templater: makes branches work correctly with stringify (issue4108)

mercurial/templatekw.py

@@ -188,6 +188,7 b' def showbranches(**args):'
     branch = args['ctx'].branch()
     if branch != 'default':
         return showlist('branch', [branch], plural='branches', **args)
+    return showlist('branch', [], plural='branches', **args)
 
 def showbookmarks(**args):
     """:bookmarks: List of strings. Any bookmarks associated with the

tests/test-command-template.t

@@ -1606,3 +1606,8 b' Test recursive evaluation:'
   {rev}
   $ hg log -r 0 --template '{if(rev, "{author} {rev}")}\n'
   test 0
+
+Test branches inside if statement:
+
+  $ hg log -r 0 --template '{if(branches, "yes", "no")}\n'
+  no