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, 7 insertions, 5 deletions

diff --git a/lib/sqlalchemy/orm/context.py b/lib/sqlalchemy/orm/context.py
index 8e9cf66e2..34f291864 100644
--- a/lib/sqlalchemy/orm/context.py
+++ b/lib/sqlalchemy/orm/context.py
@@ -5,16 +5,18 @@
 # This module is part of SQLAlchemy and is released under
 # the MIT License: https://www.opensource.org/licenses/mit-license.php
 import itertools
+from typing import List
 
 from . import attributes
 from . import interfaces
 from . import loading
 from .base import _is_aliased_class
+from .interfaces import ORMColumnDescription
 from .interfaces import ORMColumnsClauseRole
 from .path_registry import PathRegistry
 from .util import _entity_corresponds_to
 from .util import _ORMJoin
-from .util import aliased
+from .util import AliasedClass
 from .util import Bundle
 from .util import ORMAdapter
 from .. import exc as sa_exc
@@ -1570,7 +1572,7 @@ class ORMSelectCompileState(ORMCompileState, SelectState):
 
         # when we are here, it means join() was called with an indicator
         # as to an exact left side, which means a path to a
-        # RelationshipProperty was given, e.g.:
+        # Relationship was given, e.g.:
         #
         # join(RightEntity, LeftEntity.right)
         #
@@ -1725,7 +1727,7 @@ class ORMSelectCompileState(ORMCompileState, SelectState):
                     need_adapter = True
 
                 # make the right hand side target into an ORM entity
-                right = aliased(right_mapper, right_selectable)
+                right = AliasedClass(right_mapper, right_selectable)
 
                 util.warn_deprecated(
                     "An alias is being generated automatically against "
@@ -1750,7 +1752,7 @@ class ORMSelectCompileState(ORMCompileState, SelectState):
             # test/orm/inheritance/test_relationships.py.  There are also
             # general overlap cases with many-to-many tables where automatic
             # aliasing is desirable.
-            right = aliased(right, flat=True)
+            right = AliasedClass(right, flat=True)
             need_adapter = True
 
             util.warn(
@@ -1910,7 +1912,7 @@ class ORMSelectCompileState(ORMCompileState, SelectState):
 
 def _column_descriptions(
     query_or_select_stmt, compile_state=None, legacy=False
-):
+) -> List[ORMColumnDescription]:
     if compile_state is None:
         compile_state = ORMSelectCompileState._create_entities_collection(
             query_or_select_stmt, legacy=legacy