syntax_data: {"ast_node_type":"variable","tokens":[{"end":50,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:     let mut selcx = SelectionContext::new(&infcx);
context_before:     let (infcx, param_env) = tcx.infer_ctxt().ignoring_regions().build_with_typing_env(typing_env);