Merge "Avoid circular references in Macro class"

heat/engine/function.py

@@ -140,9 +140,19 @@ class Macro(Function):
     def __init__(self, stack, fn_name, raw_args, parse_func, template):
         """Initialise with the argument syntax tree and parser function."""
         super(Macro, self).__init__(stack, fn_name, raw_args)
-        self.template = template
+        self._tmplref = weakref.ref(template) if template is not None else None
         self.parsed = self.parse_args(parse_func)
 
+    @property
+    def template(self):
+        ref = self._tmplref
+        if ref is None:
+            return None
+
+        tmpl = ref()
+        assert tmpl is not None, "Need a reference to the Template object"
+        return tmpl
+
     @abc.abstractmethod
     def parse_args(self, parse_func):
         """Parse the macro using the supplied parsing function.