syntax_data: {"ast_node_type":"function","tokens":[{"end":87,"kind":"keyword","start":0,"text":"fn"}]}
source_snippet:     fn add_wf_preds_for_negative_trait_pred(&mut self, trait_ref: ty::TraitRef<'tcx>) {
context_before:     // given that it is a *negative* trait predicate.
context_after:         for arg in trait_ref.args {