Specific return types for values and values list (#53)

* Instead of using Literal types, overload QuerySet.values_list in the plugin. Fixes #43.

- Add a couple of extra type checks that Django makes:
  1) 'flat' and 'named' can't be used together.
  2) 'flat' is not valid when values_list is called with more than one field.

* Determine better row types for values_list/values based on fields specified.

- In the case of values_list, we use a Row type with either a single primitive, Tuple, or NamedTuple.
- In the case of values, we use a TypedDict.
- In both cases, Any is used as a fallback for individual fields if those fields cannot be resolved.

A couple other fixes I made along the way:
- Don't create reverse relation for ForeignKeys with related_name='+'
- Don't skip creating other related managers in AddRelatedManagers if a dynamic value is encountered
  for related_name parameter, or if the type cannot be determined.

* Fix for TypedDict so that they are considered anonymous.

* Clean up some comments.

* Implement making TypedDict anonymous in a way that doesn't crash sometimes.

* Fix flake8 errors.

* Remove even uglier hack about making TypedDict anonymous.

* Address review comments. Write a few better comments inside tests.

* Fix crash when running with mypyc ("interpreted classes cannot inherit from compiled") due to the way I extended TypedDictType.

- Implemented the hack in another way that works on mypyc.
- Added a couple extra tests of accessing 'id' / 'pk' via values_list.

* Fix flake8 errors.

* Support annotation expressions (use type Any) for TypedDicts row types returned by values_list.

- Bonus points: handle values_list gracefully (use type Any) where Tuples are returned
  where some of the fields arguments are not string literals.

mypy_django_plugin/main.py

@@ -1,6 +1,5 @@
-from functools import partial
-
 import os
+from functools import partial
 from typing import Callable, Dict, Optional, Union, cast
 
 from mypy.checker import TypeChecker
@@ -23,6 +22,7 @@ from mypy_django_plugin.transformers.migrations import (
     determine_model_cls_from_string_for_migrations, get_string_value_from_expr,
 )
 from mypy_django_plugin.transformers.models import process_model_class
+from mypy_django_plugin.transformers.queryset import extract_proper_type_for_values_and_values_list
 from mypy_django_plugin.transformers.settings import (
     AddSettingValuesToDjangoConfObject, get_settings_metadata,
 )
@@ -165,7 +165,7 @@ def extract_and_return_primary_key_of_bound_related_field_parameter(ctx: Attribu
         if primary_key_type:
             return primary_key_type
 
-    is_nullable = helpers.get_fields_metadata(ctx.type.type).get(field_name, {}).get('null', False)
+    is_nullable = helpers.is_field_nullable(ctx.type.type, field_name)
     if is_nullable:
         return helpers.make_optional(ctx.default_attr_type)
 
@@ -292,7 +292,10 @@ class DjangoPlugin(Plugin):
         if self.django_settings_module:
             settings_modules.append(self.django_settings_module)
 
-        monkeypatch.add_modules_as_a_source_seed_files(settings_modules)
+        auto_imports = ['mypy_extensions']
+        auto_imports.extend(settings_modules)
+
+        monkeypatch.add_modules_as_a_source_seed_files(auto_imports)
         monkeypatch.inject_modules_as_dependencies_for_django_conf_settings(settings_modules)
 
     def _get_current_model_bases(self) -> Dict[str, int]:
@@ -359,10 +362,10 @@ class DjangoPlugin(Plugin):
             if sym and isinstance(sym.node, TypeInfo) and sym.node.has_base(helpers.FORM_MIXIN_CLASS_FULLNAME):
                 return extract_proper_type_for_get_form
 
-        if method_name == 'values_list':
+        if method_name in ('values', 'values_list'):
             sym = self.lookup_fully_qualified(class_name)
             if sym and isinstance(sym.node, TypeInfo) and sym.node.has_base(helpers.QUERYSET_CLASS_FULLNAME):
-                return extract_proper_type_for_values_list
+                return partial(extract_proper_type_for_values_and_values_list, method_name)
 
         if fullname in {'django.apps.registry.Apps.get_model',
                         'django.db.migrations.state.StateApps.get_model'}: