Support returning the correct values for the different QuerySet methods when using .values() and .values_list(). (#33)

* Support returning the correct values for the different QuerySet methods when using .values() and .values_list().

* Fix slicing on QuerySet. Fix django queries test, and remove some ignored errors that are no longer needed.

* Remove accidental change in RawQuerySet.

* Readded some still-necessary ignores to aggregation django test.

* Add more tests of first/last/earliest/last/__getitem__, per mkurnikov's comments.

- Fix .iterator()

* Re-add Iterator as base-class of QuerySet.

* Make QuerySet a Collection.

* - Fix return type for QuerySet.select_for_update().
- Use correct return type for QuerySet.dates() / QuerySet.datetimes().
- Use correct type params in return type for QuerySet.__and__ / QuerySet.__or__
- Re-add Sized as base class for QuerySet.
- Add test of .all() for all _Row types.
- Add test of .get() for all _Row types.
- Remove some redundant QuerySet method tests.

* Automatically fill in second type parameter for QuerySet.

... if second parameter is omitted.

mypy_django_plugin/main.py

@@ -1,3 +1,5 @@
+from functools import partial
+
 import os
 from typing import Callable, Dict, Optional, Union, cast
 
@@ -6,7 +8,7 @@ from mypy.nodes import MemberExpr, NameExpr, TypeInfo
 from mypy.options import Options
 from mypy.plugin import (
     AttributeContext, ClassDefContext, FunctionContext, MethodContext, Plugin,
-)
+    AnalyzeTypeContext)
 from mypy.types import (
     AnyType, CallableType, Instance, NoneTyp, Type, TypeOfAny, TypeType, UnionType,
 )
@@ -80,6 +82,18 @@ def determine_proper_manager_type(ctx: FunctionContext) -> Type:
         return ret
 
 
+def set_first_generic_param_as_default_for_second(fullname: str, ctx: AnalyzeTypeContext) -> Type:
+    if not ctx.type.args:
+        return ctx.api.named_type(fullname, [AnyType(TypeOfAny.explicit),
+                                             AnyType(TypeOfAny.explicit)])
+    args = ctx.type.args
+    if len(args) == 1:
+        args = [args[0], args[0]]
+
+    analyzed_args = [ctx.api.analyze_type(arg) for arg in args]
+    return ctx.api.named_type(fullname, analyzed_args)
+
+
 def return_user_model_hook(ctx: FunctionContext) -> Type:
     api = cast(TypeChecker, ctx.api)
     setting_expr = helpers.get_setting_expr(api, 'AUTH_USER_MODEL')
@@ -266,6 +280,14 @@ class DjangoPlugin(Plugin):
         else:
             return {}
 
+    def _get_current_queryset_bases(self) -> Dict[str, int]:
+        model_sym = self.lookup_fully_qualified(helpers.QUERYSET_CLASS_FULLNAME)
+        if model_sym is not None and isinstance(model_sym.node, TypeInfo):
+            return (helpers.get_django_metadata(model_sym.node)
+                    .setdefault('queryset_bases', {helpers.QUERYSET_CLASS_FULLNAME: 1}))
+        else:
+            return {}
+
     def get_function_hook(self, fullname: str
                           ) -> Optional[Callable[[FunctionContext], Type]]:
         if fullname == 'django.contrib.auth.get_user_model':
@@ -344,6 +366,14 @@ class DjangoPlugin(Plugin):
 
         return extract_and_return_primary_key_of_bound_related_field_parameter
 
+    def get_type_analyze_hook(self, fullname: str
+                              ) -> Optional[Callable[[AnalyzeTypeContext], Type]]:
+        queryset_bases = self._get_current_queryset_bases()
+        if fullname in queryset_bases:
+            return partial(set_first_generic_param_as_default_for_second, fullname)
+
+        return None
+
 
 def plugin(version):
     return DjangoPlugin