hgweb: wrap {diffstat} with mappedgenerator

This can't be a mappinggenerator since the associated templates are switched
per item.

We already have webutil.diffstatgen(). That's why the generator function is
named as _diffstattmplgen().

mercurial/hgweb/webutil.py

@@ -670,9 +670,7 b' def diffsummary(statgen):'
     return _(' %d files changed, %d insertions(+), %d deletions(-)\n') % (
              len(stats), addtotal, removetotal)
 
-def diffstat(tmpl, ctx, statgen, parity):
-    '''Return a diffstat template for each file in the diff.'''
-
+def _diffstattmplgen(context, tmpl, ctx, statgen, parity):
     stats, maxname, maxtotal, addtotal, removetotal, binary = next(statgen)
     files = ctx.files()
 
@@ -696,6 +694,11 b' def diffstat(tmpl, ctx, statgen, parity)'
             'parity': next(parity),
         })
 
+def diffstat(tmpl, ctx, statgen, parity):
+    '''Return a diffstat template for each file in the diff.'''
+    args = (tmpl, ctx, statgen, parity)
+    return templateutil.mappedgenerator(_diffstattmplgen, args=args)
+
 class sessionvars(templateutil.wrapped):
     def __init__(self, vars, start='?'):
         self._start = start