diff -r cabc5e9366c5 -r cad17d50736c mercurial/changelog.py
--- a/mercurial/changelog.py	Fri Jan 22 11:10:39 2021 +0100
+++ b/mercurial/changelog.py	Fri Jan 15 01:30:08 2021 +0100
@@ -200,6 +200,7 @@
     p1copies = attr.ib(default=None)
     p2copies = attr.ib(default=None)
     description = attr.ib(default=b'')
+    branchinfo = attr.ib(default=(_defaultextra[b'branch'], False))
 
 
 class changelogrevision(object):
@@ -372,6 +373,11 @@
     def description(self):
         return encoding.tolocal(self._text[self._offsets[3] + 2 :])
 
+    @property
+    def branchinfo(self):
+        extra = self.extra
+        return encoding.tolocal(extra.get(b"branch")), b'close' in extra
+
 
 class changelog(revlog.revlog):
     def __init__(self, opener, trypending=False):
@@ -601,8 +607,7 @@
 
         This function exists because creating a changectx object
         just to access this is costly."""
-        extra = self.changelogrevision(rev).extra
-        return encoding.tolocal(extra.get(b"branch")), b'close' in extra
+        return self.changelogrevision(rev).branchinfo
 
     def _nodeduplicatecallback(self, transaction, node):
         # keep track of revisions that got "re-added", eg: unbunde of know rev.