commitablectx: move branch from workingctx

mercurial/context.py

@@ -987,6 +987,8 b' class commitablectx(basectx):'
     def clean(self):
         assert self._clean is not None  # must call status first
         return self._clean
+    def branch(self):
+        return encoding.tolocal(self._extra['branch'])
 
 class workingctx(commitablectx):
     """A workingctx object makes access to data related to
@@ -1014,8 +1016,6 b' class workingctx(commitablectx):'
             p = p[:-1]
         return [changectx(self._repo, x) for x in p]
 
-    def branch(self):
-        return encoding.tolocal(self._extra['branch'])
     def closesbranch(self):
         return 'close' in self._extra
     def extra(self):