syntax_data: {"ast_node_type":"variable","tokens":[{"end":94,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:         let removed_span = self.spans.borrow_mut().entry(feature).or_default().pop().unwrap();
context_before:     pub fn ungate_last(&self, feature: Symbol, span: Span) {
context_after:         debug_assert_eq!(span, removed_span);