QuerySet.annotate improvements (#398)

* QuerySet.annotate returns self-type. Attribute access falls back to Any.

- QuerySets that have an annotated model do not report errors during .filter() when called with invalid fields.
- QuerySets that have an annotated model return ordinary dict rather than TypedDict for .values()
- QuerySets that have an annotated model return Any rather than typed Tuple for .values_list()

* Fix .annotate so it reuses existing annotated types. Fixes error in typechecking Django testsuite.

* Fix self-typecheck error

* Fix flake8

* Fix case of .values/.values_list before .annotate.

* Extra ignores for Django 2.2 tests (false positives due to tests assuming QuerySet.first() won't return None)

Fix mypy self-check.

* More tests + more precise typing in case annotate called before values_list.

Cleanup tests.

* Test and fix annotate in combination with values/values_list with no params.

* Remove line that does nothing :)

* Formatting fixes

* Address code review

* Fix quoting in tests after mypy changed things

* Use Final

* Use typing_extensions.Final

* Fixes after ValuesQuerySet -> _ValuesQuerySet refactor. Still not passing tests yet.

* Fix inheritance of _ValuesQuerySet and remove unneeded type ignores.

This allows the test
"annotate_values_or_values_list_before_or_after_annotate_broadens_type"
to pass.

* Make it possible to annotate user code with "annotated models", using PEP 583 Annotated type.

* Add docs

* Make QuerySet[_T] an external alias to _QuerySet[_T, _T].

This currently has the drawback that error messages display the internal type _QuerySet, with both type arguments.

See also discussion on #661 and #608.

Fixes #635: QuerySet methods on Managers (like .all()) now return QuerySets rather than Managers.

Address code review by @sobolevn.

* Support passing TypedDicts to WithAnnotations

* Add an example of an error to README regarding WithAnnotations + TypedDict.

* Fix runtime behavior of ValuesQuerySet alias (you can't extend Any, for example).

Fix some edge case with from_queryset after QuerySet changed to be an
alias to _QuerySet. Can't make a minimal test case as this only occurred
on a large internal codebase.

* Fix issue when using from_queryset in some cases when having an argument with a type annotation on the QuerySet.

The mypy docstring on anal_type says not to call defer() after it.

mypy_django_plugin/django/context.py

@@ -21,6 +21,7 @@ from mypy.types import Type as MypyType
 from mypy.types import TypeOfAny, UnionType
 
 from mypy_django_plugin.lib import fullnames, helpers
+from mypy_django_plugin.lib.fullnames import WITH_ANNOTATIONS_FULLNAME
 
 try:
     from django.contrib.postgres.fields import ArrayField
@@ -113,7 +114,15 @@ class DjangoContext:
         return modules
 
     def get_model_class_by_fullname(self, fullname: str) -> Optional[Type[Model]]:
-        # Returns None if Model is abstract
+        """Returns None if Model is abstract"""
+        annotated_prefix = WITH_ANNOTATIONS_FULLNAME + "["
+        if fullname.startswith(annotated_prefix):
+            # For our "annotated models", extract the original model fullname
+            fullname = fullname[len(annotated_prefix) :].rstrip("]")
+            if "," in fullname:
+                # Remove second type arg, which might be present
+                fullname = fullname[: fullname.index(",")]
+
         module, _, model_cls_name = fullname.rpartition(".")
         for model_cls in self.model_modules.get(module, set()):
             if model_cls.__name__ == model_cls_name: