templater: drop symbols which should be overridden by new 'ctx' (issue5612) This problem is caused by impedance mismatch between the templater and the formatter interface, which is that the template keywords are generally evaluated dynamically, but the formatter puts static values into a template mapping. This patch avoids the problem by removing conflicting values from a mapping dict when a 'ctx' is switched.

--- a/mercurial/formatter.py	Thu Mar 15 21:22:52 2018 +0900
+++ b/mercurial/formatter.py	Thu Mar 15 21:38:57 2018 +0900
@@ -504,6 +504,10 @@
             'ui': ui,
         }
 
+    def availablekeys(self, context, mapping):
+        return {k for k, g in self._gettermap.iteritems()
+                if g(self, context, mapping, k) is not None}
+
     def knownkeys(self):
         return self._knownkeys