syntax_data: {"ast_node_type":"import","tokens":[{"end":78,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:         // the given closure and use the necessary information to create upvar
context_before:         // with the closure's DefId. Here, we run through that vec of UpvarIds for
context_after:         // debuginfo and to fill `self.upvars`.