templater: factor out function that creates templater from string template

This function will host loading of template aliases. It is not defined at
templater, but at formatter, since formatter is the module handling ui stuff
in front of templater.

mercurial/cmdutil.py

@@ -1492,9 +1492,9 b' class changeset_templater(changeset_prin'
             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.t = formatter.maketemplater(ui, 'changeset', tmpl,
+                                             filters=filters,
+                                             cache=defaulttempl)
 
         self.cache = {}
 

mercurial/commands.py

@@ -46,6 +46,7 b' from . import ('
     exchange,
     extensions,
     fileset,
+    formatter,
     graphmod,
     hbisect,
     help,
@@ -3681,8 +3682,7 b' def debugtemplate(ui, repo, tmpl, **opts'
     mapfile = None
     if revs is None:
         k = 'debugtemplate'
-        t = templater.templater()
-        t.cache[k] = tmpl
+        t = formatter.maketemplater(ui, k, tmpl)
         ui.write(templater.stringify(t(k, **props)))
     else:
         displayer = cmdutil.changeset_templater(ui, repo, None, opts, tmpl,

mercurial/filemerge.py

@@ -17,6 +17,7 b' from .node import nullid, short'
 
 from . import (
     error,
+    formatter,
     match,
     scmutil,
     simplemerge,
@@ -526,7 +527,7 b' def _formatlabels(repo, fcd, fco, fca, l'
 
     ui = repo.ui
     template = ui.config('ui', 'mergemarkertemplate', _defaultconflictmarker)
-    tmpl = templater.templater(cache={'conflictmarker': template})
+    tmpl = formatter.maketemplater(ui, 'conflictmarker', template)
 
     pad = max(len(l) for l in labels)
 

mercurial/formatter.py

@@ -193,7 +193,11 b' def gettemplater(ui, topic, spec):'
     assert not (tmpl and mapfile)
     if mapfile:
         return templater.templater.frommapfile(mapfile)
-    t = templater.templater()
+    return maketemplater(ui, topic, tmpl)
+
+def maketemplater(ui, topic, tmpl, filters=None, cache=None):
+    """Create a templater from a string template 'tmpl'"""
+    t = templater.templater(filters=filters, cache=cache)
     if tmpl:
         t.cache[topic] = tmpl
     return t