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

4 files changed, 54 insertions, 8 deletions

diff --git a/lib/sqlalchemy/testing/config.py b/lib/sqlalchemy/testing/config.py
index 268a56421..c1ca670da 100644
--- a/lib/sqlalchemy/testing/config.py
+++ b/lib/sqlalchemy/testing/config.py
@@ -6,6 +6,11 @@
 # the MIT License: https://www.opensource.org/licenses/mit-license.php
 
 import collections
+import typing
+from typing import Any
+from typing import Iterable
+from typing import Tuple
+from typing import Union
 
 from .. import util
 
@@ -20,10 +25,15 @@ any_async = False
 _current = None
 ident = "main"
 
-_fixture_functions = None  # installed by plugin_base
+if typing.TYPE_CHECKING:
+    from .plugin.plugin_base import FixtureFunctions
 
+    _fixture_functions: FixtureFunctions
+else:
+    _fixture_functions = None  # installed by plugin_base
 
-def combinations(*comb, **kw):
+
+def combinations(*comb: Union[Any, Tuple[Any, ...]], **kw: str):
     r"""Deliver multiple versions of a test based on positional combinations.
 
     This is a facade over pytest.mark.parametrize.
@@ -89,25 +99,32 @@ def combinations(*comb, **kw):
     return _fixture_functions.combinations(*comb, **kw)
 
 
-def combinations_list(arg_iterable, **kw):
+def combinations_list(
+    arg_iterable: Iterable[
+        Tuple[
+            Any,
+        ]
+    ],
+    **kw,
+):
     "As combination, but takes a single iterable"
     return combinations(*arg_iterable, **kw)
 
 
-def fixture(*arg, **kw):
+def fixture(*arg: Any, **kw: Any) -> Any:
     return _fixture_functions.fixture(*arg, **kw)
 
 
-def get_current_test_name():
+def get_current_test_name() -> str:
     return _fixture_functions.get_current_test_name()
 
 
-def mark_base_test_class():
+def mark_base_test_class() -> Any:
     return _fixture_functions.mark_base_test_class()
 
 
 class _AddToMarker:
-    def __getattr__(self, attr):
+    def __getattr__(self, attr: str) -> Any:
         return getattr(_fixture_functions.add_to_marker, attr)
 
 
diff --git a/lib/sqlalchemy/testing/fixtures.py b/lib/sqlalchemy/testing/fixtures.py
index ecc20f163..7228e5afe 100644
--- a/lib/sqlalchemy/testing/fixtures.py
+++ b/lib/sqlalchemy/testing/fixtures.py
@@ -20,6 +20,7 @@ from .util import drop_all_tables_from_metadata
 from .. import event
 from .. import util
 from ..orm import declarative_base
+from ..orm import DeclarativeBase
 from ..orm import registry
 from ..schema import sort_tables_and_constraints
 
@@ -82,6 +83,21 @@ class TestBase:
         yield reg
         reg.dispose()
 
+    @config.fixture
+    def decl_base(self, metadata):
+        _md = metadata
+
+        class Base(DeclarativeBase):
+            metadata = _md
+            type_annotation_map = {
+                str: sa.String().with_variant(
+                    sa.String(50), "mysql", "mariadb"
+                )
+            }
+
+        yield Base
+        Base.registry.dispose()
+
     @config.fixture()
     def future_connection(self, future_engine, connection):
         # integrate the future_engine and connection fixtures so
diff --git a/lib/sqlalchemy/testing/plugin/plugin_base.py b/lib/sqlalchemy/testing/plugin/plugin_base.py
index 0b4451b3c..52e42bb97 100644
--- a/lib/sqlalchemy/testing/plugin/plugin_base.py
+++ b/lib/sqlalchemy/testing/plugin/plugin_base.py
@@ -19,6 +19,7 @@ import logging
 import os
 import re
 import sys
+from typing import Any
 
 from sqlalchemy.testing import asyncio
 
@@ -738,7 +739,7 @@ class FixtureFunctions(abc.ABC):
         raise NotImplementedError()
 
     @abc.abstractmethod
-    def mark_base_test_class(self):
+    def mark_base_test_class(self) -> Any:
         raise NotImplementedError()
 
     @abc.abstractproperty
diff --git a/lib/sqlalchemy/testing/requirements.py b/lib/sqlalchemy/testing/requirements.py
index 410ab26ed..41e5d6772 100644
--- a/lib/sqlalchemy/testing/requirements.py
+++ b/lib/sqlalchemy/testing/requirements.py
@@ -1326,6 +1326,18 @@ class SuiteRequirements(Requirements):
         return exclusions.only_if(check)
 
     @property
+    def no_sqlalchemy2_stubs(self):
+        def check(config):
+            try:
+                __import__("sqlalchemy-stubs.ext.mypy")
+            except ImportError:
+                return False
+            else:
+                return True
+
+        return exclusions.skip_if(check)
+
+    @property
     def python38(self):
         return exclusions.only_if(
             lambda: util.py38, "Python 3.8 or above required"