syntax_data: {"ast_node_type":"variable","tokens":[{"end":52,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:         let def_id = tcx.get_diagnostic_item(name)?;
context_before:     pub fn new_diagnostic_item(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, name: Symbol) -> Option<Ty<'tcx>> {
context_after:         Some(Ty::new_generic_adt(tcx, def_id, ty))