changelog: move branchinfo to changelogrevision

The function parses the extra dictionary after looking up the
changelogrevision. To avoid duplicated look up, it is better to provide
it as property of changelogrevision instead. Keep the function for a
release cycle as at least the topic extension depends on it.

Differential Revision: https://phab.mercurial-scm.org/D9779

mercurial/changelog.py

@@ -200,6 +200,7 b' class _changelogrevision(object):'
     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 b' class changelogrevision(object):'
     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 b' class changelog(revlog.revlog):'
 
         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.

relnotes/next

@@ -65,4 +65,5 b''
 
 == Internal API Changes ==
 
-
+ * `changelog.branchinfo` is deprecated and will be removed after 5.8.
+   It is superseded by `changelogrevision.branchinfo`.