syntax_data: {"ast_node_type":"other","tokens":[{"end":69,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:         // FIXME(explicit_tail_calls): maybe get `become` a new error
context_before:         }
context_after:         ExprKind::Closure { .. } | ExprKind::Return { .. } | ExprKind::Become { .. } => {