syntax_data: {"ast_node_type":"variable","tokens":[{"end":41,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                 let future_trait_def_id =
context_before:                 // We must additionally check that the return type impls `Future + Sized`.
context_after:                     tcx.require_lang_item(LangItem::Future, obligation.cause.span);