{"ast_node_type":"other","tokens":[{"end":99,"kind":"keyword","start":0,"text":"iter::once(ty::BoundVariableKind::Region(ty::BoundRegionKind::ClosureEnv)),"}]}
                        iter::once(ty::BoundVariableKind::Region(ty::BoundRegionKind::ClosureEnv)),
                    tcx.mk_bound_variable_kinds_from_iter(closure_sig.bound_vars().iter().chain(
                    ));