syntax_data: {"ast_node_type":"variable","tokens":[{"end":73,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:     let future_incompatible = lint.future_incompatible.as_ref().unwrap();
context_before:     let lint = UNSTABLE_SYNTAX_PRE_EXPANSION;
context_after:     err.is_lint(lint.name_lower(), /* has_future_breakage */ false);