syntax_data: {"ast_node_type":"variable","tokens":[{"end":54,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:     let (ref infcx, goal, _canonical_inference_vars) =
context_before:     debug!("evaluate_obligation(canonical_goal={:#?})", canonical_goal);
context_after:         tcx.infer_ctxt().build_with_canonical(DUMMY_SP, &canonical_goal);