syntax_data: {"ast_node_type":"variable","tokens":[{"end":32,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:         let mut def_id = def_id;
context_before:     pub fn typeck_root_def_id(self, def_id: DefId) -> DefId {
context_after:         while self.is_typeck_child(def_id) {