syntax_data: {"ast_node_type":"variable","tokens":[{"end":73,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                 let args = self.tcx.mk_args(&[self.old_yield_ty.into()]);
context_before:                 let option_def_id = self.tcx.require_lang_item(LangItem::Option, source_info.span);
context_after:                 let (variant_idx, operands) = if is_return {