diff -r c2f74b8f6b7f -r 41a5d815d2c1 mercurial/templatefuncs.py
--- a/mercurial/templatefuncs.py	Sun Mar 18 23:24:50 2018 +0900
+++ b/mercurial/templatefuncs.py	Sat Mar 17 21:42:27 2018 +0900
@@ -324,14 +324,8 @@
     joiner = " "
     if len(args) > 1:
         joiner = evalstring(context, mapping, args[1])
-
-    first = True
-    for x in pycompat.maybebytestr(joinset):
-        if first:
-            first = False
-        else:
-            yield joiner
-        yield joinfmt(x)
+    itemiter = (joinfmt(x) for x in pycompat.maybebytestr(joinset))
+    return templateutil.joinitems(itemiter, joiner)
 
 @templatefunc('label(label, expr)')
 def label(context, mapping, args):