syntax_data: {"ast_node_type":"variable","tokens":[{"end":100,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                 let placeholder_output_ty = self.infcx.enter_forall_and_leak_universe(sig.output());
context_before:                     tcx.require_lang_item(LangItem::Future, obligation.cause.span);
context_after:                 nested.push(obligation.with(