syntax_data: {"ast_node_type":"function","tokens":[{"end":95,"kind":"keyword","start":0,"text":"fn"}]}
source_snippet:     fn in_safety_context(&mut self, safety_context: SafetyContext, f: impl FnOnce(&mut Self)) {
context_before: impl<'tcx> UnsafetyVisitor<'_, 'tcx> {
context_after:         let prev_context = mem::replace(&mut self.safety_context, safety_context);