syntax_data: {"ast_node_type":"impl","tokens":[{"end":69,"kind":"keyword","start":0,"text":"segment_visitor:"}]}
source_snippet:     segment_visitor: impl FnMut(VtblSegment<'tcx>) -> ControlFlow<T>,
context_before:     trait_ref: ty::TraitRef<'tcx>,
context_after: ) -> Option<T> {