Use independent TypeVar for ColumnElement.cast

Fixed typing issue where :meth:`.ColumnElement.cast` did not allow a
:class:`.TypeEngine` argument independent of the type of the
:class:`.ColumnElement` itself, which is the purpose of
:meth:`.ColumnElement.cast`.

Fixes: #9451
Change-Id: I68119c6a9e8bf896715eea79be2b4f36b1c141de

1 files changed, 10 insertions, 0 deletions

diff --git a/test/ext/mypy/plain_files/sql_operations.py b/test/ext/mypy/plain_files/sql_operations.py
index c55442be9..d658f3d50 100644
--- a/test/ext/mypy/plain_files/sql_operations.py
+++ b/test/ext/mypy/plain_files/sql_operations.py
@@ -2,8 +2,11 @@ import typing
 
 from sqlalchemy import and_
 from sqlalchemy import Boolean
+from sqlalchemy import cast
 from sqlalchemy import column
+from sqlalchemy import DateTime
 from sqlalchemy import false
+from sqlalchemy import Float
 from sqlalchemy import func
 from sqlalchemy import Integer
 from sqlalchemy import or_
@@ -75,6 +78,13 @@ and_(c1.notlike("x"))
 and_(c1.not_ilike("x"))
 and_(c1.notilike("x"))
 
+# issue #9451
+s1 = c1.cast(Integer)
+s2 = c1.cast(Float)
+s3 = c1.op("foobar")("operand").cast(DateTime)
+s4 = cast(c1, Float)
+s5 = cast(c1.op("foobar")("operand"), DateTime)
+
 
 if typing.TYPE_CHECKING: