syntax_data: {"ast_node_type":"other","tokens":[{"end":49,"kind":"keyword","start":0,"text":"key:"}]}
source_snippet:     key: ParamEnvAnd<'tcx, ProvePredicate<'tcx>>,
context_before:     ocx: &ObligationCtxt<'_, 'tcx>,
context_after:     cause: ObligationCause<'tcx>,