diff -r e4acdf5d94a2 -r 0d0ce2529540 mercurial/configitems.py
--- a/mercurial/configitems.py	Mon Nov 29 13:09:04 2021 +0100
+++ b/mercurial/configitems.py	Fri Nov 26 17:17:49 2021 +0100
@@ -1286,6 +1286,12 @@
     generic=True,
 )
 coreconfigitem(
+    b'extensions',
+    b'[^:]*:required',
+    default=False,
+    generic=True,
+)
+coreconfigitem(
     b'extdata',
     b'.*',
     default=None,