avoid importing ForwardRef that's py3.9+ only

Change-Id: I76654f10e208d618e21ab0c884cb0abede4d6177

1 files changed, 7 insertions, 1 deletions

diff --git a/alembic/operations/base.py b/alembic/operations/base.py
index 21f7a85..59bbfc4 100644
--- a/alembic/operations/base.py
+++ b/alembic/operations/base.py
@@ -1,8 +1,8 @@
 from contextlib import contextmanager
+import re
 import textwrap
 from typing import Any
 from typing import Callable
-from typing import ForwardRef  # noqa
 from typing import Iterator
 from typing import List  # noqa
 from typing import Optional
@@ -136,6 +136,12 @@ class Operations(util.ModuleClsProxy):
                 formatvalue=lambda x: "=" + x,
             )
 
+            args = re.sub(
+                r'[_]?ForwardRef\(([\'"].+?[\'"])\)',
+                lambda m: m.group(1),
+                args,
+            )
+
             func_text = textwrap.dedent(
                 """\
             def %(name)s%(args)s: