syntax_data: {"ast_node_type":"other","tokens":[{"end":35,"kind":"keyword","start":0,"text":"debug!(?dfn,"}]}
source_snippet:         debug!(?dfn, "on_failure");
context_before:     fn on_failure(&self, dfn: usize) {
context_after:         self.map.borrow_mut().retain(|key, eval| {