syntax_data: {"ast_node_type":"variable","tokens":[{"end":56,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                 let witness = Ty::new_coroutine_witness(
context_before:                 let ty = self.infcx.shallow_resolve(args.as_coroutine().tupled_upvars_ty());
context_after:                     self.tcx(),