replace Variant with direct feature inside of TypeEngine

The :meth:`_sqltypes.TypeEngine.with_variant` method now returns a copy of
the original :class:`_sqltypes.TypeEngine` object, rather than wrapping it
inside the ``Variant`` class, which is effectively removed (the import
symbol remains for backwards compatibility with code that may be testing
for this symbol). While the previous approach maintained in-Python
behaviors, maintaining the original type allows for clearer type checking
and debugging.

Fixes: #6980
Change-Id: I158c7e56306b886b5b82b040205c428a5c4a242c

1 files changed, 7 insertions, 3 deletions

diff --git a/lib/sqlalchemy/sql/schema.py b/lib/sqlalchemy/sql/schema.py
index 9b5005b5d..dd8238450 100644
--- a/lib/sqlalchemy/sql/schema.py
+++ b/lib/sqlalchemy/sql/schema.py
@@ -1586,9 +1586,13 @@ class Column(DialectKWArgs, SchemaItem, ColumnClause):
         # check if this Column is proxying another column
         if "_proxies" in kwargs:
             self._proxies = kwargs.pop("_proxies")
-        # otherwise, add DDL-related events
-        elif isinstance(self.type, SchemaEventTarget):
-            self.type._set_parent_with_dispatch(self)
+        else:
+            # otherwise, add DDL-related events
+            if isinstance(self.type, SchemaEventTarget):
+                self.type._set_parent_with_dispatch(self)
+            for impl in self.type._variant_mapping.values():
+                if isinstance(impl, SchemaEventTarget):
+                    impl._set_parent_with_dispatch(self)
 
         if self.default is not None:
             if isinstance(self.default, (ColumnDefault, Sequence)):