syntax_data: {"ast_node_type":"other","tokens":[{"end":89,"kind":"keyword","start":0,"text":"ExprKind::Closure"}]}
source_snippet:         ExprKind::Closure { .. } | ExprKind::Return { .. } | ExprKind::Become { .. } => {
context_before:         // FIXME(explicit_tail_calls): maybe get `become` a new error
context_after:             error(GenericConstantTooComplexSub::ClosureAndReturnNotSupported(node.span))?