syntax_data: {"ast_node_type":"other","tokens":[{"end":64,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:                 // check if tuple is in list of built-in targets
context_before:             TargetTuple::TargetTuple(ref target_tuple) => {
context_after:                 if let Some(t) = load_builtin(target_tuple) {