Initialize variable for the current function to add edges from calls.

        We compute variable to call dependencies and add edges when returns
        are reach.

def visit_FunctionDef(self, node):
        """
        Initialize variable for the current function to add edges from calls.

        We compute variable to call dependencies and add edges when returns
        are reach.
        """
        # Ensure there are no nested functions.
        assert self.current_function is None
        self.current_function = node
        self.naming = dict()
        self.in_cond = False  # True when we are in a if, while or for
        self.generic_visit(node)
        self.current_function = None