templatekw: extract non-templatekw function as getgraphnode()

Prepares for switching to the (context, mapping) API. We still need (repo, ctx)
function for the fast path.

mercurial/logcmdutil.py

@@ -837,7 +837,7 b' def getlinerangerevs(repo, userrevs, opt'
 def _graphnodeformatter(ui, displayer):
     spec = ui.config('ui', 'graphnodetemplate')
     if not spec:
-        return templatekw.showgraphnode  # fast path for "{graphnode}"
+        return templatekw.getgraphnode  # fast path for "{graphnode}"
 
     spec = templater.unquotestring(spec)
     tres = formatter.templateresources(ui)

mercurial/templatekw.py

@@ -528,6 +528,9 b' def showfiles(**args):'
 def showgraphnode(repo, ctx, **args):
     """String. The character representing the changeset node in an ASCII
     revision graph."""
+    return getgraphnode(repo, ctx)
+
+def getgraphnode(repo, ctx):
     wpnodes = repo.dirstate.parents()
     if wpnodes[1] == nullid:
         wpnodes = wpnodes[:1]