syntax_data: {"ast_node_type":"variable","tokens":[{"end":75,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:     let ctfe_backtrace = Lock::new(match env::var("RUSTC_CTFE_BACKTRACE") {
context_after:         Ok(ref val) if val == "immediate" => CtfeBacktrace::Immediate,