new features for pep 593 Annotated

* extract the inner type from Annotated when the outer type
  isn't present in the type map, to allow for arbitrary Annotated
* allow _IntrospectsAnnotations objects to be directly present
  in an Annotated and resolve the mapper property from that.
  Currently implemented for mapped_column(), with message for
  others.  Can work for composite() and likely some
  relationship() as well at some point

References: https://twitter.com/zzzeek/status/1536693554621341697 and
replies

Change-Id: I04657050a8785f194bf8f63291faf3475af88781

1 files changed, 16 insertions, 0 deletions

diff --git a/lib/sqlalchemy/util/typing.py b/lib/sqlalchemy/util/typing.py
index 454de100b..eb625e06e 100644
--- a/lib/sqlalchemy/util/typing.py
+++ b/lib/sqlalchemy/util/typing.py
@@ -61,9 +61,18 @@ else:
 
 if typing.TYPE_CHECKING or compat.py310:
     from typing import Annotated as Annotated
+    from typing import get_args as get_args
+    from typing import get_origin as get_origin
 else:
     from typing_extensions import Annotated as Annotated  # noqa: F401
 
+    # these are in py38 but don't work with Annotated correctly, so
+    # for 3.8 / 3.9 we use the typing extensions version
+    from typing_extensions import get_args as get_args  # noqa: F401
+    from typing_extensions import (
+        get_origin as get_origin,  # noqa: F401,
+    )
+
 if typing.TYPE_CHECKING or compat.py38:
     from typing import Literal as Literal
     from typing import Protocol as Protocol
@@ -75,6 +84,9 @@ else:
     from typing_extensions import TypedDict as TypedDict  # noqa: F401
     from typing_extensions import Final as Final  # noqa: F401
 
+typing_get_args = get_args
+typing_get_origin = get_origin
+
 # copied from TypeShed, required in order to implement
 # MutableMapping.update()
 
@@ -140,6 +152,10 @@ def de_stringify_annotation(
     return annotation  # type: ignore
 
 
+def is_pep593(type_: Optional[_AnnotationScanType]) -> bool:
+    return type_ is not None and typing_get_origin(type_) is Annotated
+
+
 def is_fwd_ref(type_: _AnnotationScanType) -> bool:
     return isinstance(type_, ForwardRef)