syntax_data: {"ast_node_type":"variable","tokens":[{"end":86,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:     let trait_ref = ty::TraitRef::new(tcx, fn_trait_def_id, [self_ty, sig.resume_ty]);
context_before:     assert!(!self_ty.has_escaping_bound_vars());
context_after:     (trait_ref, sig.yield_ty, sig.return_ty)