diff -r f15cb5111a1e -r 8b2ea2246a5f mercurial/upgrade_utils/actions.py
--- a/mercurial/upgrade_utils/actions.py	Tue Dec 19 21:29:34 2023 +0100
+++ b/mercurial/upgrade_utils/actions.py	Wed Dec 20 11:23:09 2023 +0100
@@ -108,7 +108,7 @@
     compatible_with_share = False
 
 
-allformatvariant = []  # type: List[Type['formatvariant']]
+allformatvariant: List[Type['formatvariant']] = []
 
 
 def registerformatvariant(cls):