syntax_data: {"ast_node_type":"other","tokens":[{"end":63,"kind":"keyword","start":0,"text":"self.map.borrow_mut().retain(|fresh_trait_pred,"}]}
source_snippet:         self.map.borrow_mut().retain(|fresh_trait_pred, eval| {
context_before:         debug!(?dfn, "on_completion");
context_after:             if eval.from_dfn >= dfn {