syntax_data: {"ast_node_type":"variable","tokens":[{"end":45,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:     let lint = UNSTABLE_SYNTAX_PRE_EXPANSION;
context_before:     // Decorate this as a future-incompatibility lint as in rustc_middle::lint::lint_level
context_after:     let future_incompatible = lint.future_incompatible.as_ref().unwrap();