establish mypy / typing approach for v2.0

large patch to get ORM / typing efforts started.
this is to support adding new test cases to mypy,
support dropping sqlalchemy2-stubs entirely from the
test suite, validate major ORM typing reorganization
to eliminate the need for the mypy plugin.

* New declarative approach which uses annotation
  introspection, fixes: #7535
* Mapped[] is now at the base of all ORM constructs
  that find themselves in classes, to support direct
  typing without plugins
* Mypy plugin updated for new typing structures
* Mypy test suite broken out into "plugin" tests vs.
  "plain" tests, and enhanced to better support test
  structures where we assert that various objects are
  introspected by the type checker as we expect.
  as we go forward with typing, we will
  add new use cases to "plain" where we can assert that
  types are introspected as we expect.
* For typing support, users will be much more exposed to the
  class names of things.  Add these all to "sqlalchemy" import
  space.
* Column(ForeignKey()) no longer needs to be `@declared_attr`
  if the FK refers to a remote table
* composite() attributes mapped to a dataclass no longer
  need to implement a `__composite_values__()` method
* with_variant() accepts multiple dialect names

Change-Id: I22797c0be73a8fbbd2d6f5e0c0b7258b17fe145d
Fixes: #7535
Fixes: #7551
References: #6810

1 files changed, 30 insertions, 5 deletions

diff --git a/lib/sqlalchemy/ext/orderinglist.py b/lib/sqlalchemy/ext/orderinglist.py
index 5a327d1a5..5384851b1 100644
--- a/lib/sqlalchemy/ext/orderinglist.py
+++ b/lib/sqlalchemy/ext/orderinglist.py
@@ -119,14 +119,28 @@ start numbering at 1 or some other integer, provide ``count_from=1``.
 
 
 """
+from typing import Callable
+from typing import List
+from typing import Optional
+from typing import Sequence
+from typing import TypeVar
+
 from ..orm.collections import collection
 from ..orm.collections import collection_adapter
 
+_T = TypeVar("_T")
+OrderingFunc = Callable[[int, Sequence[_T]], int]
+
 
 __all__ = ["ordering_list"]
 
 
-def ordering_list(attr, count_from=None, **kw):
+def ordering_list(
+    attr: str,
+    count_from: Optional[int] = None,
+    ordering_func: Optional[OrderingFunc] = None,
+    reorder_on_append: bool = False,
+) -> Callable[[], "OrderingList"]:
     """Prepares an :class:`OrderingList` factory for use in mapper definitions.
 
     Returns an object suitable for use as an argument to a Mapper
@@ -157,7 +171,11 @@ def ordering_list(attr, count_from=None, **kw):
 
     """
 
-    kw = _unsugar_count_from(count_from=count_from, **kw)
+    kw = _unsugar_count_from(
+        count_from=count_from,
+        ordering_func=ordering_func,
+        reorder_on_append=reorder_on_append,
+    )
     return lambda: OrderingList(attr, **kw)
 
 
@@ -207,7 +225,7 @@ def _unsugar_count_from(**kw):
     return kw
 
 
-class OrderingList(list):
+class OrderingList(List[_T]):
     """A custom list that manages position information for its children.
 
     The :class:`.OrderingList` object is normally set up using the
@@ -216,8 +234,15 @@ class OrderingList(list):
 
     """
 
+    ordering_attr: str
+    ordering_func: OrderingFunc
+    reorder_on_append: bool
+
     def __init__(
-        self, ordering_attr=None, ordering_func=None, reorder_on_append=False
+        self,
+        ordering_attr: Optional[str] = None,
+        ordering_func: Optional[OrderingFunc] = None,
+        reorder_on_append: bool = False,
     ):
         """A custom list that manages position information for its children.
 
@@ -282,7 +307,7 @@ class OrderingList(list):
     def _set_order_value(self, entity, value):
         setattr(entity, self.ordering_attr, value)
 
-    def reorder(self):
+    def reorder(self) -> None:
         """Synchronize ordering for the entire collection.
 
         Sweeps through the list and ensures that each object has accurate