syntax_data: {"ast_node_type":"other","tokens":[{"end":41,"kind":"keyword","start":0,"text":"///"}]}
source_snippet:     ///   means the cached value for `F`.
context_before:     ///   all cache values whose DFN is >= 4 -- in this case, that
context_after:     map: RefCell<FxIndexMap<ty::PolyTraitPredicate<'tcx>, ProvisionalEvaluation>>,