templatekw: simply override {graphwidth} function by mapping variable

mercurial/logcmdutil.py

@@ -889,7 +889,7 b' def displaygraph(ui, repo, dag, displaye'
         firstedge = next(edges)
         width = firstedge[2]
         displayer.show(ctx, copies=copies,
-                       _graphwidth=width, **pycompat.strkwargs(props))
+                       graphwidth=width, **pycompat.strkwargs(props))
         lines = displayer.hunk.pop(rev).split('\n')
         if not lines[-1]:
             del lines[-1]

mercurial/templatekw.py

@@ -552,9 +552,8 b' def showgraphnode(repo, ctx, **args):'
 @templatekeyword('graphwidth')
 def showgraphwidth(repo, ctx, templ, **args):
     """Integer. The width of the graph drawn by 'log --graph' or zero."""
-    # The value args['graphwidth'] will be this function, so we use an internal
-    # name to pass the value through props into this function.
-    return args.get('_graphwidth', 0)
+    # just hosts documentation; should be overridden by template mapping
+    return 0
 
 @templatekeyword('index')
 def showindex(**args):