syntax_data: {"ast_node_type":"impl","tokens":[{"end":73,"kind":"keyword","start":0,"text":"mut"}]}
source_snippet:         mut candidate_is_applicable: impl FnMut(&NestedGoals<X>) -> bool,
context_before:         available_depth: AvailableDepth,
context_after:     ) -> Option<CacheData<'a, X>> {