_subclasses_of_queryset
     main: |
         from myapp.models import MyModel