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, 25 insertions, 0 deletions

diff --git a/lib/sqlalchemy/util/langhelpers.py b/lib/sqlalchemy/util/langhelpers.py
index 9401c249f..ed879894d 100644
--- a/lib/sqlalchemy/util/langhelpers.py
+++ b/lib/sqlalchemy/util/langhelpers.py
@@ -30,6 +30,7 @@ from typing import FrozenSet
 from typing import Generic
 from typing import Iterator
 from typing import List
+from typing import Mapping
 from typing import Optional
 from typing import overload
 from typing import Sequence
@@ -54,6 +55,30 @@ _HP = TypeVar("_HP", bound="hybridproperty")
 _HM = TypeVar("_HM", bound="hybridmethod")
 
 
+if compat.py310:
+
+    def get_annotations(obj: Any) -> Mapping[str, Any]:
+        return inspect.get_annotations(obj)
+
+else:
+
+    def get_annotations(obj: Any) -> Mapping[str, Any]:
+        # it's been observed that cls.__annotations__ can be non present.
+        # it's not clear what causes this, running under tox py37/38 it
+        # happens, running straight pytest it doesnt
+
+        # https://docs.python.org/3/howto/annotations.html#annotations-howto
+        if isinstance(obj, type):
+            ann = obj.__dict__.get("__annotations__", None)
+        else:
+            ann = getattr(obj, "__annotations__", None)
+
+        if ann is None:
+            return _collections.EMPTY_DICT
+        else:
+            return cast("Mapping[str, Any]", ann)
+
+
 def md5_hex(x: Any) -> str:
     x = x.encode("utf-8")
     m = hashlib.md5()