diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -1478,6 +1478,7 @@ class changeset_templater(changeset_prin
     def __init__(self, ui, repo, matchfn, diffopts, tmpl, mapfile, buffered):
         changeset_printer.__init__(self, ui, repo, matchfn, diffopts, buffered)
         formatnode = ui.debugflag and (lambda x: x) or (lambda x: x[:12])
+        filters = {'formatnode': formatnode}
         defaulttempl = {
             'parent': '{rev}:{node|formatnode} ',
             'manifest': '{rev}:{node|formatnode}',
@@ -1486,10 +1487,14 @@ class changeset_templater(changeset_prin
             }
         # filecopy is preserved for compatibility reasons
         defaulttempl['filecopy'] = defaulttempl['file_copy']
-        self.t = templater.templater(mapfile, {'formatnode': formatnode},
-                                     cache=defaulttempl)
-        if tmpl:
-            self.t.cache['changeset'] = tmpl
+        assert not (tmpl and mapfile)
+        if mapfile:
+            self.t = templater.templater.frommapfile(mapfile, filters=filters,
+                                                     cache=defaulttempl)
+        else:
+            self.t = templater.templater(filters=filters, cache=defaulttempl)
+            if tmpl:
+                self.t.cache['changeset'] = tmpl
 
         self.cache = {}
 
diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -2770,7 +2770,7 @@ def debuginstall(ui, **opts):
             # template found, check if it is working
             err = None
             try:
-                templater.templater(m)
+                templater.templater.frommapfile(m)
             except Exception as inst:
                 err = inst
                 p = None
@@ -3681,7 +3681,7 @@ def debugtemplate(ui, repo, tmpl, **opts
     mapfile = None
     if revs is None:
         k = 'debugtemplate'
-        t = templater.templater(mapfile)
+        t = templater.templater()
         t.cache[k] = tmpl
         ui.write(templater.stringify(t(k, **props)))
     else:
diff --git a/mercurial/filemerge.py b/mercurial/filemerge.py
--- a/mercurial/filemerge.py
+++ b/mercurial/filemerge.py
@@ -526,7 +526,7 @@ def _formatlabels(repo, fcd, fco, fca, l
 
     ui = repo.ui
     template = ui.config('ui', 'mergemarkertemplate', _defaultconflictmarker)
-    tmpl = templater.templater(None, cache={'conflictmarker': template})
+    tmpl = templater.templater(cache={'conflictmarker': template})
 
     pad = max(len(l) for l in labels)
 
diff --git a/mercurial/formatter.py b/mercurial/formatter.py
--- a/mercurial/formatter.py
+++ b/mercurial/formatter.py
@@ -190,7 +190,10 @@ def lookuptemplate(ui, topic, tmpl):
 
 def gettemplater(ui, topic, spec):
     tmpl, mapfile = lookuptemplate(ui, topic, spec)
-    t = templater.templater(mapfile, {})
+    assert not (tmpl and mapfile)
+    if mapfile:
+        return templater.templater.frommapfile(mapfile)
+    t = templater.templater()
     if tmpl:
         t.cache[topic] = tmpl
     return t
diff --git a/mercurial/hgweb/hgweb_mod.py b/mercurial/hgweb/hgweb_mod.py
--- a/mercurial/hgweb/hgweb_mod.py
+++ b/mercurial/hgweb/hgweb_mod.py
@@ -188,20 +188,22 @@ class requestcontext(object):
 
         # create the templater
 
-        tmpl = templater.templater(mapfile,
-                                   filters={'websub': websubfilter},
-                                   defaults={'url': req.url,
-                                             'logourl': logourl,
-                                             'logoimg': logoimg,
-                                             'staticurl': staticurl,
-                                             'urlbase': urlbase,
-                                             'repo': self.reponame,
-                                             'encoding': encoding.encoding,
-                                             'motd': motd,
-                                             'sessionvars': sessionvars,
-                                             'pathdef': makebreadcrumb(req.url),
-                                             'style': style,
-                                            })
+        defaults = {
+            'url': req.url,
+            'logourl': logourl,
+            'logoimg': logoimg,
+            'staticurl': staticurl,
+            'urlbase': urlbase,
+            'repo': self.reponame,
+            'encoding': encoding.encoding,
+            'motd': motd,
+            'sessionvars': sessionvars,
+            'pathdef': makebreadcrumb(req.url),
+            'style': style,
+        }
+        tmpl = templater.templater.frommapfile(mapfile,
+                                               filters={'websub': websubfilter},
+                                               defaults=defaults)
         return tmpl
 
 
diff --git a/mercurial/hgweb/hgwebdir_mod.py b/mercurial/hgweb/hgwebdir_mod.py
--- a/mercurial/hgweb/hgwebdir_mod.py
+++ b/mercurial/hgweb/hgwebdir_mod.py
@@ -491,16 +491,17 @@ class hgwebdir(object):
         if not staticurl.endswith('/'):
             staticurl += '/'
 
-        tmpl = templater.templater(mapfile,
-                                   defaults={"encoding": encoding.encoding,
-                                             "motd": motd,
-                                             "url": url,
-                                             "logourl": logourl,
-                                             "logoimg": logoimg,
-                                             "staticurl": staticurl,
-                                             "sessionvars": sessionvars,
-                                             "style": style,
-                                             })
+        defaults = {
+            "encoding": encoding.encoding,
+            "motd": motd,
+            "url": url,
+            "logourl": logourl,
+            "logoimg": logoimg,
+            "staticurl": staticurl,
+            "sessionvars": sessionvars,
+            "style": style,
+        }
+        tmpl = templater.templater.frommapfile(mapfile, defaults=defaults)
         return tmpl
 
     def updatereqenv(self, env):
diff --git a/mercurial/templater.py b/mercurial/templater.py
--- a/mercurial/templater.py
+++ b/mercurial/templater.py
@@ -1016,10 +1016,9 @@ class TemplateNotFound(error.Abort):
 
 class templater(object):
 
-    def __init__(self, mapfile, filters=None, defaults=None, cache=None,
+    def __init__(self, filters=None, defaults=None, cache=None,
                  minchunk=1024, maxchunk=65536):
         '''set up template engine.
-        mapfile is name of file to read map definitions from.
         filters is dict of functions. each transforms a value into another.
         defaults is dict of default map definitions.'''
         if filters is None:
@@ -1036,11 +1035,15 @@ class templater(object):
         self.minchunk, self.maxchunk = minchunk, maxchunk
         self.ecache = {}
 
-        if not mapfile:
-            return
+    @classmethod
+    def frommapfile(cls, mapfile, filters=None, defaults=None, cache=None,
+                    minchunk=1024, maxchunk=65536):
+        """Create templater from the specified map file"""
+        t = cls(filters, defaults, cache, minchunk, maxchunk)
         cache, tmap = _readmapfile(mapfile)
-        self.cache.update(cache)
-        self.map = tmap
+        t.cache.update(cache)
+        t.map = tmap
+        return t
 
     def __contains__(self, key):
         return key in self.cache or key in self.map