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/transformers/fields.py

@@ -1,10 +1,10 @@
 from typing import Optional, cast
 
 from mypy.checker import TypeChecker
-from mypy.nodes import ListExpr, NameExpr, StrExpr, TupleExpr, TypeInfo, Var
+from mypy.nodes import ListExpr, NameExpr, StrExpr, TupleExpr, TypeInfo
 from mypy.plugin import FunctionContext
 from mypy.types import (
-    AnyType, CallableType, Instance, TupleType, Type, TypeOfAny, UnionType,
+    AnyType, CallableType, Instance, TupleType, Type, UnionType,
 )
 
 from mypy_django_plugin import helpers
@@ -88,23 +88,13 @@ def fill_descriptor_types_for_related_field(ctx: FunctionContext) -> Type:
     return helpers.reparametrize_instance(ctx.default_return_type, new_args=args)
 
 
-def get_private_descriptor_type(type_info: TypeInfo, private_field_name: str, is_nullable: bool) -> Type:
-    node = type_info.get(private_field_name).node
-    if isinstance(node, Var):
-        descriptor_type = node.type
-        if is_nullable:
-            descriptor_type = helpers.make_optional(descriptor_type)
-        return descriptor_type
-    return AnyType(TypeOfAny.unannotated)
-
-
 def set_descriptor_types_for_field(ctx: FunctionContext) -> Instance:
     default_return_type = cast(Instance, ctx.default_return_type)
     is_nullable = helpers.parse_bool(helpers.get_argument_by_name(ctx, 'null'))
-    set_type = get_private_descriptor_type(default_return_type.type, '_pyi_private_set_type',
-                                           is_nullable=is_nullable)
-    get_type = get_private_descriptor_type(default_return_type.type, '_pyi_private_get_type',
-                                           is_nullable=is_nullable)
+    set_type = helpers.get_private_descriptor_type(default_return_type.type, '_pyi_private_set_type',
+                                                   is_nullable=is_nullable)
+    get_type = helpers.get_private_descriptor_type(default_return_type.type, '_pyi_private_get_type',
+                                                   is_nullable=is_nullable)
     return helpers.reparametrize_instance(default_return_type, [set_type, get_type])